The physicochemical interaction between PHPA polymer slurry and cement mortar

The aim of the present study was to improve understanding of the interaction of drilled shaft concrete, polymer slurry (used to stabilize boreholes during construction of the drilled shaft), and the foundation soil. Interface shear tests were performed in the laboratory to investigate the shear resistance between soil and a cement mortar interface after exposing the interface to a high-molecular-weight polymer slurry. Two types of soils were investigated: (a) stiff silty clay and (b) medium-dense sand. Results showed that for curing periods of 7 days the interface shear resistance was 28\% to 46\% higher when the interface was exposed to the polymer slurry relative to the interface shear strength of the standard unexposed samples. The ability of the polymer slurry to penetrate and stretch through the pores of silty clay and dense sand soils was demonstrated by investigating the exposed soil masses using scanning electron microscopy (SEM). Exposing the outside surface of cement mortar specimens to the polymer slurry for a period of 14 days caused pitting (roughening) of the mortar surface, which explains the increased interface shear resistance between the soil and the cement mortar after exposure to polymer slurry. The laboratory behavior was verified with full-scale field tests.