Abstract
The growth of global construction has contributed to an inevitable increase in the amount of construction and demolition (C&D) waste, and the recycling of C&D waste as aggregates in concrete is receiving increased interest, resulting in less demand for normal aggregates and bringing a potential solution for the landfilling of wastes. Recently, several studies have focused on the use of C&D waste in alkali-activated concrete to move one step closer to sustainable concretes. This paper focuses on the main mechanisms of using C&D waste in the resulting physical, mechanical, and durability properties of alkali-activated concrete in fresh and hardened state properties. The main difficulties observed with recycled aggregates (RA) in concrete, such as high levels of water demand, porous structure, and low mechanical strength, occur in RA alkali-activated concretes. These are associated with the highly porous nature and defects of RA. However, the high calcium concentration of RA affects the binder gel products, accelerates the hardening rate of the concrete, and reduces the flowability of alkali-activated concretes. For this reason, several techniques have been investigated for modifying the water content and workability of the fresh matrix and for treating RA and RA/alkali-activated binder interactions to produce more sustainable alkali-activated concretes.
Highlights
There is an increasing global demand for aggregates in the concrete industry
Several experiments report that the replacement of natural aggregates (NA) with recycled aggregates (RA) reduces the elastic modulus of alkali-activated concretes by up to 50% [36,58,59,60,61]
Proposed that saturating RA in water releases the alkalis. They used a simplified approach to assess the leaching content of Na2 Oe contributed from composition with RA during 28 days, and it was found that 0.08% of RA mass was released during 28 days soaking in water [127]
Summary
There is an increasing global demand for aggregates in the concrete industry. It is estimated that the global demand for aggregate will rise at an annual rate of about 5.2% and reach 51.79 billion metric tons in 2019 [1]. The high rates of production of OPC has been of OPC has been challenged due to its high energy consumption during the calcination process, challenged due to its high energy consumption during the calcination process, excessive quantities excessive quantities of greenhouse gas (GHG) emissions, depletion of natural resources (in 2017, of greenhouse gas (GHG) emissions, depletion of natural resources (in 2017, cement production was cement production was 4150 (Mt), and global fossil energy production was around 480 EJ/year [5]), 4150and (Mt), and global fossil energy production was around [5]), and for the alternative generation approaches of dust These factors have resulted in a high demand for alternative approaches to sustainable concretes [6].
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