Structural performance of earth blocks stabilized with rice husk ash and cement

Abstract

The conventional techniques of soil stabilization are becoming expensive day by day due to the rising cost of the stabilizing agents like, cement, lime, etc. The cost of stabilization and environmental hazards may be minimized by replacing a good proportio n of stabilizing agent using the supplementary cementitious mat erials . Rice husks are among the waste material that must be managed in rice production areas. This study investigated t he structural performance of Rice Husk Ash ( RHA ) as partial replacement of cement to stabilize clay for the production of compressed ea rth blocks . Black cotton soil collected from a construction site was used in this study. Particle size distribution of the soil together with its Atterberg limit s as well as its compaction characteristics were established according to British standard procedures ( BS 1377 - 1990: Part 2 & 4) . Stabilized soil s pecimens were prepared and tested for unconfined compressive strength, in accordance with BS 1924 - 2 : 1990 Section 4 . The soil sample used was classified as A - 7 - 5 in the AASHTO classification system. While increasing cement content resulted in decreased liquid limit, plasticity index and linear shrinkage ; the same resulted in increase d plastic limit, maximum dry density (MDD), and optimum moisture content (OMC). The cement stabilized clay blocks had an average compressive strength ranging from 0.3 MPa for 0% cement to 1.1 MPa for 12% cement at 7 days of curing ; and 0.8 for 0% cement to 3.1MPa for 12% cement after 28 days of curing. This study established that to achieve a minimum strength of 2.5 MPa for soil blocks the soil should be stabilized with at least 8% cement. Replacement of cement with RHA led to a decrease in MDD , an increase vi in OMC and a decrease in mean compressive strength of the blocks. T he 28 day compressive strength for blocks stabilized with 5 % cement and 7.5% RHA was 2. 6 MPa which was higher than the Kenyan Bureau of Standard s requirements (2.5 MPa). It was not possible to measure water absorp tion of soil blocks after soaking for 24 hours. This is because b locks stabilized with 8% cement alone crumbled after 12 hours while t he blocks stabilized with 5 % c ement and 7.5 % RHA crumbled six hours after being immersed in water . These results suggest that stabilized earth blocks should only be used in an environment which is not exposed to water .