Lithium salt-based additives for early strength-enhancement of ordinary Portland cement-high alumina cement paste

摘要

Mixtures of ordinary Portland cement (OPC)/high alumina cement (HAC) are very attractive for rapid repairs because of their quick-setting characteristics [1-3]. However, poor strength development and sulphate resistance at later ages limits their application, especially in load-bearing structural repairs. Previous investigations of the hydration behaviour of an 80%OPC-20%HAC paste using conduction calorimetry [4-5] indicated that formation of ettringite and delay of OPC hydration in the mixture occurred, resulting in poor strength development. It is known that lithium salt-based additives cause rapid setting and hardening of high alumina cement (HAC) and contribute to very early strength [6-8]. This phenomenon is attributed to the formation of lithium hydrometa-aluminate (LiH(A102)2'5H20) precipitate which acts as a heterogeneous nucleation substrate and promotes the nucleation of calcium aluminate hydrates [8]. In this letter it is shown that lithium salt-based additives enhance the strength of OPC/HAC paste, alter the OPC/HAC setting mechanism and accelerate the OPC hydration process in OPC/HAC systems. This result provides useful information relevant to the formulation of OPC/ HAC rapid-setting repair materials.