Rapid Chloride Penetration Test Research Articles

Mechanical properties and durability of concrete containing fly ash and GGBS for marine environment: A comprehensive study from laboratory perspective

The degradation of concrete structures in the marine environment is generally caused by sulfate attack and chloride ion penetration. To improve the durability of concrete in the marine environment, fly ash (FA) and ground granulated blast furnace slag (GGBS) were partially used to replace cement in a ternary system. The crushed sand was used to reduce the shortage of river sand. In this study, the concrete containing crushed sand, FA, and GGBS was prepared in the laboratory, in which river sand was partially replaced with crushed sand and cement was substituted with FA and GGBS. The amounts of FA/binder and GGBS/binder were fixed at 20% and 35%, respectively, while the content of crushed sand/fine aggregate was set at 60%. The mechanical properties were investigated via compression and splitting tensile tests. The durability of the concrete was examined using a rapid chloride penetration test, sulfate attack test, accelerated corrosion test, and abrasion-wear resistance test. The results showed that the partial replacement of cement by FA and GGBS improved both the mechanical properties and durability of concrete. The inclusion of FA and GGBS in concrete significantly improved its resistance to chloride permeability, specifically, the total charge passed of the mixture with FA and GGBS decreased from 86.2% to 136.9% in comparison with the mixture without FA and GGBS. The addition of FA and GGBS could reduce the change in the length (i.e., improved sulfate resistance) of concrete when it is in contact with the sulfate solution. The changes in the length of the mixture containing FA and GGBS were 3.5 times and 3.2 times smaller than those of the mixture without FA and GGBS. The concrete mixture containing FA and GGBS has a two-time higher corrosion resistance to chloride ion ingress than conventional concrete without FA and GGBS inclusion. The abrasion resistance was improved significantly with the inclusion of FA and GGBS, the abrasion resistance of the mixtures containing FA and GGBS significantly improved by 52 to 59% in comparison with the mixture without FA and GGBS. These results demonstrate that the inclusion of FA and GGBS in concrete can improve both the mechanical properties and durability of concrete, which can be applied in marine environments for sustainable development.

Towards a sustainable built environment: evaluating alternative water sources for concrete production

PurposeThis study explores the feasibility of substituting freshwater with alternative water sources such as potable water (PW), harvested rainwater (HRW), stormwater (SW), borewell water (BW) and seawater (Sea W) in concrete manufacturing. The aim is to evaluate the potential of these alternative sources to support sustainable development, reduce environmental impact and conserve freshwater resources in the construction industry.Design/methodology/approachThe research followed established concrete production standards and evaluated the chemical properties of various water sources. Fresh concrete characteristics, including setting time, workability and mechanical properties (compressive, split tensile and flexural strength), were tested at 7, 28 and 90 days. Durability assessments utilized the Volhard assay for chloride content, RCPT for chloride permeability and a physical sulfate attack test. Additionally, a life cycle assessment (LCA) examined the environmental impacts, while an economic analysis assessed cost implications for each water source.FindingsThe results showed only minor differences of 2%–3% in the fresh and mechanical properties of concrete using alternative water sources, with no significant changes in compressive, tensile or flexural strength compared to potable water. The Rapid Chloride Penetration Test (RCPT) and Nord Test techniques showed that all water sources, except seawater, are suitable for concrete mixing, as they enhance concrete durability due to their very low chloride ion concentrations, which minimize the risk of steel corrosion. The sulfate attack, including mass loss and expansion measurements for various water sources, indicates low susceptibility to except seawater. SEM and EDS HRW and SW also showed denser microstructures compared to Potable Water, indicating the absence of voids or cracks and the formation of ettringite needles, while seawater posed challenges due to high chloride content and corrosion risks. The LCA indicated that SW had the lowest environmental impact, while seawater posed substantial challenges. The economic analysis confirmed SW as the most cost-effective option, with all sources meeting production standards except seawater.Originality/valueThis study provides new insights into the sustainable use of non-potable water sources in concrete manufacturing. It demonstrates the viability of using HRW, SW and BW as alternative water sources to potable water, supporting sustainability goals in construction while conserving vital freshwater resources and reducing environmental impact.

Salt scaling resistance of self-consolidating concrete containing polynary pozzolanic-cement

Although numerous durability investigations on self-consolidating concrete [SCC] have urged partial replacement of cement with pozzolans, contradictory results exist regarding the salt scaling resistance of pozzolanic concrete. Hence, this study was carried out on salt scaling resistance of binary, ternary and quaternary pozzolanic SCC utilizing trass, pumice and silica fume pozzolans in nine mixtures along with two air-entrained ones. The binary, SF10, majority of ternaries, SF10T10, SF10T20 and SF10P10, and air-entrained, SF10A3% and SF10T20P20A3% mixtures showed acceptable resistance against salt scaling with scaling lower than 0.8 kg/m2, as opposed to quaternaries. The effect of pozzolans on salt scaling resistance of concrete is highly dependable on the SiO2+Al2O3+Fe2O3 content of the pozzolan. Also, microstructural analysis through SEM reflected the presence of ettringite and Friedel’s salt from scaled surface. Furthermore, except for compressive strength, ternaries and quaternaries, SF10T10P10, SF10T20P10, SF10T10P20 and SF10T20P20, performed generally better than binary in rapid chloride penetration test, while they had similar pulse velocity, depth of penetration, water absorption and electrical resistivity.

Performance Enhancement in Concrete Using Nano Silica and Fly Ash

Abstract To improve the concrete performance, combining nano materials with mineral admixtures is quite effective in refining the fresh as well as hardened properties. However, the combined effects of nano and micro level materials on the concrete performance needed to be investigated for better understanding of their synergistic effects. In this paper fly ash (FA) is blended with nano silica (NS) replacing ordinary Portland cement (OPC) grade 43 to produce high performance concrete (HPC). Experiment was conducted at fixed water binder ratio with varying percentage of superplasticizer to produce workable and cohesive mix. Ternary blending with NS gave better cube strength at early stage than the binary blended mix. Even at later stage there was enhancement in the strength at 15% FA and 2% NS replacement. This could be due to seeding effects of ultra fine NS particles providing favourable hydration conditions for FA. Nano modified concrete gave lower strength at higher proportions due to the inherent problem of agglomeration. Durability of the mix was investigated by the rapid chloride penetration test (RCPT). Also, ultrasonic pulse velocity (UPV) test was conducted to observe the homogeneity of the mix. Ternary mix of 1.5% NS and 20% FA with OPC was the optimum dosage as it showed enhanced strength and durability. The images obtained from scanning electron microscope (SEM) was analysed to understand the CSH gel formation and the hydration process. These results showed that the combined usage of NS and FA has synergistic effects which could be utilized for maximum performance.

Experimental analysis on Self Compacting Concrete by using Nano - Silica Gel

Abstract: Self-Compacting Concrete (SCC) has gained widespread recognition in modern construction due to its ability to flow under its weight, eliminating the need for mechanical vibration. Despite its numerous advantages, challenges such as maintaining stability, durability, and achieving optimal mechanical performance persist. Incorporating nano-silica gel, a material known for its high pozzolanic activity and micro-filling capability, offers a promising solution to address these challenges. This experimental study evaluates the impact of nano-silica gel on the fresh, mechanical, and durability properties of SCC. The research involves preparing SCC mixes with varying nano-silica gel dosages (0.5%, 1%, 1.5%, and 2% by weight of cement) and analyzing their performance through a series of standardized tests. Fresh properties such as slump flow, T500 flow time, and V-funnel tests are used to assess workability and flow characteristics. Hardened properties, including compressive strength, split tensile strength, and flexural strength, are evaluated at different curing ages. Durability is analyzed through Rapid Chloride Penetration and Sulfate Resistance tests to assess the resistance to chemical attacks. Results indicate that the inclusion of nano-silica gel significantly enhances the flowability, compressive strength, and durability of SCC. The optimal performance is observed at 1% nano-silica gel dosage, beyond which a reduction in workability and strength occurs due to increased particle agglomeration. This study demonstrates that nano-silica gel can substantially improve SCC properties, making it a viable material for high-performance and sustainable construction practices. These findings contribute to the ongoing development of advanced concrete technologies, paving the way for future research in optimizing SCC mixes with nano-materials.

Enhancing durability and strength of concrete through an innovative abrasion and cement slurry treatment of recycled concrete aggregates

The increasing demand for sustainable construction materials has driven significant interest in utilizing recycled concrete aggregates (RCA). However, the mechanical performance and durability of RCA are often compromised due to the presence of residual mortar. This study explores an innovative surface treatment approach combining abrasion and cement slurry coating to improve the properties of RCA and enhance the performance of recycled aggregate concrete (RAC). Recycled concrete aggregates were subjected to mechanical abrasion, followed by a cement slurry coating, resulting in the production of Surface-Treated Recycled Concrete Aggregates (STRCA). The study evaluates the impact of STRCA on the compressive strength, drying shrinkage, electrical resistivity, and chloride ion penetration resistance of concrete mixes with varying replacement ratios (25 %, 50 %, 75 %, and 100 %). Results revealed that the water absorption of RCA was significantly reduced from 5.35 % to 2.61 % following the treatment. STRCA 25 and STRCA 50 mixtures exhibited compressive strength increases of 30.16 % and 18.99 % at 7 days, and 29.37 % and 17.13 % at 28 days, respectively. Higher replacement levels (STRCA 75 and STRCA 100) resulted in strength reductions, with 3.91 % and 16.64 % decreases at 7 days. Drying shrinkage increased progressively with higher RCA content, showing 1.72 %, 10.91 %, 25.86 %, and 38.79 % increases at 28 days for STRCA 25, STRCA 50, STRCA 75, and STRCA 100, respectively. Electrical resistivity improved for lower replacement levels, with STRCA 25 showing a 3.41 % increase at 28 days, while STRCA 100 exhibited a 26.25 % reduction. The rapid chloride penetration test results showed that STRCA 100 had the highest resistance to chloride ion penetration, with a 22.72 % and 28.69 % increase in passed charge at 28 and 56 days, respectively, compared to the reference concrete. The findings indicate that surface-treated RCA can enhance the mechanical and durability properties of concrete, especially at lower replacement levels, making it a viable option for sustainable construction.

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.

Investigation of strength, durability, and microstructure properties of concrete with waste marble powder as a partial replacement of cement

Purpose Cement plays a significant part in concrete, and with the increasing demand for concrete, cement output varies day by day, allowing production to carbon dioxide emissions. As well as marble processing creates stone slurry and solid discards. These are often dumped irresponsibly on open land, polluting the soil. This improper disposal of marble waste is a major environmental concern. This study aims to propose a sustainable solution for reusing this waste material as a concrete additive. Design/methodology/approach A total of 135 concrete cubes of size 150 × 150 × 150 mm, 54 concrete cylinders of size 150 mm dia. and 300 mm height and 54 concrete beams of size 150 × 150 × 700 mm were cast. The replacement was 0%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5% and 20% by weight of cement with marble dust to create M30 concrete with a water-cement ratio of 0.45. The test was performed to find the compressive strength (CS), flexural strength (FS) and split tensile strength. Also, durability tests like rapid chloride penetration test (RCPT), acid attack, ultrasonic pulse velocity (UPV) and water permeability test were performed. Findings After 7 and 28 days of curing, it was found that replacing 5% of cement with marble powder led to an initial strength improvement of up to 25% for both curing periods. However, further increases in marble dust resulted in an inconsistent decrease in strength for all the mixtures. Also, durability properties like acid attack test, water permeability test and RCPT, showed good performance at the optimum percentage of waste marble powder (WMP) as cement replacement. The microscopic analysis revealed a denser pore structure at lower WMP replacement levels, likely due to the powder filling in gaps. Originality/value This study reveals that by substituting 5% (optimum) of cement with WMP, there was CS improvement up to 8.4% and 17% for both 7 and 28 days of curing. WMP is typically finer than cement particles and fills the voids in the concrete more effectively, resulting best performance at optimum percentage against RCPT, UPV, acid attack and water permeability.

Investigating the influence of various metakaolin combinations with different proportions of pond ash and Alccofine 1203 on ternary blended geopolymer concrete at ambient curing.

This paper explores the use of a ternary blended geopolymer concrete (TBGPC) incorporating metakaolin (MK), pond ash (PA), and Alccofine 1203 (AF). Three combinations of MK (25%, 50%, and 75%) with varying proportions of PA and AF were prepared, validating against M30 grade cement concrete (CC). TBGPC was prepared with an 8 molarity sodium hydroxide, sodium silicate to sodium hydroxide ratio of 2.0, liquid to binder ratio of 0.5, and an ambient curing mode. For CC, a water to cement ratio of 0.42 and water curing mode were adopted. The mechanical properties and durability behavior of TBGPC and CC specimens were evaluated through compressive strength, rapid chloride penetration test, permeability test, sorptivity test, and water absorption test. The M50P35A15 mix demonstrated remarkable compressive strength improvements, showing a 203% increase over the CC mix at 1day and 250% by 3days. This trend continued with a 155% increase at 7days, 68% at 28days, and 52% at 90days, consistently outperforming the CC mix. Additionally, microstructure characteristics of the M50P35A15 mix were analyzed through SEM studies, providing validation for the observed strength development. Notably, M50P35A15 mix demonstrated substantially higher early and later strength gain. This enhancement in strength was attributed to the gradual densification of the microstructure over time and the formation of additional NASH and CASH gel in M50P35A15 mix. At 28days, the M50P35A15 mix exhibited excellent durability characteristics, with a Coulomb value of 1008, permeability of 10mm, sorptivity of 0.45mm/√min × 10-4, and water absorption of 1.07%. This study demonstrates the potential of MK, PA, and AF as viable materials for sustainable geopolymer concrete, offering a low-carbon alternative to traditional cement concrete with superior strength and durability aspects.

The effect of Dolomite powder and Fly ash on durability properties of self-compacting concrete

Abstract This study aims to assess the effectiveness of dolomite mineral admixture in the production of self-compacting concrete (SCC). The characteristics of concrete at 7 and 28 days of hardening were evaluated. SCC mixtures with different amounts of dolomite powder and fly ash (FA) at a constant composition were made. It has been noted that the flow ability of SCC mixes gets better with increasing percentages of dolomite. In addition to its mechanical characteristics, the durability of mixes containing SCC has been studied, including water absorption, sorptivity, and permeability to chloride ions and acid attack. After 28 days, a strength of 61 MPa was achieved with a 20% DP replacement level mixture, which is 31.38% higher than the control SCC mix. Along with the compressive strength of SCC, parameters affecting the durability of SCC such as Rapid chloride penetration test (RCPT), Sorptivity, water absorption and hydrochloric acid attack were also studied at 28 days. The utmost resistance to permeability of chloride ions was attained.

Development of Ultra-High-Performance Concrete Using GGBS and Alccofine

Abstract: Ultra-high-performance concrete, or UHPC, is a cementitious mixture that is distinguished by its exceptionally high compressive strength—more than 120 MPa as well as its remarkable toughness, tensile ductility, and longevity. Ground Granulated Blast Furnace Slag (GGBS) and Alccofine (AF) are commonly used in the matrix composition to increase the particle system's packing density and subsequently enhance the matrix's strength in order to guarantee that UHPC has the proper strength. To investigate the engineering properties of ternary blended UHPC with GGBS, AF, a comparative study was conducted. In comparison to the control UHPC mix, the ternary blended UHPC mix's mechanical and durability qualities were improved by the percentage variation of AF within specific bounds. In this study, the experimental work included mix proportioning and preparation of ternary blended UHPC specimens and various tests like Compressive Strength, Split Tensile Strength, Flexure Strength and RCPT (Rapid Chloride Penetration Test) were performed in the laboratory. The results show that under normal water curing conditions, the strength qualities of UHPC based on GGBS are considerable, up to a cement replacement level of 40%. In addition, compared to the binary counterpart, the mixture of 20 Percent AF and 40 Percent GGBS showed better mechanical and durability properties.

Polypropylene waste plastic fiber morphology as an influencing factor on the performance and durability of concrete: Experimental investigation, soft-computing modeling, and economic analysis

The increasing waste of plastic masses raises the danger alarm due to its adverse impacts on people and the natural environment. Hence, serious attempts should be made to manage this non-biodegradable waste for practical, sustainable, and sufficient uses, such as in construction. This research discusses experimentally the possibility of improving the behavior of concrete reinforced with waste plastic fibers (WPFs) from food trays by examining the effect of fibers morphology on concrete's mechanical properties and durability. This concept was intensively studied for steel fibers but rarely for WPFs. A 0.6 percentage of 30 mm long straight, spiral, and channel fibers were tested and compared. Compressive, tensile, and flexural strengths, impact resistance, water absorption, rapid chloride penetration tests, and microstructural analysis were conducted. The results revealed that the fibers shape influences the mechanical behavior along with the water absorption considerably, and that the spiral fibers exhibited superior performance compared to the other shapes. The mechanical properties of spiral fibers specimens have improved considerably compared to specimens of other shapes. However, the ion chloride penetration resistance did not witness any substantial improvement, and the brittle fracture of concrete did not change by using WPFs, despite the considerable increase of more than 66 % of the impact resistance of specimens with spiral fibers. According to the findings, spiral WPFs enhance concrete's behavior, making WPF implementation in concrete more efficient from an environmental and structural standpoint. Moreover, machine learning modeling and cost/benefit analysis were conducted in this work to better understand the WPF effect on concrete.

Influence of Nanoparticles and PVA Fibers on Concrete and Mortar on Microstructural and Durability Properties

Nanoparticles are one of the effective methodologies implemented in concrete technology. The main objective of this research is to study the influence of nano alumina with different percentage variations ranging from 1% to 3% along with the incorporation of PVA fibers. From the mechanical properties test, the optimum dosage was determined to further study the durability behavior. This research work also investigates the hybridization of two nanoparticles such as nano silica (NS) and nano alumina (NA). The results show that the increasing quantity of NA reduces the compressive strength of the mortar due to agglomeration (cluster of particles), which results in a greater molecular attraction force. From the test results, it is concluded that the optimum dosage has been attained with an addition of 2% NA with 0.3% PVA. The compression strength test results at 14 days and 28 days reveal that the addition of NA tends the mineral admixture to react at early ages in the hydration process, which produces a new chemical compound to fill the pores. The rapid chloride penetration (RCPT) test results at 28 days significantly improved with the incorporation of nanoparticles due to their effective size and chemical reaction towards the other compounds. The test results from the hybridization of nanoparticles showed that the compressive strength was significantly enhanced compared to that of the control mortar and mortar with NA. They are effective up to certain limits beyond that addition, and the workability was reduced. Amongst all mixtures, the maximum compression strength has been attained for the mix with the addition of NA 0.5% and NS 2.5% comparatively. The microstructural properties of mortar were also studied through scanning electron microscope (SEM) analysis. The results showed that the incorporation of nanoparticles in the mortar matrix turns homogeneous with fewer pores and greater amount of hydration compounds; thereby, pore refinement has improved the hydration compounds remarkably.

Durability and microstructural characteristics of self-compacting concrete incorporating M-sand

ABSTRACT Self-Compacting Concrete (SCC) is characterized by increased fluidity and enhanced cohesion, leading to its growing prominence within the construction sector. Additive materials such as alccofine and silica fume can enhance the properties of SCC while concurrently mitigating the ecological footprint linked to cement manufacturing. Manufactured sand, also known as M-sand, is finely crushed aggregate sourced from rocks or quarry stones, providing a sustainable substitute for natural river sand in construction. The primary emphasis of this study revolves around evaluating the enduring compressive strength and durability attributes of SCC, wherein M-sand is employed to replace river sand to varying percentages of 0%, 25%, 50%, 75%, and 100%. Durability assessments encompass evaluations at 28, 56, 90, 180, and 365 days for water absorption, Rapid Chloride Penetration Test (RCPT), sorptivity, and Volume of Permeable Voids (VPV), all compared against the benchmarks of control concrete. Microstructural characterization studies entail the utilization of techniques such as Scanning Electron Microscope imagery (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). From the results it is observed that M-sand replacement in SCC enhanced durability of the concrete.

Development of ANN-based metaheuristic models for the study of the durability characteristics of high-volume fly ash self-compacting concrete with silica fume

The construction of durable and sustainable infrastructure requires the use of industrial byproducts such as fly ash (FA) and silica fume (SF) to enhance strength and durability. This study introduces novel machine learning models to forecast the results of rapid chloride penetration test (RCPT) for self-compacting concrete (SCC) containing high volumes of FA and SF. This study assessed the effects of supplementary cementitious materials (SCMs) and elevated temperature curing on the RCPT outcomes for SCC. Various metaheuristic algorithms including teaching–learning-based optimization (TLBO), ant colony optimization (ACO), the imperialist competitive algorithm (ICA), and shuffled complex evolution (SCE)—optimize the learning rate, weights, and biases of artificial neural network (ANN) models. A dataset of 360 experimental RCPT data points with seven input parameters was used to train and test the hybrid models. The accuracy of these models was assessed using eight performance indices, and the results were further analyzed through rank analysis, scatter plots, and error matrices. The training and testing sets for the AI models, specifically ANN-TLBO, exhibit a strong correlation between the experimental and predicted RCPT values, with R2 values of 0.9962 for training and 0.9676 for testing, compared to the R2 values of the other proposed models. Consequently, the results of this study suggest that the ANN-TLBO model is the optimal hybrid ANN model for predicting RCPT values in SCC. Verified experimental results and external validation indicate that the ANN-TLBO model is an effective alternative for accurately predicting real-time RCPT in SCC.

A study of chloride binding capacity of concrete containing supplementary cementitious materials

Chloride-induced steel corrosion is known to be a very common kind of deterioration of reinforced concrete. It is beneficial to bind free chloride ions to reduce the corrosion probability of the reinforcement embedded in the concrete. The binding capacity of the concrete varies according to its cementitious system. This paper investigates the chloride binding capacity of different kinds of supplementary cementitious materials (SCMs): Ground granulated blast furnace slag (GGBFS), Fly ash, and Metakaolin as a partial replacement of Ordinary Portland Cement (OPC). Different properties of concrete after chloride binding are assessed by carrying out the following tests: half-cell potential, accelerated corrosion test, compressive strength, rapid chloride penetration test, sorptivity test, measuring pH value of concrete, and XRD. The results showed that utilizing the SCMs in concrete can enhance the chloride binding capacity, especially those materials that have high quantities of aluminate and calcium in their chemical composition like GGBFS. Based on testing results, it’s recommended that the limit of the chloride content in the different codes should be revised regarding the binding capacity according to the type and quantity of the cementitious materials used.

The Use of Ground Coal Bottom Ash/Slag as a Cement Replacement for Sustainable Concrete Infrastructure.

Cement production requires considerable energy and natural resources, severely impacting the environment due to harmful gas emissions. Coal bottom ash (CBA) and coal boiler slag (CBS), byproducts of coal-fired powerplants having pozzolanic properties, can be mechanically ground and replace cement in concrete, which reduces waste in landfills, preserves natural resources, and reduces health hazards. This study was performed to determine the optimum cement replacement amount of ground CBA (GCBA) and ground CBS (GCBS) in concrete, which was 10% for GCBA and 5% for GCBS. GCBA-based concrete exhibited superior tensile strength, modulus of elasticity, and durability compared to the control. In the Rapid Chloride Penetration Test, 10% GCBA concrete resulted in 2026 coulombs at 56 days, compared to 3405 coulombs for the control, indicating more resistance to chloride penetration. Incorporating 2.5% nanoclay in GCBA-based concrete increased the optimum GCBA content by 5%, and the compressive strength of 15% GCBA concrete increased by 4 MPa. The mortar consisting of the finest GCBA(L1) having Blaine fineness of 3072 g/cm2 yielded the highest compressive strength (32.7 MPa). The study discovered that the compressive strength of GCBA and GCBS-based mortars increases with fineness, and meeting the recommended fineness limit in ASTM C618 enhances concrete or mortar properties.

Strength and Durability Properties of High-Volume Fly Ash (HVFA) Binders: A Systematic Review

South Africa is endowed with a wealth of coal-fired power stations that can produce extremely high volumes of fly ash per year exceeding 34 million tonnes. The use of high-volume fly ash (HVFA) binders in the construction sector has the capacity to significantly reduce greenhouse gas emissions associated with traditional cement production and offset the carbon footprint of Eskom. The excessive production of fly ash by Eskom warrants the need for developing ultra-high-volume fly ash binders (UHVFA, fly ash/binder > 60 wt%). Nonetheless, fly ash (FA) replacement of cement is still largely limited to 35% regardless of more ambitious research indicating the potential to surpass 60%. In view of the urgent need for South Africa to offset and reduce its carbon footprint, this work reviews and summarises the literature on the performance of HVFA binders with a focus on two specific areas: (i) strength and (ii) durability. On HVFA binder strength, the focus is drawn on work that analysed the compressive strength, flexural strength, and split tensile strength. This review focuses on the extant literature analysing the durability of HVFA binders using various tests, including sorptivity, resistivity, permeability, tortuosity, rapid chloride penetration tests, resistance to sulphate attack, and microstructural analysis. As the FA content increases towards optima, i.e., 50–80%, the most indicative composite characteristics of the strength and durability properties are UCS (30–90 MPa) and permeability (low). This review reveals the leading methodologies, instrumentation, findings, challenges, and contradictions.

Study of durability and mechanical properties for utilization of cupola slag as a coarse aggregate in M20 grade green concrete

Cupola slag is an industrial waste generated from cupola furnaces during cast iron production. The disposal of cupola slag is a matter of burden for the manufacturers of casting industry. This experimental study aims to reuse cupola furnace slag (CFS) in the construction industry, developing a novel way of solid waste management. In the M20 grade concrete, CFS is used as coarse aggregate (CA), partially replaced by 0–50 wt % in the step of 10 wt %. The mechanical and durability properties of the CFS-based concrete were examined after the required days of curing. The experimental result exposed that the dry density decreases with the increased weight percent of CFS in concrete. The cast samples with up to 40 wt% partial replacement of CFS effectively meet the requirements for the M20 grade of concrete in terms of compressive strength. A similar trend for the split tensile strength was observed, like the compressive strength. Durability test results reveal that water penetration depth increases with increased CFS weight percent in concrete. Moreover, in the case of rapid chloride penetration test, chloride ions penetration is decreased with the increase of CFS weight percent in concrete. FESEM, EDS and XRD were used to examine the microstructure, elemental mapping and phase analysis of the CFS-based concrete. According to the investigation, CFS is a sustainable material that works well as a partial replacement for natural CA in concrete.

Chemical durability evaluation of copper grit aggregate concrete against Alkali-Silica-Reaction, carbonation and chloride penetration

This study aims to explore the effects of varying proportions of copper grit (CG) as fine aggregate on the alkali-silica reaction (ASR), accelerated carbonation test (ACT), and rapid chloride penetration test (RCPT) of concrete. Other complementary experiments including the rate of water absorption and compressive strength of copper grit aggregate mortar (CGAM), as well as compressive strength, split tensile strength, and sorptivity test of copper grit aggregate concrete (CGAC), were conducted. The results indicate that a higher CG content, particularly at around 80% replacement in the concrete mix, enhances strength without inducing expansive ASR and mitigates carbonation and chlorination rates in concrete. Moreover, the compressive strength of CGAM increases up to a 60% replacement ratio. Water absorption decreases from 62.1 gm/cm2 for the control specimen to 47.9 gm/cm2 for mortar with 100% CG replacement. ASR test results show no significant expansion up to a 20% replacement ratio of CG, with further increases in replacement resulting in expansion below the threshold limit of 0.1%. A notable 27% increase in compressive strength is observed for 80% CG replacement at 28 days of CGAC. Additionally, carbonation depth decreases with an increase in CG quantity in CGAC mixes, with the lowest depth observed for 80% CG replacement. The carbonation coefficient remains below the threshold limit, indicating high-quality CGAC. Furthermore, the service life of CGAC was predicted and microstructural characteristics of both CGAM and CGAC were examined via Field Emissions Scanning Electron Microscopy (FESEM). The findings underscore the potential of utilizing CG as a substitute for conventional sand in mortar and concrete production, offering a promising ecological alternative for conserving natural resources and safeguarding the environment.