Effect of Lime-stabilization on Strength Characteristics of Bricks

Clay soils have been used locally in Sokoto to make bricks without stabilizing the soil. The bricks usually experience structural failure such as cracking and seasonal swelling when used for the construction of wall. Collapsing of wall also occurs in the area where non-stabilized bricks are used for wall construction. This research aims to assess the effect of lime-stabilization on strength of bricks made with Sokoto Red Clay Soils with a view to determining the physical properties of the soil and the optimum level of lime-stabilization required in the case of Sokoto Red Clay Soil (RCS). RCS used in this research were stabilized by lime and the method adopted for the stabilization is additive method. The method involves addition of certain percentages of stabilizer(s) to soil to improve the strength properties and durability of the soil. This study carries out laboratories work on the physical tests of the soil sample and the compressive strength test on the bricks produced. The Optimum Moisture Content of the soil and stabilized soil were determined to be 14.6% and 16.8% respectively. Percentages of lime-stabilization used in this research are 0%, 3%, 6%, 9%, 12%, 15%, 18% and 21%. A total of 120 bricks were produced and tested for compressive strength after stipulated curing period. The curing method adopted is moist curing method for 3, 7, 14, 21and 28days. The results of compressive strength at 0%, 3%, 6%, 9%, 12%, 15%, 18% and 21% in 28days are; 0.5N/mm2, 1.35N/mm2, 1.24N/mm2, 0.85N/mm2, 0.82N/mm2, 0.63N/mm2, 0.47N/mm2 and 0.37N/mm2. A continuous increase in compressive strength of the bricks from 3days to 28days in both 3% and 6% stabilizations were further observed. At 3% and 6% stabilization, the highest average compressive strengths recorded in 28days are 1.35N/mm2 and 1.24N/mm2 respectively.. However, the highest value is not up to 2.8N/mm2 as stipulated in BS 5628 part 1 (1978). This might be as a result of the low value of plasticity index (10.4) and the stabilizer used. It was also found that the highest compressive strength of the bricks at 0% stabilization was 1.11N/mm2 in 21days and the compressive strength reduced to 0.50N/mm2 at 28days. The reduction in compressive strength derived at 0% stabilization in 28days might be as a result of cracks showed on the surface of the bricks which may be attributed to lack of stabilization. Compared to 3% stabilization, compressive strength of 1.11N/mm2 was recorded in 3days due to the effect of lime on the bricks. The highest value recorded at 3% stabilization indicates that lime alone cannot be used to stabilize red clay soil for brick production. This shows that lime should be used together with one or two stabilizers to stabilize red clay soil so as to improve the strength properties of the bricks. It is also recommended that red clay soil with higher plasticity index should be adopted for lime-stabilization.

Different types of stabilizers have been used in different parts of the world to enhance the engineering properties of laterite (Moh, 1962). The most common ones are cement, lime and bitumen and the choice of a particular stabilizer depends on the soil type and degree of effectiveness of the stabilizers (Rahaman, 1968). Mustapha (2006) defined soil stabilization as the treatment of soils to enable their strength and durability to be improved such that they become totally suitable for construction beyond their classification if left untreated. Stabilization as viewed by Afjman (1994) is the process of blending and mixing materials with a soil to improve certain properties of the soil. Afjman (1994) further explained that stabilization process may include the blending of soils to achieve a desired gradation or the mixing of commercially available additives that may alter the gradation, texture or plasticity or act as a binder for cementation of the soil. Stabilization can be used to function as mechanical stabilization, additive stabilization or modification.

Mechanical stabilization is accomplished by mixing or blending soils of two or more gradations to obtain a material meeting the required specification. The soil blending may take place at the construction site, a central plant or a borrow area. Additive stabilization is achieved by the addition of proper percentages of cement, lime, fly-ash, bitumen or combination of these materials to the soil. The selection of the type and determination of the percentage of additive to be used is dependent upon the soil classification and the degree of improvement in the soil quality desired.