Effect of triethanolamine on cement paste exposed to external sulfate attack

Abstract

Triethanolamine (TEA) is a multifunctional organic additive, applied chiefly to a grinding aid and accelerator for cement. Its effect on cement paste in a sulfate-rich environment remains still unclear and elusive. In this paper, the expansion and mechanical performance of cement paste under external sulfate attack were measured. Thermodynamic model lent itself to estimate the correlation between triethanolamine and generated products content ahead of quantified phase analysis. The transformation of internal component was surveyed by multiple technologies of thermal gravimetric (TG), scanning electron microscope (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR), while inductively coupled plasma (ICP) was applied to investigate the evolution of interstitial ion concentration. Furthermore, the changes of pore structure over immersion time were separately figured and tabulated by virtue of mercury intrusion porosimetry (MIP). The above analysis shows that when cement paste suffers sulfate attack, triethanolamine intensifies the formation of calcite and exacerbates the decalcification of C-S-H, promoting a large quantity of insoluble precipitation including mirabilite of abundant crystalline water which accounts essentially for severe damage. Determined after comprehensive evaluation, the addition of TEA is conducive to the emergence of physical sulfate attack and an increment of the total porosity and permeability, contributing to an extension of microcracks and a more fragile structure, ultimately makes cement paste appear as a reduction in strength and stiffness.