The effect of replacing sand by iron slag on physical, mechanical and radiological properties of cement mortar

AbstractIn the present study, the effects of replacing sand by high percentages of basic-oxygen furnace slag on the compressive strength, bulk density and gamma ray radiation shielding properties of mortar have been investigated. Cement mortar of mix proportion 1:3 including various percentages of iron slag was designed. The percentages of replacement were 0%, 40%, 80% and 100% by weight of fine aggregate. Mortar mixes were prepared with water cement ratio of 0.44 and cured in potable water for 90days. The attenuation measurements were performed using gamma spectrometer of NaI (Tl) detector. The utilized radiation sources comprised 137Cs and 60Co radioactive elements with photon energies of 0.662MeV for 137Cs and two energy levels of 1.17 and 1.33MeV for the 60Co. Likewise, half value layer (HVL), tenth value layer (TVL) and the mean free path (mfp) for the tested samples were measured. Results of this investigation indicated that the strength properties of mortars increased significantly upon replacing sand partially by iron slag. It was also observed that the inclusion of iron slag as partial replacement with fine aggregate enhances the bulk density of mortar. On the other hand, full sand replacement by iron slag has significant effects on shielding efficiency in thick shields, as it reduces the capture gamma rays better than normal mortar incorporating sand

The effect of replacing sand by iron slag on physical, mechanical and radiological properties of cement mortar

In the present study, the effects of replacing sand by high percentages of basic-oxygen furnace slag on the compressive strength, bulk density and gamma ray radiation shielding properties of mortar have been investigated. Cement mortar of mix proportion 1:3 including various percentages of iron slag was designed. The percentages of replacement were 0%, 40%, 80% and 100% by weight of fine aggregate. Mortar mixes were prepared with water cement ratio of 0.44 and cured in potable water for 90 days. The attenuation measurements were performed using gamma spectrometer of NaI (Tl) detector. The utilized radiation sources comprised 137Cs and 60Co radioactive elements with photon energies of 0.662 MeV for 137Cs and two energy levels of 1.17 and 1.33 MeV for the 60Co. Likewise, half value layer (HVL), tenth value layer (TVL) and the mean free path (mfp) for the tested samples were measured. Results of this investigation indicated that the strength properties of mortars increased significantly upon replacing sand partially by iron slag. It was also observed that the inclusion of iron slag as partial replacement with fine aggregate enhances the bulk density of mortar. On the other hand, full sand replacement by iron slag has significant effects on shielding efficiency in thick shields, as it reduces the capture gamma rays better than normal mortar incorporating sand

The Effects of Temperature Curing on the Strength Development, Transport Properties, and Freeze-Thaw Resistance of Blast Furnace Slag Cement Mortars Modified with Nanosilica

This investigation studies the effects of hot water and hot air curing on the strength development, transport properties, and freeze-thaw resistance of mortars incorporating low-heat blast furnace slag cement and nanosilica (NS). Mortar samples were prepared and stored in ambient conditions for 24 h. After demolding, mortar samples were subjected to two different hot curing methods: Hot water and hot air curing (40 °C and 60 °C) for 24 h. For comparison purposes, mortar reference mixes were prepared and cured in water and air at ambient conditions. Strength development (from 1 to 180 days), capillary water porosity, water sorptivity, and freeze-thaw resistance were tested after 180 days of curing. The experimental results showed that both curing regimes accelerate the strength development of mortars, especially in the first seven days of hydration. The highest early strengths were reported for mortars subjected to a temperature of 60 °C, followed by those cured at 40 °C. The hot water curing regime was found to be more suitable, as a result of more stable strength development. Similar findings were observed in regard to durability-related properties. It is worth noting that thermal curing can more efficiently increase strength in the presence of nanosilica, suggesting that NS is more effective in enhancing strength under thermal curing.EC/H2020/841592/EU/Ultra-Lightweight Concrete for 3D printing technologies/Ultra-LightCon-3

Biocarbonation: a novel method for synthesizing nano-zinc/zirconium carbonates and oxides

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.EC/H2020/841592/EU/Ultra-Lightweight Concrete for 3D printing technologies/Ultra-LightCon-3

A comparative study on the role of metakaolin and diatomite in the performance of eco-friendly dolomite waste–based alkali-activated binder

The production process of dolomite aggregate yields a huge content of the rejected size, namely dolomite waste. This waste causes many environmental problems including increasing the wastage area, disposal of landfill, and increasing the air pollution. This work pay attention to the sustainable disposal of this waste in the production of an innovative binder using chemical exchange reaction. This work aims to examine the role of metakaolin (MK) and diatomite (DT) in enhancing the physicochemical properties of alkali-activated binder-based dolomite waste (AADW). The DW powder was combined with varying weight percentages of MK and DT. The resultant admixtures were activated via Na2SiO3, followed by curing at room temperature. The fabricated mixtures possess a wide range of compressive strength values, dependent on the contents of the additives (MK and DT). AADW without any additives represents a compressive strength of 34.6 MPa. DT was found to have a minimal effect on early compressive strength but significantly enhanced later strength. In contrast, incorporating MK into the alkali-activated system materially improved the early compressive strength, while it recorded 28-day strengths similar in hardness to the hardened sample with DT. Specifically, AADW-DT10 and AADW-MK10, which contain 10 wt% DT and MK, respectively, exhibited 7- & 28-day compressive strengths of 14.4 MPa & 32.1 MPa and 57 MPa & 56.2 MPa, respectively. Replacing DW with DT reduced drying shrinkage of the resultant hardened alkali-activated materials. However, incorporating MK up to 10 wt% reduced the drying shrinkage of AADW, while the sample with 15 wt% recorded the highest drying shrinkage. Nonetheless, AADW-DT exhibited lower drying shrinkage than that of AADW-MK at all curing ages up to 90 days. Overall, the result indicated that the higher reactivity and high alumina content of MK provide suitable conditions for synthesizing hardened materials with better physical and mechanical properties when compared to AADW-DT

Repurposing carbonate-based waste for producing an innovative binder: optimization and characterization

This study reports the full recycling of dolomite waste (DW) in the fabrication of a novel cementitious material through a facile and eco-efficient method. The proposed technique includes mixing different alkali-activators (i.e., NaOH and Na2SiO3) with DW powder, followed by curing at room temperature. Based on the alkali-activator type, sodium oxide concentration, and curing time, the formulated mixtures yield a wide range of compressive strengths. When DW powder is mixed with different contents of NaOH (2.5, 5, and 7.5 wt.% Na2O), the resulting hardened materials exhibited modest compressive strengths (less than 11 MPa) due to the formation of the gaylussite Na2CO3·CaCO3·5H2O phase. Concerning the other chemical activator (Na2SiO3), a significant improvement in the compressive strengths of the resulted hardened materials was detected. This was ascribed to the formation of calcium silicate hydrate, with a high binding capacity, through the exchange reaction between Na2SiO3 and CaCO3 inside DW. The sample activated with Na2SiO3 (silica modulus of 1.5) equivalent to Na2O of 7.5 wt.% offered the highest 90-day compressive strength (34 MPa). At silica modulus lower or higher than 1.5, a noticeable decrease in the performance of the hardened materials was observed, which could be attributed to the alter in binding phase composition. Overall, the present work presented a new approach in utilizing the available and low cost carbonate-based wastes as main precursors in the family of promising alkali-activated materials

An Innovative Method for Sustainable Utilization of Blast-Furnace Slag in the Cleaner Production of One-Part Hybrid Cement Mortar

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

Utilization of Foamed Glass as an Effective Adsorbent for Methylene Blue: Insights into Physicochemical Properties and Theoretical Treatment

This study reports a potential approach for the valorization of glass waste (GW) that is mainly composed of amorphous silica to prepare lightweight foamed glass (FG). The preparation of FG was achieved by mixing sodium hydroxide with GW powder followed by sintering at a temperature of 800 °C. As-synthesized FG was characterized and applied as an effective adsorbent for the removal of hazardous organic water contaminants, in particular, methylene blue (MB) dye. FG exhibited porosity of 91%, bulk density of 0.65 g/cm3, compressive strength of 4 MPa, and thermal conductivity of 0.27 W/m·K. Theoretical treatment indicated that a monolayer model with one energy site was the best in fitting the removal of MB molecules. The number of MB molecules per active site (n) ranged from 2.20 to 1.70, suggesting vertical orientation and a multi-molecular adsorption mechanism. The density of FG receptor sites (DM) increased with the temperature, and this parameter played a vital role in the adsorption process. The adsorption capacity (Qsat) increased from 255.11 to 305.58 mg/g, which signifies endothermic interactions. MB adsorption on FG was controlled by physical forces such as electrostatic interactions (i.e., the adsorption energies were <20 kJ/mol). The results of this study prove the feasibility of glass waste as an effective and low-cost adsorbent for water remediation