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Materials engineers are responsible for the research, specification, design and development of materials to advance technologies of many kinds. Their expertise lies in understanding the properties and behaviours of different substances, from raw materials to finished products. The field is also referred to as materials science or materials technology. They work with many different materials, including: ceramics; chemicals; composites; glass; industrial minerals; metals; plastics; polymers; rubber; textiles. Working in a diverse range of industries, materials engineers combine or modify materials in different ways to improve the performance, durability and cost effectiveness of processes and products. For ideas about the range of careers in materials engineering and science, go to UK Centre for Materials Education (UKCME) . Typical work activities Work activities vary according to the specific material and industry you work with, and the size of the organisation you work for, but there are a number of activities common to most posts. These include: selecting the best combination of materials for specific purposes; testing materials to assess how resistant they are to heat, corrosion or chemical attack; analysing data using computer modeling software; assessing materials for specific qualities (such as electrical conductivity, durability, renewability); developing prototypes; considering the implications for waste and other environmental pollution issues of any product or process; advising on the adaptability of a plant to new processes and materials; working to solve problems that may arise either during the manufacturing process or with the finished product (e.g., problems caused by daily wear and tear or change of environment); supervising quality control throughout the construction and production process; monitoring plant conditions and material reactions during use; helping to ensure that products comply with national and international legal and quality standards; advising on inspection, maintenance and repair procedures; liaising with colleagues in manufacturing, technical and scientific support, purchasing, and marketing; supervising the work of materials engineering technicians and other staff; considering the costs implications of materials used and alternatives, in terms of both time and money; taking account of energy usage in manufacturing and in-service energy saving, e.g., in transport and construction applications. At senior level, the work is likely to involve more innovative research or greater management responsibility. The latter will call for a range of additional skills that are not necessarily part of the routine work of a materials engineer.

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Materials engineers are responsible for the research, specification, design and development of materials to advance technologies of many kinds. Their expertise lies in understanding the properties and behaviours of different substances, from raw materials to finished products. The field is also referred to as materials science or materials technology.

They work with many different materials, including:

ceramics; chemicals; composites; glass; industrial minerals; metals; plastics; polymers;  rubber; textiles.

Working in a diverse range of industries, materials engineers combine or modify materials in different ways to improve the performance, durability and cost effectiveness of processes and products. For ideas about the range of careers in materials engineering and science, go to UK Centre for Materials Education (UKCME) .

Typical work activities

Work activities vary according to the specific material and industry you work with, and the size of the organisation you work for, but there are a number of activities common to most posts. These include:

selecting the best combination of materials for specific purposes; testing materials to assess how resistant they are to heat, corrosion or chemical attack; analysing data using computer modeling software; assessing materials for specific qualities (such as electrical conductivity, durability, renewability); developing prototypes; considering the implications for waste and other environmental pollution issues of any product or process; advising on the adaptability of a plant to new processes and materials; working to solve problems that may arise either during the manufacturing process or with the finished product (e.g., problems caused by daily

wear and tear or change of environment); supervising quality control throughout the construction and production process; monitoring plant conditions and material reactions during use; helping to ensure that products comply with national and international legal and quality standards; advising on inspection, maintenance and repair procedures; liaising with colleagues in manufacturing, technical and scientific support, purchasing, and marketing; supervising the work of materials engineering technicians and other staff; considering the costs implications of materials used and alternatives, in terms of both time and money; taking account of energy usage in manufacturing and in-service energy saving, e.g., in transport and construction applications.

At senior level, the work is likely to involve more innovative research or greater management responsibility. The latter will call for a range of additional skills that are not necessarily part of the routine work of a materials engineer.

Materials engineers are responsible for evaluating materials and creating plans and processes for manufacturing products from various raw materials. The machines they develop may be specialized for specific products. Materials engineers create machines that create products from one type of material such as metal, graphite, glass, plastic and other natural resources. As long as society needs material for construction and products that will be sold either to other consumers in or out

of the country, materials engineers will be needed.

Responsibilities

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1. Materials engineers may analyze and interpret data or laboratory results that can cause a problem or failure within the machines. They may create their own tests and supervise existing tests on raw materials, as well as finished products to determine its quality. They take under consideration economic factors such as pollution and costs to create the best method of creating a product from raw materials. They may solve any issues within the industries of mechanical, chemical, electrical and nuclear products. They may train and supervise a technical staff in developing any materials and products for future devices or natural products. They try to find synthetic ways of replicating natural materials such as metals, glass, etc.

Skills

2. Materials engineers must have science skills, be proficient in math, technology, reading comprehension, effective communication and problem-solving skills. Analytical skills are needed to understand and interpret data from materials and machines. Advanced writing skills, researching, deductive and inductive

reasoning, and interpreting information in order to convey to others are also necessary skills.

Similar Job Titles

3. Materials engineers can receive a bachelor's degree in materials engineering. The materials engineer program prepares students for the mathematical and science necessary to design, develop and operate various machines to bond, extract and create natural or synthetic materials. Students may have to consider

researching various schools in the area or out of state for specific material engineer degrees.

What is material engineer job description?

Material engineer is responsible for the research, specification, design and development of materials to advance technologies of many kinds of material. His or her expertise lies in understanding the properties and behaviors of different materials start from raw to finish products. They also called as materials technologist or materials scientist.

They work with many different materials, including: metals; industrial minerals, composites, ceramics, glass, chemicals, plastics, polymers, rubber.

Material engineer job description is diverse range of industries, aim to combine or modify materials in different ways to improve its performance, durability and off course cost effectiveness of processes and products.

Typical Material Engineer Job Description

Work activities vary depend on the industry where the material engineer works with. However, typical material engineer job description or activities include:

select the best combination of materials for specific purposes. Testing materials both destructive test or non destructive test to assess how tolerant they are to bending, tension, heat, corrosion or chemical attack,

etc. Assessing materials such as electrical conductivity or durability. Evaluate industrial minerals such as silica, sands, dolomites, limestones, magnesite, etc for glass or refractory manufacture. consider the implications for waste and other environmental pollution of any product or process. advise on the adaptability of a plant to new processes and materials. Problem solving which may arise either during the manufacturing process or with the finished product such as crack, wear and tear, or change of

environment. Supervise related to quality control throughout the construction and production process. Monitor the conditions reactions of material during use. Ensure that the products comply with national and international legal and quality standards such as ASTM, ASME, etc Advise on inspection, maintenance and repair procedures. Supervise the work of materials engineering technicians and other staff. Review the cost implications of materials used and alternatives, in terms of both time and money. Review the energy usage in manufacturing and in-service energy saving, e.g. in transport and construction applications. Research and develop materials which are amenable to recycling.

Document Review

Bid/project specifications and design

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Special provisions Agency requirements Traffic control plan Equipment specifications Manufacturers' instructions Material safety data sheets (if required for concrete slurry)

Concrete Mixers andConcrete Mixing Methods:

Introduction

As for all materials, the performance of concrete is determined by its microstructure. Its microstructure is determined by its composition, its curing conditions, and also by the mixing method and mixer conditions used to process the concrete. The mixing procedure includes the type of mixer, the order of introduction of the materials into the mixer, and the energy of mixing (duration and power). To control the workability or rheology of the fresh concrete, for example, it is important to control how the concrete is processed during manufacture. In this overview, the different mixers commercially available will be presented together with a review of the mixing methods. Further, the advantages and disadvantages of the different mixers and mixing methods and their application will be examined. A review of mixing methods in regards to the quality of the concrete produced and some procedures used to determine the effectiveness. of mixing methods will also be given. To determine the mixing method best suited for a specific application, factors to be considered include location of the construction site (distance from the batching plant), the amount of concrete needed, the construction schedule (volume of concrete needed per hour), and the cost. However, the main consideration is the quality of the concrete produced. This quality is determined by the performance of the concrete and by the homogeneity of the material after mixing and placement. There should be a methodology to determine the quality of the concrete produced, but only few methods and only one attempt of standardization were found in the literature. The methodology to determine the quality of the concrete mixed is often referred to as the measurement of the efficiency of the mixer. The efficiency parameters of a mixer are affected by the order in which the various constituents of the concrete are introduced into the mixer, the type of mixer, and the mixing energy (power and duration) used. The Mixers

Batch mixersMixers that produces concrete one batch at a time, and needs to be emptied completely after each mixing cycle, cleaned (if possible), and reloaded with the materials for the next batch of concrete. In the second type, the constituents are continuously entered at one end as the fresh concrete exits the other end. The various designs of each type of mixer will now be discussed.  The two main types of batch mixer can be distinguished by the orientation of the axis of rotation: horizontal or inclined (drum mixers) or vertical (pan mixers). The drum mixers have a drum, with fixed blades, rotating around its axis, while the pan mixers may have either the blades or the pan rotating around the axis.

Drum MixersAll the drum mixers have a container with a cross section.  The blades are attached to the inside of the movable drum. Their main purpose is to lift the materials as the drum rotates. In each rotation, the lifted material drops back into the mixer at the bottom of the drum and the cycle starts again. Parameters that can be controlled are the rotation speed of the drum and, and in certain mixers, the angle of inclination of the rotation axis. 

Mixing MethodIn describing the mixing process, the mixer hardware is only one of several components. The mixing process also includes the loading method, the discharge method, the mixing time, and the mixing energy.

Loading, Mixing, and DischargingThe loading method includes the order of loading the constituents into the mixer and also the duration of the loading period. The duration of this period depends on how long the constituents are mixed dry before the addition of water and how fast the constituents are loaded. The loading period is extended from the time when the first constituent is introduced in the mixer to when all the constituents are in the mixer. RILEM (Re´union Internationale des Laboratoires d’Essais et de Recherches sur les Mate´riaux et les constructions) divides the loading period into two parts: dry mixing and wet mixing. Dry mixing is the mixing that occurs during loading but before water is introduced. Wet mixing is the mixing after or while water is being introduced, but still during loading. This means that materials are introduced any time during the loading period: all before the water, all after the water, partially before and partially after. The loading period is important because some of the concrete properties will depend on the order in which the constituents are introduced in the mixer. It is well known that the delayed addition of high range water reducer admixture (HRWRA) leads to a better dispersion of the cement. The same workability can be thus be achieved with a lower dosage of HRWRA. 

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The discharge from the mixer should be arranged so that it increases productivity (fast discharge), and it does not modify (slow discharge) the homogeneity of the concrete. For instance, if the discharge involves a sudden change in velocity—as in falling a long distance onto a rigid surface—there could be a separation of the constituents by size or, in other words, segregation.

Mixing EnergyThe energy needed to mix a concrete batch is determined by the product of the power consumed during a mixing cycle and the duration of the cycle. It is often considered, inappropriately, a good indicator of the effectiveness of the mixer. The reason that it is not a good indicator is because of the high dependence of the power consumed on the type of mixture, the batch size and the loading method. For example, a mixer that has a powerful motor could be used to mix less workable or higher viscosity concretes. The mixing energy could be similar to that of a less powerful mixer but one filled with a more workable concrete.

Mixer EfficiencyAs it has been pointed out, the variables affecting the mixing method are numerous, not always controlled, and not a reliable indicator of the quality of the concrete produced. There is, therefore, a need for a methodology to determine the quality of the concrete produced as an intrinsic measure of the efficiency of the mixer. The concept of “mixer efficiency” is used to qualify how well a mixer can produce a uniform concrete from its constituents. RILEM defines that a mixer is efficient “if it distributes all the constituents uniformly in the container without favoring one or the other”. Therefore, in evaluating mixer efficiency, properties such as segregation and aggregate grading throughout the mixture should be monitored.

Steel Drum Concrete Mixers

4 cu.ft. 1/2hp Electric

4 cu.ft.

6 cu.ft. 1.5hp Electric

6 cu.ft.

6 cu.ft.

6 cu.ft.

9 cu.ft. 1.5hp Electric

9 cu.ft. 8

9 cu.ft.

Poly Drum Concrete Mixers

6 cu.ft. 1.5hp Electric

6 cu.ft.

6 cu.ft. 8

9 cu.ft. 1.5hp Electric

9 cu.ft.

Concrete

Concrete surfaces (specifically, Portland cement concrete) are created using a concrete mix of Portland cement, gravel, sand and water. The material is applied in a freshly-mixed slurry, and worked mechanically to compact the interior and force some of the thinner cement slurry to the surface to produce a smoother, denser surface free from honeycombing. The water allows the mix to combine molecularly in a chemical action called hydration.

Concrete surfaces have been refined into three common types: jointed plain (JPCP), jointed reinforced (JRCP) and continuously reinforced (CRCP). The one item that distinguishes each type is the jointing system used to control crack development.

Jointed Plain Concrete Pavements (JPCP) contain enough joints to control the location of all the expected natural cracks. The concrete cracks at the joints and not elsewhere in the slabs. Jointed plain pavements do not contain any steel reinforcement. However, there may be smooth steel bars at transverse joints and

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deformed steel bars at longitudinal joints. The spacing between transverse joints is typically about 15 feet for slabs 7–12 inches thick. Today, a majority of the U.S. state agencies build jointed plain pavements.

Jointed Reinforced Concrete Pavements (JRCP) contain steel mesh reinforcement (sometimes called distributed steel). In jointed reinforced concrete pavements, designers increase the joint spacing purposely, and include reinforcing steel to hold together intermediate cracks in each slab. The spacing between transverse joints is typically 30 feet or more. In the past, some agencies used a spacing as great as 100 feet. During construction of the interstate system, most agencies in the Eastern and Midwestern U.S. built jointed-reinforced pavement. Today only a handful of agencies employ this design, and its use is generally not recommended as JPCP and CRCP offer better performance and are easier to repair.

Continuously Reinforced Concrete Pavements (CRCP) do not require any transverse contraction joints. Transverse cracks are expected in the slab, usually at intervals of 3–5 ft. CRCP pavements are designed with enough steel, 0.6–0.7% by cross-sectional area, so that cracks are held together tightly. Determining an appropriate spacing between the cracks is part of the design process for this type of pavement.

Continuously reinforced designs generally cost more than jointed reinforced or jointed plain designs initially due to increased quantities of steel. However, they can demonstrate superior long-term performance and cost-effectiveness. A number of agencies choose to use CRCP designs in their heavy urban traffic corridors.

One advantage of cement concrete roadways is that they are typically stronger and more durable than asphalt roadways. They also can easily be grooved to provide a durable skid-resistant surface. Disadvantages are that they typically have a higher initial cost and are perceived to be more difficult to repair.

The first street in the United States to be paved with concrete was Court Avenue in Bellefontaine, Ohio, but the record for first mile of concrete pavement to be laid in the United States is claimed by Michigan.

Cement Concrete Paving

Cement concrete uses cement and water as the binding agent for the aggregate mix. Concrete paving also requires thick base layers of compacted aggregate to form a solid surface for the road. Workers must then construct forms, or molds, along the edges of the planned road to prevent the concrete from spreading before it sets. Cement concrete is broken up with regular joints, connected by wire baskets and dowels. This allows the concrete to expand and contract during seasonal temperature changes without cracking the surface of the road. The surface may be tined, or grooved, with a machine for better traction.

Read more: Road Construction Methods | eHow.com http://www.ehow.com/list_7826474_road-construction-methods.html#ixzz1Bw9wtUckere is a perception that concrete roads are significantly noisier than asphalt surfaces.

In order to counter this, ‘whisper concrete’ has been developed which has reduced the noise given off by vehicles by as much as three decibels, which is the equivalent of halving the traffic volume on the road.

Another aspect of concrete roads which has been open to criticism is the length of time which the concrete takes to cure before the road can be used. However, there have been developments in this area which will allow for a stretch of road to be fast-tracked overnight and be opened to traffic the next morning, causing a minimum of inconvenience to the users.

This technology is already in use in the US and Europe and Perrie hopes that it will soon be introduced into South Africa.

In the US and Europe, concrete roads are being designed to last up to 50 years with no maintenance in the first half of the roads’ life.

This is a direct result of the need for the unimpeded movement of traffic on busy routes and therefore surfaces which need to be regularly maintained interrupt this movement.

Apart from the lower maintenance costs on concrete roads, one factor which is not taken into account in comparing concrete and asphalt is the cost of delays to the road users when they are held up by maintenance and rehabilitation work which is generally more frequent on asphalt roads.

If this were taken into account then the cost of the bitumen roads, which have a much shorter life, increases dramatically.

In addition to these developments there are several other advantages to the use of concrete for roads, says Perrie.

One of these is the higher reflectiveness of the surface, this allows vehicles and pedestrians on the road to be more visible and also allows for a reduction in the lighting on the road, with fewer street lamps needed.

The skid resistance of the concrete surface is also measurably better than that of the asphalt surface.

Apart from the use of on-site concrete for the construction of high-volume roads, the use of interlocking concrete blocks is another possible use of this material in

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building low-traffic roads.

Interlocking blocks are already used in some residential areas, with a substantial degree of success.

Perrie explains that the laying of low-volume concrete roads can be much more labour-intensive than other methods, giving the government an incentive to use this technology.

The labourers who are trained to build concrete roads also acquire skills which can be used in general concrete construction, making this an option for skills development.

The institute is also attempting to increase the awareness of the possibilities for the use of concrete in roads by holding seminars and workshops.

A problem is that, because there have been relatively few large roads built in concrete in the past ten years, many of the skills which were acquired during the construction of these roads have now been lost.

Problems

Mistakes, Misconceptions, and Controversial Issues Concerning Concrete and Concrete Repairs

Mistakes and misconceptions concerning concrete and its repair have led to failures, poor performance, unnecessarily strict specifications, over-inspection, extra work, and extra costs. A better understanding of common concrete problems and issues can help to correct this situation. Article discusses common problems and issues that involve construction workers, supervisors, professors, engineers, sales representatives, inspectors, and specification writers.

Meeting the Requirements of an Architectural Concept Specification

Architectural concrete specifications must be unambiguous and capable of being met at reasonable cost. Article describes and discusses the steps that must be taken in establishing, confirming, and approving an architectural concrete specification to insure that the expense and effort incurred by all parties as a result of difficulties with meeting the specification are minimized.

Consider these real-life contractor scenarios:

* The contractor wants to meet with the owner to discuss payment of retainage. At the meeting, the owner hands the contractor a stack of F-number reports from the owner's testing agency and states that he is deducting 20% from the retainage because the reports state that the F-numbers aren't within specification requirements. The contractor has never seen these F-number reports before.

* The contractor has been using his measuring device to check F-numbers; however, this is for quality control. The test lab uses a different device to determine F-numbers. The floor flatness, [F.sub.F] numbers, is about the same, but the floor levelness, [F.sub.L] numbers, is substantially different, and [F.sub.L] values reported by the lab are too low. Since the test lab F-numbers are used for acceptance, the floor does not meet specification criteria.

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* The F-numbers are low. The data provided with the F-number report indicates there is a 3/4-inch elevation difference between two adjacent sample locations. A 3/4-inch hump within 12 inches should be easy to spot, but the F-number report doesn't indicate where the measurement lines were taken and the elevation difference can't be verified. At this point it's impossible to re-measure the floor and determine what the F-numbers were at the time of the test. The contractor is forced to try to repair or negotiate for a portion of his retainage.

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Avoiding F-number problems

Common problems in F-number measurement arise on many jobs. Following ASTM E 1155 "Standard Test Method for Determining [F.sub.F] Floor Flatness and [F.sub.L] Floor Levelness Numbers," is essential. Here are some common problems seen on many jobs.

1. Timely reporting

ASTM E 1155, note 5, states that ACI 117-90, "Standard Specification for Tolerances for Concrete Construction and Materials," requires that "specified concrete floor tolerances be checked within 72 hours after floor installation." ACI 301, "Specification for Structural Concrete," also provides the same testing requirement. Most test labs are aware of this requirement and are usually in compliance. While the slab may be measured within 72 hours after installation, the report documenting the F-numbers may not be made available to the contractor for weeks or even months. Timely reporting of the F-numbers provides immediate feedback on the contractor's work.

ACI 302-96, "Guide for Concrete Floor and Slab Construction," indicates that early F-number measurement relates directly to the contractor's performance. "If methods and procedures require modification, changes can be made early on, minimizing the amount of unsatisfactory floor surface and repair required." ACI 117-90 indicates that early F-number measurement "alerts the contractor of the need to modify finishing techniques on subsequent placements if necessary to achieve compliance."

Most projects require multiple concrete pours. Knowing the F-numbers after the first pour, and every pour thereafter, can help the contractor modify finishing techniques to minimize the potential for unsatisfactory performance and the cost and repair of subsequent pours. Failure to provide current F-numbers leads the contractor to believe that his floor will be accepted and that there is no need to adjust his methods and procedures to gain acceptance.

The contractor's quality control F-number measurements are good backup when timely reporting of F-numbers is not available. However, this can still lead to problems. On one project, the contractor's [F.sub.L] numbers were considerably higher than the test lab's [F.sub.L]. The contractor was under the false belief that his floors were acceptable. The owner used the test lab results to reject the floor and to require repair. If the contractor had had early notification of the difference in test results, he could have changed his methods and procedures so that the test lab's subsequent measured F-numbers would have met specifications.

In the prepour meeting, discuss the timeliness of the F-number report and who will receive the report. F-numbers can usually be provided verbally at the site at the time measurements are taken. We prefer this approach as it provides immediate notification and, if necessary, allows for immediate re-measuring of the slab. The written report should be available within 1 week after the floor is measured.

2. Obtaining the minimum number of readings

Section 7.6 of ASTM E 1155 dictates [N.sub.min], the minimum number of individual measurements of [z.sub.i] (the elevation difference between points 10 feet apart) within each test section. [N.sub.min] is calculated as follows:

[N.sub.min] = 2[square root of A] (320 [less than or equal to] A [less than or equal to] 1600)

= A/30 (A > 1600)

where A = test section area, [ft.sup.2]

Test labs often mistakenly interpret [z.sub.i] as the number of reading points, [n.sub.j], or as the number of elevation differences, [q.sub.i]. Often the F-number printout will list the number of readings for each line, and the operator sums the total for all the lines to determine what he believes is the minimum number of readings. The example below shows the difference in the amount of data for a single 30-foot measurement line:

0-foot measurement line

* Number of reading points, [n.sub.j], = 30

* Number of elevation differences between adjacent points, [q.sub.i], = 29

* Number of elevation differences between points 10 feet apart, [z.sub.i], = 21

Consider a test section area of 18,000 sf. The minimum number of readings would be 600 (18,000 square feet divided by 30 = 600). The operator chooses to make twenty 30-foot measurement lines, believing that he has satisfied the requirement for the minimum number of readings of 600 (20 times 30 readings = 600). However, he has actually collected only 420 of the samples required by the standard (20 lines times 21 elevation differences 10 feet apart per line ([z.sub.i]) = 420), which is 30% fewer than required.

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Since this mistake is typically found more than 72 hours after the floor installation, it's difficult to obtain additional reliable data. The test lab, and possibly the owner, will want to use the lab's data even though it doesn't conform to the requirements of ASTM E 1155.

3. Determining the number and location of measurement lines

Section 8.2.3 of ASTM E 1155 describes how to arrange sample measurement lines within each test section. The two provisions that we've had trouble with are:

A. Distributing the sample measurement lines uniformly across the entire test section.

B. Placing equal numbers of lines of equal aggregate length both parallel to and perpendicular to the longest test section boundary. (The aggregate length is the sum of the lengths of all the lines oriented in a single direction.)

Surprisingly, we've seen test reports where there were not an equal number of lines in each direction and where the lines in each direction were not equal in total length. The results are then biased in the direction of the majority of the lines with the greatest aggregate length. This problem is easily corrected by providing the operator with the information within section 8.

The requirement to uniformly distribute the sample measurement lines is sometimes more difficult to achieve--and is often overlooked. The measurement lines should be uniformly distributed to evaluate the finishing methods and techniques at both the start and end of the pour. Also, the owner must be satisfied that the F-numbers truly represent the surface characteristics of the entire floor.

Sometimes construction equipment or materials are already on the slab before the testing lab arrives onsite. Also, curing blankets might be used, making it difficult to locate and to collect data along the sample measurement lines. Many flatness-measuring-device operators will work with the contractor to determine the optimum time to lay out the lines and take the readings. Typically this is immediately after final finishing. Problems may develop when completion of final finishing falls outside normal working hours; most test labs do not include overtime pay as part of the F-number measurements.

The prepour meeting should discuss how the operator could locate and sample the uniformly distributed sample measurement lines within 72 hours after the floor is installed. Coordination of the data collection effort can be improved if the contractor provides the operator with the name and phone number of the person in charge of the pour.

. Providing a key plan and floor surface profile

The contractor's ability to modify finishing methods and techniques to improve F-numbers is directly related to the type and timeliness of information provided. A key plan is essential to understanding the layout and direction of the lines. With a key plan, the floor surface profile along those lines becomes useful information. Providing F-number results without an accompanying key plan or floor surface profile seriously limits the contractor's ability to interpret that data and to make successful changes.

Unfortunately, some devices used to measure F-numbers do not provide floor surface profiles. Section 9.2 of ASTM E 1155 requires the operator to graph the data to provide a floor surface profile "as a subjective quality control check to ensure that no gross anomalies are present in the data before reporting the results of this test method." A floor surface profile should always be included with the report.

We've found the floor surface profile useful for identifying:

* A "false sample"--a rather large elevation difference that is not consistent with adjacent samples. A "false sample" always shows up as a positive reading and is generally about 1/2 to 3/4 inch in magnitude.

* Boundaries of potential minimum local failures.

* Problems resulting from improperly adjusted or operating equipment.

* Differences in surface quality in opposing directions that may be caused by equipment or by finishing techniques.

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* Quality of parallel runs for consistency.

5. Following the manufacturer's recommendations

Too often as one operator teaches another operator how to perform F-number measurements, some of the finer points shown in the manufacturer's operating manual are overlooked. The finer points that we'd like to see understood by every operator include:

Dipstick

1. Zeroing: to ensure proper zero adjustment at the start of each run.

2. Calibration: although calibrated by the manufacturer, it should be checked periodically; we prefer at least monthly.

3. Data collection bias: this includes both surface roughness and operator bias. Operator bias should be checked every 3 months while surface roughness bias should be checked whenever the surface roughness or type of feet used are changed in a test section.

F-meter

1. The manufacturer states "A run of less than 30 feet 7 inches long will not produce a sufficient number of readings to calculate an [F.sub.L] estimate." This caveat is too often ignored and provides confusion when comparing against a Dipstick for runs of about 20 to 25 feet.

2. The manufacturer requires each unit to be returned annually to the factory for refurbishing and recalibration.

3. Measuring accuracy is compromised if

* a unit is not pulled in a straight line

* any reading is taken in reverse

* wheels lose contact or slip on the measured surface

* a unit is run across saw cuts, construction joints, and cracks without bridging the void

The contractor scenarios cited at the beginning of this article could have been avoided. Take time in the prepour meeting to discuss these issues and agree on a resolution. Good planning and communication can help avoid F-number problems.

Concrete fins fail to break off: Reduce the spacing between the blades. Light vehicles and motorcycles experience vehicle tracking: Reduce the spacing between the blades. Some areas are left without diamond-ground texture: If the untextured area exceeds project specifications, regrind it. Large amounts of concrete slurry are left on pavement surface: Stop grinding operations and check the vacuum unit and skirt surrounding the

cutting head.

  ToleranceHard Aggregate

(Typical)Soft Aggregate

(Typical)

Groove 2.0 - 4.0 mm 2.5 - 4.0 mm 2.5 - 4.0 mm

Land Area 1.5 - 3.5 mm 2.0 mm 2.5 mm

Depth 1.5 mm 1.5 mm 1.5 mm

Grooves/ Meter 164 - 194 174 - 194 164 - 177

(Note: 2.54 mm = 1 in.)

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Verify that the transverse slope of the ground surface is uniform to the extent that no misalignments or depressions that are capable of ponding water exist. Project documents typically have specific measurable criteria for transverse slope that must be met.

Verify on a daily basis that diamond-ground texture meets smoothness specifications. Verify that concrete slurry is adequately vacuumed from the pavement surface and is not allowed to flow into adjacent traffic lanes. Verify that the grinding residue is not discharged into a waterway, a roadway slope within 61 m (200 ft) of a waterway, or any area forbidden by

the contract documents or engineer. Concrete slurry from the grinding operation is typically collected and discharged at a disposal area designated in the contract document.

Weather Requirements

Measuring Water in Concrete

Should you pay attention to slump, water-cement ratio, or total amount of water in a mix?

We’ve all heard the saying, “With concrete there are two guarantees: it will get hard and it will crack.” How hard it will get and how much it will crack has a lot to do with the amount of water and cementitious material used to make it. Measuring Water in Concrete is important!

Water has always been the ingredient in concrete that contractors use to make concrete easier to place—the only ingredient they have control over on the jobsite. But almost everyone knows that adding too much water is bad because strength is reduced and more shrinkage results, causing additional cracking. So how much is too much? What’s the right way to specify how much water should be in a mix?

When you read articles about concrete or sit in ACI committee meetings, you hear these three terms: slump, water to cement (w/c) ratio, and “total water.” The terms often are used interchangeably. The assumption is that they all mean the same thing—a valid reference as to how much water is in a mix. But if they amount to three ways to say the same thing, wouldn’t it be best to discard two terms and refer to only one?

Changes in concrete mixes

Two developments further increase the confusion about water. One is the introduction of superplasticizing admixtures, also referred to as high-range water-reducing admixtures (HRWA), because they change the amount of water needed to make concrete easy to place. This is especially the case for the more recently developed polycarboxylate HRWAs. With no addition of water, the flowability of concrete can be changed greatly.

This concrete looks like the amount of water in the mix may be excessive but adding high-range water-reducing admixtures will produce the same look. Knowing the w/c ratio, or the total water in the mix, is the only way to know for sure. Photo: Joe Nasvik

The other development is the increasing interest in well-graded concrete mixes. They require less cementitious material which, in turn, reduces the amount of water that’s needed. Well-graded mixes are designed with several sizes of aggregates to reduce the volume of the open voids between aggregates, as well as the total surface area of aggregates. The net effect is that it takes less cementitious material to coat the aggregate surfaces and glue them together than the more traditional gap-graded mixes that use fewer aggregate gradations.

When you combine a well-graded mix with higher doses of polycarboxylate HRWAs and viscosity modifying admixtures (VMA), self-consolidating concrete (SCC) mixes result that change placing requirements. Projects such as the Trump Tower in Chicago (see “Reaching New Heights in Chicago” in the June 2007 issue of CONCRETE CONSTRUCTION) placed polycarboxylate treated concrete at slumps in excess of what was specified, but at w/c ratios lower than what was specified. The results were a better finished product placed on a faster schedule.

Defining terms

Here are the three ways water is specified for concrete mixes and how each is useful in terms of understanding the impact that water has on concrete.

Slump. When you want to know how much water is in concrete, your first question is probably “what is its slump?” Of the three ways to determine the amount of water in a mix (slump, w/c, or total water), it’s the only test performed in the field to provide a quick answer. But there are many things wrong with this test. It’s imprecise and relative at best. It’s possible to get different slump readings from the same batch of concrete. The age and temperature of concrete affect the results as well. High concrete temperatures, where hydration is developing quickly, result in lower slump readings than concrete at lower temperatures. Also the slump of very fresh concrete is higher than concrete an hour old. In both cases the amount of water in the mix hasn’t changed. You can continually add water to maintain a constant slump (a common practice), but this practice forever alters the w/c ratio.

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The other problem with testing slump to measure the water content of concrete occurs when adding water-reducing admixtures to the mix design. Slump readings change dramatically when there is no change to water content at all. In the case of SCC, inches of slump are completely irrelevant. “Spread” is the relevant term—how far the mix spreads out horizontally after the slump cone is pulled. SCC mixes generally have spreads between 18 to 30 inches.

The reason that the slump test still is worthwhile is that it provides workers in the field with estimates of place-ability and consistency between loads. That is the reason the test was developed originally. It was never intended to be a measure of concrete quality. Concrete with 5- to 6-inch slump readings generally is considered to be good for placement, however, concrete with 6- to 7-inch slump commonly is considered by placing crews to be more desirable.

Concrete placing crews must have concrete that can be placed efficiently and slump is the relevant test. Additionally for wall placements, higher slump concretes make good consolidation possible with fewer bug holes.

Water-cement ratio. It’s referred to as the “water to cement” (w/c) or occasionally as the “water to cementitious” (w/cm) ratio when pozzolans are included in a mix. But the normal reference is w/c, which includes all cementitious materials. The w/c ratio is calculated by dividing the weight of the water in a mix by the weight of cementitious material. This ratio usually is calculated when a mix is designed and it provides clues as to what the resulting compressive strength and durability of the mix will be. We know, for instance, that concrete with w/c ratios that fall between 0.40 and 0.55 generally is considered to be concrete with a proper amount of water. For the protection of reinforcement against corrosion, w/c ratios should be closer to 0.40. Concrete exposed to freeze/thaw conditions should be around 0.45. Interior flatwork mixes are generally between 0.47 and 0.55. This variance recognizes the differences that aggregate types and gradations have on a mix.

But there can be problems with knowing what the true w/c ratio is for concrete on the jobsite. This includes unaccounted moisture levels in the aggregates used (moisture meters are not that precise) and the amount of water left in a ready-mix truck drum when it’s cleaned can be as much as 10 gallons.

Another problem with judging the quality of a mix by depending on its w/c ratio is that the amount of cementitious material can be adjusted upward or downward with the corresponding addition or deletion of water, while the w/c ratio remains the same. The concrete performance characteristics can change greatly and the w/c ratio won’t provide any information about that.

The architect wanted to see all the detail in the form boards and the rough spacing between them in this narrow column. Using self-consolidating concrete with a low w/c ratio met all expectations and solved placing problems. Photo: Jack Gibbons

On the jobsite, most construction workers don’t understand the relevance of w/c ratios, but they do understand why slump is important.

Total water. This refers to the total amount of water required for a concrete mix. There is beginning to be more references to total water as the measure for specifying water amounts. Factors that influence the amount of water needed include the following:

Aggregate sizes and shapes Well-graded versus gap-graded mixes Total cementitious amounts, including types of cement Admixtures

Generally, good concrete has between 29 to 33 gallons of water per cubic yard. Strength and durability decreases as water exceeds these amounts. Specifying the total amount of water for a mix is very important for well-graded mixes that require less cementitious material for performance.

In the field the only way of Measuring Water in Concrete is by performing a microwave test, which is slow. It’s probable that concrete already will be in place before the test is completed. Also, most technicians are neither trained nor equipped to perform this test.

Using each method

Performing slump tests should only be used to provide information to the concrete contractor about the placeability of concrete. It also provides useful information about the consistency between loads of concrete because it doesn’t accurately define how much water is in a mix.

Whether you should think more in terms of w/c ratios or the total amount of water in concrete isn’t as clear as it is with testing slump. It’s probably best to be aware of both and how they change in relation to each other with different concrete mixes. Here are some thoughts about the relevance of each measure when you want concrete to have certain characteristics.

Shrinkage and curling. It’s important to have concrete for industrial and commercial floor construction that is resistant to shrinkage and curling over time. Reducing the amount of cementitious material and water is a primary way to achieve that goal. Concentrating on the total water in the mix is a good method.

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Durability. Several things that can affect the durability of concrete, but water content is a central concern. Water not required for hydration occupies space in fresh concrete that later becomes a void when the concrete is hard. The voids reduce the strength properties of concrete. Specifying w/c ratios is a good way to address durability issues. Under ideal conditions, a w/c ratio of approximately 0.25 is all that’s needed for hydration so anything over that is considered “water of convenience.”

Flowable concrete. When concrete must consolidate well in forms or fill highly congested steel-reinforced beams and columns, SCC-type mixes are important. Designing these mixes with water measured by w/c ratios provides relevant information.

Compressive strength. Determining the amount of water that’s best for a specified mix can be evaluated by either w/c ratios or total water.

Water often is referred to as the cheapest admixture for making flowable concrete. But look at what small additions of it does to hardened concrete . Photo: Jack Gibbons

Finishability. The amount of fines, cementitious material, and water in concrete all play a part in how well it can be finished. If there isn’t enough water, concrete can become sticky and hard to finish. Contractors experienced with low-shrinkage mixes think about total water requirements for their concrete. When several floor mixes are compared to each other, w/c ratios and total cementitious content may be more helpful.

Closing thoughts

In the past, it has been said that 33 gallons of water was needed to make concrete. But today with changes in technology and mix designs, the old rules no longer apply. Mixes can have as little as 29 gallons (27 gallons with rounded gravel aggregates) or more than 33 gallons to produce good concrete for an application. We used to think that the placeability of a mix stood at one end of a continuum and strength at the other. But this isn’t necessarily the case.

Today, the best concrete results from the interaction between specifying engineers and contractors. Engineers should specify the qualities that are important, such as strength and durability, and contractors should work with their ready-mix producers to develop the mixes that will meet the specification. In terms of water, it’s important that all parties understand the ways to measure it and which way provides the most useful information for the job at hand. Measuring Water in Concrete still remains the most important part of the process.

The project consisted of upgrading the main switchboard for the Acme Widget Company. It was my responsibility to determine the total power requirements for the new plant, calculate the power consumption of the existing plant and determine the maximum available power supplied through an existing board and the 11kV/415V transformer.After analysing the available information, I deduced that at least three alternatives for powering the new plant existed. A separate 11kV feeder could be brought onto the site to energise a new transformer and main board, the existing main board could be replaced with a new board or the existing main board could be upgraded. The last two options required the feeder cables to the main board to be upgraded.Technically, all three options were acceptable, although the first two allowed for a greater flexibility for expansion in future years.I prepared estimates for each of the options. The client engineer indicated that minimising the capital cost of the plant was of a higher priority than enhanced flexibility for expansion. On this basis, I issued a written recommendation indicating that, although other technical solutions existed, the upgrading of the main board involved the lowest capital cost and still provided the new plant with sufficient power requirements. The client accepted this option.I selected and sized power cables using Powerpack software. I simulated the limits in current-carrying capacity and length of runs on the basis of voltage drop using this tool. I also performed simulation of the maximum number of cables that could be installed on a single cable ladder and in underground conduits.For the PLC system I applied a functional specification already in use by our Company. A subsection of this specification listed requirements of a Factory Acceptable Test (FAT) to be conducted at the configuration supplier’s premises. I designed this test, the aim of which was to provide the consulting engineer with a reasonable confidence in the PLC software before it was installed and commissioned on-site. In a controlled environment and using the same PLC system hardware configuration to be installed on-site, various input signals were generated through a test rig to simulate field instruments. PLC outputs were recorded to verify the intended operation of the PLC program, as specified in the functional specification.During the test, a number of problems surfaced with the configuration. The client engineer was present at the test and, after consultation with him, I gave recommendations and directions to the PLC programmer to overcome perceived problems and improve operation of the plant

Engineering Technicians

Engineering technicians solve technical problems by using the principles and theories of engineering, science and mathematics. They work in research and development, construction, manufacturing, and inspection and maintenance. Their work is more application oriented than the work of engineers and scientists. Most engineering technicians work in a specific field.

Common job titles include engineering assistant, electronics technician, electrical engineering technician, electrical design technician, test technician, electrical technician, equipment engineering technician, engineering lab coordinator and engineering lab technician.

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Some engineering technicians assist engineers and scientists with research and development activities. They build or set-up equipment and perform experiments. They also collect data and record results. They help scientists or engineers produce prototypes of newly designed equipment. Engineering technician personnel may also help with design work and utilize computer-aided design and drafting equipment.

Some technicians work in quality control. They perform tests, check products and gather data. Engineering technicians that are employed in manufacturing industries help design and develop products. They may prepare technical or engineering drawings.

Some people in the occupation specialize in chemical engineering technology which involves developing new chemical products and processes. Another specialty is bioengineering technology which involves developing and implementing biomedical equipment.

Electrical and electronics engineering technicians assist with the designing, developing, testing and manufacturing of electronic and electrical equipment, including navigational equipment, computers, communication equipment, radar, industrial, and medical monitoring and control devices.

Aerospace engineering and operations technicians build, test and maintain aircraft and space vehicles. They often record and interpret data.

Civil engineering technicians assist civil engineers with planning and overseeing the construction of buildings, highways, water treatment systems, bridges and other structures. They also perform related research. Some civil engineering technicians determine the materials to be used and estimate construction costs.

Environmental engineering technicians assist in the development of methods and devices which are used to prevent, control or fix environmental hazards. They also inspect and maintain equipment related to recycling and air pollution. Some environmental technicians inspect water and wastewater treatment systems.

Responsibilities

Install and maintain solid state equipment and electrical control systems Make modifications to electrical parts, prototypes, systems and assemblies in order to fix functional deviations Assemble electronic and electrical systems and prototypes Set up and utilize test equipment Work with electrical engineers and others to identify and solve developmental problems Develop project cost and work-time estimates Build, maintain, troubleshoot and repair testing equipment and electrical instruments Assist engineers with product design Analyze and interpret test information Inspect products and proc

Design faults

misunderstanding the client's brief to develop the design using information which is incorrect or out of date misunderstanding of the client's expectations of quality standards lack of co-ordination between the designers. Loose or inappropriate specifications

Construction faults

Not building to drawings or specifications poor supervision leading to bad workmanship insufficient management of the quality of construction. In order to eliminate those potential problems many clients have looked to quality assurance to reassure them that they will get the right building without

undue quality problems.

To produce a building which satisfies the client To produce a building where quality is related to the price. To produce a building in which sufficient time is allowed to obtain the desired quality.

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Like most other aspects of construction management quality control has to be planned. Planning seeks 'order' and a quality control system for a construction project reflects this sense of order. It may be seen to be in five basic stages:

Setting the quality standard or quality of design required by client. Planning how to achieve the required quality, construction methods, equipments, materials and personnel to be employed. Construct the building right first time. Correct any quality deficiencies. Provide for long term quality control through establishing systems and developing a quality culture.

Materials Notebook: Materials Control

Reduced Staffing April 24, 1985 Memorandum Specification for Contractor Quality Control System Minimum Requirements For Materials Testing Laboratories

U.S. Department of TransportationFederal Highway Administration

MEMORANDUM

Materials Control/Reduced Staffing APR 24 1985

Chief, Construction and Maintenance DivisionOffice of Highway Operations

Regional Federal Highway AdministratorsRegions 1-10Regional Materials Engineers

Over the last several years, many State highway agencies have suffered budget constraints and personnel limitations or cutbacks, especially in the construction, inspection, and materials testing areas. At the same time, the level of highway funding and the number of highway construction projects have been increasing. These two factors require the more efficient use of available State personnel. Several ways to accomplish this have been discussed and/or tried experimentally by various agencies. Based on some observations from our materials reviews, we have identified three engineeringly sound and successful approaches to the problem. They are:

1. Process control by the producer;2. materials testing by consultant technicians; and3. materials testing by independent laboratories.

In each of these approaches, two critical issues arise. They are technician qualification and laboratory accreditation.

Technician Qualifications

Traditional State operation provided qualified technicians by in-house training and well defined supervisory relationships. However, where the inspecting, sampling, and testing technician is not a State employee, there is a need to establish and evaluate the qualifications of the technician performing the assigned duties.

The materials technician certification programs available and being used include:

The National Institute for Certification of Engineering Technologies (NICET) is the only nationally available program. The program provides for excellent training and examination in materials and materials testing in the areas of asphalt, concrete, and soils. The program is constantly monitored and updated by NICET.

Numerous State highway agencies (SHA's) have developed training information and certifications for both State and contractors' or consultants' technicians. Their programs vary from on-the-job training to classroom training. Certification is issued based on varying criteria which ranges from successful completion of a written exam and demonstrated testing efficiency to an oral interview with State engineers or senior technicians. Each program was

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developed informally based on State needs. Applicability from State-to-State is limited and implementation of another SHA's program may not give satisfactory assurance of qualification.

It is recommended that contractors'/consultants' technicians be required to be certified by the State prior to conducting testing on a project where this testing is required. Certification under the NICET program should be required by the State along with a State certification issued after a probation period on-the-job to ensure the technician's familiarity with State specifications, procedures, and standard forms. Recertifications should be required on a periodic basis such as every 2 years.

Laboratory Accreditation

Traditionally, materials testing was done entirely with State furnished and/or State calibrated/checked equipment. Assurance as to the adequacy of the State's laboratories, equipment, and procedures to correctly test materials was provided by the regularly performed inspections of the headquarters laboratory equipment and procedures by the American Association of State Highway and Transportation Officials Reference Laboratory (AMRL) and the National Bureau of Standards (NBS) Cement and Concrete Reference Laboratory (CCRL). The AMRL program provides for inspection of the laboratory equipment and testing procedures for compliance to AASHTO standards in the areas of soils, aggregates, and bituminous materials. The CCRL inspections are concerned with the testing equipment and procedural compliance to the American Society for Testing and Materials Standards. In addition to these inspections, there is also a program for testing of comparison samples of materials. Most of the States have programs for performing similar inspections on their district or satellite field laboratories. However, under a changed operation a State may hire independent laboratories to perform some testing. Here again, the adequacy of the equipment and the correctness of the operator's procedures in these independent laboratories is a matter of concern.

The laboratory qualification/accreditation programs available and being used include:

The AMRL program, while once confined to inspecting only the States' central laboratories, has now expanded to provide inspection services for laboratory equipment and procedures to any requesting laboratory involved in the testing of soils, aggregates, and bituminous materials. The cost of inspecting private or independent laboratories will be based on the number and type of tests which the laboratory performs. It should be noted that the AMRL program is not an accreditation program and the inspection report cannot be used for advertisement purposes. The CCRL inspection program is also available to any laboratory on a fee basis.

Several other programs including the American Association for Laboratory Accreditation (AALA) and the American Council of Independent Laboratories, Incorporated (ACIL) are available but these programs currently consist of basic reviews of available equipment and personnel without the detailed inspections which we believe are necessary.

It is recommended that those States that find it necessary to utilize independent laboratories for testing materials for use in Federal-aid highway work inspect the laboratories in the same manner as they would their district or satellite laboratories or require that they be inspected by AMRL or CCRL as appropriate. The latter is the preferred procedure since the inspection teams are comprised of recognized experts in their fields which are confined to highway materials. The State should monitor the private or independent laboratory periodically to determine if there have been any changes in the personnel performing the tests or if any of the equipment has been changed or replaced.

Each of the three approaches identified above will be detailed and key elements identified and discussed in the following paragraphs. We believe each of these approaches can be used successfully to assure materials quality and control in situations where staff reductions are occurring.

Process Control by the Producer

State testing can be reduced provided sufficient testing for control is done by the producer. As producer control is established, especially in fixed site plants, acceptance testing frequencies may be able to be reduced. The two key elements in a successful producer process control approach are (1) the producer's development and compliance with an approved control plan, and (2) the agency's monitoring of that compliance.

A producer's control plan should include the following:

1. A materials sampling and testing plan including tests and frequencies. The test results must be plotted on control charts.2. Documentation and retention of all information/certifications on incoming materials.3. Scheduled calibration and checking of testing equipment.4. Physical plant inspection schedule and documentation.5. Plant operator and tester qualifications. Testers should be certified under the NICET and by the State. The NICET certification should assure that the tester

has a basic understanding of engineering principles and testing procedures, while State certification will assure knowledge of State specifications, procedures, and forms. State certification should include a probation period.

6. Plant batcher/operator certificate of specification compliance with each shipment/load/batch of material going to State project.

The State monitoring of the producer's control should include:

1. assignment of an engineer or senior level technician to monitor the producer's control plan compliance and material quality;

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2. provision for daily inspection and unannounced periodic inspections to extract acceptance samples, review documentation such as materials invoices/certificates, producer inspection reports, control charts, etc;

3. provisions for plant inspection and approval prior to start-up and on a periodic (1 year) basis; and4. provisions for observation of the producer's sampling and testing, plant and testing equipment calibration, producer's inspection, etc., whenever possible.

A typical specification outlining these requirements is attached as Appendix A. This approach is effective in providing materials testing with a reduced number of State materials technicians.

Materials Testing by Consultant Technicians

Another approach to providing materials testing capabilities in the face of reduced State staff is by hiring outside technicians. The best approach provides for each State district to contract with a consultant to furnish qualified materials technicians, at plant or project sites within that district. The contract is best handled on a basic hourly rate for the technician's time (including consultant overhead, profit, etc.).

The consultant is responsible for training and development of the technicians prior to assignment on State projects. Technicians should be certified under the NICET program and by the State after a probationary on-the-job evaluation period and recertified as described earlier.

The State should provide an engineer or senior technician to monitor the production and testing operations on a periodic basis. Monitoring efforts should be frequent during the probationary period and any other time when problems are suspected. The contract must specify that the State has the authority and means to have the consultant remove a technician that is not performing the assigned tasks correctly.

Information and guidelines in developing a contract of this nature is described in FHPM 1-7-2, "Administration of Negotiated Contracts" and more specifically in superseded FHPM 6-1-2-2, "Engagement of Consultants for Engineering Services."

Materials Testing by Independent Laboratories

The third approach for providing materials testing is by contracting with independent laboratories. These laboratories will supply and maintain the necessary equipment and qualified technicians for conducting the testing for process and/or acceptance. These laboratories should be inspected by the State in the same manner as a State district or satellite laboratory or by AMRL/CCRL. Technicians should be State certified as described earlier.

A specific example of minimum requirements for testing laboratories is included in Appendix B.

Administration of this type agreement is generally more difficult than having a consultant merely provide technicians because of the numerous complexities and problems which occur during a project's life. The method of compensation should account for variations in testing frequencies. Agreement provisions should also provide for periodic State monitoring and unannounced inspections to assure satisfactory laboratory performance and materials quality and control.

The three approaches described can be effectively used for assuring materials quality and control testing. The first two described methods are preferred because of tighter State control of the personnel and the testing. It should be noted that all acceptance testing should be done by SHA personnel or personnel employed by the SHA and not the contractor/producer. If more information is needed, please contact the Geotechnical and Materials Branch (HMO-33, FTS 426-0436).

SIGNED P.E. CUNNINGHAMP. E. Cunningham

3 Attachments

Appendix ASPECIFICATION FOR CONTRACTOR QUALITY CONTROL SYSTEM

1. SCOPE This establishes minimum requirements and activities for a contractor quality control system. These requirements pertain to the inspections and tests necessary to substantiate material and product conformance to contract requirements and to all inspection and tests required by the contract.

2. FUNCTIONS AND RESPONSIBILITIES

a. The State highway agency (SHA). The SHA will approve mix designs, plant inspections, and monitor control of the operations to assure conformity with the specifications.

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At no time will the SHA's representatives issue instructions to the contractor or producer as to setting of dials, gauges, scales, and meters. However, the SHA's representatives may question and warn the contractor against the continuance of any operations or sequence of operations which will obviously not result in satisfactory compliance with specification requirements.

b. The Contractor. At the preconstruction conference, the contractor shall submit in writing his proposed quality control plan for approval of the SHA. The plan should contain the sampling, testing, inspection, and the anticipated-frequencies of each that the contractor expects to accomplish to maintain process control. A recommended series of sampling, testing, and inspecting activities are shown in Table 1 and Table 2.

TABLE 1RECOMMENDATIONS FOR A PRODUCER QUALITY

CONTROL PLAN FOR BITUMINOUS MIXTURES

All Types of Plants Stockpiles Determine gradation of all incoming aggregatesInspect stockpiles for separation, contamination, segregation, etc.Cold Bins Calibrate the cold gate settingsObserve operation of cold feed for uniformity

Observe pyrometer for aggregate temperature controlObserve efficiency of the burner (unburned fuel oil)

Determine gradation of aggregates in each binDetermine theoretical combined gradingBituminous Mixture Determine percent bitumenDetermine mix gradationCheck mix temperatureBatch Plants Batch Weights - Determine percent used and weight to be pulled from each bin to assure compliance with job-mix-formulaCheck mixing timeCheck operations of weigh bucket and scalesContinuous Mix Plant Determine gate calibration chart for each binDetermine gate settings for each bin to assure compliance with the job-mix-formulaDetermine gallons per revolution or gallons per minute to assure compliance with the job-mix formulaMixer Plant Calibrate the cold feed and prepare a calibration chart for each cold gateDevelop information for the synchronization of the aggregate feed and the bituminous material feedDetermine aggregate moisture contents to make necessary corrections to dry weight.

TABLE 2RECOMMENDATIONS FOR PRODUCER QUALITY CONTROL

PLAN FOR PORTLAND CEMENT CONCRETE

Incoming Materials Incoming cement certifications properCement storage properDetermine gradation of incoming aggregates and fineness modulus of fine aggregateAggregates from acceptable sourcesInspect stockpiles for separation, contamination, segregation, etc.Measuring Devices Scales calibrated/checked for accuracy and precisionFlow meters calibrated/checkedMoisture meter-check/verified by moisture testingAdmixture dispensers functioning/calibrated

Manufacturer's design details on handCentral mixer timing device operating satisfactorilyTruck mixers equipped with properly functioning revolution counters, water gauges, etc.All mixers free of hardened concreteMixers inspected weekly for proper functioning, wear, hardened concrete, etc.

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Mixing Concrete Batching sequence properMixing speed and/or time properConcrete checked for uniformity, tested for specification compliance

The activities shown in Tables 1 and 2 are considered to be normal activities necessary to control the production at an acceptable quality level. It is recognized, however, that depending on the type of process or materials, some of the activities listed may not be necessary and in other cases, additional activities may be required. The frequency of these activities will also vary with the process and the materials. When the process varies from the defined process average and variability targets, the frequency of these activities will be increased until the proper conditions have been restored.

The contractor or producer shall plot and keep up-to-date control charts for all quality control sampling and testing.

The contractor shall be responsible for the formulation of all mix design. Contractor-furnished mix designs must be submitted to the SHA for approval, prior to their use. The contractor shall be responsible for the process control of all materials during handling, blending, mixing, and placing operations.

3. QUALITY CONTROL SYSTEM

1. General Requirements. The contractor shall furnish and maintain a quality control system that will provide reasonable assurance that all materials and products submitted to the SHA for acceptance conform to the contract requirements whether manufactured or processed by contractor or procured from suppliers or subcontractors. The contractor shall perform or have performed the inspection and tests required to substantiate product conformance to contract requirements and shall also perform or have performed all inspections and tests otherwise required by the contract. The contractor shall have a quality control technician, who has been certified by the SHA available at the asphalt plant at all times the contractor is producing mix for the SHA. The SHA certification is dependent on NICET certification and satisfactory on-the-job performance during a probationary period. The contractor's quality control procedures, inspection, and tests shall be documented and that information be available for review by the SHA throughout the life of the contract.

2. Documentation. The contractor shall maintain adequate records of all inspections and tests. The records shall indicate the nature and number of tests made, the number and type of deficiencies found, the quantities approved and rejected, and the nature of corrective action taken as appropriate. The contractor's documentation procedures will be subject to the review and approval of the SHA prior to the start of the work and to compliance checks during the progress of the work. All charts and records documenting the contractor's quality control tests and inspections shall become the property of the SHA upon completion of the work.

3. Charts and Forms. All conforming and nonconforming inspections and test results shall be recorded on approved forms and charts which shall be kept up to date and complete and shall be available at all times to the SHA during the performance of the work. Test properties for the various materials and mixtures shall be charted on forms which are in accordance with the applicable requirements of the SHA. A copy of each chart and form to be used by the contractor will be furnished by the SHA. The contractor will furnish his own supply of the charts and forms. The contractor or producer may design their own forms and charts; however, these must be approved by the engineer prior to their use.

4. Corrective Actions. The contractor shall take prompt action to correct any errors; equipment malfunctions, process changes, or other assignable causes which have resulted in or could result in the submission of materials, products, and completed construction which do not conform to the requirements of the specifications. When it becomes evident to the SHA that the contractor is not controlling his process and is making no effort to take corrective actions, then the SHA will require that plant operations be ceased until such time as the contractor can demonstrate that he can and will control the process.

5. Laboratories with Measuring and Testing Equipment. The contractor or producer shall furnish a fully equipped laboratory at the production site. This facility may be permanent or portable. The laboratory shall be furnished with the necessary testing equipment and supplies for performing process control sampling and testing as well as SHA acceptance sampling and testing. To assure accuracy, the testing equipment will be checked prior to start up and periodically as directed by the SHA in accordance with applicable standards.

6. Sampling and Testing. Sampling and testing methods and procedures used by the contractor to determine quality conformance of the materials and products will be the same as those used by the SHA. Samples shall be taken in accordance with the contractor's approved procedures for random sampling. The contractor's quality control plan will include the taking of samples for other material characteristics on a random basis and the plotting of the test results on control charts.

7. Alternative Procedures. Alternative sampling methods, procedures, and inspection equipment may be used by the contractor when such procedures and equipment provide, as a minimum, the quality assurance required by the contract documents. Prior to applying such alternative procedures, the contractor shall describe them in a written proposal and shall demonstrate for the approval of the SHA that their effectiveness is equal to or' better than the contract requirements. In case of dispute as to whether certain proposed procedures of the contractor provide equal assurance, the procedures stipulated in the contract documents shall apply.

8. Nonconforming Materials. The contractor shall establish and maintain an effective and positive system for controlling nonconforming material, including procedures for identification, isolation, and disposition. Reclaiming or reworking nonconforming materials shall be in accordance with procedures acceptable to the SHA. ,he details of this system must be discussed at the preconstruction conference and become a part of the record of the conference.

9. SHA Inspection at Subcontractor or Supplier Facilities. The SHA reserves the right to inspect materials not manufactured within the contractor's facility. This inspection shall not constitute acceptance nor shall it in any way replace the contractor's inspection or otherwise relieve the contractor of his responsibility to furnish an acceptable material or product. When inspection of the subcontractor's or supplier's product is performed by the SHA, such inspection shall not be used by the contractor as evidence of effective inspection of such subcontractor's or supplier's product.

Subcontracted or purchased materials shall be inspected by the contractor when received, as necessary, to assure conformance to contract requirements. The contractor shall report to the SHA any nonconformance found on SHA source-inspected material and shall require the supplier to take necessary corrective action.

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Appendix BMINIMUM REQUIREMENTS FOR MATERIALS TESTING LABORATORIES

SCOPE

To have assurance that independent materials testing laboratories are capable of achieving an acceptable level of results, it is necessary that certain minimum standards be established. The minimum requirements necessarily include criteria for personnel, equipment, and quality control procedures. The requirements apply to all construction acceptance testing and inspection including asphalt concrete and portland cement concrete mix design.

APPLICABILITY

These requirements shall be applicable to all parties performing services associated with Federal-aid highway construction projects undertaken by the State highway agency (SHA).

REQUIREMENTS

To receive approval, the testing laboratory shall meet the latest requirements, applicable to the work for which is it to be engaged of ASTM Designation D-3666, "Evaluation of Inspection and Testing Agencies for Bituminous Paving Materials," E548, "Recommended Practice for Inspection and Testing Agencies for Concrete, Steel, and Bituminous Materials as Used in Construction," and E548, "Recommended Practice for Generic Criteria for Use in the Evaluation of testing and Inspection Agencies."

The testing laboratory shall have its laboratory equipment and procedures inspected at intervals not to exceed 2 years by a qualified national authority as evidence of its competence to perform the required tests and material designs. Acceptable national authority will include the AASHTO Materials Reference Laboratory (AMRL) and/or the Cement and Concrete Reference Laboratory (CCRL) as appropriate . In addition, testing machines and equipment must be calibrated annually or more frequently by impartial means using devices of accuracy traceable to the National Bureau of Standards.

In fields other than those covered by the referenced ASTM Standards, the testing laboratory shall accept only those assignments which it is able to perform competently by use of its own personnel and equipment. Any work to be subcontracted must be to laboratories meeting the same criteria.

The testing laboratory shall have demonstrated its competence in the applicable fields for a period of not less than 3 years.

The inspection and testing services of the testing laboratory shall be under the direction of a full-time employee registered as a professional engineer in the State. He shall have a minimum of 5 years of professional engineering experience in inspection and testing of the specific materials and construction which he directs.

aterials Notebook: Analysis of Noncomplying Material

Note: The following information is an excerpt from Technical Advisory T 5080.11 (April 6, 1989). The bulk of Technical Advisory T 5080.11 has been superseded by 23 CFR 637 (June 29, 1995).

A. Basis for Evaluation. The following discussion is intended as guidance for FHWA to be used as a basis for evaluating the State's recommendations for the acceptance of construction products if other procedures have not been established by the State and approved by FHWA.

1. Traditional pass/fail specifications typically do not have provisions for other than full payment for construction products. In most cases where there are products with test results outside of specification limits, acceptance at full pay or the determination of acceptance with equitable pay adjustments is normally ". . .as determined by the engineer." In these cases, some rational basis is necessary for the analysis of the failing products in order for a determination of Federal-aid participation to be made.

2. Statistically based specifications usually include an analysis which determines whether the construction product will be accepted at full payment or, for marginal products, will remain in place but will be accepted at an adjusted pay. If the project specifications provide a process for the acceptance of marginal construction products at an adjusted pay, the approval by FHWA of the State's specifications constitutes an approval of other procedures as noted above and no further analysis of the products will be necessary to determine Federal-aid participation.

3. There are a number of factors which can cause an indication that manufactured or project produced construction products do not meet the applicable specifications. In some cases, a visual inspection may be all that is necessary to determine if a product is acceptable. However, in a majority of the cases, sampling and testing of the construction product is the basis which is used to determine acceptability. The variability of a construction product which is indicated by the results of sampling and testing is not, however, an absolute measure but is the product of a combination of variables. These variables are the natural variability of the material, the variability induced through sampling procedures and the variability of testing procedures and/or equipment.

4. The policy of the FHWA is that a project must have been constructed ". . in reasonably close conformity with the approved plans and specifications. . ." to be eligible for Federal-aid participation. However, there will be instances when test results, as a result of the above noted variability may indicate apparent nonconformance to the specification limits, yet the construction product may be acceptable for the use intended at full or reduced pay. In these cases, an analysis of the materials and/or materials test results will be necessary before a determination of Federal-aid participation can be made.

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5. There are no exact rules which can be applied to the acceptance at full pay or the acceptance at some reduced pay for any specific construction product since the final analysis should be based on equitable payment for the value of the product. However, as a general "rule of thumb," if more than 10 percent of the test values for any construction product are outside of the applicable specifications, there may be a question of "reasonably close conformity." In these cases, an analysis of the test values should be made to determine the magnitude and extent of the nonconforming materials. The following general criteria can be used as a process to determine the degree of acceptability of construction products for Federal-aid participation purposes.

B. Categories of Compliance. Construction products which have test results not meeting specification limits can generally be classified into the following categories:

1. Category 1 - substantial conformance to the specifications. The construction product meets the specification since the number and magnitude of the deviations are such that they fall within the expected limits of material and testing variability. The construction product will provide full service life, and the State has recommended that full payment be made to the supplier/contractor. In these cases, full Federal-aid participation may be allowed.

2. Category 2 - marginal compliance. The number and/or the magnitude of the deviations fall outside the expected limits of material and testing variability. In these cases, an analysis must be made to determine acceptability based on performance and service life which can be anticipated. If the analysis indicates the construction product can be expected to provide a reasonable but reduced service life, limited Federal-aid participation may be allowed. The actual level of Federal-aid participation should be based on an analysis such as, but not limited to, life cycle costing, statistical evaluations of the degree of conformity to specifications, or other applicable engineering evaluations.

3. Category 3 - noncompliance. The magnitude and the number of deviations are such that the material will not perform acceptably. In these cases, Federal-aid participation should not be allowed in the construction product. The construction product should be removed and replaced or otherwise corrected.

C. Engineering Analysis. An analysis should be performed to determine which of the above categories describes the nonspecification construction product. The analysis should include an assessment of whether the material and workmanship are within normal construction limitations and whether the construction product can perform adequately. The following is offered as guidance on the areas which should be covered for each construction product.

1. Asphalt Paving. Although all parts of proportioning and construction operations are important, the most critical elements of the construction product are the asphalt content, amount of material passing the No. 200 sieve, and the density of the pavement. When there is a question of conformity, the analysis should concentrate on these elements. Paragraph 6b(1)(a) centers on the void structure of the pavement, and Paragraph 6b(1)(b) concerns gradation and asphalt control

a. Pavement sections which have densities of 96 percent of Theoretical Maximum Density (TMD) or greater will usually result in plastic flow and rutting. This situation is typically a function of excessive asphalt and/or minus 200 material. The asphalt content at which 3 percent voids occur in the laboratory mix design is the maximum asphalt content which should be approved.

i. Pavement sections with densities of 96 percent of TMD or greater, or which have the potential for consolidation to greater than 96 percent of TMD, i.e., high percentage of minus 200 or asphalt content, could be considered being in either marginal or noncompliance.

ii. Pavement sections which have been compacted to a density of 90 percent of TMD or less have the potential for stripping, accelerated asphalt aging, and consolidation rutting. These pavements may provide a reasonable but reduced service life and could also be considered as being in either marginal compliance or noncompliance based on the magnitude and degree of the failing materials.

iii. In each of the above cases, an analysis of the test results should be conducted prior to a final determination of acceptability, to determine the magnitude and degree of the failing materials. This analysis should be used to determine the degree or extent of Federal-aid participation in the asphalt pavement.

iv. A pavement density of 92 to 94 percent of TMD is the desired density in the field. A density of 91 to 95 percent of TMD may be considered in substantial conformance without further analysis being required.

b. The following are ranges for aggregate gradation and asphalt content for surface mixes which can be expected for normal construction. These ranges are based on standard deviations published in Public Roads, Vol.35, Nos. 6-11. The ranges include both testing variability and expected material variability for normal construction practice. With the exception of the asphalt content and the minus 200 material, the ranges will probably be within the tolerances of most State highway agencies.

Sieve Range +/-19.0 mm or 12.5 mm 2.86 Percent Passing

2.36 mm or 2.0 mm850 µm or 600 µm425 µm or 300 µm

asphalt content 0.56 Percent

c. If the project test results indicate that more than 10 percent of the actual test values are outside of these ranges or the State's specified tolerances, whichever is greater, an analysis of the construction product will be necessary to determine the degree or extent of Federal-aid participation.

2. Portland Cement Concrete. The analysis for Portland cement concrete should concentrate on three items: strength, air content, and slump. Strength and air content are directly related to performance; however, slump is generally only an indicator of workability of the mix. In some cases, slump may be considered as an indicator of the water-cement ratio of the mix. Paragraph 6b(2)(a) discusses strength, and paragraph 6b(2)(b) discusses slump and air content.

a. The strength analysis should be based on two criteria: (1) The minimum strength to perform satisfactorily and (2) the minimum strength that could be expected with good quality control.

i. For structural concrete, the compressive strength used for the structural design is the governing factor as to whether the concrete will remain in place. Any material that does not meet structural design requirements should be fully analyzed to determine if it may be left in place or must be removed.

If the project test results indicate that more than 10 percent of the actual test values are outside of these ranges or the State's specified tolerances, whichever is greater, an analysis of the construction product will be necessary to determine the degree or extent of Federal-aid participation.

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ii. In paving concrete, if 90 percent of the test results exceed the minimum specified compressive or flexure strengths, the material would generally be considered to be in substantial conformance to the specifications. If failing tests are not randomly distributed (i.e., represent a section or production run that can be readily identified as deficient) or exceed 10 percent of the tests, a further analysis of the construction product will be necessary to determine the degree or extent of Federal-aid participation.

b. The following ranges for slump and air content which can be expected for normal construction are based on standard deviations published in Public Roads, Vol. 35, Nos. 6-11. The ranges include both testing variability and expected material variability for normal construction practice.

  Range (+/-)Air Content (%)Slump (mm)

c. If the project test results indicate that more than 10 percent of the actual test values are outside of these ranges or the State's specified tolerances, whichever is greater, an analysis of the construction product will be necessary to determine the degree or extent of Federal-aid participation.

3. Soils and Soils Mixtures. The analysis should be based on the density of the material. The following range for embankment density which can be expected for normal construction is based on standard deviations published in Public Roads, Vol. 35, Nos. 6-11. The range includes both testing variability and material variability for normal construction practice.

  RangeDensity (%)

4. If the project test results indicate that more than 10 percent of the actual test values are outside of these ranges or the State's specified tolerances, whichever is greater, an analysis of the construction product will be necessary to determine the degree or extent of Federal-aid participation.

5. Aggregate and Aggregate Mixtures. The analysis for acceptance of aggregate and aggregate mixtures should concentrate on aggregate gradation, density, and stabilizer content.

a. The specification limits for both gradation and stabilizer content vary from State-to-State based on the available materials. Because of this variability, specific guidance cannot be provided for these properties.

b. The following range for base/subbase density which can be expected for normal construction is based on standard deviations published in Public Roads, Vol. 35, Nos. 6-11. The range includes both testing variability and material variability for normal construction practice. The range should apply to the target density.

Quality Control and Safety During Construction

13.1 Quality and Safety Concerns in Construction

Quality control and safety represent increasingly important concerns for project managers. Defects or failures in constructed facilities can result in very large costs. Even with minor defects, re-construction may be required and facility operations impaired. Increased costs and delays are the result. In the worst case, failures may cause personal injuries or fatalities. Accidents during the construction process can similarly result in personal injuries and large costs. Indirect costs of insurance, inspection and regulation are increasing rapidly due to these increased direct costs. Good project managers try to ensure that the job is done right the first time and that no major accidents occur on the project.

As with cost control, the most important decisions regarding the quality of a completed facility are made during the design and planning stages rather than during construction. It is during these preliminary stages that component configurations, material specifications and functional performance are decided. Quality control during construction consists largely of insuring conformance to these original design and planning decisions.

While conformance to existing design decisions is the primary focus of quality control, there are exceptions to this rule. First, unforeseen circumstances, incorrect design decisions or changes desired by an owner in the facility function may require re-evaluation of design decisions during the course of construction. While these changes may be motivated by the concern for quality, they represent occasions for re-design with all the attendant objectives and constraints. As a second case, some designs rely upon informed and appropriate decision making during the construction process itself. For example, some tunneling methods make decisions about the amount of shoring required at different locations based upon observation of soil conditions during the tunneling process. Since such decisions are based on better information concerning actual site conditions, the facility design may be more cost effective as a result. Any special case of re-design during construction requires the various considerations discussed in Chapter 3.

With the attention to conformance as the measure of quality during the construction process, the specification of quality requirements in the design and contract documentation becomes extremely important. Quality requirements should be clear and verifiable, so that all parties in the project can understand the requirements for conformance. Much of the discussion in this chapter relates to the development and the implications of different quality requirements for construction as well as the issues associated with insuring conformance.

Safety during the construction project is also influenced in large part by decisions made during the planning and design process. Some designs or construction plans are inherently difficult and dangerous to implement, whereas other, comparable plans may considerably reduce the possibility of accidents. For example, clear separation of traffic from construction zones during roadway rehabilitation can greatly reduce the possibility of accidental collisions. Beyond these design decisions, safety largely depends upon education, vigilance and cooperation during the construction process. Workers should be constantly alert to the possibilities of accidents and avoid taken unnecessary risks.

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13.2 Organizing for Quality and Safety

A variety of different organizations are possible for quality and safety control during construction. One common model is to have a group responsible for quality assurance and another group primarily responsible for safety within an organization. In large organizations, departments dedicated to quality assurance and to safety might assign specific individuals to assume responsibility for these functions on particular projects. For smaller projects, the project manager or an assistant might assume these and other responsibilities. In either case, insuring safe and quality construction is a concern of the project manager in overall charge of the project in addition to the concerns of personnel, cost, time and other management issues.

Inspectors and quality assurance personnel will be involved in a project to represent a variety of different organizations. Each of the parties directly concerned with the project may have their own quality and safety inspectors, including the owner, the engineer/architect, and the various constructor firms. These inspectors may be contractors from specialized quality assurance organizations. In addition to on-site inspections, samples of materials will commonly be tested by specialized laboratories to insure compliance. Inspectors to insure compliance with regulatory requirements will also be involved. Common examples are inspectors for the local government's building department, for environmental agencies, and for occupational health and safety agencies.

The US Occupational Safety and Health Administration (OSHA) routinely conducts site visits of work places in conjunction with approved state inspection agencies. OSHA inspectors are required by law to issue citations for all standard violations observed. Safety standards prescribe a variety of mechanical safeguards and procedures; for example, ladder safety is covered by over 140 regulations. In cases of extreme non-compliance with standards, OSHA inspectors can stop work on a project. However, only a small fraction of construction sites are visited by OSHA inspectors and most construction site accidents are not caused by violations of existing standards. As a result, safety is largely the responsibility of the managers on site rather than that of public inspectors.

While the multitude of participants involved in the construction process require the services of inspectors, it cannot be emphasized too strongly that inspectors are only a formal check on quality control. Quality control should be a primary objective for all the members of a project team. Managers should take responsibility for maintaining and improving quality control. Employee participation in quality control should be sought and rewarded, including the introduction of new ideas. Most important of all, quality improvement can serve as a catalyst for improved productivity. By suggesting new work methods, by avoiding rework, and by avoiding long term problems, good quality control can pay for itself. Owners should promote good quality control and seek out contractors who maintain such standards.

In addition to the various organizational bodies involved in quality control, issues of quality control arise in virtually all the functional areas of construction activities. For example, insuring accurate and useful information is an important part of maintaining quality performance. Other aspects of quality control include document control (including changes during the construction process), procurement, field inspection and testing, and final checkout of the facility.

13.3 Work and Material Specifications

Specifications of work quality are an important feature of facility designs. Specifications of required quality and components represent part of the necessary documentation to describe a facility. Typically, this documentation includes any special provisions of the facility design as well as references to generally accepted specifications to be used during construction.

General specifications of work quality are available in numerous fields and are issued in publications of organizations such as the American Society for Testing and Materials (ASTM), the American National Standards Institute (ANSI), or the Construction Specifications Institute (CSI). Distinct specifications are formalized for particular types of construction activities, such as welding standards issued by the American Welding Society, or for particular facility types, such as the Standard Specifications for Highway Bridges issued by the American Association of State Highway and Transportation Officials. These general specifications must be modified to reflect local conditions, policies, available materials, local regulations and other special circumstances.

Construction specifications normally consist of a series of instructions or prohibitions for specific operations. For example, the following passage illustrates a typical specification, in this case for excavation for structures:

Conform to elevations and dimensions shown on plan within a tolerance of plus or minus 0.10 foot, and extending a sufficient distance from footings and foundations to permit placing and removal of concrete formwork, installation of services, other construction, and for inspection. In excavating for footings and foundations, take care not to disturb bottom of excavation. Excavate by hand to final grade just before concrete reinforcement is placed. Trim bottoms to required lines and grades to leave solid base to receive concrete.

This set of specifications requires judgment in application since some items are not precisely specified. For example, excavation must extend a "sufficient" distance to permit inspection and other activities. Obviously, the term "sufficient" in this case may be subject to varying interpretations. In contrast, a specification that tolerances are within plus or minus a tenth of a foot is subject to direct measurement. However, specific requirements of the facility or characteristics of the site may make the standard tolerance of a tenth of a foot inappropriate. Writing specifications typically requires a trade-off between assuming reasonable behavior on the part of all the parties concerned in interpreting words such as "sufficient" versus the effort and possible inaccuracy in pre-specifying all operations.

In recent years, performance specifications have been developed for many construction operations. Rather than specifying the required construction process, these specifications refer to the required performance or quality of the finished facility. The exact method by which this performance is obtained is left to the construction contractor. For example, traditional specifications for asphalt pavement specified the composition of the asphalt material, the asphalt temperature during paving, and compacting procedures. In contrast, a performance specification for asphalt would detail the desired performance of the pavement with respect to impermeability, strength, etc. How the desired performance level was attained would be up to the paving contractor. In some cases, the payment for asphalt paving might increase with better quality of asphalt beyond some minimum level of performance.

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Example 13-1: Concrete Pavement Strength

Concrete pavements of superior strength result in cost savings by delaying the time at which repairs or re-construction is required. In contrast, concrete of lower quality will necessitate more frequent overlays or other repair procedures. Contract provisions with adjustments to the amount of a contractor's compensation based on pavement quality have become increasingly common in recognition of the cost savings associated with higher quality construction. Even if a pavement does not meet the "ultimate" design standard, it is still worth using the lower quality pavement and re-surfacing later rather than completely rejecting the pavement. Based on these life cycle cost considerations, a typical pay schedule might be:

Load Ratio Pay Factor

<0.500.50-0.690.70-0.890.90-1.091.10-1.291.30-1.49

>1.50

Reject0.900.951.001.051.101.12

In this table, the Load Ratio is the ratio of the actual pavement strength to the desired design strength and the Pay Factor is a fraction by which the total pavement contract amount is multiplied to obtain the appropriate compensation to the contractor. For example, if a contractor achieves concrete strength twenty percent greater than the design specification, then the load ratio is 1.20 and the appropriate pay factor is 1.05, so the contractor receives a five percent bonus. Load factors are computed after tests on the concrete actually used in a pavement. Note that a 90% pay factor exists in this case with even pavement quality only 50% of that originally desired. This high pay factor even with weak concrete strength might exist since much of the cost of pavements are incurred in preparing the pavement foundation. Concrete strengths of less then 50% are cause for complete rejection in this case, however.

13.4 Total Quality Control

Quality control in construction typically involves insuring compliance with minimum standards of material and workmanship in order to insure the performance of the facility according to the design. These minimum standards are contained in the specifications described in the previous section. For the purpose of insuring compliance, random samples and statistical methods are commonly used as the basis for accepting or rejecting work completed and batches of materials. Rejection of a batch is based on non-conformance or violation of the relevant design specifications. Procedures for this quality control practice are described in the following sections.

An implicit assumption in these traditional quality control practices is the notion of an acceptable quality level which is a allowable fraction of defective items. Materials obtained from suppliers or work performed by an organization is inspected and passed as acceptable if the estimated defective percentage is within the acceptable quality level. Problems with materials or goods are corrected after delivery of the product.

In contrast to this traditional approach of quality control is the goal of total quality control. In this system, no defective items are allowed anywhere in the construction process. While the zero defects goal can never be permanently obtained, it provides a goal so that an organization is never satisfied with its quality control program even if defects are reduced by substantial amounts year after year. This concept and approach to quality control was first developed in manufacturing firms in Japan and Europe, but has since spread to many construction companies. The best known formal certification for quality improvement is the International Organization for Standardization's ISO 9000 standard. ISO 9000 emphasizes good documentation, quality goals and a series of cycles of planning, implementation and review.

Total quality control is a commitment to quality expressed in all parts of an organization and typically involves many elements. Design reviews to insure safe and effective construction procedures are a major element. Other elements include extensive training for personnel, shifting the responsibility for detecting defects from quality control inspectors to workers, and continually maintaining equipment. Worker involvement in improved quality control is often formalized in quality circles in which groups of workers meet regularly to make suggestions for quality improvement. Material suppliers are also required to insure zero defects in delivered goods. Initally, all materials from a supplier are inspected and batches of goods with any defective items are returned. Suppliers with good records can be certified and not subject to complete inspection subsequently.

The traditional microeconomic view of quality control is that there is an "optimum" proportion of defective items. Trying to achieve greater quality than this optimum would substantially increase costs of inspection and reduce worker productivity. However, many companies have found that commitment to total quality control has substantial economic benefits that had been unappreciated in traditional approaches. Expenses associated with inventory, rework, scrap and warranties were reduced. Worker enthusiasm and commitment improved. Customers often appreciated higher quality work and would pay a premium for good quality. As a result, improved quality control became a competitive advantage.

Of course, total quality control is difficult to apply, particular in construction. The unique nature of each facility, the variability in the workforce, the multitude of subcontractors and the cost of making necessary investments in education and procedures make programs of total quality control in construction difficult. Nevertheless, a commitment to improved quality even without endorsing the goal of zero defects can pay real dividends to organizations.

Example 13-2: Experience with Quality Circles

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Quality circles represent a group of five to fifteen workers who meet on a frequent basis to identify, discuss and solve productivity and quality problems. A circle leader acts as liason between the workers in the group and upper levels of management. Appearing below are some examples of reported quality circle accomplishments in construction:

1. On a highway project under construction by Taisei Corporation, it was found that the loss rate of ready-mixed concrete was too high. A quality circle composed of cement masons found out that the most important reason for this was due to an inaccurate checking method. By applying the circle's recommendations, the loss rate was reduced by 11.4%. 2. In a building project by Shimizu Construction Company, may cases of faulty reinforced concrete work were reported. The iron workers quality circle examined their work thoroughly and soon the faulty workmanship disappeared. A 10% increase in productivity was also achieved.

3.5 Quality Control by Statistical Methods

An ideal quality control program might test all materials and work on a particular facility. For example, non-destructive techniques such as x-ray inspection of welds can be used throughout a facility. An on-site inspector can witness the appropriateness and adequacy of construction methods at all times. Even better, individual craftsmen can perform continuing inspection of materials and their own work. Exhaustive or 100% testing of all materials and work by inspectors can be exceedingly expensive, however. In many instances, testing requires the destruction of a material sample, so exhaustive testing is not even possible. As a result, small samples are used to establish the basis of accepting or rejecting a particular work item or shipment of materials. Statistical methods are used to interpret the results of test on a small sample to reach a conclusion concerning the acceptability of an entire lot or batch of materials or work products.

The use of statistics is essential in interpreting the results of testing on a small sample. Without adequate interpretation, small sample testing results can be quite misleading. As an example, suppose that there are ten defective pieces of material in a lot of one hundred. In taking a sample of five pieces, the inspector might not find any defective pieces or might have all sample pieces defective. Drawing a direct inference that none or all pieces in the population are defective on the basis of these samples would be incorrect. Due to this random nature of the sample selection process, testing results can vary substantially. It is only with statistical methods that issues such as the chance of different levels of defective items in the full lot can be fully analyzed from a small sample test.

There are two types of statistical sampling which are commonly used for the purpose of quality control in batches of work or materials:

1. The acceptance or rejection of a lot is based on the number of defective (bad) or nondefective (good) items in the sample. This is referred to as sampling by attributes. 2. Instead of using defective and nondefective classifications for an item, a quantitative quality measure or the value of a measured variable is used as a quality indicator.

This testing procedure is referred to as sampling by variables.

Whatever sampling plan is used in testing, it is always assumed that the samples are representative of the entire population under consideration. Samples are expected to be chosen randomly so that each member of the population is equally likely to be chosen. Convenient sampling plans such as sampling every twentieth piece, choosing a sample every two hours, or picking the top piece on a delivery truck may be adequate to insure a random sample if pieces are randomly mixed in a stack or in use. However, some convenient sampling plans can be inappropriate. For example, checking only easily accessible joints in a building component is inappropriate since joints that are hard to reach may be more likely to have erection or fabrication problems.

Another assumption implicit in statistical quality control procedures is that the quality of materials or work is expected to vary from one piece to another. This is certainly true in the field of construction. While a designer may assume that all concrete is exactly the same in a building, the variations in material properties, manufacturing, handling, pouring, and temperature during setting insure that concrete is actually heterogeneous in quality. Reducing such variations to a minimum is one aspect of quality construction. Insuring that the materials actually placed achieve some minimum quality level with respect to average properties or fraction of defectives is the task of quality control.

13.6 Statistical Quality Control with Sampling by Attributes

Sampling by attributes is a widely applied quality control method. The procedure is intended to determine whether or not a particular group of materials or work products is acceptable. In the literature of statistical quality control, a group of materials or work items to be tested is called a lot or batch. An assumption in the procedure is that each item in a batch can be tested and classified as either acceptable or deficient based upon mutually acceptable testing procedures and acceptance criteria. Each lot is tested to determine if it satisfies a minimum acceptable quality level (AQL) expressed as the maximum percentage of defective items in a lot or process.

In its basic form, sampling by attributes is applied by testing a pre-defined number of sample items from a lot. If the number of defective items is greater than a trigger level, then the lot is rejected as being likely to be of unacceptable quality. Otherwise, the lot is accepted. Developing this type of sampling plan requires consideration of probability, statistics and acceptable risk levels on the part of the supplier and consumer of the lot. Refinements to this basic application procedure are also possible. For example, if the number of defectives is greater than some pre-defined number, then additional sampling may be started rather than immediate rejection of the lot. In many cases, the trigger level is a single defective item in the sample. In the remainder of this section, the mathematical basis for interpreting this type of sampling plan is developed.

More formally, a lot is defined as acceptable if it contains a fraction p1 or less defective items. Similarly, a lot is defined as unacceptable if it contains a fraction p2 or

more defective units. Generally, the acceptance fraction is less than or equal to the rejection fraction, p1 p2, and the two fractions are often equal so that there is no ambiguous range of lot acceptability between p1 and p2. Given a sample size and a trigger level for lot rejection or acceptance, we would like to determine the probabilities that acceptable lots might be incorrectly rejected (termed producer's risk) or that deficient lots might be incorrectly accepted (termed consumer's risk).

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Consider a lot of finite number N, in which m items are defective (bad) and the remaining (N-m) items are non-defective (good). If a random sample of n items is taken from this lot, then we can determine the probability of having different numbers of defective items in the sample. With a pre-defined acceptable number of defective items, we can then develop the probability of accepting a lot as a function of the sample size, the allowable number of defective items, and the actual fraction of defective items. This derivation appears below.

The number of different samples of size n that can be selected from a finite population N is termed a mathematical combination and is computed as:

(13.1)

where a factorial, n! is n*(n-1)*(n-2)...(1) and zero factorial (0!) is one by convention. The number of possible samples with exactly x defectives is the combination associated with obtaining x defectives from m possible defective items and n-x good items from N-m good items:

(13.2)

Given these possible numbers of samples, the probability of having exactly x defective items in the sample is given by the ratio as the hypergeometric series:

(13.3)

With this function, we can calculate the probability of obtaining different numbers of defectives in a sample of a given size.

Suppose that the actual fraction of defectives in the lot is p and the actual fraction of nondefectives is q, then p plus q is one, resulting in m = Np, and N - m = Nq. Then, a function g(p) representing the probability of having r or less defective items in a sample of size n is obtained by substituting m and N into Eq. (13.3) and summing over the acceptable defective number of items:

(13.4)

If the number of items in the lot, N, is large in comparison with the sample size n, then the function g(p) can be approximated by the binomial distribution:

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(13.5)

or

(13.6)

The function g(p) indicates the probability of accepting a lot, given the sample size n and the number of allowable defective items in the sample r. The function g(p) can be represented graphical for each combination of sample size n and number of allowable defective items r, as shown in Figure 13-1. Each curve is referred to as the operating characteristic curve (OC curve) in this graph. For the special case of a single sample (n=1), the function g(p) can be simplified:

(13.7)

so that the probability of accepting a lot is equal to the fraction of acceptable items in the lot. For example, there is a probability of 0.5 that the lot may be accepted from a single sample test even if fifty percent of the lot is defective.

Figure 13-1  Example Operating Characteristic Curves Indicating Probability of Lot Acceptance

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For any combination of n and r, we can read off the value of g(p) for a given p from the corresponding OC curve. For example, n = 15 is specified in Figure 13-1. Then, for various values of r, we find:

The producer's and consumer's risk can be related to various points on an operating characteristic curve. Producer's risk is the chance that otherwise acceptable lots fail the sampling plan (ie. have more than the allowable number of defective items in the sample) solely due to random fluctuations in the selection of the sample. In contrast, consumer's risk is the chance that an unacceptable lot is acceptable (ie. has less than the allowable number of defective items in the sample) due to a better than average quality in the sample. For example, suppose that a sample size of 15 is chosen with a trigger level for rejection of one item. With a four percent acceptable level and a greater than four percent defective fraction, the consumer's risk is at most eighty-eight percent. In contrast, with a four percent acceptable level and a four percent defective fraction, the producer's risk is at most 1 - 0.88 = 0.12 or twelve percent.

In specifying the sampling plan implicit in the operating characteristic curve, the supplier and consumer of materials or work must agree on the levels of risk acceptable to themselves. If the lot is of acceptable quality, the supplier would like to minimize the chance or risk that a lot is rejected solely on the basis of a lower than average quality sample. Similarly, the consumer would like to minimize the risk of accepting under the sampling plan a deficient lot. In addition, both parties presumably would like to minimize the costs and delays associated with testing. Devising an acceptable sampling plan requires trade off the objectives of risk minimization among the parties involved and the cost of testing.

Example 13-3: Acceptance probability calculation

Suppose that the sample size is five (n=5) from a lot of one hundred items (N=100). The lot of materials is to be rejected if any of the five samples is defective (r = 0). In this case, the probability of acceptance as a function of the actual number of defective items can be computed by noting that for r = 0, only one term (x = 0) need be considered in Eq. (13.4). Thus, for N = 100 and n = 5:

For a two percent defective fraction (p = 0.02), the resulting acceptance value is:

Using the binomial approximation in Eq. (13.5), the comparable calculation would be:

which is a difference of 0.0019, or 0.21 percent from the actual value of 0.9020 found above.

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If the acceptable defective proportion was two percent (so p1 = p2 = 0.02), then the chance of an incorrect rejection (or producer's risk) is 1 - g(0.02) = 1 - 0.9 = 0.1 or ten percent. Note that a prudent producer should insure better than minimum quality products to reduce the probability or chance of rejection under this sampling plan. If the actual proportion of defectives was one percent, then the producer's risk would be only five percent with this sampling plan.

Example 13-4: Designing a Sampling Plan

Suppose that an owner (or product "consumer" in the terminology of quality control) wishes to have zero defective items in a facility with 5,000 items of a particular kind. What would be the different amounts of consumer's risk for different sampling plans?

With an acceptable quality level of no defective items (so p1 = 0), the allowable defective items in the sample is zero (so r = 0) in the sampling plan. Using the binomial approximation, the probability of accepting the 5,000 items as a function of the fraction of actual defective items and the sample size is:

To insure a ninety percent chance of rejecting a lot with an actual percentage defective of one percent (p = 0.01), the required sample size would be calculated as:

Then,

As can be seen, large sample sizes are required to insure relatively large probabilities of zero defective items.

13. Quality Control and Safety During Construction-03 13.7 Statistical Quality Control with Sampling by Variables

As described in the previous section, sampling by attributes is based on a classification of items as good or defective. Many work and material attributes possess continuous properties, such as strength, density or length. With the sampling by attributes procedure, a particular level of a variable quantity must be defined as acceptable quality. More generally, two items classified as good might have quite different strengths or other attributes. Intuitively, it seems reasonable that some "credit" should be provided for exceptionally good items in a sample. Sampling by variables was developed for application to continuously measurable quantities of this type. The procedure uses measured values of an attribute in a sample to determine the overall acceptability of a batch or lot. Sampling by variables has the advantage of using more information from tests since it is based on actual measured values rather than a simple classification. As a result, acceptance sampling by variables can be more efficient than sampling by attributes in the sense that fewer samples are required to obtain a desired level of quality control.

In applying sampling by variables, an acceptable lot quality can be defined with respect to an upper limit U, a lower limit L, or both. With these boundary conditions, an acceptable quality level can be defined as a maximum allowable fraction of defective items, M. In Figure 13-2, the probability distribution of item attribute x is illustrated. With an upper limit U, the fraction of defective items is equal to the area under the distribution function to the right of U

(so that x U). This fraction of defective items would be compared to the allowable fraction M to determine the acceptability of a lot. With both a lower and an upper limit on acceptable quality, the fraction defective would be the fraction of items greater than the upper limit or less than the lower limit. Alternatively, the limits could be imposed upon the acceptable average level of the variable

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Figure 13-2  Variable Probability Distributions and Acceptance Regions

In sampling by variables, the fraction of defective items is estimated by using measured values from a sample of items. As with sampling by attributes, the procedure assumes a random sample of a give size is obtained from a lot or batch. In the application of sampling by variables plans, the measured characteristic is virtually always assumed to be normally distributed as illustrated in Figure 13-2. The normal distribution is likely to be a reasonably good assumption for many measured characteristics such as material density or degree of soil compaction. The Central Limit Theorem provides a general support for the assumption: if the source of variations is a large number of small and independent random effects, then the resulting distribution of values will approximate the normal distribution. If the distribution of measured values is not likely to be approximately normal, then sampling by attributes should be adopted. Deviations from normal distributions may appear as skewed or non-symmetric distributions, or as distributions with fixed upper and lower limits.

The fraction of defective items in a sample or the chance that the population average has different values is estimated from two statistics obtained from the sample: the sample mean and standard deviation. Mathematically, let n be the number of items in the sample and xi, i = 1,2,3,...,n, be the measured

values of the variable characteristic x. Then an estimate of the overall population mean is the sample mean :

(13.8)

An estimate of the population standard deviation is s, the square root of the sample variance statistic:

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(13.9)

Based on these two estimated parameters and the desired limits, the various fractions of interest for the population can be calculated.

The probability that the average value of a population is greater than a particular lower limit is calculated from the test statistic:

(13.10)

which is t-distributed with n-1 degrees of freedom. If the population standard deviation is known in advance, then this known value is substituted for the estimate s and the resulting test statistic would be normally distributed. The t distribution is similar in appearance to a standard normal distribution, although the spread or variability in the function decreases as the degrees of freedom parameter increases. As the number of degrees of freedom becomes very large, the t-distribution coincides with the normal distribution.

With an upper limit, the calculations are similar, and the probability that the average value of a population is less than a particular upper limit can be calculated from the test statistic:

(13.11)

With both upper and lower limits, the sum of the probabilities of being above the upper limit or below the lower limit can be calculated.

The calculations to estimate the fraction of items above an upper limit or below a lower limit are very similar to those for the population average. The only difference is that the square root of the number of samples does not appear in the test statistic formulas:

(13.12)

and

(13.13)

where tAL is the test statistic for all items with a lower limit and tAU is the test statistic for all items with a upper limit. For example, the test statistic for

items above an upper limit of 5.5 with = 4.0, s = 3.0, and n = 5 is tAU = (8.5 - 4.0)/3.0 = 1.5 with n - 1 = 4 degrees of freedom.

Instead of using sampling plans that specify an allowable fraction of defective items, it saves computations to simply write specifications in terms of the allowable test statistic values themselves. This procedure is equivalent to requiring that the sample average be at least a pre-specified number of standard

deviations away from an upper or lower limit. For example, with = 4.0, U = 8.5, s = 3.0 and n = 41, the sample mean is only about (8.5 - 4.0)/3.0 = 1.5 standard deviations away from the upper limit.

To summarize, the application of sampling by variables requires the specification of a sample size, the relevant upper or limits, and either (1) the

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allowable fraction of items falling outside the designated limits or (2) the allowable probability that the population average falls outside the designated limit. Random samples are drawn from a pre-defined population and tested to obtained measured values of a variable attribute. From these measurements, the sample mean, standard deviation, and quality control test statistic are calculated. Finally, the test statistic is compared to the allowable trigger level and the lot is either accepted or rejected. It is also possible to apply sequential sampling in this procedure, so that a batch may be subjected to additional sampling and testing to further refine the test statistic values.

With sampling by variables, it is notable that a producer of material or work can adopt two general strategies for meeting the required specifications. First, a producer may insure that the average quality level is quite high, even if the variability among items is high. This strategy is illustrated in Figure 13-3 as a "high quality average" strategy. Second, a producer may meet a desired quality target by reducing the variability within each batch. In Figure 13-3, this is labeled the "low variability" strategy. In either case, a producer should maintain high standards to avoid rejection of a batch.

Figure 13-3  Testing for Defective Component Strengths

Example 13-5: Testing for defective component strengths

Suppose that an inspector takes eight strength measurements with the following results:

4.3, 4.8, 4.6, 4.7, 4.4, 4.6, 4.7, 4.6

In this case, the sample mean and standard deviation can be calculated using Equations (13.8) and (13.9):

= 1/8(4.3 + 4.8 + 4.6 + 4.7 + 4.4 + 4.6 + 4.7 + 4.6) = 4.59s2=[1/(8-1)][(4.3 - 4.59)2 + (4.8 - 4.59)2 + (4.6 - 4.59)2 + (4.7 - 4.59)2 + (4.4 - 4.59)2 + (4.6 - 4.59)2 + (4.7 - 4.59)2 + (4.6 - 4.59)2] = 0.16

The percentage of items below a lower quality limit of L = 4.3 is estimated from the test statistic tAL in Equation (13.12):