Study On The Properties And Mechanism Of UHPC Shrinkage Regulation By Internal Curing And Expansion Agent

Ultra-high strength concrete(UHPC)is an engineering material with high mechanical strength and excellent performance,which is an important research direction for cement-based materials.However,the low water ratio and high admixture of UHPC are characteristics that ensure high strength,but also cause low hydration and high shrinkage,which tend to crack and is a serious challenge for engineering applications.In order to reduce the risk of cracking and promote the application of UHPC,specifically,in this paper,perforated cenospheres(PCs)and expansion agent(HME)were introduced to regulate UHPC performance.And the effect of different amounts of PCs with HME on the shrinkage and mechanical properties of UHPC are investigate.Meanwhile,this paper studied the hydration regulation of UHPC cementitious materials by isothermal calorimetry,XRD,TGA,BSE,BET and SEM,characterized the UHPC hydration products and microstructure,and revealed the hydration characteristics of UHPC.Finally,the UHPC enhancement process with internal curing and expansion agent regulation is developed to provide a significant way of theoretical basis for its development and application.The specific research findings are as follows.(1)As an internally cured materials,saturated PCs effectively regulate the mechanical,self-shrinkage and hydration process of UHPC.Saturated PCs can significantly reduce the self-shrinkage of UHPC by up to 45.5%.When the IC water-cement ratio of 0.03(UC3),at this time,UHPC mortar has a high compressive strength 7 days and 28 days increased by 4.15% and 5.14% respectively,overcoming the problem of high shrinkage reduction rate and low strength in the traditional internal curing materials.The curing within saturated PCs accelerates the hydration of UHPC increases the peak and total amount of UHPC hydration heat,and makes the peak of hydration heat appear earlier.In addition,the degree of hydration of the matrix was improved,significantly increasing the content of the major hydration product CH,while the SEM-BSE images were combined to reveal smaller particles of anhydrate cement around the internal curing agent.(2)As an expansion agent,with different mixing of HME(3%、4% and 5%)effectively regulate the mechanical,self-shrinkage and hydration process of UHPC.Expansion products produced by the hydration of HME,such as calcium alumina and CH,effectively,filled the porosity in the UHPC and produce expansion stresses to make up for shrinkage stresses.HME effectively regulate the performance of UHPC when the amount of admixture was 5%,the auto-shrinkage of UHPC was only 21.29% compared with the control group.Although the shrinkage reduction effect was excellent additionally,the addition of HME slowed the hydration of the cement and affected the mechanical strength of UHPC,which was only 89.6 MPa at 28 days.(3)The compound of the two materials showed an excellent compatibility "superposition" effect,showing a mechanical strength similar as the control group at 28 days.Furthermore,at about 96 h,the curve showed a slight expansion of 55.53 με,which reduced or cancelled the auto-shrinkage problem of UHPC.The presence of saturated PCs primarily influences the degree of hydration,leading to improved hydration of UHPC and remove the negative impact of HME on the heat of hydration.Furthermore,the release of internal curing water accelerated the hydration of HME,resulting in the production of CH and calcium aluminate that can efficiently fill the pores.Pores with diameters greater than 50 nm are reduced by 64.06%,56.68%,and59.9%,respectively.Eventually,achieving the expected effect of UHPC performance regulation.Figure 33 Table 13 References 157...