Effects of combined admixtures on properties of ultrafine cement grouting materials and fitting characterization of water absorption

Abstract

Due to their larger particle size, traditional ordinary silicate grouting materials cannot be effectively injected into the cracks of tunnel rock, resulting in suboptimal grouting performance. In this study, orthogonal experiments were conducted to systematically investigate the effects of fly ash (FA), sulphate aluminium cement (SAC), and nano-calcium carbonate (Nano-CaCO 3 ) on the fluidity, setting time, compressive and flexural strength, and impermeability of ultrafine cement. At the same time, the effects of phase composition and microstructure following cement reaction were elucidated using X-ray diffraction (XRD) and scanning electron microscopy (SEM), and a theoretical formula for "water absorption mass - time" was established using nuclear magnetic resonance (NMR). To develop modified ultrafine cement grouting materials that feature high fluidity, fast-setting, early strength, and high impermeability. The results of the study indicate that: (1) It revealed the patterns of how the dosage of three types of admixtures affects fluidity, setting time, compressive strength, flexural strength, and impermeability. (2) Among the nine formulations investigated and according to the adopted comprehensive evaluation criteria, the combination containing 10% FA, 10% SAC, and 1% Nano-CaCO 3 exhibited the best overall performance. (3) When used at appropriate content, these three admixtures can significantly promote cement hydration reaction, resulting in a denser microstructure of the hardened cement paste. (4) A formula relating water absorption to pore structure was established, which not only reveals the influence of pore structure on water absorption but also serves as a new characterization method to verify the effectiveness of three admixtures in improving the pore structure of the matrix.