Study On Progressive Failure Charateristics And Repair Features Of Microencapsulated Self-healing Cement-based Materials

Solution of tensile cracking has been the main subject of concrete durability research.However,traditional repair methods have limits such as low repair efficiency and environment pollution.Thus,microencapsulated self-healing system based on bionic self-healing technology has gradually become an emerging research.In this paper,the conventional uniaxial compression test and MIP(Mercury Intrusion Porosimetry)test are conducted to study the progressive failure characteristics and energy mechanism of microencapsulated self-healing cement-based materials.The mechanical properties and microstructure repair efficiencies of cement-based materials were analyzed by the vibration of influence factors(the dosage of microcapsules,the pre-stressing level and the cure age).The relationship model between macro-mechanical properties and microstructure was established.Finally,the gray correlation between influence factors and their repair efficiency were studied.They were achieved the following research results as:(1)The mechanical parameters(the UCS,peak strain and elastic modulus)of the cement-based materials are significantly affected by microcapsules:In the initial state,the UCS and elastic modulus decreased with the increase of the dosage of microcapsules,which shows a negative hybrid effect;the peak strain increased accordingly showing a positive correlation.However,after pre-compression,the UCS and elastic modulus decreased further with the increase of the dosages,and the peak strain still maintained an increasing trend.The effects of pre-compression on the mechanical parameters are similar to the dosage of microcapsules,but its effect is higher than the dosage.Instead,the repair rate of the peak strain decreased with the increase in the dosages of microcapsules.The UCS and elastic modulus showed inversely.It indicates that the repair agent was released from the ruptured microcapsules by the pre-compression to fill the defects in cement improving the stiffness of the material.(2)The energy distribution of microencapsulated self-healing cement-based materials under uniaxial load was analyzed.BIM and Up were introduced to analyze the energy evolution law during the deformation process.After repair,BIM and Up were both smaller than the damage state and the initial state at the 3d age.Farthermore,there were obvious time phases in the repair cycle.BIM and Up have the same trend,which proves that it is feasible that the BIM can reflect the effect of variation of the dosage and the pre-stressing level on the degree of plastic deformation.The σci and σcd were determined based on the two inflection points of the"N" type evolution of BIM during progressive failure.Increasing the dosages and the pre-stressing level can increase the σci and σcd,which are more than pure cement material(3)The repair rate and recovery rate of the pore structure parameters were defined to evaluate the repair effect on the pore structure of the cement.the models related to the parameters and their repair rate and recovery rate were established based on the dosage and pre-stressing level.The models can be linked with the repair rate and recovery rate of mechanical parameters to establish the repair relationship model between macro-mechanical properties and micro-pore structure.The ideal repair rate and recovery rate was obtained eventually.(4)According to the gray theory,an GM(1,N)model among the influence factors,pore structure,and mechanical properties was established to quantitatively analyze the effect and mechanism of the microencapsulated self-healing system.The GM(1,N)model related to the repair rate of the UCS and peak strain is consistent with the gray correlation degree.In accordance with the prediction of the influence weight coefficient,it is concluded that the repair rate of the UCS and peak strain will keep increasing as the dosages of microcapsule and cure age;the increase of pre-stressing level will restrain the growth of the repair rates.and the porosity,average pore size and strain repair rate have the same grey correlation degree.