Effects of triethanolamine on autogenous shrinkage and drying shrinkage of cement mortar

Abstract

Impacts of triethanolamine (TEA) on autogenous shrinkage, drying shrinkage and strength development of cement mortars were investigated. Hydration kinetics, pore structure and microstructure of hardened cement pastes (hcps) incorporated with TEA were systematically analyzed to reveal the working mechanism of TEA. Results show that TEA at dosages of 0.05%, 0.10% and 0.50% by weight of cement increases the autogenous shrinkage of cement mortars at 7d, which is mainly resulted from the promoting effect of TEA on the secondary hydration of aluminate phases (C3A and C4AF) and inhibiting effect on the hydration of the silicate phase (C3S) especially at 0.50% dosage. The morphology change of CH in the presence of TEA may also accelerate the development of autogenous shrinkage. In addition, TEA has no obvious effect on the drying shrinkage of cement mortars due to the similar moisture diffusion trends of cement mortars with and without TEA from 7d to 56d. Moreover, 0.05% and 0.10% TEA enhance the early strength of cement mortars while 0.50% TEA leads to an opposite effect. However, 0.05%, 0.10% and 0.50% TEA reduce the late strength at 28d and 56d. Pore structures are not responsible for the strength reduction, as indicated from the MIP and DVS results. Therefore, it is believed that strength reduction may be resulted from the incorporation of CH microcrystals into C-S-H structures.