To improve the dispersion performance of graphene oxide(GO)in the cement materials,nano SiO2 and CaCO3 powder were used as support of the GO and the SiO2-GO(SG)and SiO2-CaCO3-GO(SCG)were prepared.The effects of the SG and SCG on the mechanical strength,self-repairing performance,hydration products and microstructure of the cement materials were studied.The results show that the mechanical strength of the cement material is improved as the addition of SG and SCG,the flexural strength and compressive strength of the cement-based materials with SCG at 28 days are improved by 7.3%and 18.7%,respectively.The self-repairing performance of SCG composite cement is also improved which shows a higher compressive strength repairing rate of about 110.6%and a higher water permeability repairing rate of 100%.The crack area testing shows that SCG has a more significant repair effect on cracks in the cement materials.XRD analysis shows that the early stage cement hydra-tion is accelerated as the addition of SG and SCG,especially for the SCG,the hydration degree at 3 days is obviously improved.TG analysis shows that with the extension of hydration age,a higher reaction degree of Ca(OH)2 and SiO2 is achieved in the SCG composite cement,compared with the early 3 days hydration stage,the Ca(OH)2 content of SCG composite cement at 28 days reduces to 14.90%.Microstructure analysis shows that the SCG has better com-patibility with the cement,more hydrate calcium silicate(C-S-H)gels in the late hydration stage is generated and the microcracks of cement could be filled,which makes the excellent self-repairing performance of the SCG composite cement.
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