Effects of poly(vinyl alcohol) on fiber cement interfaces. Part II: Microstructures

Abstract

Changes in the microstructure of hydrated cement paste around steel, brass, brass-coated steel, and polypropylene fibers induced by the addition of 1.4% poly(vinyl alcohol) (PVA) have been examined by scanning electron microscopy. The microstructures were examined both after the fibers had been carefully peeled from the matrix and after the fibers had been pulled from the matrix along their axes. The previously noted enhancement by PVA of the pull-out properties from ordinary Portland cement matrix of steel fibers is attributed to the formation of a ductile, fine-grained interfacial layer. The formation of this microstructure is suggusted to arise from the effect of PVA on the nucleation of CH and C---S---H at the fiber surface and on the presence of polymer around the fibers. The enhancement of the pull-out properties for brass and brass-coated steel fibers is attributed to the formation of a strong bond between the fiber and matrix that diverts failure to the porous zone surrounding the fiber. Interfacial structures against low surface energy fibers, like poly-propylene, showed minimal effect from the polymer.