Durability of Recycled Aggregate Concrete Subjected to High Concentration Mg2+-SO42--Cl- Compound Salts
WANG Jiabin1,2,3,*, HOU Zeyu1,3, ZHANG Kaifeng4, LI Heng1
1 Civil & Architecture Engineering,Xi'an Technological University, Xi'an 710021, China 2 State Key Laboratory of Green Building in Western China, Xi'an University of Architecture and Technology,Xi'an 710055, China 3 Xi'an Key Laboratory of Civil Engineering Testing and Destruction Analysis on Military-Civil Dual Use Technology, Xi'an Technological University,Xi'an 710021, China 4 China West Construction North Co., Ltd., Xi'an 710065, China
Abstract: In Northwest China, the soil and the underground water contains high concentration corrosion ions of magnesium, sulfate and chloride, which has negative influence on the durability of in-service concrete structure and hinders the recycled aggregate concrete (RAC) application in modern structural engineering. Based on the characteristics of environment and durability corrosion factors in Northwest China, the durability experiment of RAC subjected with high concentration compound salt solution of 7.5%MgSO4-7.5%Na2SO4-5%NaCl was carried out by using drying & wetting cycles (D&W) method. For the durability indexes of the relative elastic dynamic modulus, weight change ratio, relative compressive and splitting tensile strength, and damage depth, the durability degradation law and the influence factors were researched. In addition, the durability degradation process was suggested through analyzing the mineral phases composition and microstructure of damaged RAC with XRD, FTIR, TG-DSG and SEM-EDX. Brucite, anhydrite, ettringite and Friedel's salt filled in pores of RAC what reduced the chemical corrosion rate. Correspondingly, the durability of RAC showed a temporary improvement and/or relatively stable state. Afterword, ettringite, Friedel's salt and C-S-H decomposed, and the non-gelling corrosion product of M-S-H and expansive physical salt crystallization of Na2SO4 and others formed, which damaged the microstructure of RAC, caused durability rapidly decreased. The durability degradation process was divided into three phases of false performance improvement, performance stabilization and performance deterioration. The physical and mechanical properties of damaged RAC were obviously related to the combination of supplementary cementitious materials (SCM). The ions attack resistance of RAC with multiple CMS was great higher than that of RAC with two types of SCMs. The RAC with 10% fly ash, 10% silica fume and 10% metakaolin had the best durability, while that of RAC with 10%fly ash and 20% silica fume was the worst.
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2022, Vol. 36 
