Mechanical properties of concrete using MICP modified recycled concrete aggregates

Chao-Wei Tang, How-Ji Chen and Yun-Chih Lu

Abstract

With the sharp reduction of natural resources and the surge of construction and demolition waste, recycled concrete aggregate (RCA), which uses waste concrete as the source of aggregate, has emerged. It aims to replace natural aggregate (NA) for the production of recycled aggregate concrete (RAC). However, compared to NA, the performance of RCA is relatively poor. These differences are mainly due to the adhered mortar (AM) on the RCA surface. RCA modification methods can be roughly divided into two categories: removal of attached mortar and strengthening attached mortar. However, these two modification methods still have shortcomings. In contrast, microbiologically induced calcium carbonate precipitation (MICP) has naturally become a hot spot in research on the modification of regenerated aggregate (RA). Because of its environmentally friendly characteristics. To ensure the high quality of RAC, appropriate modifications must be made for RCA. This study applied MICP technology to improve the properties of recycled concrete aggregate (RCA). We analyzed the physical properties and microscopic characteristics of three types of RCA before and after modification to ensure that these RCAs' basic properties meet the requirements of engineering applications. The test results showed that the originally loose interfacial transition zones (ITZ) of RCA became quite dense due to the intensive filling of the products produced by MICP, thus improving its physical and mechanical properties. The 24-hour water absorption rates of the three RCAs were significantly reduced after modification. The one with the best effect was reduced by 27.8%. In addition, the best results for dry specific gravity increased by 26.7%, and the best results for dry rodded unit weight increased by 5.2%. Moreover, compared with recycled aggregate concrete (RAC) using unmodified RCA, the compressive strength and splitting strength of RAC using MICP-modified RCA increased by 7.0% and 6.9%, respectively. This result indicated that applying MICP technology to strengthen the properties of RCA could ensure the mechanical properties of RAC.

Key Words

biomineralization; compressive strength; recycled aggregate concrete; recycled concrete aggregate

Address

Chao-Wei Tang: 1) Department of Civil Engineering and Geomatics, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan (R.O.C.), 2) Center for Environmental Toxin and Emerging-Contaminant Research, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan (R.O.C.), 3) Super Micro Mass Research and Technology Center, Cheng Shiu University, No. 840, Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan (R.O.C.) How-Ji Chen and Yun-Chih Lu: Department of Civil Engineering, National Chung Hsing University, 145 Xingda Rd., South District, Taichung City 40227, Taiwan (R.O.C.)

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