Experimental Study On Rapid Repair Mortar For Concrete Structure Damage

In recent years,according to the development strategy of national marine power,our countries’marine economy has developed rapidly.The engineering application of marine concrete facilities such as breakwater,harbor wharf,sea crossing bridge and subsea tunnel become also more and more widely.Due to the long-term immersion of seawater,sulfate erosion,chloride ion penetration,dry wet cycle and other multiple factors,the durability problems such as concrete cracking and peeling and reinforcement corrosion are prominent,which seriously affects the long-term safe use of concrete infrastructure.In addition,the construction mileage of expressway and high-speed railway in China ranks first in the world.However,due to overload and frequent traffic accidents,pavement and pier are damaged to varying degrees,which seriously affects traffic safety.Because the repair work of the above concrete structures often faces the problems of poor environment,short working window time and difficult construction,it needs to be repaired quickly and timely.The traditional concrete repair mortar can not meet the construction requirements.Therefore,it is urgent to develop marine concrete rapid repair materials with high corrosion resistance,high bond strength and high durability.In view of the above background,a high performance repair mortar and high viscosity interface agent were prepared by using high belite sulphoaluminate cement（HBSAC）as cementitious material and high strength quartz sand as fine aggregate through composite polymer toughener（VAE）,polymer thickener（HPMC）,polypropylene fiber and specific additives,which has the characteristics of good bonding performance with the repaired materials,low shrinkage,impact resistance and high durability,and can be produced into ready mixed products,which is convenient for packaging,storage and stacking,so as to achieve the purpose of immediate use and rapid repair.Firstly,the effects of VAE and HPMC on the basic properties of HBSAC were studied,and then the applicability and suitable dosage of polymers were determined.Subsequently,the optimal mix proportion of repair mortar and interface agent was determined by orthogonal test.Finally,the durability of repaired mortar-concrete system was studied,and the following research results were obtained:（1）The two polymers can both significantly improve the water consumption of standard consistency,setting time,mortar fluidity and water retention rate of HBSAC.Of which,the influence of VAE on mortar fluidity is more obvious,when the content of VAE reaches 5%,the fluidity of mortar is increased by 29.8%;HPMC can significantly improve the setting time and water retention rate,the initial setting time is delayed by 6.5 min and the water retention ratio can reach more than 90%at 0.1%content of HPMC.Both polymers can reduce the flexural and compressive strength of mortar in general,and with the increase of polymer-cement ratio,VAE has greater damage to the strength;in contrast,polymer significantly enhance the bond strength of mortar,compared to control group of pure cement mortar,the bond strength of 5%VAE and 0.1%HPMC groups increased by 61.9%and 15.1%respectively.（2）The hydration heat,XRD,TG-DTG and SEM micro-test results show that the addition of polymer delayed the onset time of dissolution exothermic peak and AFt formation exothermic peak of HBSAC,but the total heat release of hydration in 48h is higher than that of pure cement;the diffraction peak of AFt in the hydration products of VAE-HBSAC at 3d and 28d is strengthened obviously but the diffraction peak strength of C₂S decreased;in HBSAC doped with polymer,the weight loss peak intensity of AFt,AH₃ and AFm increased,indicating that polymer promoted the formation of hydration products;VAE can form a network film on the surface of hydration products and refine the size of AFt crystals;HPMC can encapsulate more flocculent substances around the hydration products to reduce structural porosity and improve the compactness of cement stone.（3）The four-factor and four-level orthogonal test is used to study the effects of cement-sand ratio（C/S）,polymer-cement ratio（P/C）,fiber content(ω_xw)and sand type gradation（SA）on the mechanical properties of mortar,and the optimal combination of repair mortar is determined,the results show that the order of influence of various factors on flexural strength of mortar is C/S>P/C>ω_xw>SA,that on compressive strength is P/C>C/S>SA>ω_xw,and that on tensile bond strength is C/S>P/C>ω_xw>SA;the mix proportion of high performance repair mortar with excellent mechanical properties and strong adhesion determined by efficacy coefficient method is:C/S=1:1.25,P/C=2.5%,ω_xw=1kg/m³,the fine aggregate is 26-40mesh quartz sand,water reducing agent is 0.2%,defoamer is 0.1%,W/C=0.335.Similarly,the effects of water cement ratio（W/C）,OPC replacement rate(R_OPC),VAE content（VAE/C）and HPMC content（HPMC/C）on the bonding properties of the interfacial agent are studied by orthogonal test.Finally,it is concluded that the mix proportion of high adhesive interface agent is W/C=0.32,R_OPC=20%,VAE/C=7.5%,HPMC/C=0.15%,both water reducing agent and defoamer is 0.1%.（4）The durability test results of repair mortar-concrete system shows that the repair bond interface is the weak area of repairing mortar-concrete system,where freeze-thaw fracture,CO₂ and Cl^-penetration are more likely to occur;the incorporation of polymer and polypropylene fiber effectively improved durability such as the freeze-thraw resistance,carbonation resistance,anti-chloride ion permeability and shrinkage performance of repair mortar and repair interface;compared to the control group of pure cement mortar,after the addition of fiber+VAE+HPMC,the mass loss rate after100 freeze-thaw cycles decreased by 3.12%,the carbonation depth of the repair interface decreased by 7.3mm after 28d carbonation,the Cl^-penetration depth of the repair interface decreased by 5.9mm,and the shrinkage rate decreased by 77×10^-6;after precoating the interface agent on the surface of the substrate to be repaired,the durability of the repaired interface can be further improved.Taking the composite fiber+VAE+HPMC group as an example,compared with the group without interface agent,the bonding strength after 100 freeze-thaw cycles increased by 25.3%,the carbonation depth of the repaired interface after 28d decreased by 3.5mm,and the Cl^-penetration depth decreased by 10mm.