Scanning electron micrographs and their interpretation in the context of a theory proposed for the hardening behaviour of cementitious materials

The results of scanning electron micrographs (SEM) obtained from samples of Pulverised Fuel Ash (PFA)-lime, PFA-lime-gypsum and PFA-cement mixtures subjected to various curing times are presented and interpreted in the context of a mechanism previously developed for the hardening behaviour of cementitious materials. Additionally energy dispersive X-ray analysis (EDAX) has also been carried out on the same samples. The micrographs suggest that the strength of the materials increase with time, partly as a result of the growth of cementitious materials in places where PFA particles are in contact with each other, and partly due to the needle-like growths which eventually link the PFA particles. Using EDAX it is found that when the beam of electrons is focused on the cementitious material a higher proportion of aluminium, potassium and silicon ions is found compared with that in a more overall field of view. The results suggest that the rate of hardening of these materials would be, in ascending order, PFA-lime, PFA-lime gypsum and PFA-cement.