Material properties of mortar specimens at early stage of hydration in the presence of polymeric nano-aggregates

This work presents results on the influence of polymeric nano-aggregates on mortar microstructure and mechanical properties at very early hydration stage, starting 24h and until 28 days of age. The polymeric nano-aggregates were core-shell micelles, produced from Poly(ethylene oxide)-block-Polystyrene (PEO-b-PS) di-block copolymer (PEO113-b-PS218). The micelles were added to the mortar matrix as a solution (i.e. the mixing water was a solution of stabilized nano-aggregates in demi-water in concentration of 0.5 g/l). The morphology and microstructure of the mortar matrix were investigated by ESEM. Image analysis was employed for calculating porosity and pore size distribution. The amounts of hydration products and un-hydrated cement (in percent with hydration time) were calculated, using image segmentation by thresholding. The percent of hydrated water per dry cement weight was also determined wet chemically. Compressive strength was tested on intervals of 24h, 3, 7, 14, 28 and 56 days. For the period of 24h to 28 days, and compared to rest conditions, the mortar mixture, containing nano-aggregates exhibits : lower capillary porosity ; higher compressive strength ; contains similar to rest conditions amount of hydrated water and lower amount of un-hydrated cement. The nano-aggregates most likely act as uncleation sites for the formation of hydration products, consequently have positive influence on the cementitious matrix. The result is a denser pore structure of the mortar matrix and enhanced mechanical properties