Microstructure and composition of fly ash and ground granulated blast furnace slag cement pastes in 42-month cured samples

Microstructure and composition of 42-month cured pastes using Portland cement (OPC), fly-ash cement (FAC), and ground-granulated-blast-furnace-slag cement (GGBFSC) were investigated. The granular structure of C-A-S-H in outer products of GGBFSC and FAC pastes was finer than in OPC paste. Fly ash offered higher capacity in increasing the Si/Ca ratio of C-A-S-H than slag in the pastes. However, their effects on the chain length were opposite. The incorporation of aluminum into silicate anions in GGBFSC paste was greater compared to others. AlO45− played an essential role in bridging the shorter silicate anions together, forming a longer chain of aluminosilicate anions in the pastes. Mg-Al layered-double hydroxide (LDH) was abundant in the inner products of slag particles with the interbedding of TAH, leading to a low ratio of Mg/Al ratio on hydrotalcite-like phase.