Critical state desiccation induced shrinkage of biomass treated compacted soil as pavement foundation

Abstract

Volumetric shrinkage critical state induced by desiccation of compacted earth treated and improved with Rice Husk Ash (RHA) and utilized as pavement foundation has been investigated in the laboratory. The critical state study was important to determine at what level of earth improvement with the biomass material can be considered safe in terms of shrinkage behavior of treated soft soil utilized in pavement construction. Rice Husk (RH) is an agricultural waste discharged during rice production and is disposed on landfills. It causes land pollution in places like Abakaliki and Ebonyi State, Nigeria as whole where rice farming is the predominant occupation. Ground and soil improvement with the use of rice husk ash has contributed in the management of solid waste in the developing countries where rice production is a common occupation with its attendant solid waste generation. However, the use of biomass-based binders like RHA has reduced the rate at which oxides of carbon are released into the atmosphere, which contribute to greenhouse emission effects. This exercise is an environmentally conscious procedure that keeps the environment safe from the hazards of carbon and its oxides. the preliminary investigation on the test soil showed that it is classified as an A-7-6 soil group according to AASHTO classification. The index properties showed that the soil was highly plastic with high clay content. The RHA was utilized at the rate of 2%, 4%, 6%, 8% and 10% by weight of treated solid to improve the soil volumetric shrinkage induced desiccation at molding moisture conditions of 2% dry, 0%, 2% wet, and 4% wet of optimum moisture. This was necessary to establish the behavior of hydraulically bound foundation materials subjected to dry and wet conditions during the rise and fall of water tables. Results of the laboratory investigation have shown that at 2% dry of optimum moisture, the volumetric shrinkage (VS) behavior performed best and reduced below the critical line of 4% at 8% by weight addition of RHA and maintained that consistent reduction at 10% addition of RHA. Generally, the critical point was achieved at 8% by weight addition of RHA at all the molding moisture conditions. This is an indication that at molding moisture conditions between -2% to 4%, 8% by weight addition of the admixture, RHA can be utilized as an environmentally conscious construction material to improve the VS of soils for use as hydraulically bound materials in pavement foundation construction.