Alkali-activated calcined clay blended cement: Effect of NaOH activator on performance of HPEG PCEs and on early strength

The effect of NaOH on dispersing performance of HPEG PCE superplasticizers and early strength was studied in a calcined clay (CC) blended cement (OPC:CC = 70:30 wt./wt.). Activator impact on workability and mechanical properties was investigated on mortar via fluidity and strength tests. The results revealed a time-dependent impact. At early ages (16 h - 3 d), the strength of the NaOH-activated OPC/CC blend exceeds that of OPC, while at longer curing times (> 3 d) it is similar to 30 % below that of OPC. Among the HPEG PCEs tested, the polymer possessing a medium long side chain (nEO = 50) performed best. Generally, NaOH addition prompted significantly increased PCE dosages. Heat flow calorimetry and in-situ XRD measurements suggest that NaOH promotes initial hydration of both OPC and CC, but later delays OPC reaction. Zeta potential measurements confirmed that NaOH significantly reduces the adsorbed amount of PCE on the binder, thus explaining higher dosage requirement.