Dosage-dependent effects of DElPA on hydration and strength development of Low-heat Portland cement

Based on the problem of slow early strength development of low-heat Portland cement (LHPC), the effects of various dosages (especially ultra-low dose) of diethanol-isopropanolamine (DEIPA) on the hydration and mechanical properties of LHPC were investigated in this study. Results showed that the effect of DEIPA dosage on strength exhibited a nonlinear relationship, specifically manifested as: trace DEIPA (0.0075%) enhanced the compressive strength of LHPC at all selected age before 28d, specially, increased the 3d compressive strength by 10.5% with increasing in heat releases by 2%. Conversely, low DEIPA additions (0.03%-0.09%) reduced 1d and 3d strength but significantly increased 28d strength. 0.0075% DEIPA accelerated C ₄ AF hydration and enhanced the kinetic for silicate hydrates growth, thus improving the early hydration of the LHPC to enhance the compressive strength. However, 0.03%-0.09% DEIPA additions initially impended early strength development, possibly due to increased supersaturation indices required for C-S-H and CH nucleation, but resulted in reacceleration of silicates hydration at later stage to enhance the 28d compressive strength. Correlations of compressive strength with the LHPC hydration process and pore structures were established. It is confirmed that synergistic hydration of C ₄ AF and silicates resulted in the pore structure refinement and strength enhancement. Furthermore, the AFt-to-AFm conversion, amorphous or microcrystalline CH formation were triggered by DEIPA additions, which also affect the strength development of the LHPC. These findings offer valuable theoretical insights for regulating the strength development of LHPC.