Behavior of polymer-stabilized sandy soil

One of the main objectives of using soil stabilizers or grouts is to decrease soil permeability by filling the voids and therefore reducing soil porosity and compressibility. Numerous particle-based cementations materials have been introduced since the middle of the 20th century to fulfill this purpose with calcium as the primary element in these grouts. One of the the several problems associated with the traditional stabilizers is their calcium component reacts with the soil itself and consequently, the outcome will not meet the requirements and sometimes the soil collapses are reported. Additionally, traditional grouts are very viscous, which results in difficulties in achieving optimal performance in grout injection. To address these drawbacks, many alternative stabilizers have become available in the market; among which polymers have been under particular considerations. Polymers are relatively cheap, light-weighted, and stable for the rehabilitation and construction of infrastructure system all over the world, with minimal environmental footprints, and, therefore, could be justified as a general substitute for lime or cement stabilizer. Considering the extensive potentials of using polymers in civil engineering, this study focuses on using Diphenylmethane Diisocyanate (MDI) precursor in combination with water to stabilize poorly-graded (SP) fine sand. Various combinations of polymer-water-soil mixtures, as well as different curing periods, at optimum moisture content and porosity level were attempted to determine the optimal polymer-water ratio and curing time. Specimens were consequently tested for their unconfined compressive strength (UCS). The results of this study indicated that the optimal mixture ratio is twenty percent polymer and ten percent water for any amount of soil used to fill all the porosity of the soil. Moreover, the optimal curing period for specimencs was evaluated as follows: Dried for 4 days in air followed by 4 days submerging in water. Indicating an elastic response to cyclic loadings, the possibility of using the polymerized soils as an alternative sub-base material for pavements was also evaluated by performing several flexural fatigue tests for up to 100,000 cycles of loading. Beam specimens applied for flexural fatigue tests showed significant performance with a elastic response up to 400,000 of loading cycles while the flexural stiffness showed an increase approximately between the 40,000th and 100,000th cycle. The occurrence of such phenomena was attributed to the self-healing of the specimens, and rearrangement of the aggregates to a stiffen texture. Finally, recommendations were outlined to continue this study.