Aluminum Silicate Hydrate Research Articles

Performance assessment and cost-benefit analysis of low-carbon binders containing calcined sediments from Chorfa II dam as new building materials

Recently, considerable attention has been given to the valorization of dredged sediments around the world, which are considered waste. The reuse of dredged sediments has significantly contributed to Sustainable Development Goals. However, the efficiency and cost assessments of calcined sediments as a partial replacement for cement are not well understood. In this present investigation, the use of calcined sediments from dams as a green construction material on the properties of eco-pastes and mortars formulation is explored. Properties measurements, microscopic observation, eco-strength efficiency, and cost assessments were performed on fresh, hardened mortars in order to valorize calcined sediments in the cement industry. The best findings for the compressive and tensile strengths of mortars containing calcined sediments were obtained after 180 days, which was compared to the control mortar. Furthermore, microscopic analyses showed that an increase in the substitution rates of calcined sediment resulted in the increasing germination of calcium aluminate silicate hydrate gel (C-A-S-H) and calcium silicate hydrate gel (C-S-H). The control mortar showed an efficiency of 0.0902 MPa/kgCO2 eq for 28 days while the eco-strength efficiency of mortars containing 5%, 15%, and 25% of calcined sediments presented an efficiency of 0.0920 MPa/kgCO2 eq, 0.0922 MPa/kgCO2 eq, and 0.0997 MPa/kgCO2 eq, which represents an increase of 1.9%, 2.21% and 10.51%, respectively. However, the replacement of cement with calcined sediments up to a rate of 25% decreases embodied carbon. In conclusion, the cost of treatment of one (1) ton of sediments is lower than cement, which represents a reduction from 81.96% to 86%.

Design and characterization of iron–calcium–aluminium–silicate–hydrate as low-temperature binder

This work aims to synthesize new cementitious materials (binders) using marble powder, rice husk ash, activated laterite and NaOH solution by applying low energy process. The binder was used to stabilize solid precursors (laterite and pozzolan). To achieve this objective, calcium–silicate–hydrate (CSH) was first synthesized at different temperatures (26, 50, 80 and 100 °C). The best physical–mechanical properties were chosen to produce iron–calcium–aluminium–silicate–hydrate [Fe–C(A)SH] at different concentrations of sodium hydroxide solution: 4, 5, 6 M. Finally, the formulated binder at 6 M of NaOH solution was used to stabilize laterite and pozzolans at the following proportions 20%, 30%, 40% and 50%. The samples were characterized after 28 days of curing at room temperature. FT-infrared spectroscopy, X-ray diffraction, and environmental scanning electron microscope ESEM-EDS permitted to confirm the formation of CSH, and Fe–C(A)SH. The mechanical test used to evaluate the performance showed that the incorporation of 10% iron-rich laterite into CSH increased the strength up to 42.93 MPa and the addition of Fe–C(A)SH in the laterite/pozzolans increased the compressive strength of the final product (15.34 and 15.8 MPa for laterite and pozzolan, respectively). The highest concentration (6 M) increases the alkalinity and reduces the efficiency of silicate polymerization affecting the final structural compound. From the results, low-energy Fe–C(A)SH-based cement and stabilized compounds appeared promising for the development of sustainable infrastructures.

Understanding erosion resistance mechanisms of sodium aluminate silicate hydrate in erosion environments: a molecular dynamics study.

Sodium-aluminate-silicate-hydrate (NASH) gel, as the primary reaction product stimulated by alkali in silica-aluminum-rich minerals, influences the mechanical and durability properties of geopolymers. In erosion environments, NASH demonstrates superior compressive strength and erosion resistance compared to hydration products of ordinary Portland cement. However, the underlying erosion resistance mechanism of NASH under such conditions remains unclear. Therefore, this study employs molecular dynamics research methodology to investigate the alteration in performance and deterioration mechanism of NASH in erosive environments. The findings reveal that in Na2SO4 solution, the infiltration of H2O molecules and Na+ ions into the three-dimensional mesh structure of NASH results in slight expansion and reduced tensile strength. Although H2O intrusion induces hydrolysis of the three-dimensional skeleton, the adsorption sites within NASH possess the capability to capture externally introduced Na+ ions. During tensile loading, Na+ ions can interact with reactive oxygen species produced through stretching or H2O molecule-induced decomposition of the internal framework, facilitating the repair of fractured structures. Consequently, this process partially alleviates tensile rupture, modifies the fracture damage mode, enhances overall toughness, and improves resistance against sulfate attack.

Effect of mix proportion parameters on chloride erosion resistance of fly ash/slag-based engineered geopolymer composites

The incorporation of ground granulated blast furnace slags (GGBS) into fly ash-based engineered geopolymer composites (EGC) was explored to enhance their resistance against chloride-induced erosion. An investigation was conducted to understand how variations in the slag content, the water-to-binder ratio, the quantity of alkali activator, and the inclusion of polyethylene fibers affect the EGC's ability to resist chloride erosion. The study found an enhancement in the chloride erosion resistance with an increase in the water-binder ratio from 0.32 to 0.38. Conversely, the resistance decreased when the proportion of slag was raised from 40% to 100%, when the alkali activator content went up from 4% to 6%, and when the percentage of polyethylene fibers grew from 1.0% to 2.0%. Microstructural analyses revealed that a higher water-binder ratio of 0.38 reduced the peak intensity of calcium aluminate silicate hydrate, increasing the porosity and, thereby, compromising the chloride erosion resistance of the EGC. In contrast, increasing the slag content, alkali activator, and polyethylene fiber percentage generated the reverse effect, reinforcing the material's resistance to chloride penetration. The optimized EGC demonstrated promising chloride erosion resistance with a low chloride diffusion coefficient of 0.0661 × 10−12 m2/s, paired with robust mechanical properties including compressive strength ranging from 70 to 80 MPa, ultimate tensile strength between 5 and 6 MPa, and ultimate tensile strain reaching up to 8%.

Improving the strength of metakaolin-lime based binder

Pozzolanic reaction of low-calcium metakaolin (MK) with calcium hydroxide (CH) at ambient temperature in the presence of water forms a series of hydrated phases such as tetracalcium aluminate hydrate (C4AH13), calcium silicate hydrate (C-S-H) and calcium aluminum silicate hydrate (stratlingite - C2ASH8). Stratlingite is the main crystalline phase and is responsible for the strength of the binder. Tetracalcium aluminate hydrate (C4AH13) is carbonated upon contact with air or converted to hemicarboaluminate and/or monocarboaluminate if the system contains excess carbonate phases (calcite or calcareous aggregates). However, the calcium aluminate hydrates formed after the reaction of MK with lime lose their strength over time due to their instability. Especially in a high humidity environment where there is no carbonation, the presence of both stratlingite and (CH) in the binder creates weak phases called katoite (Ca3Al2(SiO4)(OH)8) and can reduce the mechanical strength and durability. On the other hand, it has been determined that using chemical activators to increase the pozzolanic reactivity is the most feasible method, although it increases the cost of the material. In this study, it is aimed to eliminate the phases that cause katoite formation and improve the performance of the binder by using alkaline hydroxide solution in a mixture of metakaolin and slaked lime, similar to the pore solution caused by hydrated cement. For this aim, the effect of sodium carbonate (N-Na2CO3), quicklime (C-CaO) and calcite (CC-CaCO3) on the (CH-Ca(OH)2) activated metakaolin system is investigated through the experimental campaign. The preparation of the mixtures is done by the novel one-part mixing method.

Molecular insights into the microstructure, dynamics, wettability and mechanical properties of sodium aluminum silicate hydrate with saturated nanopores

Sodium aluminosilicate hydrate (NASH) serves as the primary binding phase governing the physical, mechanical, and durability characteristics of geopolymer binders. However, the intricate interactions at the water-nanopore interface and the inherent heterogeneity of geopolymer binders present formidable challenges in exploring the intrinsic microstructure and micromechanical properties of this pivotal binding phase. In response to these challenges, we conducted reliable molecular dynamics simulations aimed at unraveling the intricate molecular-level features of NASH within saturated nanopores. Using the state-of-the-art simulations, results reveal that the structural properties of NASH remain unaffected by variations in nanopore size. Nevertheless, a critical nanopore size is identified, impacting the distribution of water molecules within the nanopore, as evidenced by the convergence of the water molecule number density. In terms of dynamics, diffusion of water molecules within the nanopore exhibits quasi-two-dimensionality, while in NASH demonstrates characteristics of supercooled liquids due to constraints imposed by the aluminosilicate network. Notably, the mechanical properties of NASH within saturated nanopores exhibit a significant decline as nanopore size increases, with uniaxial tension tests indicating the absence of strain softening. Additionally, the presence of hydroxyl groups on the NASH surface influences the adhesion of water molecules through hydrogen bonding, resulting in a pronounced hydrophilicity with a contact angle of 12.2°. The findings offer valuable insights into the behavior of NASH with saturated nanopores, shedding light on the molecular-level details of its structure, dynamics, mechanical properties, and wettability.

Effects of retarders on the rheological properties of coal fly ash/superfine iron tailings-based 3D printing geopolymer: Insight into the early retarding mechanism

To increase the utilization rate of superfine iron tailings (SIT), a novel coal fly ash (CFA)/SIT-based three-dimensional printing geopolymers (CS-3DPG) were synthesized for high-value resource application of SIT. The optimal preparation parameters of CS-3DPG were sodium citrate of 0.4%, water-solid ratio of 38%, SiO2/Na2O molar ratio of 1 and alkali activator of 6%, with the compressive strength of 32.14 MPa. Besides, the yield stress and plastic viscosity (rheological properties) of CS-3DPG reached 284 Pa and 18.8 Pa·S, respectively. The sodium aluminum silicate hydrate (N-A-S-H) gels were identified as dominant hydration products by the selective chemical extractions. Microstructural analysis also successfully indicated that the retarder caused some CFA and SIT to be unreacted, resulting in the decrease of early compressive strength compared with CS-3DPG. Based on the full width at half-maximum (FWHM) values, kinetics of hydration and hydration kinetic contribution degree results, retarders effectually inhibited nucleation and growth (NG) and diffusion (D). The phase-boundary interaction (I) reaction played a major role after adding retarders. This work successfully reveals the early retarding mechanism of CS-3DPG, and provides the possibility of large-scale resource application of SIT-based 3DPG in 3D printing construction.

Recycling of phosphogypsum and clay by-products from phosphate mines for sustainable alkali-activated construction materials

This work investigated the recycling the large quantities of phosphogypsum, generated by phosphoric acid plants, by exploring its potential use as a precursor in alkali-activated materials. The alkali-activation involved using phosphogypsum and calcined clays as precursors and an alkaline activator. The compressive strength of elaborated materials was evaluated after 28 days of curing. Additionally, various techniques were used to characterize the diverse samples. The results demonstrated the effectiveness of the alkaline activation process to induce the formation of Calcium Aluminum Silicate Hydrate and Sodium Aluminum Silicate Hydrate gels in the elaborated samples. The samples with 22.4% phosphogypsum, 11.28 M NaOH, and a liquid/solid ratio of 0.86 presented the maximum compressive strength of 27.3 MPa as they presented a more dense and less porous structure. The Toxicity Characteristic Leaching Procedure test showed no release of harmful substances. These findings suggest that phosphogypsum could be recycled in alkali-activation technology in the construction industry.

Mechanical and Microstructural Properties of Bamboo Fiber-Reinforced Concrete Containing a Blend of Waste Marble Powder and Waste Glass Powder

Using blended supplementary cementitious materials in the production of concrete has a contribution to make in reducing cement consumption, as well as having a negative environmental impact. The main objective of this study was to investigate the mechanical and microstructural properties of bamboo fiber-reinforced concrete containing a blend of waste marble powder (WMP) and waste glass powder (WGP) as a partial replacement for cement. To achieve these objectives, the physical and chemical properties of concrete ingredients were studied. The design mix was done as per the American Concrete Institute (ACI) mixing procedure by using 5%, 10%, 15%, and 20% blended WMP and WGP as a replacement for cement and 0.75% bamboo fiber as an addition. The mechanical tests were conducted after samples were cured for 7 and 28 days in water. The microstructural properties of the hardened concrete from three different mixes were also determined for the 28-day cured specimens. The study result indicated improvement in compressive strength, shear stress, and bond stress at M2 (10%), whereas maximum splitting tensile strength was achieved at M1 (5%). Moreover, scanning electron microscopy (SEM) showed a denser microstructure, whereas X-ray diffraction (XRD) illustrated portlandite, calcium aluminum silicate, quartz, and calcium silicate hydrate as common phases of the concrete structure. Eventually, the experimental finding implied that using a 10% blend of WMP and WGP as a partial replacement for cement and 0.75% bamboo fiber improves fresh and hardened concrete properties.

Strength characteristics of marine clay mixed with coal ash and cement with microstructural verification

This study uses coal ash obtained from the Tanjung Bin coal power plant consisting of a mixture of fly ash and bottom ash at different ratios. Such mixtures will be used with the minimum amount of Ordinary Portland Cement to stabilise marine clay. Compaction data corresponding to a mixture of coal ash and OPC mixed with marine clay soil provides 1535 and 1600 kg/ m 3 MDD and 18–22.2% OMC ranges, as additive percentages are increased. The unconfined compressive strength test indicated the highest increase at 50BA:50FA ratio with a value of 536 kPa at 15% of additive. The strength of the treated soil sample would also increase with increasing additive percentage and curing period. The XRD of untreated soil sample indicates composition intensity for minerals like quartz, mica, kaolinite, calcite, montmorillonite, and muscovite generally decreased with curing time; on the other hand, halloysite composition reduced. However, a new mineral is formed: calcium aluminium silicate hydroxide hydrate. Moreover, the FESEM results show that the treated marine clay surface particles looked denser with time. Structural voids were also reduced. In line with the XRD and FESEM test outcomes, the EDX results indicated that the formed cementitious products comprised calcium aluminate silicate hydrate.

Improvement of cemented rockfill by premixing low-alkalinity activator and fly ash for recycling gangue and partially replacing cement

Recycling mining wastes such as gangue for cemented rockfill is a key approach for sustainable development while ensuring the safety of underground structures in the mining industry. However, achieving sufficient strength for this low-cost material remains a fundamental challenge. This study explores an approach to strengthen cemented rockfill by using well-graded gangue, and by partially replacing Portland cement with fly ash and a premixed low-alkalinity activator. The effects of activator dosage and curing time on mechanical properties, composition and microstructure of cemented rockfill were investigated through uniaxial compression, XRD, FTIR, TG/DTG, MIP and SEM-EDS analyses. Results show overall improvements in the performance of cemented rockfill despite its low cement content, and the use of a low-cost low-alkaline activator. The 28-d compressive strength improved by over 30 % to reach 8 MPa with only 7.7 % wt. Portland cement and incorporating more than 60 % wt. of waste gangue in its mix composition. The main source of strength is calcium silicate hydrate and calcium aluminate silicate hydrate, the latter playing an increasing contribution with longer curing due to fly ash activation. Addition of premixed activator to fly ash enhanced the formation of Ca6Si6O17(OH)2, and CaO∙Al2O3∙xSiO2∙yH2O. Activator causes densification of the microstructure and this occurs predominantly on pores smaller than 1 μm. The optimum mix having the highest performance-cost ratio contains between 10 % and 15 % activator. This work reveals an effective and low-cost method of premixing fly ash with a low-alkalinity activator for recycling mining wastes and reducing cement.

Formulation and properties of a new cleaner double liquid alkali-activated grouting material

Herein, a new cleaner double liquid alkali-activated grouting material (DLAG) was successfully developed, which could be applied similarly to cement by adding water. Desulphurisation gypsum (DG) was selected to activate ground granulated blast-furnace slag (GGBFS) and fly ash (FA) to completely replace cement. The optimum proportion of the basic materials and admixtures were determined by a series of orthogonal and single-factor controlled variable experiments. The mechanism for the strength enhancement of the materials was interpreted by microscopic experiments. The optimum proportion of the basic materials was determined that slurry A comprised of only GGBFS, whereas DG, FA, and metakaolin (MK), were present in a mass ratio of 6:3:1 in slurry B. The single slurry maintained good workability over a long period before mixing, and the fluidity of mixed slurry could be dynamically adjustable from 138 mm to 215mm. The strength of solidified specimens reached 45.7 MPa at 28 days curing time, which was 220% higher than that of Portland cement. Microscopic analyses showed that Al2O3 and SiO2 in the precursor materials were continuously dissolved and reorganised to produce hybridised phase gels (C, N)-A-S-H (calcium, sodium aluminium silicate hydrate), and also hydrated with Ca2+, SO42− provided by DG to produce ettringite and calcium silicate hydrate (C-S-H) in the alkaline environment. The size and content of hydration products gradually increased with increasing curing time and acted together to enhance the strength of solidified body. The proposed material can promote the development of alkali-activated technology in the field of special grouting materials.

Effect of Micro Lime on The Ambient Cured Sugarcane Bagasse Ash-Based Geopolymer Concrete

Geopolymer concrete has been the ideal replacement for Ordinary Portland cement concrete in producing green concrete. The binder in geopolymer concrete is a cementitious paste made from amorphous Aluminosilicate and activated by an Alkaline solution. The geopolymerization process is initiated at elevated temperatures. Thus, the curing requires elevated temperatures. This curing method limits the application of geopolymer concrete in the construction industry. In a geopolymer mix, the presence of Calcium ions allows the formation of Calcium Aluminate Silicate and Calcium Silicate Hydrate gels, allowing ambient temperature curing. Therefore, this study investigates the effect of micro lime on the Sugarcane Bagasse Ash-based geopolymer concrete. The micro lime was added to the geopolymer concrete in 1, 3, 5 and 7% by the Sugarcane Bagasse Ash weight. A mix design was based on a Densified Mix Design Algorithm. The tests carried out included compressive strength and water absorption. Ambient curing of the SCBA-based geopolymer concrete was achieved with 1% of the micro lime. The compressive strength increased with the increase of the micro lime, 10N/mm2 at 1%, to 18.25N/mm2 at 7% micro lime. The ambient temperature-cured geopolymer concrete at 3% micro lime had the lowest water absorption rate.

Sustainable application of coal fly ash: One-step hydrothermal cleaner production of silicon-potassium mineral fertilizer synergistic alumina extraction

Coal fly ash (CFA) is the main solid waste discharged from coal-fired power plants, a new method for preparing silicon-potassium mineral fertilizer using KOH hydrothermal treatment CFA was proposed to improve its comprehensive utilization rate and reduce its threat to ecological environment security. In this paper, the characteristics of CFA raw material and transformation residue were studied, the agricultural applicability of the process was verified by pakchoi planting experiments, and the effects of the silicon-potassium mineral fertilizer on soil physical-chemical characteristics were investigated. The results show that increasing the leaching temperature and time can improve the extraction rate of alumina from CFA, and the reaction rate is controlled by the mixing of interfacial chemical reaction and solid product layer diffusion. The CFA raw material was hydrothermally leached at 280 g/L K2O 200 °C for 1 h, in which the Al2O3 extraction rate was 27.46%. The main component of the transformation residue was potassium aluminum silicate hydrate, which is the main component of the silicon-potassium mineral fertilizer, and the effective K2O and SiO2 content is 25.07% and 34.56%. The application of CFA residue can effectively improve the fertility and productivity of the soil, providing nutrients for the growth of pakchoi and improving the soil quality. This research provides theoretical guidance for the preparation of silicon-potassium mineral fertilizer using CFA and has the potential for practical production, which is important for the resourceful use of CFA and its application in agriculture.

Experimental study of mixtures soil-industrial waste using simplex design for application in paving

The large amount of solid waste generated by industry is a concern for society. A possible solution is to incorporate these wastes into soils to improve their properties and contribute to sustainable development. The objective of this research was to conduct an experimental study on the chemical stabilization of two samples of tropical soils using two industrial wastes, electric arc furnace slag (EAFS) and fly ash (FA), using a design of experiments (DoE) of mixtures in a simplex centroid network. Seven mixtures were determined from the DoE for each soil sample. Using specimens of these mixes prepared at optimum moisture content, after a curing period of 7 days in a humid chamber, the properties were evaluated: unconfined compressive strength (UCS), California Bearing Ratio (CBR), and resilient modulus (RM). An improvement in the evaluated mechanical properties was observed with the addition of waste, especially with the addition of EAFS. The statistical software Minitab 18 allowed to obtain response surfaces for each mechanical property studied as a function of the pseudo-components of the mixtures. To determine the proportion of components that optimized the soil-waste mixtures, the desirability function was used, which resulted in the proportions of 80% soil, 20% EAFS, and 0% FA for both soil samples. Based on SEM and XRD tests, it was found that calcium silicate hydrate (C–S–H), calcium aluminate silicate hydrate (C-A-S-H), and calcium aluminate hydrate (C-A-H) were formed, which were responsible for improving the mechanical strength. The use of industrial waste to stabilize tropical soils with low bearing capacity proved to be a technically and environmentally viable alternative.

Utilizing lithium slag to improve the physical-chemical properties of alkali-activated metakaolin-slag pastes: Cost and energy analysis

The utilization of lithium slag (LS) poses an imminent challenge in the solid waste disposal industry. In this work, ternary alkali-activated materials (AAM) were synthesized for the first time using a combination of LS, metakaolin (MK) and granulated blast furnace slag. The roles of LS replacing MK ratio (LRMR) on rheology, initial fluidity, setting time, compressive strength, heat release, phase composition, microstructure, cost and energy consumption were investigated. The results show that the substitution of LS leads to a reduction in the yield stress of the paste and an increase in its initial fluidity, which can be attributed to the comparatively lower specific surface area of LS compared to MK. Additionally, incorporating LS deepens the early reaction degree of the paste, so the setting time is shortened. Moreover, the incorporation of LS improves the compressive strength of the samples by promoting increased calcium (aluminate) silicate hydrate gel formation and refining pore structure. In terms of cost and energy consumption, the samples with LRMR of 25 % and 50 % exhibit a cost index that is respectively 37.2 % and 48.7 % lower than that of the control sample without LS, resulting in corresponding decreases in energy indexes by 24.1 % and 21.4 %. The findings may shed valuable light for the rational utilization of natural mineral resource (MK) and industrial by-product (LS).

Investigating the synergistic effect of graphene nanoplatelets and fly ash on the mechanical properties and microstructure of calcium aluminate cement composites

Nanomaterials like graphene nanoplatelets (GNP) have been extensively applied in various fields as reinforcing materials offering excellent mechanical properties. However, for calcium aluminate cement (CAC) composites, the investigation of the GNP reinforcing effect is lacking. The synergistic effects of GNP and fly ash (FA) in CAC composites were evaluated in this study. The GNP was initially dispersed in mixing water using a dispersant combined with ultrasonication. The CAC composites with different GNP contents were prepared and their mechanical performance was investigated. In addition, partial replacement of CAC with FA was investigated for increasing sustainability and material cost of GNP-CAC composites. Their fresh properties, mechanical properties, and microstructural performance were analyzed using different techniques involving flowability, bulk density, volume of permeable void, water absorption, compressive strength, splitting tensile strength, flexural strength, nitrogen adsorption, TGA, and SEM-EDS tests. Using FA and GNP in CAC composites offers a positive impact by significantly increasing their strengths. Optimized mix was achieved by replacing 20% of FA and adding 0.3% of GNP in CAC composites. Results revealed that the 20% FA replacement of cement with 0.3% GNP addition remarkably increased the compressive, splitting tensile and flexural strengths at 28 days by about 57.2%, 35.5%, and 21.7%, respectively. The results suggest that using FA and GNP contributes to synergistic effects to promote the formation of silica tetrahedron in calcium aluminate silicate hydrate (CASH) gel, to refine pore characteristics, and to reduce conversion effects of metastable phases of CAC such that it can ultimately produce a green rapid-set high-performance concrete system.

Enhancing the properties of alkali-activated slag through dry ice addition: Investigation of hydration products and performance characteristics

To study the effect of dry ice on the performance of alkali-activated binders, we added dry ice to an alkali-activated slag (AAS). The addition amount was set to 5%, 10%, and 15% of the slag mass, depending on the amount of CO2 emitted by the material used in the preparation process. Microscopic experiments were performed to analyze the effect of dry ice on the hydration products of the AAS paste; transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the hydration products. Furthermore, experimental tests for the compressive strength, ultrasonic pulse velocity, and electrical resistivity were performed. The results showed that compared with the content of the overall reaction products, the effect of dry ice on the reaction rate was more evident. The addition of dry ice slowed the hydration of the AAS, and the production of the hydration products, such as calcium aluminum silicate hydrate (C-A-S-H) gels, was significantly reduced in the early stage (1 d). Experiments on the strength showed that adding more than 5% dry ice degraded the early mechanical properties of the AAS. However, the mechanical properties of the AAS with dry ice added in the middle (3 and 7 d) and late (28 d) stages rapidly improved because the dry ice was added to the AAS to form potassium and calcium carbonate. In the middle (3 and 7 d) and late (28 d) stages, CO32− underwent a carbonation reaction to form carbonate compounds, enhancing the mechanical properties of the AAS.

Fiber-Reinforced Alkali-Activated Cements from Ceramic Waste and Ladle Furnace Slag without Thermal Curing

Alkaline-activated cement, as an alternative to conventional portland cement, is being increasingly studied due to its environmental advantages and engineering properties. However, research on the feasibility of using both uncommon precursors and curing at ambient temperature is still limited. This study aims to investigate the potential of ceramic wastes, specifically from brick and tile production and ladle furnace slag, as precursors in alkaline activated cement reinforced with polyacrylonitrile fibers cured at 20°C. Sodium silicate, in solution form, was used to activate the precursors, and three different fiber contents were tested, namely 0%, 0.5%, and 1%, by volume. Physical properties, such as capillarity and porosity, were assessed. Moreover, the mechanical behavior was thoroughly characterized by uniaxial compressive, flexural, and elasticity modulus tests. In addition, a thorough microstructural characterization, including scanning electron microscopy, X-ray energy dispersive analyzer, X-ray diffraction, and Fourier transform infrared spectroscopy was conducted at 14, 28, and 90 days. The results revealed that environmentally friendly alkali-activated binders were produced from wastes with limited industrial recycling possibilities. The mixture with 0.5% fibers was the one that presented better results, i.e., a flexural strength of 8.84 N/mm2 and compressive strength of ∼29 MPa at 90 days. The mechanical performance of this material is relevant, especially considering that a relatively low curing temperature was applied. The results also showed that calcium aluminum silicate hydrate (C-A-S-H) was detected as the main reaction product.Practical ApplicationsAlkali-activated cement has been identified as a potential alternative to traditional portland cement due to advantages such as the reduction of CO2 emissions to the atmosphere, and the conservation of natural resources, because wastes can be transformed into useful products. All over the world, ceramic materials are widely used in different types of construction, and significant amount (between 30% and 45%), end up as waste. Therefore, this study aims to show the possibility of reusing ceramic waste for the development of a fiber-reinforced alkaline activated cement composite with acceptable physical and mechanical properties that allow it to be used in non-structural applications; for example, bricks, tiles, partition walls, and other building materials. It also is a low-energy consumption process, because curing can be done at ambient temperatures. Finally, the obtained results, e.g., flexural strength of 8.84 N/mm2 and compressive strength of 29 MPa, open the door for several applications in the construction industry.

Crystallization of C-S-H and C-A-S-H in artificial seawater at ambient temperature

Calcium silicate hydrate (C-S-H) or calcium aluminum silicate hydrate (C-A-S-H) are the primary binding phases of Portland and blended cementitious systems. This study investigated the effect of seawater on the crystallization of C-S-H and C-A-S-H with different Al dosages and pH conditions up to 90 days of curing using different experimental techniques. The results showed that the gel phases converted to the crystalline phase, which is known as tobermorite, after 56 days of exposure to seawater under ambient temperature and pressure. It was also observed that relatively low pH (8.2– 10) and Al content within a specific range aided the crystallization of the tobermorite from the gel phase. However, at a high dosage of Al, katoite was observed to precipitate instead of tobermorite. The hydrothermally synthesized tobermorite in different pH conditions and Al-contents also confirmed the role of pH and Al on the crystallization of this phase.