Modified Zeolite To Improve Rheological Properties And Shrinkage Performance Of Cement-based Materials

With great plasticity,high strength,good durability,traditional cement-based materials have been widely used in the construction field,especially in the high-rise building structure,largespan bridge structure,etc.However,due to the large amount of cement and insufficient curing,high shrinkage and poor volume stability have been founded in cement-based materials.Cracking caused by differential shrinkage has become a common problem of cement-based materials.Therefore,it is of great importance to explore the shrinkage mechanism of the cement-based materials.Relying on the internal curing agent,the internal curing method with high efficiency and low cost is a method of self-curing inside the cement-based materials.Zeolite,the represented internal curing agent,has the characteristics that the porous structure is able to trap water,which can not only improve the shrinkage performance of the cement-base materials,but also keep the strength basically stable.However,the addition of zeolite reduces the early working ability of the cement-base materials.Hence,by modifying its porous structure,this study aims at exploring the influence of natural/modified zeolite on the rheology of cementbase materials,and the shrinkage regulation effect of natural/modified zeolite on cement-base materials is obtained.In terms of high-temperature calcination,the calcination modification of 100℃ was not obvious.Above 500℃,the coarsening effect of pore with diameter of 1-35 nm enhanced,which increased pore volume distribution of 35-80 nm and decreasing the specific surface area.Thanks to the pore structure was optimized and specific surface area decreased,rheological tests results demonstrated that zeolite calcinated above 500℃ helps to improve the negative effects of zeolite on the rheology of cement-based materials.Consequently,it was found that the incorporation of natural zeolite effectively is able to mitigate shrinkage of cement-based materials,and calcination at 500℃ or 700℃ optimized the pore structure of the zeolite,which had a better significant effect on the shrinkage regulation.As for acid solution immersion modification,the pore volume with diameter of 1-80 nm and specific surface area increased.To be noticed,pore volume distribution of 1-35 nm is dramatically increased after immersion in 1.0 mol/L acid solution.Results showed that prewet zeolite have negative effect on the rheological properties of cement-based materials,while zeolite modified by 0.5 mol/L acid solution improved the rheological properties.By comparing the change of hydrothermal rate curve and microstructure analysis,the influence mechanism of acid-treated zeolite on compressive strength and shrinkage performance of cement-based materials was obtained.Although the addition of zeolite modified by 0.5 mol/L acid solution reduced the compressive strength of cement-based materials,the shrinkage strain decreased by up to 50%.