The construction sector is facing new challenges in developing sustainable concepts and creating innovative technologies to sustain transition to climate neutrality. Concerns regarding the reduction of carbon footprint in cement and concrete industries have intensified over the last century and continue to be relevant as the world economy is growth and quality of life is increased. In this chapter, a literature review of recent studies is presented, highlighting the potential of using industrial by-product, agricultural residues, construction, and demolition recycle waste and natural pozzolans as partial replacement of cement or natural aggregate in the production of sustainable concrete.
Top1. Introduction
Concrete has the most widely application in constructions. Used in buildings as reinforced concrete for columns, beams, slabs, staircase, and infrastructure, have a high impact on their energy performance and carbon footprint. Their good mechanical properties have made it proper for buildings with high number of stories, bridges or viaducts of larger span, roads, or highways. Its appearance in the middle of XIXth century, have marked an important technological progress in the construction industry, bringing a remarkable contribution to the people’s well-being and economy progress. Made of binder (cement, supplementary cementitious materials - SCMs), aggregates, water, and various additives with role in improving the physical and mechanical properties, are large consumer of natural resources, waste generated, and greenhouse gases (GHG) emissions.
Portland cement, the main binder used in the production of concrete, is an energy-intensive material which play an important role in their mechanical properties and constructions carbon footprint. One tone of cement Portland releases about 950 kgCO2eq (Hammond & Jones, 2011) more than half of them resulted in the clinker calcination process. Aggregates usually account for more than half of the 1 m3 of concrete volume, are available everywhere in the world, has a very low environmental impact in comparison with cement, but their extraction causes environmental degradation and mining footprint. Water is a valuable resource which needs to be preserved especially in scarcity areas.
Concerns regarding the reduction of carbon footprint in cement-based construction materials were intensified in the last century by fostering innovation in research and development. New concepts and innovative technologies were proposed by scholars and practitioners and the technical know-how was transferred to the stakeholders involved in decision making process and practical applications. CO2 emission generated in cement clinker production are resulted both from calcination of raw materials and from fuel combustion, being variable depending on the type of fuel and technology used. To accomplish technical properties required for specific applications in constructions, ordinary Portland cement (OPC) is used in different ratios in the concrete composition based on grade and exposure class (XC1-XM1). It is well known that the concrete carbon footprint increases with the cement content increase being higher for concrete with higher compressive strength. Environmental impact of concrete is influenced by the design strength, and composition, and range between 0.100 - 0.151 kgCO2eq/kg from C16/20 to C40/50 (Hammond & Jones, 2011).
Green or environmentally friendly concrete is a material which contains in their composition secondary raw materials (Al-Mansour et al., 2019) and has a lower embedded carbon in relation to conventional concrete. Low carbon concrete is seen as a material with lower carbon footprint in comparison to traditional one, while sustainable concrete is a material who meets all the environmental, economic, and social performance criteria. Therefore, concrete is green or sustainable if is made of raw materials with low embodied carbon (local, natural, or recycled), have a good mechanical property, is long lasting, recyclable at the end of their life cycle, and remains as valuable resources in the economy as long as possible.
Construction and demolition waste (CD&W) represents globally more than 30% of the total waste generated while the recycled ones have a very small share, resulting annually in high amounts of waste disposal with high environmental impact (Cobîrzan et.al., 2022a). Reducing the imbalance between the two is desirable in ensuring the security of natural resources and protecting the environment.
At the European level, the main source of waste are resulted from the construction and demolition activities, which represent more than 800 million tons or near 36% of the total waste generated. The data presented in the report Energy, transport, and environment statistics — 2020 edition (https://ec.europa.eu/eurostat), show the very different contribution of construction and demolition activities to total national waste generation, ranging from 79% in Malta to almost 0% in Bulgaria.