# Numerical and Experimental Investigation of Recycled Brick Coarse Aggregate Concrete
## 1 Introduction  
Concrete is the most widely used construction material in engineering construction [1]. China's total commercial concrete production reached 2.843 billion cubic meters in 2020 [2]. However, the coarse aggregate which forms the skeleton of concrete is a non-renewable resource, and its exploitation leads to resource depletion and environmental pollution. Furthermore, construction waste pollutes the water, air, and soil, which is not conducive to the development of urban construction. An effective way to avoid this is to use construction waste to produce recycled concrete aggregate. Research on using recycled concrete coarse aggregate (RCCA) instead of natural coarse aggregate (NCA) has made significant progress in the past decade, and several standard specifications, including GB/T25177-2011 and GB/T25176-2011, have been completed. The RCCA concrete research mainly focuses on construction waste aggregates such as rubber, ceramic, red brick, cement, and foam [3]. In addition, a large amount of brick construction waste exists in China's urban and rural areas as a result of urbanization and development [4, 5]. Therefore, the cyclic utilization of recycled brick coarse aggregate (RBCA) is significant to energy conservation and emission reduction in China. When a brick building reaches the end of its service life, it is demolished, which generates waste bricks generated. Currently, most of the removed bricks are used in landfills and roadbeds, which causes waste of resources and creates environmental problems. RBCA can partially or fully replace the natural crushed coarse aggregate in concrete. The research and utilization of RBCA have greatly improved the utilization of brick resources, savednon-renewable natural gravel, and protected the environment. RBCA is obtained by crushing waste bricks with a jaw crusher followed by screening, cleaning, and oven drying. Brick particles with particle sizes between 75 \(\upmu\)m and 4.75 mm are defined as recycled fine aggregates, while those with particle sizes greater than 4.75 mm are recycled coarse aggregates [6]. RBCA with larger particle sizes has a flat and angular appearance; the aggregate surface is relatively rough, with many voids. RBCA with smaller particle sizes has many angles, rough surfaces, and microcracks. Currently, recycled brick aggregate is mostly used in non-load-bearing structures such as concrete pavement blocks [7] and porous concrete bricks [8]. Current research shows that low RCCA content influences recycled concrete's physical and mechanical properties [9; 10; 11; 12; 13], with the compression strength reduced by up to 30% after 100% replacement of raw aggregate (coarse aggregate) by RCCA [14]. RBCA has higher non-uniform composition than RCCA. In recent years, studies have been conducted to evaluate the compressive and working performance of RBCA concrete. For example, [PERSON] et al. [15] studied the physical performance of concrete replaced by ordinary bricks and by over-fired bricks, including the unit weight of hardened concrete and the slump value of freshly mixed concrete. The results showed that the unit weight of concrete decreases with increasing coarse aggregate content of over-fired bricks, and the unit weight reached at least 79% of the regular unit weight of concrete. [PERSON] et al. [16] studied recycled concrete with a 100% waste brick replacement rate and evaluated its slump, density, compressive strength, and flexural strength. [PERSON] et al. [17] investigated waste brick aggregate concrete's functional performance and mechanical properties with different dosages. Research results have concluded that the operational performance is better if the dosage is less than 40% and that 30% recycled aggregate concrete meets the requirements of the strength standard. [PERSON] et al. [18] discussed the influence of the moisture state of recycled aggregate on concrete performance, finding that recycled concrete with 100% air-dried recycled aggregate had severe slump loss. [PERSON] et al.