# Feasibility of Developing Sustainable Concrete Using Environmentally Friendly Coarse Aggregate
## 1 Introduction  
Concrete continues to be one of the most dominant materials in modern day construction activities. Concrete has many versatile uses such as being adaptable, mouldable, and freely available in the market and affordable. Regrettably, despite all of these benefits concrete has an adverse effect on the environment [1; 2]. Around 65-75% of the volume of concrete is occupied by aggregates, where 35-45% of the volume of is taken up by coarse aggregates and the rest is occupied by fine aggregates [3]. More than 10 billion tonnes of concrete is produced annually worldwide [4]. Australia alone produces around 30 million cubic meters of concrete annually, consuming about 130 million tonnes of aggregates [5; 6]. It has been predicted that in order to satisfy the demand for new infrastructure due to the rising population demand Australia will need to produce around 210 million tonnes of coarse aggregates by 2050, which is a 60% increase in production [5]. It is noted that the concrete construction industry contributes to CO\({}_{2}\) emissions worldwide. Global cement production contributes 5-7% to anthropogenic CO\({}_{2}\) emissions [7; 8], emitting 0.66-0.8 tonnes of CO\({}_{2}\) from 1 tonne of cement production [9; 10; 11; 12]. In addition, the process energy usage and greenhouse gas emissions from natural crushed aggregate is around 7.4 to 8.0 kg of equivalent CO\({}_{2}\) emission per tonne. The emissions from trucks and dumpers, as well as use of crushers which result in considerabledust and particulate emissions, increase global warming [13; 14; 15]. The concrete production process generates a high demand for aggregates which will inevitably lead to a sparsity of resources as demand increases. Quarrying for aggregates involves the removal of rock which can impact the natural drainage patterns, stability of slopes, and the aesthetic value of the environment. This may involve the removal of trees by means of blasting which both directly impacts global warming and the local fauna. Further, naturally crushed aggregates can also contain crystalline silica or free silica which is created and released during production and handling which can pose serious health problems. Hence, finding alternative aggregate sources is essential for the construction industries. The practice of recycling concrete demolition waste, which has been widely adopted, is an excellent source of recycled coarse aggregate for new concrete production. In the last few decades, there has been a progression in the utilization of recycled coarse aggregates, derived from construction and demolition waste, for concrete production in many developed countries [16]. However, developing countries lag behind in the use of recycle aggregate in construction [16], as illustrated by the recovery percentage of construction and demolition waste in Japan, UK and Australia, USA, China, Thailand and South Africa are 80% [17], 65% [18], 62% [19], 48% [20], 40% [21], 32% [22], and 16% [23], respectively. Furthermore, there are numerous recent advancements on techniques of producing recycled aggregates and techniques of utilization [24]. In USA, the majority of the recycled aggregates are being used in road base construction followed by bitumen concrete [16]. In Europe, the majority of the recycled aggregates are utilized in building construction followed by utilization in roadways and railways [25]. Recycled aggregate produced from construction and demolition waste recycling plants can be classified into two groups: recycled concrete aggregates, (i.e., aggregates from waste concrete crushing) and mixed recycled aggregates (i.e., aggregates from recycling ceramic and concrete waste). Mixed recycled aggregate is produced extensively worldwide compared to recycled concrete aggregates. It has been established that concrete made using recycled coarse aggregate can be compared with traditional concrete [26].