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A study was conducted to stabilize low stiffness road surface material with high carbon fly ash. The non-cementitious Maryland fly ash was activated with another recycled material, lime kiln dust (LKD). California bearing ratio (CBR) and resilient modulus tests were conducted to determine the strength and stiffness, respectively, of the stabilized materials. Addition of LKD and curing of specimens generally increased CBR and summary resilient modulus (SM R ) and lowered plastic strains, whereas fly ash addition alone decreased the strength and stiffness due to the non-cementitious nature of the ash.CBR increased with increasing CaO content as well as with CaO/SiO 2 and CaO/(SiO 2 + Al 2 O 3 ) ratio of the mixtures; however, these parameters could not be correlated with the SM R . The unpaved road materials stabilized with LKD and fly ash is expected to lose 31 to 67% of their initial moduli after twelve cycles of freezing and thawing. Finally, required base thicknesses were calculated using the laboratory-based strength parameters. STABILIZATION OF RECYLED BASE MATERIALS WITH HIGH CARBON FLY ASH

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This paper examines the bio-derived stabilization of sand-only or sand-plus-silt soils using an extracted bacterial enzyme application to achieve induced calcite precipitation (ICP). As compared to conventional microbial induced calcite precipitation (MICP) methods, which use intact bacterial cells, this strategy that uses free urease catalysts to secure bacterial enzyme–induced calcite precipitation (BEICP) appears to offer an improved means of bio-stabilizing silty-sand soils as compared to that of MICP processing. Several benefits may possibly be achieved with this BEICP approach, including bio-safety, environmental, and geotechnical improvements. Notably, the BEICP bio-stabilization results presented in this paper demonstrate (i) higher rates of catalytic urease activity, (ii) a wider range of application with sand-plus-silt soil applications bearing low-plasticity properties, and (iii) the ability to retain higher levels of soil permeability after BEICP processing. Comparative BEICP versus MICP results for sand-only systems are presented, along with BEICP-based results for stabilized soil mixtures at 90:10 and 80:20 percentile sand:silt ratios. This BEICP method’s ability to obtain unconfined compressive strength results in excess of 1000 kPa with sand-plus-silt soil mixtures is particularly noteworthy.