thesis

The Use of Lightweight Concrete Blocks in Multistory Buildings.

Farhat Ullah (Registration No. 10-pwciv-3325)

S M Tariq Shah (Registration No. 10-pwciv-3380)

____________________

Prof. Dr. Qaisar Ali

Project Supervisor

___________________

Prof. Dr. Akhtar Naeem

Chairman

DEPARTMENT OF CIVIL ENGINEERING

16

12

1.5

Times new roman

UNIVERSITY OF ENGINEERING AND TECHNOLOGY PESHAWAR

Session 2010-14

ABSTRACT

This research shows the feasibility and sequential approach for producing lightweight concrete using different techniques that can be easily adopted in underdeveloped country like Pakistan. A number of options available to create lightweight concrete, are thoroughly studied and practically tested. The target was to reduce the unit weight. Specific volume principle was utilized to observe the effect of inclusion of coarse aggregate, cement, water, sand and different admixtures in the mixture to achieve the goal. Molds were used to accommodate volumetric expansion of mixture. Six inch cubic specimens were prepared for tests. Density and compressive strength were determined for each specimens.

From the results it was concluded that the use of foaming agents is the most suitable method for the production of lightweight concrete. For which a simple foam generator was made at a cost of Rs.2000. It was seen that density and compressive strength decreased with increased percentage of foaming agent. Finally, lightweight concrete with density and compressive strength within range of 70-100 lb. /ft3 and 700-1000 lb. /inch2 respectively was produced.

KEY WORDS: Lightweight concrete, Foam generator, Foaming agents, Aluminum powder.

viii

ACKNOWLEDGMENTS

First and foremost, we pay our deepest gratitude to Allah for providing us with the opportunity and strength to complete such a distinguished work.

We would like to express our appreciation and thanks to our supervisor Prof. Dr. Qaisar Ali, who provided us with the opportunity to work with him. His support, guidance, advice throughout the research project is greatly appreciated. The experience of working with him has been an interesting and rewarding one.

Our profound gratitude is due to the Civil Engineering Department and to the person who inspires us all – Dr. Akhtar Naeem Khan. The prevalent research environment in the department can be attributed to his untiring efforts for the betterment of the department.

Last, we pay our sincere gratitude to our kind parents, whose love, affection and priceless prayers helped us complete our project work with devotion.

In the service of our motherland

(To update this table of content after you have created your own thesis or dissertation, right-click on the table and select “Update Field,” or else left-click on the table and left-click on “Update Table,” which should appear in the upper left hand corner. Generally you will want to select “Update entire table.”)TABLE OF CONTENTSABSTRACTiiiACKNOWLEDGMENTSivLIST OF FiGuresixLIST OF TABLES10CHAPTER 1 INTRODUCTION111.1Lightweight Concrete111.2Problem Statement111.3Objective121.4Organization of Thesis12CHAPTER 2 Literature review142.1Concrete142.1.1Types of concrete142.2Lightweight concrete162.2.1Introduction162.2.2Advantages182.2.3Disadvantages192.2.4Production of lightweight concrete192.2.4.1Using lightweight aggregates202.2.4.2Using admixtures202.3Types of lightweight aggregates202.3.1Natural aggregates202.3.2Artificial lightweight aggregates212.4Admixtures222.4.1Air entraining agents222.4.2Admixtures that evolve gases22CHAPTER 3 METhedology243.1Background243.2First Phase of the Project253.3Working Methodology253.4Experimental data253.4.1Standard Concrete Samples253.4.2Chemrite Aer Concrete Samples263.4.3Lightcrete-02 Concrete Samples283.4.4Standard Sandcrete Sample293.4.5Chemrite Aer Sandcrete Sample293.4.6Lightcrete-02 Sandcrete Samples293.4.7Overall Performance303.4.8Conclusions about Chemrite Aer and Lightcrete-02313.5Second Phase of the Project313.5.1Foaming Agent313.5.1.1Concrete Samples333.5.1.2Sandcrete Samples343.5.2Aluminum Powder353.5.2.1Concrete Sample353.5.2.2Sandcrete Samples373.5.3Overall Performance373.5.4Conclusion about Foaming agent and Aluminum powder383.5.5Increasing Strength of Foaming Agent Sample38CHAPTER 4 CONCLUSION AND RECOMMENDATIONS404.1Conclusion404.2Recommendations40APPENDIX ADetail Of admixturesxiA.1Chemrite AerxiA.2Lightcrete -02xiiA.3Rheocell 10xivReferencesxviii

xi

LIST OF FiGures

Figure 2.21 The Pantheon17

Figure 2.31 Pumice Stone21

Figure 2.41 Admixture23

Figure 3.41 Standard Samples26

Figure 3.42 Chemrite Aer Concrete Sample27

Figure 3.43 Lightcrete-02 Concrete Sample28

Figure 3.51 Foam Generator32

Figure 3.52 Foam Generated32

Figure 3.53 Foaming Agent Samples33

Figure 3.54 Foaming Agent Sample34

Figure 3.55 Aluminum Powder35

Figure 3.56 Aluminum Powder Gradual Progress36

LIST OF TABLES

Table 3.41: Standard Sample Data26

Table 3.42 Chemrite Aer Concrete Sample27

Table 3.43 Lightcrete-02 Concrete Sample28

Table 3.44 Standard Sandcrete Sample Data29

Table 3.45 Chemrite Aer Sandcrete Data29

Table 3.46 Lightcrete-02 Sandcrete Sample Data30

Table 3.47 Performance in concrete30

Table 3.48 Performance in Sandcrete30

Table 3.51 Foaming Agent Concrete Data33

Table 3.52 Foaming Agent Sandcrete Data34

Table 3.53 Aluminum Powder Concrete Data35

Table 3.54 Aluminum Powder Sandcrete Data37

Table 3.55 Performance in Concrete37

Table 3.56 Performance in Sandcrete38

Table 3.57 Effect of Cement39

(Use two soft returns after "Chapter 1." (Shift-Enter instead of Enter))INTRODUCTION

Lightweight Concrete

Lightweight concrete can be defined as a type of concrete which includes an expanding agent in it that increases the volume of the mixture while reducing its weight. It is lighter than the conventional concrete with a dry density of 40 lb. /ft3 to 100 lb. /ft3. Besides its light weight it has many other advantages in which its sound and thermal insulation are the most famous. Lightweight concrete can be produced in many ways which are broadly classified into two categories:

1. Lightweight aggregates:

· Natural lightweight aggregates.

· Artificial lightweight aggregates.

2. Admixtures:

· Air entraining.

· Admixtures that evolve gases.

Problem Statement

The world population is increasing day by day, and the innovation in the modern construction technology has made it possible to accommodate more in limited space, by constructing high rise buildings (sky scrapers). This trend has now become a vital and intense need of modern world.

Now the problem is that people are using solid bricks made of clay in high rise building, having huge weight because of their solid nature. A brick masonry wall 10 ft. high and 4.5 inch thick, will have 500 lb. /ft. weight. Its weight will be 1000 lb. /ft. if the wall is 9 inch thick. Which is very heavy load. Now if it is 11 story building, multiply 1000 with 11 which becomes very heavy, exerting very large demand on foundations. Therefore very strong foundations are required to overcome these forces. Making the structure uneconomical. Furthermore during the earthquake we will have more base-shear which is the function of weight of the structure and when base shear increases the forces and stresses will increase. Thus we will need more reinforcement and more heavy sections.

Objective

Now our objective is to reduce the weight of the masonry unit. There may be different techniques to reduce the weight of the masonry unit. One technique is to use hollow bricks. Currently we have not seen any hollow bricks producing industry Pakistan and therefore this is not an option to be considered. However some industries are producing hollow blocks and which has already reducing the weight by 35%.

However in some cases people are reluctant to use hollow blocks due to some practical point of view. The first problem is, making groove in hollow blocks is relatively difficult because of its thin walls. There are some instruments available that can be used for this purpose but their economy make them less useable. The second problem is that the shearing area is also smaller than the bricks because of the hollow nature of the blocks when they are placed over another.

Our research will be to produce lightweight concrete that can be used in solid blocks so that it can be easily used in field as well as to be used in hollow blocks in order to further reduce the weight.

Organization of Thesis

This thesis consists of 4 chapters. Following is the brief summary of each chapter.

Chapter 1:

It provides general introduction to the thesis.

Chapter 2:

This chapter provide literature review on the concrete, lightweight concrete and different methods to produce lightweight concrete.

Chapter3:

Methodologies adopted for the research and experimental data of various tests is provided.

Chapter 4:

Conclusions and recommendations of the project are provided.

Literature review

Concrete

Concrete is a composite building material made from the combination of aggregate and cement binder. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland cement and water. It is commonly believed that concrete dries after mixing and placement.

Actually, concrete does not solidify because water evaporates, but rather cement hydrates, gluing the other components together and eventually creating a stone-like material. When used in the generic sense, this is the material referred to by the term concrete. Concrete is used to make pavements, building structures, foundations, highways & roads, overpasses, parking structures, bases for gates/fences/poles, and cement in brick or block walls. An old name for concrete is liquid stone.

0. Types of concrete

There are many types of concrete, designed to suit a variety of purposes coupled with a range of compositions, finishes and performance characteristics.

Based on unit weight, concrete can be classified into three broad categories:

• Normal-weight concrete (150 lb. /ft3)

• Lightweight concrete (<112 lb. /ft3)

• Heavyweight concrete (>200 lb. /ft3)

Based on compressive strength, concrete can be classified into three broad categories:

· Low-strength concrete: less than 3000 psi compressive strength.

· Moderate-strength concrete: 3000 to 6000 psi compressive strength.

· High-strength concrete: more than 6000 psi compressive strength.

There are special ways of strengthening concrete or of making concrete building materials. These include:

· Reinforced concrete

Reinforced concrete is made by casting concrete around steel rods or bars. The steel strengthens the concrete. Almost all large structures, including skyscrapers and bridges, require this extra-strong type of concrete. Shown in Figure 21.

· Prestressed concrete

Prestressed concrete usually is made by casting concrete around steel cables stretched by hydraulic jacks. After the concrete hardens, the jacks are released and the cables compress the concrete. Concrete is strongest when it is compressed. Steel is strong when it is stretched, or in tension. In this way, builders combine the two strongest qualities of the two materials. The steel cables can also be bent into an arc, so that they exert a force in any desired direction, such as upward in a bridge. This force helps counteract the weight of the bridge. Prestressed concrete beams, roofs, floors, and bridges are often cheaper for some uses than those made of reinforced concrete.

· Precast concrete

Precast concrete is cast and hardened before being used for construction. Precasting firms make concrete sewer pipes, floor and roof units, wall panels, beams, and girders, and ship them to the building site. Sometimes builders make such pieces at the building site and hoist them into place after they harden. Precasting makes possible the mass production of concrete building materials. Nearly all prestressed concrete is precast.

· Concrete masonry

Concrete masonry includes many shapes and sizes of precast block. It is used to make about two-thirds of all the masonry walls built each year in the United States. Some concrete masonry is decorative or resembles brick.

Engineers have also developed special kinds of concrete for certain uses. These include:

· Air-entrained concrete

Air-entrained concrete contains tiny air bubbles. These bubbles are formed by adding soap like resinous or fatty materials to the cement, or to the concrete when it is mixed (see RESN). The bubbles give the water in concrete enough room to expand as it freezes. The bubbles also protect the surface of the concrete from chemicals used to melt ice. Such qualities make air-entrained concrete a good material for roads and airport runways.

· High-early-strength concrete

High-early-strength concrete is chiefly used in cold weather. This concrete is made with high-early-strength Portland cement, and hardens much more quickly than ordinary concrete. It costs more than ordinary concrete. But it is often cheaper to use, because it cuts the amount of time the concrete must be protected in cold weather.

Lightweight concreteIntroduction

Lightweight concrete can be defined as a type of concrete which includes an expanding agent in it that increases the volume of the mixture while reducing the dead weight. It is lighter than the conventional concrete with a dry density of 40 lb. /ft3 up to 100 lb. /ft3. The main specialties of lightweight concrete are its low density and low thermal conductivity. The use of LWC (Lightweight concrete) has been a feature in the construction industry for centuries, but like other material the expectations of the performance have raised and now we are expecting a consistent, reliable material and predictable characteristics.

It was first introduced by the Romans in the second century where ‘The Pantheon’ has been constructed using pumice, the most common type of aggregate used in that particular year. From there on, the use of lightweight concrete has been widely spread across other countries such as USA, United Kingdom and Sweden.

Its advantages are that there is a reduction of dead load, faster building rates in construction and lower haulage and handling costs. The building of ‘The Pantheon’ of lightweight concrete material is still standing eminently in Rome until now for about 18 centuries as shown in Figure 1. It shows that the lighter materials can be used in concrete construction and has an economical advantage.

Figure 2.21 The Pantheon

Generally, the properties of LWC can be indicated by doing laboratory testing, but the overall performance of the material can only be demonstrated adequately by its performance in the field by testing LWC structure under service. LWC has been successfully used for marine applications and in shipbuilding. LWC ships were produced in the USA during the 1914-1918 war, and their success led to the production of the USS Selma (a war ship). In both 1953 and 1980 the Selma’s durability was assessed by taking cored samples from the water line area. On both occasion little corrosion was noted.

In 1984, Thomas A. Holm estimated that there were over 400 LWC bridges throughout the world especially in USA and Canada. The research carried out by The Expanded Clay and Slate Institute proves that most of the bridges appeared to be in good condition. According to ACI Material Journal by Diona Marcia, Andrian Loani, Mihai Filip and Ian Pepenar (1994), it was found that in Japan LWC had been used since 1964 as a railway station platform. The study on durability was carried out in 1983 has proven that LWC exhibited similar carbonation depths as normal concrete. Even though some cracks were reported, but these posed no structure problems. A second structure comprising both LWC and normal concrete which had been in sea water for 13 years was examined for salt penetration.

Advantages

Lightweight concrete is of utmost importance to the construction industry. The advantages of lightweight concrete are its reduced mass and improved thermal and sound insulation properties, while maintaining adequate strength. The marginally higher cost of the lightweight concrete is offset by size reduction of structural elements, less reinforcing steel and reduced volume of concrete, resulting in overall cost reduction. The reduced weight has numerous advantages; one of them is reduced demand of energy during construction.

· Light Weight:

Density range from 40 lb. /ft3to 115 lb. /ft3 as compared to 122 lb. /ft3 to 150 lb. /ft3 for conventional brick and concrete respectively. Despite millions of tiny air filled cells, it is strong and durable. There is Lightweight advantage for the structure design, leading to savings in supporting structures and foundation.

· Compressive Strength:

Its compressive strength varies from 600 to 3700 psi.

· Excellent Acoustic Performance:

It can be used as effective sound barrier and for acoustic solutions. Hence, highly suitable for partition walls, floor screens / roofing and panel material in auditoriums.

· Earthquake Resistant:

Since lighter than concrete & brick, the lightness of the material increases resistance against earthquake.

· Insulation:

Superior thermal insulation properties compared to that of conventional brick and concrete, so reduces the heating and cooling expenses. In buildings, light-weight concrete will produce a higher fire rated structure.

· Workability:

Products made from lightweight concrete are lightweight, making them easy to place using less skilled labor. The bricks can be sawed, drilled and shaped like wood using standard hand tools, regular screws and nails. It is simpler than brick or concrete.

· Lifespan:

Weather proof, termite resistant and fire proof.

· Savings in Material:

Reduces dead weight of filler walls in framed structures by more than 50% as compared to brickwork resulting in substantial savings. Due to the bigger and uniform shape of blocks, there is a saving in bed mortar and plaster thickness. In most cases the higher cost of the light-weight concrete is offset by a reduction of structural elements, less reinforcing steel and reduced volume of concrete.

· Water Absorption:

Closed cellular structures and hence have lower water absorption.

· Skim Coating:

Do not require plaster and water repellent paint suffices. Wallpapers and plasters can also be applied directly to the surface.

Disadvantages

· Modulus of Elasticity:

The modulus of elasticity of the concrete with lightweight aggregates is lower, 0.5 – 0.75 to that of the normal concrete. Therefore more deflection is there in lightweight concrete.

· Lower strength:

Due to lower density and porous structure the compressive strength of light weight concrete is less than the normal concrete. The ACI code does not allow light weight concrete of strength above 5000 psi.

Production of lightweight concrete

Lightweight concrete can be prepared either by injecting air in its composition or it can be achieved by omitting the finer sizes of the aggregate or even replacing them by a hollow, cellular or porous aggregate.

Particularly, lightweight concrete can be categorized into two groups:

Using lightweight aggregates

This type is produced using lightweight aggregate such as volcanic rock or expanded clay. It can be produced with the use of naturally mined lightweight aggregates (bulk density in the range of 55 lb. /ft3) or manmade lightweight aggregates like “Aardelite” or “Lytag” (bulk density 50 lb. /ft3).

Using admixtures

This one is produced through the addition of an admixture in concrete. This creates a fine cement matrix which has air voids throughout its structure. Aerated cement mortar is produced by the introduction of a gas into cementitious slurry so that after hardening a cellular structure is formed.

Types of lightweight aggregates

Lightweight aggregates used in structural lightweight concrete are typically expanded shale, clay or slate materials that have been fired in a rotary kiln to develop a porous structure. Other products such as air cooled blast furnace slag are also used. Also there are some nonstructural lightweight aggregates with lower density made with other aggregate materials and higher air voids in the cement paste matrix. These are typically used for their insulation properties. (1)

Natural aggregates

· Inorganic Natural Aggregates:

Diatomite, pumice, scoria and volcanic cinders are natural, porous volcanic rocks with a bulk density of 30 – 50 lb. /ft3 which make a good insulating concrete. Pumice stone is shown in figure 2.3.1

Figure 2.31 Pumice Stone

· Organic Natural Aggregates:

Wood chips and straw can be mixed with a binder to provide a lightweight natural aggregate. These are cellular materials which have air trapped within their structures once they have low moisture content.

Artificial lightweight aggregates

Artificial LWA can be manufactured by means of two types of processes: cement-base granulation and high temperature sintering. Of these the later has been widely studied and the pertinent literature is rich of applications in which many waste materials proved to have potential for use as feedstock: Bottom and fly ashes from combustors, municipal solid waste from incinerators, dusts from furnaces, mine and quarry tailings, sediments etc.

· Bloated clay, sintered fly ash and foamed blast furnace slag.

· Lightweight expanded clay aggregate: This is produced by heating clay to a temperature of 1000 – 1200 Co, which causes it to expand due to the internal generation of gases that are trapped inside. The porous structure which forms is retained on cooling so that the specific gravity is much lower than what was before heating it. (2)

Admixtures

There are two main types of admixtures for the production of lightweight concrete.

Air entraining agents

There are some foaming agents which are very powerful air entraining agents. The foam is generated using foam generator which is a very sophisticated instrument costing more than two lacks and is not available in Pakistan we have to import it. Using these foaming agents we can reduce the weight up to 50%. However the drawback of using foaming agent is that the strength is reduced drastically. The maximum strength achieved so far is less than 3700 psi even at higher density of between 100 and 110 lb. /ft3. Strength development of foamed concrete depends largely on some factors which are the constituents of the base mix, the density of foam and the water cement ratio of the base mix. (3)

Admixtures that evolve gases

Some admixtures like aluminum powder when added to cement slurry evolve gases and due to these evolution of gases they tends to expend the concrete. These types of admixtures are very hazardous and have unpredictable natures. The expansion of concrete occurring due to these admixtures can damage the formwork and can lead to unwanted shapes of the concrete. However these admixtures are currently successfully in use in many countries in a very control environment. Autoclaved aerated concrete is one of the most famous example of such admixtures. Shown in figure 2.4.2:

Figure 2.41 Admixture

METhedology

Background

As already discussed that lightweight concrete can be produced in different ways. We started working on the very first option that was using lightweight aggregates.

Since greater part of concrete consists of aggregates (course) so if the density of these aggregates is reduced the density of concrete can be reduced as well. The bulk density of fine lightweight aggregates is around 75 lb. /ft3. The bulk density of coarse lightweight aggregates is around 60 lb. /ft3.

In the initial stages of our project our main objective was to find pumice stone. Pumice is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored.

Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano. The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases (including water and CO2) that are dissolved in the lava, causing the gases to rapidly evolve (like the bubbles of CO2 that appear when a carbonated drink is opened). (4)

Therefore it is found in those areas which are near to some volcanic eruption zones. Fortunately in Khyber Pakhtunkhwa we could not found any such zone from which we can economically obtained pumice stone. There are some areas in Baluchistan in which large quarries are found but transporting pumice stone from there is very uneconomic.

On the other hand as already discussed artificial light weight aggregates requires very huge temperature to be obtained lightweight property. Therefore it is not an option to be consider.

After not considering these options we moved towards the next options that was to use admixture to create lightweight concrete. The use of admixtures in concrete is becoming very popular now a days in Pakistan and there are many construction chemical suppliers in Pakistan like Sika Group, Imporient Chemicals, Pagel, BASF and Apepak. We started contacting these chemical suppliers and positively responded by few chemical suppliers. Therefore we have divided our project into two phases in which different admixtures are discussed.

First Phase of the Project

In the first phase of our project we were positively responded by IMPORIENT CHEMICALS (PVT) LTD. We got two types of admixtures from them. Chemrite Aer and Lightcrete-02. The complete detail of these chemicals is provided in the appendix A.1 and A.2 respectively. The supplier was calming that these admixtures are very efficient in sandcrete.

Working Methodology

After a lot of discussion with our supervisor we came up with the methodology to check the efficiency of these admixture in both sandcrete and concrete. Therefore we made standard samples of both sandcrete and concrete and then we made samples of Chemrite Aer and Lightcrete -02 in both sandcrete and concrete. The experimental data and the results are provided in the coming pages.

Experimental data

Standard Concrete Samples

We decided to make 2000 psi concrete block. Therefore we did mix design for 3000 psi according ACI standards. After conduction the required tests the ration obtained was 1:2.61:4.8.

After mix design six standard samples were casted on 6th December 2013. In which initially three samples were tested after 7 days curing to check whether the mix design was ok or not. Then the rest were tested after 28 days. The experimental data and the pictures of the samples are shown below in table no.3.3.1 and figure 3.3.1 respectively:

Sample no.

Weight

Lb.

Volume

In3

7 days strength

Psi

28 days strength

Psi

1

15

6x6x6

2300

-

2

15

6x6x6

2100

-

3

15.5

6x6x6

2200

-

4

14

6x6x6

-

2900

5

15

6x6x6

-

2850

6

16

6x6x6

-

2870

Table 3.41: Standard Sample Data

Figure 3.41 Standard Samples

Chemrite Aer Concrete Samples

After the successful results of the standard concrete samples Chemrite Aer concrete samples where casted on 20th December 2013 with maximum dosage in order check the efficiency of the admixtures in concrete the results are reported as under.

The 28 days strength and the weight of the samples where test show in the table 3.3.2 as under:

Table 3.42 Chemrite Aer Concrete Sample

Sample no.

Dosage

%age

Volume

Inch3

Weight

Lb

28 days strength

psi

1

0.15

6x6x6

15

2540

2

0.15

6x6x6

14.5

2500

3

0.15

6x6x6

15

2530

4

0.15

6x6x6

15

2400

5

0.15

6x6x6

15.5

2560

6

0.15

6x6x6

15

2520

Figure 3.42 Chemrite Aer Concrete Sample

Lightcrete-02 Concrete Samples

Similarly Lightcrete-02 concrete samples where casted on 27th December 2013 with maximum dosage in order check the efficiency of the admixtures in concrete the results are reported as under.

The 28 days strength and the weight of the samples where test show in the table 3.3.3 as under:

Table 3.43 Lightcrete-02 Concrete Sample

Sample no.

Dosage

%age

Volume

Inch3

Weight

Lb

28 days strength

Psi

1

1

6x6x6

13

1020

2

1

6x6x6

13.5

1050

3

1

6x6x6

14

1070

Figure 3.43 Lightcrete-02 Concrete Sample

Standard Sandcrete Sample

1:1 sandcrete standard samples were made in order to have a standard for comparison. Three standard samples were casted on 10th January 2014. The samples were tested after 28 days and the results are reported as under in table 3.3.4:

Table 3.44 Standard Sandcrete Sample Data

Sample no.

Volume

Inch3

Weight

Lb

28 days Strength

Psi

1

6x6x6

14

2770

2

6x6x6

13

2780

3

6x6x6

15

2760

Chemrite Aer Sandcrete Sample

Similarly 1:1 Chemrite Aer sandcrete samples were casted on 17th January 2014 with maximum dosage in order to check the efficiency of Chemrite Aer in sandcrete. The samples were tested after 28 days and the results are reported as under in table 3.3.5:

Table 3.45 Chemrite Aer Sandcrete Data

Sample no.

Dosage

%age

Volume

Inch3

Weight

Lb

28 days strength

Psi

1

0.15

6x6x6

14

2200

2

0.15

6x6x6

13

2300

3

0.15

6x6x6

15

2250

Lightcrete-02 Sandcrete Samples

1:1 lightcrete-02 sandcrete samples were casted on 31th January 2014 with maximum dosage in order to check the efficiency in sandcrete. The samples were tested after 28 days and the results are reported as under in table 3.3.6:

Table 3.46 Lightcrete-02 Sandcrete Sample Data

Sample no.

Dosage

%age

Volume

Inch3

Weight

Lb

28 Days Strength

Psi

1

1

6x6x6

13

790

2

1

6x6x6

12

780

3

1

6x6x6

13

785

Overall Performance

The overall performance of the two admixtures Chemrite Aer and Lightcrete-02 in both concrete and sandcrete are shown in the table 3.3.7a and 3.3.7b respectively as under:

Table 3.47 Performance in concrete

Sample type

Unit Weight Reduced

(%age )

Strength Reduced

(%age )

Chemrite Aer

0.00

8.30

Lightcrete -02

2.86

62.1

Table 3.48 Performance in Sandcrete

Sample type

Unit Weight Reduced

(%age )

Strength Reduced

(%age )

Chemrite Aer

0.00

18.86

Lightcrete -02

1.78

71.44

Conclusions about Chemrite Aer and Lightcrete-02

The above performance tables clearly shows that these two admixture fails to fulfill our main objective of the project that was to reduce the weight. On the other hand they have reduced the strength. The main reason for their failure that we concluded was that Chemritre Aer is actually a less efficient air entraining agent, which is basically used for controlling freezing and thawing action. While Lightcrete-02 was not the actual product of the supplier (IMPORIENT CHEMICALS (PVT) LTD). Lightcrete-02 is the actual product of Sika group who produce and supply it in powder form.

Second Phase of the Project

After testing and rejecting the admixtures in the first phase of the project we were having the following options:

· Contact Sika group for actual Lightcrete-02.

· Contact other chemical suppliers in Pakistan for some other admixture.

· Use aluminum powder.

Without working on the options available one by one, work was started on all the options simultaneously. Several visits were made to the regional office of Sika group in Islamabad for the actual product. Contacts were also made with them through email and telephone calls. However they did not responded positively, leaving us with last two options.

0. Foaming Agent

After contacting a number of chemical suppliers we were responded positively by BASF chemical supplier. They supplied Rheocell 10. The complete detail of Rheocell 10 is provided in appendix A.3. It was found that Rheocell 10 was a foaming agent, which we have already discussed that it requires a very sophisticated instrument known as foaming generator. As the foaming generator is very costly instrument and we have to import it from abroad therefore it was out of scope our project to buy such instrument. However the main principal on which the foam generator works was investigated and it was conclude that the foam generator simply mix the air in the water containing the foaming agent. Based on these conclusions a simply and very economical foam generator was manufactured, costing only Rs.2000. Shown in the figure 3.4.1:

Figure 3.51 Foam Generator

The foam generator was first of all test by taking one liter of water and adding 50ml of the faming agent. The figure 3.4.1a shows the foam generated. The figure shows that very favorable results were obtained.

Figure 3.52 Foam Generated

After successful test of the foam generator the efficiency of the foaming agent was checked, both in concrete and sandcrete by making four samples, one standard sample having zero percent foaming agent, and the rest three with 2, 4 and 6 percent (by weight of cement) of the foaming agent.

Concrete Samples

Four 1:2:2 concrete samples were casted on 2th May 2014, with water cement ration of 0.4, one standard without any foaming agent and the other three with 2, 4 and 6 percent (by weight of cement) of the foaming agent.

The compressive strength and the weight of the samples were tested and reported as under in table 3.4.1.1:

Table 3.51 Foaming Agent Concrete Data

Sample No.

Dosage

Weight

Strength

1

0

15

2850

2

2

10.5

900

3

4

10

800

4

6

9.5

680

Figure 3.53 Foaming Agent Samples

Figure 3.54 Foaming Agent Sample

Sandcrete Samples

Two 1:1 sandcrete samples were casted on 9th May 2014, with water cement ratio of 0.4, one standard without any foaming agent and the other with maximum dosage i.e. 6 percent (by weight of cement) of the foaming agent.

The compressive strength and the weight of the samples were tested and reported as under in table 3.4.1.1:

Table 3.52 Foaming Agent Sandcrete Data

Sample No.

Dosage

Weight

Strength

1

0

14.5

2500

2

6

8

650

0. Aluminum Powder

As we have already discussed that aluminum powder is that admixture which when added to cement slurry evolve gases and tends to expend the concrete or snadcrete mix. It costs from Rs.4000 to Rs.6000 per kg in Pakistan and it is used 0.1 percent by weight of cement, will require 0.5 kg i.e. costing minimum Rs.400 per bag of the cement. Which makes it very costly. However it as tested and the experimental data is as under.

2. Concrete Sample

Four 1:2:2 concrete samples were casted on 25th April 2014, with water cement ration of 0.4, one standard without aluminum powder and the other three with 0.01, 0.05 and 0.1 percent (by weight of cement) of the aluminum powder.

The compressive strength and the weight of the samples were tested and reported as under in table 3.4.1.1:

Table 3.53 Aluminum Powder Concrete Data

Sample No.

Dosage

Weight

Strength

1

0

15

2850

2

0.01

12

880

3

0.05

12

800

4

0.1

11

650

The figures below shows the expended volume of the concrete due to addition of concrete.

Figure 3.55 Aluminum Powder

It was observed that the concrete expanded to the full capacity within five minutes. The expansion of concrete with 1 minute increment of time is shown in the below figures:

Figure 3.56 Aluminum Powder Gradual Progress

2. Sandcrete Samples

Similarly two 1:1 sandcrete samples were casted on 9th May 2014, with water cement ratio of 0.4, one standard without aluminum powder and the other with maximum dosage i.e. 6 percent (by weight of cement) of the aluminum powder.

The compressive strength and the weight of the samples were tested and reported as under in table 3.4.1.1:

Table 3.54 Aluminum Powder Sandcrete Data

Sample No.

Dosage

Weight

Strength

1

0

14.5

2500

2

0.1

9

600

0. Overall Performance

The performance tables as shown below for both aluminum powder and foaming agent.

Performance in Concrete:

Table 3.55 Performance in Concrete

Sample type

Unit Weight Reduced

(%age )

Strength Reduced

(%age )

Foaming Agent

40.0

74.0

Aluminum Powder

27.0

76.0

Performance in Sandcrete:

Table 3.56 Performance in Sandcrete

Sample type

Unit Weight Reduced (%age )

Strength Reduced

(%age )

Foaming Agent

45.0

75.0

Aluminum Powder

38.0

74.0

0. Conclusion about Foaming agent and Aluminum powder

Both the foaming agent and the aluminum powder were fulfilling over main objective that was to reduce the weight of the concrete. However, both reduces the strength to an unacceptable limit, however the strength can be increased, for which a number of methods are available. Which we are going to discuss in the next section.

0. Increasing Strength of Foaming Agent Sample

The effect of the cement content on the samples containing the foaming agent was tested by taking three mixtures with different rations from poor mix to medium mix and then to rich mix. 1:3:6, 1:2:2, and 1:1:1 mix were taken. Two samples of each mix, one standard and one with the medium dosage of foaming agent were casted. The compressive strength and weight was tested after curing. The results are reported as under in table 3.4.5:

Table 3.57 Effect of Cement

Sample type

Volume

Inch3

Dosage

%age

Unit Weight

lb.

Strength

Psi

1:3:6

6x6x6

0

14

2600

1:3:6

6x6x6

4%

10

650

1:2:2

6x6x6

0

15

2850

1:2:2

6x6x6

4%

10

800

1:1:1

6x6x6

0

15

3000

1:1:1

6x6x6

4%

14

2000

During these tests it was observed that the efficiency of foaming agent depends on the efficiency of the foam generator to produce very small pores in the foam. It was also observed that with the increase in the cement quantity the efficiency of the foaming agent was reduced. The cement was rapidly absorbing the water in which the foaming agent was mixed and breaking the bubbles or pores of the foam.

39

CONCLUSION AND RECOMMENDATIONS

Conclusion

The results of the various experiments have revealed the following:

· Due to the hazardous and unpredictable nature of Aluminum powder, its use in concrete is discouraged.

· We can safely and easily use foaming agents to reduce the unit weight of concrete. Using our foam generator and Rheocell 10 we can reduce the weight of concrete by 40%. But special control on strength is required.

Recommendations

· Foam generator should be used with a more powerful external motor.

· Strength reduction should be controlled by using some alternatives like silica fume etc.

· Foaming agents should be used with lightweight aggregates for better results.

· The actual economic analysis should be carried out to compare the cost of lightweight concrete production and benefits due to decrease in dead load.

· The thermal insulation properties of concrete should be investigated.

Detail Of admixtures

Detail information about the different admixture obtained during the research from different construction chemicals suppliers are provided as under.

Chemrite Aer

A ready to use highly concentrated air entraining concrete admixture. Its efficiency is based upon a very large number of minute-sized, evenly distributed air pores. It complies with ASTM C 260. It is a surface active agent having brown color and density of approximately 1.03 kg/lt. Its self-life is 12 months minimum if stored properly in the original unopened packing. Store away from sunlight. It is supplied in 200 liter drum. The dosage provided by the supplier is 0.03-0.15% by weight of cement. Exact dosage rates are determined by trials at site. Factors affecting air contents, include: type, grading and proportion of sand, cement, aggregates, type and fineness of cement, water/cement ratio, and temperature. In certain cases therefore, it may be necessary to increase the dosage above 0.15% rate. Air meter tests should be taken consistently and adjustments made to the dosage rate to completely control the amount of air entrainment, which should be preferably in the range of 3-6%. Chemrite Aer is added to the mixing water prior to its addition to the dry concrete mix. Chemrite Aer can be combined with all admixtures. It is also compatible with sulfate resistant cement. Increased air contents generally have a reduction effect on strengths. This can be adequately compensated by using other admixtures. It is also nonhazardous and nontoxic.

Chemrite Aer is used to produce easily workable and durable concrete for:

· Roads

· Runways and taxiways

· Concrete aprons.

· Dams and reservoirs

· Mass concrete structures

Chemrite Aer provides the following advantages:

· Improved workability

· Improved durability

· Increased cohesion reducing the risk of segregation

· Reduced water content without loss of workability

· Unaltered setting time even when overdosed (5)

Lightcrete -02

Lightcrete -02 is a liquid admixture for concrete and mortar to produce lightweight concrete. Foam concrete, e.g. for the filling of trenchers, lightweight concrete for thermal and acoustic insulation purposes, the filling of pipes etc., may be produced with the aid of Lightcrete-02 . Lightweight concrete (LB) classified according to SIA 162 can also be produced with Lightcrete-02. Lightcrete -02 is suitable for the production of lightweight concrete for every kind of application. The liquid admixture is being added at the batching plant or directly onto the transit mixer. Its application is suitable for site mixed as well as ready mixed concrete. The key figures like density, air pore content or strengths depend on the composition of the aggregate, their partial replacement with lightweight aggregates, water content, binder content and mixing times. It is not possible to produce frost and de-icing salt resistant concrete with Lightcrete -02. It is in liquid form brown in color and with density of 1.01 kg/lit. Its self-life is 12 months from date of production if stored properly in unopened and undamaged original sealed containers, at temperatures between + 5°C and + 35°C. Protected from direct sunlight and frost.

Recommended dosage (by weight of cement).

For classified lightweight concrete

0.5 - 1.0% in combination with sand and lightweight aggregates.

For lightweight (pore) concrete

0.5 - 2.0%

Lightcrete -02 is being added to the gauging water or added simultaneously together with the gauging water into the concrete mixer.

The mixing time necessary to achieve a specific density of fresh concrete depends on type of mixer used, aggregates and binder. Therefore trials to achieve certain air pore content are indicated. The results from these trials with regard to the mixing procedure should be strictly adhered to.

Lightcrete -02 may also be added to the pre-mixed concrete directly into the transit mixer at the point of discharge. An additional mixing time of at least 2 minutes per m3 concrete must be strictly observed. Before being discharged, the concrete must be tested for the intended density.

With the use of Lightcrete -02 lightweight or foam concrete may be produced.

The standard rules of good concrete production and placing must also be observed for Lightcrete - 02 concrete.

Proper curing procedures must be observed for surfaces which are to be exposed to weathering. Otherwise, premature drying out close to the surface may cause lightweight concrete to lose mechanical strengths. It is also nontoxic and nonhazardous.

Lightcrete -02 produces the necessary quantity of airpores during the mixing process. No reactive air production takes place.

The following advantages may be obtained when using Lightcrete -02:

· Safe introduction of air pores up to 35%.

· Dry density of approx. 800 up to 1’600 kg/m3 in combination with lightweight aggregates.

· Stable air content also after placing of the concrete.

· Conveyance of lightweight concrete with concrete pump possible.

· Combinations with lightweight aggregates, e.g. expanded clay are possible.

· Easy production of concrete and mortar in ready mix plants using standard dosing equipment.

· Lightcrete -02 does not contain chlorides or other components which promote steel corrosion. It may therefore be used without any restrictions in steel-lightweight concrete construction. (6)

Rheocell 10

Rheocell 10 is a liquid admixture for the production of lightweight concrete. RHEOCELL 10 is a ready to use liquid foaming agent which is used in conjunction with the RHEOCELL Foam Gun to produce rheoplastic lightweight foam concrete for a variety of insulation and construction applications. RHEOCELL 10 lightweight concrete has a very fine cellular structure and optimum workability for a given water cement ratio. This combination offers lower materials weight per unit volume, and therefore a lower dead load imposed on the structure. Significant reductions in heat conductivity will also be achieved.

Primary uses

· As thermal insulation

Plastic density approx. 1000kg/m³

RHEOCELL 10 rheoplastic lightweight foam concrete is particularly suitable as a light, insulating, levelling layer on roofs and floors. As it can be pumped easily, it offers significant advantages over other lightweight building materials. Placing by pump can be achieved on sites where access would otherwise be difficult, as with the repair and maintenance of buildings.

· As encasement concrete

Plastic density approx. 600kg/m³ Pipes can be encased with RHEOCELL 10 rheoplastic lightweight foam concrete and held in place. At some later stage should access be required to these encased services, the foam concrete can easily be removed. If conventional concrete had been used this would be difficult.

· As backfill concrete

Plastic density approx. 1350kg/m³ RHEOCELL 10 rheoplastic lightweight foam concrete can be placed directly from the truck mixer and requires no compaction, unlike granular fill materials, which need careful compaction. RHEOCELL 10 rheoplastic lightweight foam concrete is particularly suitable for filling old sewer pipes and drains which have been taken out of service. Also underground fuel storage tanks, disused cellars or tunnels. It is important in these applications that the cavity is entirely filled with a material that will not settle or shrink.

Through the heat of hydration of the cement, the air enclosed in the air pores of the RHEOCELL 10 is heated thereby causing the pores to expand. RHEOCELL 10 rheoplastic lightweight foam concrete expands against the walls of the cavity through its own internal pressure without imposing any additional load on the wall. When specifying densities a margin of ± 50kg/m³ should be allowed for.

Advantages

· Self-compacting.

· Simple placing by means of chutes, pipes or pumps.

· No additional transfer equipment.

· Pre-selected strength density values.

· High placing performance.

· Extremely economical.

Packaging

RHEOCELL 10 is supplied in liters. One liter costs Rs.200.

Method

A mortar of specific composition is delivered to the site in a truck mixer. Using the compact RHEOCELL foam generator, (which operates using a 2 bar water source) the required volume of foam is produced in a short time. With a water pressure of 2 bar, each second, 11 liters of foam are produced: 660 liters of foam per minute are produced. 26 liters of water are consumed per minute. 1 liter of RHEOCELL 10 is needed per minute. The foam dosage can be regulated very simply by adding the foam produced by the foam gun in a given time, to achieve a certain density.

Density of required concrete in kg/m³

Foaming time for 1m³ foam concrete

800

58 seconds

1000

52 seconds

1200

42 seconds

1350

39 seconds

1600

29 seconds

Density of required concrete in kg/m³ Foaming time for 1m³ foam concrete

The foam, fed directly into the truck mixer with the mixer turning at maximum speed, is rapidly incorporated into the base mix to produce a homogeneous foam concrete. Foaming is enhanced at higher ambient temperatures. Density can be checked using a standard 1 liter plastic density pot. Should the density be low more foam can be added, too high and additional mixing will displace a certain amount of air.

Typically for 6m³ of RHEOCELL 10 foamed concrete, 3.6m³ of sand/cement slurry shall be delivered from the ready-mix supplier. (BASF can assist with mix designs). To this is added 2.4m³ of foam at the site.

Storage

RHEOCELL 10 may be stored for 6 months in properly sealed original containers at a temperature of at least +10°C. Should the temperature drop below 0°C the product should be carefully heated and mixed thoroughly before use.

Safety precautions

RHEOCELL 10 is not a fire or health hazard. Spillages should be washed down immediately with cold water. For further information refer to the Material Safety Data Sheet.

Field service, where provided, does not constitute supervisory responsibility. For additional information contact your local BASF representative. BASF reserves the right to have the true cause of any difficulty determined by accepted test methods.

Quality and care

All products originating from BASF’s Dubai, UAE facility are manufactured under a management system independently certified to conform to the equirements of the quality, environmental and occupational health & safety standards ISO 9000, ISO 14001 and OHSAS 18001. (7)

References

1. [Online] http://en.wikipedia.org/wiki/Concrete.2. Desai, Dhawal. Development Of Light Weight Concrete. 2007.3. Experimental Production of Sustainable Lightweight Concrete. Alonge O. Richard, Mahyuddin Ramli. 4, British : British Journal of Applied Science & Technology, 2013, Vol. iii. 994-1005.4. [Online] 5. [Online] 6. [Online] 7. [Online]

The Use of Lightweight Concrete Blocks in

Multistory Buildings.

By

Farhat Ullah

S M Tariq Shah

Supervised by

Prof. Dr. Qaisar Ali

DISSERTATION

A Thesis Presented in Partial Fulfillment of the Requirements of the Degree

Bachelor of Science

DEPARTMENT OF CIVIL ENGINEERING

UNIVERSITY OF ENGINEERING AND TECHNOLOGY,

PESHAWAR

© UET Peshawar, 2014

The Use of Lightweight Concrete Blocks in Multistory Buildings.

By

Farhat Ullah

S M Tariq Shah

Supervised by

Prof. Dr. Qaisar Ali

DISSERTATION

A Thesis Presented in Partial Fulfillment of the Requirements of the Degree

Bachelor of Science

16

12

1.5

Times new roman

DEPARTMENT OF CIVIL ENGINEERING

16

12

1.5

Times new roman

UNIVERSITY OF ENGINEERING AND TECHNOLOGY,

PESHAWAR

© UET Peshawar, 2014

The Use of Lightweight Concrete Blocks in Multistory Buildings.

Farhat Ullah (Registration No. 10-pwciv-3325)

S M Tariq Shah (Registration No. 10-pwciv-3380)

____________________

Prof. Dr. Qaisar Ali

Project Supervisor

_________________

Prof. Dr. Akhtar Naeem

Chairman

DEPARTMENT OF CIVIL ENGINEERING

16

12

1.5

Times new roman

UNIVERSITY OF ENGINEERING AND TECHNOLOGY,

PESHAWAR

Session 2010-14

ABSTRACT

This research shows the feasibility and sequential approach for producing lightweight concrete using different techniques that can be easily adopted in underdeveloped country like Pakistan. Almost all the options available to create lightweight concrete in Pakistan are thoroughly studied and practically tested. The target was to reduce the unit weight. Specific volume principle was utilized to observe the effect of inclusion of coarse aggregate, cement, water, sand and different admixtures in the mixture to achieve the goal. Molds were used to accommodate volumetric expansion of mixture. Six inch cubic specimens were prepared for tests. Density and compressive strength were determined for each specimens.

From the results, the use of foaming agents is the most suitable method for the production of lightweight concrete. For which own foam generator was developed costing RS.2000. It was seen that density and compressive strength decreased with increased percentage of foaming agent. Finally, lightweight concrete with density and compressive strength within range of 70-100 lb. /ft3 and 700-1000 lb. /inch2 respectively was produced.

KEY WORDS: Lightweight concrete, Foam generator, Foaming agents, Aluminum powder.

iii

35

DEDICATION

These thesis are dedicated to our parents and all our well-wishers, especially our teachers who supported us throughout the journey towards the goal and gave us confidence to strive for the success.

(To update this table of content after you have created your own thesis or dissertation, right-click on the table and select “Update Field,” or else left-click on the table and left-click on “Update Table,” which should appear in the upper left hand corner. Generally you will want to select “Update entire table.”)TABLE OF CONTENTSABSTRACTvDEDICATIONviLIST OF FIGURESxLIST OF TABLESxiiACKNOWLEDGMENTS1CHAPTER 1 INTRODUCTION11.1Lightweight Concrete11.2Problem statement11.3Objective2CHAPTER 2 Literature review32.1Concrete32.2Types of concrete32.2.1Reinforced concrete42.2.2Prestressed concrete42.2.3Precast concrete42.2.4Concrete masonry42.2.5Air-entrained concrete52.2.6High-early-strength concrete52.3Lightweight concrete52.3.1Introduction52.3.2Advantages72.3.3Disadvantages82.3.4Production of lightweight concrete92.3.5Using lightweight aggregates92.3.6Using admixtures92.4Types of lightweight aggregates92.4.1Natural aggregates92.4.2Artificial lightweight aggregates102.5Admixtures102.5.1Air entraining agents102.5.2Admixtures that evolve gases11CHAPTER 3 METhedology123.1Background123.2First phase of the project133.2.1Chemrite Aer133.2.2Lightcrete -02143.2.3Working methodology163.3Experimental data163.3.1Standard samples163.3.2Chemrite Aer Samples233.3.3Lightcrete -02 samples233.4Experimental data23CHAPTER 4 CONCLUSION AND RECOMMENDATIONS244.1Conclusion244.2Recommendations24CHAPTER 5 DISCUSSION25CHAPTER 6 CONCLUSIONS AND FUTURE WORK266.1Conclusions266.2Future Work26APPENDIX APurpose and format of an appendix28A.1Appendix Subsection28A.2Figures in Appendices28A.3Equations in Appendices29APPENDIX BDetails about Captions30B.1Figures30B.2Tables32B.3Comments on Equation Numbering in Word 200733Bibliography34

xii

LIST OF FIGURES

Figure 11: The down-arrow (circled) can be used to page through different styles. The arrow in the lower right-hand corner (in the diamond) can be used to view all styles available to you.4

Figure 21: Template for inserting figures.6

Figure 22: Cross-reference dialog box for referencing figures, tables, paragraphs, and other links within the narrative.7

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Figure 24: Incorrectly formatted List of Figures entry.8

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Figure A1: Template for inserting figures into appendices.24

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LIST OF TABLES

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Table A1: Template for inserting tables in Appendices.24

ACKNOWLEDGMENTS

First and foremost, we are thankful to almighty Allah for his blessings conferred upon us.

We would like to express our sincere gratitude to our Supervisor Dr. Qaisar Ali senior professor at NWFP UET Peshawar, KP, Pakistan, on the continuous support of our B.Sc. final year project, for his patience, motivation, enthusiasm, and immense knowledge. His guidance helped us throughout the project work and thesis writing. We could not have imagined having such a better advisor and mentor for our B.Sc. project.

Besides our advisor, we would like to thank the rest of our thesis committee: Engr. Arsalaan Khan, lecturer at NWFP UET Peshawar, KP, and Pakistan for his suggestion on the topic, encouragement to do our research on a topic which is state-of-the-art.

Our sincere thanks also go to the Honorable and Eminent Prof. Dr. Akhtar Naeem Khan, chairman Department of Civil Engineering, NWFP UET Peshawar, KP, Pakistan, for accepting our interest and offer to carry out our final year project on this topic.

We would like to thank our dear friends and colleagues, especially our batch fellows.

Last, we pay our sincere gratitude and praise to our parents whose love, affection, support and prayers for our success made us what we are.

34

(Use two soft returns after "Chapter 1." (Shift-Enter instead of Enter))INTRODUCTION

Lightweight Concrete

Lightweight concrete can be defined as a type of concrete which includes an expanding agent in it that increases the volume of the mixture while reducing the dead weight. It is lighter than the conventional concrete with a dry density of 40 lb/ft3 up to 100 lb/ft3. The main specialties of lightweight concrete are its low density and low thermal conductivity. Besides its light weight it has many other advantages in which its sound and thermal insulation are the most famous. Light weight concrete can be produced in many ways which are broadly classified into two categories:

1. Lightweight aggregates:

· Natural lightweight aggregates.

· Artificial lightweight aggregates.

1. Admixtures:

· Air entraining.

· Admixtures that evolve gases.

Problem statement

The world population is increasing day by day, and the innovation in the modern construction technology has made it possible to accommodate more in limited space, by constructing high rise buildings (sky scrapers). This trend has now become a vital and intense need of modern world.

We know that more than 90% of the construction is made of concrete and the concrete has enough unit weight i-e 150 lb/ft3. This shows that the taller the structure the more will have its weight and the greater will the demand for steel and larger sections. It will make the structure costlier.

Since we are always faced with significant earthquakes, causing sever damages and sometimes complete collapse of such high rise structures.

Safety is one of the primary requirements of an engineering discipline, so we will either make the structure more strong to have greater resistance to such demands, making it uneconomical, or reducing the demand (weight of the structure).

The problem is that people are using solid bricks made of clay in high rise building. Which has high weight because of their solid nature. A 10 ft. high wall, if it is 4.5 inch thick than its weight is 500 lb/ft. Its weight is 1000 lb/ft. if the wall is 9 inch thick. Which is very heavy load. Now if it is 11 story building, multiply 1000 with 11 which becomes very heavy giving very large demand to foundations. Therefore very strong foundations are required making the structure uneconomical. Furthermore during the earthquake we will have more base shear which is the function of weight of the structure and when base shear increases the forces and stresses will increase. Thus we will need more reinforcement and more heavy sections.

Objective

Now our objective is to reduce the weight of the masonry unit. There may be different techniques to reduce the weight of the masonry unit. One technique is to use hollow bricks. Currently we have not seen any hollow bricks producing industry Pakistan and therefore this is not an option to be considered. However some industries are producing hollow blocks and which has already reducing the weight by 25% as they have 375 lb/ft. weight.

However in some cases people are reluctant to use hollow blocks due to some practical point of view. The first problem is, making groove in hollow blocks is relatively difficult because of its thin walls. There are some instruments available that can be used for this purpose but their economy make them less useable. The second problem is that the shearing area is also smaller than the bricks because of the hollow nature of the blocks when they are placed over another.

Literature review

Concrete

Concrete is a composite building material made from the combination of aggregate and cement binder. The most common form of concrete is Portland cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland cement and water. It is commonly believed that concrete dries after mixing and placement.

Actually, concrete does not solidify because water evaporates, but rather cement hydrates, gluing the other components together and eventually creating a stone-like material. When used in the generic sense, this is the material referred to by the term concrete. Concrete is used to make pavements, building structures, foundations, highways & roads, overpasses, parking structures, bases for gates/fences/poles, and cement in brick or block walls. An old name for concrete is liquid stone.

Types of concrete

There are many types of concrete, designed to suit a variety of purposes coupled with a range of compositions, finishes and performance characteristics.

Based on unit weight, concrete can be classified into three broad categories:

• Normal-weight concrete (150 lb/ft^3)

• Lightweight concrete (<112 lb/ft^3)

• Heavyweight concrete (>200 lb/ft^3)

Based on compressive strength, concrete can be classified into three broad categories:

· Low-strength concrete: less than 3000 ps compressive strength.

· Moderate-strength concrete: 3000 to 6000 psi compressive strength.

· High-strength concrete: more than 6000 psi compressive strength.

There are special ways of strengthening concrete or of making concrete building materials. These include:

Reinforced concrete

Reinforced concrete is made by casting concrete around steel rods or bars. The steel strengthens the concrete. Almost all large structures, including skyscrapers and bridges, require this extra-strong type of concrete. Shown in Figure 21.

Prestressed concrete

Prestressed concrete usually is made by casting concrete around steel cables stretched by hydraulic jacks. After the concrete hardens, the jacks are released and the cables compress the concrete. Concrete is strongest when it is compressed. Steel is strong when it is stretched, or in tension. In this way, builders combine the two strongest qualities of the two materials. The steel cables can also be bent into an arc, so that they exert a force in any desired direction, such as upward in a bridge. This force helps counteract the weight of the bridge. Prestressed concrete beams, roofs, floors, and bridges are often cheaper for some uses than those made of reinforced concrete.

Precast concrete

Precast concrete is cast and hardened before being used for construction. Precasting firms make concrete sewer pipes, floor and roof units, wall panels, beams, and girders, and ship them to the building site. Sometimes builders make such pieces at the building site and hoist them into place after they harden. Precasting makes possible the mass production of concrete building materials. Nearly all prestressed concrete is precast.

Concrete masonry

Concrete masonry includes many shapes and sizes of precast block. It is used to make about two-thirds of all the masonry walls built each year in the United States. Some concrete masonry is decorative or resembles brick.

Engineers have also developed special kinds of concrete for certain uses. These include:

Air-entrained concrete

Air-entrained concrete contains tiny air bubbles. These bubbles are formed by adding soap like resinous or fatty materials to the cement, or to the concrete when it is mixed (see RESN). The bubbles give the water in concrete enough room to expand as it freezes. The bubbles also protect the surface of the concrete from chemicals used to melt ice. Such qualities make air-entrained concrete a good material for roads and airport runways.

High-early-strength concrete

High-early-strength concrete is chiefly used in cold weather. This concrete is made with high-early-strength Portland cement, and hardens much more quickly than ordinary concrete. It costs more than ordinary concrete. But it is often cheaper to use, because it cuts the amount of time the concrete must be protected in cold weather.

Lightweight concreteIntroduction

Lightweight concrete can be defined as a type of concrete which includes an expanding agent in it that increases the volume of the mixture while reducing the dead weight. It is lighter than the conventional concrete with a dry density of 40 lb/ft3 up to 100 lb/ft3. The main specialties of lightweight concrete are its low density and low thermal conductivity. The use of LWC (Lightweight concrete) has been a feature in the construction industry for centuries, but like other material the expectations of the performance have raised and now we are expecting a consistent, reliable material and predictable characteristics.

It was first introduced by the Romans in the second century where ‘The Pantheon’ has been constructed using pumice, the most common type of aggregate used in that particular year. From there on, the use of lightweight concrete has been widely spread across other countries such as USA, United Kingdom and Sweden.

Its advantages are that there is a reduction of dead load, faster building rates in construction and lower haulage and handling costs. The building of ‘The Pantheon’ of lightweight concrete material is still standing eminently in Rome until now for about 18 centuries as shown in Figure 1. It shows that the lighter materials can be used in concrete construction and has an economical advantage.

FIGURE 1: ‘The Pantheon’

Generally, the properties of LWC can be indicated by doing laboratory testing, but the overall performance of the material can only be demonstrated adequately by its performance in the field by testing LWC structure under service. LWC has been successfully used for marine applications and in shipbuilding. LWC ships were produced in the USA during the 1914-1918 war, and their success led to the production of the USS Selma (a war ship). In both 1953 and 1980 the Selma’s durability was assessed by taking cored samples from the water line area. On both occasion little corrosion was noted.

In 1984, Thomas A. Holm estimated that there were over 400 LWC bridges throughout the world especially in USA and Canada. The research carried out by The Expanded Clay and Slate Institute proves that most of the bridges appeared to be in good condition. According to ACI Material Journal by Diona Marcia, Andrian Loani, Mihai Filip and Ian Pepenar (1994), it was found that in Japan LWC had been used since 1964 as a railway station platform. The study on durability was carried out in 1983 has proven that LWC exhibited similar carbonation depths as normal concrete. Even though some cracks were reported, but these posed no structure problems. A second structure comprising both LWC and normal concrete which had been in sea water for 13 years was examined for salt penetration.

Advantages

Lightweight concrete is of utmost importance to the construction industry. The advantages of lightweight concrete are its reduced mass and improved thermal and sound insulation properties, while maintaining adequate strength. The marginally higher cost of the lightweight concrete is offset by size reduction of structural elements, less reinforcing steel and reduced volume of concrete, resulting in overall cost reduction. The reduced weight has numerous advantages; one of them is reduced demand of energy during construction.

· Light Weight:

Density range from 40 lb/ft3to 115 lb/ft3 as compared to 122 lb/ft3 to 150 lb/ft3 for conventional brick and concrete respectively. Despite millions of tiny air filled cells, it is strong and durable. There is Lightweight advantage for the structure design, leading to savings in supporting structures and foundation.

· Compressive Strength:

2.0 to 7.0 N/mm2.

· Excellent Acoustic Performance:

It can be used as effective sound barrier and for acoustic solutions. Hence, highly suitable for partition walls, floor screens / roofing and panel material in auditoriums.

· Earthquake Resistant:

Since lighter than concrete & brick, the lightness of the material increases resistance against earthquake.

· Insulation:

Superior thermal insulation properties compared to that of conventional brick and concrete, so reduces the heating and cooling expenses. In buildings, light-weight concrete will produce a higher fire rated structure.

· Workability:

Products made from lightweight concrete are lightweight, making them easy to place using less skilled labour. The bricks can be sawed, drilled and shaped like wood using standard hand tools, regular screws and nails. It is simpler than brick or concrete.

· Lifespan:

Weather proof, termite resistant and fire proof.

· Savings in Material:

Reduces dead weight of filler walls in framed structures by more than 50% as compared to brickwork resulting in substantial savings. Due to the bigger and uniform shape of blocks, there is a saving in bed mortar and plaster thickness. In most cases the higher cost of the light-weight concrete is offset by a reduction of structural elements, less reinforcing steel and reduced volume of concrete.

· Water Absorption:

Closed cellular structures and hence have lower water absorption.

· Skim Coating:

Do not require plaster and water repellent paint suffices. Wallpapers and plasters can also be applied directly to the surface.

Disadvantages

· Modulus of Elasticity:

The modulus of elasticity of the concrete with lightweight aggregates is lower, 0.5 – 0.75 to that of the normal concrete. Therefore more deflection is there in lightweight concrete.

· Lower strength:

Due to lower density and porous structure the compressive strength of light weight concrete is less than the normal concrete. The ACI code does not allow light weight concrete of strength above 5000psi.

Production of lightweight concrete

Lightweight concrete can be prepared either by injecting air in its composition or it can be achieved by omitting the finer sizes of the aggregate or even replacing them by a hollow, cellular or porous aggregate.

Particularly, lightweight concrete can be categorized into two groups:

Using lightweight aggregates

This type is produced using lightweight aggregate such as volcanic rock or expanded clay. It can be produced with the use of naturally mined lightweight aggregates (bulk density in the range of 55 lb/ft3) or manmade lightweight aggregates like “Aardelite” or “Lytag” (bulk density 50 lb/ft3).

Using admixtures

This one is produced through the addition of an admixture in concrete. This creates a fine cement matrix which has air voids throughout its structure. Aerated cement mortar is produced by the introduction of a gas into cementitious slurry so that after hardening a cellular structure is formed.

Types of lightweight aggregates

Lightweight aggregates used in structural lightweight concrete are typically expanded shale, clay or slate materials that have been fired in a rotary kiln to develop a porous structure. Other products such as air cooled blast furnace slag are also used. Also there are some nonstructural lightweight aggregates with lower density made with other aggregate materials and higher air voids in the cement paste matrix. These are typically used for their insulation properties.

Natural aggregates

· Inorganic Natural Aggregates:

Diatomite, pumice, scoria and volcanic cinders are natural, porous volcanic rocks with a bulk density of 30 – 50 lb/ft3 which make a good insulating concrete

· Organic Natural Aggregates:

Wood chips and straw can be mixed with a binder to provide a lightweight natural aggregate. These are cellular materials which have air trapped within their structures once they have low moisture content.

Artificial lightweight aggregates

Artificial LWA can be manufactured by means of two types of processes: cement-base granulation and high temperature sintering. Of these the later has been widely studied and the pertinent literature is rich of applications in which many waste materials proved to have potential for use as feedstock: Bottom and fly ashes from combustors, municipal solid waste from incinerators, dusts from furnaces, mine and quarry tailings, sediments etc

· Bloated clay, sintered fly ash and foamed blast furnace slag.

· Lightweight expanded clay aggregate: This is produced by heating clay to a temperature of 1000 – 1200 oC, which causes it to expand due to the internal generation of gases that are trapped inside. The porous structure which forms is retained on cooling so that the specific gravity is much lower than what was before heating it.

Admixtures

There are two main types of admixtures for the production of lightweight concrete.

Air entraining agents

There are some foaming agents which are very powerful air entraining agents. The foam is generated using foam generator which is a very sophisticated instrument costing more than two lacks and is not available in Pakistan we have to import it. Using these foaming agents we can reduce the weight up to 50%. However the drawback of using foaming agent is that the strength is reduced drastically. The maximum strength achieved so far is less than 3700 psi even at higher density of between 100 and 110 lb/ft3. Strength development of foamed concrete depends largely on some factors which are the constituents of the base mix, the density of foam and the water cement ratio of the base mix. (Reference 1374242511-Richard342013BJAST4242)

Admixtures that evolve gases

Some admixtures like aluminum powder when added to cement slurry evolve gases and due to these evolution of gases they tends to expend the concrete. These types of admixtures are very hazardous and have unpredictable natures. The expansion of concrete occurring due to these admixtures can damage the formwork and can lead to unwanted shapes of the concrete. However these admixtures are currently successfully in use in many countries in a very control environment. Autoclaved aerated concrete is one of the most famous example of such admixtures.

METhedology

Background

As already discussed that lightweight concrete can be produced by different ways. We started working on the very first option that was using lightweight aggregates.

Since greater part of concrete consists of aggregates (course) so if the density of these aggregates is reduced the density of concrete can be reduced as well. The bulk density of fine lightweight aggregates is around 1200 kg/m3. The bulk density of coarse lightweight aggregates is around 960 kg/m3.

In the initial stages of our project our main objective was to find pumice stone. Pumice is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored.

Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano. The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases (including water and CO2) that are dissolved in the lava, causing the gases to rapidly exsolve (like the bubbles of CO2 that appear when a carbonated drink is opened). The simultaneous cooling and depressurization freezes the bubbles in the matrix. Eruptions under water are rapidly cooled and the large volume of pumice created can be a shipping hazard.

Therefore it is found in those areas which are near to some volcanic eruption zones. Fortunately in Khyber Pakhtunkhwa we could not found any such zone from which we can economically obtained pumice stone. There are some areas in Baluchistan in which large quires are available but there economy made them unfavorable to be used.

On the other hand as already discussed artificial light weight aggregates requires very huge temperature to be obtained lightweight property. Therefore it was not an option to be consider.

After not considering these options we moved towards the next options that was to use admixture to create lightweight concrete. The use of lightweight concrete is becoming very popular now a days in Pakistan and there are many construction chemical suppliers in Pakistan like Sika, Imporient, Pagel, BASF and Apepak.

First phase of the project

In the first phase of our project we were positively responded by IMPORIENT CHEMICALS (PVT) LTD. We got two types of admixtures from them.

Chemrite Aer

A ready to use highly concentrated air entraining concrete admixture. Its efficiency is based upon a very large number of minute-sized, evenly distributed air pores. It complies with ASTM C 260. It is a surface active agent having brown color and density of approximately 1.03 kg/lt. Its self-life is 12 months minimum if stored properly in the original unopened packing. Store away from sunlight. It is supplied in 200 lit. drum. The dosage provided by the supplier is 0.03-0.15% by weight of cement. Exact dosage rates are determined by trials at site. Factors affecting air contents, include: type, grading and proportion of sand, cement, aggregates, type and fineness of cement, water/cement ratio, and temperature. In certain cases therefore, it may be necessary to increase the dosage above 0.15% rate. Air meter tests should be taken consistently and adjustments made to the dosage rate to completely control the amount of air entrainment, which should be preferably in the range of 3-6%. Chemrite-Aer is added to the mixing water prior to its addition to the dry concrete mix. Chemrite- Aer can be combined with all admixtures. It is also compatible with sulfate resistant cement. Increased air contents generally have a reduction effect on strengths. This can be adequately compensated by using other admixtures. It is also nonhazardous and nontoxic. Chemrite Aer is used to produce easily workable and durable concrete for:

· Roads

· Runways and taxiways

· Concrete aprons.

· Dams and reservoirs

· Mass concrete structures

Chemrite Aer provides the following advantages:

· Improved workability

· Improved durability

· Increased cohesion reducing the risk of segregation

· Reduced water content without loss of workability

· Unaltered setting time even when overdosed

Lightcrete -02

Lightcrete -02 is a liquid admixture for concrete and mortar to produce lightweight concrete. Foam concrete, e.g. for the filling of trenchers, lightweight concrete for thermal and acoustic insulation purposes, the filling of pipes etc., may be produced with the aid of Lightcrete-02 . Lightweight concrete (LB) classified according to SIA 162 can also be produced with Lightcrete-02. Lightcrete -02 is suitable for the production of lightweight concrete for every kind of application. The liquid admixture is being added at the batching plant or directly onto the transit mixer. Its application is suitable for site mixed as well as ready mixed concrete. The key figures like density, air pore content or strengths depend on the composition of the aggregate, their partial replacement with lightweight aggregates, water content, binder content and mixing times. It is not possible to produce frost and de-icing salt resistant concrete with Lightcrete -02. It is in liquid form brown in color and with density of 1.01 kg/lit. Its self life is 12 months from date of production if stored properly in unopened and undamaged original sealed containers, at temperatures between + 5°C and + 35°C. Protected from direct sunlight and frost.

Recommended dosage (by weight of cement).

For classified lightweight concrete

0.5 - 1.0% in combination with sand and lightweight aggregates.

For lightweight (pore) concrete

0.5 - 2.0%

Lightcrete -02 is being added to the gauging water or added simultaneously together with the gauging water into the concrete mixer.

The mixing time necessary to achieve a specific density of fresh concrete depends on type of mixer used, aggregates and binder. Therefore trials to achieve certain airpore content are indicated. The results from these trials with regard to the mixing procedure should be strictly adhered to.

Lightcrete -02 may also be added to the pre-mixed concrete directly into the transit mixer at the point of discharge. An additional mixing time of at least 2 minutes per m3 concrete must be strictly observed. Before being discharged, the concrete must be tested for the intended density.

With the use of Lightcrete -02 lightweight or foam concrete may be produced.

The standard rules of good concrete production and placing must also be observed for Lightcrete - 02 concrete.

Proper curing procedures must be observed for surfaces which are to be exposed to weathering. Otherwise, premature drying out close to the surface may cause lightweight concrete to lose mechanical strengths. It is also nontoxic and nonhazardous.

Lightcrete -02 produces the necessary quantity of airpores during the mixing process. No reactive air production takes place.

The following advantages may be obtained when using Lightcrete -02:

· Safe introduction of air pores up to 35%.

· Dry density of approx. 800 up to 1’600 kg/m3 in combination with lightweight aggregates.

· Stable air content also after placing of the concrete.

· Conveyance of lightweight concrete with concrete pump possible.

· Combinations with lightweight aggregates, e.g. expanded clay are possible.

· Easy production of concrete and mortar in ready mix plants using standard dosing equipment.

· Lightcrete -02 does not contain chlorides or other components which promote steel corrosion. It may therefore be used without any restrictions in steel-lightweight concrete construction.

Working methodology

After a lot of discussion with our supervisor we came up with the methodology to check the efficiency of these admixture in both sandcrete and concrete. Therefore we made standard samples of both sandcrete and concrete and then we made samples of chemrite Aer and lightcrete -02 in both sandcrete and concrete. The experimental data and the results are provided in the coming pages.

Experimental data

Standard samples

We decided to make 2000 psi concrete block. Therefore we did mix design of 3000 psi according ACI standards. After conduction the required tests the ration obtained was 1:2.61:4.8.

After mix design 6 standard samples were casted. In which initially 6 samples were tested after 7 days curing to check whether the mix design was ok or not. Then the rest were tested after 28 days. The experimental data and the pictures of the samples are shown below:

All the first phase samples were prepared using maximum dose of admixtures and they were laid for 28 days curing and then were tested, as given below.

Experimental data of concrete samples:

Performance in Concrete:

Sample type

Unit Weight Reduced

(%age )

Strength Reduced

(%age )

Chemrite Aer

0.00

8.30

Lightcrete -02

2.86

62.1

Experimental data of sandcrete samples:

Sample type

No. Of samples

Dosage

%age

Unit Weight

pcf

Strength

psi

Standard

3

Nil

112

2773

Chemrite Aer

3

0.15

112

2250

Lightcrete -02

3

1

110

792

Performance in sandcrete:

Sample type

Unit Weight Reduced

(%age )

Strength Reduced

(%age )

Chemrite Aer

0.00

18.86

Lightcrete -02

1.78

71.44

We see that the results of the first phase are not acceptable because there is negligible reduction in unit weight and a huge reduction in strength which is totally against our objective.

In order to find the reason we contacted the supplier but they did not give any response, and an interesting thing is that there is another chemical supplier “SIKA” who claimed that these chemicals; chemrite aer and lightcrete-02, are our products and and the Imporient Chemicals (PVT) LTD are selling them as their own products which is an illegal job.

Hence the possible reason is either these chemicals were expire or the supplier’s are not true in their claim about the performance of these chemicals.

Second phase:

All the samples of second phase were prepared using the corresponding dose within the specified dose range and were cured for 28 days and then tested as given below.

Option No.01

Foaming agent concrete samples:

Sample type

Dosage

%age

Unit Weight

pcf

Strength

psi

Standard

Nil

120

2770

Foam sample

2

106

1200

Foam sample

4

71

780

Foam sample

6

71

720

Perfo