Manufacturing Techniques and Properties of Cementitious and Alkali-Activated Artificial Aggregates: A Comparative Review

The increasing need for aggregates, combined with the loss of natural resources, has prompted numerous academicians to seek alternatives to natural aggregates. Artificial aggregates (AAs) are human-made aggregates manufactured from waste resources to improve environmental sustainability. With the industrial revolution, the amount of unwanted industrial waste generation has increased rapidly. This has led to the emergence of environmental and land shortage challenges. Using industrial waste as raw materials to manufacture AA provides a dual advantage of resource conservation and waste management. This comparative evaluation examined the various raw materials, manufacturing procedures, hardening techniques, and curing regimens used to produce AA. In this review, the manufactured aggregates are classified broadly according to the binder used, i.e., cementitious and alkali-activated. Cementitious artificial aggregates (CAAs) and alkali-activated artificial aggregates (AAAAs) are compared in terms of their physicochemical, mechanical, durability, and microstructural properties. Pelletization, crushing, and compaction granulation are the three types of manufacturing methods most commonly used for the AA production. It is concluded that of various manufacturing methods, compaction granulation produces AA with the highest strength. In curing regimes, CO2 is most suitable for CAA and heat curing is most suitable for AAAA. Experimental characterization of both types of aggregates shows that AAAA has a denser microstructure due to the formation of additional hydration products (such as C-S-H and C/N-A-S-H). This denser microstructure leads to the reduced porosity, reduced water absorption, and enhanced durability of AAAA.