Difference in the reaction process of slag activated by waterglass solution and NaOH solution

Abstract The reaction processes of waterglass‐activated slag (WAS) and NaOH‐activated slag (NAS) with a high liquid‐to‐solid ratio were observed by using in‐situ polarization microscope. During these processes, the phase evolution in the alkali‐activated slag (AAS) was analyzed non‐destructively by means of X‐ray diffraction and scanning electron microscope (SEM). In parallel, hardened pastes of AAS were prepared and investigated by means of SEM and mercury intrusion porosimetry. The results showed that the reaction of NAS was dissolution‐precipitation process at the early age, and the reaction products tended to form around or on the surface of slag particles. A few kinds of intermediate products, such as Ca[OH] 2 , were formed at the beginning. At the later age, the reaction mechanism of NAS changed into solid‐phase reaction, and the reaction products tended to generate in the space that originally occupied by the slag particles. In comparison, the whole process of the reaction between waterglass and slag was dissolution‐precipitation under the condition of a high liquid‐to‐solid ratio. The reaction products tended to form in the solution, which was beneficial for pore‐filling. The aforementioned difference in reaction process made the hardened paste of NAS had a higher porosity and a lower early strength than the hardened paste of WAS.