UNIVERSITY OF NAIROBI

Transcription

1 2015 UNIVERSITY OF NAIROBI STUDY ON THE FEASIBILITY OF USING SAWDUST AS PARTIAL REPLACEMENT FOR SAND IN CONCRETE Thomas Joseph Odero F16/1291/

2 ABSTRACT This experimental study considered the use of sawdust particles as substitute to fine aggregate in the production of concrete. It investigated the physical properties of sawdust as well as the workability, compressive and tensile strength properties of concrete produced by replacing 5%, 10% and 25% by volume of sand with sawdust. It also aimed to provide new knowledge on how to improve the construction industry methods by using a sawdust concrete mixture that would guarantee product performance and contribute to saving the environment. A conventional concrete mixture was prepared as a reference mix and compared to sawdust concrete mixture. Slump and compaction factor tests were carried out on the fresh concrete and compressive and tensile strength on hardened concrete. Increased sawdust proportions resulted in stiffer mixes thus reducing the workability of the concrete produced. Cubes of 100mm by 100mm were prepared and their compressive strengths at 7 and 28 days were determined. Results showed that the compressive strength decreased with higher sawdust content with replacements beyond 10% resulting in a considerable strength decrease. Similarly, cylinders of diameter 150mm by 300mm height were prepared and their tensile strength determined. As witnessed with compressive strength there was a decrease in tensile strength with an increased replacement of sand with sawdust. It was concluded that 10% substitution offered an optimum replacement level. However, the resulting concrete density was still beyond the maximum limit for lightweight concrete hence a number of recommendations on modifications to the sawdust were made to increase the amounts that can be incorporated in concrete. This would ultimately result in lower density while maintaining the required strength.

3 DEDICATION This report is dedicated to my parents who have been a constant source of inspiration, motivation and a reminder that all is possible; there are no giant steps, just lots of little steps.

4 ACKNOWLEDGEMENT My utmost gratitude goes to my supervisor Dr.Mwero for all the assistance and directions he gave me in the course of this work. I would also like to sincerely thank the lab technicians Nicholas and Martin for their help during the experimental work. I will not forget to thank the Almighty for the blessings and strength throughout this entire exercise.

5 TABLE OF CONTENTS Abstract... Dedication... Acknowledgment... CHAPTER I: INTRODUCTION... Scope. Problem Statement. Objectives.. Significance of Study CHAPTER II: LITERATURE REVIEW CONCRETE Fresh Concrete Properties.. Workability. Water to Cement Ratio... Hardened Concrete Properties.. AGGREGATES.. Functions of Aggregates in Concrete.. Classification by sizes. Fine Aggregates Functions of fine aggregates in Concrete.. SAWDUST Origin... Chemical Composition Physical Properties.. Sawdust use in Concrete. CHAPTER III: METHODOLOGY INTRODUCTION.

6 RESEARCH DESIGN.. Collection of Materials... Preliminary Sawdust sample preparations.. DETERMINATION OF PHYSICAL PROPERTIES OF SAND AND SAWDUST Grading Test.. Introduction. Apparatus. Procedure... Moisture Content Introduction. Procedure. Specific Gravity.. Introduction.. Apparatus.. Procedure.. CASTING OF CUBES AND CYLINDERS Batching by weight... Mixing of Fresh Concrete Determination of Workability of Fresh Concrete.. Slump test Scope.. Objective.. Apparatus. Procedure.. Compaction Factor Test Scope Objective. Apparatus.. Procedure. Filling of Concrete in moulds..

7 Curing TESTS ON HARDENED CONCRETE Compressive Strength Introduction.. Apparatus... Procedure.. Tensile Splitting Strength.. Introduction.. Apparatus. Procedure. CHAPTER IV: ANALYSIS AND DISCUSSION OF RESULTS GRADING Grading of Sand Grading of Sawdust. SPECIFIC GRAVITY Specific gravity of sand Specific gravity of sawdust. MOISTURE CONTENT.. Sand Moisture Content. Sawdust Moisture Content COMPACTION FACTOR RESULTS. SLUMP TEST RESULTS. HARDENED CONCRETE PROPERTIES.. Compressive Strength.. Strength Development Density of Concrete.. Tensile Splitting Strength. CHAPTER V: CONCLUSION AND RECOMMENDATIONS

8 List of Tables Table 3.1: Mix proportions of Sawdust Concrete. Table 4.1: Results of sieve analysis of sand Table 4.2: Results of sieve analysis of sawdust Table 4.3: Determination of specific gravity of sand. Table 4.4: Determination of specific gravity of sawdust.. Table 4.5: Determination of sand moisture content Table 4.6: Determination of sawdust moisture content Table 4.7: Compaction factor values of sawdust concrete Table 4.8: Slump values of sawdust concrete. Table 4.9:7 Day Compressive Strength.. Table 4.10:28 Day Compressive Strength.. Table 4.11: Strength Development in Concrete... Table 4.12: 28 Day Tensile Splitting Strength. List of Figures Figure 1.1: Different type of slumps. Figure 4.1: Particle size distribution of sand. Figure 4.2: Particle size distribution of sawdust Figure 4.3: Slump versus % Sawdust Content.. Figure 4.4: Variation of 7 days Compressive Strength with increase in sawdust content... Figure 4.5: Variation of 28 day Compressive Strength with increase in sawdust content Figure 4.6: Variation in Strength Development.. Figure 4.7: Variation in cube densities with increase in sawdust content List of Pictures Picture 1: Heap of sawdust. Picture 2: Portland cement.. Picture 3: Batch Mixer loaded with materials.. Picture 4: An example of an obtained true slump

9 Picture 5: Compacted Concrete in moulds Picture 7: An example of a cube after failure.. Picture 8: An example of cylinder after tensile failure. REFERENCES..

10 CHAPTER I: INTRODUCTION 1.1 Scope Over the last few years, Kenya has experienced a boom in its construction industry resulting in multiple infrastructure development projects across the country. This has been largely attributed to the steady economic growth and the stable political situation that has attracted both local and foreign investment. Consequently, there has been increased demand for not only suitable but cheaper construction materials. The demand is set to be further heightened as the country seeks to be a middle income economy by the year Concrete has been predominantly used as the preferred material for construction due to its various qualities especially strength that have made it suitable for numerous construction purposes. Selection of aggregates used in concrete is important as aggregate makes up approximately 60 to 75% of the total volume of concrete. Not only do they contribute to the strength exhibited by concrete but also to its bulkiness, a property that enables the concrete to be placed. There has been research carried out on aggregates leading to a better understanding of the basic mechanisms governing concrete strength, rheology, cracking etc. This has resulted in modifications of aggregates contained in concrete with an aim of either enhancing or completely changing the properties of the concrete produced hence the use of special concretes such as no fines concrete, porous concrete and light weight concrete. Various materials have been used in concrete to make it less dense especially highly porous materials. These can been classified by their origin as either natural or artificial aggregates. Examples of natural lightweight aggregates include pumice, scoria and tuff. These are derived from igneous rocks and often glassy in nature but have different network of voids with pumice exhibiting tube like voids; scoria has spherical voids whereas tuff has an irregular pore structure. Before use the materials are first crushed and sieved to obtain the right gradation. Actually use of lightweight concrete can be traced back to Ancient Rome where pumice was used to construct the Pantheon dome to reduce its weight. The building still stands today attesting to the durability of light weight

11 concrete. Artificial lightweight aggregates used include slate, shale and expanded clay. These often have similar properties hence treated as single type. Similar to natural aggregates, they are crushed and graded. They are then heated at temperatures of between C causing expansion and partial melting that forms an impervious viscous coating that prevents escape of gases generated during combustion. The material resulting is then crushed and screened. Examples of commercial artificial lightweight aggregates include leca, aglite and sintag. This experimental study focuses on using raw sawdust as partial replacement of fines contained in concrete, with an aim of coming up with acceptable concrete mixture that results in lighter concrete that can be used in building construction particularly partitions and residential class concrete slab while ensuring properties of concrete such as compressive strength, tensile strength and workability are maintained within standard limits. 1.2 Problem Statement The use of treated sawdust in concrete has been in practice in some countries in the world due to wide research they have carried out on it. However this has not been witnessed in Kenya due to the limited research leading to deficit of detailed information to form a basis for use and create awareness on the benefits derived. This study aims to generate data that can be used as reference on application of raw sawdust in concrete. 1.3 Objectives a) General Objective To evaluate the structural performance of concrete whose fine aggregates have been partly replaced by sawdust. b) Specific Objectives 1) To determine the workability of fresh concrete that contains different proportions of sawdust.

12 2) To determine the compressive strengths of cubes made resulting from partial replacement of sand with sawdust and compare them to those of cubes made from conventional concrete. 3) To determine tensile strength of cylinders resulting from partial replacement of sand with sawdust and comparing these against cylinders made using normal concrete. 4) To establish the optimum replacement level of sawdust in the specific grade of concrete 1.4 Significance of Study The most widely used fine aggregate for the making of concrete is the natural sand mined from the riverbeds. However, the availability of river sand is becoming scarce due to the excessive nonscientific methods of mining from the riverbeds hence there has a risen a need to consider substitute materials for use as filler. The use of sawdust as partial filler would reduce the quantity of sand required for building resulting in sustainability of aggregate resources. Secondly, since sawdust is lighter than sand, there would be a considerable reduction in dead weight in buildings resulting in reduced reinforcement and ultimately construction costs. Finally, the environmental impact of utilizing sawdust cannot be overlooked considering it s a waste that is widely generated and disposal is mostly done on uncontrolled waste pits and open areas..

13 CHAPTER II: LITERATURE REVIEW 2.1 CONCRETE Concrete simply can be referred to as a homogenous mixture consisting of aggregates, water and cement acting as an adhesive. This description may depict concrete manufacture to seem simple and straightforward, however it is very easy to make bad concrete that would make your design useless if actual concrete properties differ from those assumed during design calculations. Hence the question what can be defined as good concrete considering that both types of concrete have similar ingredients. The difference therefore arises from the mode of preparation. Good concrete refers to concrete that is satisfactory in its in desired properties both in its fresh and hardened state Fresh Concrete Properties Workability Concrete mix in its fresh state should be consistent in such manner that it can be compacted easily by the desired manner without excessive effort, a property broadly referred to as workability. The American Concrete Institute describes workability as that property of freshly mixed concrete or mortar that determines the ease with which it can be mixed, placed, consolidated and finished to a homogenous condition. Similarly, Japanese Association of Concrete Engineers defines workability as that property of concrete or mortar that determines the ease and homogeneity with which it can be mixed, placed and compacted due to its consistency, the homogeneity with which it can be made into concrete, and the degree with which it can resist separation of materials. Neville (1981, 203) simply defined workability as the amount of useful internal work necessary to produce full compaction. Workability is dependent on concrete properties especially the water to cement ratio. Excessively dry mixes have low workability hence difficult to compact. The need for compaction becomes apparent when we compare the degree of compaction to the resulting strength. Poorly compacted concrete results in presence of voids which greatly reduces its strength: with research showing that 5% voids can reduce strength by as much

14 as 30%.The workability of fresh concrete can be determined by a simple, inexpensive and relatively accurate test referred to as the slump test which is fully described in BS 1881:103:1993.The apparatus consists of a mould in the shape of a frustum of a cone. The mould is filled with concrete in three layers of equal volume. Each layer is compacted with 25 strokes of tamping rod. The slump cone is lifted and the change in height of the concrete is measured. Often the only type of slump permissible is the true slump where the concrete remains intact and retains a symmetric shape. A collapsed slump or shear slump is considered out of range of workability that can be determined by the workability test. Concretes with the same slump can exhibit different behavior when tapped with a tamping rod. For example few fines concrete will tend to fall apart when tapped. Such concrete is only suitable for applications such as pavements or mass concrete. This can be a useful basis in evaluating our concrete considering that this study involves partial substitution of fines. Figure 1.1 Different types of slump The slump test has several advantages. It is widely used worldwide hence can be used as a common basis of measurement of workability. It is relatively accurate hence can be applied in a site to quickly determine if a concrete is to be accepted or rejected. Finally it s simple and inexpensive to perform.

15 Cohesiveness is an aspect of workability, it affects segregation of which bleeding is a special case. This is especially important in instances of transporting before being placed. Segregation of concrete refers to the separation of the constituents of the heterogeneous mixture so that their distribution is no longer uniform. This often results due to differences in size of particles and their specific gravities of the mix constituents. There are two types of segregation exhibited in concrete. One involves separation of coarse aggregates as they tend to settle more than the finer aggregates. The second form of segregation is manifested by separation of the grout which is the cement plus water from the mix. This property is specifically essential in this study considering that the sawdust is relatively light compared to the other concrete constituents. However the actual extent of segregation depends on the handling and placing of the concrete. If the concrete does not have to travel far and is transferred directly to the final position, risk of segregation is reduced. The method of compaction would also influence degree of segregation. Even though vibration provides the most valuable means of compacting concrete, improper use of the vibrator increases the danger of segregation Water to Cement ratio Water is required for various functions in a concrete mix. Primarily, it is needed for cement hydration, which consists of series of processes that are responsible for development of strength in concrete. It is also required for workability of the concrete, a feature referred to in detail in section of this report. When concrete is fully compacted, its strength can be taken to be inversely proportional to the water cement ratio. This implies that for fully compacted concrete made with sound and clean aggregates, strength can improved by reducing the weight of water used per unit weight of cement. This would imply that use of minimal amount of water would result in a stronger concrete. However this is not entirely true as this would render the concrete not workable making compaction difficult. Lack of proper compaction results in voids in concrete and consequently reduced strength. On the other hand excess water causes development of capillary voids in concrete causing porosity and permeability hence reduced strength. From the above it can be deduced that just the right balance of water to cement ratio needs to be determined to obtain a strong but also workable concrete mix.

16 Water contained in concrete consists of that added to the mix and that originally held by the aggregates at the time when they were introduced into the mixers. The latter water may be absorbed within the pore structure of the aggregate whereas some exists as free water on the surface of the aggregate hence not different from the water added direct into the mixer. When the aggregate is not saturated and some of its pores are therefore airfilled, a part of the water added to the mix will be absorbed by the aggregate. Aggregates are often assumed to be saturated with surface dry conditions when used in concrete. This implies that the effective water in the concrete mix is the water in excess of that contained in the pores of the aggregate. For this reason, the mix proportioning data are based usually on the water in excess of that absorbed by the aggregate that is the free water. It is therefore necessary that in translating laboratory results into mix proportions to be used on a site, care be taken to specify if water cement ratio referred to is total or free water Hardened Concrete Properties The primary requirement of concrete in its hardened state is satisfactory compressive strength and durability. The strength of concrete is often considered its most important property and is used as a basis to determine the quality of concrete. This is vital since it s the element ultimately considered in structural design. Test for compressive strength is done by crushing cast concrete cubes made according to specifications contained in BS 1881:108:1983.The 28 th day strength is always taken as a depiction of the concrete strength, although the 7 th day strength can be determined to check development in strength. The strength of concrete is greatly influenced by two factors namely the water/cement ratio and the degree of compaction. Although there are other factors that may have influence such as porosity of the concrete, the above two are considered critical especially when referring to strength of concrete at a certain age that has been cured in water at a certain temperature. These have been broadly looked at below as the would have a significant impact on the concrete strength in the study..

17 2.2 AGGREGATES Aggregates accounts to up to 75% of concrete by volume thus have a significant effect in its properties and performance. Cement without aggregates can only be applied to a few special purposes, a majority of concrete applications are only possible due to the presence of aggregates. Modern construction has seen the use of aggregates of various types with the evolution of technology. This has led to development of highly complex mixtures which may consist of several binders, admixtures and aggregates of different types and sizes. In short, the use of aggregates has become a little more than simply being a bulk constituent for mass and economy Functions in Aggregates in Concrete Aggregates have a number of functions in concrete: They contribute to concrete strength through mechanical interlock between aggregate particles hence making the concrete stiff and rigid, a property necessary for its engineering uses. Reduce moisture related deformations in concrete such as shrinkage hence providing volumetric stability to the concrete. They provide durability to the concrete as they are generally more stable of all the constituents in concrete. Provide bulk of concrete allowing it to be placed. Impart wear resistance to concrete making it suitable for use on pavements and hydraulic structures. They restrain creep and thus aid in limiting long term deformations Classification of Aggregates Classification of aggregates can be based on size, specific gravity or source of the aggregates Classification by sizes Classification by sizes groups aggregates into two groups namely: Fine aggregates have particle size less than 4.75mm and are retained on 75µm sieve.

18 Coarse aggregate have particle size more than 4.75mm Fine Aggregates Fine aggregates consist of particles between the sizes stated above. Sand is the most common fine aggregate used in concrete. It consists small angular or rounded grains of silica. Grading of fine aggregates has a great influence on the workability of a concrete mix. This is because it influences the total aggregate area to be wetted and the relative aggregate volume in the mix.inorder to ensure proper workability, one should conform to standard grading which ensures that the voids one particle are filled by particles of the next smaller size. Apart from workability, finer fractions of fine aggregates with sizes minus 150µm have a great influence on the segregation and bleeding of the concrete. This is because they are light and are easily separated from other concrete constituents. Functions of fine aggregates in concrete Fine aggregates perform the following functions in concrete: a) Act as filler and fill the voids between the coarse aggregates. They are smaller hence are able to occupy the small voids between the larger coarse aggregates. b) Reduce porosity of concrete. Porosity in concrete results due to presence of voids which can adequately be filled by well graded fine aggregates as smaller particles are able to occupy the very tiny voids. 2.3 SAWDUST Origin Sawdust refers to fine particles of wood resulting from cutting, grinding or drilling of timber. It may also result from the burrowing on wood by small animals like ants. Sawdust has been applied to various uses due to its varied properties Chemical Composition The chemical composition of sawdust is complex often similar to the wood from which they are derived. Wood tissue is made of chemical components which are distributed non uniformly as a result of the anatomical structure. As a result, the chemical behavior of

19 wood cannot be determined in detail from the properties of the component substances. The principal components of wood include Carbon, Hydrogen, Oxygen (O) and small amounts of Nitrogen. The chemical analysis of a number of species of softwoods and hardwoods shows that proportion of these elements in percentage of oven dry weight of wood are approximately: Carbon 49-50%,Hydrogen 6%,Oxygen 44-45% and Nitrogen 0.1-1%. Carbon, hydrogen and oxygen combine to form the principal organic components of wood substances namely cellulose, hemicellulose, lignin and small amounts of pectin substances. The terms cellulose and hemicellulose are generic, and each include a number of chemically related compounds. Separation and quantitative analysis of each in the laboratory has shown that the proportions in percentage of oven dry weight of wood are approximately: Cellulose :40-45%, about the same for both hardwoods and softwoods Hemicellulose: 20% in softwoods,15-35% in hardwoods Lignin :25-35% in softwoods,17-25% in hardwoods Physical properties 1. Flammable Sawdust is flammable especially when dry hence has been used as a ready source of fuel by manufacturing charcoal briquettes which are then burnt to produce energy. 2. Hygroscopic Sawdust is hygroscopic, it has a tendency to absorb moisture when in contact with liquid water or water vapour.due to this property, it has been used to absorb spills Sawdust Use in Concrete In the construction industry, sawdust has been used to develop sawdust concrete which consists of Portland cement, sand, sawdust and water to give a slump of between 25-50mm.This kinds of concrete has been found to bond well with ordinary concrete. The sawdust used often requires treatment. Chemical treatment is necessary to prevent rotting since it s organic. Secondly it serves to make the sawdust neutral to prevent reactions that

20 would adversely affect the concrete during hydration and setting. This has often been achieved by making sure the sawdust is clean without a large amount of bark. Finally it would lower moisture movement in the sawdust as it has a tendency to absorb water. Best results are obtained when sawdust of between mm in size. However due to the variable nature of different kind of sawdust, use of a trial mix is recommended. This kind of concrete can achieve density ranging from 650 to 1600 kg/m3.sawdust concrete resulting from use of sawdust from tropical hardwoods have recorded compressive strengths of 30N/mm 2, splitting strength of 2.5N/mm2 with a density of 1490kg/m3.Recent studies have shown successful use of sawdust as a brick material However due to the limited research on it, there has been no standard and codes developed to guide use.

21 CHAPTER 3: METHODOLOGY 3.1 INTRODUCTION The main objective of the project is to utilize sawdust as a partial substitute of sand in the production of concrete in order to draw a conclusion if use of sawdust in concrete was acceptable by carrying out tests on the concrete produced and comparing this against normal concrete. Three types of aggregates are used in this project. These included; Natural coarse aggregates- ballast of maximum size 10mm, Natural fine aggregates- river sand and Research fine aggregate-sawdust. Concrete cubes and cylinders were cast for 5%, 10% and 25% replacement of sand by sawdust on basis of volume and subsequently tested for 7 and 28 days for determination of both compressive and tensile strength. 3.2 RESEARCH DESIGN Experimental study design was employed with the main research method which involved laboratory testing. This involved preparing samples of concrete mixes containing varying amounts of sawdust and then carrying out appropriate tests to determine the optimum sand replacement amount. Prior to this, physical properties of both sawdust and sand were determined by laboratory tests. The highlights of the methodology were as below: Collection of materials. In this research, the following materials were used 1. Sawdust The sawdust samples required were obtained from the timber laboratory from a heap of wood shavings and sawdust which were considered as waste. It was established that the sawdust available was a mixture from different types of wood with the most common being Blue gum and Grevillea.Both of these are available in Kenya hence could be acquired locally.

22 2. Cement Picture 1: Heap of Sawdust Bamburi Nguvu cements CEM 1V/B 32.5N. 3. Fine Aggregates Locally available sand. Picture 2: Portland cement

23 4. Coarse Aggregates This consisted of ballast maximum size 10mm. 5. Water Tap water was used Preliminary sawdust sample preparations Air Drying The sawdust samples were air dried by spreading the material on suitable size tray. There was occasional stirring to ensure uniform drying Rifling Thorough mixing of the samples was achieved by use of a rifler.this was done to achieve a homogenous mixture Determination of physical properties of sand and sawdust Grading Test Introduction The grading of the sand and sawdust were determined by sieve analysis. A sample of both materials of known weight was passed through a series of sieves with progressively smaller openings. Apparatus required 1. Balance accurate to 0.5g of mass of test sample 2. Test sieves as per BS Oven Procedure The test samples were dried to a constant mass by oven drying at about 1050C.An approximate sample was taken from the original and the required sample was weighed out. The sieves were then arranged one over the other in relation to their size of opening 10mm,5mm,2.36mm,1.18mm,0.6,0.3,0.150,0.075,< The sieves were shaken horizontally with a jerking motion in all directions for at least 2 minutes and until all material passing fell into the tray. Any material retained on each sieve was weighed and the results tabulated. The cumulative weight passing each sieve was calculated as a

24 percentage of the total sample. Finally, grading curve for the sample was plotted in the logarithmic chart Moisture Content Introduction Moisture content represents the water in excess of saturated surface dry state. Procedure The weight of surface dried fines were determined each recorded as (W1).They were then placed in an oven at 105 C 24 hours. After removal from the oven, their weight determined and recorded as ( W2).The moisture content is determined as a percentage by (W1 W2)/W Specific Gravity Introduction Specific gravity is a measure of material density relative to that of water. It shows how many times the material is denser than water. Apparatus 1.100ml volumetric flask with a stopper. 2. A balance to weigh accurately to 0.5g 3. Distilled water Procedure The fines aggregates were passed through sieve number 7.The weight of the empty volumetric flask fitted with a stopper was measured (W1).A sample of the fines (15g) was placed in the volumetric flask and the weight measured (W2).The volumetric flask was then filled with water, stopper fitted and weight determined (W3).Finally, the weight of the volumetric flask completely filled with water only and fitted with a stopper was determined (W4). The specific gravity was then given by: Gs = (W2 - W1) (W4 W1) (W3-W2)

25 3.2.4 Casting of Cubes and Cylinders Batching by Weight Batching of the concrete was done by weighing the constituents and introducing them into a mixer. A standard ratio of 1: 1.5: 3 was adopted which represented the ratio of Cement: Fine Aggregates: Coarse aggregates. Water: Cement ratio of 0.64 was used. The materials were measured in individual batches within the following percentages of accuracy: cement 1%, aggregates 2%, water 1%. The batch calculations were as shown below: Control Concrete Mix Proportions Cement: Fine Aggregates: Coarse Aggregates 1 : 1.5 : 3 1. Cubes Volume of each cube = Length Width Height = = m 3 Number of cubes = 4 Volume of concrete used = 4 ( ) = m 3 2. Cylinders Volume of each cylinder = Πr 2 h =Π = m 3 Number of cylinders = 2 Volume of concrete used = ( ) 2 = m 3 Total volume used for cubes and cylinders = ( ) + ( ) = m 3

26 Density of concrete = 2400kg/m 3 Total mass of the concrete = Density Volume = 2400 ( ) = 35.1kg Accounting for 10% wastage = = 38.5 kg 100 Mix % of Cement Sand (kg) Sand Ballast Water Replacement (kg ) Replaced(kg) (kg) (litres) 1 0% % % % Table 3.1: Mix proportion for sawdust concrete Mixing of the fresh concrete The concrete was mixed using the concrete batch mixer. The following process was followed: The mixer was loaded with the material quantities shown in the table for each mix, beginning with the coarse aggregates at the bottom, followed by a layer of sand and finally a layer of cement. In the case of the 2 nd, 3rd and 4 th mixes, a proportion of sawdust equal to the volume occupied by the quantity of sand to be replaced was added uniformly over the sand layer before adding cement. This was done by filling a container of known weight with the quantity of sand to be replaced.the marking the level of the sand in the container. The same container was then filled with sawdust to the level marked prior to determine the amount of sawdust to be used as replacement. The mixer was then closed and contents blended for 5 minutes to form a homogenous dry mix. Water was added and distributed evenly over the mix as the mixer rotated until the concrete was well mixed. The concrete workability was determined before casting in moulds.

27 Picture 3: Batch mixer loaded with materials Determination of workability of fresh concrete Slump Test Scope The slump is a measure of workability of concrete. Workability refers to the ease to the ease of mixing, placing and compacting concrete. It is greatly influenced by the water: cement ratio in the concrete which also has an influence on the strength of the concrete obtained. A detailed description of the test can be found in Chapter 2 of this report. Objective To determine the workability of the concrete mixes. Apparatus 1. Tamping rod 2. A Steel Frustum 3. Trowel Procedure The frustum was held in position on a flat surface and its interior dampened. It was then filled with fresh concrete in three layers, each layer approximately one third of the volume of the frustum. Each layer received 25 strokes of the tamping rod uniformly

28 distributed over the concrete surface. After tamping the top layer the excess concrete was stricken off using the tamping rod. The mould was then carefully raised in a vertical position. The slump was then determined by measuring the difference between the height of the frustum and the height of the collapsed concrete. Picture 4: An example of an obtained true slump Compaction Factor Test Scope The compaction factor tests measures the degree of compaction resulting from application of a standard amount of work. Objective To establish the amount of work necessary to achieve full compaction of the concrete mixes. Apparatus 1. A frame consisting of two conical hoppers vertically aligned above each other and mounted over a cylinder. 2. Trowel 3. Vibration table

29 4. Weighing balance Procedure The inner surface of the hoppers and the cylinders were oiled to prevent sticking of the concrete.the empty cylinder was weighed and the flaps at the bottom of the hoppers fastened. The cylinder was then fixed at the bottom of the frame in such manner that it was aligned with the hoppers. The top hopper was filled with concrete to the brim. The flap at the bottom was then opened to allow the concrete drop to the bottom hopper. Once all the concrete had fallen from the top hopper, the flap to the lower hopper was opened to allow the concrete fall into the cylinder. The excess concrete was struck off the top of the cylinder and mass of concrete contained in the cylinder determined on the weighing balance. The cylinder with the concrete was then moved to the vibrating table where it was vibrated and more concrete added till the cylinder was completely filled. The cylinder was weighed to determine the mass of fully compacted concrete. The compaction factor was determined from the formula below: Compaction factor = (Weight of partially compacted concrete) (Weight of fully compacted concrete) Filling of concrete in moulds The moulds were cleaned and oiled to enable easily removal of the hardened concrete cubes and cylinders once they had set. The concrete was filled in the moulds in layers and placed on the vibrating table for proper compaction.

30 Picture 5: Compacted concrete in moulds Curing The cubes and cylinders were left in the open for 24 hours before being moved to a curing tank where they underwent wet curing. Picture 6: Curing tank

31 3.2.9 Tests on hardened concrete Compressive strength Introduction The test on compressive strength was done according to BS 1881: Part 116: 1983.It is a measure of the concrete s ability to resist loads. Megapascals. The 28 th day strength is taken as the characteristic strength of the concrete. However concrete compressive strength can be determined at 7 or 14 days to check development in strength. Apparatus 1. Compression testing machine 2. Weighing balance Procedure The cubes were removed from the curing tank and allowed to drain before being weighed and their masses recorded. The cubes dimensions were determined to check any distortion in shape. Each cube was then centrally aligned on the base of the compression testing machine. They were then loaded gradually while turning the fine straining knob to prevent sudden failure. Upon failure, the load applied was determined from the appropriate scale and recorded. Compressive tests on the cubes were carried out on the 7 th and 28 th day from the date of casting. Picture 7: An example of cube after failure

32 Tensile Splitting Strength Introduction Tensile splitting strength test is used to determine concrete tensile strength. Apparatus 1. Compression testing machine 2. Weighing balance 3. Two strips of wood 300mm long Procedure The cylinders were removed from curing tank and allowed the water on their surface wiped. They were then weighed and their weights recorded. One strip of wood was placed on the base plate of the compression test machine and the specimen laid over it ensuring that the wood was centrally placed. The second strip of wood was placed over the cylinder while ensuring that it was aligned to the one at the bottom. The upper plate of the testing machine was lowered till the top wood strip was held in position. The cylinder was then loaded gradually until failure. The failure load was noted. Picture 8: An example of a cylinder after tensile failure

33 CHAPTER IV: ANALYSIS AND DISCUSSION OF RESULTS 4.0 RESULTS, ANALYSIS AND DISCUSSION The data collected was analyzed and the processed data presented in this chapter as follows: 4.1 GRADING Grading of sand. Pan mass= 100.0g Fines mass = 3.3g Initial Dry Sample mass + Pan = 300.0g Fines = 1.65% Initial Dry Sample mass = g Reference = BS 882 :1992 Sieve Mass Retained % Retained Cumulative % Cumulative % (mm) (g) Retained Passing Table 4.1: Results of sieve analysis of sand Total cumulative % retained = g Fineness modulus = = 2.34

34 Cumulative % Passing Sample Lower limits Upper limits Sieve sizes in mm Figure 4.1: Particle size distribution for sand

35 4.1.2 Grading of sawdust Pan mass= 100g Fines mass =1.3g Initial Dry Sample mass + Pan = 265.5g Fines % = 0.8% Initial Dry Sample mass =165.5g Reference = BS 882 :1992 Sieve Mass % Cumulative % Cumulative % Passing (mm) Retained (g) Retained Retained Table 4.2: Results of sieve analysis of sawdust Total cumulative % Retained = 211.1g Fineness modulus = = 2.11

36 Cumulative % Passing upper limit Sawdust Lower limits Sieve sizes in mm Figure 4.2: Particle size distribution for sawdust The results of the sieve analysis of the sand and sawdust are presented in figure 1 and 2 respectively. The curves for both sand and fell within the overall limits as provided for in BS The fineness modulus of sand was determined to be 2.34 and that for sawdust to be 2.11 thus the sand was coarser than the sawdust. The sawdust was very fine hence would increase the water demand in the concrete produced and subsequently the water-cement ratio.

37 4.2 SPECIFIC GRAVITY Specific gravity of sand Mass in grams Mass of sand 15 Mass of empty volumetric flask ( W1 ) Mass of volumetric flask + Sand ( W2 ) Mass of volumetric flask filled with water+ Sand (W3 ) Mass of volumetric flask filled completely with water (W4) Table 4.3: Determination of the specific gravity of sand Gs = W2 W1 (W4-W1) (W3 W2) = ( ) ( ) = = Specific gravity of sawdust Mass in grams Mass of sawdust 15 Mass of empty volumetric flask ( W1 ) Mass of volumetric flask + Sawdust ( W2 ) Mass of volumetric flask filled with water+ Sand (W3 ) Mass of volumetric flask filled completely with water (W4) Table 4.4: Determination of the specific gravity of sawdust

38 Gs = W2 W1 (W4-W1) (W3 W2 = ( ) ( ) = = The results showed a specific gravity of for sand whereas that for sawdust was determined to be This showed that sand was nearly twice as dense as a sawdust hence the sawdust concrete obtained would be expected to be less dense compared to the conventional concrete. 4.3 MOISTURE CONTENT Sand moisture content Sample 1 Sample 2 Weight of tin + sand (W1) Weight of tin + oven dried sand (W2) Moisture content ( % of dry mass) 5.40% 4.88% Table 4.5: Determination of the sand moisture content Average moisture content = = 5.14% Adjustment to the Water-Cement ratio = Quantity of sand Moisture content = /100 = 0.54kg

39 Amount of water present in the sand = 0.54 litres Sawdust moisture content Sample 1 Sample 2 Weight of tin + sawdust (W1) Weight of tin + oven dry sawdust ( W2) Moisture content ( % of dry mass) 1.17% 1.23% Table 4.6: Determination of the sawdust moisture content Average moisture content = = 1.20% The average moisture content of the sand was significantly high at 5.14% compared to that of sawdust at 1.20%.This necessitated the adjustment of the water-cement ratio used to prevent use of excess water that would result in a decline of the concrete strength. 4.4 COMPACTION FACTOR TEST % of Mass of partially Mass of fully compacted CF= W2/W3 sawdust Compacted concrete concrete (kg) W3 (kg) W Table 4.7: Compaction factor values of sawdust concrete

40 4.5 SLUMP TEST % of Sawdust Content Slump, mm Table 4.8: Slump values of sawdust concrete 40 Slump versus % Sawdust Content 35 Slump mm % Sawdust Content Figure 4.3: Slump versus % Sawdust content The results of the slump and compaction factor, indicating the workability of the sawdust concrete are shown on table 4.7 and table 4.8 above. The values indicated a decrease in slump with increase in sawdust content.

41 Similarly, there was a decrease in compaction factor with increase in sawdust content hence workability of the concrete was observed to be decreasing as the percentage of sawdust replacement of sand increased. This implied that more effort would be required to place, compact and finish the freshly mixed concrete. The decrease in workability could be attributed to the high water absorption of the sawdust hence as the sawdust content increased, more water was absorbed resulting in a stiffer mix. It could also be attributed to the increase in surface area as the sawdust particles were finer than the sand particles hence required more water for surface lubrication of the particles resulting in less water for the cement paste. Sawdust Content 4.6 HARDENED CONCRETE PROPERTIES Compressive Strength Age (Days) Cube Label Cube dimension mm Length Width Height Volume Weight 10-3 m 3 (kg) Density ( kgm 3 ) Strength N/mm 2 Average Density 0% 7 S S Average Strength 5% 7 S S % 7 S S % 7 S S Table 4.9: 7 day Compressive Strength Figure 4.4 shows the various 7 day compressive strengths. Generally the results showed a decrease in compressive strength with increase in the fraction of sawdust. Values of 17.5N/mm 2, 17.75N/mm N /mm 2 and 12.0 N/mm 2 were obtained for compressive strengths with 0%, 5%, 10% and 25% sawdust as partial replacement. The compressive strength at 5% replacement was slightly higher than that for the control concrete. This could be attributed to the concrete obtained being denser than the reference concrete as it had an average density of Kg/m 3 compared to Kg/m 3.

42 Compressive Strength (N/mm2) The increase in density could have resulted from the sawdust particles which were finer than the sand particles hence were able to fill the tiny voids within the concrete mix % of Sawdust Figure 4.4: Variation of 7 day compressive strength with increase in sawdust content Sawdust Age Cube Cube dimension mm Volume Weight Density Strength Average Average Content (Days) Label Length Width Height (kg) ( kgm 3 ) N/mm 2 Density Strength 0% 28 S S % 28 S S % 28 S S % 28 S S Table 4.10: 28 day Compressive Strength

43 Compressive Strength (N/mm2) The figure 4.5 below shows the variation of concrete compressive strength of the various concrete mixes after 28days of curing. It can be seen that there is an increase in compressive strength for all the classes of concrete except in the concrete mix with 25% replacement of sawdust. Values ranging from 26.75N/mm 2 for control, to 23.5N/mm 2,18.0N/mm 2 and 10.5N/mm 2 were recorded for cubes with 5%, 10% and 25% sawdust replacement respectively. At this age the control concrete had the highest strength. The increase in 28 day concrete strength from the 7 day strength could be attributed to the fact that strength development in concrete is a function of the cement hydration process which is a slow. Thus as the hydration reaction proceeded with time, concrete developed more strength. This can be clearly seen in the case of the control mix and the 5%, 10% sawdust replacement mixes % Sawdust Content Figure 4.5: Variation of 28 day compressive strength with increase in sawdust content However, the overall reduction in strength in all the concrete classes as the sawdust content increased could be attributed to a number of reasons. One of this was the high voids content in the concrete mixes resulting from the low workability as the content of sawdust increased.

44 The low workability made it difficult to achieve proper compaction of the concrete during molding. Secondly, sawdust is hygroscopic hence as it absorbed water it experienced volumetric changes resulting in internal stresses within the concrete mix. This could have resulted in poor bonding between the sawdust particles and the cement paste. Nonetheless, the concrete mixes with 5% and 10% sawdust replacement of sand exhibited 28 day strength in excess of 17N/mm2 which is the minimum strength required for lightweight aggregate concrete Strength Development % Sawdust Content 7 day compressive strength 28 day compressive strength % Ratio of 7 day strength to 28 day strength % % % Table 4.11: Strength Development in concrete From figure 4.6, it can be seen that the trend of strength development was varied between the different concrete classes. The control concrete had achieved 65.42% of its 28 day compressive strength by the 7 th day of curing. The concrete mixes with 5% and 10% sawdust content showed considerable early development of strength attaining 75.53% and 90.27% respectively of their 28 day compressive strength. However, in the case of the concrete with 25% replacement the 28day strength was less than the 7 day strength. From this, it can be observed that the presence of sawdust in concrete affected the rate of strength development. Considering that concrete strength development is a function of hydration of the cement, the sawdust must have been impeding this reaction. From chapter 2, the chemical composition of sawdust was found to include organic components such as cellulose, hemicellulose, lignin and small amounts of pectic substances.

45 Strength ratio in % When the sawdust absorbs water, these components decompose with time into the cement hence hindering continuous hydration and consequently impeding strength development. This is well exhibited in the sawdust concrete with a 25% partial replacement as the sawdust amounts were considerable to effectively hinder cement hydration day strength 28 day strength % Sawdust Content Figure 4.6: Variation in strength development Density of Concrete The figure 4.6 shows the variation of density of the concrete cubes after 28 days of curing. The results showed that there was a decrease in concrete density with increase in sawdust proportion with values ranging from kg/m 3 for the control to kg/m 3, kg/m kg/m 3 for 5%,10% and 25% respectively. This could be attributed to the low density of sawdust compared to sand and the hygroscopic nature of sawdust. However, all the densities exceeded the 1850kg/m 3 which is the maximum density required for lightweight aggregate concrete.

46 Dry Density (kg/m3) % Sawdust Content Figure 4.7: Variation in cube densities with increase in sawdust content Tensile Splitting Strength % sawdust content Cylinder label Weight of cylinder Load applied Tensile Strength(N/mm 2 ) Average tensile strength(n/mm 2 ) (Kg) (KN) 0 S S S S S S S S Table 4.12: 28 day Tensile Splitting strength