Optimal density for effective chemical stabilization of deficient soils for road structures

Abstract

Clays are deficient soils in pavement construction due to presence of secondary clay minerals which are usually stabilized to improve its engineering properties. Calcium carbide residue (CCR) and Zeolite wastes have both been identified as soil stabilization additives due to presence of calcium ion in the CCR and amorphous silica in zeolite. However, various researchers uses varied compaction energy level to mold specimen for relevant tests. This study is aimed at compacting CCR and zeolite treated clay at five different energy levels to determine the energy level that gives the highest strength and stability. For each compaction energy, the untreated and treated clay were prepared and some selected mixtures were sent for microstructural tests. Unconfined compressive strength (UCS) and California bearing ratio (CBR) specimen were cured tested at predetermined maximum dry density (MDD) and Optimum moisture content (OMC). The MDD increased with compaction energy while the OMC reduced in the same order. The XRD micrograph of specimen treated with CCR and zeolite revealed disappearance of delayed ettringite peaks from untreated clay with formation of microcline and anorthite. The SEM showed the formation of cementitious calcium silicate hydrate (C-S-H) filling the pores in the untreated clay to form a compact mass. The unconfined compressive strength (UCS) increased to 2300kN/m2 for the treated clay after 180 days curing. The CBR values increased from 3% for untreated clay to 260% for treated clay. The durability test showed result of between 72% and 84% for treated clay which satisfy the 70% minimum specified by standard. These UCS and CBR values satisfy the requirement for sub-base of highly trafficked roads. The UCS and CBR results for specimen cured for 180 and 60 days respectively revealed that the optimum compaction energy for effective CCR and zeolite stabilization occurred in Reduced Modified Proctor energy level.