Properties and development of the microstructure in cement pastes modified by a styrene–butadiene co-polymer

This paper considers the effects on properties and texture of adding a styrene-butadiene co-polymer dispersion to Portland cement pastes. In studying the rheology of fresh pastes it was found that their flow characteristics decreased at lower levels of polymer addition, yet improved when the level of polymer added was increased. The rate of hydration was significantly reduced by the presence of the polymer. In the hardened paste the polymer was distributed as a continuous three-dimensional network, interlocked with the cement hydration products. As to the physico-mechanical properties of the hardened pastes, the addition of the polymer – at a constant water/solid ratio – increased the flexural strength and work of fracture of the material and at the same time lowered its compressive strength, modulus of elasticity and hardness.