Properties of Fresh Concrete Kurdistan

Introduction Chapter1

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Properties of Fresh Concrete University of Polytechnic Technical Engineering College / Erbil In partial fulfillment of the requirements for the degree of B.S.C Of science Civil Engineering

2013/2014

Directed By Supervised By

Rahand K. Hussein Avin D. Ahmed

Ahmed B. Noori

Rediar H. Salih

Omar I. Muhammed

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CONTENTS

PREFACE ............................................................................................................................................................................ iv

Chapter 1 INTRODUCTION TO PROPERTIES OF FRESH CONCRETE ............................................. 1

1.1 Introduction: ................................................................................................................................................... 1

1.2 FRESHLY MIXED CONCRETE .................................................................................................................... 3

1.3 Mixing ................................................................................................................................................................. 3

1.4 Definition of workability ............................................................................................................................ 4

1.4.1 Workability of Fresh Concrete ....................................................................................................... 5

1.4.2 Measurement of workability........................................................................................................... 5

1.4.3 Factors affecting workability .......................................................................................................... 6

1.5 Segregation ................................................................................................................................................... 10

1.6 Bleeding .......................................................................................................................................................... 10

1.7 Slump loss ..................................................................................................................................................... 11

1.8 Principal requirements for concrete .................................................................................................. 12

1.9 Admixtures for Concrete ......................................................................................................................... 13

1.9.1 Air-Entraining Admixture ............................................................................................................. 14

1.9.2 Water-Reducing Admixture ......................................................................................................... 15

Chapter 2 Fresh Concrete Tests .............................................................................................................. 16

2.1 Measurements of Workability ................................................................................................................... 16

2.1.1 The Slump test ........................................................................................................................................ 16

2.1.1.1 The instruments ................................................................................................................................ 17

2.1.1.2 The purpose of slump test ............................................................................................................ 17

2.1.1.3 Procedure of Slump Test ............................................................................................................... 18

2.1.1.4 Results ................................................................................................................................................... 18

2.1.1.5 Interpretation of results ................................................................................................................ 19

2.1.1.6 Limitations of the slump test ....................................................................................................... 20

2.1.1.7 Differences in standards ......................................................................................................... 20

2.1.2 Compacting Factor Test ...................................................................................................................... 20

2.1.2.1 Introduction: ....................................................................................................................................... 20

2.1.2.2 Purpose ................................................................................................................................................. 21

2.1.2.3 Apparatus............................................................................................................................................. 21

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2.1.2.4 Materials ............................................................................................................................................... 21

2.1.2.5 Procedure............................................................................................................................................. 22

2.1.3 Vebe test of fresh concrete ................................................................................................................ 23

2.1.3.1 Introduction: ....................................................................................................................................... 23

2.1.3.2 Purpose: ................................................................................................................................................ 23

2.1.3.3 Materials: ............................................................................................................................................. 23

2.1.3.4 Apparatus............................................................................................................................................. 24

2.1.3.5 Procedure............................................................................................................................................. 25

2.2 Flow test.............................................................................................................................................................. 26

2.2.1 Equipment ........................................................................................................................................... 26

2.2.2 Procedure of the test ....................................................................................................................... 27

2.2.3 Calculation ........................................................................................................................................... 27

2.3 Test for the bleeding ...................................................................................................................................... 28

Chapter 3 FRESH CONCRETE IN SITE .................................................................................................... 40

3.1 Delivery of Concrete ...................................................................................................................................... 40

3.2 TRANSPORTING AND HANDLING CONCRETE ................................................................................... 42

3.2.1 Delays .................................................................................................................................................... 42

3.2.2 Early Stiffening and Drying Out. ................................................................................................. 43

3.2.3 Segregation.......................................................................................................................................... 43

3.3 Concrete Placing .............................................................................................................................................. 43

CONCLUSION ................................................................................................................................................................... 44

References ........................................................................................................................................................................ 45

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PREFACE

Concrete is the most widely used material in the world. It plays an important role in infrastructure and private buildings construction. There have been some very good books regarding concrete, including Advanced Concrete Technology by Zongjin Li Advanced Concrete Technology -Constituent Materials -Concrete Properties -Processes -Testing and Quality By John Newman & Ban Seng Choo Design and Control of Concrete Mixtures By Steven H. Kosmatka, Beatrix Kerkhoff, and William C. Panarese This Project Consists of three chapters, chapter 1 gives a brief introduction of fresh concrete, Chapter 2 is about the tests which are used to calculate the properties of fresh Concrete, Chapter 3 is about Fresh Concrete in site from the time it’s transported till it’s placed and compacted.

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CHAPTER 1

INTRODUCTION TO PROPERTIES OF FRESH CONCRETE

1.1 Introduction:

Concrete is basically a mixture of two components: aggregates and paste. The paste, comprised of Portland cement and water, binds the aggregates (usually sand and gravel or crushed stone) into a rocklike mass as the paste hardens because of the chemical reaction of the cement and water (Fig.1-1). Supplementary cementitious materials and chemical admixtures may also be included in the paste.

- Aggregates are generally divided into two groups: fine and coarse.

Fine aggregates consist of natural or manufactured sand with particle sizes ranging up to 9.5 mm (3⁄8 in.); coarse aggregates are particles retained on the 1.18 mm (No. 16) sieve and ranging up to 150 mm (6 in.) in size. The maximum size of coarse aggregate is typically 19 mm or 25 mm (3⁄4 in. or 1 in.).

An intermediate-sized aggregate, around 9.5 mm (3⁄8 in.), is sometimes added to improve the overall aggregate gradation.

For any particular set of materials and conditions of curing, the quality of hardened concrete is strongly influenced by the amount of water used in relation to the amount of cement, Unnecessarily high water contents dilute the cement paste.

Fig.1-1. Concrete components: cement, water, fine aggregate and coarse aggregate, are combined

to form concrete.

Introduction to Fresh Concrete Properties Chapter1

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- Following are some advantages of reducing water content:

• Increased compressive and flexural strength

• Lower permeability, thus lower absorption and increased Water tightness

• Increased resistance to weathering

• Better bond between concrete and reinforcement

• Reduced drying shrinkage and cracking

• Less volume change from wetting and drying

-The less water used, the better the quality of the concrete provided the mixture can be consolidated properly.

Smaller amounts of mixing water result in stiffer mixtures; but with vibration, stiffer mixtures can be easily placed. Thus, consolidation by vibration permits improvement in the quality of concrete.

The freshly mixed (plastic) and hardened properties of concrete may be changed by adding chemical admixtures to the concrete, usually in liquid form, during batching.

Chemical admixtures are commonly used to

Adjust setting time or hardening, reduce water demand, increase workability, intentionally entrain air, and adjust other fresh or hardened concrete properties.

After completion of proper proportioning, batching, mixing, placing, consolidating, finishing, and curing, concrete hardens into a strong, noncombustible, durable, abrasion resistant, and watertight building material that requires little or no maintenance. Furthermore, concrete is an excellent building material because it can be formed into a wide variety of shapes, colors, and textures for use in an unlimited number of applications.

Fig.1-2 Ten cement-paste cylinders with water-cement ratios from 0.25 to 0.70. The band indicates that each cylinder contains the same amount of cement. Increased water dilutes the effect of the cement paste, increasing volume, reducing density, and lowering strength.


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1.2 FRESHLY MIXED CONCRETE

Freshly mixed concrete should be plastic or semi-fluid and generally capable of being molded by hand. A very wet concrete mixture can be molded in the sense that it can be cast in a mold, but this is not within the definition of “plastic” that which is pliable and capable of being molded or shaped like a lump of modeling clay.

In a plastic concrete mixture all grains of sand and pieces of gravel or stone are encased and held in suspension. The ingredients are not apt to segregate during transport; and when the concrete hardens, it becomes a homogeneous mixture of all the components. During placing, concrete of plastic consistency does not crumble but flows sluggishly without segregation.

In construction practice, thin concrete members and heavily reinforced concrete members require workable, but never soupy, mixes for ease of placement.

A plastic mixture is required for strength and for maintaining homogeneity during handling and placement. While a plastic mixture is suitable for most concrete work, plasticizing admixtures may be used to make concrete more flow-able in thin or heavily reinforced concrete members.

1.3 Mixing

In Fig. 1-1, the basic components of concrete are shown separately. To ensure that they are combined into a homogeneous mixture requires effort and care. The sequence of charging ingredients into a concrete mixer can play an important part in uniformity of the finished product.

The sequence, however, can be varied and still produce a quality concrete.

Different sequences require adjustments in the time of water addition, the total number of revolutions of the mixer drum, and the speed of revolution. Other important factors in mixing are the size of the batch in relation to the size of the mixer drum, the elapsed time between batching and mixing, and the design, configuration, and condition of the mixer drum and blades. Approved mixers, correctly operated and maintained, ensure an end-to-end exchange of materials by a rolling, folding, and kneading action of the batch over itself as concrete is mixed.


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1.4 Definition of workability

Workability of concrete is defined in ASTM C125 as the property determining the effort required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity (uniform). The term manipulate includes the early-age operations of placing, compacting, and finishing. Mindess et al. (2003) defined the workability of fresh concrete as “the amount of mechanical work, or energy, required to produce full compaction of the concrete without segregation.”

The effort required to place a concrete

mixture is determined largely by the overall work needed to initiate and maintain flow, which depends on the rheological properties of the cement

-The properties of fresh concrete are short-term requirements in nature,

and should satisfy the following requirements:

It must be easily mixed and transported.

It must be uniform throughout a given batch, and between batches.

It must keep its fluidity during the transportation period.

It should have flow properties such that it is capable of completely filling the forms.

It must have the ability to be fully compacted without segregation.

It must set in a reasonable period of time.

It must be capable of being finished properly, either against the forms or by means of troweling or other surface treatment.

Compaction plays an important role in ensuring the long-term properties of the

hardened concrete, as proper compaction is vital in removing air from concrete and in achieving a dense concrete structure. Subsequently, the compressive strength of concrete can increase with an increase in the density. Traditionally, compaction is carried out using a vibrator.

Fig. 1-3 Effect of casting temperature on the slump (and relative workability) of two concretes made with different cements (Burg 1996).


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1.4.1 Workability of Fresh Concrete

paste and the internal friction between the aggregate particles, on the one hand, and the external friction between the concrete and the surface of framework, on the other hand. Workability of fresh concrete consists of two aspects: consistency and cohesiveness.

Consistency describes how easily fresh concrete flows, while cohesiveness describes the ability of fresh concrete to hold all the ingredients together uniformly. Traditionally, consistency can be measured by a slump-cone test, the compaction factor, or a ball penetration compaction factor test as a simple index for fluidity of fresh concrete.

Cohesiveness can be characterized by a Vebe test as an index of both the water-holding capacity (the opposite of bleeding) and the coarse-aggregate-holding capacity (the opposite of segregation) of a plastic concrete mixture.

The flowability of fresh concrete influences the effort required to compact concrete. The easier the flow, the less work is needed for compaction. A liquid-like self-compacting concrete can completely eliminate the need for compaction. However, such a concrete has to be cohesive enough to hold all the constituents, especially the coarse aggregates in a uniform distribution during the process of placing. Workability is not a fundamental property of concrete; to be meaningful it must be related to the type of construction and methods of placing, compacting, and finishing. Concrete that can be readily placed in a massive foundation without segregation would be entirely unworkable in a thin structural member. Concrete that is judged to be workable when high-frequency vibrators are available for consolidation would be unworkable if hand tamping were used.

The significance of workability in concrete technology is obvious. It is one of the key properties that must be satisfied. Regardless of the sophistication of the mix design procedures used and other considerations, such as cost, a concrete mixture that cannot be placed easily or compacted fully is not likely to yield the expected strength and durability characteristics.

1.4.2 Measurement of workability

Unfortunately, there is no universally accepted test method that can directly

measure the workability as defined earlier. The difficulty in measuring the mechanical work defined in terms of workability, the composite nature of the fresh concrete, and the dependence of the workability on the type and method of construction makes it impossible to develop a well-accepted test method to measure workability. The most widely used test, which mainly measures the consistency of concrete, is called the slump test. For the same purpose, the second test in order of importance is the Vebe test, which is more meaningful for mixtures with low consistency. The third test is the compacting factor test, which attempts to evaluate the compactability characteristic of a concrete mixture. The fourth test method is the ball penetration test that is somewhat related to the mechanical work.


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1.4.3 Factors affecting workability

The workability of concrete contains two aspects, consistency and

cohesiveness. Due to the different requirements and characteristics of the two aspects, the influence of a factor on workability may be opposite. In general, through the influence on consistency and/or cohesiveness, the water content, the cement content, the aggregate grading, and other physical characteristics, and admixtures can affect the workability of concrete mixtures.

1.4.3.1 Water content

Water content is regarded as the most important factor influencing the

workability of concrete. After adding water to a concrete mix, the water is absorbed on the surface of the particles of the cement and aggregates. Additional water fills the spaces among the particles and “lubricates” the particles by a water film. Decreasing the water content will result in a low fluidity. If the water content is too small, the concrete will become too dry to mix and place. Increasing the amount of water will increase the amount of water for lubrication and hence improve the fluidity and make it easy to be compacted. However, too much water will reduce cohesiveness. This not only leads to segregation and bleeding, but also reduces the concrete strength. The water content in a concrete is determined by w/c or w/b and cement or binder content. 1.4.3.2 Cement content

Cement content influences the workability of concrete in two ways. First, for

given w/c ratio, the larger the cement content, the higher the total water amount in the concrete; hence, the consistency of concrete will be enhanced. Second, cement paste itself plays the roles of coating, filling, and lubrication for aggregate particles. In normal concrete, a considerably low cement content tends to produce a harsh mixture, with poor consistency and, subsequently, poor finishability. High cement content implies that more lubricant is available for consistency improvement. Finally, with an increase of the cement content at a low w/c ratio, both consistency and cohesiveness can be improved. Under the same w/c ratio, the higher the cement content, the better the workability. Increasing the fineness of the cement particles will decrease the fluidity of the concrete at a given w/c ratio, but will increase the cohesiveness. Concretes containing a very high proportion of cement or very fine cement show excellent cohesiveness but tend to be sticky.


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1.4.3.3 Aggregate characteristics

Aggregates can influence the workability of concrete through their need for

surface coating and their friction and mobility during mixing, placing, and compaction. Maximum aggregate size, aggregate/cement ratio, fine aggregate/coarse aggregate ratio, and aggregate shape and texture are four aspects influencing the workability of concrete. The particle size of coarse aggregates influences the paste requirement for coating through the surface area. The larger aggregates have smaller surface area than smaller aggregates with the same volume. Subsequently, the amount of the paste available for lubrication is increased for concrete with large aggregates, and consistency is improved. Hence, for a given w/c ratio, as the maximum size of aggregate increases, the fluidity increases. Moreover, very fine sands or angular sands will require more paste for a given consistency; alternatively, they will produce harsh and unworkable mixtures at water contents that might have been adequate with coarser orwell-rounded particles. In general, to get a similar consistency of concrete, more water is needed when crushed sand is used instead of natural sands. The aggregate/cement ratio influences the paste requirement. A higher aggregate/cement ratio implies more aggregates and less cement paste. Thus, the concrete consistency decreases with aggregate/cement ratio increase due to less cement paste being available for lubrication. Fine aggregate/coarse aggregate ratio also affects the cement paste requirement. With an increase of the fine aggregate/coarse aggregate ratio, concrete contains more fine aggregates and less coarse aggregates. Thus, the total surface area of the aggregates increases, which leads to a higher demand on the cement paste for surface coating. As a result, the consistency of concrete decreases and the cohesiveness improves. Increasing the fine aggregate/coarse aggregate ratio is the most effective measure to increase the cohesiveness of concrete. The shape and texture of aggregate particles can affect the workability of concrete through the influence on paste requirement, particle moving friction, and moving ability. Cubical, irregular, granular, and rough aggregates require more coating cement paste and have higher friction than spherical, glassy, and smooth aggregates. As a general rule, the more spherical the particles the more workable is the concrete.


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1.4.3.4 Admixtures

Both chemical and mineral admixtures can influence the workability of concrete.

Their effects have been discussed in Chapter 2. For instance, an air-entraining agent increases the paste volume and improves the consistency of concrete for a given water content through the entrained air. The entrained air also increases cohesiveness by reducing bleeding and segregation. Improvement in consistency and cohesiveness by air entrainment is more pronounced in harsh and unworkable mixtures, such as in mass concrete, which has low cement content. Water-reducing admixtures can improve the fluidity of concrete due to the dispersing effect on cement particles and the releasing of entrapped water by cement clusters. Similarly, when the water content of concrete mixtures is held constant, the addition of water-reducing admixtures (plasticizer) will increase the consistency.

Different mineral admixtures have different effects on workability, although they

all tend to improve the cohesiveness of concrete. Fly ash, when used as a partial replacement for cement, generally increases the consistency at a given water content due to the spherical shape and glassy surface. When silica fume is used to replace part of the cement, it tends to reduce the amount of water used for lubrication, due to its very large surface area and hence the need for a water film coating.

1.4.3.5 Temperature and time

Freshly mixed concrete stiffens with time due to evaporation of the mixing water,

particularly when the concrete is directly exposed to sun or wind, absorption by the aggregate, and consumption in the formation of hydration products. The stiffening of concrete is effectively measured by a loss of workability with time, known as slump loss, which varies with richness of the mix, type of cement, temperature of the concrete, and initial workability. A high temperature reduces the workability and increases the slump loss because the hydration rate is higher and the loss of water is faster at a higher temperature. In practice, when the ambient conditions are unusual, it is best to perform actual site tests to determine the workability of the mix.


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Table 1-1 Workability, slump, and compacting factor of concretes with 19 or 38 mm

maximum size of aggregate

Degree of Slump Compacting

Workability (mm) (in.) Factor Use for which Concrete is Suitable

Very low 0 – 25 0 – 1 0.78 Roads vibrated by power-operated

machines.

At the more workable end of this

group, concrete may be compacted

in certain cases with hand-operated

machines.

Low 25 – 50 1 – 2 0.85 Roads vibrated by hand-operated

machines.

At the more workable end of this

group, concrete may be manually

compacted in roads using aggregate

of rounded or irregular shape. Mass

concrete foundations without

vibrated or lightly reinforced

sections with vibration.

Medium 25 – 100 2 – 4 0.92 At the less workable end of this group,

manually compacted flat slabs using

crushed aggregate. Normal

reinforced concrete manually

compacted and heavily reinforced

sections with vibration.

High 100 – 175 4 – 7 0.95 For sections with congested

reinforcement.

Not normally suitable for vibration.

Source. Building Research Establishment, Crown copyright.

Table 1-2 Recommended values of slump for various

types of construction as given by ACI 211.1-81

Range of Slumpa

Type of Construction (mm) (in.)

Reinforced foundation walls and footings 20 – 80 1 – 3 Plain footings, caissons and substructure walls 20 – 80 1 – 3 Beams and reinforced walls 20 – 100 1 – 4 Building columns 20 – 100 1 – 4 Pavements and slabs 20 – 80 1 – 3 Mass concrete 20 – 80 1 – 2

The upper limit of slump may be increased by 20 mm for compaction by hand.


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1.5 Segregation

In discussing the workability of concrete, it has been pointed out that

cohesiveness is an important characteristic of the workability. A proper cohesiveness can ensure concrete to hold all the ingredients in a homogeneous way without any concentration of a single component, and even after the full compaction is achieved. An obvious separation of different constituents in concrete is called segregation, as shown in Figure 1-4. Thus, segregation can be defined as concentration of individual constituents of a heterogeneous (nonuniform) mixture so that their distribution is no longer uniform. In the case of concrete, it is the differences in the size and weight of particles (and sometimes in the specific gravity of the mix constituents) that are the primary causes of segregation, but the extent can be controlled by the concrete proportion, choice of suitable grading, and care in handling.

1.5.1 Some factors that increase segregation are:

Larger maximum particle size (25mm) and proportion of the larger particles.

High specific gravity of coarse aggregate.

Decrease in the amount of fine particles.

Particle shape and texture.

Water/cement ratio.

1.6 Bleeding Bleeding is a form of local concentration of water in some special positions in

concrete, usually the bottom of the coarse aggregates, the bottom of the reinforcement, and the top surface of the concrete member.

1.6.1 Bleeding may be reduced by:

Increasing cement fineness.

Increasing the rate of hydration.

Using air-entraining admixtures.

Reducing the water content.


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During placing and compaction, some of water in the mix tends to rise to the surface of freshly placed concrete. This is caused by the inability of the solid constituents of the mix to hold all the mixing water when they settle downward due to the lighter density of water. Bleeding can be expressed quantitatively as the total settlement (reduction in height) per unit height of concrete, and bleeding capacity as the amount (in volume or weight) of water that rises to the surface of freshly placed concrete.

As a result of bleeding, an interface between aggregates and bulk cement paste is formed, and the top of every lift (layer of concrete placed) may become too wet. If the water is trapped by the superimposed concrete, a porous and weak layer of nondurable concrete may result. If the bleeding water is remixed during the finishing process of the surface, a weak wearing surface can be formed. This can be avoided by delaying the finishing operations until the bleeding water has evaporated, and also by the use of wood floats and avoidance of overworking the surface.

On the other hand, if evaporation of water from the surface of the concrete is faster than the bleeding rate, plastic shrinkage cracking may be generated.

Fig. 1-4 Segregation of concrete mixture

1.7 Slump loss Slump loss can be defined as the loss of consistency in fresh concrete with

elapsed time. Slump loss is a normal phenomenon in all concretes because it results from gradual stiffening and setting of hydrated cement paste, which is associated with the formation of hydration products such as ettringite and calcium silicate hydrate. Slump loss occurs when the free water from a concrete mixture is removed by hydration reactions, by absorption on the surface of hydration products, and by evaporation. Slump loss should be controlled to an acceptable value, especially for concrete transported with a long delivery time, to ensure that it is still place=able and compactable when shipped to the construction site. Slump loss can be minimized by using a setting retarder.


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1.8 Principal requirements for concrete The main purpose of the mix design is to obtain a product that will perform

according to predetermined requirements. These requirements include the following concrete properties.

(a) Quality (strength and durability): Strength and permeability of hydrated

cement paste are mutually related through the capillary porosity that is controlled by w/c ratio and degree of hydration. Since durability of concrete is controlled mainly by its permeability, there is a relationship between strength and durability. Consequently, routine mix design usually focuses on strength and workability only. When the concrete is exposed to special environmental conditions, provisions on durability (e.g., limit on w/c ratio, minimum cement content, minimum cover to steel reinforcement) will also be considered.

(b) Workability: As mentioned earlier, workability is a complicated concept for

fresh concrete and embodies various properties, including consistency and cohesiveness. There is still not a single test method that can fully reflect workability. Since the slump represents the ease with which the concrete mixture will flow during placement, and the slump test is simple and quantitative, most mix design procedures rely on slump as a crude index of workability. Sometimes, the Vebe time may be employed.

(c) Economy: Among all the constituents of the concrete, the admixture has the

highest unit cost, followed by cement. The cost of aggregates is about one-tenth that of cement. Admixtures are often used in small amounts, or they are required to achieve certain properties.

To minimize the cost of concrete, the key consideration is the cement cost. Therefore, all possible steps should be taken to reduce the cement content of a concrete mixture without sacrificing the desirable properties, such as strength and durability. The scope for cost reduction can be enlarged further by replacing a part of the Portland cement with cheaper materials, such as fly ash or ground blast-furnace slag.

As mentioned earlier, under normal conditions, it is sufficient to consider workability and strength for concrete design. For special conditions, additional considerations on dimensional stability and durability have to be taken into account.


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1.9 Admixtures for Concrete

Admixtures are those ingredients in concrete other than portland cement, water, and aggregates that are added to the mixture immediately before or during mixing Admixtures can be classified by function as follows: Air-entraining admixtures

Water-reducing admixtures

Plasticizers

Accelerating admixtures

Retarding admixtures

Hydration-control admixtures

Corrosion inhibitors

Shrinkage reducers

Alkali-silica reactivity inhibitors

Coloring admixtures

Miscellaneous admixtures such as workability, bonding, damp-proofing, permeability reducing, grouting, gas-forming, anti-washout, foaming, and pumping admixtures

The major reasons for using admixtures are:

To reduce the cost of concrete construction

To achieve certain properties in concrete more effectively than by other means

To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in adverse weather conditions

To overcome certain emergencies during concreting operations

Despite these considerations, it should be borne in mind that no admixture of any type or amount can be considered a substitute for good concreting practice. The effectiveness of an admixture depends upon factors such as type, brand, and amount of cementing materials; water content; aggregate shape, gradation, and proportions; mixing time; slump; and temperature of the concrete. Admixtures being considered for use in concrete should meet applicable specifications as presented in Trial mixtures should be made with the admixture and the job materials at temperatures and humidities anticipated on the job. In this way the compatibility of the admixture with other admixtures and job materials, as well as the effects of the admixture on the properties of the fresh and hardened concrete, can be observed. The amount of admixture recommended by the manufacturer or the optimum amount determined by laboratory tests should be used.

Fig. 1-5 Different type of Admixtures


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1.9.1 Air-Entraining Admixture Air-entraining admixtures are used to purposely introduce and stabilize

microscopic air bubbles in concrete. Air-entrainment will dramatically improve the durability of concrete exposed to cycles of freezing and thawing. Entrained air greatly improves concrete’s resistance to surface scaling caused by chemical deicers. Furthermore, the workability of fresh concrete is improved significantly, and segregation and bleeding are reduced or eliminated. Air-entrained concrete contains minute air bubbles that are distributed uniformly throughout the cement paste. Entrained air can be produced in concrete by use of air-entraining cement, by introduction of an air-entraining admixture, or by a combination of both methods. Air-entraining cement is a port-land cement with an air-entraining addition inter-ground with the clinker during manufacture. An air-entraining admixture, on the other hand, is added directly to the concrete materials either before or during mixing.

1.9.1.1 Freez-Thaw Resistance

The resistance of hardened concrete to freezing and thawing in a moist condition is significantly improved by the use of intentionally entrained air, even when various deicers are involved. Convincing proof of the improvement in durability effected by air entrainment As the water in moist concrete freezes, it produces osmotic and hydraulic pressures in the capillaries and pores of the cement paste and aggregate. If the pressure exceeds the tensile strength of the paste or aggregate, the cavity will dilate and rupture. The accumulative effect of successive freeze-thaw cycles and disruption of paste and aggregate eventually cause significant expansion and deterioration of the concrete. Deterioration is visible in the form of cracking, scaling, and crumbling. .

1.9.1.2 Air-Entraining Admixture Effect on Workability

Entrained air improves the workability of concrete. It is particularly effective in lean (low cement content) mixes that otherwise might be harsh and difficult to work. In one study, an air-entrained mixture made with natural aggregate, 3% air, and a 37-mm (11⁄2-in.) slump had about the same workability as a non-air-entrained concrete with 1% air and a 75-mm (3-in.) slump, even though less cement was required for the air-entrained mix (Cordon 1946). Workability of mixes with angular and poorly graded aggregates is similarly improved. Because of improved workability with entrained air, water and sand content can be reduced significantly. A volume of air-entrained concrete requires less water than an equal volume of non-air-entrained concrete of the same consistency and maximum size aggregate. Freshly mixed concrete containing entrained air is cohesive, looks and feels fatty or workable, and can usually be handled with ease; on the other hand, high air contents can make a mixture sticky and more difficult to finish. Entrained air also reduces segregation and bleeding in freshly mixed and placed concrete.


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1.9.2 Water-Reducing Admixture

Water-reducing admixtures are used to reduce the quantity of mixing water

required to produce concrete of a certain slump, reduce water-cement ratio, reduce cement content, or increase slump. Typical water reducers reduce the water content by approximately 5% to 10%. Adding a water-reducing admixture to concrete without reducing the water content can produce a mixture with a higher slump. The rate of slump loss, however, is not reduced and in most cases is increased (Fig. 1-6). Rapid slump loss results in reduced workability and less time to place concrete. An increase in strength is generally obtained with water-reducing admixtures as the water-cement ratio is reduced. For concretes of equal cement content, air content, and slump, the 28-day strength of a water-reduced concrete containing a water reducer can be 10% to 25% greater than concrete without the admixture. Despite reduction in water content, water-reducing admixtures may cause increases in drying shrinkage. Usually the effect of the water reducer on drying shrinkage is small compared to other more significant factors that cause shrinkage. cracks in concrete. Using a water reducer to reduce the cement and water content of a concrete mixture—while maintaining a constant water-cement ratio—can result in equal or reduced compressive strength, and can increase slump loss by a factor of two or more (Whiting and Dziedzic

1992).

Water reducers decrease, increase, or have no effect on bleeding, depending on the chemical composition of the admixture. A reduction of bleeding can result in finishing difficulties on flat surfaces when rapid drying conditions are present. Water reducers can be modified to give varying degrees of retardation while others do not significantly affect the setting time.

Fig. 1-6 Slump loss at 23°C (73°F) in concretes containing conventional water reducers (ASTM C 494 and AASHTO M 194 Type D) compared with a control mixture (Whiting and Dziedzic 1992).


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CHAPTER 2

FRESH CONCRETE TESTS

2.1 MEASUREMENTS OF WORKABILITY

The following are the methods of measurements of workability: 1. Slump test 2. Compacting factors test 3. vebe consistometer test

2.1.1 The Slump test

The concrete slump test is an empirical test that measures the workability of

fresh concrete.

Slump test is one of fresh concrete tests. Slump test is made to measure the

consistency of fresh concrete mix , It's the most commonly used all over the world

according to (ASTM c143-78) . The main purpose of measuring consistency by

slump test is to achieve acceptable fresh concrete workability.

Also slump test is one of the simple and important tests which helps us to get a

homogenous fresh concrete mix before casting.

Slump test has a direct effect on compressive strength of the hardened concrete as

slump test shows the water/cementing material ratio. In other words, when slump is

big then water/cement ratio is big and the compressive strength of concrete is low.

http://en.wikipedia.org/wiki/Concrete

Fresh Concrete Tests Chapter2

17

Fig. 2-1 Slump Test

2.1.1.1 The instruments

* Frustum cone made of strong metal with 1.5mm thickness at least, opened from

above and down, the above hole has 10cm diameter and the down hole has 20cm

diameter. The cone height is 30cm.

* Compacting steel bar with 15mm diameter and 60cm height.

Fig. 2-2 Slump Test Instruments

2.1.1.2 The purpose of slump test

Define the consistency of concrete mix by measuring the slump after deformed as a

frustum cone in the site or laboratory to assure that the concrete mix components

ratios are accurate. It is the simplest test to achieve concrete quality control in

mixing stations and in the sites.


18

2.1.1.3 Procedure of Slump Test

1- Make sure that all instruments are clean.

2- Fill the cone with concrete to 3 layers, every layer is 1/3 the cone.

3- Compact every layer by 25 times by using the compacting bar with equal way

then, surface is resolved.

4- Raise the cone vertically slowly without any lateral or torsional movement.

5- All this steps must be done in 150 second without stopping.

6- Measure the slump for the concrete by standard ruler.

2.1.1.4 Results

The slump = The height of the cone – The height of the concrete cone after the slump.

*Slump value of this concrete will be compared with the acceptable values which the

CODE mentioned.

Table 2-1 Recommended slumps for placement in various conditions

S.NO Slump in mm Degree of

workability

Placing

Conditions

1.

(compacting

factor is suitable)

Very low

(i) Blinding concrete

(ii) Shallow sections

(ii) Pavements

using pavers

2.

25-75

Low

(i) Mass concrete

(ii) Lightly reinforced

(ii) Floors

(iv) Canal linings

(v) Strip footings

3.

50-100

Medium

(i) Heavily reinforced

sections in slabs, beams,

walls ,columns

(ii) Pumped concrete

(ii) Slip form work

4. 100-150 High (i) Trench fill

(ii) in-situ piling


19

2.1.1.5 Interpretation of results

The slumped concrete takes various shapes, and according to the profile of slumped

concrete, the slump is termed as true slump, shear slump or collapse slump. If a

shear or collapse slump is achieved, a fresh sample should be taken and the test

repeated. A collapse slump is an indication of too wet a mix. Only a true slump is of

any use in the test. A collapse slump will generally mean that the mix is too wet or

that it is a high workability mix, for which slump test is not appropriate.

Table 2-2 Slump Results

Collapse Shear True

In a collapse slump the

concrete collapses

completely.

In a shear slump the top portion of

the concrete shears off and slips

sideways.

In a true slump the concrete

simply subsides, keeping more or

less to shape.


20

Fig. 2-3 Slump Results in graph

2.1.1.6 Limitations of the slump test

The slump test is suitable for slumps of medium to high workability, slump in the

range of 5 – 260 mm, the test fails to determine the difference in workability in stiff

mixes which have zero slump, or for wet mixes that give a collapse slump. It is

limited to concrete formed of aggregates of less than 38 mm (1.5 inch).[1]:128

2.1.1.7 Differences in standards

The slump test is referred to in several testing and building codes, with minor

differences in the details of performing the test.

2.1.2 Compacting Factor Test

2.1.2.1 Introduction:

The principle of compacting factor is determining the degree of compaction achieved

by a standard amount of work done by allowing the concrete to fall through a

standard height. The degree of compaction is measured by the density ratio, ( The

ratio of density actually achieved in the test to density of same concrete fully

compacted) This test primarily for use in the laboratory but it can also be used in the

field, useful for concrete mixes of low, medium and high workable.

http://en.wikipedia.org/wiki/Construction_aggregate

http://en.wikipedia.org/wiki/Concrete_slump_test#cite_note-Gambhir-1

http://en.wikipedia.org/wiki/Building_code


21

2.1.2.2 Purpose

To determine the compacting factor or the degree of compaction that achieved by

applying a standard amount of work, which gives an indication to the workability of

fresh concrete

2.1.2.3 Apparatus

Compacting factor apparatus which consists of: Upper hopper with a dimension

(Top: D1= 254 mm , bottom: D2=127 mm and height: H1= 279 mm) , lower hopper

with a dimension ( Top : D3= 229 , Bottom: D4= 127, and height : H2= 229 mm ) and

cylinder (with dia. D5=152 and height H3=305 mm ) connected, the total height

measuring from the base of upper hopper to the base of cylinder (H1 + h1 + H2 + h2

+ H3 ) about 1 m.

Fig. 2-4 Compacting Factor instrument

2.1.2.4 Materials

Same fresh concrete used for slump test, uses also to test the degree of compaction

of fresh concrete


22

2.1.2.5 Procedure

1. Clean and moist the internal sides of the upper and lower hoppers using dampen

cloth. 2. Place the sample of prepared fresh concrete in the upper hopper; and let

the sliding door closed.

3. Open the top slide door, so that the concrete falls into the lower hopper

4. Open the slide door of the lower hopper, so that the concrete is allowed to fall into

the cylinder

5. Remove the excess concrete above the top level of the cylinder, the outside is

wiped clean

6. Weigh the concrete in the cylinder that is partially compacted let be W1

7. Empty the cylinder and fill it with the concrete from the same sample in 3 layers

approximately of equal volumes.

8. Each layer heavily rammed or vibrated so as to obtain full compaction

9. Struck off level the top surface of the fully compacted concrete with the top of the

cylinder, and weigh it , let to be W2

Calculation

.

Result: The compaction factor of the given fresh concrete mix is .....

(Note: Relation between the compaction factor and work-ability is that higher the

compaction factor higher is the work-ability. Theoretical maximum value of the

compaction factor can be 0.96 to 1.0)


23

2.1.3 Vebe test of fresh concrete

2.1.3.1 Introduction:

The name vebe is derived from the initials of V.bahrner of Sweden who developed

the test. In this test the workability of concrete measured by the amount of work

required to change the shape of concrete sample form a frustum of cone to cylinder.

This is done using a vibrating table with eccentric rotation at 50 Hz. This method is

very suitable for very dry mixes.

2.1.3.2 Purpose:

This test is to determine the amount of work expressed by time in seconds of

working the vibrating machine required to transform shape of concrete from the

slump cone to cylindrical shape. This time is a measure to workability of fresh

concrete.

2.1.3.3 Materials:

1- Cement

2- fine aggregate (Sand)

3- Coarse aggregate (gravel)

4- Water


24

2.1.3.4 Apparatus

►Vebe consistometer apparatus which includes the followings:

1. Slump con , the same con uses for slump test placed inside the sheet metal

cylindrical pot

2. Cylindrical container placed on a vibrating table

3. Glass disc attached to the swivel arm

4. Electrical vibrator.

►Standard tamping rod

►Scoop

►Stop watch

Fig. 2-5 Vebe test Instrument


25

2.1.3.5 Procedure

1. Place the slump cone inside the sheet metal cylindrical pot of the consistometer

2. Fill slump con with fresh concrete in 3 layers, each layer compacted 25 times

stroke using tamping rod.

3. Rise up the slump cone vertically

4. Let the glass disc to attach the surface of the slumped concrete in the cylindrical

pot.

5. Switch on the electrical vibrator and simultaneously a stop watch started.

6. Continue the vibration until the conical shape of the concrete disappears and the

concrete assumes a cylindrical shape. This can be judged by observing the glass

disc from the top for disappearance of transparency

7. Switch off the stop watch when the concrete shape assumed is fully cylindrical.

8. Record the time in seconds required for the concrete to change from conical to

cylindrical, this gives a measure to workability of concrete.

Table 2-3 Comparison between the three methods and problems in each one:

The method Problems

Slump Test

• Not useful for stiff mixes ((Zero Slump)). Same slump ► Different

workability. • Not reliable for lean mixes with tendency to harshness.

Different slumps (Types or values) ► same workability. • There is no

unique slump value for a specific workability. Same slump ► Different

workability ► Different aggregates.

Compaction

factor test

• Very stiff mixes might stick in the hoppers and so it will be needed to

ease by poking with a steel rod (External effect). • Stiff mixes (very low

workability) the amount of work needed for full compaction depends

on the richness of the mix, but the compacting factor does not depend

on the richness of the mix. Same Compacting Factor ► Different

workability. • The apparatus is heavy and complicated.

VEBE test Difficulties in establishing the end point of the test is a source of error.


26

2.2 FLOW TEST

Definition The flow table test or flow test is a method to determine the consistence of

fresh concrete.

•Application When fresh concrete is delivered to a site by a truck mixer it is

sometimes necessary to check its consistence before pouring it into formwork.

•If the consistence is not correct, the concrete will not have the desired qualities

once it has set, particularly the desired strength. If the concrete is too pasty, it may

result in cavities within the concrete which leads to corrosion of the rebar, eventually

leading to the formation of cracks (as the rebar expands as it corrodes) which will

accelerate the whole process, rather like insufficient concrete cover. Cavities will

also lower the stress the concrete is able to support.

2.2.1 Equipment

-Flow table with a grip and a hinge, 70 centimeters (28 in) square.

-Abrams cone, open at the top and at the bottom - 30 centimeters (12 in) high, 17

centimeters (6.7 in) top diameter, 25 centimeters (9.8 in) base diameter.

-Water bucket and broom for wetting the flow table.

-Tamping rod, 60 centimeters (24 in) long

Fig. 2-6 Flow test Instrument


27

2.2.2 Procedure of the test

-The flow-table is wetted.

-The cone is placed in the center of the flowtable and filled with fresh concrete in two

equal layers layers. Each layer is tamped 10 times with tamping rod.

-Wait 30 seconds before lifting the cone

-The cone is lifted, allowing the concrete to flow.

-The flowtable is then lifted up 40mm and then dropped 15 times, causing the

concrete to flow

-After this the diameter of the concrete is measured.

2.2.3 Calculation

D1: Diameter of base which is equal to 200mm

D2: Average Diameter of Concrete for 6 directions .

Table2-4 Flow Degrees

Flow % Consistency

0-20 Dry

15-60 Stiff

50-100 Plastic

90-120 Wet

110-150 Sloppy


28

Bleeding of Concrete

Bleeding – a type of segregation where water appears at the concrete surface after placing and compacting, but before set. Water may also form a film under aggregate and reinforcing bar.

2.3 TEST FOR THE BLEEDING

Characteristics of concrete are normally carried out in the laboratory to evaluate trial

mixes or to evaluate the influence of different materials, e.g. for the evaluation of

admixtures under AS 1478. A sample of the concrete to be tested is placed in a

cylindrical container and compacted, either by rodding it or by vibration. The

container is then covered and placed on a level surface. Bleed water is drawn off

with a pipette at regular intervals until the amount collected during a 30-minute

period is less than 5 ml. The results may be expressed either as the volume of bleed

water collected in a given time per unit surface area of the cylinder, or as a ratio of

bleed water to total mixing water if the latter is known.

Fig. 2-7 Bleeding in Concrete


29

Lab Tests

Slump Test

Cone Frustum Volume = (1/3) - h ( r2+ rR + R2)

= (1/3) - 0.3 ( 0.052+ 0.05*0.1 + 0.1

2)

= 0.005497 m3

Mixture proportion Cement = 1 Sand = 2 Gravel = 4

Slump Test Calculations For W/C 0.5

Cement sand gravel w/c


30

cement content * volume = 1.77 kg

cement weight = (cement weight*volume)* 5% loose of material during working

=

1.86 kg

cement 1.86 kg

sand 3.72 kg

gravel 7.45 kg

water 0.93 L

Slump test Calculations for W/C 0.6

Cement sand gravel w/c



= 1.80 kg

cement 1.80 kg

sand 3.61 kg

gravel 7.22 kg

water 1.08 L


31

Slump Tests discussion and results of Lab.

w/c ratio 0.5 Set 1 ► sample one . During our tests we observed some points that may act negatively on our result during the test: 1- The Gravel and Sand were still hot and their temperature was still high, here the gravel and the sand absorb a quantity of the water added to equalize the temperature of the water and the lab temp. by that an amount of water will evaporate. 2- As we were adding the water to the mix we realized that a muddy color appears this means the sand and the gravel were not totally clean. 3- As we see in this figure the gravel sizes are so big and caused a bad mixing among the mixed materials because of the lack of bad grading.

Set 1 ► Sample two After the bad Result of the first test we decided to correct the errors that were possible to correct them by: 1- Changing the gravel sizes to smaller (correcting the grading) 2-Cooling the Sand to equalize the temperature of the lab. As we see the result differs from the result of the first test by having a value of

slump which is 4.5 cm low degree of workability.

Fig. 2-8

Fig. 2-9


32

Set 1 ►Sample three

- Shear Type of Slump shown in figure - Caused by bad mixing of the components

Set 1 ► Sample four

- Medium Degree of workability - This result comes after correcting all the

mistakes happened in the last three samples , although 2 more samples were needed to make sure that the result is correct .

Fig. 2-10

Fig. 2-11


33

Set 2 ► sample one & two & three Trying another W/C ratio 0.6 the results were as we were expecting a high workability value as we see in the figure. High degree of workability

Fig. 2-12


34

Flow Tests discussion and results of Lab.

Fig. 2-13


35

Set 1 W/C is 0.6

Cone Frustum Volume = (1/3) h ( r2 + rR + R2)

= (1/3) 0.2 ( 0.0652 + 0.065*0.1 + 0.12)

= 0.00434063 m3

Mixture proportion

Cement = 1 Sand = 2 Gravel = 4 w/c = 0. Solution Cement sand gravel w/c

X=



= 1.426 kg

cement 1.24 kg sand 2.85 kg gravel 2.70 kg

water 0.85 L


36

Sample 1

= 1.15 * 100

= %115

Sample 2

= 1.12 * 100

= %112

Fig. 2-14

Fig. 2-15


37

Sample 3

= 1.13 * 100

= %113

Set2 W/C equal to 0.5

Mixture proportion

Cement = 1 Sand = 2 Gravel = 4 Solution Cement sand gravel w/c


Fig. 2-16


38


= 1.47250 kg

cement 1.47 kg

sand 2.94 kg

gravel 5.88 kg

water 0.73 L

FF X=

Sample1

%Flow= 0.77*100

= 77%

Sample 2

%Flow =0.72 *100

=72%


39

Sample 3

%Flow=0.7*100

= 70%

Average of Set 1 =114% >>> Wet

Average of Set 2 =73% >>> Plastic

Flow % Consistency

0-20 Dry

15-60 Stiff

50-100 Plastic

90-120 Wet

110-150 Sloppy

40

CHAPTER 3

FRESH CONCRETE IN SITE

3.1 Delivery of Concrete

The delivery of fresh concrete from the concrete plant to the construction site is usually done by agitators, either truck mixers or truck agitators. The truck is equipped with a rotating drum for agitation. The truck mixer receives raw materials from the plant and completely mixes them into workable fresh concrete on the way to the construction site. The advantage of truck mixing is that the water can be stored separately and added into the solid materials for mixing according the time of shipping, to avoid slump loss. If the construction site is offshore, a ferry is used to carry a large number of trucks from land to the site.

In this case, due to a long shipping period, special care has to be paid to the slump loss. Usually retarding admixtures have to be used to keep concrete workable for a period of 5 to 6 h, and an initial setting time of 7 to 8 h. In this case, A truck mixer has priority to be selected, if available.

A truck mixer has to meet the requirements of environmentally friendly production nowadays.

- Effects of transportation on concrete properties

The principal difference between ready-mixed and site- or laboratory-mixed concrete is the time and method of transportation from batching to the point of placing. There are four major influences which arise during delivery and/or agitation of concrete:

• Evaporation • Hydration • Absorption • Abrasion Evaporation and hydration effects are the most significant while absorption is

only significant with dry or highly absorptive aggregates. Abrasion is only an issue where abrad-able aggregates are used leading to increased fineness. It has been suggested some limited grinding of cement may also occur due to abrasion processes although this is less well documented.

Fresh Concrete in Site Chapter 3

41

- The effects of these influences are:

• Evaporation and absorption leads to a lower effective water/cement ratio in the paste thus reducing workability and potentially enhancing strength.

• Hydration reduces water available for workability but has no real effect on the effective water/cement ratio.

• Abrasion increases fineness and reduces workability.

- The rate of workability loss is influenced by a number of factors: • Cement content Dewar (1973) showed that mixes of lower cement content

lose workability at a lower rate because a smaller proportion of water is utilized in hydration (see Fig. 3-1).

Fig. 3-1 Workability loss versus cement content.

• Water content Mixes of higher water content or higher initial workability lose workability at a lower rate because the effect of a given water loss due to evaporation or hydration is diluted (see Figure 3-2).

• Admixtures can influence the water content, hydration characteristics, rheology and air content of the concrete and thus the rate of workability loss. Mixers incorporating water-reducing admixtures (wra) can lose workability faster than concrete without wra at the same initial workability. This is because the effects of water loss will be concentrated due to the lower initial water content.

• Weather Higher temperatures increase the rate of hydration and evaporation

and thus increase the rate of workability loss.


42

• Volume of concrete delivered Larger volumes of concrete are less susceptible to workability loss because of a lower surface area/volume ratio which reduces the significance of the lost water. On the other hand, larger volumes retain more heat and may increase the rate of hydration although practical experience indicates that larger volumes lose workability at a slower rate than small loads. Strength generally increases with time at about 5 per cent per hour provided concrete can still be compacted as the workability reduces, according to Dewar (1962). This value depends on a range of factors such as:

• cement content and type • initial workability • time of agitation • ambient conditions Fig. 3-2 Workability loss and initial water content.

3.2 TRANSPORTING AND HANDLING CONCRETE

Good advanced planning can help choose the appropriate handling method for an application. Consider the following three occurrences that, should they occur during handling and placing, could seriously affect the quality of the finished work: 3.2.1 Delays

The objective in planning any work schedule is to produce the fastest work with the best labor force and the proper equipment for the work at hand. Machines for transporting and handling concrete are being improved all the time. The greatest productivity will be achieved if the work is planned to get the most out of personnel and equipment and if the equipment is selected to reduce the delay time during concrete placement.


43

3.2.2 Early Stiffening and Drying Out. Concrete begins to stiffen as soon as the cementitious materials and water

are mixed, but the degree of stiffening that occurs in the first 30 minutes is not usually a problem; concrete that is kept agitated generally can be placed and compacted within 11⁄2 hours after mixing unless hot concrete temperatures or high cement contents speed up hydration excessively. Planning should eliminate or minimize any variables that would allow the concrete to stiffen to the extent that full consolidation is not achieved and finishing becomes difficult. Less time is available during conditions that hasten the stiffening process, such as hot and dry weather, use of accelerators, and use of heated concrete. 3.2.3 Segregation

is the tendency for coarse aggregate to separate from the sand-cement mortar. This results in part of the batch having too little coarse aggregate and the remainder having too much. The former is likely to shrink more and crack and have poor resistance to abrasion. The latter may be too harsh for full consolidation and finishing and is a frequent cause of honeycombing. The method and equipment used to transport and handle the concrete must not result in segregation of the concrete materials.

3.3 Concrete Placing

Placing concrete is a construction process that can be divided into four operations: site preparation to receive the concrete, conveying and placing the concrete into the forms, compacting concrete, and taking care of the concrete after it has been compacted. Concrete should be placed as close to its final position as possible. To minimize segregation, it should not be moved over too long a distance. After concrete is placed in the formwork, it has to be compacted to remove entrapped air. Compaction can be carried out by hand rodding or tamping, or by the use of mechanical vibrators. In this section, the focus is on preparation, conveying, placing, and compacting.

44

CONCLUSION

From this project we observed that the type of aggregate, amount of water, and temperature of mixture has a great effect on the properties of fresh concrete. We also observed that when a large amount of water is added to the mixture bleeding or segregation will occur. Another material which has alot of effect on fresh concrete are admixtures that are added to the mixture. We also observed that round aggregate particles will provide good workability of fresh concrete but lower compressive strength. While crushed aggregate provides lower workability but better compressive strength.

Rediar H. Salih

Our observation on the project is that alot of factors affect the properties of fresh such as aggregate sizes, shapes and temperature. We observed that high water cement ratio increases workability but decrease the concrete compressive strength

Omar I. Muhammed

Fresh Concrete is the Start point of producing a Harden Concrete, so it must be treated

very carefully to Produce a high quality Concrete mixture by taking to the account the good properties and neglect the bad properties, Our goal in this project was to find what are the points which affect positively or negatively on the result of the produced concrete. Our conclusion was that any change in the quantity of materials used in the production of concrete and the temperature of the surrounded area or the additives used in concrete production affects on its result.

Rahand K. Hussein

Our aim of this research was finding the problems that arise during the production of Concrete and find the way to solve these problems, which can be controlled when the concrete is still fresh and able to deal with it.

Ahmed B. Noori

Miss Avin Signature

45

REFERENCES

Advanced Concrete Technology by Zongjin Li Advanced Concrete Technology -Constituent Materials -Concrete Properties -Processes -Testing and Quality By John Newman & Ban Seng Choo Design and Control of Concrete Mixtures By Steven H. Kosmatka, Beatrix Kerkhoff, and William C. Panarese

Documents

Properties of Fresh Concrete Kurdistan