Alkali-activated Concrete Research Articles

Effects of Na2SiO3/NaOH ratio in alkali activator on the microstructure, strength and chloride ingress in fly ash and GGBS based alkali activated concrete

In this study, the impact of alkaline solutions composed of various Na2SiO3/NaOH ratio and NaOH molarity on the strength, chloride ingress and chloride binding capacity of fly ash (FA) and ground granulated blast furnace slag (GGBS) based alkali activated concrete (AAC) was investigated. The microstructural properties of alkali activated binders (AAB) composites was also studied to understand its influence on the chloride permeability of AAC. Chloride permeability of concrete was tested by using the rapid chloride penetration test (RCPT) and by immersing concrete in NaCl solution (ASTM C1556). The compressive strength, chloride ingress and chloride binding capacity of AAC was compared with Portland cement-based concrete (OPC). Results showed that higher Na2O/SiO2 ratio in alkaline solutions resulted in a weak microstructure with, low strength and high chloride ingress. Concrete activated by alkaline solutions with Na2O/SiO2 molar ratio =1 (+3), exhibited greater compressive strength and resistance to chloride ion penetration. The increase of SiO2 concentration in alkaline solution greatly reduces the binding capacity of AAC while the bound chlorides increased with the NaOH molarity. No chemical chloride binding was observed in AAC but for OPC concrete, calcium salts formed in the microstructure after immersion in NaCl solution. Compared to OPC concrete, AAC showed superior performance in terms of strength and chloride diffusion making it a potential candidate for application in marine structures.

Effects of mix composition on the mechanical, physical and durability properties of alkali-activated calcined clay/slag concrete cured under ambient condition

Alkali-activated concrete (AAC), a possible alternative to ordinary Portland cement (OPC), provides increased environmental advantages, notably lower carbon emissions. Likewise, similar to OPC, it faces durability problems under severe environments. This study evaluated the effectiveness and durability of alkali-activated concretes containing low-grade calcined clay and granulated blast furnace slag (GGBFS), using NaOH/KOH as activators and MgO and superabsorbent polymer (SAP) as additives. The study's focus was on their physical-mechanical characteristics and performance under accelerated carbonation and chloride diffusion. Findings showed that calcined clay-GGBFS alkali-activated concretes exhibited a compressive strength range of 41.2–53.3 MPa, positioning them as a viable concrete for many structural usages. Nevertheless, the modified-RCPT (10 V) and NT Build 492 tests showed all concretes falling into the "high chloride penetrability" category, with values exceeding 350 coulombs and 13.5 (×10−12 m2/s) for the non-steady-state migration coefficient (Dnssm). NaOH and sodium silicate led to higher compressive strengths compared to KOH. Furthermore, the chloride migration coefficient of alkali-activated concrete blends ranged from 55.68 to 121.14 (× 10−12 m2/s). The incorporation of 0.6 % SAP decreased compressive strength but improved the non-steady-state migration coefficient (Dnssm). Lastly, MgO-enriched samples showed the lowest water absorption and carbonation depth, attributed to the buffering action of magnesium phases, reducing carbonate formations, as revealed by XRD analysis.

Integrating Data Imputation and Augmentation with Interpretable Machine Learning for Efficient Strength Prediction of Fly Ash-Based Alkali-Activated Concretes

Fly ash-based alkali-activated concrete (AAC) is renowned for its superior mechanical performance and sustainability, presenting an attractive alternative to traditional Portland cement concrete. Despite these advantages, the broad compositional range of AACs presents challenges in precisely tailoring material properties. In this context, machine learning (ML) offers promising prospects to streamline and fast-track the development of advanced materials design strategies by predicting mechanical properties from compositional variations. Effective ML model development, however, hinges on the availability of a comprehensive, high-quality dataset. Previous studies often relied on literature-derived datasets, which typically include outliers, noise, and missing values, potentially leading to biased predictions. Moreover, limited dataset sizes could undermine the robustness of the models. Traditional ML methods applied to AACs also tend to lack interpretability. To address these issues, this paper utilizes several data imputation methods and Generative Adversarial Networks (GANs) for data augmentation, effectively doubling the dataset size. Following this, ML algorithms such as Random Forest (RF), Extreme Gradient Boosting (XGBoost), and Neural Networks (NNs) are leveraged to predict compressive strength. The NN model, especially when enhanced by k-nearest neighbors (kNN) imputation (k = 5), demonstrated superior predictive accuracy compared to RF and XGBoost models. Further, SHAP (SHapley Additive exPlanations) analysis reveals key determinants of compressive strength, such as water content, SiO2, and curing conditions. Visualizations such as SHAP violin and river flow plots further elucidated feature contributions and property distributions. Overall, this study provides a robust framework for exploring composition-strength relationships in AACs, advancing the design of these environment-friendly materials.

INFLUENCE AND PREDICTION OF SINTERED AGGREGATE SIZE DISTRIBUTION ON THE PERFORMANCE OF LIGHTWEIGHT ALKALI-ACTIVATED CONCRETE

The most effective method for mitigating the adverse environmental impacts of traditional concrete involves substituting cement and natural aggregate with waste and byproduct resources. Utilizing sintered lightweight aggregate (fly ash) in geopolymer concrete emerges as an efficient solution for managing and disposing of significant amounts of fly ash. The influence of sintered aggregate size distribution on the performance of alkali-activated concrete, focusing on compressive strength improvement. The study employs sintered fly ash aggregate (SFA) as coarse aggregate, aiming to optimize packing density through proper particle distribution. The highest compressive strength is achieved with a mix featuring 75% 4-8mm and 25% 8-12mm SFA. Regression-based strength models are developed, exhibiting good alignment with conventional concrete models. Thin section techniques reveal enhanced aggregate-matrix interaction due to the porous structure of SFA. The study emphasizes the potential of SFA in geopolymer concrete for sustainable construction. Lightweight geopolymer concrete, owing to its lower density, significantly reduces the overall structural load.

A New Performance-Based Test for Assessing Chloride-Induced Reinforcement Corrosion Resistance of Geopolymer Mortars.

The widespread adoption of geopolymer concretes in the industry has been slow, mainly due to concerns over their long-term performance and durability. One of the main causes of concrete structures' deterioration is chloride-induced corrosion of the reinforcement. The reinforcement corrosion process in concrete is composed of two main stages: the initiation phase, which is the amount of time required for chloride ions to reach the reinforcement, and the propagation phase, which is the active phase of corrosion. The inherent complexities associated with the properties of precursors and type of activators, and with the multi-physics processes, in which different transfer mechanisms (moisture, chloride, oxygen, and charge transfer) are involved and interact with each other, have been a major obstacle to predicting the durability of reinforced alkali-activated concretes in chloride environments. Alternatively, the durability of alkali-activated concretes can be assessed through testing. However, the performance-based tests that are currently available, such as the rapid chloride permeability test, the migration test or the bulk diffusion test, are only focusing on the initiation phase of the corrosion process. As a result, existing testing protocols do not capture every aspect of the material performance, which could potentially lead to misleading conclusions, particularly when involving an electrical potential to reduce the testing time. In this paper, a new performance-based test is proposed for assessing the performance of alkali-activated concretes in chloride environments, accounting for both the initiation and propagation phases of the corrosion process. The test is designed to be simple and to be completed within a reasonable time without involving any electrical potential.

Optimized Machine Learning Model for Predicting Compressive Strength of Alkali-Activated Concrete Through Multi-Faceted Comparative Analysis

Alkali-activated concrete (AAC), produced from industrial by-products like fly ash and slag, offers a promising alternative to traditional Portland cement concrete by significantly reducing carbon emissions. Yet, the inherent variability in AAC formulations presents a challenge for accurately predicting its compressive strength using conventional approaches. To address this, we leverage machine learning (ML) techniques, which enable more precise strength predictions based on a combination of material properties and cement mix design parameters. In this study, we curated an extensive dataset comprising 1756 unique AAC mixtures to support robust ML-based modeling. Four distinct input variable schemes were devised to identify the optimal predictor set, and a comparative analysis was performed to evaluate their effectiveness. After this, we investigated the performance of several popular ML algorithms, including random forest (RF), adaptive boosting (AdaBoost), gradient boosting regression trees (GBRTs), and extreme gradient boosting (XGBoost). Among these, the XGBoost model consistently outperformed its counterparts. To further enhance the predictive accuracy of the XGBoost model, we applied four state-of-the-art optimization techniques: the Gray Wolf Optimizer (GWO), Whale Optimization Algorithm (WOA), beetle antennae search (BAS), and Bayesian optimization (BO). The optimized XGBoost model delivered superior performance, achieving a remarkable coefficient of determination (R2) of 0.99 on the training set and 0.94 across the entire dataset. Finally, we employed SHapely Additive exPlanations (SHAP) to imbue the optimized model with interpretability, enabling deeper insights into the complex relationships governing AAC formulations. Through the lens of ML, we highlight the benefits of the multi-faceted synergistic approach for AAC strength prediction, which combines careful input parameter selection, optimal hyperparameter tuning, and enhanced model interpretability. This integrated strategy improves both the robustness and scalability of the model, offering a clear and reliable prediction of AAC performance.

Performance-Based Design of Ferronickel Slag Alkali-Activated Concrete for High Thermal Load Applications.

This study aimed to develop optimized alkali-activated concrete using ferronickel slag for high-temperature applications, focusing on minimizing environmental impact while maintaining high compressive strength and slump. A response surface methodology, specifically the mixture design of experiments, was employed to optimize five components: water, FNS-based alkali-activated binder, and three aggregate sizes. Twenty concrete mixes were tested for slump and compressive strength before and after exposure to 600 °C for two hours. The optimal mix achieved 88 MPa compressive strength before heat exposure and 34 MPa after, with a slump of 140 mm. An upscaled version with improved workability (210 mm slump) maintained similar unheated strength but showed reduced post-heating strength (23.5 MPa). Replacing limestone with olivine aggregates in the upscaled mix resulted in 65 MPa unheated and 32 MPa post-heating strengths. Life Cycle Analysis revealed that the optimized ferronickel slag alkali-activated concrete's CO2 emissions were 77% lower than those of ordinary Portland cement concrete of equivalent strength. This approach demonstrated the applicability of mixture design of experiments as an alternative design methodology for alkali activated concrete, providing a valuable performance-based design tool to advance the application of alkali-activated concrete in the construction industry, where no prescriptive standards for alkali-activated ferronickel concrete mix design exist. The study concluded that the developed ferronickel slag alkali-activated concrete, obtained through a performance-based mixture design methodology, offers a promising, environmentally friendly alternative for high-strength, high-temperature applications in construction.

Evaluation on Preparation and Performance of a Low-Carbon Alkali-Activated Recycled Concrete under Different Cementitious Material Systems.

A green, low-carbon concrete is a top way to recycle waste in construction. This study uses industrial solid waste slag powder (S95) and fly ash (FA) as binders to completely replace cement. This study used recycled coarse aggregate (RCA) instead of natural coarse aggregate (NCA). This is to prepare alkali-activated recycled concrete (AARC) with different cementitious material systems. Alkali-activated concrete (AAC) mixtures are modified for strength and performance based on the mechanical qualities and durability of AARC. Also, the time-varying effects of the environment on AARC properties are explored. The results show that with the performance enhancement of RCA, the mechanical performance of AARC is significantly improved. As RCA's quality improves, so does AARC's compressive strength. At a cementitious material content of 550 kg/m3, AARC's 28d compressive strengths using I-, II-, and III-class RCA were reduced by 2.2%, 12.7%, and 21.8%, respectively. I-class AARC has characteristics similar to natural aggregate concrete (NAC) in terms of shrinkage, resistance to chloride penetration, carbonization, and frost resistance. AARC is a new type of green building material that uses industrial solid waste to prepare alkali-activated cementitious materials. It can effectively reduce the amount of cement and alleviate energy consumption. This is conducive to the reuse of resources, environmental protection, and sustainable development.

Approach to Design Sustainable Alkali-Activated Slag Recycled Aggregate Concrete: Mechanical and Microstructural Characterization

There is a steep increase in demand for concrete as the need for infrastructure is increasing with a rapid increase in urbanization. Consequently, there has been a surging demand for cement across the globe. By using alkaline concrete activated with ground granulated blast furnace slag (GGBS), cement usage can be eliminated in concrete, which addresses the issue of CO2 emissions concerned with the cement manufacturing process and promotes the use of industrial by-products as sustainable building materials. The current study focuses on proposing a methodology to design sustainable GGBS-based alkali-activated concrete incorporated with 100% coarse recycled coarse aggregates (RCA) recovered from construction and demolition (C&D), for various strengths by optimizing the mix proportions and verifying the same through experiments. From the current study, it is evident that this mix design procedure can be adopted to design alkali-activated slag recycled aggregate concrete (AASRAC) mixes for strengths ranging from 44MPa to 85MPa. The optimum values of alkalinity factor (λ) and NaOH concentration (M) i.e., 1.5 and 12, have a significant role in the development of high strengths which is attributed to the formation of hydrotalcite. Micrographs captured using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) studies reveal that the alkaline binders promote the development of a denser and stronger interfacial transition zone (ITZ) that enhances the strength of lower AA/B concretes at the microstructural level as Ca/Si ratio is higher for lower AA/B concretes. Global warming potential (GWP) analysis reveals that the alkali-activated concretes have significantly lower GWP compared to conventional OPC-based concrete by approximately 2.5 times. The mix-design chart proposed in this study may pave the way to designing structural grade AASRAC with enhanced performance for the desired strength, which may find its application in fast-track construction and manufacturing of prefabricated elements.

An investigation of the mechanical strength, environmental impact and economic analysis of nano alkali-activated composite

The current study explores both the mechanical strength and life cycle assessments of fly ash (FA)-based alkali-activated concrete (AAC) with/without colloidal nano-silica (NS) addition at high and low molar concentrations of sodium hydroxide in the activator fluid (12 M and 3 M). The cradle-to-gate approach is used to establish the system boundaries for life cycle assessments (LCA). The environmental impact of AAC (with/without NS) and conventional cement concrete (CC) mixtures was determined using the ReCiPe midpoint and endpoint approaches across various impact categories. The AAC mixes with and without NS addition reduce greenhouse gas (GHG) emissions by 30 % and 25 % with respect to CC mix, respectively. Within the majority of impact categories, sodium silicate and sodium hydroxide production are the primary contributors, accounting for up to 91 %. However, in water depletion, global warming potential, and fuel depletion, the overall contribution is as high as 65 %. Also, the AAC mix with and without NS addition consumes 34 % and 14 % less electricity during its production with respect to the CC mixture. The CC mixes have almost 70 % more ecological damage and approximately 30 % more health risk than AAC with and without NS. However, the NS-modified AAC shows 20 % lower ecological and health risks than AAC without NS. The effect of resource scarcity on NS modified AAC is 50 % less than that of other mixes, including both AAC mix without NS and CC mix. In comparison to AAC without NS, the NS modified AAC demonstrates an 18 % reduced impact on resource scarcity. Finally, cost analysis demonstrates that AAC with NS is 16 % less expensive than CC, while AAC without NS is 26 % cheaper than CC. AAC containing 6 % NS inclusions exhibits environmental and economic benefits in addition to its enhanced mechanical performance, indicating its potential for widespread practical usage.

Sulfate resistance of alkali-activated flyash-slag-lime concrete: comparative study of drying-wetting cycles and conventional exposure

Abstract Sulphate resistance of concrete is a crucial parameter for design of offshore structures. Of late alkali-activated materials are been given due consideration for infrastructure projects. In this context, the present study aims to assess the sulphate resistance of Alkali-Activated Concrete (AAC) with ternary blend of flyash-Ground Granulated Blast furnace Slag (GGBS) and limestone as the principal binder. The first phase of the study includes the optimization of ternary AAC mix with the inclusion of limestone as a potential binder to popularly used flyash slag blends. The inclusion of 5% limestone powder into the binder matrix is found to have beneficial effect on the mechanical properties of the ternary blended AAC. Further, an increase in the limestone powder content is not found to influence mechanical properties positively. The AAC mix with 5% limestone of total binder content was therefore selected for further evaluation of sulphate resistance. The sulfate resistance is evaluated under the alkaline media by subjecting AAC specimens to constant immersion and alternative drying and wetting cycles. The mechanical characteristics and mass reduction of the exposed samples were tested and compared with the conventional Ordinary Portland Cement (OPC) specimens. Evaluations were conducted over periods of 30, 45, 120, and 365 days of exposure. Scanning Electron Microscopy (SEM), and Energy Dispersion Spectroscopy (EDS) were also used to determine the surface morphology and mineral composition of samples after 365 days of exposure periods. The Flyash-Slag-Lime AAC exhibits denser morphology in comparison to OPC-based concrete, which in turn offers enhanced sulphate resistance.

Carbonation resistance of alkali-activated GGBFS/calcined clay concrete under natural and accelerated conditions

The carbonation resistance of alkali-activated materials (AAMs) is a crucial parameter for their applicability in concrete construction, yet the parameters influencing it are insufficiently understood to date. In the present study, the carbonation resistance of alkali-activated concretes with varying fractions of ground granulated blast furnace slag (GGBFS) and calcined clay (i.e., high, intermediate, and low Ca contents) were assessed under natural and accelerated conditions. Corresponding hardened AAM pastes were studied using X-ray diffraction, thermogravimetry, Raman microscopy, and mercury intrusion porosimetry. The carbonation resistance of the concretes at natural CO2 concentration depended principally on their water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio. The remaining variability for similar ratios was caused by differences between the pore structures of the AAMs. For concrete with favorable water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio and pore structure, the carbonation resistance was comparable to that of Portland cement concrete. The relationship between carbonation coefficients obtained under accelerated and natural conditions differed for concretes with high and low fractions of calcined clay, indicating that accelerated carbonation testing is less suitable to study the carbonation of low-Ca AAMs.

Intrinsic self-sensing piezoresistive behaviors of ultra-high strength alkali-activated concrete

In this work, the self-sensing piezoresistive behaviors of carbon fiber (CF)-reinforced ultra-high strength concrete (UHSC) are investigated using alternating current impedance spectroscopy (ACIS) technique. The effects of different fiber contents, fiber lengths, and curing ages are considered. The electrical behaviors of alkali-activated slag (AAS)-based UHSC (AAS-UHSC) and ordinary Portland cement (OPC)-based UHSC (OPC-UHSC) at similar strength from 80 to 110 MPa are compared. The findings reveal that the intrinsic electrical resistivity of AAS-UHSC is significantly lower than that of OPC-UHSC, approximately 1/30 of the latter. The addition of CF results in a substantial reduction in electrical resistivity for both UHSC types, with reductions of up to 96 %, and shows better compatibility with the AAS-UHSC matrix. The piezoresistive properties of CF-reinforced UHSC are investigated using ACIS at a fixed frequency and further evaluated by parameters including sensitivity, linearity, repeatability, and hysteresis. The results indicate that plain OPC-UHSC does not exhibit piezoresistivity, whereas the addition of CF enhances both the sensitivity and linearity of piezoresistivity. In contrast, AAS-UHSC demonstrates inherent piezoresistive behaviors even without CF. The introduction of 0.5 wt% CF improves the sensitivity (by up to 50 %) and linearity (R2 increased from 0.76 to above 0.90) of piezoresistivity in AAS-UHSC. However, increasing the CF content to 1.0 wt% diminishes the sensitivity (by up to 62.5 %) due to decreased fiber dispersion uniformity. Moreover, the addition of 1.0 wt% 8-mm CF reduces the hysteresis of UHSC regardless of the binder type, with the maximum reduction reaching 62.2 %.

Effect of waste glass powder on the durability and microstructural properties of fly ash-GGBS based alkali activated concrete containing 100 % recycled concrete aggregate

This research investigates the effective utilization of waste glass powder (WGP) in fly ash (FA)-ground granulated blast furnace slag (GGBS) based alkali-activated concrete (AAC) containing 100 % recycled concrete aggregate (RCA) cured at ambient temperature. FA substituted with WGP in the range of 0–25 %, and the percentage of GGBS was kept unaltered at 50 %. The influence of WGP on the strength, durability, and microstructural properties of FA-GGBS based AAC was evaluated. The experimental results showed that the strength and durability were enhanced with the increases of WGP of up to 20 %, and then started to decrease. The highest compressive strength (51.4 MPa) and ultrasonic pulse velosity (UPV) (4.35 km/s) were obtained for F30W20 (FA:GGBS:WGP - 30:50:20). In addition, sorptivity, chloride, and water permeability were reduced by 39.92 %, 56 %, and 64.13 %, respectively for optimized specimens as compared to a control sample (without WGP). Furthermore, the microstructural analysis was carried out to investigate the alteration in the mineralogical and morphology. On the basis of microstructural investigations, WGP notably enhanced the microstructure of FA-GGBS-based AAC by enhancing the formation of reaction products, including C-S-H and C-(N)-A-S-H gel. At last, this study found that CO2 emissions, energy consumption, and cost analysis were lowered by approximately 60 %, 28 %, and 41 % compared to conventional concrete of the same quality.

Development and evaluation of alkali-activated concrete with thermal energy storage capability for energy geostructures

Energy geostructures, such as energy piles, tunnels, and continuous underground walls, offer an innovative solution for harnessing shallow geothermal energy while serving structural functions. However, their limited energy density often leads to inefficient heat exchange and fluctuations in structural stability, along with significant challenges related to ion erosion in practical applications. This study introduces Alkali-Activated Concrete with Thermal Energy Storage Capability (AAC-TESC), which incorporates Phase Change Material (PCM) with high thermal storage density into Alkali-Activated Concrete (AAC), for energy geostructures. For the first time, the mechanical properties, volume stability, and durability of AAC-TESC under the operational conditions of energy geostructures were systematically investigated. The results reveal that the inclusion of Thermal Energy Storage Aggregate (TESA) containing PCM significantly reduces temperature-induced deformations by 44.8–76.9 % while maintaining compressive strength within the range of 30–60 MPa, making AAC-TESC highly suitable for energy geostructure applications. Additionally, AAC-TESC shows enhanced resistance to chloride diffusion, attributed to increased thermal cycling and lower operating temperature, potentially reducing its activation energy. This study offers valuable insights into the potential of AAC-TESC to improve the volume stability and durability of energy geostructures, presenting a sustainable solution to contemporary construction challenges.

Flexural and fracture performance of fiber reinforced self compacting alkali activated concrete– A DOE approach

Owing to their much-reduced carbon footprint and lower embodied energy, compared to conventional Portland Cement (OPC-based) Concrete mixes, Alkali Activated Concrete (AAC) mixes represent a pivotal advancement towards achieving sustainability goals. The fracture properties were investigated using Three-Point Bending Tests (3-PBT) under the mode I failure mechanism. This study utilises Taguchi analysis to analyse and optimise Self-Compacting Alkali-Activated Concrete (SAAC), focusing mainly on its flexural strength and fracture characteristics. An L-16 orthogonal array of experiments with three input parameters − replacement of Blast Furnace Slag (BFS) with Fly ash (FA) (0 %, 30 %, 40 %, and 50 %), Steel Fibers (SF) volume content (0 %, 0.25 %, 0.5 % and 0.75 %) and Notch to Depth (a0/d) ratio (0.2,0.3,0.4 and 0.5), at four levels each, was adopted. The Work of Fracture Method (WFM) and Double K Fracture Criterion (DKFC) were utilised to determine the Fracture Energy (GF) and fracture toughness, respectively. The results obtained from all the sixteen mixes showed that the F0-S0.75-N0.5 mix demonstrated better values in several parameters, such as flexural strength of 7.82 MPa,KICini of 0.928 MPa√m, KICuns of 6.99 MPa√m and KICini/ KICuns of 0.133. A maximum GF of 2350 N/m was obtained with F50-S0.75-N0.2 mix. However, all the inferior values of these parameters were observed with F50-S0-N0.5 mix, which recorded a flexural strength of 4.90 MPa, KICini of 0.612 MPa√m,KICuns of 1.16 MPa√m, KICini/ KICuns of 0.528 and GF of 125 N/m. Through Taguchi analysis, the optimal combination for flexural strength was identified as FA 0 %, SF 0.75 %, and a0/d 0.5 and for both Initial Fracture Toughness (KICini) and Unstable Fracture Toughness (KICuns) at FA 0 %, SF 0.75 % and a0/d 0.4. For both the ratio of initial to unstable fracture toughness (KICini/ KICuns) and fracture energy (GF), the optimum combination was FA 0 %, SF 0.75 % and a0/d 0.2. Furthermore, the results indicate that FA significantly influences KICini, while SF predominantly affects all other parameters. The predictive performance of the regression equations demonstrates good agreement with experimental outcomes.

Two-step approach to manufacture sustainable artificial steel slag aggregate used in alkali-activated concrete

This study utilized 3 mol/L hydrochloric acid to activate steel slag powder in combination with carbonation and produced the artificial steel slag aggregate (ASSA) for the use in alkali-activated concrete. The composition, microstructure, and properties of the ASSA were investigated. The results indicated that acid activation enhanced the compressive strength of the ASSA by 26.7 %, reduced the total porosity by 5.2 %, and facilitated the formation of portlandite, C-S-H gel, and monocarbonate in the hydration products. Carbonation enhanced the compressive strength of the ASSA by 28.5 %, reduced the total porosity by 14.5 %, and led to the formation of calcite and aragonite. The effect of acid activation coupled with carbonation on the ASSA manifested in a 43.6 % enhancement in compressive strength, a 17.9 % reduction in porosity, and an expansion rate reduction to 1.2 %. The alkali-activated concrete produced with the modified ASSA exhibited enhanced compressive strength by up to 21 % compared with the control group, facilitated internal curing to balance internal humidity, and mitigated drying shrinkage deformation. This study provides a viable and secure approach to the reutilization of steel slag.

Numerical Analysis on Fatigue Behavior of Plain Concrete and Alkali-activated Concrete

Abstract Alkali-activated concrete (AAC) has recently gained a lot of potential to become one of the most recommended sustainable replacements for Ordinary Portland cement concrete (OPCC). In the present investigation, an attempt has been made to study the static and fatigue flexural behavior of AAC compared to that of OPCC by using numerical modeling FEA software, ABAQUS. The nonlinear behavior of the stress-strain curve of the concrete has been studied using the concrete damage plasticity (CDP) model. A 2D notched beam was modelled using plane stress condition and three-point bending tests were performed under monotonic loading to obtain the static behavior of concrete. The result obtained has been utilized to fix the loading range for cyclic loads in fatigue analysis and at different loading frequencies. The load-CMOD curves and load-deflection curves were obtained for both static and fatigue loading, and the number of cycles to failure during fatigue. From the results, it has been observed that the Ordinary Portland cement concrete specimens sustain more load than that of Alkali-activated concrete under monotonic loading. However, AAC has shown more resistance to fatigue than that of the OPCC and the frequency of loading significantly influences the fatigue performance.

Numerical Study on Static and Fatigue Behavior of Alkali-Activated Fly Ash Concrete Modelled using Concrete Damage Plasticity (CDP) Model

Abstract Alkali-activated concretes (AAC) are considered as an alternative to Portland cement concretes because of their much lower carbon emissions. To study its characteristics is of utmost importance. In the present research, an attempt is made to create a numerical model to analyze the static and fatigue flexural behavior of alkali-activated fly ash concrete (FC) and compare them with ordinary Portland cement concrete (PCC). Three-point bending tests are simulated for the monotonic load to obtain the static behavior of a 2D notched rectangular beam. A 2D beam specimen of size 262.5 mm x 75 mm, with a notch of size 15 mm x 3 mm was provided at the bottom middle. Fly ash-based alkali-activated concrete (FC) and corresponding PCC of similar strength are modeled in ABAQUS CAE using the concrete damage plasticity (CDP) model. The ultimate loads, maximum deflection, and CMOD for each of them were obtained from the history output manager. The results of monotonic tests are utilized for creating a sinusoidal load cycle for fatigue tests with various loading frequencies and stress ratios. Different structural responses are examined under the fatigue test. The results showed that FC performs better than PCC under static and fatigue tests. Fatigue performance of both FC and PCC is influenced by the frequency of loading and fatigue life increases at higher frequencies. It is also found that stress reversal negatively impacts the fatigue life of both FC and PCC.

Influence of Sulfuric Acid Exposure on Mechanical Properties of Alkali-Activated Concrete

Influence of Sulfuric Acid Exposure on Mechanical Properties of Alkali-Activated Concrete