Preparation,performance And Modified Mechanism Of Repair And Protection Integrated Mortar For Structure Low-Carbon Repairing

Under the background of"carbon peak,carbon neutral",all industries should follow the"resource-saving and environment-friendly"development mode.Carbon emissions in the construction industry account for more than 10%of global CO₂emissions.The use of high-performance repair and protection materials to repair and protect existing damaged concrete structures in a timely manner can well extend their service life,avoid excessive or even repeated construction,reduce material waste,and achieve healthy and sustainable development of the industry.In this study,high-performance repair and protection integrated mortar for structural low-carbon repair is prepared,and the comprehensive performance of the new mortar and the realization mechanism of each external admixture to improve the repair and protection performance are systematically studied.（1）Two types of sulfur aluminate cements（SAC）and two types of tough fiber materials were combined to form four types of repair and protection mortars,and the flowability,setting time,flexural strength（f_t）,compressive strength（f_c）and bond strength（f_b）of these four types of mortars were compared and tested to determine an optimal combination of materials.Finally,crack-resistant fast-setting and fast-hardening high-belite sulfur aluminate cement（HBSAC）,and copper-plated short steel fibers（SF）were selected as the materials used in the subsequent study,respectively.（2）After the material types were determined,a set of 3-factor,3-level orthogonal test was designed to further optimize the material ratios of the SF-modified polymer repair protective mortar:the effects of the mass ratio of ordinary Portland cement（OPC）to HBSAC（OPC/HBSAC）,the amount of ethylene vinyl acetate（EVA）redispersible emulsion powder(w _EVA)and the amount of SF(V_SF)on the comprehensive performance of the mortar were investigated respectively.Through overall analysis and consideration of each performance,a group of fiber modified polymer repair and protection integrated mortar（SCPRM5）with the best overall performance was finally determined.Its flowability,setting time,f_t,f_c,f_b,90-d drying shrinkage,72-h water absorption,contact angle,chloride migration coefficient（λ）and the strength loss rate after 200 freeze-thaw cycles reach 226.0 mm,41 min/63 min（initial/final）,5.2/17.1 MPa（1 d/28 d）,16.7/73.2MPa（1 d/28 d）,3.61 MPa,16.44×10^-5,0.16%,70.04°,0.9486×10^-12m²·s^-1and 7.31%.Then,the mortar performance improvement mechanism was analyzed by microscopic morphological analysis,FTIR and XRD tests,and HBSAC can be rapidly hydrated to form calcium alumina（AFt）,which is also beneficial to the later hydration of mortar and improve the material compactness;EVA can not only fill the tiny pores inside the mortar,but also shape the hydration products,retard the hydration rate and reduce the degree of hydration;reasonable dosage SF can be used to effectively disperse the internal stress of the mortar to avoid stress concentration.（3）It was found that SCPRMs can be improved significantly by adding graphene oxide（GO）to SCPRMs,which can further enhance the toughness,strength and durability of SCPRMs,enabling the preparation of GOSCPRMs,a new material capable of repair and protection in more complex environments.It was found that SCPRM5mixed with 0.03 wt%GO has the best comprehensive performance improvement.The flowability,setting time,f_t,f_c,f_b,90-d drying shrinkage,72-h water absorption,contact angle,chloride migration coefficient（λ）and the strength loss rate after 200 freeze-thaw cycles are 192.0 mm,35 min/50 min（initial/final）,8.0/19.9 MPa（1 d/28 d）,21.3/79.3MPa（1 d/28 d）,4.93 MPa,10.51×10^-5,0.09%,80.96°,0.2322×10^-12m²·s^-1and 4.67%.Moreover,the study of the mechanism of GO-enhanced mortar revealed that GO not only plays nano-filling,nucleation and templating roles in the interfacial transition zone（ITZ）and pore structure inside the mortar,but also promotes the hydration of the cementitious material and optimized the hydration product distribution and densification.Minimal amounts of GO can further optimize the comprehensive performances of SCPRMs,making them more effective in the repair and protection of damaged structures.