Ordinary Portland Cement Concrete Research Articles

Effect of pore solution alkalinity on alkali–silica reaction (ASR) in metakaolin‐based geopolymer

AbstractGeopolymer concretes have shown better resistance against alkali–silica reaction (ASR) than ordinary Portland cement concretes, which was attributed to the low pore solution alkalinity of the geopolymer. However, the alkalinity of the geopolymer pore solution depends on the concentration and volume of the activating solutions used and age of the geopolymer. The main objective of this study was to investigate the effects of pore solution alkalinity on the ASR expansion of the metakaolin‐based geopolymer concrete. The chemistry of the pore solution of metakaolin‐based geopolymer was studied, and its reaction with reactive and non‐reactive aggregates was investigated. The concrete prism expansion tests showed no ASR‐induced expansion in geopolymer despite sufficient pore solution alkalinity to attack the reactive aggregates. The SEM and XRD characterizations confirmed that no ASR‐related gel was formed during the reaction between reactive aggregates and extracted pore solution. The chemical structure of the reaction product between aggregates and pore solution was characterized using MAS NMR and revealed no difference in the reaction products with reactive and non‐reactive aggregates. The results suggest that the pore solution alkalinity is not the sole governing parameter for ASR expansion in the geopolymer.

Experimental Study on the Mechanical Properties of Sustainable Concrete using Recycled Plastic and Glass Waste

This study explores using recycled waste glass and plastic fibers as substitutes for fine aggregates in concrete to meet the growing need for sustainable building materials. The basic materials consist of OPC 43 grade and locally obtained river sand. The research incorporates glass powder from crushed beer bottles and plastic fibers from recycled plastic bottles into the concrete mixture. Various tests, including slump, compressive strength (CS), and split tensile strength (STS) assessments, are performed to ascertain the characteristics of the modified concrete in both its fresh and hardened states. The findings demonstrate a significant enhancement in the ease of handling when glass powder is used, exhibiting a surge of 170% and 270% for mixtures, including 15% and 25% glass powder, respectively, compared to conventional OPC concrete. Although including these recycled materials reduces compressive strength (19.95% for SP15 and 21.39% for SP25); tensile strength is significantly improved, with gains of 35% for SP15 and 53.75% for SP25. This research emphasizes the feasibility of integrating waste glass and plastic fibers into concrete as a practical method for sustainable building.

Experimental and modelling analysis of waste material-based geopolymer concrete incorporated with crumb rubber particles

Rubberized geopolymer concrete (RuGPC) emerges as an eco-friendly alternative to conventional concrete, significantly reducing greenhouse gas emissions. This study investigates the use of steel slag (SS) in varying proportions (30 %, 35 %, and 40 %) as a replacement for ground granulated blast furnace slag (GGBS) in geopolymer concrete, with crumb rubber (CR) replacing crusher dust (CD) as fine aggregate due to its increasing demand. The research focuses on understanding the impact of aluminosilicate materials on the mechanical, thermal, and microstructural properties of geopolymer concrete cured at 60°C. Advanced characterization techniques, including Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR), were employed. SEM and EDX analyses revealed that the microstructural properties of GGBS and SS materials, mainly Na/Si, Si/Al, H₂O/Na₂O, and Na/Al ratios, significantly influence RuGPC performance through gel formation. FTIR analysis indicates a shift in the stretching vibrations of GGBS and SS to lower wavenumbers due to geopolymerization changes. XRD results show the formation of C-S-H gel at around 27–30° 2theta, attributed to increased GGBS and SS content. Despite efforts to incorporate CR into geopolymer matrices, challenges in mitigating strength degradation persist. To address this, a predictive model was developed to understand the key factors affecting RuGPC performance. Six machine learning techniques—M5P (pruned and unpruned), random forest, random tree, linear regression, and support vector machine with various kernels (PUK, RBF, PK, and NPK), and artificial neural network (ANN)—were employed to predict the physical and thermal behavior of RuGPC. The analysis identified ANN-based models as the most effective. Sensitivity analysis highlighted the grade of rubber and the CR replacement percentage by volume of CD as the most influential parameters determining RuGPC compressive strength, density, and thermal conductivity. Moreover, The economic analysis revealed that RuGPC mixtures were 1.2–11.61 % more cost-effective than OPC concrete. These findings underscore the importance of predictive model development in optimizing RuGPC properties for practical applications, offering valuable insights for decision-making processes.

Multi-scale thermo-poro-mechanical simulation of the frost resistance of low-heat and moderate-heat hydraulic concrete considering the aging microstructure

Hydraulic concrete structures in cold regions are vulnerable to freeze-thaw damage. This paper proposes a multi-scale simulation analysis approach to investigate the mechanical properties and frost resistance of Low-heat Portland (LHP) cement, Moderate-heat Portland (MHP) cement, and Ordinary Portland cement (OPC) concrete. The hydration heat, hydration degree, pore size distribution, and compressive strength of LHP, MHP, and OPC concrete at different curing ages, as well as the ice amount, expansion strain, and mechanical properties under different freeze-thaw cycles are calculated and compared. Due to the lower early-hydrated C3S content of LHP and the higher later-hydrated C2S content, the porosity of LHP after 90d curing is lower than that of MHP and OPC, resulting in better mechanical properties and frost resistance. On this basis, the evolution model proposed in this paper can quantitative analysis the frost resistance of cement paste based on different content of C3S and C2S, which provided a feasible method for predicting the frost resistance of hydraulic concrete structures in cold regions.

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.

Mix proportion design and carbon emission assessment of high strength geopolymer concrete based on ternary solid waste

To achieve dual optimization of the mechanical properties and environmental impacts of geopolymer concrete (GPC), this study proposes a high-strength geopolymer concrete (HSGPC) without coarse aggregate. The mix proportion of HSGPC was optimized using the response surface methodology, targeting compressive strength and splitting tensile strength to determine the optimal mix. Additionally, the carbon emission impact of HSGPC was assessed and compared with ordinary Portland cement concrete, ultra-high-performance concrete, and reactive powder concrete. The results indicate that the optimal mix proportion for HSGPC includes 15% fly ash content, 10.30% silica fume content, alkali activator ratio of 2.5, and a NaOH molar concentration of 10 M. Simultaneously, the carbon emissions of HSGPC are reduced by about 30% compared to ordinary Portland cement concrete. Compared to ultra-high-performance concrete and reactive powder concrete of the same strength, the production of HSGPC respectively reduces carbon emissions by 59.87% and 68.24%. This study not only provides valuable technical support for the practical application of GPC in engineering but also holds significant implications for promoting sustainable development in the construction industry.

Fracture toughness of alkali-activated concrete subjected to aggressive environment

This study investigates the fracture toughness of alkali-activated granulated blast-furnace slag (GBFS)-based geopolymer concrete (GPC), non-activated slag cement concrete, and ordinary Portland cement (OPC) concrete in acidic, alkaline, and chloride solutions over six months. A total of 580 centrally straight-notched Brazilian disc (CSNBD) specimens were cast to assess pure mode-I (0°), pure mode-II (28.7°), and mixed-mode (15° and 45°) fractures under these conditions. Microstructural analyses (SEM) were performed to evaluate microstructural changes after six months of exposure. Results showed that GPC exhibited the lowest initial fracture toughness but the smallest reduction (7 %-11 % depending on the mode) across all environments, with slag cement concrete and OPC experiencing reductions of 11 %-14 % and 14 %-21 %, respectively, in acidic conditions. In alkaline environments, GPC showed a 3 %-6 % decrease in fracture toughness, while OPC and slag cement concrete showed reductions of 6 %-13 %. The gradient boosting regressor accurately predicted the failure load of CSNBD specimens, achieving an R² score of 0.948. Finally, SHAP sensitivity analysis identified concrete type, exposure time, and environment as critical input features, consistent with experimental results.

Strength, durability, and heat development characteristics of high-performance concrete containing ground coal bottom ash with low and high calcium

Currently, the availability of fly ash has reduced continuously due to the shutdowns of coal-fired power generating plant as climate change concerns have increased. Therefore, the aim of this paper is to find an alternative pozzolan by examining the employment of low- and high-calcium oxide (CaO) ground bottom ash which has been abandoned rather using in concrete production. The bottom ashes were blended with fly ash as a partial substitution of cement (OPC) by observing their generic effects on the compressive strength, cumulative heat generation, chloride ion penetration, and water sorptivity of high-performance concrete. The samples of bottom ash were prepared by oven drying, particle size cutting, and grinding to enhance the reactivity and consistency. High-performance concretes were made at a water-to-binder (W/B) ratio of 0.27 and partial replacement of OPC up to 50 % by weight of the binder. The results indicated that the concretes with 28-day compressive strengths of 101.0 and 109.0 MPa (21.6 % and 28.2 % stronger than OPC concrete) were produced with 50 wt% OPC replacement with high- and low-calcium ground coal bottom ashes (HCBA and LCBA), respectively. These findings suggest that HCBA and LCBA have high pozzolanic reactivity and high possibility for utilization as pozzolan or supplementary cementitious materials in concrete. In addition, the binary blended binders (OPC-HCBA and OPC-LCBA) and ternary blended binders (OPC-HCBA-FA and OPC-LCBA-FA) produced had better chloride ion penetration resistance, less cumulative heat evolution, and lower water sorptivity than 100 % OPC as a cementitious material. Partial OPC replacement by HCBA and LCBA improved the chloride ion penetrability class of OPC concrete from “very low” to “negligible.” The cumulative heat generation due to the pozzolanic reaction of HCBA and LCBA from the partial replacement of OPC up to 50 % reduced 30–44 % relative to the OPC-based mixture throughout during 72 hours after mixing. The CaO content strongly influenced early compressive strength development and cumulative heat evolution but had less impact on chloride ion penetration resistance and water sorptivity.

Study on the Influence of Thermoplastic Microcapsules on the Sulfate Resistance and Self-Healing Performance of Limestone Calcined Clay Cement Concrete.

Limestone calcined clay cement (LC3), enhanced through reactions with volcanic ash and the interaction between limestone and clay, significantly improves the performance of cementitious materials. It has the potential to cut CO2 emissions by up to 30% and energy consumption in cement manufacture by 15% to 20%, providing a promising prospect for the large-scale production of low-carbon cement with a lower environmental effect. To effectively manufacture LC3 concrete, this study utilized limestone (15%), calcined clay (30%), and gypsum (5%) as supplementary cementitious materials (SCMs), replacing 50% of ordinary Portland cement (OPC). However, in regions abundant in sulfate, sulfate attack can cause interior cracking of concrete, reducing the longevity of the building. To address this issue, microcapsules containing microcrystalline wax, ceresine wax, and nano-CaCO3 encapsulated in epoxy resin were prepared and successfully incorporated into LC3 concrete. Sulfate resistance tests were conducted through sulfate dry-wet cycles, comparing samples with and without microcapsules. The findings revealed that the initial mechanical and permeability properties of LC3 concrete did not significantly differ from OPC concrete. LC3 concrete with added microcapsules (SP4) exhibited enhanced resistance to sulfate attack, reducing mass loss and compressive strength degradation. SEM images displayed a mesh-like structure of repair products in SP4. After 14 days of self-repair, SP4 exhibited a 44.2% harmful pore ratio, 98.1% compressive strength retention, 88.7% chloride ion diffusion coefficient retention, 91.12 mV maximum amplitude, and 9.14 mV maximum frequency amplitude. The experimental results indicate that the presence of microcapsules enhances the sulfate attack self-healing performance of LC3 concrete.

Influence of alkaline activators on mechanical properties of environmentally friendly geopolymer concrete under different curing regimes.

Previous studies highlighted the significance of tailoring alkaline activators (AA) to specific fly ash (FA) sources for optimal properties of geopolymer concrete (GPC). This study examines the influence of various AA's properties on mechanical properties and microstructures of local low-calcium FA-based GPC under varying curing conditions. A comprehensive investigation consists of several factors such as NaOH molarities (10M, 12M, 14M, 16M), ratios (1.5, 2.0, 2.5) and ratios (0.5, 0.6). The results reveal a complex relationship, demonstrating that NaOH molarity positively influences compressive strength up to a threshold of 14M, beyond which an adverse effect was observed while, the flexural strength was increased up to 16M. Moreover, the study highlights the complex relationship between ratios and mechanical strengths. Notably, these properties exhibited an increase as the ratio rose up to 2.0, but a subsequent decrease was observed when the ratio reached 2.5. Moreover, proposed regression equations predict the compressive and flexural strengths of both ambient-cured GPC and heat-cured GPC with marginal statistical errors. The optimal GPC mix exhibited 49% lower embodied emissions than the corresponding OPC concrete. GPC has higher cost, but it exhibited lower cost-to-strength ratio compared to OPC concrete.

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.

Developing greener concretes from spent bleaching earth and sugarcane bagasse ash

Concrete is by far the most widely utilized construction material due to its excellent mechanical and durability properties. However, the concrete industries are notorious for their anthropogenic activities that contribute to climate change. Cement production alone consumes immense amounts of energy and trails a significant CO2 footprint. One solution that researchers have deemed promising over the last couple of decades is the substitution of cement with agricultural waste products, which subsequently serves to alleviate waste disposal problems. This study investigates the suitability of spent bleaching earth (SBE) and sugarcane bagasse ash (SCBA) as partial replacement of ordinary Portland cement (OPC) in increments of 0, 5, 10 and 15% by mass. Tests were conducted in accordance to British Standards to assess the consistence, compressive strength, split tensile strength and drying shrinkage strain of SBE and SCBA based concretes. Results indicated that while these concretes displayed similar degrees of consistency, the SCBA concretes exhibited superior compressive and tensile strengths. Optimum SCBA dosages were revealed to be about 5-10%, yielding a 7-12% and 3-8% increase in compressive and tensile strengths, respectively, as compared to OPC concrete. Drying shrinkage behavior was also improved in the SCBA concretes. Further, comparisons of the mechanical and durability performances of the concretes with British and American codes suggest that up to 10% replacement of cement with SCBA may be a viable approach to developing sustainable materials for the concrete industry.

Effect of particle size distribution and content of limestone powder on compressive response of high-early-strength cement mortars

This study examined the effect of particle size distribution and content of limestone powder on the compressive response of high-early-strength portland cement mortars cured either in water or under ambient conditions. Nineteen mortar mixtures were classified into three groups based on the particle size distribution of the pulverized limestone powders: L (blaine = 3467 cm2/g), M (blaine = 4710 cm2/g), and H (blaine = 5764 cm2/g). The design equations for the compressive strength gain rates and stress–strain relationship of ordinary portland cement (OPC) concrete were adapted for the present mortars. The test results revealed that the 28-d compressive strength (fc′) of the mortars tended to decrease with an increase in limestone powder content, even for mortars containing 5 % limestone powder with small particle sizes. This contrasts with the common trend of the positive effect of limestone powder on the compressive strength of OPC concrete up to a certain substitution level. Furthermore, mortars containing finer limestone powders exhibited a greater rate of decrease in fc′, regardless of the curing conditions. The modified equations show promise for reliably assessing both the compressive strength gain rates at different ages and the stress–strain behavior of high-early-strength portland cement mortars containing limestone powders.

Mechanical behavior and microscopic damage mechanism of hybrid fiber-reinforced geopolymer concrete at elevated temperature

Geopolymer concrete (GPC) that is prepared from eco-friendly materials exhibits much more excellent resistance on high temperature compared with ordinary Portland cement concrete. In this study, hybrid fibers containing varying proportions of steel fiber (0.5%-2.0%) and polyvinyl alcohol (PVA) fiber (0.2%-0.8%) were incorporated in GPC. The hybrid fiber-reinforced geopolymer concrete (HFRGC) was subjected to temperatures ranging from 200 °C to 800 °C. The physical properties tests, mechanical properties tests, and microstructure tests of HFRGC were carried out at elevated temperatures, while the environmental impact and cost-effectiveness of HFRGC were assessed. The results of physical properties tests showed that the appearance and mass loss of the HFRGC were mainly affected by temperature, while hybrid fibers had a negligible effect on both. The appearance of HFRGC gradually transformed from gray to brick red with increasing temperature, and the mass loss of HFRGC at 800 °C was as high as 9.4%. The mechanical performance test results indicated that the mechanical strength of HFRGC increased at 200 °C and then decreased with elevated temperature. At 200 °C, the compressive strength, splitting tensile strength, and flexural strength of HFRGC containing 1.5% steel fibers and 0.6% PVA fibers were respectively increased by 13.1%, 14.7%, and 4.4% as compared with ambient conditions. The microstructure test results showed that further geopolymerization at 200 °C promoted the densification of the matrix. The matrix was damaged at higher temperatures violently while the porosity of HFRGC was dramatically increased from 13.35% at 25 °C to 27.83% at 800 °C. Based on the thermal behavior, environmental impact, and cost-effectiveness of HFRGC, a reference for future research in the fire prevention of GPC was provided.

Simultaneously Enhancing the Dynamic Damping and Static Strength Capabilities of Structures: A Case Study Conducted on Fly Ash-based Geopolymer Concrete Specimens using Modal, Mechanical and Microstructural Investigations

Enhancing both the dynamic damping and static strength of ordinary Portland cement (OPC) concrete simultaneously is a significant challenge. Geopolymer concrete (GPC), particularly fly ash-based GPC, offers a promising alternative. This study explores the relationship between damping and strength in heat-cured, low-calcium fly ash-based GPC using sodium silicate (SS) and sodium hydroxide (SH) activators. The findings reveal that SS activators demonstrate stronger positive correlations between damping and strength compared to SH activators. Microstructural analysis indicated that increasing SS dosage from 55 kg/m³ to 98 kg/m³ resulted in a 17% increase in dynamic damping ratios and a 39% increase in static compressive strength. These results highlight the potential of GPC to surpass OPC concrete in applications requiring both enhanced damping and strength, offering a dual benefit not typically achievable with OPC. The study contributes to a deeper understanding of GPC's capabilities, paving the way for its broader adoption in construction projects.

Theoretical investigation on elastic property evolutions of low volume fly ash concrete

AbstractToward expanding the application of fly ash in cement‐based materials, this study proposes a comprehensive study on predicting the elastic properties of low‐volume fly ash concrete, with the replacement levels limited to 30% or less. Unlike conventional ordinary Portland cement concrete, the inclusion of fly ash in concrete brings alterations in properties from both chemical and physical perspectives: (1) the presence of fly ash liberates the alkaline solution that consumes calcium hydroxide to generate secondary calcium silicate hydrate gels; (2) unreacted fly ash particles exhibits a refinement effect on the micropore structure and contributes to forming a denser solid matrix. In order to characterize these effects on the mechanical properties of fly ash concrete, this paper conducts qualitative assessment of hydration reactions and quantitative calculations of volumetric compounds in the material. Utilizing the Mori‒Tanaka scheme, a predictive model is then developed to integrate the hierarchical effects of constituents at multiple scales on the modulus of elasticity of low‐volume fly ash concrete. The reliability of the proposed model is validated through a series of mechanical tests involving various mix designs, as well as comparison with other published test data.

Calcined Clays as Concrete Additive in Structural Concrete: Workability, Mechanical Properties, Durability, and Sustainability Performance.

Calcined clays (CCs) as supplementary cementitious materials (SCMs) can be a promising option to reduce clinker content and CO2 emissions in eco-friendly concretes. Although CCs as components of composite cements in combination with Ordinary Portland Cement (OPC) and limestone powder (LSP) have attracted industry interest, their use as concrete additives is limited. This study investigates the effects of the addition of CCs on the fresh and hardened properties of industry-standard ready-mixed concretes. Four concrete mix designs, each with three superplasticizer dosages, were tested, resulting in 12 variations. The CCs used, which are typical of 2:1 bentonite clays with low metakaolin content, reflect the clays available in Germany. The results showed that CCs significantly influenced the workability, which could be controlled with a high superplasticizer dosage. Increased CC contents reduced bleeding tendencies, which was beneficial for certain structural applications. Early age strength decreased with CCs, but the 28-day strength exceeded that of pure OPC concretes up to 30 wt% CCs. Resistance to CO2-induced carbonation decreased with higher levels of CCs but was comparable up to 15 wt%. Freeze-thaw damage decreased, and chloride migration resistance improved due to a denser microstructure. The global warming potential (GWP) of the concretes tested is in line with that reported in the literature for concretes made from highly blended cements, suggesting that CCs can improve the sustainability of concrete production.

Strength and microstructure of geopolymer recycled brick aggregate concrete after high temperatures

Geopolymer recycled brick aggregate concrete (GRBC), as a new environmentally friendly material, exhibits excellent mechanical performance at ambient temperature, but its properties after exposure to high temperatures are not clear. In this paper, the strength and microstructure of GRBC after high temperatures were investigated and compared with ordinary recycled brick aggregate Portland cement concrete (ORBC) through compressive strength, splitting tensile strength, and microscopic tests. The main parameters varied in the strength tests were temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and recycled brick aggregate (RBA) replacement ratio (0 %, 25 %, 50 %, 75 %, and 100 %). The results indicated that the strength of GRBC decreased less than that of ORBC after high temperatures. The compressive strength retention rate of GRBC after exposure to 800 °C was 0.359−0.456, and the tensile strength retention rate was 0.415−0.442. The strength of GRBC with 50 % RBA replacement ratio was about 0.70 that of the case without RBAs. The microscopic test results showed that the structure of GRBC was denser than that of ORBC, and the interfacial transition zone (ITZ) between matrix and RBAs was less affected by the temperature. The first weak zone after high temperatures was RBA itself for GRBC, but ITZ between matrix and RBAs for ORBC. The X-ray diffraction analysis indicated that the phase composition of GRBC and ORBC after high temperatures was basically similar to that at ambient temperature. The strength of GRBC was mainly provided by the N-A-S-H and C-A-S-H gels, while the strength of ORBC was mainly relied on the C-S-H gel.

Experimental investigation of quarry rock dust incorporated fly ash and slag based fiber reinforced geopolymer concrete circular columns

Manufacturing ordinary Portland cement (OPC) poses significant challenges for sustainable construction practices. OPC manufacturing emits substantial greenhouse gases into the atmosphere and demands extensive raw materials. In pursuit of greener alternatives, researchers explore geopolymer concrete (GPC), a revolutionary material that entirely replaces OPC, comprising industrial wastes/by-products activated through an alkaline solution. The study aims to investigate the feasibility of incorporating quarry rock dust (QRD) into GPC production for environmentally sustainable structural applications. Circular columns (200 mm diameter, 1000 mm length) were formulated using GPC blends with fly ash, slag (SG), and QRD as a partial SG replacement. The structural performance of these columns, with and without steel fiber reinforcement, was evaluated under varied loading conditions. Results show that QRD is a valuable ingredient in GPC for structural concrete elements, offering performance comparable to traditional OPC concrete. Furthermore, the incorporation of steel fibers significantly enhances the peak axial loads, displacement response, and overall performance of GPC columns with or without QRD. Fiber-reinforced GPC columns demonstrated approximately 8–10% higher ultimate load capacity than equivalent OPC columns. Eccentricity was found to significantly reduce ductility, but fiber reinforcement offers substantial ductility improvements (25–55%).

Bond behavior of reinforcing steel bars in metakaolin – calcium carbide residue-based geopolymer concrete

The bond property of concrete is a key characteristic of concrete that affect the structural activity of reinforced concrete beams. Concrete produced from geopolymer has the prospect to replace concrete produced from ordinary Portland cement (OPC) for structural applications. Therefore, this research evaluates the bond behavior of metakaolin-calcium carbide residue (CCR)-based geopolymer concrete for use in in situ structural applications. Comparative studies were carried out on concrete made of geopolymer and OPC. The embedment lengths (5ϕ and 7ϕ) and reinforcing bar diameters (14 and 16 mm) were varied and the bonding activity of the different concrete types was studied. Additionally, the qualities of the concrete produced were assessed, including density, ultrasonic pulse velocity, and compressive and flexural strengths. Generally, the metakaolin-CCR-based geopolymer concrete samples had the best mechanical properties, followed by metakaolin-based geopolymer and OPC concrete, respectively. Bond activity enhanced when embedment length and diameter of reinforcement were reduced in all types of concrete. Thus, with a reinforcing bar diameter of 14 mm and an embedment length of 5ϕ, the average bond strength of the metakaolin-CCR-based geopolymer concrete was 14.3MPa, which was 18.87% and 105.46% higher than that of the metakaolin-based geopolymer and OPC concrete, respectively. Influenced by experimental conclusions, it can be established that the metakaolin-CCR-based geopolymer concrete has the capacity to be used in place of OPC concrete in bond applications where steel reinforcing bars are employed.