Effects of polyvinyl alcohol on aggregate-paste bond strength and the interfacial transition zone

Small amounts of polyvinyl alcohol (PVA) were added to cement paste in an attempt to increase the aggregate-paste bond strength. Specimens consisted of ordinary Portland cement mixed with PVA/water solutions and cast against ground surfaces of limestone and granite. The aggregate-paste bond strength after curing was tested in a wet state by three-point bending. The morphology of the interfacial transition zone was observed with scanning electron microscopy, and the composition was analyzed with infrared spectroscopy. The addition of 1.4 wt% PVA based on the mass of cement increased the strength for both limestone-paste and granite-paste bonds. The strength increase was about five-fold for limestone and nearly two-fold for granite. The failure mode also changed, from pure adhesive failure without PVA to cohesive failure of the aggregate with limestone and to a mixed cohesive failure of the paste and adhesive failure with granite. The gain in bond strength with the addition of PVA seems to arise from suppression of the porous interfacial transition zone and an inhibition of calcium hydroxide nucleation on the aggregate surface. (C) 1998 Elsevier Science Ltd.