EFFECTS OF POLYVINYL-ALCOHOL ON AGGREGATE-PASTE BOND STRENGTH AND THEINTERFACIAL TRANSITION ZONE

Small amounts of polyvinyl alcohol (PVA) were added to cement paste in an attempt to increase the aggregate-paste bond strength. Specimens c onsisted of ordinary Portland cement mixed with PVA/water solutions an d cast against ground surfaces of limestone and granite. The aggregate -paste bond strength after curing was tested in a wet state by three-p oint bending. The morphology of the interfacial transition zone was ob served with scanning electron microscopy, and the composition was anal yzed 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 li mestone and nearly two-fold for granite. The failure mode also changed , from pure adhesive failure without PVA to cohesive failure of the ag gregate with limestone and to a mixed cohesive failure of the paste an d adhesive failure with granite. The gain in bond strength with the ad dition of PVA seems to arise from suppression of the porous interfacia l transition zone and an inhibition of calcium hydroxide nucleation on the aggregate surface. (C) 1998 Elsevier Science Ltd.