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Cement matrices were prepared by autoclaving portland cement-silica mixtures having various percentages by weight of silica, with water-to-cement ratios of from 0.22 to 0.45. Normal cement paste samples were also made for comparison. Samples were heated to 100°C in vacuum for 24 h before impregnation with methyl methacrylate monomer (MMA), which was then polymerized; impregnation was repeated for complete impregnation. Young's modulus and microhardness were measured as a function of volume fraction of PMMA and results compared with those obtained from similar samples conditioned to 11% RH. Autoclaved impregnated and unimpregnated specimens and room-temperature-cured cement paste specimens at both conditions were exposed to 100% RH and their length changes measured for up to four years. Permeation to water vapour in the impregnated specimens, although decreased, still occurs and impregnation increased long-term expansion on exposure. Expansion on exposure to 100% RH is much larger for D-dried than for 11% RH-conditioned matrices; the latter produced stronger bodies on impregnation.

Dimensional changes of porous 96% silica glass have been determined during exposure to aqueous NaOH solution. Depending on the thickness of the specimen (1, 3, 4, or 8 mm) and the concentration of the alkali (0.1, 0.4, 0.8, 1.6, 3.2 and 6.4 M), either expansion or contraction or both were observed, the maximum being 0.7%. The features of the extension curves cannot yet be fully explained, but the results suggest that dissolution of glass leads to expansion and that surface reaction and chemisorption lead to contraction. The presence of CaCl[2] in the solution in 1M concentration significantly retards dissolution and expansion.

Two areas of research are discussed; namely, clarifying the reasons for volume instability that accompanies all degradation processes and establishing the relationship between the characteristics of the pore system and freeze- thaw resistance of concrete. Studies in these areas are needed, and promise to yield significant progress in improving durability of concrete., 8 'CIQC: 8o Congresso Internacional de Quimica do Cimento/ 8th International Congress on the Chemistry of Cement/ 8e Congrès International de la Chimie des Ciments: 22 September 1986, Rio de Janeiro, Brazil

This paper includes the study of the following problems: The local stress concentration in the large particles of the coarse aggregate in non-reinforced concrete during setting and as a result of conversion of water. Stress and deformation patterns in specimens of non-reinforced concrete under constant load and constant elongation, respectively, i. e., stress and deformation patterns due to contraction and relaxation, respectively.

The various types of volume change starting from when concrete is placed to when the hardened state is attained are discussed. It is pointed out that volume changes may lead to complications externally because of structural interaction as well as internally which results in cracking. Cracking impairs the ability of a structure to carry its design load and affects its durability., Canadian Building Digest, CBD-119