Strength characteristics of genetically different rice and coconut husk ash compacted shales

Abstract

Background: The strength characteristics of two genetically different shales treated with both Rice Husk Ash (RHA) and Coconut Husk Ash (CHA) was evaluated to elucidate responses and effects, examine effectiveness of the additives with a view to ultimately provide economically viable and environmental friendly options for modification and hence stabilization. Methods: 2 to 20 % by weight of both RHA and CHA were separately added to Okitipupa (SW) and Enugu (SE) shales with the subsequent determination of Plasticity Index (PI), Maximum Dry Density (MDD), Optimum Moisture Content (OMC), Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR). Results: RHA and CHA were found to possess pozolanic properties such that their addition to shale in modest amounts (not more than 10 % by weight) has beneficial effect on the strength characteristics. Addition of RHA produced shales with reduced PI, higher UCS, increased MDD and more pronounced reduction in OMC when compared with the CHA stabilized shales. However in general, addition of 10 % RHA and 6-10 % CHA brought about optimal effect on the geotechnical properties of shales and as such can be regarded as the optimum content. Conclusions: These materials can thus serve as suitable alternatives to modify and stabilize problematic shale and hence help reduce construction costs, environmental hazards and ultimately bring about shales with improved geotechnical properties.

Comparative effect of microbial induced calcite precipitate, cement and rice husk ash on the geotechnical properties of soils

“…The decrease in liquid limit of the soil is in agreement with the results in Al-Rawas et al [6]. The decrease in liquid limit and the plasticity index as RHA increased from 5 to 10% is attributable to the reaction between the RHA and the soil in which the RHA replaces the clay content in the soil [11,46] thereby causing reduction in the liquid limit and plasticity index. The decrease in the liquid limit of the soil-RHA mix might be attributed to the fact that the rice husk ash, which is a pozzolanic material that is high in silica oxide, react with water to form compound possessing cementitious properties (calcium silicate) in soil particles [40].…”

“…The decrease could also be due to the precipitation of calcite, which results in the decrease in pore space of the soil particles with the pore spaces being filled with the calcite precipitate thereby binding the soil particles together [28]. Decrease in plasticity index shows that the engineering properties of the soils were improved as indicated by other researchers including [32,44,46].…”

“…A portion of the resulting mixture was used for the test. Furthermore, compaction tests was also carried out using the Modified AASHTO level of compaction (this was used because it is usually achievable with conventional field equipment [46], to determine the maximum dry density (MDD) and optimum moisture content (OMC) on BS mould. Hence compaction was achieved using 3 kg of air dried samples mixed thoroughly with 3% of water (150 ml) and later compacted into a pre-weighed mould in 5 layers with each layer subjected to 55 blows of 4.5 kg rammer falling through a height of 0.45 m uniformly.…”

“…The increased OMC with increased RHA content at 15% may be as a result of the extra water required for the pozzolanic reactions and increased affinity for water. This may also be attributable to the additional water held within the flocculent soil structure [46]. The additional water is accounted for as excess water absorbed or additional water being absorbed by the excess RHA as a result of its porous properties [15].…”

“…Authors including [1,2,4,5,7,15,17,26,28,44,46,48,56] amongst others have shown the possibility of using agricultural waste materials, microorganisms and others as additives for soil stabilization. These materials have attracted the attention of researchers because of their low cost and high cementation reaction.…”