Influence of new compound admixture on shotcrete performance

Abstract

To analyze the influence of new compound admixture on shotcrete performance, the ordinary Portland cement pr425 was used as matrix components. The optimum proportion of admixture was obtained by analyzing the influence of content on cement setting time and compressive strength. The microstructure of cement test block and the mechanism of reducing dust of composite macromolecule admixture were analyzed by scanning electron microscopy and infrared spectroscopy. It was shown that the ratio of polyacrylic acid was 0.02%. The ratio of J85 accelerator was 5%. The ratio of bentonite was 4.5% in composite admixture. The most optimal content of admixture in the slurry was 7%. The compound coagulant formed by additive together with C₃A, C₄AF which provided nucleation for hydration and crystallization of C₃S and C₃S, and played an active role to promote the activity of the mineral admixture in cement, and increased the elastic modulus of C-S-H gel and accelerated the hydration process of portland cement. Bentonite and polyacrylic acid promote the wettability, cohesiveness and workability of cement paste in the process of hydration. The formation of cement test block gel was even. The interface between the matrix phase and the aggregate phase was not obvious which ensured the matching between the matrix and the aggregate phase. The addition of bentonite formed hydrogen bonds in cement paste and improved the cohesiveness of the system. The J-85 accelerator promoted the combination of aluminate and gypsum which hindered the formation of calcium carbide around the cement particles which made cement rapid condensation. Polyacrylic acid mainly changed the strength of hydroxyl absorption peak in cement paste to improve the initial strength of cement test block. The addition of new admixtures promoted the process of cement hydration to be more thorough and affected the later strength development of concrete by affecting the formation of calcium carbonate stone.

Keywords

shotcrete / compound admixture / optimum proportion / microstructure / hydration

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