Effect of Metakaolin on Early Mechanical Property and Microstructure of High Fluidity Steel Fiber Reinforced Concrete

Abstract

Abstract: To improve the workability of the pumped concretes at early curing stage, which are normally used in driven cast-in-place piles, this paper investigated thefluidity, compressive and tensile strength, elastic modulus, destruction morphology and microstructure of high fluidity metakaolin (MK) and steel fiber (SF) concrete. Then, the effects of metakaolin and steel fiber on concrete properties were evaluated. The results show that the fluidity of the paste decreases with the increase of steel fiber or metakaolin respectively. As metakaolin contents increased, the increment of metakaolin dominates the fluidity of concrete, and the effect of steel fiber is not evident. The compressive strength, tensile strength and elastic modulus after 7 d curing increase with SF or metakaolin respectively, and metakaolin is the key factor effecting the strength of high fluidity MK-SF concretes. Whist the residual tensile strength and crack development are significantly dominates by steel fiber. From the scanning electronic microscope (SEM) images and X-ray diffraction (XRD) spectrogram, more stable hydrated calcium silicate (CSH) gel, monosulfide calcium sulphoaluminate hydrate (AFm) and polysulfide calcium sulphoaluminate hydrate (AFt) are produced by metakaolin addition. These products reduce the porosity and defects, and strengthen the bonding in interfacial transition zone. The metakaolin and steel fiber increase the viscosity of paste and the shear resistance of interfaces, which is essentially to hinder the relative movement of each component. Then, they have a coupling effect on reducing the fluidity of concrete. The mechanisms of metakaolin and steel fiber influencing the mechanical behavior of concretes are different. Generally, the steel fiber effects the cracking stage and the metakaolin influences the non-cracking stage in strain-stress curves.

Key words: metakaolin, steel fiber, high fluidity concrete, mechanical property, micromechanism

CLC Number:

TU528

YU Zihao, ZHANG Tongwei, CUI Kewang. Effect of Metakaolin on Early Mechanical Property and Microstructure of High Fluidity Steel Fiber Reinforced Concrete[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2021, 40(9): 2911-2920.

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