Sulfoaluminate Cement Research Articles

Effects of Urea and Sodium Tripolyphosphate on the Hydration and Leaching of Cr(VI) in Solid Waste–Based Sulfoaluminate Cement

Effects of Urea and Sodium Tripolyphosphate on the Hydration and Leaching of Cr(VI) in Solid Waste–Based Sulfoaluminate Cement

Preparation activated tailings by pH swing process: Towards yielding cemented tailings backfill and in-situ CO2 mineralization

In-situ CO2 mineralization of tailings has shown great potential for large-scale CO2 sequestration, but its development is seriously limited by the low CO2 conversion rate. This study proposed an innovative pH swing process to produce activated tailings through magnesium extraction from raw tailings and subsequent leachate precipitation. By the combination of activated tailings and high-belite calcium sulfoaluminate cement, a new type of cemented activated tailings backfill (CATB) was developed. The results demonstrate that 82.33% of magnesium is extracted from raw tailings and precipitates in the form of Mg(OH)2 serving as the dominating carbonation active phase during the pH swing process. Besides the aragonite forms in the carbonated cemented raw tailings backfill (CRTB), carbonated CATB also contains calcite, nesquehonite, and hydromagnesite. Substituting activated tailings for raw tailings led to the higher CO2 absorption capability (ranging from 8.88% to 14.17% with various binder-to-tailings ratios). These indicate that the activated tailings have a promising application scenario in large scale in-situ CO2 mineralization.

Study on the chloride ion binding rate of sulfoaluminate cement mortars containing different mineral admixtures

In this study, the chloride ion (Cl−) binding rate of sulfoaluminate cement (SAC) mortars containing different mineral admixtures was investigated. This is essential to improve the durability of concrete structures in high Cl− environments, especially where they are susceptible to Cl− attack such as coastlines and marine structures. The effects of Cl− concentration, curing age, and the type and amount of mineral admixture on the Cl− binding rate of SAC mortars were analyzed. It was found that the content of water-soluble Cl− in SAC mortars decreased with the increase of curing age, while the Cl− binding ratio increased accordingly, indicating that its resistance to internal Cl− permeation increased. The addition of fly ash (FA) and ground granulated blast furnace slag (GGBS) can significantly improve the Cl− binding rate of SAC mortars, and the Cl− binding rate increases to 46.6% with 20% of FA and 38.7% with 40% of GGBS. The effects of mineral admixtures on the microstructure and phase composition of SAC mortars were further investigated by X-ray diffraction (XRD) analysis. The results showed that the addition of FA and GGBS promoted the formation of C-S-H (calcium silicate hydrate) gels and improved the resistance of SAC mortars to Cl− penetration. On the other hand, the excessive addition of silica fume (SF) decreased the Cl− binding rate, whereas a moderate amount of limestone powder (LP) improved the Cl− binding rate. The study of the Cl− binding rate of SAC mortars can help to evaluate their resistance to Cl− erosion in real projects, thus guiding the optimization of concrete formulations and the improvement of durability.

Effect of different amounts of barium substitution for calcium on the hydraulic activity of the high belite binary C2S-C4A3$ system

The substitution of Ba2+ for Ca2+ in both dicalcium silicate (C2S) and ye'elimite (C4A3$) has the potential to stimulate the development of early hydration activity of high belite sulfoaluminate cement (HBSAC). To relieve the emission pressure of CO2 in the cement industry and promote the early compressive strength development of HBSAC, the C2S-C4A3$ binary system with different amounts of Ba2+ substitution for Ca2+ was synthesized and investigated in this study. The SEM-EDS and XRD test methods confirmed the stoichiometric composition of Ba-bearing C2S-C4A3$ binary systems. The results showed that Ba2+ tends to preferentially replace Ca2+ in C4A3$ compared to replacing Ca2+ in C2S, resulting in more substitution amount of Ba2+ in C4A3$ mineral, as the designed substitution amount of barium increased from 25 wt.% to 55 wt.%, the stoichiometric formula of Ba-bearing C2S was transformed from Ca1.66Ba0.34SiO4 to Ca1.45Ba0.55SiO4, and the stoichiometric formula of Ba-bearing C4A3$ was transformed from Ca2.29Ba1.71Al6SO16 to Ca0.86Ba3.14Al6SO16. While excessive amount of barium (more than 45 wt.%) resulted in the increased content of by-products, such as BaSO4 and BaAl2O4, as well as the formation of C3S. The hydration properties of each group of synthetic clinker were investigated, including compressive strength, qualitative and quantitative analyses of the hydration products, leaching solution environment, and micromorphological analysis. The hydration products including C-(A)-S-H and AH3, as well as hydroxide (Ca(OH)2 and Ba(OH)2·8H2O), which can be carbonated to form carbonates (BaCO3 and CaCO3) by CO2 in the air. As the substitution amount of Ba2+ increased from 25 wt. % to 35 wt. %, the hydration degree of Ba-bearing α′L-C2S was promoted in the early stage, and the presence of C3S may affected the increase of early hydration activity of Ba-bearing α′L-C2S, however, the hydration degree of α′L-C2S with the most amount doping of barium in A055 samples exhibited the highest hydration degree of 88.0 % after hydration for 90 days. The compressive strength of high belite C2S-C4A3$ binary system of 3-day displayed a rapid increase from 8.6 MPa to 16.1 MPa, with the amount of barium increased from 25 wt. % to 55 wt. %. The compressive strength of A025 and A035 after hydration for 90 days increased steadily, reaching 35.0 MPa and 34.0 MPa respectively. However, the compressive strength of hydrated A045 and A055 samples for 90 days deteriorated and even cracked seriously for the hydrated A055 sample, which was attributed to the formation of a large amount of Ba(OH)2·8H2O and BaCO3 by excessive barium amount, and leading to the expansion and broken of the matrix. Thus, the designed amount of barium substitution for calcium in the C2S-C4A3$ binary system should be controlled, for a higher content of barium more than 35 wt. % could be damage to the development of the long-term hydration strength of the clinker. These results provided a theoretical basis to make it possible for the large-scale application of activated HBSAC, devoted to the sustainable development of infrastructure.

Carbon dioxide emission evaluation of biochar based vegetation concrete for ecological restoration projects

Vegetation concrete is increasingly being used for slope stabilization in highways, green roofing in urban developments, and erosion control in coastal areas due to its sustainable solutions for enhancing landscape aesthetics, mitigating pollution, and protecting the environment. However, the environmental and economic impacts of different mix proportions, particularly concerning CO2 emissions, remain insufficiently explored. This study aimed to identify the optimal mix proportions of vegetation concrete through laboratory testing that minimize CO2 emissions while ensuring compatibility with plant growth and cost-effectiveness. The vegetation concrete mix were prepared using different quantities of biochar (5 %, 10 %, and 15 %) and cement content (4 %, 8 %, and 12 %) by weight to evaluate their impact on porosity, unconfined compressive strength (UCS), alkalinity, plant compatibility, cost-effectiveness, and CO2 emissions from raw materials. The results indicate that increasing the biochar content from 0 % to 15 % led to a 16 % reduction in porosity and a 92 % increase in UCS of vegetation concrete. Similarly, increasing the cement content from 0 % to 12 % resulted in an 11 % decrease in porosity and a substantial 200 % increase in the UCS of vegetation concrete. Moreover, the addition of 5 % biochar had a beneficial effect on plant growth, however, increasing the biochar content beyond this level adversely impacted plant development. Based on laboratory test results, the recommended optimal mix for vegetation concrete includes a mix of 5 % biochar, 8 % low-alkaline sulfoaluminate cement, 6 % sawdust, and 6 % ferrous sulfate. The analysis of CO2 emission of the materials studied showed that cement contributed the most to CO2 emissions, followed by biochar, sawdust, water, and soil. Notably, the utilization of sulfoaluminate cement led to a 31.8 % reduction in CO2 emissions compared to Portland cement, while also lowering the overall cost of vegetation concrete by 24.7–33.8 %. This research underscores the necessity of scientifically establishing relationships between the composition of plant-based concretes and their environmental and economic performance. In summary, this study identifies optimal mix proportions for vegetation concrete, leveraging low-alkaline sulfoaluminate cement and biochar to minimize CO2 emissions, enhance landscape aesthetics, and ensure compatibility with plant growth, thus emphasizing its potential as a sustainable and cost-effective construction material.

Enhancement in clinker hydration degrees and later stage-ettringite stability of calcium sulfoaluminate cements by the incorporation of dolomite

The hydration degrees of clinkers and ettringite stability in calcium sulfoaluminate (C A) cements in the presence of externally supplied dolomite were investigated in this study. The mineralogical and microstructural characteristics of C A cements containing different dosages of dolomite were characterized using X-ray diffractometry, Rietveld refinement-based quantification analysis, thermogravimetry analysis, mercury intrusion porosimetry, scanning electron microscopy observation, and energy dispersive spectroscopy point analysis. Furthermore, the binder systems were simulated using thermodynamic modeling to observe the phase changes of hydration products and the underlying hydration kinetics. The incorporation of dolomite accelerated clinker consumption and enhanced the stability of ettringite throughout the testing period, due possibly to the nucleation seeding effect and provision of carbonate ions by dolomite. The modeling outcomes showed the stability of ettringite at later stage by the incorporation of dolomite in the simulated timeframe, yet the active dissolution of dolomite assumed in the modeling procedure overestimated the Mg-bearing hydrates in the samples.

Rapid CO2 catalytic activation of binary cementing system of CSA and Portland cement

This study presents a novel approach to activating a binary cementing system composed of calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC) using an instant CO2 catalysis. The activation led to significant and rapid strength enhancement, with the binary cement achieving a strength of 15.42 MPa immediately after activation, all within 1 min. The rapid CO2 activation catalyzed a notable heat release, accelerating the hydration of ye'elimite to form ettringite, which is a crucial component capable of bridging gaps and imparting high initial strength. Simultaneously, the CO2 activation catalyzed the increase in sulfur concentration, which in turn, also facilitated the formation of ettringite at an early age. Subsequent strength development was attributed to belite hydration. Apart from the rapid strength gain, employing CO2 activation facilitated control over the pH value of the pore solution, thus enabling the manipulation of ettringite's crystal morphology to strategically enhance the microstructure. Samples with lower pH values exhibited needle-like ettringite formations, whereas samples with higher pH values yielded rod-like and column-like ettringite crystal structures. Comprehensive analytical investigations were analyzed using XRD, FTIR, TGA, 27Al NMR, MIP, SEM, and ICP-OES. The present study provides a new perspective on the potential application of CSA-based cement, such as precast concrete element, instant concrete product delivery, and urgent reconstruction.

Hydration characteristics of calcium sulfoaluminate cements synthesized using an industrial symbiosis framework

Calcium sulfoaluminate (CSA) cement offers a sustainable alternative to ordinary portland cement by using less energy and producing fewer CO2 emissions. However, the high cost and limited availability of alumina-rich resources like bauxite pose significant challenges for CSA cement production. This study addresses these issues by synthesizing CSA cement through an industrial symbiosis framework, incorporating natural materials (limestone and gypsum) with industrial wastes and by-products (Serox, ladle furnace slag, ceramic waste, and glass waste). This approach aims to minimize these challenges to CSA production while promoting environmental sustainability in the construction industry. Laboratory studies have resulted in the successful synthesis of three distinct CSA cements with at least 40 % recovered material content. Ye'elimite, anhydrite, merwinite, and fluorellestadite were identified as major compounds of the CSA cements. Hydration studies revealed ettringite as the primary hydration product, contributing to rapid strength gains with compressive strengths over 30 MPa within a day. In addition, a tendency to ettringite carbonation was observed over the long term, the adverse effects of which need to be further investigated. These results demonstrate the feasibility of producing environmentally friendly CSA cements through industrial symbiosis and highlight their potential for scalable and sustainable construction applications.

Performance optimization design of high ductility concrete rapid repair material incorporating coal gangue aggregate

In order to solve the problem of efficient and effective repair after brittle cracking of concrete on road and bridge deck pavements, and to consider the resource utilization of coal gangue solid waste, the river sand was replaced by coal gangue and a high ductile concrete rapid repair material (HDCRRM) was prepared through performance optimization design. First, the fluidity and compressive strength of materials mixed with different amounts of sulfoaluminate cement (SAC), fly ash, lithium carbonate, calcium hydroxide, calcium formate, sand-binder ratio, water-binder ratio and polycarboxylate superplasticizer were studied, so as to determine the preferred benchmark mix proportion. Then, the replacement rate of coal gangue was optimized to develop HDCRRM. Test results show that the reduction of SAC cement and the increase of fly ash content can weaken the compressive strength of material. The rational design content of lithium carbonate, calcium hydroxide, calcium formate, sand-binder ratio, water-binder ratio and polycarboxylate superplasticizer all can improve the fluidity and compressive strength of the materials within a certain range. When the replacement rate of coal gangue aggregate increases, the tensile elastic modulus and ultimate tensile strength of HDCRRM material decrease, while the ultimate tensile strain increases. When the replacement rate of coal gangue aggregate is 100 %, the compressive strength of HDCRRM is 40.5 MPa, the ultimate tensile strain is 2.83 %, and the average crack width is 50.27μm. The early compressive strength of HDCRRM is mainly provided by a large amount of ettringite and C-S-H gel.

Early Hydration of Calcium Sulfoaluminate Cement at Elevated Temperatures

Early Hydration of Calcium Sulfoaluminate Cement at Elevated Temperatures

Hydration characteristics and hydration products of calcium sulfoaluminate cement and fly ash blended pastes

This study investigated a binary blend of calcium sulfoaluminate cement and fly ash with a target compressive strength of more than 32.5 MPa based on the EN 197-1 standard, using as much fly ash as possible. In the binder system of calcium sulfoaluminate cement and fly ash, a decrease in the replacement level of fly ash results in an increase in compressive strength. Mortar with a 40% replacement level of fly ash for calcium sulfoaluminate cement and added gypsum shows 49.41 MPa strength at 28 d. Its hydrates are hydroxy-AFm, ettringite, crystalline aluminum hydroxide, amorphous aluminum hydroxide, strätlingite, and monosulfate. They are attributed to the hydration of ye’elimite, C2S, and C3A in calcium sulfoaluminate cement. The reactivity of fly ash is not observed until 28 d of hydration. The formation of ettringite is the main cause of the gains in compressive strength.

Phase quantification of anhydrous CSA cements: a combined X-ray diffraction and Raman imaging approach

Calcium sulfoaluminate (CSA) cements are known for their special properties, such as shrinkage compensation and high early-age strength. These properties are dependent on the hydrated phase assemblage, which in turn is governed by the phases present in the initial anhydrous cement. However, the anhydrous CSA phase quantification by X-ray diffraction (XRD) Rietveld can be challenging due to the presence of overlapping peaks, polymorphs and preferred orientation. To overcome this problem, an approach involving high-resolution large-area Raman imaging (5 mm × 5 mm, 250 000 pixels, with 10 μm/pixel resolution) complemented by XRD analysis is introduced. This integrated approach of combined XRD and Raman imaging is found to be crucial in the initial identification of phases that are present in a CSA system. Most importantly, quantitative analysis shows a strong correlation (R2 > 0.99) and agreement (variation <5 wt%) between the two independent methods, adding confidence and reliability to the phase assemblage obtained by this dual-technique approach.

Evaluating carbonation resistance and microstructural behaviors of calcium sulfoaluminate cement concrete incorporating fly ash and limestone powder

This study investigates the effects of accelerated carbonation on calcium sulfoaluminate (CSA) cement concrete, focusing on mixtures enhanced with 20 % fly ash (FA), 20 % remediated fly ash (RF), 15 % limestone powder (LP), and a combination of 20 % FA with 15 % LP (35 %). The study further evaluates the mechanical properties including compressive strength, splitting tensile strength, elastic modulus, along with drying shrinkage and bulk resistivity. To delve into the microstructural characteristics of moist curing versus carbonation exposure on the CSA cement system, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were employed, particularly analyzing phase assemblage changes. The results show that the addition of FA reduced the carbonation depth in concrete mixtures over time (105 days). However, LP and the combination of FA and LP presented mixed effects. The microstructural analysis highlighted ettringite as the predominant phase in samples moist cured for 3 days. In contrast, carbonation-cured samples were characterized by different calcium carbonate (CaCO3) polymorphs alongside aluminum hydroxide (Al(OH)3) and residual ye'elimite, with the formation of low-pH carbonic acid facilitating the conversion of ettringite into CaCO3. This study highlights the impact of different SCMs on the durability and microstructural characteristics of CSA cement concrete, underscoring the interplay between curing methods, effects of SCM, and carbonation processes.

Performance of high-strength green strain-hardening cementitious composites incorporating CSA/CAC cements and GGBS

Strain-hardening cementitious composites (SHCCs) possess crack control and durability properties. In the pursuit of reducing CO2 emissions and addressing potential issues of slow strength development for SHCCs with pozzolans, the objective of this study was to develop high-strength green SHCCs (HSG-SHCCs) that exhibit improved early strength, drying shrinkage, and environmental friendliness. A ternary binder system was proposed, comprising of ground granulated blast furnace slag (GGBS), ordinary Portland cement (OPC), and either calcium sulfoaluminate cement (CSA) or calcium aluminate cement (CAC). The fresh, mechanical, and durability properties of the proposed HSG-SHCCs were experimentally investigated. Additionally, the microstructures and chemical phases of the developed CSA/CAC-GGBS-OPC ternary binder system were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that the developed HSG-SHCCs demonstrated 6-hour and 28-day strengths of up to 11 MPa and 110 MPa, respectively. The CSA/CAC-based ternary binder system also exhibited enhanced durability and improved drying shrinkage. However, the inclusion of CSA and CAC in HSG-SHCCs could lead to a reduction in tensile performance, specifically in strain capacity. The main hydration products of the CSA/CAC-GGBS-OPC ternary binder system were C-S-H, ettringite, gibbsite, and calcium hydrate. In addition to the fresh, mechanical, and durability properties, the environmental impact of the developed HSG-SHCCs was also assessed. The results indicated that a 30 % replacement of OPC with CSA cement in the HSG-SHCC mix notably improved the trade-off among CO2 emissions, compressive strength, and tensile cracking resistance.

Synthesis and properties of a belite–calcium sulfoaluminate cement obtained using only waste materials

Synthesis and properties of a belite–calcium sulfoaluminate cement obtained using only waste materials

Feasibility of Sprayable Engineered Cementitious Composites Using Natural Sand and Low Fiber Content: Effect of Hybrid Fiber System, Silica Fume, and Air-Entraining and Shrinkage-Reducing Admixtures

Deterioration of corrugated steel culverts (CSCs) is a significant problem for the Virginia Department of Transportation and other U.S. transportation agencies. Spray-on lining using shotcrete engineered cementitious composites (ECCs) is a promising structural repair strategy for deteriorated CSCs. This study evaluates the feasibility of practical sprayable ECCs using natural silica sand and low fiber content, while forgoing the use of commonly utilized calcium sulfoaluminate cement to allow for delivery of the materials via ready-mixed concrete trucks. Aspects of the compositional space evaluated include the effect of a hybrid polyvinyl alcohol/polyethylene fiber system, silica fume (SF), shrinkage reducing admixture (SRA), and air-entraining admixture (AEA) on the properties of the composites. Experimental results suggested that the development of the proposed materials is feasible, because flow characteristics associated with shotcrete ECCs and ECC-like tensile ductility were achieved in the fresh and hardened state, respectively. Notwithstanding, further mixture optimization may be required for satisfactory field performance, which should be assessed through field testing. Generally, the use of the hybrid fiber system tended to improve the strength and ductility of the composites, especially when coupled with the use of SF. Furthermore, SF was effective at mitigating the strength loss associated with the incorporation of AEA and SRA, and meaningfully improved surface resistivity. SF also tended to reduce the mixture’s flow, whereas the contrary occurred with the use of SRA and AEA. SRA contributed to the reduction in drying shrinkage at early ages. However, the effect of SRA in reducing shrinkage was negligible at later ages.

Sulfoaluminate cement-modified loess as bioretention cell filler for nutrient removal from stormwater runoff

In order to reduce the consumption of sand and gravel resources, the use of loess can reduce transportation costs and realize the in-situ construction of spongy in areas with rich loess resources. But the collapsibility and low permeability of loess make it unable to be directly used as the filler of bioretention cells. In this study, sulfoaluminate cement (SAC) mixed with a small amount of basalt fiber was considered to be used for loess modification, and the physicochemical properties and nutrient removal effect of SAC-modified loess as filler in bioretention cells were comprehensively evaluated. The results showed that when the SAC dosage was 15% and the basalt fiber addition was 0% (S15B0) and 0.6% (S15B6) and the curing time was 14 days, the stability and appropriate permeability can be exhibited, which can preliminarily satisfy the requirements of bioretention cell. SAC made the maximum adsorption capacity of S15B0 and S15B6 for ammonia nitrogen (NH4+-N) and phosphate higher than that of sand by 10.96%–31.51% and 45.92%–76.72%, respectively. The hydration products in SAC modified loess can fill the internal pores of loess particles and provide structural support, and ultimately reduce the accumulated pores, mesoporous pore size (20%) and surface homogeneity. Both S15B0 and S15B6 showed good removal effects of NH4+-N and COD. The TP removal efficiency was stable at 95.43%∼99.95%. Both the antecedent drying days and the submerged zone have an effect on the nitrogen removal in the bioretention cells, where a longer antecedent drying days is detrimental to the nitrogen removal, and the installation of a submerged zone improves the nitrogen removal. The basalt fiber can enhance the transformation process from nitrate-nitrogen to nitrite-nitrogen in the bioretention cell. Therefore, the modification of SAC can provide a certain idea for the in-situ use of loess as the filler of the bioretention cell.

Effect of phosphorus impurities on sulfoaluminate cement-modified gypsum-based self-leveling mortar and improvement method

The preparation of gypsum-based self-leveling mortar (GSLM) from solid waste-derived sulfoaluminate cement-modified hemihydrate gypsum is an effective path to enhance its mechanical properties. However, the phosphorus impurities in phosphogypsum (PG) still pose a challenge to the hemihydrate gypsum & sulfoaluminate cement composite system. To evaluate the impact of phosphorus impurities and develop targeted removal strategies, this study first assessed the effects of different types of phosphorus impurities on the mechanical properties and hydration characteristics of the GSLM. Then, a method of pretreating PG with carbide slag (CS) was proposed, and the removal efficiency and mechanism of phosphorus were examined by ICP-OES and XPS testing. The results indicated that the soluble phosphorus impurities severely inhibit the hydration of both CŜH0.5 and C4A3Ŝ, leading to a most notable reduced mechanical performance. The sequence of inhibitory action was as follows: H3PO4 >> Ca(H2PO4)2·H2O > CaHPO4·2H2O > Ca3(PO4)2. CS could effectively immobilize the soluble phosphorus in PG. The pretreatment by CS notably enhanced the hydration degree of the GSLM by converting soluble phosphorus into Ca3(PO4)2 beforehand. In addition, the alkaline environment provided by CS promoted the ettringite formation. When the CS content approaches 3%, a PG-based GSLM with good performances meeting the G20 standard requirements of GSLM can be prepared.

Study on the composite compatibility and interfacial properties of excess sulfate phosphogypsum cementing system to OPC and C[formula omitted]A

Releasable sulfate contained in the Excess Sulfate Phosphogypsum Cementing System (ESPCS) potentially degrades interfaces when contacted with conventional cements, raising incompatibility concerns. This work evaluated fresh connection, adhesion, and aggregate embedment of ESPCS to ordinary Portland cement (OPC) and Calcium sulfoaluminate cement (CS¯A), with mechanical and interfacial properties studied. Results indicate the discrepancy in hydration properties gives Excess-sulfate Phosphogypsum Slag Cement (EPSC) uncoordinated expansion to OPC, followed by cracks (95 μm) generation. Meanwhile, expansive ettringite forms in the interface due to bleeding sulfate-rich water concentration, thus leaving a porous contact zone (1240 μm, 11.29%) and resultant flexural strength reduction of OPC-EPSC mortar (by > 36%). Conversely, EPSC and CS¯A are close in phase assemblages, resulting in compact interface and higher bond strength. Incorporating the Phosphogypsum-based Cold Bonded Aggregates (PCBAs) into OPC induces the interfacial ettringite formation-sulfate attack by internal curing water, yielding the worst composite performance, i.e., the lowest 360 d compressive strength (38.8 MPa) of concrete OPCC, lower than EPSCC (48.6 MPa) and CS¯AC (50.3 MPa). ESPCS is more compatible to CS¯A than OPC which is advised against exposing directly with ESPCS. This work helps specify composite feasibility and conditions of ESPCS with typical cement composites.

Utilization of recycled coral sand and aluminum scraps in foam concrete: Preparation, insulation of environmental noise and heat, and pore structure

The utilization of industrial and marine wastes in building materials can significantly mitigate resource consumption and environmental hazards. In this study, the waste aluminum scraps and coral sand were utilized as foaming agent and fillers for foam concrete (FC) to address application challenges associated with industrial and marine wastes. Simultaneously, their impact on the mechanical property, heat and noise insulation properties, as well as pore structure of FC were investigated. The response surface methodology was used to optimize the mix design of FC. Heat and noise insulation characteristics of FC were tested by a visible infrared thermometer and a self-manufactured soundproof device, while the pore characteristic was analyzed by digital image processing technique. Additionally, the effect of foaming agents and coral sand on the internal pore structure of FC was studied by means of microscopic analysis(FTIR, XRD, SEM). The results show that foam content significantly influenced the performance of FC. As the foam content reached 15%, the compressive strength was the worst (ranging from 1.26 to 1.59MPa). Additionally, foam and coral sand inhibited the expansion of sulfoaluminate cement. At 15% foam content and 30% coral sand content, the thermal conductivity decreased to 0.082 W/(m·℃), representing a reduction of 52.5% compared to the control group. Regarding noise reduction performance, a foam content of 10% yields optimal results. The heat and noise insulation properties were both improved due to the enhanced porous structure of coral sand. However, excessive admixtures, such as 50 % content of coral sand, could weaken the strength by destroying the fine pore structure. Microscopic analysis further revealed that foaming agents could affect the hydration of cement with little impact on macro performance. Moreover, they also enhanced the toughness of bubbles and changed the surface structure of pore walls to ensure the integrity of the pore structure of FC.