# Meta-Analysis of the Performance of Previous Concrete with Cement and Aggregate Replacements
## 1 Introduction  
Concrete is the most widely utilized construction material globally [1]. It is a mixture of coarse and fine aggregates, cement, water, and other additives. Aggregates are primarily obtained from non-renewable natural resources, and thus aggregate extraction is considered to be a source of environmental burden. High demands for natural aggregates (NA) have led to the scarcity of their sources and prompted the search for more sustainable alternatives [2]. Meanwhile, cement production significantly contributes to global greenhouse gas (GHG) emissions [2]. Its production results in the liberation of harmful GHG into the atmosphere, leading to air pollution [3]. Studies have shown that the ordinary Portland cement (OPC) industry produces approximately 7% of the world's CO\({}_{2}\) emissions, with about 74% of the CO\({}_{2}\) being emitted during concrete production [4]. It has been reported that the manufacture of 1 ton of OPC consumes 1.6 tonbs of raw materials and about 6.5 million British thermal units (BTUs) of energy while emitting 1 ton of CO\({}_{2}\)[5]. Thus, there is a need to reducecement consumption in concrete by replacing it with more sustainable binders with lower energy and carbon footprints. The release of poisonous gases and the energy consumption during cement production coupled with the harmful storage of industrial wastes are some environmental factors that encourage the use of alternative binding materials instead of cement [6; 7]. The most suitable replacements for cement and aggregates are typically industrial wastes. Not only do they reduce the consumption of cement and aggregates in the production of concrete, but they are also beneficially recycled rather than stockpiled or landfilled. Indeed, the landfilling of industrial wastes raises concerns about environmental pollution and human wellbeing [8]. In addition, the cost implications of replacing cement in concrete is another crucial factor to be considered in the adoption of this concept [9]. The excessive utilization of these natural resources leads to an unstable environment and the eventual scarcity of NA [10]. Furthermore, environmental problems associated with RA and industrial waste disposal pose a hazard to the environment [11]. As such, different materials have been investigated as substitutes for NA in order to tackle these problems. The emission of GHG is responsible for global climate change and the subsequent heatwaves and storms [8]. Owing to rapid urbanization, about 3% of the world's surface is impervously paved, thus preventing water and air passage [12]. Such an increase in impervious surfaces has led to a decrease in groundwater recharge from precipitation events and an increased tendency of non-skid-resistant surfaces with low friction to promote surface runoff [12]. Flooding has become more frequent because of climate change-induced storms and impervious pavements [13; 14]. An engineered solution is thus required to prevent flooding and efficiently manage stormwater. Previous concrete (PC) is an open-graded pavement material that consists of coarse and little or no fine materials [12; 15], and whose permeable network of voids offers a sustainable solution to the challenges of stormwater management and flood control. PC pavement is characterized by a pore structure composed of a high volume of interconnected and capillary pores, typically with a total void content ranging from 15 to 30%, with pore sizes in the range of 2-8 mm [16] and water permeability of about 2-6 mm/s [15]. PC has been considered as one of the strategies for low-impact development (LID) in pavements due to its structural, economic, and road-user benefits [17]. It is recognized by the United States Environmental Protection Agency (EPA) as a best management practice for stormwater control [18]. It can mitigate the effect of Urban Heat Islands (UHI), where impervious pavement acts as heat storage during the day and releases heat to the atmosphere at night [16].