Improvement of mechanical properties and carbonation durability of recycled fine aggregate engineered cementitious composites for structural strengthening

Abstract

External wrapping with engineered cementitious composite (ECC) extends the service life of concrete structures after reinforcement corrosion, but the low economics of this strengthening measure limits its application. In this study, recycled fine aggregate engineered cementitious composite (RFA-ECC) for structural strengthening was prepared using recycled fine aggregate (RFA) as a 100% replacement for natural fine aggregate (NFA). The effects of fiber and fly ash on the mechanical properties of RFA-ECC were investigated for component optimization design. Additionally, the carbonation durability of RFA-ECC with initial crack damage was investigated by a preloaded carbonation test, and a carbonation model of RFA-ECC was established. The results demonstrated that the compressive strength of ECC decreased by 13.75% when RFA replaced NFA completely, but the flexural strength was still as high as 7.2 MPa. The self-cementing ability of RFA densifies the matrix microstructure, thereby enhancing the fiber bridging stress capacity. The tensile strength of RFA-ECC reached 2.5 MPa at 2% fiber volume fraction, which was 5.77% higher than that of natural ECC. The increased fly ash content enhanced the matrix strain capacity, but the tensile strength decreased significantly. The economic analysis indicates that RFA-ECC, with a 1.5% fiber volume fraction and 40% fly ash content, meets the performance requirements while offering a cost-saving of 15.4%.