Study on the curing performance and microscopic action mechanism of OPC-MCA curing agent on shield waste muck
A new shield waste muck modification material,OPC-MCA,was prepared by adding ground granulated blast-furnace slag(GGBS),fuel gas desulfurization gypsum(FGDG),calcium aluminate powder,quicklime,and alum to ordinary Portland cement P.O42.5(OPC).Firstly,the optimal ratio of each raw material in OPC-MCA was determined through orthogonal experiments.Then,the shield waste muck generated from the Chengnan Cross-river Tunnel Project in Wuhu City was treated with OPC-MCA and OPC at various dosages ranging from 10%to 40%,and the compressive strength at different curing times(3,7 and 28 d)was tested.Furthermore,the microstructure,pore and crack characteristics,and mineral composition of the solidified waste muck specimens were observed and analyzed using scanning electron microscope(SEM),industrial CT system,and X-ray diffraction(XRD).The results show that the optimal material ratio of OPC-MCA is 51%OPC,32%GGBS,8%FGDG,5%calcium aluminate powder,3%quicklime,and 1%alum.OPC-MCA exhibits stronger curing ability on the Wuhu shield waste muck compared to OPC,especially at low dosages.The increase in dosage and curing time results in higher strength and brittleness of the specimens,and some specimens exhibit tensile failure.Calcium aluminium silicate hydrate(C-A-S-H)and monosulfate(AFm),which are not detected in the OPC cured specimens,are detected in the OPC-MCA cured specimens,and the ettringite(AFt)content is also higher.Under the same dosage,the proportion of larger-sized pores as well as the total volume of pores in OPC-MCA cured specimens are smaller than those in OPC cured specimens.
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