| In order to explore the influence of volcanic rocks and metakaolin (MK) on the cube compressive strength of ultra-high performance concrete (UHPC), the influence rules of volcanic rocks particle size and MK content are investigated. At the same time, SEM, XRD and TG microscopic analysis methods are used to reveal the influence mechanism of material microscopic morphology changes, phase composition, material composition and crystallinity of mineral composition on the compressive performance of UHPC. The results show that the mechanical locking effect structure formed by the holes of volcanic rocks and mortar can effectively improve the shear resistance of UHPC-volcanic rocks interface. In the range of 9.5-31.5 mm of volcanic rocks particle size, the cube compressive strength of UHPC increases with the increase of volcanic rocks particle size. When the MK content is less than or equal to 4%, the cube compressive strength of UHPC, the contents of CaCO3, calcium silicate hydrate (C-S-H) gel and vanadite (AFt) in UHPC increase with the increase of MK content. At the age of 28 d, compared with 1% of MK, the addition of 4% of MK increases the production of C-S-H gel and AFt in UHPC matrix by 24.82%. When the MK content is 4%, the crystallinities of CaCO3, C-S-H gel and AFt in UHPC are higher. MK can promote the crystallization of CaCO3 into a large amount of calcite, which can provide UHPC with higher strength. On the one hand, the addition of volcanic rocks coarse aggregate increases the crystallinity of CaCO3, on the other hand, it also makes CaCO3 crystal more stable. The crystallization of CaCO3 can be significantly promoted by the combined action of 4% of MK and volcanic rocks. |
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