Optimization of Bagasse Ash Content in Cement-stabilized Lateritic Soil

The frequent rises in the price of cement and other binders have resulted in the escalation of the cost of construction, rehabilitation and maintenance of roads. One of the possible ways of cost reduction is to convert waste bagasse residue into ash and use it as a supplement/partial replacement for cement. Therefore this study is an attempt to optimize bagasse ash content in cement-stabilized lateritic soil for low-cost roads. The bagasse ash and lateritic soil were characterized by carrying out Atomic Absorption Spectrometer and soil preliminary tests as well as X-ray diffraction respectively. Compaction test, California bearing ratio, unconfined compressive strength and durability tests were carried out on the soil stabilized with 2%, 4%, 6% and 8% cement contents and bagasse ash ranging from 0% to 20% at 2% intervals; all percentages of the bagasse ash and cement were by the weight of dry soil. Cost analysis was carried out for the constituents of the stabilized material and a model was formed for cost evaluation. Also three regression models were developed that involved relationships of cost of bagasse ash, cement content, optimum moisture content, California bearing ratio and unconfined compressive strength at 7 days curing period. The three regression models were used to form a non-linear model which was linearized and solved with the simplex method including sensitivity analysis on the objective function and the constraints. Attempt was also made to apply Scheffe’s regression method from obtained results. It was observed that the increase in bagasse ash content increased the optimum moisture content but reduced maximum dry density. On the other hand higher bagasse ash tremendously improved the strength properties of the stabilized matrix. The optimum contents for bagasse ash, cement and optimum moisture content for an economic mix were 14.03%, 4.52% and 22.46% respectively at a cost of 39.50 kobo for stabilizing 100 grams of the lateritic soil as against 43.52 kobo for stabilizing with only cement.

Bagasse-ash is an agricultural material obtained after squeezing out the sweet juice in sugarcane and incinerating the residue to ash. Bagasse is the fibrous residue obtained from sugarcane after the extraction of sugar juice at sugarcane mills or sugar producing factories (Osinubi and Stephen, 2005). The climatic and soil conditions favourable for the production of sugarcane are present in the Northern part of Nigeria and consequently, there is abundant production of it in the area. Sequel to the foregoing is massive generation of sugarcane residue waste which constitutes disposal problems and requires handling. There is yet no adequate awareness about the usefulness of the sugarcane residue in the country, in other words very little value has been attached to it. In some cases, the residue is being utilized as a primary fuel source for sugar mills and also for paper production. However incinerating it to ash and adopting it as admixture in stabilized soils because it has been found to be a good pozzolana, adds to its economic value.

The major part of Nigeria is underlain by basement complex rocks, the weathering of which had produced lateritic materials spread over most part of the area. It is virtually impossible to execute any construction work in Nigeria without the use of lateritic soil because they are virtually non-swelling (Osinubi, 1998a). The climatic and geological position of Abia state with her alternating humid and dry periods enhanced the rich deposition and formation of lateritic soils which have been very often utilized as fill materials in road construction and other civil engineering works.