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As known, calcium oxide (CaO) is an alkaline material, which can be used widely to increase the clay-containing soils load carrying capacity, to produce aerated concrete and calcium aluminate cement. In the last few years, introducing CaO into alkali-activated materials (AAMs) became a hot topic and attained more attention than other times. Generally, CaO can be incorporated into AAMs as an additive/a part of the main precursor and a sole activator without/with an auxiliary activator. Incorporating CaO into the matrices may improve some properties and worsen others. This mainly depends on the ratio of CaO, curing conditions, activator type and activator concentration, precursor type and testing age. This review collected, summarized and analyzed the available studies focused on the effect of CaO on the fresh (reaction kinetic, workability, setting time) and hardened (mechanical strength, durability and length change) properties of AAMs. In addition, some recommendations for future works were included. The results showed that the inclusion of CaO in AAMs decreased workability and setting time. In spite of there are contradictory results about the effect of CaO on the compressive strength of AAMs, most of them reported higher compressive strength, especially at the early ages. The incorporation of CaO up to 5% in the matrix is more effective than the incorporation of higher ratios. The inclusion of CaO in the matrix decreased water absorption, decreased total porosity, increased wetting/drying as well as acid attack resistivity. The CaO (5–10%) can be used as a sole activator for precursors. Auxiliary activators such as Al2(SO4)3, Na2CO3, Na2SiO3, Na2SO4, CaSO4, NaOH, Ca(NO3)2, NaNO3, Mg(NO3)2, Mg(HCOO)2, Ca(HCOO)2, SO3, gypsum and MgO can be used to enhance the compressive strength of CaO-activated materials, especially at the early ages.

Pumice stone is a natural sponge-like lightweight aggregate formed during the rapid cooling and solidification of molten lava. After suitable preparation, it can be used as an aggregate to produce lightweight concrete or as a cementitious material to produce blended cement or geopolymer. This article focused on the influence of pumice powder (PP) on fresh properties and hardened properties of conventional cementitious materials and geopolymers. Additionally, different modification methods carried out to modify some properties of conventional cementitious materials containing PP have been included. This review showed that the incorporation of PP in the traditional cement matrix has some benefits such as increasing thermal and acoustic insulation, increasing fire resistance, increasing abrasion resistance, decreasing unit weight, decreasing hydration heat, decreasing drying shrinkage, decreasing autoclave expansion, increasing sulfate resistance, increasing seawater resistance, increasing acid resistance, increasing electrical resistivity, decreasing alkali silica reaction (ASR) expansion, decreasing porosity, water absorption and permeability. On the other hand, it has a negative effect on workability, mechanical strength and increasing carbonation rate. This review also confirmed that PP has a promising future in the field of alkali-activated and geopolymer materials.

As is well established, slag precursor offers promising performance characteristics; however, its origin as an industrial byproduct leads to variability in both mineralogical and chemical composition. Furthermore, the global availability of slag is limited compared to that of Portland cement (PC), raising concerns about long-term supply stability. To address these issues, this study investigates the incorporation of natural materials—specifically Egyptian natural basalt powder (BP)—as a partial replacement for slag. The research explores BP as a supplementary component in alkali-activated slag (AAS) systems. Blends containing 2.5 wt% to 40 wt% BP were prepared, and both pure slag and slag/BP mixtures were subjected to alkali activation to produce BP-modified AAS cement. The study aimed to assess the impact of varying BP ratios on flow characteristics, setting time, compressive strength, resistance to simulated real-world environmental conditions, and transport properties of the produced cement cured in air and water. In addition, the impact of varying BP ratios on drying shrinkage was monitored. This study also involved interpreting the key results through the use of a variety of contemporary scientific tools. Notwithstanding, BP might have slightly hindered the mixture flowability (up to 10.9% reduction) and prolonged setting time (1.23-fold for initial and 1.28-fold for final setting), the results demonstrated that including 2.5–20% BP improved the overall properties of the cement. An optimal ratio of 20% yielded the highest compressive strength, with an increase of up to 17.65% at 90 days under water curing, the lowest transport properties, with a decrease of 20%, and the lowest strength loss (3.63%) due to environmental conditions exposure under water curing, alongside reduced drying shrinkage. However, including 30% BP showed only a marginal effect, whilst including 40% BP showed a detrimental effect. Additionally, water curing proved superior to air curing, exhibiting higher strength, lower transport properties, and mitigating microcrack formation, thereby enhancing durability against wetting-drying cycles.

Calcium hydroxide (Ca(OH) 2 , or CH) presents a sustainable, cost-effective, and safer alkaline activator for slag compared to traditional activators like NaOH and sodium silicate. However, its application is constrained by the lower mechanical strength of the resulting binder. To address this, calcium formate (CF) was introduced for the first time at varying levels (2–10 wt%, in 2% increments). The effect of different levels of CF on a wide range of slag-CH cement properties was thoroughly investigated. The study applied powerful analytical tools to elucidate the underlying mechanisms. The findings revealed that CF addition reduced flowability and accelerated setting time. Incorporating 2–8% CF enhanced mechanical strength, mitigated the strength degradation after aging, improved transport properties, and reduced drying shrinkage. The optimal dosage of 6% CF was found to promote C-S–H gel formation and refine the pore structure. Conversely, an excessive dosage of 10% CF was detrimental, causing increased porosity and compromising performance.

The environmental impact of conventional concrete underscores the urgent need for sustainable alternatives. Alkali-activated slag (AAS) concrete offers a lower-carbon solution, Yet its performance remains open to optimization. This study evaluates the mechanical and durability enhancements achieved by partially substituting slag with 10–50% locally available feldspar powder. The optimal replacement level of 10% is shown to provide a synergistic performance enhancement, not only improving flexural strength (24.58% at 7 days) but also, for the first time, demonstrating a significant reduction in abrasion wear (10.33%), a 15.5% improvement in water permeability, and a crucial mitigation of drying shrinkage. These findings move beyond simple strength optimization to validate 10% feldspar as a strategic additive for producing a holistically durable and serviceable AAS concrete. Microstructural evidence attributes these gains to feldspar’s role in refining pore structure and promoting the development of a dense, chemically complex sodium aluminosilicate hydrate (N-A-S-H) binder matrix. Beyond 10%, performance declines due to porosity increase and incomplete reaction. These findings support feldspar’s viability as a strategic additive in AAS concrete, aligning with global efforts to decarbonize construction.

Due to the high increase in the consumption of building energy in the world, it is urgent to develop and use thermal insulation materials to limit the demand of energy. In this article, the possibility of producing thermal insulation plasters from common cementitious materials such as fly ash (FA), metakaolin (MK), and silica fume (SF) without employing any foaming agent or lightweight aggregate was investigated. Either cement or gypsum was used as a binder material. Eight different types of plaster based on different pozzolanic materials were investigated and compared with the traditional cement mortar plaster (TC). The compressive strength, bulk density, total porosity, thermal conductivity, and thermal resistance were measured. The results showed that it is possible to produce thermal insulation plasters based on pozzolanic materials without including foaming agent or lightweight aggregate. The obtained insulating plasters exhibited low density (888.75-1575.63 kg/m 3 ), high porosity (39.5-57.75%), low thermal conductivity (0.30-0.48 W/mK) and suitable compressive strength. Using gypsum as a binder material was better than cement for insulation purposes. SF showed the highest insulation efficiency followed by FA and MK.

In this study, portland cement (PC) has been partially replaced with a Class F fly ash (FA) at level of 70 % to produce high-volume FA (HVFA) concrete (F70). F70 was modified by replacing FA at levels of 10 and 20 % with silica fume (SF) and ground granulated blast-furnace slag (GGBS) and their equally combinations. All HVFA concrete types were compared to PC concrete. After curing for 7, 28, 90 and 180 days the specimens were tested in compression and abrasion. The various decomposition phases formed were identified using X-ray diffraction. The morphology of the formed hydrates was studied using scanning electron microscopy. The results indicated higher abrasion resistance of HVFA concrete blended with either SF or equally combinations of SF and GGBS, whilst lower abrasion resistance was noted in HVFA blended with GGBS.

The effect of a fixed ratio of different additives on the carbonation behavior of ground-granulated blast-furnace slag (shortened as slag) activated with a fixed concentration of [Na.sub.2][SO.sub.4] was investigated. Slag was activated by 1% ([Na.sub.2]O-equivalent) [Na.sub.2][SO.sub.4] (M0) and partially replaced with 10%, by weight, of one of the following additives: limestone powder (LS10), fly ash ( FA10), portland cement (PC10), silica fume (SF10), metakaolin (MK10), and hydrated lime (HL10). The compressive strength values were measured and compared with those activated with the traditional common activators. After 28 days of curing, the pastes were exposed to 5% concentration of [CO.sub.2] coupled with 20 [+ or -] 1[degrees]C and 65% surrounding temperature and relative humidity, respectively, for different durations of 2, 4, and 8 weeks. Compressive strength, pH value, and carbonation depth of carbonated specimens were determined and compared with noncarbonated ones exposed to the same conditions but at a natural [CO.sub.2] concentration. The results were analyzed with special tools to determine the different phases. The results revealed that it is possible to increase the carbonation resistance of slag activated with [Na.sub.2][SO.sub.4] by using some additives. The specimens of LS10 exhibited the highest carbonation depth, while SF10 specimens exhibited the lowest carbonation depth. The remaining additives showed intermediate results between LS10 and SF10. Keywords: blast-furnace slag; carbonation depth; compressive strength; different additives; pH value; sodium sulfate.

Egypt’s thriving marble industry produces extensive waste marble powder (WMP) amounts. Recycling plentiful waste safely and effectively is a key national concern, as improper disposal poses a serious threat to the environment. This study addressed this challenge by exploring a new method to produce CaO from WMP by appropriate calcination (CWMP), which can be used as an effective additive for alkali-activated slag (AAS) cement. The CaO extracted from WMP (CWMP) was introduced into AAS cement at varying levels, ranging from 2.5 up to 15%, in 2.5% increments, by weight, as a partial slag replacement. Multiple assessments were conducted to evaluate the influence of CWMP (i.e., CaO derivative from WMP) on specific features of AAS cement. Superior analytical techniques were utilized to achieve a deeper comprehension of the results. The findings revealed a decrease in both flowability and setting time with including CWMP. As the CWMP amount increased, flowability decreased, and setting time became shorter. The introduction of CWMP up to 10% improved performance, with the optimal at 7.5%, improving compressive strength and the ability to withstand environmental conditions. Specifically, the optimal 7.5% CWMP addition increased the 28-day compressive strength by 22.96% and reduced the strength loss after durability cycling from 14.43 to 10.93%. Additionally, the persistent issue of drying shrinkage within this system could also be alleviated by including CWMP up to 10%, particularly at 7.5%. Amounts of CWMP over 10% showed detrimental effects. Repurposing WMP as a CaO source not only manages a problematic waste stream but also saves CaO produced from natural limestone.

Herein, the first trial to investigate the possibility of using one type of sugar beet waste, named carbonation lime residue after calcination (CCR), as an additive for alkali-activated slag (AAS) cement was explored. For this reason, typical AAS cement was prepared, then slag was partially replaced with CCR at levels ranging from 2.5 to 15% by weight. To explore the effect of CCR on the properties of AAS pastes, typical traditional tests such as flowability, setting time, and compressive strength at various ages were measured. In addition, different types of durability such as accelerated aging, water-air cycles, water-hot air cycles, HCl attack, and cyclic wetting in 5% [Na.sub.2][SO.sub.4] and drying at 80[degrees]C (176[degrees]F) were explored. The results were analyzed with different advanced devices. The results showed that it is possible to use CCR as an additive, similar to CaO, for AAS cement. The flowability and setting time decreased with the inclusion of CCR. The inclusion of 5% CCR in AAS cement was the optimal content, which proved the best compressive strength, microstructure, and durability. On the contrary, the inclusion of 15% CCR showed a negative effect. The pronounced outcomes of this investigation may be the solution for sugar beet waste landfills and improving the properties of AAS cement. Keywords: alkali-activated slag; compressive strength; durability; setting time; sugar beet waste; workability.