**1. Introduction**

The most extensively used building material around the globe is concrete [1]. Normal concrete is made by mixing coarse aggregate, fine aggregate, cement, water, and admixture in a mixer according to ASTM C192-02. In TSC, coarse aggregates are set in formwork, and then grout or mortar is infused through a pipe with high pressure from the bottom to the top. The grout fills the pores between the coarse aggregates [2]. Maximum density is achieved without mechanical compaction or using a vibrator [3]. In contrast to conventional concrete, compressive stresses in TSC are first passed through the body of coarse aggregates due to point-to-point contact and, after deformation, they then pass through the hardened mortar [2]. TSC is environmentally friendly concrete as the coarse aggregates are not mixed in a mixer, which reduces the consumption of energy. The grout is made on-site, which eliminates the usage of transit trucks, which in turn results in decreasing pollution and reduces cost [4]. The cost of TSC is 40% less than that of traditional concrete because it consists of about 70% coarse aggregate, consuming about 30% less cement [5]. Due to

**Citation:** Javed, M.F.; Durrani, A.A.; Kashif Ur Rehman, S.; Aslam, F.; Alabduljabbar, H.; Mosavi, A. Effect of Recycled Coarse Aggregate and Bagasse Ash on Two-Stage Concrete. *Crystals* **2021**, *11*, 556. https:// doi.org/10.3390/cryst11050556

Academic Editor: Yifeng Ling

Received: 16 April 2021 Accepted: 13 May 2021 Published: 16 May 2021

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point-to-point contact of the coarse aggregates, the modulus of elasticity of TSC is very high [6]. Drying shrinkage in TSC is lower than in normal concrete, which results in less volume change [7]. TSC is mainly used where a low heat of hydration is required, such as mass concreting in tunnels, and underwater construction and repair [6].

Around 25 billion tons of concrete is produced annually, making it the largest consumer of Earth's natural resources, which are water, natural aggregates (gravel and crushed rock), and sand [8]. Around 12.6 billion tons of natural aggregate is used annually [9]. Due to urbanization, a lot of construction and demolition waste (CDW) is produced. CDW has a serious impact on our environment as it creates pollution when it is disposed of in landfills. Over 1 billion tons of CDW is produced annually [9]. To protect our environment from depleting virgin aggregate resources, recycled coarse aggregates (RCA) have been used to produce concrete [10]. RCA consists of natural aggregates and adhered mortar. Concrete obtained from demolished buildings is crushed to obtain RCA. Due to increased absorption capacity, 5% more water is required for concrete made with RCA to acquire a similar workability as that of normal concrete [11]. Due to traverse cracks in RCA, increased porosity, less information regarding the interfacial transition zone (ITZ) between RCA and cement paste, impurities, adhered mortar, and inferior quality, this makes the use of RCA as structural concrete difficult [12]. RCA has two ITZs, one with new cement paste and the other with old mortar. Therefore, the structure of concrete made with RCA demonstrates a more complex structure than that of concrete made with natural aggregates. Old ITZ has micro-cracks that decrease the strength of the concrete and also increase its water consumption [13]. RCA may contain impurities such as organic matter, sulphates, carbonates, and chlorides [14]. When Sheen et al. [15] made concrete using RCA, it was observed that the compressive strength of the concrete with RCA decreased because of fine particles. The compressive strength of the concrete with RCA can be increased by adding natural admixtures [16]. The permeability of the concrete can be increased by increasing the amount of the RCA [17]. The shape and texture of RCA depends on the crusher plant, which directly affects the workability of the concrete [18]. Pakistan is an agricultural country. Sugar cane is the second largest cash crop of Pakistan, which accounts for 3.6% of gross domestic product [19]. Bagasse is a by-product of the sugar industry and is used as an energy source for sugar production in this industry [20]. Sugarcane contains about 25% bagasse. Fourteen million tons of bagasse is produced in Pakistan annually. Bagasse is also used in the paper industry. When bagasse is burnt for energy purposes, it produces 3% ash, which is dumped in landfills [21]. Waste obtained from agriculture and some other industries can be used as a partial replacement of cement in concrete [22]. One of the ways to decrease the negative environmental impact of concrete is to use mineral admixtures as a partial replacement of cement, which will not only reduce pollution but will also decrease the cost and improve the strength of the concrete [23].

The objective of this research is to evaluate the mechanical properties of TSC made with NCA and RCA. In order to achieve the objective, four mixes of TSC were prepared. One mix was prepared with 100% NCA, while in the other three mixes, NCA was replaced with 100% RCA. Bagasse ash was used as a partial replacement of the cement at 10% and 20% in two mixes of the TSC that had RCA. Compressive strength, compressive strength at 250 ◦C, tensile strength, and mass loss at 250 ◦C were then determined. In addition, two mixes of conventional concrete were also prepared. One mix was prepared with 100% NCA, while the other mix was prepared with 100% RCA. The results of the compressive strength of the conventional concrete were then compared to that of the TSC.

### **2. Materials and Methods**

### *2.1. Materials*
