THE EFFECT OF VARYING RANGE OF SOIL GRAIN SIZES ON CASSAVA STARCH STABILIZED COMPRESSED EARTH

ABSTRACT

This study evaluated the strength and durability characteristics of cassava starch stabilized compressed earth bricks at 3 different grain size ranges. Laterite obtained locally from Zaria was sieved into 3 constituent grain sizes ranges of ≤ 2.36mm, ≤ 1.18mm and ≤ 600µm. Earth bricks of size 140mm × 140mm × 80mm were produced with earth brick production machine through the application of a pressure of 4N/mm². The bricks were produced at 6 different stabilization levels with cassava starch as stabilizer for all the grain size combinations. The stabilization level are; 0%, 4%, 8%, 12%, 16% and 20%. Result shows that cassava starch stabilized bricks attained a maximum compressive strength of 1.83N/mm² at 28 days strength gain. This is 10.9% higher than the NBRRI specified minimum strength of 1.65N/mm² for compressed stabilized earth bricks. The study also reveals grain size ≤ 2.36mm and 20% stabilization as the overall best grain size combination and stabilization level respectively. Maximum water absorption of 13.23% was revealed at 28 days curing period while a good abrasion resistance accounting for 0.15% loss in weight was attained. The study therefore concluded that earth bricks produces with soil grain size ≤ 2.36mm and stabilized at 20% cassava starch content are of satisfactory strength and abrasion resistance and therefore recommended for use as interior walls and in areas of low exposure to moisture.

CHAPTER 4: DATA PRESENTATION, ANALYSIS AND DISCUSSION

CHAPTER 5: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND OF STUDY

Earth as a building material is available everywhere. In developing countries, earth construction is economically the most efficient means to house the greatest number of people with the least demand of resources (Al-Sakkaf, 2009). Traditional earth construction materials such as adobe bricks suffer from moisture attack and cracks, thus the need to continuously maintain them in order to keep them in good condition. According to Adam and Agips (2001), traditional earth construction technology has undergone considerable developments that enhance earth’s durability and quality as a construction material for low-cost buildings. Such methods include rammed earth and machine pressed compressed stabilized earth bricks. Stabilization of these earth bricks is achieved using various methods that often involve the use of a variety of stabilizers. Adam and Agip (2001) identified these stabilizers to include artificial ones such as Portland cement and lime and the natural ones such as agricultural waste amongst others.

Cassava starch which is the stabilizer in view in this research was recently evaluated for its suitability as stabilizer and found to improve some mechanical properties of selected soil types (Khalil 2005). Incidentally the abundance of the cassava crop in Nigeria is not in doubt. Phillips et al (2004) pointed out that Nigeria is the highest cassava producer in the world.

The effects of soil grain sizes in imparting changes in mechanical behavior of soils have also been pointed out by researchers like Wang, Lu and Shi. (2010), Rahardjo et al (2002) and many more.

This research work intends to evaluate the possibility of further improving the strength and durability characteristics of the cassava starch stabilized compressed earth bricks through the exploration of mechanical behavior of different grain size range of a selected soil type.

1.2 STATEMENT OF RESEARCH PROBLEM

Despite the diverse number of policies and programme adopted by the Nigerian Government, housing delivery has remained a major challenge leading to deficits in delivery. Oluwakiyesi (2011) puts the housing shortfall at between 16 and 18 million housing units. Ajanlekoko

(2011) pointed out that the National housing programme launched by the Nigerian Government in1994 had a delivery target of 121,000 units to be distributed throughout the states of the Federation. Only 1,367 were completed and another 17,792 units were under construction. The National Rolling Plan (NRP) on the other hand, puts the housing requirement of Nigeria at a conservative annual estimate of between 500,000 and 600,000 thus needing an estimated 250 to 300 million Naira to make up for the shortfall. It can therefore be inferred that initiatives at enhancing housing delivery need not be limited to housing policies and programs of Government alone but should more importantly include reduction in overall construction cost particularly amongst the rural populace. Ajanlekoko (2001) asserted that the rapid up-swing in the prices of building materials in the last five years has further reduced the affordability for most Nigerians. Oresegun (2011) noted high cost of building materials and labour to be amongst major problems affecting housing delivery in Nigeria. Satprem (2009) recommended among other measures, a reduction in the amount of cement for brick making in other to enhance cost effectiveness.

Cement availability in Nigeria has recently been characterized by high cost, fluctuating price, scarcity and profiteering by cement manufacturers. This fact has been attested to in a Thisday news paper report of 24^th April, 2011 captioned “amid scarcity cement producers post bumper profit”. The report states “indications emerged last week that the unabated shortage of cement products and its correspondent exorbitant price are raising the profitability of local manufacturers, which are alleged to have conspired to frustrate calls for higher importation as a way of bridging the gap between demand and supply”. Despite the cement challenge particularly in Nigeria, it still remains the main stabilizer in compressed earth brick production. This research therefore intends to consolidate on the gains in the cheaper and more readily available cassava starch stabilized compressed earth brick by evaluating the effects of grain sizes of soil (which in this case is laterite).

1.3 JUSTIFICATION

Compressed stabilized earth bricks have been noted to be probably the most cost effective alternative for solving the housing problems in Nigeria. However, cement still remains the main stabilizer in earth brick production with its attendant problems particularly in Nigeria. According to Adam and Agips (2001) Portland cement is amongst the most widely used and readily available stabilizer in developing countries. Satprem (2009) affirmed that compressed earth blocks are most times stabilized with cement or lime. Even the Nigerian Building and Road Research (NBRRI) Technological Innovation Catalogue considers only cement as stabilizer for Compressed Stabilized Earth Brick in its brick making technological innovation even though it (NBRRI), has established that cement content in compressed stabilized earth bricks above 5% is uneconomical (Agbede and Joel, 2008). There is therefore a need to search not only for cheaper and more environmentally friendly alternative stabilizers but also for optimization of their application as brick stabilizers. An analysis at the commencement of this study reveals that starch paste produced from 200g of dry cassava starch powder for stabilization of 140mm ×140mm × 80mm earth brick was sufficient for production of a minimum of 12 bricks at 5% stabilization. However 200g of cement for the production of same size of bricks at same stabilization level (5%) was sufficient for production of 5.2 bricks. Furthermore, equal amount of cassava starch is at least 4 times cheaper than cement.

The effect of soil grain sizes in imparting changes on mechanical behavior of soils was noted by various authors. According to Wang, et al. (2010) the mechanical properties can be obviously different even if there is a little difference in the grain size distributions of the undisturbed fine sand while the mechanical properties of the remoulded and the undisturbed fine sand are different even if the grain size distributions are the same. Verruijt (2010) classified soils according to their grain sizes and noted that grain size is a major factor in the different mechanical behaviour of the main types of soils i.e. sand, clay and peat while Rahardjo et al (2002) opined that the result of index and engineering properties of soils indicates that variation in index and engineering properties of soils are influenced largely by the pore-size distributions (which relates with grain sizes). These changes in mechanical behaviour as a result of changes in grain sizes may yield an optimum result in the application of cassava starch as stabilizer in compressed earth bricks.

1.4 AIM AND OBJECTIVES

1.4.1 Aim

The aim of this research work was to investigate the effect of varying soil grain sizes on stabilized compressed earth bricks using cassava starch as stabilizer.

1.4.2 Objectives

i. To establish the effects of varying soil grain sizes on durability of compressed stabilized earth bricks

ii.   Establish the active chemical compounds in laterite and cassava starch

iii.   To determine the chemical reactions of laterite and cassava starch

iii.   Identify the best grain size range (within the scope of study) for stabilization with cassava starch

iv.   Establish the effects of varying soil grain sizes on strength of starch stabilized compressed earth bricks

1.5 METHODOLOGY

The methodology adopted for this research was an extensive review of literature, publications, journals etc on soil stabilization as well as characteristics of the stabilizer under consideration i.e. cassava starch. Laboratory tests were carried out in conformity with already established procedures obtained from relevant literatures. Three sets of cube samples each of 140 X 140 X 80mm compressed stabilized earth bricks were cast, cured and tested at 7, 14, and 28 days respectively.

One set each of the test sample was prepared with soil of grain size passing sieve sizes 2.36mm, 1,18mm and 600µm respectively. Stabilization of sets of bricks was done at 0%, 4%, 8%, 12% 16% and 20%. Similar stabilization levels with different method of compaction (using the California Bear Ratio and Proctor mould) were established from literature.

1.6 SCOPE AND LIMITATIONS

1.6.1 Scope

Only chemical, physical and mechanical analyses were carried out on test samples. This research work was also carried out on single soil type (laterite) which was locally sourced from Biye Borough pit Zaria. As such no comparism was made with the performance of other soil types.

1.6.2 Limitations

1. Tests on stabilized bricks were confined to;

a.      Compressive strength test

b.     Abrasion resistance

c.      Water absorption

2.  Brick size was limited to 140mm×140mm×80mm obtainable from the press machine

3.  Compressive pressure for brick molding was limited to 4N/mm² applicable to the moulding machine used for brick production.

4.   Only the NBRRI manual brick making machine was used. Not comparism was made with bricks molded with other brick making machines.