This study investigates the structural evolution of the blended cement pastes at micro-, nano-, and atomic-scale due to environmental factors, such as, water leaching, ageing and curing temperature, with the aid of the analytical techniques, i.e. thermal analysis, XRD, SEM, TEM and SS MAS NMR.
The water leaching experiments are performed on the one year old WPC cement paste blended with 30% PFA, as well as 13 years old WPC cement paste blended with 30% and 50% PFA. It is observed that the water leaching induces the phase dissolution and precipitation, e.g. CH, anhydrous cement, AFm and TAH dissolution, C-S-H secondary formation and decalcification, AFt secondary formation and dissolution. The microstructure of the cement paste changes from compact feature to dry cracked land like feature. The Op C-S-H transfers from fine fibrillar or foil-like feature to three dimensional net like feature, and the porosity of Ip C-S-H has increased. The aluminosilicate structure changes from single chain to double chain as the chains have cross-linked across the interlayer. It is also observed with higher replacement of PFA, the leaching speed is slower. Additionally, it is observed the chemical composition, the micro- and nano-scale structure evolve with ageing.
The effects of curing temperature on OPC:BFS blended cement hydration is studied. It is found that as curing temperature increases: the general microstructure of the cement paste becomes more porous; more slag reacts, and more Ip C-S-H with high Al and Mg forms; and the MCL of aluminosilicate anion chain increases.
For comparison, synthetic C-A-S-H is also characterized to better understand the structure of the C-A-S-H in the cement paste, especially the atomic-scale structure.
