Effect of gypsum on low-heat Portland cement early mechanical properties and hydration in the presence of DEIPA

• Published in: Construction & building materials Vol. 449; p. 138477
• Main Authors: Yao, Guang, Wan, Hao, Tang, Guanbao, Gao, Xianshu, Zhang, Kunyue, Huang, Wen, Yu, Yang, Shen, Xin, Cui, Suping
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 25.10.2024
• Subjects: Diethanol-isopropanolamine; Gypsum; Hydration; Low-heat Portland cement; Mechanical properties; Synergistic effects; Gypsum; Mechanical properties; Synergistic effects; Hydration; Low-heat Portland cement; Diethanol-isopropanolamine
• ISSN: 0950-0618
• DOI: 10.1016/j.conbuildmat.2024.138477

Low-heat Portland cement (LHPC) is an environmentally friendly, low-carbon cementitious material. However, its limited early mechanical properties significantly restricts its applications. This work aimed to improve the early mechanical properties of LHPC through the synergistic effect of diethanol-isopropanolamine (DEIPA) and gypsum (CaSO4·2 H2O). The research investigated the effects of DEIPA and gypsum on the early mechanical properties, hydration kinetics, pore solution, hydration products, pore structure, and microstructure of LHPC. The results demonstrated that the addition of 0.03 % DEIPA alone (3D group) increased the compressive strength of LHPC at 1d but reduced the compressive strength at 3d and 7d. When 0.03 % DEIPA and 2 % gypsum (3D+2 G group) were co-added, the compressive strength of LHPC was significantly improved. The compressive strength of LHPC at 3d and 7d reached 23.0 MPa and 31.7 MPa, respectively, which were 8.49 % and 12.01 % higher than those of the reference group (REF group). When 0.03 % DEIPA and 3 % gypsum (3D+3 G group) were co-added, the compressive strength of LHPC at 3d and 7d increased to 23.5 MPa and 31.4 MPa, respectively, which were 10.85 % and 10.95 % higher than that of the REF group. After DEIPA and gypsum were co-added, the hydration shoulder peak of LHPC paste appeared later and broader compared with the 3D group, with a significant increase in cumulative heat release over 3d. At 3d and 7d of hydration, after co-adding DEIPA and gypsum, the amount of portlandite (CH) generated increased compared with the 3D group, the content of chemically bound water (CBW) significantly increased, and the degree of hydration significantly improved. The addition of gypsum further enhanced the effect of DEIPA on promoting the hydration of the ferrite phase (C4AF) in the LHPC paste. It alleviated the inhibitory effect of DEIPA on C3S hydration, accelerated the formation of hydration product monosulfoaluminate (AFm), optimized pore size distribution, and densified the microstructure, effectively improving the early mechanical properties of LHPC. This study provides a new approach to enhance the early reactivity of LHPC. •Co-addition of DEIPA and gypsum can effectively improve the early strength of LHPC.•Rising sulfate content enhances the effect of DEIPA in promoting C4AF hydration.•DEIPA and gypsum synergistically promote the formation of AFm.•Increased sulfate content alleviates the inhibitory effect of DEIPA on C3S hydration