In this paper,the influence of the dosage of calcined diatomite on the autogenous and drying shrinkage of ultra-high performance concrete(UHPC)was investigated by using calcined diato-maceous as a partial replacement for cement in the preparation of UHPC.The influence mechanism of calcined diatomite on the shrinkage performance of UHPC was explained by internal relative humidity,mercury intrusion method and microstructure.The results showed that calcined diatomite,which has porous structure and effective internal curing function,can absorb free water during the slurry mixing process and subsequently release it during the early stages of cement hydration.XRD of calcined diatomite with the increase of calcined diatomite content(0 to 15%,mass fraction),the compressive strength of UHPC in the early stage decreased slightly,and the compressive strength of UHPC in the later stage did not change much.The relative humidity inside the slurry gradually increased,the pores of 10 to 50 nm and less than 100 nm gradually decreased,and the autogenous shrinkage and drying shrinkage of UHPC gradually decreased.When the content of calcined diatomite is 15%,the autoge-nous shrinkage and drying shrinkage are the lowest.Compared with UHPC without calcined diatomite,the 7 d autogenous shrinkage value of UHPC with 15%calcined diatomite decreased by 27.0%,and the 90 d drying shrinkage decreased by 31.0%.
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