Structure and properties of poly(vinyl alcohol)-modified cement-based composites and polymer gels.

This thesis reports the effects of a water-soluble polymer on cementitious materials and of the cementitious materials on the polymer. Because the principal effect of ordinary portland cement on the polymer was to create a crystalline gel, the efficient gelation of polymers by self-nucleated crystallization was also studied. Small amounts of poly(vinyl alcohol), PVA, in aqueous solution were added to cement to improve the aggregate-paste bond. The flat aggregate-cement paste bond strength measured by 3-point bending was significantly increased. The failure mode was also changed, from pure adhesive failure to cohesive failure of the aggregate or the paste. When PVA was added to concrete, cohesive failures of aggregate stones also occurred in the compression test because of the improved bond strength. The compressive strength of concrete, however, did not increase with PVA because of the increased air content, although air void formation was minimized by using a pre-wetting mixing technique. When the air voids were removed by vacuum, the strength was increased 15% with the addition of 2% PVA based on cement. The gain in bond strength with PVA seems to arise from a reduction of the interfacial transition zone and an inhibition of calcium hydroxide formation on the aggregate surface. The PVA solutions separated from ordinary portland cement by centrifugation formed gels after various length of time, with gelation probably arising from the crystallization of fully hydrolyzed PVA. The solutions separated from high-alumina cement or containing aluminate ion, however, did not form gels. The mechanism of thermoreversible gelation of polyethylene/decalin mixtures was studied using self-nucleated crystallization. The decrease in the critical gelation concentration by low-temperature crystallization or by self-nucleation was caused by a better interlinking of the large number of crystalline units having fewer lamellae per unit. The decrease of lamellae size by the further increase of the number of self-nuclei, however, did not lower the critical gelation concentration. Brownian motions of the growing lamellae possibly caused an efficient edge-to-edge joining of nearly equal-sized lamellae at the final stage of gelation.Ph.D.Applied SciencesPlasticsPolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130278/2/9722016.pd