The influence of polymers on the hydration of portland cement phases analyzed by soft X-ray transmission microscopy

The soft X-ray transmission microscope, which allows the in situ observation of wet samples of cement at normal pressures with high spatial resolutions (25 nm), was used to observe and compare the effects of two polymers — a water soluble polymer (HPMC — hydroxypropyl methylcellulose) and a latex EVA-poly(ethylene-co-vinyl acetate)] on the early hydration of C₃S and C₃A. These polymers are used to modify the properties of fresh and hardened mortars and concretes, especially when adhesive characteristics are required. The images show that the cellulose ether delays the hydration of the cementitious particles and promotes the formation of inner products rather than outer products. On the other hand, EVA particles agglomerate around the hydrating C₃S grains, and act as nucleation agents in the development of the composite microstructure. While HPMC slightly changed the aspect of C₃A hydration, EVA inhibited or even prevented the formation of ettringite crystals during the early stage of hydration, and resulted in a cloud of small, bright particles concentrated around the hydrating C₃A grains.