Chloride Resistance Research Articles

Advantages and disadvantages of PVA-fibre-reinforced slag- and fly ash-blended geopolymer composites: Engineering properties and microstructure

• Engineering properties and microstructure of the composites are investigated. • The positive and negative roles of PVA fibres in the composites are revealed. • This study promotes the recycling of industrial wastes (GGBFS and FA). • This study serves as an important reference for engineers and designers. Alkali-activated ground-granulated blast-furnace slag (GGBFS) and fly ash (FA) geopolymers are sustainable alternatives to cement. The incorporation of polyvinyl alcohol (PVA) fibres can help minimise their shortcomings, such as drying shrinkage and brittleness, but may lead to other negative effects. Only a few studies have focused on geopolymer composites based on PVA-fibre-reinforced binary phases (GGBFS and FA). The positive and negative roles of PVA fibres in the performance of composites have not been systemically investigated in previous studies. To promote the application of the composites, the mechanical properties, workability, durability, high-temperature resistance, fibre dispersion, phases, and microstructure of composites with 0, 0.3 and 0.6 vol% of PVA fibres were systematically investigated in this study. The results showed that the incorporation of PVA fibres significantly increased the flexural and splitting tensile strengths of the GGBFS- and FA-blended and single FA-based composites at ambient and high temperatures, and the drying shrinkage was significantly reduced. On the other hand, PVA fibre incorporation caused a decrease in the compressive strength, flowability, consistency, sorptivity, and chloride penetration of the composites; however, the values are still acceptable in construction. Compared to the single FA-based composites, the GGBFS- and FA-blended composites showed improved mechanical properties, sorptivity, chloride resistance, and high-temperature resistance owing to their decreased porosity. This study serves as an important reference for engineers and designers for the use of green composites.

Improvement of the durability of cement-based material through surface modification with nano-engineered releasing agents

• Modified releasing agent with NS/NT to make nano-engineered releasing agent. • NS and NT increased the contact angle of releasing agent and help their adhesion on mold. • Reduction of the surface porosity (within 2 mm thick). • Nano-engineered releasing agent can achieve durable concrete surface. Aggressive substances can gain access to the inner structure of cement-based materials through the surface, resulting in deterioration of the structure. This work developed an effective way of improving the quality of cement-based materials surface by applying nanoSiO 2 -/nanoTiO 2 -engineered releasing agents (nSRa/nTRa) on the formwork surface. Continued with our previous work, the positive effects of nSRa/nTRa on cement hydration were used to improve the surface quality of the cement-based samples through its spraying on the mold surface. This work firstly characterized the adhesive properties of these agents on mold surface (contact angle and viscosity measurement), and then their effects on the surface microstructure and the durability of cement-based materials such as 1) sulfate resistance, 2) chloride resistance, and 3) freeze–thaw resistance were determined. Results showed that nanoparticle addition increased the contact angle of releasing agents and helped their adhesion to mold. Applying nSRa/nTRa on cement-based samples benefited the reduction of surface porosity (within 2 mm thick) by 14.2 %, 19.4 %, 8.6 %, and 18.9 % in the nS2Ra-, nS4Ra-, nT4Ra- and nT16Ra-engineered samples. After 120 days of sulfate attack, mortar samples cast in Ra-, nS4Ra-, and nT16Ra-coated molds showed reductions in compressive strength loss of 1.57 %, 0.73 %, and 0.23 %. Noticeable reductions in the chloride migration coefficient of 23.9 % and 26.6 % were found in the nS4Ra-/nT16Ra-modified mortar sample, while their relative dynamic modulus elasticity was 6.72 % and 12 % higher than Ra-sample after 200 freeze–thaw cycles. This work proved that nano-engineered releasing agents can effectively improve the durability of the concrete structure.

The Durability of Lightweight Geopolymer Concrete (LGC) on Chloride Resistance

Lightweight geopolymer concrete is an innovative concrete from a combination of environmental-friendly geopolymer concrete and lightweight concrete which has a density of less than 2,400 kg/m³. This concrete does not use Ordinary Portland Cement (OPC) but uses type F fly ash which has the same main composition as OPC namely silica and aluminum. Reducing the use of OPC aims to reduce the production of CO₂ gas emissions which are the main contributors to global warming. This study aims to provide the information needed to develop lightweight geopolymer concrete to reduce carbon emissions and create environmental-friendly concrete materials. The constituent materials of lightweight geopolymer concrete include type F fly ash as precursors, Na₂SiO₃ and NaOH 14 M as activators, fine aggregates in the form of sand as concrete fillers, superplasticizers, and foam. The use of foam helps in reducing the density of lightweight geopolymer concrete. The ratio used in this study is 1:2 for activators and precursors, 1:2 for precursors and fine aggregates, 2.5:1 for Na₂SiO₃ and 14 M NaOH, and 1:40 for foam agents and water with a percentage of foam that is 50% of test object volume. The amount of plasticizer used is 3% of the weight of the precursor. Treatment of the lightweight geopolymer concrete using an oven with a temperature of 60°C for 24 hours and then the specimen coated with plastic wrap for 28 days to achieve maximum compressive strength. Curing for 28 days, the specimen has a compressive strength of 27.9 MPa with a specific gravity of 1,702.5 kg/m³. This research focuses on the durability of lightweight geopolymer concrete using 5% HCl acid solution under different conditions, which are left at room temperature, fully immersed in 5% HCl acid solution, and cyclic conditions. Tests were carried out on days 28 and 56 with observations of changes in compressive strength, density, visual conditions, Scanning Electron Microscope, and XRD. The results showed that acid solutions' long duration and soaking conditions, especially hydrochloric acid, affect lightweight geopolymer concrete.

Mix design and characteristics evaluation of high-performance concrete with full aeolian sand based on the packing density theory

• A newly high-performance concrete was prepared by using aeolian sand. • The modified Andreasen & Andersen model was employed to determine the volume fractions of solid powders. • The optimization values of W/C, SP and FA content are 0.19, 1.0 and 25.86 respectively. • The internal pores of developed FAS-HPC are harmless and the pore porosity is 7.3%. • This study further enriches the raw materials for HPC and proposes a fully calculated design method. To solve the shortage issue of high-quality construction aggregates in desert areas and improve the utilization rate of aeolian sand, this study introduces the mix design and characteristics evaluation of high-performance concrete with full aeolian sand (FAS-HPC). The modified Andreasen & Andersen model is employed to determine the volume fractions of solid materials when the mixture system reaches the best packing density. Then the Response Surface Method (RSM) is utilized to conduct the orthogonal design and evaluate the effect of water-cementitious materials (W/C), superplasticizer (SP) and fly ash (FA) content on the flowability, mechanical properties, shrinkage and impermeability of the developed concrete, thus the raw materials proportion of FAS-HPC is optimized. After that, the pore structure and microstructure of the developed concrete are tested and analyzed to verify its durability and compactness. The results show that the volume fractions of AS, silica fume, and cement are determined as 0.482, 0.093, and 0.425 respectively, and the introduction of FA is found to be effective in improving the fluidity and impermeability while reducing the early strength and shrinkage. Under the determined response goals, the optimal values of W/C, SP and FA content are 0.19, 1.0 and 25.86 respectively. While the developed FAS-HPC formed by this ratio has a flowability of 220 mm, 28d flexural strength and compressive strengths of 20.26 MPa and 97.09 MPa respectively, meeting the requirements of HPC. Additionally, the developed FAS-HPC has a porosity of 7.3 % and 76.4 % pores are harmless, which can ensure its superior chloride resistance and durability. This study further enriches the raw materials for HPC and proposes a fully calculated design method, which is of great significance to the sustainable development of HPC.

Durability aspects of blended concrete systems subjected to combined mechanical and environmental loading using piezo sensor

• Durability of LC 3 and OPC concrete systems was investigated. • Comparison between combined and ideal chloride effect. • Equivalent structural parameter model was developed to identify the deterioration. • Deterioration of concrete under combined effect is less than ideal chloride effect. • LC 3 concrete system exhibits higher chloride resistance than OPC. In real-life structures, the structural elements are exposed to combined effect of mechanical load and environmental action simultaneously. So, monitoring these structures under combined effect is very crucial to understanding their behaviour under effect. This study compares and monitors the durability aspects of two different concrete systems namely ternary blended concrete and conventional concrete subjected to combined effect of chloride-induced corrosion and compression loading using piezo sensor based electro-mechanical impedance (EMI) technique. Experiments were conducted on two different types of concrete systems, one made with limestone calcined clay cement (LC 3 ) with 50 % by weight as a replacement to ordinary Portland cement (OPC), and the second made with OPC. Chloride penetration, chloride profiles, diffusion coefficient, and surface concentrations were the various parameters considered for the evaluation of durability performance. Further, an equivalent structural parameter (mass, stiffness, and damping) model has been proposed to identify the deterioration in these two concrete systems and an empirical relation has been established between equivalent stiffness and surface concentration for non-destructively monitoring. The results indicate that the percentage loss of equivalent stiffness in OPC concrete system under ideal chloride effect is 27 % more than combined effect, while in LC 3 concrete system it is 40 %. On comparing the deterioration of equivalent stiffness in OPC and LC 3 systems, it is found that in LC 3 concrete system the loss is 20 to 25 % less than that of OPC concrete system. Hence, it is concluded that the deterioration of concrete under the combined effect is significantly less than ideal chloride effect and LC 3 concrete system exhibits higher chloride resistance than the OPC concrete system.

Prediction of chloride resistance level of concrete using machine learning for durability and service life assessment of building structures

The resistance of concrete to chloride penetration determines the durability and service life of reinforced concrete building structures in coastal or chloride-laden environments. This work adopted five machine learning algorithms, naïve bayes, k-nearest neighbors, decision trees, support vector machine, and random forests, to predict the chloride resistance level of concrete based on its ingredients, considering two scenarios. The first scenario considers all features describing the mix components, whereas the second scenario considers only a subset of the features. All models are validated by performing intensive evaluation matrices using unseen data. The validation results confirm that the developed models predict the level of chloride resistance of concrete with high accuracy. Of all the algorithms, the support vector machine performed best, with 89% and 88% accuracy in the first and second scenarios, respectively.

Microstructure and macro properties of sustainable alkali-activated fly ash mortar with various construction waste fines as binder replacement up to 100%

Utilizing construction waste fines as eco-friendly binder for sustainable alkali-activated materials provides new approach to recycling construction waste. This work investigated the characterization of alkali-activated fly ash mortar (AAM) incorporating construction waste fines at varied types and replacement levels. The results showed that incorporating waste paste powder containing abundant hydrated products refined the pore size of AAM, but mixing waste mortar powder and waste concrete powder that contained massive inert quartz and calcite adversely affected the alkali-activated reaction and pore structure of AAM. The incorporation of construction waste fines was found to reduce the fluidity but increased the drying shrinkage of AAM. At identical replacement level of construction waste fines, the waste paste powder incorporated AMM has lower fluidity and greater drying shrinkage than the waste mortar powder or waste concrete powder incorporated AAM. Substituting waste paste powder for fly ash improved the mechanical strength of AAM, but the strength decreased as waste mortar powder or waste concrete powder was incorporated. Particularly, the AAM blended with 100% construction waste fines still owned good strength. Mixing construction waste powder reduced the chloride diffusion coefficient and chloride ingress depth of AAM, and the waste paste powder mixed AAM had better chloride resistance than the waste mortar powder or waste concrete powder mixed AAM. Therefore, the hydrated products in construction waste fines was revealed to benefit the micro-characteristics of alkali-activated materials, and optimizing the type and replacement level of construction waste fines can achieve sustainable AAM with good mechanical strength and chloride ingress resistance.

An efficient approach for sustainable fly ash geopolymer by coupled activation of wet-milling mechanical force and calcium hydroxide

Geopolymer is a potential substitute for high-emission cement production. Therefore, the use of fly ash with high emission as a geopolymer is an environmentally friendly and inexpensive direction. However, fly ash (FA) is a high amorphous precursor with low pozzolanic reactivity making it difficult to be activated by calcium hydroxide. In this study, the coupling of wet-milling mechanical force and calcium hydroxide was used to prepare high-performance alkaline calcium activated geopolymers. Two kinds of FA slurries with different particle sizes of D50 = 2.96 μm and 14.2 μm were prepared, activated by calcium hydroxide (CH) with the content of 4%, 11% and 19%. Results indicated that the increase of calcium hydroxide content was beneficial to developing strength, effectively improving the chloride resistance, compacting the microstructure, but increasing the autogenous shrinkage of the geopolymers. These improvements are especially apparent in the wet-milled fly ash geopolymers (WFA) due to the pre-depolymerization implemented by wet-milled mechanical forces, and coupled with the activation effect of CH to improve the depolymerization efficiency and condensation reaction. The compressive strength of WF-CH-19 was three times higher than that of FA-CH-19, reaching 29.3 MPa at 28 d, and the compressive strength growth of WF-CH-11 even reached 591.67% at 1 d. Meanwhile, the main chain length (MCL) and Al/Si of calcium silicate hydrates were clearly improved, and pore structure was significantly refined with capillary pore increased from 29.79% to 89.23%. In addition, FA and WFA geopolymers have significant advantages over Portland cement in the environmental impact indicators such as E-energy and E-CO2.

Chloride Ingress Resistance, Microstructure and Mechanical Properties of Lightweight Mortars with Natural Cork and Expanded Clay Prepared Using Sustainable Blended Cements

The use of lightweight aggregates in construction materials is a good solution for increasing the contribution to sustainability of civil engineering works, such as maritime ones. In this regard, the possibility of using cork granulates and expanded clay is a current research topic. The combination of eco-friendly cements with lightweight aggregates could provide solutions for developing new building materials. In this work, it has been studied mortars prepared with sustainable cements and the lightweight aggregates of natural cork and expanded clay. These cements incorporated slag, limestone and fly ash. Reference mortars with only sand as aggregate were also made. The total porosity and pore size distributions were obtained. The non-steady-state chloride migration coefficient and compressive and flexural strengths were also determined. The tests were performed at 28 days and 1 year. The differences in the total porosity between the natural cork and expanded clay series were not high, depending on the binder. Natural cork mortars showed similar or slightly higher migration coefficients than the reference and expanded clay mortars at 1 year. This adequate chloride resistance and the low mechanical strengths observed for the natural cork mortars recommend the possible use of this new aggregate in non-structural cement-based materials for civil engineering works exposed to maritime environments.

Effect of recycled aggregate and supplementary cementitious material on mechanical properties and chloride permeability of concrete

With impending demand for sustainable development, construction wastes as recycled aggregate (RA) to produce recycled aggregate concrete (RAC) is inevitable. However, RA makes adverse effect on performance of RAC. To enhance its performance, the supplementary cementitious materials (SCM), including ground granulated blast furnace slag, red mud, and glass powder, were used to partially substitute cement. In this investigation, the plain cement concrete and mineral-admixture concrete with four replacement ratios of RA were poured. For each mixture, the compressive strength, dynamic elastic modulus, and resistivity were determined; Besides, chloride penetration test was conducted in a tidal cycling simulation device, in which specimens with dimension of 100 × 100 × 400 mm3 were used to explore the effect of drying-wetting time ratios RD/W on chloride diffusion. It was found concrete with 50% RA exhibits improved compressive strength and equivalent chloride resistance through 25% SCM addition. Concrete containing 100% RA achieves equivalent or even superior chloride resistance to control group as SCM added by 45%. With the increase of RD/W, the diffusion of chloride is more serious. Considering the inhomogeneity of concrete pores, a double-porosity transport model solution was derived based on Fick's second law. Combined with test results, a time-dependent model was then established to predict chloride concentration in concrete containing RA and SCM. Furthermore, an analytical solution of cumulative chloride content diffused into concrete was derived to quantify chloride permeability. Subsequently, a linear correlation between chloride permeability and resistivity is confirmed. This investigation will encourage the use of RA in marine engineering, thereby leading to a more sustainable and cleaner production.

Permeation Behaviour of Coal Bottom Ash Concretes

Low volume Coal Bottom Ash (CBA) was introduced as a substitute for Portland Cement (PC) and Fine Natural Aggregates (FNA) in concretes that were tested for permeation performance. Carbonation and chloride resistance was measured through accelerated carbonation tests and rapid chloride tests respectively while water penetration was evaluated through capillary water absorption tests for the aforesaid concretes. This paper particularly investigates the effectiveness of CBA in regard of permeation behaviour in concrete. The experimental investigation inferred that as level of CBA increases, the resistance towards carbonation, chloride penetration and water penetration decreases to some extent for low volume alterations while higher decrements were observed for higher replacements. The joint replacement of CBA as PC and FNA for the level of 10% and 25% respectively resulted in satisfactory behaviour comparing to control concrete demonstrating the efficacy and potential of CBA for its successful application in concrete.

Prediction of rapid chloride penetration resistance of metakaolin based high strength concrete using light GBM and XGBoost models by incorporating SHAP analysis

• Light GBM and XGBoost prediction models for estimating RCPT of metakaolin-containing concrete. • Accuracy Analysis of the developed models using statistical evaluation. • Optimization of water-binder ratio and percentage of metakaolin using interpretable machine learning SHAP analysis. • Light GBM surpasses in accuracy compared to XGBoost. This study investigates the non-linear capabilities of two machine learning prediction models, namely Light GBM and XGBoost, for predicting the values of Rapid Chloride Penetration Test (RCPT). Chloride penetration is one of the most significant issues affecting reinforced concrete (RC) structures, which necessitate frequent maintenance and repair. The mix design of concrete play a vital role in the formation of pore structure that is relatively more resistant to chloride attacks. For estimating the chloride resistance of concrete, 201 experimental records, incorporating aging of concrete, binder content, water-binder ratio, percentage of metakaolin, and content of fine and coarse aggregates as input variables. The models were trained using grid search optimization for tuning setting parameters to yield the best performance for the models. The performance of the models using statistical indices indicated LightGBM surpasses in prediction accuracy as compared to XGBoost model. The coefficient of determination (R 2 ) values revealed 0.9738 and 0.9379 for LightGBM and XGBoost models, respectively. The minimum value of MAE was recorded for the training data of the LightGBM model equalling 172.7 C. The best fit model, i.e., the LightGBM model, was used for SHAP analysis to see the relative importance of contributing attributes and optimization of input variables. The SHAP analysis revealed f c ’, aging, and W/B ratio as most significant in yielding RCPT, whereas individual interpretation of Shapley values showed that W/B ratio of 0.30 – 0.35 and 15% MK replacement highly resisted chloride penetration at higher compressive strength values.

The Mechanism of Anticorrosion Performance and Mechanical Property Differences between Seawater Sea-Sand and Freshwater River-Sand Ultra-High-Performance Polymer Cement Mortar (UHPC).

There are abundant sea-sand resources on the earth. Traditional sea-sand concrete faced various problems relating to insufficient anticorrosion ability. In this paper, artificial seawater, sea sand, industrial waste, steel fiber, and polycarboxylate superplasticizer were used to prepare ultra-high-performance polymer cement mortar (SSUHPC). At the same time, freshwater river-sand ultra-high-performance polymer cement mortar (FRUHPC) with the same mixing ratio was prepared for comparative study. The compressive strength of SSUHPC reached 162.1 MPa, while the that of FRUHPC reached 173.3 MPa, which was slightly higher. Meanwhile, SSUHPC showed excellent anticorrosion characteristics in terms of carbonization, frost resistance and chloride resistance, and especially for sulfate resistance. The composition of SSUHPC was separated into three parts: mortar, pore and steel fiber, and the performance difference mechanisms of SSUHPC and FRUHPC were investigated by X-ray computed tomography (X-CT), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The hydration degree of mortar in SSUHPC was higher, with higher content of CSH and CH, and its better optimized gel pore characteristics gave SSUHPC better corrosion resistance. The mechanical properties of SSUHPC were slightly poor due to the uneven dispersion of steel fibers and air pores, with an- air pore porosity of 1.52% (above 200 μm) that was twice that of FRUHPC (0.6%). In this paper, the mechanics and anticorrosion performance of ultra-high-performance polymer cement mortar prepared with seawater sea sand were comprehensively evaluated, and the mechanism of performance difference between SSUHPC and FRUHPC was revealed, conducive to the targeted improvement of sea sand concrete.

Genomic and physiological traits provide insights into ecological niche adaptations of mangrove endophytic Streptomyces parvulus VCCM 22513

PurposeEndophytic Streptomyces parvulus VCCM 22513 isolated from Bruguiera gymnorrhiza in Quang Ninh mangrove forest, northern Vietnam showed abiotic stress tolerance consisting of antioxidant, salt-tolerant, and aromatic-compound degrading activities. The goal of this study was to shed light on genomic bases rendering mangrove endophytic S. parvulus more resilient to environmental stressors.MethodsPhenotypic analysis including antioxidant activities, hydrogen peroxide and sodium chloride resistance, and aromatic compound utilization were evaluated. The genome of strain VCCM 22513 was sequenced using Illumina Miseq sequencing platform and assembled using SPAdes.ResultsOut of 15 endophytic actinomycetes associated with B. gymnorrhiza in Quang Ninh mangrove, northern Vietnam, VCCM 22513 extract showed remarkable antioxidant activities through (1,1-diphenyl-2-picrylhydrazyl) DPPH and superoxide radical scavenging assays of 72.1 ± 0.04% and 38.3 ± 0.16% at 1.6 mg/ml, respectively. The genome consists of a 7,688,855 bp linear chromosome, 6782 protein-coding sequences, and 68 tRNAs. Genomic analysis identified strain VCCM 22513 as Streptomyces parvulus and confirmed a highly conserved core genome and stability of S. parvulus under natural selection. Genome mining revealed the presence of genetic determinants involved in mycothiol and ergothioneine biosynthesis (26 genes), oxidative stress resistance (43 genes), osmoadaptation (87 genes), heat and cold stress (34 genes), aromatic compound degradation (55 genes). Further genome-wide comparison between S. parvulus VCCM 22513 and 11 Streptomyces genomes showed that VCCM 22513 possesses significantly higher copies of genes involved in mycothiol and ergothioneine biosynthesis. In support of this finding, the strain exhibited much resistance to 0.6–1.0 M H2O2 and 6% (w/v) NaCl as compared to Streptomyces cavourensis YBQ59 isolated from Cinnamomum cassia Prels. In addition, the complete pathways for degradation of aromatic compounds including protocatechuate, gentisate, 4-hydroxyphenylpyruvate, cinnamate, 3-phenylpropionate, and styrene were only identified in the genome of VCCM 22513.ConclusionsThe present study revealed for the first time adaptive responses of mangrove endophytic S. parvulus VCCM 22513 to survive in hostile environment. The information shown here provided better understanding of underlying mechanisms related to adaptation and partially plant-microbe interaction of Streptomyces associated with mangrove plants.

Performance study on strength, morphological, and durability characteristics of coal pond ash concrete

ABSTRACT Concrete-based construction provides enormous advantages by utilizing waste materials and by-products from various sources such as industries, power plants, etc. One of the significant waste materials from the coal-based power plants, pond ash (PA), is highly dumped into landfills, causing critical environmental issues. This study examined the strength, morphological and durability characteristics of coal pond ash concrete. In this investigation, the cement was replaced with 10% of coal pond ash by weight of cement and water – binder ratio of 0.44 was used in all mix proportions. Strength properties were evaluated by using modulus of elasticity test. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) were also performed to evaluate its morphological characteristics. Durability properties such as rapid chloride penetration test, weathering resistance test, acid resistance test and chloride resistance test were conducted. The test results confirmed the efficiency of adding ash to cement material. Ten percent of coal pond ash in concrete had significant resistance against chloride penetration, weathering action, chloride and acid attack. SEM and EDAX analysis confirmed the presence of a higher amount of CSH gels at the increase in age, which promotes more – denser, less porous and compacted microstructure in concrete.

Robustness of self-compacting concrete incorporating bone china ceramic waste powder along with granite cutting waste for sustainable development

Keeping sustainability at the centre of this work, two solid waste materials have been selected for this study. First is bone china ceramic waste powder (BCCWP) obtained from broken or distorted bone china ceramic waste products, and the second is granite cutting waste (GCW) from the granite cutting and shaping industry. The present study aims at assessing fresh state, mechanical and durability characteristics of the SCC mixes incorporating BCCWP and GCW as cement and fine aggregate replacement, respectively. In a preliminary state, the raw BCCWP was evaluated for various pozzolanic activity tests such as the Frattini test, strength activity index and lime saturation test. SCC mixes were tested for compressive strength, splitting tensile strength, corrosion and chloride resistance tests. SCC mixtures were also tested at elevated temperatures by conducting thermogravimetric analysis (TGA) and differential thermal analysis (DTA) tests. Outcomes of fresh properties were found in the satisfactory limit as per EFNARC standard, except the SCC mix prepared with 30% BCCWP and 40% GCW. SCC mix with 10% BCCWP and 30% GCW showed the maximum strength properties. Moreover, statistical analysis using ANOVA was carried out to find the effectiveness of BCCWP and GCW parameters on various hardened state characteristics. From ecological and economic analysis, lesser embodied energy and embodied carbon dioxide emission, as well as cost reduction, was observed for SCC mixes containing BCCWP and GCW.

Development of aggregate from bottom ash in environmentally friendly concrete

This research presents a study of bottom ash for using as fine and coarse aggregates in concrete, B-F and B-C, respectively. Results of compressive strength and durability of the concrete containing B-F and B-C aggregates were investigated. Normal fine and coarse aggregates were replaced with the B-F and B-C aggregates at 0, 25, 50, 75 and 100% by weight of the normal aggregates. The results showed that the compressive strengths of the concretes were increased when the B-F and B-C aggregates were used at replacement levels of 25% and 50%. The water absorption and chloride resistances of the concretes were reduced with curing age. Moreover, it was found that the use of B-F and B-C aggregates in concretes effectively improved the compressive strength and the chloride resistances at low replacement levels of 25 and 50%.

Effect of dual-modified CNTs on strength and chloride resistance of cementitious systems

This study is undertaken to explore, first, the dispersibility of dual-modified carbon nanotubes (CNTs) by way of non-covalent modification. Various non-ionic and ionic surfactants were employed and mutually combined with varying relative proportions. Then, the best few combinations from the dispersion test were used further for producing mortar mixtures reinforced with CNTs. These samples were later assessed for their mechanical strength and chloride resistance. A suite of morphological, thermal and microstructural characterisations was carried out to understand the underlying mechanisms. The results show that, compared with the single modification, the dispersibility of CNT could be improved more significantly by way of the dual modification. In particular, 70–90% of non-ionic surfactant, in proportion to the total surfactant addition, imparted the best dispersibility to CNTs in an aqueous solution. In addition, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry and scanning electron microscopy outputs reveal that the enhanced dispersion of CNTs by dual modification promoted the hydration process and the ensuing microstructure evolution of mortar specimens. Together, these offset the strength reduction imparted by entrained pores when introducing chemical surfactants and, more importantly, empowered the chloride resistance of CNT-reinforced mortars.

Investigation of steel fiber reinforced high-performance concrete with full aeolian sand: Mix design, characteristics and microstructure

High-performance concrete with full aeolian sand (FA-HPC) has the characteristics of low water binder ratio, large cementitious materials content and no restriction of coarse aggregates, resulting in a high risk of shrinkage cracking. Aiming at reducing the shrinkage of FA-HPC and improving its cracking resistance, mechanical properties and durability, steel fibers with different lengths are employed to reinforce FA-HPC and develop a new type of cement-based composites (FA-HPFRC). For this purpose, the modified Andreasen & Andersen (MAA) model was adopted to determine the volume fractions of aeolian sand (AS), cement, fly ash (FA) and silica fume (SF). Then, the water binder ratio (W/C), superplasticizer (SP) and steel fiber content of FA-HPFRC were optimized through wet packing compactness, flowability, mechanical properties and shrinkage tests. Furthermore, the cracking resistance and microstructure of the developed FA-HPFRC were tested and analyzed from macro-micro perspectives. The results show that the volume fractions of AS, cement, FA and SF are determined as 0.482:0.316: 0.109:0.093 when the powder materials in FA-HPFRC are stacked to the most compact state. The wet packing compactness decreases with a higher W/C ratio while it increases first and then decreases with the increase of SP content. Considering the influences on mechanical properties, the W/C and SP content shall be 19% and 1% of the cementitious material separately. The introduction of steel fibers in FA-HPC reduces the concrete's flowability, destroys its dense packing system and lowers its wet packing compactness. However, the characteristics such as high toughness, and large elastic modulus of steel fibers endow FA-HPFRC with excellent mechanical properties, chloride resistance and shrinkage resistance. Especially steel fibers with 12 mm length perform well in improving the comprehensive performance of FA-HPFRC and increasing the cracking resistance 15.03% higher than that of 6 mm steel fibers. This research further improves FA-HPC's mechanical properties and durability, especially the shrinkage cracking resistance, and provides technical and theoretical support for the application of FA-HPFRC.

The role of CaO and MgO incorporation in chloride resistance of sodium carbonate-activated slag

Partial substitution of CaO or MgO for slag accelerates the reaction kinetics and strength gains of sodium carbonate (Na2CO3)-activated slags, yet their impact on the durability performance remains unknown. This study compares the effects of CaO and MgO substitution at various contents (2.5% and 5%) on the fresh properties, reaction kinetics, phase assemblage, pore structure, chloride binding capacity and chloride diffusion resistance of Na2CO3-activated slags. The results show that in addition to its higher effectiveness in boosting strength development, the substitution of CaO for slag results in superior enhancement in chloride binding and resistance of Na2CO3-activated slag compared to the system modified by MgO. Hydrotalcite is identified to have a comparable contribution to the chloride binding of CaO- and MgO-modified AAS, but the greater Friedel's salt formation is the main reason for the higher chloride immobilisation capacity of the CaO-modified AAS. The results demonstrate the technical promises of CaO and MgO as substitutes to control reaction kinetics of Na2CO3-activated slag while improving its chloride durability.