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A comprehensive review of the durability and microstructural properties of alkali-activated materials (AAMs) made with waste glass as a precursor is presented in this paper. AAMs are potentially sustainable alternatives that can be utilized to replace Portland cement (PC) materials due to the total elimination of PC as the binder. The traditional precursors utilized in the production of AAMs are fly ash and slag. However, other waste products such as glass powder (GP) can be applied as a precursor in the production of AAMs. Due to the limited research and application of waste glass as a precursor in AAMs, a thorough analysis was made to investigate current studies where the durability and microstructural characteristics of AAMs made with waste glass were evaluated. The durability properties explored are permeability properties, shrinkage, alkali-silica reaction and resistance to aggressive environments. Microstructural properties discussions were also made to support the corresponding physical properties of GP-based AAMs.

The evolution of sustainable binders for various construction applications has resulted in the development of various geopolymer binders using various materials as aluminosilicate precursors. Geopolymer binders can be utilized as an alternative to Portland cement in the production of various materials such as mortar and concrete. In this study, geopolymer binders were synthesized using metakaolin (MK) and meta-halloysite (MH) as the aluminosilicate precursors and activated with an alkali solution having a silica modulus of 1.3 and 1.5. The resulting geopolymer binders were assessed in terms of the mechanical, permeability and durability properties. The findings from this study showed that the use of MH as the precursor resulted in better performance compared to when MK was used due to its higher reactivity and fineness. It was also found out that the use of a silica modulus of 1.5 is favourable to the hardened properties of the geopolymer binders. Geopolymer binders synthesized with MH and an activator with a silica modulus of 1.5 exhibited an increase in compressive and flexural strength of approximately 9 MPa and 1 MPa, respectively compared to when a silica modulus of 1.3 was used. Also, the corresponding porosity and water absorption is 14.5% and 10.9%, respectively lower.

Alkali-activated materials (AAMs) are promising materials that can be used as alternatives for conventional Portland cement (PC) materials. In this paper, the fresh properties, and mechanical properties of AAMs made with glass powder (GP) as the precursor were explored and discussed. The discussions presented in this paper showed that the incorporation of GP as the precursor in AAMs resulted in an improvement in the workability and extension of the set times. However, the use of GP especially at early ages could result in a detrimental impact on the mechanical performance of AAMs due to the lower reactivity of GP compared to other precursors. Nonetheless, AAMs with acceptable mechanical performance for non-structural and structural applications can still be produced with the use of GP as the precursor.

Brazil is a country of continental dimensions and characteristics with enormous biodiversity of fauna and flora which confers a prominent role in the sector of extraction of agricultural products. However, one of the current challenges is the increasing amounts of agricultural solid wastes generated by different local production processes which end up resulting in enormous environmental liabilities. One way to effectively manage these agro-industrial wastes is by their application in the development of alternative cementitious materials such as mortars and concretes. Thus, the objective of this paper is to discuss the recent advances, challenges and future perspective of the application of some solid agro-industrial wastes generated specifically in Brazil and some other parts of the world in cementitious materials. The application of wastes from pineapple, sugar cane, açai, coconut and rice were explored and discussed. The discussion presented in this paper is anticipated to strongly contribute to the advancement of public policies that enable the real application of these wastes in the development of eco-friendly cementitious materials for civil construction.

Steam curing at atmospheric pressure is a method used to raise concrete strength at early ages. The steam curing method is based on the application of hot water vapor at a temperature between 40 °C and 100 °C for a limited period. The highest temperatures and the longest curing period are determined based on the characteristics of the target concrete, the cost, and the production cycle. This study presents the effect of steam curing regime application on concrete properties. Steam curing has a negative effect on the microstructure of concrete, and this effect increases with higher temperatures. The curing period and the precuring period in addition to the cooling period influence the properties and the strength of concrete. This study summarizes the previous literature related to the effect of steam curing regime application on the properties of concrete. Previous studies confirm that concrete exposed to steam curing regime at low temperatures ranging between 45 °C and 80 °C and a longer period within a 24-hour cycle achieve better concrete properties. In addition, raising the steam curing temperatures above 80 °C has a negative effect on concrete microstructure and other concrete properties in general. This study also concludes that adding pozzolanic or complementary cement materials contributes to reducing the damage resulting from the application of steam curing regime on concrete at later ages. Such verification is required to clarify the behavior of concrete under the influence of steam curing systems, understand their effect on the properties of concrete, and look for ways to reduce the damage from degrees of application of steam curing regime.

This study presents the results from the microbiological induction of bacterial biomass (i.e. biocementation) in concrete mixtures to enhance the mechanical and durability properties. Bacteria isolated from manufactured sand (i.e. bacillus megaterium) were incorporated into concrete mixtures and the corresponding effects on the mechanical and durability properties were investigated. The influence of the bacteria concentration was assessed in terms of compressive strength, split tensile strength, flexural strength, acid resistance, chloride ion penetration and water permeability. In addition, microstructural investigations were also carried out. Findings from this study indicated that the compressive strength, split tensile strength and flexural strength of concrete made with 105 cells/ml of bacteria is 11.3%, 97.5% and 10.7%, respectively. Similarly, concrete made with 105 cells/ml of bacteria exhibited lower permeability (i.e. lower chloride ion penetration and water permeability) and higher resistance to acid attack compared to the plain concrete without any induced bacteria. The improvement in the properties of the concrete with the incorporation of bacillus megaterium was associated with the precipitation of calcite and the presence of bacterial biomass within the pores of the concrete matrix. Microstructural investigations also showed that concretes made with bacteria at a concentration of 105 cells/ml have more calcite formation as evident in the scanning electron microscopy images and elemental composition of the concrete. Hence, it was concluded that the use of the bacillus megaterium at a concentration of 105 cells/ml is optimum to achieve enhanced performance of the concrete.

The development and application of fibre-reinforced cementitious composites (FRCC) have evolved significantly over the last decade. However, there is a need to find innovative ways to improve the sustainability of composites. The production and transportation of the major binder (i.e. Portland cement) and aggregates used for FRCC consumes high energy and natural resources. Therefore, finding ways to incorporate recycled materials to replace these conventional components can be used to improve the sustainability of the FRCC. Also, the special micro silica sand used to produce certain types of FRCC is a major concern due to its limited availability and higher cost. On the other hand, there exist various waste materials that can be incorporated into FRCC as a replacement of either the binder or aggregate. Hence this current paper aims to investigate the performance of FRCC made with high volume fly ash as partial replacement of Portland cement, and reclaimed asphalt pavement/crumb rubber as replacement of the natural aggregates. The performance of the FRCC incorporating these recycled materials was evaluated in terms of its crack properties, toughness and sorption. Results from this study showed that the use of recycled crumb rubber is beneficial in terms of crack properties and lower sorption. The sorption of FRCC incorporating crumb rubber as the only aggregate was reduced by 31.8%. However, FRCC made with reclaimed asphalt pavement exhibited higher sorption and lower toughness.

In this study, an ecofriendly binder was developed by using rice husk ash (RHA) and sodium hydroxide as the activator alongside fly ash (FA) as the aluminosilicate precursor at ambient conditions. The developed binder was used in the production of mortars with varying proportions of sand. A total of three mortar mixtures were developed with sand to binder ratios of 0.55, 0.83 and 1.11. The corresponding behaviour of the mortars and influence of the sand proportions was assessed in terms of the compressive strength, water absorption, density, porosity. Microstructural investigations such as scanning electron microscopy, energy dispersive x-ray spectroscopy, infrared spectrum analysis and mercury intrusion porosimetry were also used to validate the physical properties. The findings from this study demonstrated that RHA can be used successfully as an activator component in the production of mortars. In terms of the sand content, it was found out that increasing the sand to binder ratio has detrimental effects on the performance of the mortars due to the reduction in the binder content primarily. The microstructure analysis of the mortars made with sand to binder ratio of 0.55 showed a compact and strong structure justifying the higher compressive strength achieved. The MIP analysis confirmed that the formation of C-A-S-H gel at the advanced ages allowed the pores refinement with a significant decrease in the fraction of the capillary and macroscopic pores within the geopolymer mortars.

The type of aluminosilicate precursor used in the synthesis of geopolymer binders plays a huge role in the resulting performance. Thus, it is critical to understand the properties of precursors and how they influence the corresponding performance of geopolymer binders. In this study, metakaolin and meta halloysite are used as the aluminosilicate precursor in the synthesis of geopolymer binders. These precursors are obtained locally in order to propel the sustainable development and application of geopolymers. The precursors were characterized and the corresponding influence on the reactivity, rheology and setting times of geopolymers was investigated. In addition to the influence of precursor type on the properties of the geopolymers, the effect of two silica moduli (i.e. 1.3 and 1.5) was also evaluated. The results from this study indicated that increasing the activator silica modulus from 1.3 to 1.5 extended the setting times and increased the stress strain of the geopolymer binders. Characterization of the precursors indicated that metakaolin has a higher amorphous content compared to that of meta halloysite. However, the finer particles of meta halloysite embodied it with the ability to participate in a faster geopolymerization and result in more formation of activation products.