Phase compositions, microstructures and causes of high strength

2 Phase compositions, microstructures and causes of high strength 

Pastes inpregnated with PMMA or sulphur are still sufficiently permeable to water that expansion occurs on long exposure (F46). In polymer-impregnated (S108) and MDF (R64) cement pastes, there is evidence of interaction between Ca ions and carboxylate and possibly other groups of the polymer. In MDF pastes made with calcium aluminate cement, the polymer (PVA) was found to inhibit the normal hydration reactions of the cement, but to react with Ca and AH to give an ionically cross-linked polymer and calcium acetate. TEM showed the material to be essentially a dispersion of grains of clinker or hydration products in a continuous polymer matrix. 

Kendall el al. (K64) considered that MDF cements owed their high strengths primarily to the absence of large flaws, which they held to be the reason for the relative weakness of normal cement pastes. This view has been challenged (B115,K65,E4). Beaudoin and Feldman (B115) discussed ways in which stress concentrations were reduced in very strong cement pastes, and both they and Eden and Bailey (E4) considered that in MDF pastes the polymer plays a major role. 

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