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In the present work, sustainable use of cement kiln dust (CKD) and feldspar (FS) in the production of pozzolanic materials with different reactivity and whiteness were investigated. The proposed method includes thermal treatment of CKD and FS at 1000 °C in the presence of sodium hydroxide to convert crystalline- FS/CKD -structure to amorphous one. Different FS/CKD mixtures were designed at weight ratios of 50/50, 66.66/33.33, and 80/20 (P-1, P-2, and P-4, respectively) to optimize the whiteness and amorphous content of the produced pozzolans. A preliminary study revealed that the amorphous content and the whiteness of the prepared pozzolan strongly depend on FS/CKD weight ratio. The optimum pozzolanic materials with high 89% whiteness and 100% amorphous content were obtained in the case of P-4. The individual replacement of white Portland cement by 30 wt % of the synthetic pozzolans resulted in the enhancement of 28-days compressive strength. The use of P-4 pozzolan not only increased the mechanical properties of white Portland cement, but also enhanced its whiteness. Non-thermally treated FS/CKD blend (as the counterpart of P-4 pozzolan) showed a lower pozzolanic activity as compared with thermally treated one. Regardless of the change in the strength activity index (SAI) and the rate of Ca(OH)2 consumption, all synthetic pozzolans demonstrated a higher pozzolanic activity.

A cleaner production of one-part alkali activated cement (AAC) was implemented by mixing chemically treated concrete waste (CTC) with slag. The treatment process was conducted by the addition of NaOH to concrete waste (CoW) at NaOH to CoW weight ratios of 0.2, 0.1, and 0.05 (namely, CTC-1. CTC-2, and CTC-3, respectively), followed by mixing with water and drying. The solidified material was ground then dry-mixed with slag to create one-part alkali AAC powder with fixed particle size. The amount of CTC was varied to achieve constant Na2O content (2 wt %) in all mixtures. The results indicated that the prepared one-part AACs can react with water to yield hardened materials with acceptable compressive strength. Comparing with CTC-1 and CTC-3, the CTC-2 was found to have a dominant impact on the activation of slag hydration, which associated with the higher mechanical properties, lower pore volume, and drying shrinkage. The addition of lead bearing sludge (LBS) to one-part AAC containing CTC-2 resulted in a positive impact on the performance of the prepared cement. According to toxicity characteristic leaching procedures the prepared cement showed a potential effect on solidification/stabilization of Pb-containing-sludge.

The motivation behind this work is to sustainable utilization of water-cooled steel-slag and lead-bearing sludge (LBS: from glass crystal industry) in the cleaner production of alkali activated cement (AAC) with high performance and microbial resistivity. To prepare AAC, slag was individually blended with different LBS contents (0, 10, 30, and 50% with respect to weight of slag), then activated with sodium hydroxide (NaOH). Due to high CO2 emission resulting from NaOH-manufacturing, alkali activator was used with low concentration (3 wt, %) for activating the aluminosilicate precursors. A preliminary investigation proved that the mechanical and physical properties of AAC significantly enhanced with the increase of LBS content up to 30 wt %; meanwhile, 50 wt % LBS had a negative effect. The leaching test indicated that Pb-concentrations (mg/l) in leachate of all AAC-mixtures were below the safe limit of toxicity characteristic leaching procedure (TCLP). Agar diffusion test showed that the anti-bacterial and -fungal activity of AAC enhanced with increasing LBS content up to 50 wt %. From the standpoint of environmental impact assessment, the prepared cement showed 50-times lower CO2 emission compared with Portland cement.

The key point of this investigation is to valorize CaCO3-rich wood biomass ash (WBA) from brick industry in the preparation of one-part white geopolymer cement (WGPC) using diatomite as main ingredient. The suggested method not only implemented for cleaner production of eco-friendly cement, but also used to WBA disposal. In the present work, WBA was treated with different sodium hydroxide concentrations (at NaOH: CaCO3 molar ratios of 2, 1, 0.5, and 0.25), followed by dying and pulverizing to produce dry activator powder with a fixed fineness. The impact of dry activator content, containing the same NaOH content (3 wt. %), on the performance of one-part WGPC was evaluated by setting times, total porosity, and compressive strength measurements. The results revealed that the compressive strength development enhances with time, associating with the continuation of aluminosilicate (in diatomite) dissolution and formation of strength-giving-phases such as calcium silicate hydrate and calcium aluminosilicate hydrate. The synergistic filling and nucleating effects of CaCO3 were recorded when 21.5 wt.,% of pretreated WBA, at NaOH/CaCO3 molar ratio of 0.5, added to diatomite to yield one-part WGPC with optimal 28-days compressive strength (48 MPa) and relatively high whiteness (85%). This qualifies the prepared one-part WGPC to be beneficially used as alternative to white Portland cement in decorative works and prestige construction projects.

Hazardous wastes produced from different industrial activities mainly contribute to serious environmental problems, notably their negative impact on the human health. Therefore, there is a great need to implement an innovative protocol for the safe disposal of these wastes in the production of widely-used materials. This study focused on the sustainable consumption of hazardous lead-bearing and dry-bed sewage sludges (LBS and DBS, respectively) in the production of lightweight bricks using alkali-activation process in which cement kiln dust (CKD) used as alkali-rich-waste. Very simple procedures were carried out to prepare the hardened bricks comprising wet mixing sludge-CKD blend and humidity-curing at 23±2 °C for 24 h. The performance of the prepared bricks mainly depends on CKD content, chemical composition and physical characteristics of sludges, and thermal treatment. The increase of CKD content (up to 50 wt %) within LBS-CKD mixtures leads to a significant improvement in the mechanical properties of the produced bricks; whereas, it demonstrated a marginal effect on DBS-CKD set. The main reason behind too low compressive strength (≤1.5 MPa) of DBS-CKD is the low pozzolanic activity caused by the high organic matter content (∼42 wt %) within DBS composition. Nevertheless, all DBS-CKD bricks recorded the lowest bulk density values ranging from 0.92 to 0.99 g/cm3 at 28-days of humidity curing. The full replacement of untreated sludges with thermally-treated one, yields hardened bricks with higher bulk density and compressive strength. Achieving eco-sustainability, low energy demand, and cost minimization, we recommend to use the LBS-CKD (50-50 wt %) mixture in the fabrication of lightweight bricks as it showed desirable mechanical properties, relatively low bulk density, low drying shrinkage, and low Pb-concentration in leachate.

The main feature of the present paper is the eco-sustainable use of industrial solid wastes and organic-based activator (OBA) powder in the cleaner production of ready-mix alkali activated cement (RM-AAC) which interacts with water like Portland cement. The reasonable reason behind the preparation of RM-AAC (Just added water) is the corrosive nature of alkaline solutions which negatively affect the mass production and commercial viability of AAC. Accordingly, this work has resolved this shortcoming by the preparation of a novel activator powder which was synthesized by mixing NaOH solution with ethylene glycol, followed by drying and grinding to yield OBA-powder. The designation of RM-AAC was conducted by blending ground granulated blast-furnace slag (GGBFS: from steel-industry) and/or slag-lead bearing sludge (LBS: from glass crystal industry) with OBA-powder. The results revealed that the desirable OBA-content has resulted in a significant improvement in the performance of RM-AAC containing GGBFS. Although a further increase in OBA-content caused a remarkable improvement in the workability of RM-AAC, it represented a negative effect on its compressive strength development. The prepared RM-ACC showed 180-days compressive strength 157% higher than that of the conventional two-part mixture (at the same Na2O and EG contents). This is due to the fact that OBA-powder enhances the polymerization degree and stability of the prepared cement as proved by the suggested reaction mechanism. The inclusion of 10 wt % LBS has a positive impact on the mechanical properties of RM-AAC as it enhances strength-giving-phases formation by providing the alkali activated system with reactive silicate. Moreover, All RM-AAC/LBS composites demonstrated Pb-concentrations in leachate too lower than that of the safe limit of toxicity characteristic leaching procedure (TCLP). This means the high Pb-immobilization property of the prepared cement, reflecting on its beneficial and safe use in the construction sector.

The key point of this study is the fabrication of magnesia-based cement with promising mechanical properties and high efficiency of CO2-capture. The naturally occurring volcanic ashes (white & red ashes) and reactive magnesium oxide are the main materials used in the synthesis of eco-friendly CO2-capture materials. Volcanic ashes were individually mixed with reactive magnesium oxide at ash to magnesium oxide ratio of 25:75 wt %. The dry blends can react with water to yield hardened materials (at ambient temperature) with compressive strength depends on the type of volcanic ash. A considerable change in the features of the hardened samples was recorded when the fabricated materials exposed to 100% CO2 gas for 28-days. This change is mainly due to CO2-capture by magnesium hydroxide Mg(OH)2 within the fabricated materials, resulting in the formation of Nesquehonite minerals MgCO3.3H2O as proved by X-ray diffraction, thermo-gravimetric, and infra-red instrumental techniques. The thermo-gravimetric analysis demonstrates that, the fabricated sample containing low amorphous red ashes has higher CO2-capture capacity (∼260 kg/ton) compared to that having high amorphous white volcanic ashes (∼220 kg/ton) at 28-days of CO2-exposure. Accordingly, the fabricated magnesia-based cement is not only used as cementitious material with outstanding mechanical properties, but also used as a super CO2-absorbent precursor. This can strongly contribute in the mitigation of global warming potential caused by different industrial activities.

The beneficial use of alkali-activation/sintering process in the fabrication of open-celled cellular materials and lead solidification/stabilization (S/S) is the biggest challenge of the present work. Waste glass (WG), red-clay brick waste (RCBW), and lead-bearing-sludge (LBS) were used as silicate-rich-wastes in the foaming process. Porous materials with porosity ranging from 50 to 89% accompanied by low bulk density (0.73–0.27 g/cm3), low thermal conductivity (0.3–0.14 W/mK), and high compressive strength (3.4–14.2 MPa) were obtained when alkali activated WG, WG-RCBW, and WG-LBS fired at different elevated temperatures (700-900 °C). The results revealed that comparing with WG-foamed materials, the heating of WG activated by 4M-NaOH at 800 °C has resulted in the formation of foamed-glass with higher porosity, lower thermal conductivity, and lower bulk density. The use of RCBW, as a partial substituent of WG, represents the potential impact on the enhancement of foamed-material homogeneity. The dominant feature of the foamed-WG-LBS set is the formation of a porous structure with the biggest pore size and the lowest thermal conductivity. The leaching test proved that the applied alkali activation/sintering process has high efficacy on the Pb-stabilization.