Properties Of MC/NC/CS Modified Cement Paste At Ambient Temperature And After High Temperature Exposure

Micro-Calcium carbonate(MC),nano-Calcium carbonate(NC)and calcium silicate(CS),which could improve the pore structure of matrix by filling effect,and enhanced mechanical properties.Under the condition of high temperature and humid heat,the microstructure of the matrix was optimized through the filling effect and nucleation effect,and the high-temperature resistance was improved in a certain temperature range.Under the high temperature environment,micro-and nano-calcium could improve the high-temperature resistance of matrix with appropriate dosage in a certain temperature range.In order to focus on the influence mechanism of temperature and micro-and nano-calcium on cement paste,this paper adopted micro-and nano-calcium modified cement paste for experimental research.The main research contents and conclusions were summarized as follows:(1)The influence of different size and dosage of CS on the rheological property of cement paste was explored when the water-cement ratio was different.It was found that when the size of CS was smaller and the dosage was larger or when the water-cement ratio was lower,the yield stress and plastic viscosity of the mixture were larger.Because the smaller size of CS has a large specific surface area.The larger the dosage,the more obvious the adsorption of water on the mixture would be,and resulting in the change of the rheological properties.The decrease of the water-cement ratio,which would also affect the rheological properties of cement paste.(2)At room temperature,and the water cement ratio was 0.40,four kinds of CS(400,800,1250 and 3000 mesh)were mixed into the cement paste.When the CS(400,800,1250)content was not more than 10%,the compressive strength of CSP was improved.No matter what the dosage of CS3000 was,its compressive strength decreased.The flexural strength were increased to the maximum when the content was 20%.When the water cement ratio was0.35,CS had no obvious reinforcement effect on the compressive strength of the composites.When the water cement ratio was 0.30,and the content of CS(1250 and 3000)was 20%,the compressive strength of the matrix rise to the maximum.When CS content was less than 30%,and the flexural strength was increased with the increase of CS content.CS enhanced the compressive strength through filling effect and the flexural strength through bridging effect.(3)In high temperature environment,when the water-cement ratio was 0.40,0.35 and 0.30,and the content of CS3000 was no more than 10%,20% and 30%,respectively,the high temperature resistance of the composites could be improved before 600.The CS3000 could improve the high temperature resistance of the matrix to some extent when the content of CS3000 was 10%.Before 600℃,the compressive strength was always greater than that of the pure cement paste.CS1250 had no significant improvement effect on the high temperature performance of the composites.The CS3000 with smaller size could enhance the compressive strength through the filling effect,crystal nucleation effect and high temperature resistance.(4)At room temperature,the compressive strength of MC modified cement paste(MCP)was greater than that of pure cement paste(PCP),while that of NC modified cement paste(NCP)was slightly lower than that of PCP.The addition of NC with smaller particle size into the cement paste increased the interface defects between the materials,and resulting in a slight decrease in compressive strength of the sample instead of an increase trend.NC and MC could make the microstructure of composites more compact through filling effect.(5)When 3% NC or MC was added to cement paste,the compressive strength of NCP,MCP and PCP rise to the maximum at 600℃,500℃ and 400℃,respectively,and the specific compressive strength was 62.93 MPa,73.30 MPa and 57.05 MPa,respectively.NC and MC could improve the mechanical properties of the composites at high temperature by giving filling effect and nucleation effect in hot and humid environment.(6)Before 600℃,high temperature had no serious deterioration effect on the microstructure of NCP,MCP and CSP(3000).NC and MC with smaller size could make the microstructure of the matrix became more compact through the crystal nucleation effect and filling effect.CS3000 with a small size could also maintain a good microstructure before600℃ through filling effect,crystal nucleation effect,high temperature resistance and potential volcanic ash properties.After 600℃,the microstructure of the matrix deteriorated rapidly.