1. Introduction
Recently, concrete scientists have been leaning toward saving energy, lowering the emissions of CO
2, a primary greenhouse gas (GHG), into the atmosphere, with an eye toward controlling the heating of the Earth, and producing more durable, sustainable, user- and eco-friendly green construction materials that are preferably cost-effective too [
1]. In recent times, the application of various solid wastes available in profuse quantities has been of key interest to engineers to manufacture novel construction composites, with a view toward getting rid of these hazardous wastes. Therefore, incorporating wastes to synthesize new construction composites is currently the most attractive topic for managing and reducing solid wastes and conserving restricted nonrenewable natural resources, irrespective of the production technology.
It is reported that producing one ton of ordinary Portland cement (OPC) via the present-day process not only consumes 1.7 tons of essential nonrenewable restricted resources of rocks and minerals [
2,
3] but also emits an almost equivalent quantity (about 0.85 tons) of anthropogenic CO
2 into the atmosphere [
4], which accounts for about 5% to 7% of all CO
2 emissions [
5]. CO
2 alone is responsible for roughly 65% of global warming, and the cement industry is to blame for about 6% [
6]. Provis and van Deventer [
7] accounted for the next step: according to the prediction of the International Energy Agency (IEA), there will be around 9–10% (28 Gt.) of total CO
2 emissions in the world by 2050. Regrettably, at present, no energy efficiency measures are sufficient for mitigation. The greenhouse effect is factor that is largely responsible for global warming. This is a matter of immense concern in terms of preserving pleasant environments, and it is also a warning signal for living communities on Earth [
8].
According to the statistics of the Environmental Protection Agency (EPA) of Taiwan, 520.29 kg of carbon dioxide are emitted into the air for every ton of cement clinker produced [
9]. Of note, according to the report, Taiwan’s CO
2 emissions in 2018 reached 266.88 million metric tons [
10]. On the other hand, there is plenty of waste that has diverse origins (such as marble waste (MW)), coming from a variety of sources; it creates landfill problems, resulting in health concerns and air pollution, driving climatic alterations and, in some places, affecting surface and sub-surface waters and water supplies.
Consequently, all of the above challenges have encouraged concrete scientists and researchers to seek alternative construction composites that are durable, sustainable, cost-effective, and user- and eco-friendly with a low carbon footprint and less burning of energy. Recently, geopolymer construction technology has emerged as a possible substitute for conventional construction systems. Geopolymers (GPs) belong to the category of novel inorganic polymers that are cementitious alumino-silicates, demonstrating an amorphous three-dimensional (3D) structure and made up of AlO
4 and SiO
4 tetrahedral units linked by shared oxygen atoms [
11]. Geopolymerization is an exothermic reaction among precursors rich in alumina and silica of either industrial or geological origin with concentrated alkali activators in a combined solution of silicate and alkali hydroxide [
7,
12,
13], at a temperature ranging from as low as ambient or even room temperature up to 100 °C and at an atmospheric pressure [
14,
15,
16]. Geopolymeric composites demonstrate outstanding and unique characteristics in terms of durability, higher initial strength and mechanical properties; resistance to attack by chemicals like sulfates and acids; fire and thermal stability at elevated temperatures; exceptional resistance to freeze/thaw; anti-corrosion behavior; a carbon footprint that is nine times lower [
16,
17,
18] and an energy use that is six times lower than current systems of OPC production [
11]; little shrinkage; the ability to be cured by autoclave, etc., making them attractive alternatives to conventional systems [
8,
19,
20]. All of these exceptional characteristics, as a whole, make them promising green structural materials for the future. Not only that, but GPs offer tremendous cost savings, in the range of 10% to 30%, as compared to the cost of conventional construction technologies [
21].
Globally, an acceleration in the kinds and quantities of solid waste originating from industries, mining, agricultural and other domestic activities has posed a serious threat to the environment and ecology. In this regard, one of the chief industrial wastes comes from the marble industry and its mining processing stages in the form of sludge, powder or solid wastes. By and large, these wastes are disposed of on open land spaces, creating not only landfill predicaments but also environmental pollution. Furthermore, waste can be generated in the cladding or surrounding rock when the mine is being excavated in the form of a huge quantity of abandoned earth and stones. More often than not, the waste is dumped in any pit or vacant land in the vicinity. This leads to additional risks to the environment in the form of pollution through dust spreads covering a vast area. Particularly in dry conditions, the dust dries up and floats in the atmosphere, and it can deposit on vegetation, plants and crops, creating decaying ecological conditions for flora and fauna. Pure drinking water supply systems or water bodies can get contaminated. There are several ways to reuse marble waste for particular purposes, such as in the brick industry [
22], transport infrastructure [
23], cementitious material [
24,
25,
26,
27], geopolymer concrete [
28], and aggregate or mineral additives [
29]. Therefore, this research attempts to apply marble waste as a valuable construction material to geopolymer concrete manufacturing, thereby turning waste into wealth.
According to a report by the Taiwan Bureau of Mines, marble waste amounts to about 0.62 million tons annually in Taiwan [
30]. This research work was planned in order to develop a novel marble-waste-based concrete at room temperature through the process of geopolymerization. Mine waste was sorted into coarse and fine materials, and they were recycled separately. Mine waste can be effectively resourced, so it can be applied to structural or nonstructural buildings without the high-temperature production steps and energy consumption of traditional cement production and related fields in which mine waste concrete can be applied and developed. Furthermore, this study explores the long-term durability and weathering ability of this novel green concrete. Since marble-based geopolymer concrete does not need to be fired at a high temperature, it can be manufactured at room temperature and can fully achieve the goals of energy saving and carbon reduction, as shown in this research. Thus, this research is actively involved in promoting eco-friendly technology in the building material sector.