Silicate Modulus Research Articles

Performance optimization and environmental assessment of novel alkali-activated binders containing carbonated recycled concrete powder

This study investigates the influence of carbonated recycled concrete powder (CRCP), alkali content (AC), and silicate modulus (SM) on the compressive strength, chemical composition, and environmental benefits of CRCP-blast furnace slag blended alkali-activated binders (AABs). The results show that increasing CRCP content reduces the compressive strength of AABs due to lower geopolymeric reactivity. Using response surface methodology, the optimal values for AC and SM in AABs containing 50 wt.% CRCP were determined as 14.28% and 0.92, respectively, resulting in predicted and actual strengths of 49.9 MPa and 46.8 MPa. Chemical analyses reveal that calcite and vaterite are the predominant crystalline phases in AABs, while both Si-Al gels and calcite from CRCP participate in geopolymeric reactions. The effects of AC and SM on AAB strength are further elucidated through the combined analysis of precursor dissolution amount, geopolymeric gel formation amount, and calcium carbonate decomposition amount. Moreover, CRCP demonstrates negative carbon emissions, with a global warming potential of -0.16 kg CO2 eq/kg. The optimally proportioned AAB containing 50 wt.% CRCP shows global warming potential and carbon intensity values significantly lower than those of Portland cement, at 54.4% and 50.8%, respectively. These findings emphasize that AABs containing 50 wt.% CRCP not only meet the 43-grade strength classification but also offer notable environmental benefits. In summary, this study contributes to the development of a novel 43-graded low-carbon binder containing high-volume CRCP.

Optimization of Proportions of Alkali-Activated Slag-Fly Ash-Based Cemented Tailings Backfill and Its Strength Characteristics and Microstructure under Combined Action of Dry-Wet and Freeze-Thaw Cycles.

To enhance the application of alkali-activated materials in mine filling, cemented tailings backfill was prepared using slag, fly ash, sodium silicate, and NaOH as primary constituents. The effects of the raw material type and dosage on the backfill were examined through a single-factor experiment. Additionally, response surface methodology (RSM) was utilized to optimize the mixing ratios of the backfill, with a focus on fluidity and compressive strength as key objectives. The evolution of backfill quality and compressive strength under the combined effects of dry-wet and freeze-thaw (DW-FT) cycles was analyzed. The hydration products, microstructure, and pore characteristics of the specimens were analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and nitrogen adsorption tests (NATs) across varying cycles. The results demonstrate that the optimal backfill composition includes 47.8% fly ash, 6.10% alkali equivalent, and a 1.44 sodium silicate modulus. The macroscopic behavior of the backfill under DW-FT coupling followed this progression: pore initiation → pore expansion → crack formation → crack propagation → structural damage. After a minor initial increase, the backfill strength steadily decreased. Microscopic analysis revealed that the decline in internal cementation products and the deterioration of pore structure were the primary causes of this strength reduction. Thus, the DW-FT coupling can cause significant erosion of the backfill. The technical solutions presented in this paper offer a reference for solid waste utilization and provide valuable insights into the durability of backfill under DW-FT coupling.

New insights into the effects of silicate modulus, alkali content and modification on multi-properties of recycled brick powder-based geopolymer

Utilizing recycled brick powder (RBP) as a green precursor to prepare alkali-activated RBP-based geopolymer (AABG) not only broadens the existing system of alkali-activated materials but also achieves the high-value and low-carbon utilization of clay brick waste. This paper aims to systematically investigate the influence of silicate modulus and alkali content of the alkali-activator on the multi-properties of AABG, while proposing multi-path modification methods to optimize AABG performance. Substituting an appropriate amount of metakaolin with RBP contributes to optimizing the performance of metakaolin-based geopolymers. However, the micro-macro properties of AABG are significantly inferior to those of metakaolin-based geopolymer. Under the same silicate modulus, the micro-macro properties of AABG first improve and then deteriorate with the increase in alkali content. With the alkali content of 8 %, the AABG owns the best microstructure and macro properties. When the alkali content remains constant, an appropriate increase in the silicate modulus of alkali-activator contributes to the performance enhancement of AABG mortar. The average pore diameter of AABG-1.2M-8%, AABG-1.4M-8%, and AABG-1.4M-4% paste is 69.4 nm, 61.8 nm and 111.9 nm. Overall, the AABG with 1.6M silicate modulus and 8 % alkali content shows good performance. For the multi-path modification methods of AABG, decreasing the w/b ratio of AABG can enhance its compressive strength and permeability resistance. Besides, increasing the curing temperature of AABG can optimize its micro-pore structure and macro-properties, achieving optimal performance at a curing temperature of 80 °C. Finally, mixing Ca(OH)2 into AABG promotes the formation of more C-A-S-H, thereby further enhancing the AABG performance. Optimizing the silicate modulus, alkaline content and modification methods, it is feasible to produce AABG with superior micro-macro properties.

Silicate-lunar regolith composite: A vacuum self-hardened and comprehensively durable extraterrestrial construction material

Extraterrestrial exploration, represented by Lunar base construction, has been promoted worldwide as a multi-disciplinary, cutting-edge and strategic issue. Herein we proposed a novel extraterrestrial construction material composed of Lunar/Martian regolith simulants and only 4 wt% of silicate adhesive. This silicate-regolith composite can be directly self-hardened in vacuum within 4.5 h without any curing to achieve 29 MPa of hardening strength. Meanwhile, it shows comprehensive durability with stable microstructures and >70 % of residual strength against long-term vacuum exposure, huge temperature difference and intense γ-ray and proton radiations. Its in-situ solidification and durability originate from vacuum dehydration, where silica clusters in solution spontaneously cohere into a solid network with strong connections of silica tetrahedra and bound water. A moderate silicate modulus around 2.5 and appropriate modifications can disperse finer silica clusters to increase oligomer silica units in solution and enhance hardening strength. Compared with lunar geopolymer and other existing extraterrestrial construction materials, this vacuum self-hardening composite allows a cryogenic preparation even below −40 ℃ using diverse regolith with a wide range of compositions and sizes, proposing a facile, durable and versatile solution towards in-situ extraterrestrial constructions.

Effect of alkali dosage and silicate modulus on the deterioration of alkali-activated concrete properties subjected to sodium chloride attack and freeze thaw cycles

The deterioration mechanism of alkali-activated slag-fly ash-steel slag concrete (AAC) under sodium chloride attack and freeze-thaw (SF-T) cycles was investigated through a multi-scale methodology. Results showed that appropriate water glass modulus and higher Na2O dosage increased the compressive strength and salt-frost resistance of AAC. The mass loss in AAC was concentrated in the first 100 SF-T cycles, but PCC increases linearly with the SF-T cycles. The salt-frost resistance of PCC was similar to that of AAC samples Na2O dosage of 5 %. Higher Na2O dosage reduces the amount of unreacted precursor, thus reducing the porosity and improving the pore structure of concrete. However, increasing Na2O dosage has not limited the crack development, and the crack width in AAC was greater than in PCC after SF-T cycles. The porosity and average pore size of the concrete increased after SF-T cycles. Friedel's salt was only present in PCC, and NaCl crystals were observed in AAC.

Mechanical, freeze-thaw resistance and heavy metals leaching properties of alkali-activated recycled concrete powder solidified sludge

Solidified sludge was an efficient method to consume the large amount of sludge, which can be used as the subgrade filler in road engineering. However, the traditional solidified materials, such as cement and lime, consumed a large amount of natural resources and increased carbon emissions. This study used the alkali-activated recycled concrete powder (ARCP) to solidify sludge, which could be used as a potential subgrade stabilization filler. The optimal factors of ARCP were firstly determined by orthogonal test according to the compressive strength. Then the influences of different ARCP dosage, sludge moisture content and curing method on the mechanical properties, freeze-thaw resistance and heavy metals immobilization of the ARCP solidified sludge (ARCPS) were investigated. At last, microstructures of ARCPS were analyzed by SEM, XRD and TG-DTG tests. The experimental results demonstrated that the optimal mixture for ARCP: the silicate modulus of 1, liquid-solid ratio of 0.48 and calcium hydroxide content of 3 %. The solidified process by ARCP improved the mechanical properties and freeze-thaw resistance of ARCPS greatly. The 7 d unconfined compressive strength of ARCPS could reach 1305–2033 kPa when the sludge moisture content was 15 %, which meet the requirement of 500 kPa from the Chinese standard. The frost heaving rates of ARCPS were between non-frost heaving and mild frost heaving. The sludge moisture content was the most important factor affecting the freeze-thaw resistance of ARCPS. The properties of ARCPS were further improved after carbonation curing. The leaching mass concentration of heavy metals decreased significantly after the solidification of sludge. After 5 freeze-thaw cycles, the heavy metal leaching concentration increased but was still met the requirement of standards. SEM results showed that the surface of carbonated ARCPS was covered by dense scale-like carbonation products, which further enhanced the strength and freeze-thaw resistance of ARCPS. The results can be used to guide the application of sludge and ARCP in construction.

Influences of silicate modulus and alkali content on macroscopic properties and microstructure of alkali-activated blast furnace slag-copper slag

The stacking of copper slag (CS) has led to the resource wastage and environmental issues. Utilizing CS as a green precursor in the production of alkali-activated materials (AAMs) offers a promising avenue for sustainable resource usage. To obtain a deeper understanding and enhance its practical application, the effects of silicate modulus and alkali content of water glass (WG) on the performances of alkali-activated blast furnace slag-copper slag (AAS-CS) are systematically investigated though the fluidity, setting time, hydration heat, compressive strength and drying shrinkage rate. Additionally, the microstructure is characterized using nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and scanning electron microscope (SEM), respectively. When the alkali content is a constant of 6.0 wt%, the compressive strength and drying shrinkage rate initially increases with increasing silicate modulus, but eventually decrease beyond a certain threshold. At a given silicate modulus of 1.5, the compressive strength and drying shrinkage rate firstly increases and then decrease as increasing the alkali content from 4.0 wt% to 8.0 wt%. The microstructure analyses reveal that the suitable silicate modulus and alkali content promote the dissolution of precursors to form C-A-S-H gels. The M1.5N6.0 sample has a relatively tight microstructure, which benefits to the development of compressive strength, but increases the capillary stress. Therefore, the M1.5N6.0 sample has the highest 28-day compressive strength of 71.7 MPa and the largest 182-day drying shrinkage rate of 0.1532 %.

Elucidating the role of recycled concrete aggregate in ductile engineered geopolymer composites: Effects of recycled concrete aggregate content and size

Utilizing recycled fine aggregate (RFA) as silica sand replacement for ductile engineered geopolymer composites (EGC) provides a high value-added approach to recycling concrete waste and reduces the needs for high-cost silica sand. RFA contains abundant active alkaline substances which can promote the secondary geopolymerization of EGC. Substituting RFA for silica sand can improve EGC micro-characteristics, and the micro-structure of RFA-EGC is further refined with the decreased RFA size. The compressive/flexural strength of EGC is elevated as RFA is incorporated, and the decreased RFA size further enhances the compressive/flexural strength of RFA-EGC. Attributed to the micro-pores and micro-cracks in RFA, including RFA benefits the formation and development of crack, leading to an enhancement in the uniaxial tensile behavior of EGC. The tensile strength and tensile strain capacity of 100 % RFA blended EGC are 5.7 % and 8.6 % higher than those of 100 % silica sand blended EGC. The decreased RFA size can enhance the tensile strength, and an appropriate increase in RFA size improves the tensile strain capacity of RFA-EGC. When RFA size is 0.15–0.3 mm and 0.3–0.6 mm, the tensile strain capacity of 100 % RFA blended EGC is 8.6 % and 12.9 % larger than the reference EGC with 100 % silica sand (0.15–0.3 mm). A moderate increase in silicate modulus can further improve the tensile behavior, and the RFA-EGC with 1.5 M shows the best tensile behavior; besides, the longer fiber length results in the higher tensile strength of RFA-EGC. By optimizing the replacement rate and size of RFA, adjusting the silicate modulus and fiber characteristics, one can achieve a sustainable high-ductility RFA-EGC with exceptional mechanical behavior.

Promoting low carbon construction using alkali-activated materials: A modeling study for strength prediction and feature interaction

Abstract In place of Portland cement concrete, alkali-activated materials (AAMs) are becoming more popular because of their widespread use and low environmental effects. Unfortunately, reliable property predictions have been impeded by the restrictions of conventional materials science methods and the large compositional variability of AAMs. A support vector machine (SVM), a bagging regressor (BR), and a random forest regressor (RFR) were among the machine learning models developed in this study to assess the compressive strength (CS) of AAMs in an effort to gain an answer to this topic. Improving predictions in this crucial area was the goal of this study, which used a large dataset with 381 points and eight input factors. Also, the relevance of contributing components was assessed using a shapley additive explanations (SHAP) approach. In terms of predicting AAMs CS, RFR outperformed BR and SVM. Compared to the RFR model’s 0.96 R 2, the SVM and BR models’ R 2-values were 0.89 and 0.93, respectively. In addition, the RFR model’s greater accuracy was indicated by an average absolute error value of 4.08 MPa compared to the SVM’s 6.80 MPa and the BR’s 5.83 MPa, which provided further proof of their validity. According to the outcomes of the SHAP research, the two factors that contributed the most beneficially to the strength were aggregate volumetric ratio and reactivity. The factors that contributed the most negatively were specific surface area, silicate modulus, and sodium hydroxide concentration. Using the produced models to find the CS of AAMs for various input parameter values can help cut down on costly and time-consuming laboratory testing. In order to find the best amounts of raw materials for AAMs, academics and industries could find this SHAP study useful.

The research on the mechanical properties, microstructure, environmental impacts of environmentally friendly Alkali-activated ultra high performance concrete (AAUHPC) matrix with varied design parameters

Alkali-activated material prepared by the silicon aluminum solid wastes are commonly considered as the low-carbon cementitious material, which has important significance for promoting the sustainable development of construction materials. The mechanical properties, reaction mechanisms, and microstructure evolutions of Alkali-activated Ultra High Performance Concrete (AAUHPC) matrix with 7 design parameters were comprehensively studied through testing the fluidity, 28 days compressive strength, 28 days flexural strength, hydration heat, and microstructures. The environmental impacts including carbon emissions and energy consumption are evaluated. Appropriately increasing Na2O dosage, silicate modulus (Ms), and granulated blast furnace slag (GBFS) to fly ash (FA) mass ratio (GBFS/FA) and decreasing silica fume (SF) content and water to binder ratio (W/B) are conducive to accelerating the early reaction of AAUHPC. High Na2O dosage, Ms, SF content, and W/B are not conducive to increasing the 3 days reaction degree of AAUHPC, while the moderate GBFS/FA is corresponding to the higher 3 days reaction degree of AAUHPC. The optimal Na2O dosage, Ms, GBFS/FA, SF content, sand to binder ratio (S/B), fine sands content in quartz sands, W/B are 8 %, 1.4, 4.5:1, 10 %, 1.0, 50 %, and 0.34 for the 28 days mechanical properties. The acquired AAUHPC matrix with fluidity of 218 mm and the lowest porosity has 28 days compressive strength of 114.8 MPa and 28 days flexural strength of 10.6 MPa, whose microstructure has more high polymerization degree C(N)-A-S-H gels with higher Al/Si, lower Na/Al, and lower Ca/Si molar ratios. Compared to the traditional Ultra High Performance Concrete (UHPC), the environmentally friendly AAUHPC can reduce the carbon emission by 42%–52 % and the energy consumption by 5%–18 %. The total CO2 emission of per unit compressive strength (1.0 MPa) of concrete per cubic meter (CI) is in range of 2.5–3.7 kg, which is significantly lower than the traditional UHPC (6.98 kg/MPa•m3).

Quasistatic nature of subsurface densification of soda lime silicate glass under nano- and Vickers indentation

Mechanical properties of glass are critical for technical applications, thus comprehending the material response to mechanical tests is of great importance. In this study, we employ the nanoindentation combined with nanoscale infrared (nano-IR) spectroscopy combined with scattering-type scanning near-field optical microscopy (s-SNOM) and ToF-SIMS, to elucidate the nanoindentation rate dependence of plastic deformation of soda lime silicate glass. Experiment results show that the nanohardness and elastic modulus of soda lime silicate (SLS) glass exhibit a strong dependence on loading rate, while those of fused quartz (FQ) shows a much weaker dependence. The residual indent volume at fast loading conditions is smaller for SLS glass than FQ; but as the loading rate decreases, the residual indent volume of FQ and SLS glass becomes similar. The indent volume of SLS glass after sub-Tg annealing (reverting subsurface densification) shows negligible dependence on the loading rate, suggesting that the densification of SLS glass is strongly enhanced at lower indentation rate, but the shear flow is independent or weakly dependent. Using nanoscale infrared spectroscopy and ToF-SIMS techniques, the sodium ion migration in SLS glass surface in the indent is found to be associated with the subsurface densification. These results suggest the possible role of highly mobile sodium ions on in nano- and micro-scale plastic deformation behavior of SLS glass.

Effect of Steel Slag on Hydration Kinetics and Rheological Properties of Alkali-Activated Slag Materials: A Comparative Study with Fly Ash.

The effects of steel slag (SS) and fly ash (FA) on hydration heat, fluidity, setting time and rheological properties of alkali-activated slag (AAS) pastes with different silicate modulus (Ms) values were comparatively investigated. The results show that the incorporation of SS shortens the induction period, increases the cumulative hydration heat, improves the initial fluidity and decreases the setting time at low Ms, but the opposite trend is found at high Ms. FA significantly retards the reaction, reduces the hydration heat, increases the fluidity and prolongs the setting time. The addition of SS or FA reduces the yield stress and plastic viscosity of AAS paste. SS improves the rheological properties of AAS paste more significantly than that of FA at high Ms. The yield stress and plastic viscosity of AAS paste with SS or FA rise with the increasing Ms and decline with the increasing water/binder (w/b) ratio.

Immobilization properties and reaction mechanism of municipal solid waste incineration fly ash with alkali activation technology

Municipal solid waste incineration fly ash (MSWIFA) needs proper treatment prior to security landfilling because of considerable amounts of heavy metals and soluble chloride. Nowadays, alkali activation technology has become an effective solidification/stabilization (S/S) technology for MSWIFA. But few studies have been systematically carried out on the preparation techniques and reaction mechanism of MSWIFA S/S body. The effects of the technical parameters (alkali activator, sodium silicate modulus, alkali equivalent, water-solid ratio, curing regime) on the immobilization properties (compressive strength and heavy metal leaching toxicity) of MSWIFA S/S bodies were studied in this work. The hydration characteristics and reaction mechanism were also explored in depth based on the structure properties and microstructure characterization. Ca2+, Na+, SiO42−, [Al(OH)4]-, OH− dissociated from MSWIFA and alkali activator solution chemical reaction to form the silicates, aluminates and aluminosilicates with lower polymerization, and promoted the gel hydration products formation via depolycondensation. Lower Ca/Si molar ratio was conductive to the formation of amorphous substance, compactness of matrix pore structure and immobilization properties. Compared to the hydration products including halite, sylvine, glauberite, gypsum, calcite crystal, C–S–H gel contributed much more to the pore structure and strength improvement of MSWIFA S/S bodies. These findings will provide valuable theoretical basis for MSWIFA management and resource utilization promotion.

Valorization of biomass bottom ash in alkali-activated GGBFS-fly ash: Impact of biomass bottom ash characteristic, silicate modulus and aluminum-anodizing waste

Growing production of green energy from biomass has led to a surge in biomass bottom ash (BBA) generation, often relegated to landfills due to high leachable heavy metal content. This study proposed solidifying BBA in alkali-activated granulated ground blast furnace slag (GGBFS) and class F fly ash (CFA) blended binders. Investigations into the influence of BBA content, fineness, silicate modulus of activators, and aluminum-anodizing waste (AAW) on solidification performance were conducted, focusing on reaction mechanisms, phase assemblages, mechanical properties and leaching behavior. Results indicate relatively low reactivity of BBA and high leachable chloride (Cl-), sulphate (SO42-), chromium (Cr), molybdenum (Mo), lead (Pb) and zinc (Zn) contents from BBA. Increased BBA substitution leads to strength deterioration, while ground biomass bottom ash (GBBA) improves the mechanical performance slightly. This improvement is attributed to the increased reactive aluminosilicate content and an enhanced packing system resulting from finer particles. However, GBBA induces an increased heavy metals leaching. Higher silicate modulus activators enhance mechanical properties and reduce the leaching of Mo and Cl-, while lower silicate modulus activator accelerates the reaction process, promoting the formation of hydrotalcite-like phases and reducing the leaching of Cr and SO42-. Incorporating 0.5 wt% aluminum-anodizing waste improves immobilization efficiency of toxic ions, but further increases in dosage lead to higher leaching due to weakened mechanical performance. Overall, hybrid binders with 10 wt% G/BBA exhibit desirable mechanical properties, along with sufficient immobilization of leachable heavy metals, enabling their use as potential construction materials.

Research on mix design and mechanical performances of MK-GGBFS based geopolymer pastes using central composite design method

In order to alleviate environmental problems and reduce CO2 emissions, geopolymers had drew attention as a kind of alkali-activated materials. Geopolymers are easier access to raw materials, green and environment friendly than traditional cement industry. Its special reaction mechanism and gel structure show excellent characteristics such as quick hardening, high strength, acid and alkali resistance. In this paper, geopolymer pastes were made with metakaolin (MK) and ground granulated blast furnace slag (GGBFS) as precursors. The effects of liquid–solid ratio (L/S) and modulus of sodium silicate (Ms) on the performances of MK-GGBFS based geopolymer paste (MSGP) were characterized by workability, strength and microstructural tests. The regression equations were obtained by central composite design method to optimize the mix design of MSGP. The goodness of fit of all the equations were more than 98%. Based on the results of experiments, the optimum mix design was found to have L/S of 0.75 and Ms of 1.55. The workability of MSGP was significantly improved while maintaining the strength under the optimum mix design. The initial setting time of MSGP decreased by 71.8%, while both of the fluidity and 28-d compressive strength increased by 15.3%, compared with ordinary Portland cement pastes. Therefore, geopolymers are promising alternative cementitious material, which can consume a large amount of MK and GGBFS and promote green and clean production.

An innovative intelligent design method of alkali-activated foamed geopolymer: Mixture optimization and performance prediction

The complex design parameters and lack of standard mix design methods generate a difficulty in the high efficiently preparation of alkali-activated foamed geopolymer (AAFG). Therefore, this paper proposes an innovative intelligent design method of AAFG based on machine learning (ML) and Metaheuristic Optimization Algorithms (MOA). The effects of twelve factors on drying density (DD) and compressive strength (CS) of AAFG are revealed. The DD and CS predictive models of AAFG with high accuracy (R2 = 0.96 and 0.84) and strong generalization are trained through Random Forest (RF). The enlargements of proportions of granulated blast furnace slag (GBFS) and metakaolin (MK) in precursors can improve the CS but are not conducive to reduction of DD. Higher proportion of fly ash (FA) in precursors can efficiently reduce DD but can weaken the CS. Higher or lower Na2O content, silicate modulus (Ms) and water to binder (W/B) can reduce DD and CS with the optimal foaming conditions of 20 %, 1.0 and 0.75. More additions of foaming agents and foam stabilizers can reduce DD, while the CS has a remarkable degradation. Higher or lower foaming temperature (FT) is both not beneficial for the reduction of DD and enhancement of CS with the optimal FT of 60 °C. The intelligent design system of AAFG developed by RF and Slime Mould Algorithm (SMA) has easy operability, high efficiency, and good stability. The optimal preparation parameters can be efficiently acquired and the corresponding performances can be quickly and accurately predicted.

A fireproof insulation block with three-dimensional pore structure fabricated using alkali activated steel slag

In an effort to fully harness the potential of steel slag, it has been employed in the production of fire-resistant insulation blocks. A comprehensive investigation was conducted to examine the influence of sodium silicate modulus, water addition, hydrogen peroxide addition, and curing temperature on various properties such as porosity, apparent density, thermal conductivity, and compressive strength of the blocks. The results reveal that the prepared fireproof insulation block possesses a porosity of 89.6%, an apparent density of 0.334 g/cm3, a thermal conductivity of 0.177 W/(m∙K), and a compressive strength of 0.12 MPa, achieved with preparation parameters including a sodium silicate modulus of 1.5, a water content of 20%, a foaming agent addition of 4%, and a curing temperature of 50 °C. The relationship between the thermal conductivity and porosity can be accurately predicted using the NEMT model. Furthermore, to further decrease the thermal conductivity of the material, it is possible to reduce both the size and connectivity of the pores present within it. This research offers insights and avenues for the expanded utilization of steel slag in the development of building materials.

Pretreatment of alkali activation and carbonation of steel slag for using as binding material

Steel slag (SS) exhibits low hydration activities and expansive phases, which should be pretreated prior to using as binding materials. Thus, these properties of SS were improved through a combined treatment of alkali and then wet carbonation (A_C) in this study. Effect of sodium silicate modulus (M = 1.0–2.5) and carbonation temperature (50–200 °C) on cementitious property of SS was investigated. Results showed that the optimum modulus and temperature were 2.0 and 150 °C under single alkali and single carbonation treatment of SS, respectively. In case of combined treatment, the optimal modulus was 2.0 with an optimum temperature of 100 °C (A2.0_C100°C-SS). The 28 d compressive strength increased by 27.1% and expansion rate decreased by 17.7% of A2.0_C100°C-SS-PC compared to untreated SS-PC. This was attribute to the fact that the newly formed CaCO3 with micro-nano size and high activity existed in A_C-SS can react with Al-containing minerals in OPC to form monocarboaluminate, and Si-gels produced during carbonation can react with CH to form C-S-H phases. The early hydration activity of OPC was more obviously improved by adding A_C-SS compared to adding A_SS or C_SS. This was due to the micro-nano size effect of CaCO3 and Si-gels can provide nucleation sites for C-S-H formation. Alkali pretreatment can improve the SS carbonation, reaching the maximum carbonation degree of 53% at 100 °C compared to carbonation alone (47% at 150 °C). The embodied CO2 index of A2.0_C100-SS-OPC system decreased to 9.843 compared to OPC (10.511), indicating that the A_C treatment for SS was a more sustainable and environmentally friendly method.

Sustainable utilization of alkali-activated steel slag material: Effects of silicate modulus and GBFS on fresh, mechanical and pore structure properties

To improve the sustainable utilization of alkali-activated steel slag material, experiments were conducted to systematically investigate effects of sodium silicate modulus and GBFS content on the setting time, workability, mechanical properties and pore structure of alkali-activated steel slag cementitious material. Results show that the setting time is prolonged and workability is reduced as silicate modulus increases. The setting time is first shortened and then prolonged and workability is slightly reduced as GBFS content increases. Increasing silicate modulus and adding GBFS have positive effects on the development of elastic modulus, compressive and splitting tensile strength of alkali-activated steel slag material due to more refined pore structure. The highest compressive strength at 28 d can reach C35 strength level. Manufacturing alkali-activated steel slag material can achieve low energy consumption and carbon emission. If chemical activators can be replaced by some industrial wastes, cost, energy consumption and carbon footprint will be further decreased.

Effect of Surface Acidity/Basicity of Cr/Zn−BEA Zeolite Catalysts on Performance in CO2‐PDH Process

AbstractThe influence of adding Cr(III) compounds into Zn−BEA zeolite samples (with silicate modulus Si/Al=17, 100, and 1000) on the redox and acid–base characteristics of Cr/Zn−BEA zeolites were studied, and their catalytic properties in propane dehydrogenation with CO2 to propylene. It was established (based on the XRD, low–temperature (77 K) ad/desorption of N2, TPR−H2, TPD−MSC−NH3(CO2), C3H8(C3H6), FTIR−Py data) that the acid–base characteristics of the surface of bifunctional Cr/Zn−BEA catalysts, namely the amount, strength, and nature (Lewis and Brønsted sites), determine their activity/selectivity, and operation stability in the process of CO2−PDH. This indicates that over Cr/Zn−BEA catalysts, the process runs along the route of direct propane dehydrogenation combined with the reverse water gas shift reaction.