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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.

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.

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.

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.

The properties of sodium sulfate-activated ground-granulated blast-furnace slag (shortened as slag) pastes under carbonation attack were analyzed and compared with the uncarbonated specimens in this paper. A slag with two different finenesses-namely, 250 and 500 m2/kg-was activated by sodium sulfate at two concentrations (1 and 3% Na2O equivalent). After the initial 28 days of curing, the hardened pastes were carbonated in 5% CO2 and relative humidity (RH) of 65% at 20 ± 1°C for 2, 4, and 12 weeks. The carbonation depth, compressive strength, and pH value of the carbonated specimens were measured and compared with the uncarbonated counterparts exposed to a natural concentration of CO2. X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy were employed to characterize the reaction products and microstructure of both carbonated and uncarbonated alkali-activated slag (AAS) samples. The results indicated that the specimens prepared with the coarse slag and low Na2SO4 concentration (1% Na2O equivalent) showed the worst carbonation resistance. Increasing slag fineness has a leverage effect on increasing the carbonation resistance. However, increasing Na2SO4 concentration (3% Na2O equivalent) led to more notable carbonation resistance than increasing slag fineness. By combining the fine slag with high Na2SO4 concentration, almost no changes in the pH, carbonation depth, and compressive strength were noticed even after 12 weeks of carbonation, showing a superb resistance to carbonation attack.

Alkali-activated slag (AAS) cement is one type of alkali-activated binders free from Portland cement. The main problems of this type of cement are its high drying shrinkage and low carbonation resistance that hinder its wide use. In the current paper, the authors tried to suppress this high drying shrinkage and enhance the carbonation resistance of this type of binder by incorporating quartz powder (QP). For that reason, slag was partially replaced with QP at ratios of 10–30 wt%. The flowability of each mixture was measured using a hand-driven flow table. The initial reading of drying shrinkage was monitored after 24 h from casting and continued up to 90 days. After initial curing, some specimens were exposed to atmospheric natural carbonation for one year, whilst the remaining specimens were sealed and used as references. Different techniques such as thermogravimetric analysis and its derivative (TGA/DTG), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) were used to analyze the results. The results showed that the incorporation of QP in the matrix increased the flowability and compressive strength, decreased the drying shrinkage, increased the carbonation resistance, and refined the microstructure.

Tocilizumab (TCZ) and Dexamethasone are used for the treatment of critically ill COVID-19 patients. We compared the short-term survival of critically ill COVID-19 patients treated with either TCZ or Dexamethasone. 109 critically ill COVID-19 patients randomly assigned to either TCZ therapy (46 patients) or pulse Dexamethasone therapy (63 patients). Age, sex, neutrophil/ lymphocyte ratio, D-dimer, ferritin level, and CT chest pattern were comparable between groups. Kaplan–Meier survival analysis showed better survival in Dexamethasone group compared with TCZ ( P  = 0.002), patients didn’t need vasopressor at admission ( P  < 0.0001), patients on non-invasive ventilation compared to patients on mechanical ventilation ( P<0.0001  ), and in patients with ground glass pattern in CT chest ( P<0.0001  ) compared with those who have consolidation. Cox regression analysis showed that, TCZ therapy (HR = 2.162, 95% CI, 1.144–4.087, P  <0.0001) compared with Dexamethasone group, higher neutrophil/Lymphocyte ratio (HR = 2.40, CI, 1.351–4.185, P  = 0.003), lower PaO 2 /FiO 2 , 2 days after treatment, (HR = 1.147, 95% CI, 1.002–1.624, P  < 0.0001) independently predicted higher probability of mortality. Dexamethasone showed better survival in severe COVID-19 compared to TCZ. Considering the risk factors mentioned here is crucial when dealing with severe COVID-19 cases. Clinical trial registration No clinicalTrials.gov: Nal protocol approved by Hospital Authorities, for data collection and for participation in CT04519385 (19/08/2020).

There are inconsistent results in previous studies that focused on the effect of elevated temperatures on metakaolin (MK) geopolymers. Likewise, some studies reported a positive effect of silica fume (SF) on the compressive strength of MK geopolymers, while others reported a negative effect. In this paper, the authors tried to get suitable reasons for these contradictions. Therefore, two different concentrations of sodium silicate and different ratios of SF that affect the Si/Al and Na/Si molar ratios were used. For each concentration of activator, MK was partially replaced with 5 to 25 wt.% SF. The flowability was measured and the compressive strength of the specimens before and after exposure to 400 to 1000[degrees]C was recorded. The results were analyzed by different techniques and showed higher flowability with the inclusion of SF. The incorporation of SF may increase or decrease the compressive strength before and after heating, depending on activator concentration--that is, Si/Al and Na/Si. Keywords: activator concentration; compressive strength; elevated temperatures; flowability; metakaolin; silica fume.

In this work, the effect of different contents of Portland cement (PC) on the heat of hydration, pH value, compressive strength and drying shrinkage of 1 % Na 2 O equivalent of Na 2 SO 4 activated ground granulated blast-furnace slag (hereafter referred as slag) has been investigated and compared to slag activated with other common activators. Slag was partially replaced with PC at levels of 0, 5, 10 and 15 %, by weight. The various decomposition phases formed were indentified using X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The results showed an increase in the heat of hydration and compressive strength with the inclusion of 10 and 15 % PC. On the other hand, 5 % PC reduced the compressive strength. The pH value increased with increasing PC content, whilst drying shrinkage decreased with increasing PC content.