This research work was carried out to investigate the effects and suitability of Cassava starch as an admixture in cement paste and concrete. A standard consistency test was carried out on the cement paste with concentrations of the cassava starch at 0%, 0.5%, 1%, 2%, 3%, 4% and 5% by weight of the cement used in the paste. A prescribed concrete mix ratio of 1:2:4 concrete cubes (150mm by 150mm) and water-cement ratio of 0.5 were cast with the same concentrations as above. A total of eighty four (84) cubes were cast and cured for 3, 7, 14 and 28 days and compressive strength subsequently determined in comparison with the relevant specifications. Consistency test on the cement paste at the various concentrations exhibited an increase in the setting time as the concentration increases with the highest value recorded at 5% cassava starch concentration as 219 minutes for the initial setting time and 275 minutes for the final setting time as against the control specimen of 159 minutes and 234 minutes for both initial and final setting times respectively. The 28 days compressive strength of the concrete cubes; compared with that of the control; showed a slight increase in both strength values and strength gain at 0.5% and 1% starch concentrations with compressive strength of 21.24N/mm2 and 21.63N/mm2 and strength gain of 4% and 6% respectively. Also, the rate of strength development within the same concentration in terms of test ages was also realized to be higher at starch concentrations of 0.5%, 1% and 2% with the highest recorded as15% at 1% from 7 to 14 days.
TABLE OF CONTENTS
Title Page i
Table of Contents vii
List of Figures xi
List of Tables xii
List of Plates xiii
List of Appendices xiv
Abbreviations and Symbols xvi
CHAPTER ONE: INTRODUCTION
1.1 General 1
1.2 Statement of Research problem 3
1.3 Justification for Research 3
1.4 Aim and Objectives 3
1.5 Scope and Limitation of Research 4
1.5.1 Scope of Research 4
1.5.2 Limitations of Research 5
CHAPTER TWO: LITERATURE REVIEW.
2.1 Introduction 6
2.2 Historical Background and Review on the use of Admixtures 6
2.3 Concrete 10
2.3.1 Setting times (Initial and Final) 11
2.3.2 Heat of hydration 12
2.3.3 Workability 13
220.127.116.11 Slump test 14
18.104.22.168 Compaction factor test 14
2.3.4 Compressive strength 15
2.3.5 Flexural Strength 15
2.4 Admixtures 16
2.4.1 Water reducers 17
2.4.2 High range water reducers 18
2.4.3 Air entraining 18
2.4.4 Retarders 19
2.4.5 Accelerators 19
2.4.6 Pozzolanic and Mineral admixtures 20
2.4.7 Retarding plasticizers and Accelerating plasticizers 20
2.5 Cassava 21
2.6 Properties of Starch 24
2.6.1 Rheological properties of starch 25
2.6.2 Cassava Starch 26
CHAPTER THREE: MATERIALS AND METHODS
3.1 Preamble 28
3.2 Materials 28
3.2.1 Cement 30
3.2.2 Aggregates 32
3.2.3 Cassava starch 34
3.3 Specimen Preparation and Testing 34
3.3.1 Cement paste (Consistency test) 35
3.3.2 Concrete 35
3.4 Batching and Mixing of Concrete Materials 35
3.5 Workability Test 37
3.5.1 Slump test 37
3.5.2 Compaction factor test 38
3.6 Compressive Strength Test 39
CHAPTER FOUR: RESULTS AND DISCUSSIONS
4.1 Preamble 41
4.2 Cement 41
4.2.1 X- ray fluorescence test on cement 41
4.2.2 Soundness 42
4.3 Fine Aggregates 43
4.3.1 Particle size distribution 43
4.3.2 Fines content of fine aggregates 44
4.3.3 Finess modulus of the fine aggregates 44
4.3.4 Properties of the fine aggregates 45
4.4 Coarse Aggregates 46
4.4.1Particle size distribution 46
4.4.2 Geometrical properties on coarse aggregates 47
4.5 Cassava Starch 48
4.5.1 X- ray diffraction test 48
4.6 Consistency Test 49
4.7 Workability Test 52
4.7.1 Slump test 52
4.7.2 Compaction factor test 53
4.8 Compressive Strength 54
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.2 Recommendations 60
In most developed and developing countries concrete and mortar have been major construction/building and civil engineering materials alongside steel and wood. The use of concrete in the building industries cannot be overemphasized. Therefore, ways of improving or modifying some of its properties such as strength, setting characteristics and durability; in order to effectively maximize its use and most likely reduce the cost of construction; are constantly been developed. The use of admixtures in concrete works are some of the ways of improving the qualities of concrete (Mamlouk and Zaniewski, 2006).
Concrete as a construction material encompasses hydraulic cement, aggregate and water, each with its individual or unique properties but all acting together to form a composite structure. However, it is important to note that by improving or modifying some of the properties of the individual constituents of the concrete; it could provide a means of producing a new composite material with enhanced characteristics that complies with the demands of Engineers and Architects.
For several decades, admixtures have been widely used in concrete and mortar, providing advanced specific properties needed during construction. By definition, Admixtures are materials other than hydraulic cement, aggregates, water and fiber reinforcements used as an ingredient in a cementitious mixture to modify its properties, setting or hardening properties, and it is added to the batch before or during its mixing (Suchorski et al., 2003).
Admixtures usually classified according to their intended use as Water Reducing, Set-controlling, Corrosion inhibiting; etc are some of the classes specified by the British standard; BS 8500 -1:2002, BS-EN 934 -2: 2001 etc. (Adamu, 2001). Materials used as admixtures could range from purpose designed chemicals or materials (either in solid or liquid form) to waste materials for which an outlet is sought (Afolayan, 1997). It is important to note that majority of admixtures for concrete are used primarily on the basis of experience or ad-hoc test (Neville, 1997). Therefore, the performance of admixtures is determined by using a control concrete mixture (one without the admixture).
Cassava (a chief source of starch) is grown in many tropical countries including Nigeria as one of her important commercial crops. Cassava is an attractive crop for industrial uses because of its low cost of production and for many industrial applications less cassava starch is required than maize starch to achieve a particular function (Ferris et al.,2005). Starch from cassava processing is a highly versatile, renewable natural resource which can be used in virtually all industrial sectors. In its natural state, starch is used as a binder, stabilizer, surfactant, texturizer and bulk agent (Ferris et al., 2005). In this research, starch extracted from cassava is investigated to determine its effects as an admixture in cement paste and concrete.
1.2 STATEMENT OF RESEARCH PROBLEM
A major challenge faced by concrete users is its limited performance in unpredictable circumstances, such as changing climatic and jobsite conditions for instance, hot or cold weather concreting, underwater concreting, concreting in corrosive environments (acidic or
alkaline), delays in placing fresh concrete etc. Most of the conventional materials used as admixtures are too expensive and usually not readily available. Therefore, the use of locally available and renewable materials with unique properties, (say Cassava starch) is investigated to determine its suitability as concrete admixtures.
1.3 JUSTIFICATION OF RESEARCH
Cassava products like starch are multifaceted products finding many industrial applications and the increasing uses of this renewable resource is ecologically and economically of great interest since they are being and have been used in other technical areas such as textiles, paper production, adhesives etc. Generally, carbohydrates have been documented as excellent admixtures.
Nigeria as a nation is one of the major producers of cassava, a chief source of starch in the world, therefore seizing this advantage and harnessing the possible desirable contributions starch can offer to the concrete industry as an admixture may be a step forward.
1.4 AIM AND OBJECTIVES
The aim of this research is to determine the suitability of cassava starch as an admixture in concrete and cement paste mortar.
The objectives of this research work are:
a. Determination of some engineering properties of the constituent materials.
b. Starch characterization using X-Ray Diffraction (XRD) test.
c. Determination of the consistency and setting time (initial and final) of cement paste mixes with starch as an admixture.
d. Determination of the workability of concrete with various admixture (starch) concentrations at different concrete ages.
e. Determination of the compressive strength of concrete at various starch percentage concentrations.
f. Relating the results obtained in 3, 4 and 5 above with standard specifications according to ASTM C494 and/or BS 5075: Part 1: 1982 for admixtures.
1.5 SCOPE AND LIMITATION OF RESEARCH
1.5.1 Scope of Research
The scope of this research work is restricted to the use of cassava starch content of 0%, 0.5%, 1%, 2%, 3%, 4% and 5% of the cement weight. Effects of these starch concentrations are being considered on the consistency of the cement paste and on the workability of fresh concrete mixes. The workability will be based on results from the slump test and compaction factor test. Concrete cubes (150mm by 150mm) are cast with the same concentration as stated above.
1.5.2 Limitations of Research
The curing and compressive strength determination is limited to 3, 7, 14 and 28 days. Starch percentage concentration is limited to 5% based on section 5.2.6 of BS EN 206-1: 2000 on the use of admixtures in concrete.