Experimental Study on Durability Degradation of Recycled Aggregate Concrete by Compound Salt Corrosion

Abstract

Abstract: There are a great number of corrosion ions in the soil and groundwater of Northwest China, which causing rapid degradation of durability of recycled aggregate concrete structures severely limit the application of recycled aggregate concrete in modern concrete structures. Based on the composition of corrosive ions and the characteristics of regional climate and environment in the durability environment of Northwest China, the experiment of durability degradation of recycled aggregate concrete subjected to compound salts was carried out by dry-wet cycles method with 7.5% (mass fraction) MgSO₄-7.5% (mass fraction) Na₂SO₄-5% (mass fraction) NaCl as the corrosive medium. The effects of mineral admixtures on durability of recycled aggregate concrete were studied by using active mineral admixtures such as fly ash, slag, silica fume and metakaolin instead of cement. And then, the mineral composition and relative content of mineral phases, and microstructures of corrosion products were characterized by XRD, FTIR, TG-DSC, SEM and EDS, respectively. In addition, the durability degradation process of recycled aggregate concrete was suggested. As the dry-wet cycles increase, the relative dynamic elastic modulus, mass change rate, relative compressive strength, relative splitting tensile strength, and damage depth are significantly related to the collocation of mineral admixtures. With the corrosion ions diffusing into concrete, the alkalinity of concrete decreases and the dense corrosion layers with brucite, gypsum and ettringite as the mainly corrosion products are successively formed on the surface of concrete, which temporarily hinders the further diffusion of corrosion ions. With the continuous accumulation of corrosion products and the formation of non-gelling products, the surface of recycled aggregate concrete is spalled and cracked under the combined action of expansion stress and salt crystallization pressure. The durability of recycled aggregate concrete is rapidly degraded.

Key words: recycled aggregate concrete, durability, compound salt corrosion, dry-wet cycle, mineral admixture, degradation mechanism

CLC Number:

TU528.44

HOU Zeyu, WANG Jiabin, GUO Qingjun, LI Heng, ZHANG Kaifeng. Experimental Study on Durability Degradation of Recycled Aggregate Concrete by Compound Salt Corrosion[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2021, 40(11): 3617-3626.

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