Sulfate Environment Research Articles

Durability Evaluation of GGBS-RHA-Based Geopolymer Concrete Along with Lightweight Expanded Clay Aggregate Using SEM Images and EDAX Analysis

The durability of geopolymer concrete containing Ground Granulated Blast Furnace Slag (GGBS) and Rice Husk Ash (RHA), along with Lightweight Expanded Clay Aggregate (LECA), was investigated. Six different LWGPC mixtures were made with NaOH molarities of 8, 10, and 12M. For each molarity, two combinations of source materials were selected: 100% GGBS (G) and 80% GGBS with 20% RHA (RG). In all the mixtures, coarse aggregate was substituted with 35% LECA. LWGPC mixtures were exposed to 3% HCl, 5% MgSO4, and 3.5% NaCl for studying the durability properties. The test results demonstrate that 100% GGBS with 12M NaOH (12G) outperformed all other mixtures. The residual compressive strength of 12G mix LWGPC specimens after six months of exposure was found to be 86.4% in an acid environment, 90.6% in a sulfate environment, and 91.4% in a salt environment. The elemental composition analyzed using EDAX reveals that silica, alumina, calcium, and sodium are the predominant elements that form a dense microstructure with N-A-S-H, C-A-S-H, and C-S-H. Further, the inner properties of the specimens exposed to chemicals were examined using MATLAB R2023b and ImageJ 1.54f based on SEM images. The SEM image showed that the porosity of LWGPC specimens ranged from 0.5194 to 0.6748 µm, signifying an enhanced durability performance. The experimental results and microstructural analysis show that the LWGPC incorporating RHA and GGBS with LECA offers a superior performance, making it a promising solution for sustainable and durable construction.

Durability properties of ambient-cured fly ash-phosphogypsum blended geopolymer mortar in terms of water absorption, porosity, and sulfate resistance

This paper aimed to investigate the durability of ambient-cured fly ash-phosphogypsum blended geopolymer mortar (GPM) when exposed to a water and sulfate environment at different durations. Water absorption, porosity, and sulfate resistance tests were conducted to determine the durability. The GPM was prepared at 0 wt%, 30 wt%, and 40 wt% PG replacement of fly ash content in the mixture. The mix proportions were determined experimentally at 10 M sodium hydroxide, alkaline liquid/precursor of 0.4, sodium silicate/sodium hydroxide of 1.5, and binder/aggregate of 1.0. The samples were immersed in potable water and magnesium sulfate solution. The changes in weight, length, and compressive strength were monitored. Scanning electron microscopy-energy dispersive X-ray spectroscopy was used to analyze the structure and composition. The findings showed that GPM with 30 wt% phosphogypsum added had lower water absorption, porosity, and sulfate attack than GPM with 0 wt% phosphogypsum attributed to the formation of hydrated gels leading to a dense microstructure and improved strength. The changes in weight, length, and strength variations trend for GPM were within optimal performance standards. This has implications for the practical application of GPM in construction where it can be used as an alternative to Portland cement mortar in sulfate-rich environments.

Study on the Chloride–Sulfate Resistance of a Metakaolin-Based Geopolymer Mortar

The chloride–sulfate corrosion environment of concrete is a significant engineering problem. This paper investigates the effect of the complete/semi–immersion mode on the durability of concrete in a chloride–sulfate environment by using different granulated blast furnace slag (GBFS) dosage rates (10–50%) of a metakaolin (MK)-based geopolymer mortar. The chloride–sulfate corrosion environment is discussed by analyzing the apparent morphology, mass change, and mechanical property change in specimens at the age of 120 d of erosion combined with XRD and SEM. The high Ca content in GBFS has an important effect on the strength and erosion resistance of the metakaolin geopolymer (MGP) group mortar; an increase in the GBFS dosage makes the MGP group mortar denser, and the initial strength of the MGP group mortar is positively correlated with the dosage of GBFS. After 120 d of erosion, the GBFS dosage is negatively correlated with erosion resistance, with the high GBFS dosage groups showing more severe damage. Semi-immersion resulted in more severe deterioration at the immersion–evaporation interface zone due to the difference in the ionic concentration and the ‘wick effect’ at the immersion–evaporation interface zone. Compared with the commonly used OPC mortar, the M40 and M50 groups have improved strength and corrosion resistance and are suitable for engineering environments in highly erosive areas.

Tensile Performance and Aging Increase Factor Constitutive Model of High-Strength Engineered Cementitious Composites under Sulfate Salt Attack

This study investigates the uniaxial tensile behavior of high-strength engineered cementitious composites (HS-ECCs) in sulfate erosion environments. Five different sulfate erosion ages were established (0 days, 30 days, 60 days, 90 days, and 120 days), and the development of the macro-mechanical properties of HS-ECCs was revealed from a microscopic perspective using scanning electron microscopy (SEM). The results indicate that, under the influence of sulfate erosion, the strength of HS-ECCs exhibits a trend of initial increase followed by a decrease, while ductility shows a continuous decline. This phenomenon is primarily attributed to changes in the microstructure and reaction products. Based on the test results, an aging growth factor was introduced to fit the stress–strain curve, demonstrating that the model can effectively predict the tensile performance of HS-ECCs with greater accuracy compared to traditional models. This study not only provides data references for the engineering application of HS-ECCs in sulfate environments but also offers a novel approach for constructing predictive models in other environmental contexts.

Compressive strength prediction of cement base under sulfate attack by machine learning approach

Cement-based materials in underground structures, bridge foundation, and offshore platforms often face sulfate environments. It has been widely reported that the compressive strength (CS) of these materials post sulfate attack is crucial for structural stability and durability. However, existing experimental and analytical methods require extensive resources and lengthy period. For addressing this challenge, therefore, a novel stacking model is proposed to accurately predict the CS of cement base under sulfate attack in this study. The stacking model integrates Support Vector Regression (SVR), Random Forest (RF), and Extreme Gradient Boosting (XGB) as base learners, with Linear Regression (LR) as the meta-learner. In this novel model training, the 330 data sets used are obtained from the relevant literatures. The water-cement ratio, cement content, water content, sand content, sulfate concentration, wetting temperature, wetting time, drying temperature, drying time, exposure time are selected as inputs while the output is CS of cement-based materials subjected to sulphate deterioration. To improve the forecast capability, particle swarm optimization (PSO) is adopted for optimizing hyperparameters of stacking model, which can be implemented by reducing the discrepancy between model prediction and measured CS. By comparing with the results of experiments and the solely machine learning (ML) models, it is found that the stacking model optimized by PSO presents the best prediction accuracy of R²=0.992, RMSE=2.248 MPa, and MAE=1.782 MPa. Moreover, the examination of the influence of individual input variables on the CS of cement-based material subjected to sulfate attack is conducted through the application of Shapley Additive Explanations (SHAP) and Partial Dependence Plot (PDP) analyses. The PSO optimized stacking model proposed in this study can effectively predict the CS of cement-based materials under sulfate attack. Our study provides a new reference for future research in this field.

Antimony sorption to schwertmannite in acid sulfate environments

Schwertmannite is a poorly-crystalline Fe(III) oxyhydroxysulfate mineral that may control Sb(V) mobility in acid sulfate environments, including acid mine drainage and acid sulfate soils. However, the mechanisms that govern uptake of aqueous Sb(V) by schwertmannite in such environments are poorly understood. To address this issue, we examined Sb(V) sorption to schwertmannite across a range of environmentally-relevant Sb(V) loadings at pH 3 in sulfate-rich solutions. Antimony K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that Sb(V) sorption (at all loadings) involved edge and double-corner sharing linkages between SbVO6 and FeIIIO6 octahedra. The coordination numbers for these linkages indicate that sorption occurred by Sb(V) incorporation into the schwertmannite structure via heterovalent Sb(V)-for-Fe(III) substitution. As such, Sb(V) sorption to schwertmannite was not limited by the abundance of surface complexation sites and was strongly resistant to desorption when exposed to 0.1 M PO43-. Sorption of Sb(V) also conferred increased stability to schwertmannite, based on changes in the schwertmannite dissolution rate during extraction with an acidic ammonium oxalate solution. This study provides new insights into Sb(V) sorption to schwertmannite in acid sulfate environments, and highlights the role that schwertmannite can play in immobilizing Sb(V) within its crystal structure.

Mechanical behavior of glass fiber-reinforced polyester in a humid environment

Glass fiber composite materials have been well known in certain maritime applications for a long time, being used in several applications in different fields. The characteristics of Glass fiber-reinforced Polyester (GFRP) depend on the contained fibers, the matrix used, and the fiber-to-total volume ratio. GFRP is a polymer material used in various fields; it is generally preferred for its ease of installation and its very long lifespan, even in the presence of aggressive fluids. The aim of this research is to study the evolution of mechanical properties (tensile strength and flexural strength) of GFRP preserved in different environments such as open air (control), drinking water, and seawater (harsh environment). Additionally, tests on GFRP are conducted through chemical characterization studies or SEM observation of the resin. Lastly, GFRP is considered to be chemically stable for a conservation period of one year in seawater. Finally, despite the conservation of GFRP for a year in a humid and sulphate environment, we note that the connection between the fibers and the matrix is ​​in good condition, or the conservation environment has no influence on the GFRP composite.

Investigation of the mechanical and durability properties of concrete containing modified fly ash and modified zeolite powder: An effective transport model for sulfate ions in concrete

The application of conventional fly ash and zeolite powder in the field of concrete durability is limited. In this study, durability tests coupling dry-wet cycling and sulfate erosion were conducted on concrete with varying dosages of modified fly ash (MFA) and modified zeolite powder (MZP). The compressive strength, failure mode, water absorption rate, and ion concentration changes were systematically investigated. The reaction products and structure were analyzed through SEM, EDS, and XRD tests, correlating with macroscopic parameters. An effective transport model for sulfate ions in concrete was established, considering the material influence coefficient km and the effective diffusion coefficient De. The results indicate that a higher content of Ca phases in MFA leads to a reduction in concrete early strength, while later stages exhibit rapid strength growth due to pozzolanic reactions. MZP contains a significant amount of Al and Si phases, which promote both early and later-stage concrete strength. MFA and MZP enhance the resistance of concrete to sulfate erosion, with MZP exhibiting a significantly superior improvement effect compared to MFA. This is attributed to the following factors: on the one hand, the addition of MFA and MZP reduces the porosity and improves the pore structure of concrete, thus delaying the diffusion of sulfate ions into the concrete; on the other hand, the pozzolanic reactions of MFA and MZP consume available calcium hydroxide, leading to the formation of C–S–H and C-A-S-H gels, which densify the microstructure and reduce the probability of leaching erosion of hydration products, thereby limiting the formation of ettringite. The applicability and reliability of the sulfate-ion effective transport model were verified based on experimental data. The model can be employed to predict the distribution of sulfate ions in different types of concrete under various erosion durations, reducing workload and providing a theoretical basis for the durability design and service life prediction of concrete structures in sulfate environments.

The flexural strength of high-ductile concrete in saline-alkali area

Sulfate corrosion is an important cause of accelerated structural failure in concrete structures in coastal and saline alkali areas. High ductility concrete has good tensile and durability properties, and is therefore widely used for the repair and reinforcement of damaged structures. To investigate the flexural performance of high ductility concrete on ordinary concrete structures in saline alkali environments, experimental methods were used to test it. The experimental data validated that the bearing capacity of the 10 mm specimen reinforced with high ductility concrete before and after corrosion is 125 kN and 117 k, respectively. After reinforcement and corrosion, the bearing capacities of the specimens were 115 kN, 129 kN, and 139 kN, respectively. In addition, sodium sulfate reduced the deformation capacity of the original specimen by 13.9 %, but after reinforcement, the deformation capacity of the specimen increased by at least 97.1 %. Compared to reinforced specimens in non saline alkali environments, the deformation capacity of reinforced specimens in saline alkali environments decreases by no more than 23 %. Compared to unreinforced specimens, the strain capacity of reinforced concrete and longitudinal bars in sulfate environments increased by at least 28.1 % and 34.5 %, respectively. However, compared to reinforced specimens in conventional environments, the strain capacity of reinforced specimens in sulfate environments decreased by no more than 19 %. The above results indicate that high ductility concrete can effectively improve the bending resistance of specimens, while also slowing down the corrosion of sulfates on specimens and effectively extending the service life of concrete structures.

Durability performance of BFRP-confined coal gangue concrete exposed to the sulfate-rich mine environment

The combination of basalt fiber reinforced polymer (BFRP) confinement and coal gangue concrete (CGC) is an economical and innovative approach for serving as a supporting structure in the underground mine. Nevertheless, the sulfate-rich mine water and mist exist in the mine environment, which may cause the performance deterioration of structures. Thus, the long-term behavior of BFRP-confined CGC in the sulfate-rich environment was systematically explored, based on the sulfate durability investigation of BFRP sheets and CGC. The tensile test of BFRP sheets and the compressive test of CGC were first carried out to evaluate their deterioration laws and mechanism in different sulfate environment. More importantly, axial compression test of FRP-confined concrete cylindrical specimens after sulfate attack were conducted, considering the effect of inner concrete, FRP layer, sulfate concentration and corrosion time on the stress-strain response and dilation properties. The results indicate that the tensile strength of BFRP sheet declined to a small extent with the extension of sulfate corrosion due to the degradation of epoxy resin and matrix-fiber interface. Additionally, the compressive strength of CGC exhibits a first increase and then decrease trend as the secondary hydration occurs and the sulfate ions react with the hydrated production to form expansive gypsum and ettringite crystals. The strength and ductility of CGC were improved by FRP confinement regardless of sulfate attack or not, whereas sulfate corrosion degraded the improvement ratio, especially the deformation capacity. Most importantly, the sulfate degradation coefficients were introduced into ultimate strength and strain models for sulfate-attacked BFRP-confined CGC, providing a basis for its design and life cycle assessment in the underground mine.

The Deterioration of C-S-H Gel in a Severe Sulfate Environment

The Deterioration of C-S-H Gel in a Severe Sulfate Environment

Improved mechanistic performance of natural rubber latex modified pavement concretes in sulfate environments

ABSTRACT Sulfate attack causes significant degradation in the concrete matrix, including softening, expansive cracking, and other disruptive processes. This research examined the impact of incorporating a Natural Rubber Latex (NRL) additive on the mechanical and durability improvement of concrete pavements. The study evaluated the influence of water to cement (w/c) ratios and dry rubber to cement (r/c) ratios on compressive and flexural strengths, as well as flexural fatigue characteristics, before and after immersion in a 5% sulfate solution at various intervals. Optimal r/c ratios for the highest flexural strength and fatigue life were 0.58, 1.16, and 1.73 for w/c ratios of 0.3, 0.4, and 0.5, respectively. The highest durability was achieved at an r/c ratio of 5.78, resulting in a compressive strength loss of 4.2–7.7 times lower compared to that of normal concrete, hence extending the service life against severe environment. The fatigue model equation proposed by the Portland Cement Association (PCA) was utilised to predict the fatigue life of both normal and NRL-concretes. The outcome of this research will lead to a fundamental knowledge in the development of a design guideline of sustainable concrete pavements, and eventually promote the usage of NRL, which is abundant in Southeast Asia, including Thailand.

Exploring the potential of nitrophosphogypsum and calcined water-treatment plant sludges in mortar mixtures: A study on workability and strength

Mortar mixtures that consider alternative mineral admixtures are of constant research interest to reduce ordinary Portland cement (OPC) content thereby lowering final cost and carbon footprint. An additional concern is the proper management of industrial process residues that could be used in mortar mixes to avoid their disposal in landfills or water bodies. This work investigated the potential of using calcined water treatment plant sludge (CWTPS) and nitrophosphogypsum (NPG) - a byproduct of the fertilizer industry - as partial replacements of OPC in mortar mixtures. For this purpose, this research evaluates the crystallographic, chemical, and physical properties of NPG and CWTPS through X-ray diffraction (XRD), X-ray fluorescence (XRF), and Scanning Electron Microscope (SEM). XRF and XRD findings strongly suggests that CWTPS qualifies as supplementary cementitious materials, due to its high content of silicon and aluminum oxides in a non-crystalline state. On the other hand, NPG could be used as a mineral admixture. The design of mixtures was based on the workability of 85% flow. The evaluation of properties encompasses the measurement of density, compressive strength, durability (pH and sulfate environments), and water absorption. The results demonstrate that incorporating of NPG and CWTPS to mortar mixes, each at a 5% inclusion rate (with a total replacement of 10% of OPC), increase compressive strength by up to 6.65% at 90 days compared to the control group in mortar mixes. However, the inclusion of NPG and CWTPS significantly decreases the workability of mortar mixes by up to 51.49%. The utilization of NPG as a partial replacement for OPC increases the water-to-cement ratio proportionally compared to the control sample, which can be explained by the anhydrite content of this byproduct. For its part, replacing 10% of OPC with NPG and CWTPS results in a 1.99% decrease in resistance after 28 days in sulfated environments compared to specimens cured in lime water. This protection of NPG against sulfate attack on mortars is based on the fact that SO3 saturation hinders the phase change from AFt to AFm during curing, as demonstrated by the XRD results. Additionally, the inclusion of NPG in mortar mixes increases capillary water absorption by up to 19.8%, while CWTPS, due to its pozzolanic nature, reduces it by up to 5.75%. Finally, this study explores the potential combined use of NPG and CWTPS in mortar mixes as a partial replacement for cement, presenting a viable and sustainable alternative for these cementitious-based construction materials.

Study on the Effect of Post-Freezing Mechanical Properties of Polypropylene Fibre Concrete Based on BAS-BPNN

An indoor accelerated freezing and thawing test of polypropylene fibre-reinforced concrete in chloride and sulphate environments was conducted using the “fast-freezing method” with the objective of investigating the damage law of the post-freezing mechanical properties of hydraulic concrete structures and studying the effects of different mixing amounts of polypropylene fibres on the mechanical properties of concrete. Furthermore, in order to reduce the cost of concrete tests and shorten the time required for conducting concrete tests, a backpropagation neural network based on a Beetle Antenna Search algorithm (BAS-BPNN) was established to simulate and predict the mechanical properties of polypropylene fibre-reinforced concrete. The accuracy of the model was verified. The results indicate that the order of improvement in the macro-physical properties of concrete due to fibre doping is as follows: PPF1.2 exhibited the greatest improvement in macro-physical properties of concrete, followed by PPF0.9, PPF1.5, PPF0.6, and PC. When the freezing and thawing medium and the number of cycles are identical, all four assessment indexes (R2, RMSE, SI, MAPE) demonstrate that the four groups of polypropylene fibre concrete exhibit superior performance to the control group of ordinary concrete. This indicates that polypropylene fibre can enhance the mechanical properties and freezing resistance of the concrete matrix, delay the process of freezing and thawing damage to the matrix, and extend the lifespan of the matrix, yet cannot prevent the ultimate failure of the matrix. The application of intelligent algorithms to optimise the parameters of an artificial neural network model can enhance its capacity to generalise and predict the mechanical properties of concrete. In terms of the coefficient of determination (R2), the Beetle Antenna Search algorithm (0.9782) outperforms the Particle Swarm Optimization (PSO; 0.9676), the Genetic Algorithm (GA; 0.9645), and the backpropagation neural network (BPNN; 0.9460). The improved backpropagation neural network based on the Beetle Antenna Search algorithm not only avoids the trap of local optimality but also improves the model accuracy while further accelerating the convergence speed. This approach can address the complexity, non-linearity, and modelling difficulties encountered during the freezing process of concrete. Moreover, it offers relatively accurate prediction outcomes at a reduced cost in comparison to traditional experimental methodologies.

Investigation of tensile strength performance of green concrete incorporating steel slag

This study examined the compressive and tensile strength performance of steel slag-containing concrete composites in a sulphate environment. Steel slag sourced locally was mechanically crushed and sieved into aggregates ranging in size from 20 to 1 mm. The control concrete of grade 20 and other five (5) batches of concrete with 10 to 50% steel slag at a step of 10% as replacement for natural coarse aggregate were produced. The physical properties of the aggregate specimens (steel slag and granite) were evaluated in the laboratory, as well as the concrete workability and the 7- and 28-day compressive and tensile strengths after exposure to 50 g/l of magnesium and sodium for 7 and 28 days. According to the results, the concrete workability decreased as the steel slag content increases. The 20 N/mm2 desire strength with rise in compressive and split tensile strengths as the steel slag contents increased from 0 to 50% after curing in water for 28 days. The concrete compressive and tensile strengths improved with steel slag content ranging from 0 to 40% but decreased with increase in steel slag content from 30 to 50% after exposure to Na2SO4 for 28 days. For the concrete exposed to MgSO4, the compressive and split tensile strengths increased when the steel slag content increased from 0 to 40% before it decreased with further increase in steel slag from 40 to 50% after 28 days. The experimental findings revealed that up to 40% steel slag is sufficient as replacement for natural coarse aggregate in concrete work exposed to aggressive sulphate climate. Thus, for improved compressive and tensile performance, the optimum of 40% steel slag is suggested as replacement for natural coarse aggregate substitution for healthier sulphate attack resistance.

Aluminium substitution affects jarosite transformation to iron oxyhydroxides in the presence of aqueous Fe(II)

Jarosite is an abundant mineral in acidic environments, often found in acid sulfate soil (ASS) and acid-mine drainage (AMD). As a store of Fe, K, S and acidity, and a scavenger for major and trace elements, jarosite plays an important role in the biogeochemistry of acid sulfate environments. When ASS and AMD become anoxic, reducing conditions can set in, producing conditions that are outside the thermodynamic stability field of jarosite. In this study, we investigated the transformation of synthetic and natural jarosite with various degrees of Al-for-Fe substitution under circumneutral anoxic conditions in the presence of Fe(II), to understand the rates and pathways of jarosite and Al-jarosite transformation, the role of competing transformation pathways, the fate of Al during transformation and the different reactivity of natural and synthetic Al-jarosite. Synthetic jarosite (containing 0 %–7 % Al-for-Fe substitution) and a natural Al-substituted jarosite sample from an ASS in Thailand were suspended in solutions of 57Fe(II) at pH 7 for 24 h under anoxic conditions. The chosen experimental conditions mimic the Fe(II) concentrations and pH found in flooded ASS under reducing conditions. Changes in mineral composition of the suspensions were determined by Rietveld analysis of X-ray diffraction patterns at six time points. The fate of Al was determined by XRD, Raman spectroscopy and energy dispersive X-ray spectroscopy analysis of the jarosite and product minerals. Different transformation pathways that occurred simultaneously were traced by using 57Fe Mössbauer spectroscopy and aqueous Fe isotope composition. The analysis showed that 7 % Al-for-Fe substitution in jarosite more than halved the mineral transformation rate compared to unsubstituted jarosite, regardless of the Fe(II) concentrations. Indeed, 7 % Al-for-Fe substitution had a greater effect on the transformation rate than an order-of-magnitude decrease in the Fe(II) concentrations in all Al-for-Fe substitution treatments. The transformation products in all samples were goethite, lepidocrocite and ferrihydrite, with minor amounts of magnetite forming from jarosite with no or low Al-for-Fe substitution reacted with high Fe(II) concentrations. Lepidocrocite was the dominant product in reactors without aluminium, but lepidocrocite was not strongly enriched in 57Fe, suggesting that it may not have formed exclusively from Fe in solution during the Fe(II)-catalysed transformation of other minerals. In high-Al systems, lepidocrocite appeared to be a sink for Al, although its formation in Al-rich samples was suppressed. Natural jarosite reacted more than an order of magnitude more slowly than the synthetic jarosite and Al-jarosite, indicating that the properties of the synthetic jarosite do not completely account for the stability of natural jarosite under anoxic circumneutral conditions. The results provide an important baseline for understanding the drivers of jarosite transformation or stability in ASS and AMD.

Long-Term Effects of External Sulfate Attack on Low-Carbon Cementitious Materials at Early Age

Placed in a sulfate-rich environment, concrete reacts with sulfate ions, influencing the long-term durability of reinforced concrete (RC) structures. This external sulfate attack (ESA) degrades the cement paste through complex and coupled physicochemical mechanisms that can lead to severe mechanical damage. In common practice, RC structures are generally exposed to sulfate at an early age. This early exposition can affect ESA mechanisms that are generally studied on pre-cured specimens. Moreover, current efforts for sustainable concrete construction focus on replacing clinker with supplementary cementitious materials, requiring a 90-day curing period, which contradicts real-life scenarios. Considering all these factors, the objective of this study is to explore ESA effects at an early age on cement-blended paste samples using various low-carbon formulations. The characterization techniques used demonstrated that the reference mix (100% CEM I) exhibits the weakest resistance to sulfate, leading to complete deterioration after 90 weeks of exposure. This is evident through the highest mass gain, expansion, cracking, formation of ettringite and gypsum, and sulfate consumption from the attacking solution. Conversely, the ternary mix, consisting of CEM I, slag, and metakaolin, demonstrates the highest resistance throughout the entire 120 weeks of exposure. All the blended pastes performed well in the sulfate environment despite being exposed at an early age. It can be recommended to substitute clinker with a limited quantity of metakaolin, along with blast furnace slag, as it is the most effective substitute for clinker, outperforming other combinations.

Compressive strength resistance coefficient of sustainable concrete in sulfate environments: Hybrid machine learning model and experimental verification

The compressive strength corrosion resistance coefficient of sustainable concrete (SC-SCRC) is a crucial indicator for evaluating the mechanical performance degradation of SC after erosion. Therefore, this study collected 326 sets of SC-SCRC data from 20 literature sources and established an optimized machine learning algorithm-based SC-SCRC prediction model, evaluating its performance. To validate the model's accuracy, thirteen different SC mix ratios were prepared for SC-SCRC testing. The results demonstrate that the grey wolf optimization supported vector regression (GWO-SVR) model provides predictions that better align with the actual values. The model exhibits lower standard deviation and mean of model residuals. The performance evaluation indicators of the GWO-SVR model (R=0.972; MSE=1.46e-3; MAE=2.9e-2; MAPE=3.1e-2; RMSE=3.9e-2) are also outstanding. Furthermore, Shapley Additive Explanations reveal that the dry-wet cycle count and the water-binder ratio are the two most critical influencing factors on SC-SCRC, with both showing negative correlations. A graphical user interface (GUI) based on the GWO-SVR model has been developed to enable efficient predictions of SC-SCRC. Test results indicate that the error between the experimental values and the predicted values is less than 6%, demonstrating the model's high accuracy and generalizability. This work lays the foundation for optimizing the performance of SC and predicting SC-SCRC. The findings provide valuable guidance for engineering projects in areas with high concentrations of sulfate ions.

Application of sulfate ion fixation in internal sulfate attack: The gel containing barium salt

Sulfate attack is one of the most important factors affecting the durability of concrete, and the corrosion sources of internal sulfate attack (ISA) mostly come from the raw materials of concrete. Adding corrosion resistance admixtures to concrete is one of the most effective ways to prevent internal sulfate attack. By wrapping barium salt with SA gel, the modified barium chloride admixture (MB) is obtained which can exist stably in concrete and release barium ions to form barium sulfate in a sulfate environment. The modified barium salt has little effect on the cement workability and hydration process and even can improve the mechanical properties slightly. When the MB content reaches 6% (MB-6), the strength improvement effect is most obvious. Compared with the P-0, the 7d compressive strength of MB-6 is increased by 9.14%, and the 28d compressive strength is increased by 5.77%. It can be seen by SEM that the amount and crystal size of ettringite in the cement mixed with admixtures are reduced. The corrosion resistance of the matrix can be further improved by using a modified barium chloride-silica fume composite admixture (MB-F). After 90 days of internal sulfate attack, the strength of the MB-F even improves slightly. When the modified barium chloride to silica fume ratio is 4:6, the cement-based material achieved the best resistance to internal sulfate attack. In addition to MB, which can make sulfate ions fixation and inhibit the formation of ettringite, silica fume can also consume calcium hydroxide and generate more C-S-H gel, which compacts the weak part of the matrix and greatly improves the resistance to internal sulfate attack of cement-based materials. It provides the possibility for the application of modified barium salt in external sulfate attack.

Study of the damage characteristics and corrosion mechanism of tunnel lining in a sulfate environment

Sulfate corrosion is one of the main causes of tunnel lining deterioration. An accurate understanding of the damage characteristics and corrosion mechanism of sulfate-corroded tunnels is the basis for the anti-corrosion design and damage control of the tunnel lining. Based on a project concerning a sulfate-corroded tunnel in the mountainous area of Southwest China, this study conducted a field investigation and laboratory tests and, combined with existing research data, summarized the damage characteristics and corrosion mechanism of this type of tunnel and proposed the characteristic corrosion state of tunnel lining in a sulfate environment. The results show that 1) sulfate corrosion led to leakage, surface spalling crystallization, and strength loss, and the corrosion typically occurred at the arch waist and arch foot. 2) Physical and chemical corrosion occurred in the tunnel lining, and the corrosion products included sodium sulfate, calcium carbonate, gypsum, ettringite, and thaumasite. 3) In China, this type of tunnel is mainly located in the Southwest and Northwest, and its lining is in a special state of “one-sided accelerated corrosion.”