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This study focuses on utilizing a plant-derived urease enzyme (PDUE)–urea mixture to remove heavy metals from water as constituents of nano-carbonate minerals. The bio-removal process was conducted by individually mixing PbCl2, CuCl2, and NiCl2 solutions with a PDUE–urea mixture, followed by incubation for 24 h at 23 ± 2 °C. The preliminary results revealed that the proposed method exhibited high Pb removal efficiency (˃ 99%) in a short time (8 h); meanwhile, moderate Cu and Ni removal efficiencies (67.91% and 58.49%, respectively) were obtained at the same incubation time. The concentration of heavy metals (50–200 mM) had an insignificant effect on the bio-removal rate, indicating that the PDUE–urea mixture is highly effective for the removal of heavy metals at different concentrations. The bio-removal process involved the transformation of soluble heavy metals into insoluble carbonate materials. A spherically shaped nano-cerussite (4–15 nm), a malachite hexahydrate nanosheet (thickness 8 nm), and an ultrafine micro-hellyerite (thickness 0.3 μm) were the main minerals produced by the Pb, Cu, and Ni bio-removal processes, respectively. As a beneficial application, nano-cerussite was used as an additive in an alkali-activated slag/ceramic waste-based geopolymeric coating. A preliminary study proved that increasing the nano-cerussite content enhanced the resistance of the geopolymeric coating to sulfur-oxidizing bacteria, which is detrimental to normal concrete, particularly in sewer systems.

Hybrid cement (HC) can be defined as alkali activated-blended-Portland cement (PC). It is prepared by the addition of an alkaline solution to high-volume aluminosilicate-blended-PC. Although this cement exhibits higher mechanical performance compared to conventional blended one (aluminosilicate–PC blend), it represents lower commercial viability because of the corrosive nature of alkaline solution. Therefore, this study focuses on the preparing one-part HC using dry activator–based BFS (DAS). DAS was prepared by mixing sodium hydroxide (NaOH) with BFS at low water to BFS ratio, followed by drying and grinding to yield DAS-powder. Different contents of DAS (equivalent to 70 wt.% BFS and 1, 2, and 3 wt.% NaOH) were blended with 30 wt.% PC. A mixture containing 70 wt.% BFS and 30 wt.% PC was used as a reference sample. The mortar was adjusted at a sand–powder (BFS-PC and/or DAS-PC) weight ratio of 3:1. The microstructural analysis proved that DAS-powder is mainly composed of sodium calcium aluminosilicate–activated species and unreacted BFS. These species can interact again with water to form calcium aluminum silicate hydrate (C-A-S-H) and NaOH, suggesting that the DAS acts as a NaOH-carrier. One-part HC mortars having 1, 2, and 3 wt.% NaOH recorded 7th day compressive strength values of 82%, 44%, and 27%, respectively, higher than that of the control sample. At 180 days of curing, a significant reduction in compressive strength was observed within the HC mortar having 3 wt.% NaOH. This could be attributed to the increase of Ca (within C-S-H) replacement by Na, forming a Na-rich phase with lower binding capacity. The main hydration products within HC are C-S-H, C-A-S-H, and chabazite as part of the zeolite family.

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.

This work aims at enhancing the concrete performance using a new protective coating named as asphaltic polyurethane (As/PU) coating, which prepared at different NCO/OH molar ratios (1, 1.1, 1.2, 1.3 and 1.4). As/PU coating was prepared by the reaction of a fixed amount of methylene diphenyl diisocyanate (MDI) with the equivalent weight of mixed polyol (80% asphalt and 20% polyester). The performance of the prepared coatings was examined by the determination of curing time, dry film thickness (DFT), adhesion strength, and flexibility. The formulated coatings were applied on 28-days-cured concrete. The coated and uncoated concrete samples were evaluated regarding contact angle, water absorption, and chloride permeability. The resistivity of coated and uncoated concrete against sulfuric acid and sodium chloride solutions was evaluated. The preliminary results proved that the increase of NCO/OH molar ratio results in a remarkable increase in DFT, adhesion strength accompanied by decrease in curing time and flexibility of the prepared coatings. The concrete sample coated by As/PU with NCO/OH molar ratio of 1.4 demonstrates the highest contact angle associating with the lowest water absorption and chloride permeability. In addition the increase in NCO/OH molar ratio of the applied coating has a positive impact on the mechanical properties of concrete. The coated concrete samples recorded higher resistivity against acid and salt attack compared to uncoated one. This proves the eco-efficient use of the prepared As/PU as an innovative protective coating for concrete.

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 motivation behind this work is to evaluate the impact of nano-magnesium calcite (NMC) waste on the performance of cement mortar (CM) and its resistivity to sulfate attack. The addition of urea and urease enzyme to ground water resulted in the removal of Ca2+ and Mg2+ as NMC precipitate (byproduct of treatment process). As a beneficial recycling method, NMC with different proportions were individually blended with CM to enhance its performance in normal and sulfate-rich media. The results revealed that the NMC has a positive impact on the early-ages compressive strength of CM. Where, the addition of 1 wt% of NMC led to a significant enhancement in the rates of strength development and total porosity reduction at all ages of hydration. Comparing with reference mixture, a highest performance in sulfate medium was obtained in case of all CMs containing NMC. Complementary, the CM incorporated with 1 wt% NMC showed the highest resistance to sulfate attack (up to 12-months) which associated with lower compressive strength regression, total porosity increment, sulfate expansion and consequently lower ettringite formation rate.

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.

This work investigated the synergistic impact of silicate- and MgO-reactivity on the performance of Mg-silicate-based cement. Ceramic waste (CW) and glass waste (GW) as two silicate sources were used. Different decarbonation temperatures (800 and 1200 °C) were applied on magnesium carbonate to yield MgOs with different reactivities (MgO800 and MgO1200). Highest strength and shortest setting times associated with an enhancement in silicate dissolution rate and the formation of large magnesium silicate hydrate (MSH) were recorded in case of GW-MgO800-H2O system. The use of MgO1200 resulted in the retardation of MSH-formation rate in both of GW-MgO-H2O and CW-MgO-H2O systems. Comparing with GW-MgOs set, the CW-MgOs one showed the lowest performance at all curing ages. Due to high alumina content in CW, secondary hydrotalcite-like phases were detected in CW-MgOs alongside MSH-phase.

It is well known that the chemical precipitation is regarded as an effective approach for the preparation of nano-materials. Nevertheless, it represented several drawbacks, including high energy demand, high cost, and high toxicity. This work investigated the eco-sustainable application of plant-derived urease enzyme (PDUE)-urea mixture for synthesizing Zn–/Zr–carbonates and –oxides nanoparticles. Hydrozincite nanosheets and spherical-shaped Zr-carbonate nano-particles were produced after adding PDUE-urea mixture to the dissolved Zn and Zr salts, respectively. PDUE not only acts as a motivator for urea hydrolysis, but it is also used as a dispersing agent for the precipitated nano-carbonates. The exposure of these carbonates to 500 °C for 2 h has resulted in the production of the relevant oxides. The retention time (after mixing urea with urease enzyme) is the dominant parameter which positively affects the yield% of the nano-materials, as confirmed by statistical analyses. Compared with traditional chemical-precipitation, the proposed method exhibited higher efficiency in the formation of nano-materials with smaller particle size and higher homogeneity.

An environmentally friendly alkali activated cement powder was prepared by the transformation of air cooled slag (ACS), with low reactivity, into high reactive cementitious material. The recycling process was carried out by thermal activation of ACS in the presence of fluxing materials followed by quenching and crushing to produce cement powder with a fixed particle size, yielding alkali activated cement powder, which can react with water like Portland cement. Type and content of fluxing material were investigated in this communication. The results proved that there is no change in the crystalline structure of ACS when it exposed to 1200 °C (with no fluxing materials). Meanwhile, it can convert to amorphous material with a complete vitreous structure in the presence of sodium hydroxide and feldspar. The dissolution/condensation process of the amorphous aluminosilicate initiated after adding water to the prepared cement powder, yielding hardened cement pastes with higher mechanical properties as compared to untreated alkali activated ACS.

This work aims at preparing different nano-minerals using bio-precipitation method (BPM). Nano-calcite (NC), nano-giorgiosite (NG), nano-witherite (NW) have been prepared by the addition of plant-derived urease enzyme (PDUE) to urea/CaCl2, urea/Ca(CH3COO)2, urea/MgCl2 and urea/BaCl2 solutions, respectively. Nano-Mg-calcite (NMC) was precipitated by dissolving PDUE and urea in ground water (GW). Salt type plays an important role in the morphology, crystallinity, and particle size of nano-minerals. PDUE has higher effectiveness on Ca2+ removal from GW; meanwhile, it has a lower impact on Mg2+ removal. Where, the Ca-hardness varied from 1460 to 20 mg/l after the treatment of GW with PDUE. At the same pH, the Mg-hardness (1833 mg/l) slightly reduced to be 1210 mg/l. By raising pH, using one-molar sodium hydroxide solution, the removal of Mg2+ enhances. The BPM not only used to prepare innovative NMC-mineral from GW, but also applied to reduce GW-hardness.

An experimental investigation was performed to evaluate the impact of curing conditions on the physico-mechanical properties and firing resistivity of cement mortar (CM) containing reactive magnesium oxide (MgO). Three different curing media including Tap water (TW), normal carbonation (NC) and accelerated carbonation (AC), have been applied. Two MgOs with different reactivity were used (MgO550 and MgO1250); where, 550 and 1250 are referred to the calcination temperatures applied on hydromagnesite. 10 mass % of MgO550 as well as MgO1250 were individually added to CM. The cured CMs were exposed to different elevated temperatures (250, 500 and 750 °C) for 2 h soaking time. The phases composition and microstructure of CMs were investigated via Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) techniques. The results proved that the physico-mechanical properties and firing resistivity of control CM without MgOs cured in TW were superior to those exposed to NC and AC. The MgOs have detrimental impact on the properties of TW-cured-CM, due to the formation magnesium silicate hydrate with lower binding capacity compared to calcium silicate hydrate. Interestingly, the CM-MgOs cured in AC or NC showed the highest mechanical properties as well as firing resistivity compared to control sample at the same curing media, respectively. In AC and NC, the MgO1250 has a higher impact on compressive strength development and firing withstanding of CM compared to MgO550. The optimum curing condition and MgO type, which gave the highest engineering properties and the highest resistivity to elevated temperature were AC and MgO1250.

The goal of this study is to produce an environmentally, and user friendly ready-mix alkali activated cement (RM-AAC) by thermal activation of concrete waste (CW) in the presence of sodium hydroxide (NaOH). Two major compositional factors, which play an important role in the performance of RM-AAC, i.e. temperature and NaOH percentage, were investigated. The CW showed high stability under thermal treatment up to 1200 °C; meanwhile it can be converted to distorted structure with high amorphicity in the presence of appropriate NaOH content. RM-AAC powder can react with water, forming hardened material with an acceptable compressive strength. Due to the white color of RM-AAC powder, it can be beneficially used in prestige construction projects and decorative works.

The key point of this work is to study the impact of sulfur oxidizing bacteria (SOB), namely Acidithiobacillus Thiooxidans NCIMB 8343, on the properties of eco-friendly alkali activated slag (AAS), ceramic waste (AACW) and glass waste (AAGW) industrial solid wastes. Ordinary Portland cement (OPC) was used as reference. After 14-days of curing in tap water, all hardened cement pastes were exposed to pure carbon dioxide, which decreased the pH value of hardened cement surface, allowing the bacterial attack. The detrimental impact of biogenic sulfuric acid, induced by SOB, was evaluated by measuring the cationic leaching, weight, compressive strength and total porosity variations. The change in phase composition and the morphology of cement phases was investigated by Fourier transformer infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The AAS (with low Ca/Si ratio) showed the higher resistivity against SOB attack comparing with OPC-paste (with high Ca/Si ratio) up to 360-days of incubation. On the other hand, the AAGW (containing low alumina content) exhibited biodegradable signs with higher Na-leaching rate, higher compressive strength declination and porosity increment rates as well as larger weight loss as compared to AACW (containing high alumina mass, %).

This study investigates the impact of low-cost barium carbonate and barium silicate nanoparticles (NBC and NBS, respectively) on the performance and phase composition of cement mortar (CM). The results reveal that the individual addition of NBC and NBS causes setting times shortening and mechanical properties increment. Nevertheless, the NBS exhibits the higher efficiency at all addition levels (1, 2, and 3% by weight of cement). The incorporation of NBC results in the consumption of sulfate within cement matrix and the formation of insoluble barite (BaSO 4 ) and calcium monocarboaluminate phases. Although the NBS also represents high efficiency in the uptake of sulfate, the reactive silicate within NBS plays a significant role in the formation of additional calcium silicate hydrate content through the consumption of portlandite (resulted from cement hydration). This could enhance the successful application of cement-NBS mixtures as super sulfate resistant cements.

It is recognized that the presence of amorphous aluminosilicates, which have high ability to interact with alkalis, is one requirement for synthesizing conventional alkali-activated cements. This paper presents an innovative method for preparing alkali-activated calcium carbonate (CaCO3)-based cement, in which weathered-cement kiln dust (W-CKD) is the main precursor. Sodium oxide (Na2O) source (sodium hydroxide, sodium silicate, and sodium aluminate), Na2O-content (1.93, 3.87, 5.82, and 7.75 wt%), type of mixing water (tap and sea water), and the content of lead glass sludge (LGS: 10, 30, and 50 wt%) are the main compositional factors, which strongly affect the performance of the prepared cement. Pirssonite double salt CaCO3.Na2CO3·2H2O is alone main binding phase within sodium hydroxide-activated W-CKD with modest 28-day compressive strengths (~2–9 MPa). A significant enhancement in 28-day compressive strength (~15–21 MPa), which associated with the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) was observed when sodium silicate and sodium aluminate used as alkali activators. On the other hand, mixing sea water with alkali activators results in the formation of nano materials with high effectiveness in the improvement of the mechanical performance of the prepared cement. Incorporating LGS within sodium aluminate-activated W-CKD enhances the formation of C-S-H accompanied by a significant improvement in the compressive strength of the hardened cement (25–52 MPa at 28-day of air curing). Moreover, all hardened W-CKD/LGS mixtures exhibit low Pb-leachability in acidic media. This strongly reflects on the safe application of these mixtures in the construction works.

This study focused on the stabilization of lead glass sludge (LGS) using reactive magnesia (MgO) via the fabrication of lightweight building bricks. Two types of MgO with different reactivities were prepared by the thermal treatment of magnesium carbonate at 800 °C and 1200 °C (MgO-800 and MgO-1200, respectively). The fabrication of bricks and Pb stabilization were performed by wet mixing LGS with MgO followed by humidity incubation. Results showed that the Pb immobilization and performance of the produced bricks were strongly affected by MgO reactivity, curing time, and LGS–MgO weight ratios. Pb immobilization was performed by the transformation of soluble lead into an insoluble hydrocerussite phase, particularly in hydrated mixtures with high MgO content (> 25 wt%). Pb immobilization inside a magnesium silicate hydrate skeleton is the main mechanism in the hydrated samples containing 25 wt% MgO. To achieve “sustainability,” we recommend the use of a hydrated mixture containing 75 wt% of LGS and 25 wt% of MgO-800 in the production of building bricks because this mixture exhibits high compressive strength, high Pb immobilization, low energy demand, and low environmental pollution.

In this paper, low-cost nano-zinc ferrite (NZF) was used to evaluate its efficacy, as compared with nano-zinc oxide (NZO), on the performance of the fresh and hardened alkali activated slag (AAS). An elongation in setting times and a reduction in early-ages’ compressive strengths were recorded in the case of AAS individually containing 0.5, 1, and 1.5 wt% NZO. A turning point was observed after 3 days of curing as AAS-NZO set represents compressive strengths higher than those of reference sample. The embedding NZF in alkali activated system has resulted in setting time shortening and mechanical properties improvement at both early and later ages. This means that the acceleration effect of nano-ferrite compensates the retardation impact of NZO on the activation of AAS-hydration. Regardless its promising properties, AAS-NZF composites demonstrate compressive strength, γ-ray radiation shielding, and anti-fungal activity higher than those recorded in the case of AAS-NZO one at all addition levels.

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.

High drying shrinkage is considered as one of the main drawbacks which hinder the mass production of alkali activated slag (AAS). The formation of expansive phases was found to be the dominant factor for drying shrinkage reduction in sodium silicate-activated system. This work aims at studying single and synergistic effects of the prepared nano-magnesia (NM) and -alumina (NA) on compressive strength and drying shrinkage of AAS. A preliminary study revealed that the NM has a positive impact on the early age’s compressive strength of AAS; meanwhile NA had an opposite effect. Complementary, the drying shrinkage of AAS-NM significantly decreases with the increase of NM-content. Comparing with reference sample, the hybrid inclusion of 1 wt% NM and 1 wt% NA resulted in a significant drying shrinkage reduction and considerable compressive strength increment. The main reason behind this effect is the synergistic formation of calcium silicate hydrate and calcium aluminosilicate hydrate in parallel with expansive hydrotalcite and stratlingite phases as they have a potential effect on the performance of AAS including the retardation of water evaporation, reduction of pore volume, and drying shrinkage. This makes AAS-NM-NA composite can be beneficially used as a binder in the production of structural concrete with high durability.

This study aims at synthesizing porous coconut ash (CA)-based geopolymer foam with high thermal insulation property. Sodium hydroxide (NaOH), alumina slag (AS) and water contents as the main parameters, which affect the performance hardened CA, have been studied. The porosity was developed by hydrogen gas resulted from the interaction of Al metal, in AS, with NaOH. The compressive strength, bulk density, porosity and thermal conductivity were evaluated. The results proved that the AS has a potential impact on the reduction of thermal conductivity of CA-based geopolymer foam by creation of high porous system. Open celled hardened CA-based geopolymer with high porosity (∼87%), low thermal conductivity (∼0.045 W/m·K), compressive strength (1.3 MPa) and bulk density (∼0.60 g/cm3) was obtained when 7% AS (by weight of CA powder) and water to CA powder ratio of 0.4 were used.

Calcite is one of the most common and wide spread mineral on Earth constituting 4 wt% of the Earth’s crust. It is naturally found in extensive sedimentary rock masses, as lime stone marble and calcareous sandstone in marine, fresh water and terrestrial environments. Calcium carbonate is one of the most well known mineral that bacteria deposit by the phenomenon called biocementation or microbiologically induced calcite precipitation (MICP). Such deposits have recently emerged as promising binders for protecting and consolidating various building materials. Microbially enhanced calcite precipitation on concrete or mortar has become an important area of research regarding construction materials. This study describes a method of strength and water absorption improvement of cement–sand mortar by the microbiologically induced calcium carbonate precipitation. A moderately alkalophilic aerobic Sporosarcina pasteurii was incorporated at different cell concentrations with the mixing water. The study showed that a 33% increase in 28 days compressive strength of cement mortar was achieved with the addition of about one optical density (1 OD) of bacterial cells with mixing water. The strength and water absorption improvement are due to the growth of calcite crystals within the pores of the cement–sand matrix as indicated from the microstructure obtained from scanning electron microscopy (SEM) examination.

Geopolymer cement is the result of reaction of two materials containing aluminosilicate and concentrated alkaline solution to produce an inorganic polymer binder. The alkali solutions are corrosive and often viscous solutions which are not user friendly, and would be difficult to use for bulk production. This work aims to produce one-mix geopolymer mixed water that could be an alternative to Portland cement by blending with dry activator. Sodium hydroxide (SH) was dissolved in water and added to calcium carbonate (CC) then dried at 80°C for 8h followed by pulverization to a fixed particle size to produce the dry activator consisting of calcium hydroxide (CH), sodium carbonate (SC) and pirssonite (P). This increases their commercial availability. The dry activator was blended with granulated blast-furnace slag (GBFS) to produce geopolymer cement powder and by addition of water; the geopolymerization process is started. The effect of W/C and SH/CC ratio on the physico-mechanical properties of slag pastes was studied. The results showed that the optimum percent of activator and CC content is 4% SH and 5% CC, by the weight of slag, which give the highest physico-mechanical properties of GBFS. The characterization of the activated slag pastes was carried out using TGA, DTG, IR spectroscopy and SEM techniques.

The microbes can hydrolyze urea by urease enzyme to produce ammonium as well as carbonate ions and in the presence of calcium ions which can precipitate calcium carbonate; this process is called “biocalcification” or microbial induced calcite precipitation (MICP).This technology is environmentally friendly not only because it gives strength to sand body, but also it allows water to penetrate to sand body, which is unlike silicate cement that will destroy the ecosystem of the earth. Calcium carbonate precipitated by bacteria acts as a binding material to sand particles, so incompact sand will be consolidated. Calcium chloride, calcium acetate and calcium nitrate (1 M) as calcium sources were tested for their ability to consolidate sand by mixing with urea (1 M) and bacteria cells (one optical density, 1 OD). The key point of this study aimed to choose the suitable calcium source which produces higher compressive strength and lower water absorption. The results showed that the degree of crystallinity and amount of precipitated calcium carbonate, as well as the consequent increase in strength of consolidated sand, in case of calcium chloride medium are higher than those precipitated in case of calcium acetate as well as calcium nitrate media. In addition, consolidated sand by calcium chloride was also used for cement mortar crack remediation.