Influence of sepiolite fiber on the performance of cement-based grouting material for earth-rock DAMS remediation

Abstract To improve the early strength and flexural strength of the cement-based grouting material used for anti-seepage grouting projects for earth-rock dam, a sepiolite fiber reinforced cement-based grouting material was prepared, using fly ash, ultra-fine silica fume, bentonite, accelerating agent and water-reducing agent as admixture. The effects of the sepiolite content, fiber length, and the addition of ultra-fine silica fume and fly ash on the viscosity, bleeding rate, setting time, compressive strength, and flexural strength of the composite grouting materials were investigated. Compared with the reference sample, the bleeding rate of the slurry, under the optimal condition (fiber: 5% long fibers, silica fume: 9.5%, and fly ash: 9.5%), decreased by 6.6%, and the initial setting time and final setting time were shortened by 29.1% and 33.0%, respectively. The addition of sepiolite fibers also significantly improved the consolidation strength. The best mechanical property was obtained with the addition of 4% long fibers. At 3 d age, the bending strength and compressive strength of the test block increased by 146.7% (3.7 MPa) and 55.3% (19.3 MPa), respectively, compared with the reference sample. At 28 d age, the flexural and compressive strength of the test block increased by 87.8% (7.7 MPa) and 42.6% (40.6 MPa), respectively. The influence of the contents of sepiolite fibers, ultra-fine silica fume and fly ash on the early strength performance was studied using the response surface analysis method. The highest early strength of the test block was obtained under the mixing formula (fiber: 4.21%, silica fume: 14.0%, and fly ash: 10.19%). An investigation into the structure and micro-morphology indicates that sepiolite fibers not only play a bridging role among various cement hydration products but accelerate the hydration and bonding process of cement mixtures. The fiber-reinforced composite structure can effectively prevent the growth of microcracks and significantly enhance early strength.