Green Construction Material Research Articles

Soil Water Characteristics Curves (SWCC) of Residual Soils Stabilized using Emerging and Novel Bioinspired Technique

The development of unsaturated soil mechanics stemmed from the inadequacies of classical soil mechanics in addressing the partial pore spaces found in real-world soil systems. However, assessing soil parameters under partial saturation is resource-intensive. To streamline this, the Soil-Water Characteristic Curve (SWCC) theory was introduced. Widely applied across geotechnical engineering, water resources, and agriculture, SWCC predicts parameters of unsaturated soil systems. In geotechnical engineering, SWCC is vital for designing systems near the Earth's surface, like slopes, clay liners and foundations. Furthermore, most of conventional soil improvement techniques pose a lot of environmental concerns. thus, emergence of green construction materials widely known as bio mediated and bioinspired soil improvement techniques like Enzymatic induced calcite precipitation (EICP). EICP, an emerging eco-friendly as it employs use of simply chemical compound that reduces carbon footprints, bioinspired technique as it mimics natural forming process, was applied to stabilize tropical soil for SWCC determination. SWCC parameters were derived by subjecting EICP-treated soils at varying concentration of cementation solutions (0 – 1.00 M) using pressure plate method. Results revealed that saturated water content θs, retention water content θr, and air entry value Ψa increased with higher cementation solution concentration. The values of θs, θr, and Ψa improved from of 0.663, 0.23405, and 3.4832 at 0 concentration of cementation solution to 0.701, 0.22864, and 7.7086, respectively upon treatment with 1.00 M cementation solution. Finally, it has been demonstrated EICP is capable of improving the SWCC parameters of residual soil, thus the EICP technique can be exploited in stabilization of residual for construction of compacted clay liner.

Mechanical properties and probabilistic models of wood and engineered wood products: A review of green construction materials

Wood and engineered wood products are green construction materials with excellent mechanical properties, widely utilized in various buildings and bridges. This paper reviews their short-term and long-term mechanical properties and probabilistic models. Short-term mechanical properties analysis reveals strong tensile (up to 165 MPa) and bending strengths (up to 264 MPa), contrasted by lower compressive strength (up to 103 MPa) and minimal shear/rolling strength (up to 14 MPa). These properties vary based on species type, lay-up angle, and dimensions, and are mutually influential. It also demonstrated that innovative techniques such as compression and cross-laminated lay-ups enhance the strength and sustainability of wood products, utilizing smaller logs effectively and reducing carbon emissions. For long-term mechanical properties, empirical models typically used for creep strength assessment fail to account for load duration variability, a gap partly addressed by damage accumulation models which require further development. The considerable time for long-term tests underlines the need for developing accelerated load tests to more effectively assess durability. As for probabilistic models, numerical methods and machine learning provide advanced probabilistic models by analyzing extensive data, offering significant improvements over traditional experimental methods.The global contribution of the work is mainly to enhance the understanding of wood and engineered wood products for properly design and extensive application of timber structures in civil engineering and promoting sustainable development.

Compressive Strength Characteristics of Compressed Stabilized Earth Block (CSEB) Units and Walls

This paper is mainly focused on compressive strength behavior of Compressed Stabilized Earth Block (CSEB) units and CSEB walls. Compressed Stabilized Earth Block (CSEB) is a rectangular block used in wall construction. The ingredients of CSEB are soil, cement, fine aggregate, crusher dust, and a small amount of water. These blocks have less energy consumption and carbon emission, and they provide improved thermal insulation. In addition, they use local resources and disseminate appealing aesthetics with elegant profile and uniform size. Due to these advantages CSEB can be used as a green construction material. This research aims to study the strength characteristics of CSEB wall in compression and evaluate the suitability of CSEB walls as load bearing walls in structures. This research studies physical and mechanical characteristics of CSEB units made from red residual soil of Lele (Lalitpur) with 8% cement for stabilization. This paper discusses the compressive strength behavior of walls constructed of size 0.660m x 1.100m x 0.220m using CSEB units in cement sand mortar and stabilized mud mortar separately which were tested after 28 days. The experimental values after laboratory testing of CSEB masonry wall with height to thickness ratio 5:1 for cement sand mortar (1:6) and stabilized mud mortar (stabilized with 8% cement and 16% extra sand) separately are compared with relevant values from different codes. Results obtained from compressive strength tests of masonry walls constructed in the laboratory and those values from different codes concerning the strength of masonry unit and mortar are compared and found to be in agreement. The comparison of laboratory results with codal provisions of design of masonry walls illustrate that CSEB masonry walls can be designed in the similar way as brick masonry walls.

Bio-inspired synthesis of nanocrystalline calcite demonstrating significant improvement in mechanical properties of concrete: a construction-nanobiotechnology approach.

The bioinspired synthesis of construction material, known as biocement, represents a significant advancement in addressing the environmental sustainability issues associated with traditional cement use in the built environment. Biocement is produced through the process of microbially induced bio-mineralization (MIBM), which offers a promising alternative or supplement to conventional cement, potentially reducing its consumption. Despite extensive literature on the application of biocement in construction biotechnology, the fundamental mechanisms underlying its ability to enhance concrete quality remain poorly understood. This study focuses on the kinetics of biomineral synthesis by two Bacillus species; Bacillus megaterium RB05 and Bacillus foraminis DRG5, to identify the most effective strain for biomineralization. Bioconcrete specimens were created by adding inoculum containing Bacillus megaterium RB05 cells with a nutrient solution to the concrete mixture in a layer-by-layer approach. After 28days of water curing, nanoparticles of CaCO3, ranging in size from 27 to 82nm, were produced in the bioconcrete specimens. The resulting concrete, containing nanocrystalline biogenic calcite, demonstrated significant improvements in mechanical properties. Specifically, compressive and tensile strengths of the bioconcrete, tested using a universal testing machine (UTM), increased by 7.69 ± 0.08% and 22 ± 0.1%, respectively, after 72h of curing. Additionally, the biocement was found to exhibit an organic-inorganic hybrid nature, as identified by TEM, EDAX, FESEM, FTIR, and XRD analyses. The enhanced mechanical properties were attributed to the high surface-to-volume ratio and hybrid nature of the calcite nanoparticles. The findings of this investigation are encouraging, suggesting the potential development of future green and self-sustainable construction materials or bioconcrete.

Revolutionizing Waste Management: Solidification of Landfill Leachates Using Alkali-Activated Slag

AbstractLandfill leachate is a highly hazardous effluent characterized by a high concentration of recalcitrant pollutants, presenting a significant environmental challenge. This study investigated the solidification of landfill leachate contaminants using sodium hydroxide-activated Granulated Blast Furnace Slag (GBFS). The stability of the resulting geopolymer was evaluated through unconfined compressive strength and leaching tests. Optimal curing conditions were identified as 7 days at a sodium hydroxide concentration of 12 M, achieving an unconfined compressive strength of 45.738 MPa at a liquid-to-solid ratio of 15%. A linear relationship was observed between the liquid-to-solid ratio and flow workability, with maximum flow workability evidenced by an average diameter of 242 mm at a liquid-to-solid ratio of 0.25. However, a minimum liquid-to-solid ratio of 0.15 was necessary to obtain a workable mortar. The produced geopolymers were characterized using X-ray Fluorescence (XRF) for mineralogical analysis, Scanning Electron Microscopy (SEM) for morphological examination, and the Toxicity Characteristic Leaching Procedure (TCLP) for leaching tests. The findings demonstrated the successful solidification of landfill leachate using GBFS geopolymer. The leachability tests revealed that the geopolymer did not release metals in concentrations exceeding the allowable limits set by the United States Environmental Protection Agency (USEPA), indicating effective encapsulation of the pollutants within the geopolymer matrix. Furthermore, the resultant geopolymer brick is eco-sustainable and can be classified as a green construction material.

Comparative studies on the seismic performances of precast segmental columns with different concrete, reinforcement and tendon materials

In recent years, precast segmental columns cast with ordinary Portland cement (OPC) and reinforced with steel rebars have gained popularity in engineering practices owing to its obvious advantages. However, the use of OPC in the construction associates to significant emission of carbon dioxide. Moreover, the corrosion of steel reinforcements and tendon are unavoidable during the lifetime of the structure, which will significantly lower the structural strength and durability. To overcome these issues, very recently, this study proposes using green and sustainable construction materials, i.e., the geopolymer concrete (GPC), together with basalt fibre reinforced polymer (BFRP) reinforcements and tendons, which possess the characteristics of less CO2 emission and excellent corrosion resistant capability, to construct precast segmental columns (i.e., to construct GPC-BFRP segmental columns) for seismic resistant applications. Experimental studies on the proposed GPC-BFRP and the conventional OPC-steel segmental columns were then performed to examine the performances of the proposed design. However, the comparisons of the experimental results were not strictly fair since the key parameters of the two types of columns, e.g., concrete strength and posttension force, in the experiments could not exactly be the same even though they were designed to be the same. This paper therefore extends the recent experimental study and performs numerical simulations. In particular, the experimentally tested columns were used to validate the three-dimensional (3D) finite element models (FEMs) of the two segmental columns with different materials (i.e., OPC-steel and GPC-BFRP). The validated numerical models are then used to examine the seismic performances of these two types of columns under the same design parameters. Numerical results show that under small earthquakes, two types of columns present almost identical structural responses. Under moderate to severe earthquakes, the two columns also have comparable performances, but GPC-BFRP segmental column presents larger displacement responses and failed earlier because of the smaller BFRP elastic modulus. The results in this study demonstrate the potentials of constructing sustainable and durable GPC-BFRP segmental columns in seismic regions.

Effect of polyvinyl alcohol on the mechanical and sound properties of recycled rubber mortar

Recycled rubber mortar is a novel green construction material which alleviates the environmental impact of waste rubber tires and greatly improves the sound insulation performance. Existing cement mortar with high rubber content exhibits poor mechanical properties, limiting its application in construction field. In this study, polyvinyl acetate (PVA) was introduced to modify recycled rubber mortar and the effect of PVA contents on its fluidity, flexural, compressive, impact strengths, and drying shrinkage was analyzed. To improve the analytical accuracy, analytic hierarchy process (AHP) was used to select the optimal mix proportion. The results indicate that PVA has positive effects on the mechanical properties of recycled rubber mortar. Further, comparing the trend of the normalized impact sound pressure level with an increase in frequency and the weighted normalized impact sound pressure level revealed that mixing 50 % recycled rubber particles and 8 % polyvinyl acetate effectively improved the sound insulation performance of cement mortar. These findings can promote the application of recycled rubber mortar in housing construction projects and having environmental benefits.

Chemical shrinkage, autogenous shrinkage, drying shrinkage, and expansion stability of interfacial transition zone material using alkali-treated banana fiber for concrete

ABSTRACT It might be of interest for authors to learn more that in the early 1900s, fibers were used in cement-based material, as cement-based materials exhibit shrinkage cracking over time, which can be controlled by adding fibers. The main aim of the inserting natural fiber into cement-based material is to decrease the shrinkage of cement-based material, prevent the rising of shrinkage cracks, and develop low-cracking cement-based material. In the research, the same aim aforementioned was kept same way. For carrying out the aim, agricultural waste, known as banana fiber (BF), can be considered a shrinkage reducer, expansion stabilization, a renewable material and has potential to make cement-based material transformed into a green construction material. This research investigated the effect of BF incorporation on cement paste shrinkage. Thus, five mixes were developed with different BF additions based on the total volume of cement paste (0, 0.5, 1, 1.5 and 2%). For each mixture, four tests were carried out to assess the impact of BF addition on the paste’s volume stability: chemical, autogenous, drying shrinkage and expansion. Testing was conducted for up to 90 days. Compared to the control mix, the addition of 2% BF reduced chemical shrinkage, autogenous shrinkage, drying shrinkage, and expansion by 27%, 57%, 47%, and 66%, respectively. Furthermore, a positive correlation was observed between chemical shrinkage and both autogenous and drying shrinkage and the percentage of BF content. Conversely, there was an inverse relationship between chemical shrinkage and expansion. The most significant conclusion to emerge from this study is that the incorporation of banana fiber (BF) into alkali-treated concrete results in a reduction in chemical shrinkage, autogenous shrinkage, drying shrinkage, and expansion. This is attributed to the molecular structure of BF, which is characterized by uninterrupted glycosidic linkages, leading to alkaline breakdown within the alkaline environment. Consequently, the alkali-treated BF can be described as a volume stability admixture in concrete technology.

Compressive Strength of Paver Block Using Rubber Tyre Waste and Bamboo Fibre Under Extreme Conditions

The utilisation of by-products in paver block production has gained significant attention due to its potential in environmental condition. This research investigates the effect of incorporating rubber tyre waste and bamboo fibre into the fabrication of paver block on compressive strength, water absorption, density and ultrasonic pulse velocity tests. This research comprises two batches of paver blocks fabrications following a 1:2:3 ratio(cement: fine aggregate: coarse aggregate). Batch 1 involves the fabrication of paver blocks by incorporating varying percentages of rubber tyre waste (0, 10, 20, 30, 40 and 50%), which replace a portion of the sand (referred to as rubber paver block). In Batch 2, various dosages of bamboo fibre, used as a reinforcement material were added to the paver block containing 40% rubber tyre waste, which are referred to as rubber-bamboo fibre paver blocks. Nevertheless, the compressive strength of the rubber-bamboo fibre paver blocks was further examined under two simulated environmental conditions: (1) air and dry cycle, and (2) wet and dry conditions. These conditions aim to assess the block’s resistance to temperature fluctuations, moisture effects, and theiroverall durability. The strength of the paver blocks decreases with the additional inclusion of rubber tyre waste. While the utilisation of 0.3% bamboo fibre has shown improvement in its strength performance compared to 0.2% and 0.4%. It suitable to used for non-loading structural applications that require strength below 25 kPa. This study was able to promote sustainable and green construction materials for paving applications through the efficient recycling of waste materials. It aligns with Sustainable Development Goals (SDG) 9 (Industry, Innovation, and Infrastructure) and 11 (Sustainable Cities and Communities).

Enhancing flame retardant wood’s versatility and adjustable properties through multi-scale micro-coating strategy

Wood, a naturally renewable material with a porous structure and breathability, rendering it a green construction material that can absorb sound, isolate heat and regulate moisture. Efforts to enhance wood’s resistance to combustion while maintaining its porous nature are hindered by the potential impact of physical and chemical treatments on its porous structure, posing a challenge in achieving flame-retardant wood that retains its breathability. Inspired by the multi-layer coating decoration method used on walls of various rooms in frame structure buildings, the study applies multi-scale micro-coating strategy to the multi-scale microstructure of wood. This strategy applied polyamino polyether methylene phosphonate (PAP), metal ions (Al3+/ Mg2+/ Ca2+), and alkali solutions to create a persistent multifunctional protective coating for the multi-scale wood structure. This coating effectively preserved the wood’s vessel, ray tissue, cell cavity, and pit structure, protecting its permeability. The modified wood demonstrated an increased limited oxygen value from 19.7 % to 38.4 % and a 55.9 % decrease in the total smoke release compared to natural wood, obtaining high fire safety. Furthermore, the modified wood exhibited adjustable antibacterial, photoaging-resistant and corrosion resistance properties depends on the type of metal. This strategy demonstrated proven reliability, versatility, and durability in the treatment of various metal ions, enabling the production of functional wood with tailored properties.

Date palm wood-derived cellulose aerogel dissolved in ionic liquids as a green thermal insulation construction material

Heat insulation materials used in the construction industry are essential for energy conservation. Nonetheless, the majority of current commercial heat insulators are fossil-fuel derived materials; thus, it is vital to provide sustainable, biodegradable, and environmentally friendly alternatives. In this work, an innovative method for producing cellulose II aerogels extracted from date palm waste and from microcrystalline lab-grade cellulose, targeting thermal insulation applications in the construction industry was introduced. A key aspect of the investigated approach is the use of a co-solvent system that combines 1-butyl-3-methylimidazolium chloride (Bmim)Cl and dimethylformamide (DMF), chosen for its efficiency in dissolving cellulose. The cellulose (at 3, 5, 7, and 9 wt%) was dissolved in a co-solvent system of 70 wt% (Bmim)Cl ionic liquid and 30 wt% DMF, saving costs associated with using purely ionic liquid solvents. The prepared aerogels exhibited low thermal conductivity (0.033–0.065 W/m⋅K), low densities (0.08–0.15 g/cm3), high porosity (89.85–94.69 %) and good thermal diffusivity (0.06–0.022 mm2/s). Furthermore, the developed insulators required a compressive strength of 75 kPa to reach 50 % strain and exhibited a sound absorption coefficient of 0.9. Structural characterization of the materials, including X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis, highlights the prospect of cellulose extracted from date palm wood in aerogel preparation and the potential for the (Bmim)Cl/DMF co-solvent system in dissolving cellulose.

Effects of alkaline activators and other factors on the properties of geopolymer concrete using industrial wastes based on GEP-based models

This study aims to develop reliable and practical models for estimating the compressive strength and CO2 emission of geopolymer concrete (GPC) using the Gene-expression programming (GEP) technique. Approximately 274 data points on the strength and CO2 emission of GPC using fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used to generate two prediction models considering the effects of 19 input variables. The research results show that the proposed GEP-based models perform well with high correlation coefficients (R > 0.95) and reasonable errors. The parametric study demonstrates that increasing the GGBFS content, the Na2O (dry) content, and the molarity of NaOH solution, and decreasing the FA content, the FA/GGBFS ratio, and the added water or total water/binder ratio could significantly enhance the strength of GPC. Besides, the proposed GEP-based models were used to optimise the mix proportions of GPC concrete with minimisation of CO2 footprint. The range and reasonable values of the FA and GGBFS contents, the alkaline activators, the aggregates, and other parameters were suggested based on the in-depth analyses. This significant reference data source could promote the use of GPC widely in the construction industry as green construction materials for sustainable development.

Potential for Recycling Metakaolin/Slag-Based Geopolymer Concrete of Various Strength Levels in Freeze-Thaw Conditions.

Geopolymer concrete (GPC) represents an innovative green and low-carbon construction material, offering a viable alternative to ordinary Portland cement concrete (OPC) in building applications. However, existing studies tend to overlook the recyclability aspect of GPC for future use. Various structural applications necessitate the use of concrete with distinct strength characteristics. The recyclability of the parent concrete is influenced by these varying strengths. This study examined the recycling potential of GPC across a spectrum of strength grades (40, 60, 80, and 100 MPa, marked as C40, C60, C80, and C100) when subjected to freeze-thaw conditions. Recycling 5-16 mm recycled geopolymer coarse aggregate (RGAs) from GPC prepared from 5 to 16 mm natural coarse aggregates (NAs). The cementitious material comprised 60% metakaolin and 40% slag, with natural gravel serving as the NAs, and the alkali activator consisting of sodium hydroxide solution and sodium silicate solution. The strength of the GPC was modulated by altering the Na/Al ratio. After 350 freeze-thaw cycles, the GPC specimens underwent crushing, washing, and sieving to produce RGAs. Subsequently, their physical properties (apparent density, water absorption, crushing index, and attached mortar content and microstructure (microhardness, SEM, and XRD) were thoroughly examined. The findings indicated that GPC with strength grades of C100, C80, and C60 were capable of enduring 350 freeze-thaw cycles, in contrast to C40, which did not withstand these conditions. RGAs derived from GPC of strength grades C100 and C80 complied with the criteria for Class II recycled aggregates, whereas RGAs produced from GPC of strength grade C60 aligned with the Class III level. A higher-strength grade in the parent concrete correlated with enhanced performance characteristics in the resulting recycled aggregates.

Perface: Proceedings of the first International Conference on ‘Sustainable Experimentation and Modeling in Civil Engineering (SEMCE-2023)

The current volume comprised the proceedings of the first International Conference on ‘Sustainable Experimentation and Modeling in Civil Engineering (SEMCE-2023)’ which was organized by the School of Civil Engineering, Lovely Professional University, Punjab, India in association with Dr B R Ambedkar National Institute of Technology Jalandhar and Indian Geotechnical Society (IGS), Jalandhar Chapter in a hybrid mode during 10th-11th August 2023.Research articles were invited covering six themes Green and Sustainable Construction Materials, Innovation, Infrastructure and Management, Material Recycling and Reuse, Modelling, Simulation and Analysis, Energy and Climate and Water and Sanitation. The two-day event attracted 188 abstracts of research articles, out of which only 125 were selected for conference presentation after peer review. The event witnessed 145 participants including a few ‘attendees only’ also. The primary goal of SEMCE-2023 was to provide a common platform to bridge the gap between researchers, engineers, scientists and industry professionals to initiate an innovative dialogue on academic and technical exchange related to Civil Engineering. Deep-dive deliberations on diverse topics in physical inventions and engineering were also part of the agenda of SEMCE-2023.The success of SEMCE-2023 is attributed to all those who have contributed to the event. The organizers sincerely express their gratitude to all.List of Committee is available in this Pdf.

Performance assessment and cost-benefit analysis of low-carbon binders containing calcined sediments from Chorfa II dam as new building materials

Recently, considerable attention has been given to the valorization of dredged sediments around the world, which are considered waste. The reuse of dredged sediments has significantly contributed to Sustainable Development Goals. However, the efficiency and cost assessments of calcined sediments as a partial replacement for cement are not well understood. In this present investigation, the use of calcined sediments from dams as a green construction material on the properties of eco-pastes and mortars formulation is explored. Properties measurements, microscopic observation, eco-strength efficiency, and cost assessments were performed on fresh, hardened mortars in order to valorize calcined sediments in the cement industry. The best findings for the compressive and tensile strengths of mortars containing calcined sediments were obtained after 180 days, which was compared to the control mortar. Furthermore, microscopic analyses showed that an increase in the substitution rates of calcined sediment resulted in the increasing germination of calcium aluminate silicate hydrate gel (C-A-S-H) and calcium silicate hydrate gel (C-S-H). The control mortar showed an efficiency of 0.0902 MPa/kgCO2 eq for 28 days while the eco-strength efficiency of mortars containing 5%, 15%, and 25% of calcined sediments presented an efficiency of 0.0920 MPa/kgCO2 eq, 0.0922 MPa/kgCO2 eq, and 0.0997 MPa/kgCO2 eq, which represents an increase of 1.9%, 2.21% and 10.51%, respectively. However, the replacement of cement with calcined sediments up to a rate of 25% decreases embodied carbon. In conclusion, the cost of treatment of one (1) ton of sediments is lower than cement, which represents a reduction from 81.96% to 86%.

Evaluation of Three Common Green Building Materials Using ELECTRE Method

This research paper examines various options for replacing halogenated flame retardants with non-halogenated green construction material choices. Cellulosic construction materials like bamboo do not form compounds with conventional flame retardants. Due to a number of circumstances, including the minimal effectiveness of the flame-retardant activity, they may thus be an unnecessary component of the substrate and simply peel off. Utilizing an additive that comes into direct contact with at least one component of the "green building material" will provide long-lasting flame retardancy since the flame retardant will become a structurally integral element of the substrate. The response mechanisms of various treatment approaches are also discussed in this research to ensure that non-halogenated flame retardants effectively protect sustainable building materials like wood and bamboo. This paper demonstrates how various ELECTRE approaches may be used to choose effective tactics that take into account both technical and human behavioral barriers using a typical case study inside an organization. The impact of impedance from each system subsystem is investigated to assure the dependability of the selected method. When employee participation is a deciding element in the multidimensional strategic planning problem, a comparison of a range of compensated and non-compensatory models reveals that the models may produce less. Resistance strategies; However, ELECTRE shows very reasonable sensitivity. The alternatives are Gladstone, Port Augusta, Collie and Tarong. the evaluation parameters are Construction cost, Procurement cost, Waste reduction, GHG emissions, Cement replacement and Self-consolidating. The Final Result of Net superior value and rank the Gladstone is in fourth rank, The Port Augusta is in second rank, The Collie is in third rank, The Tarong is in first rank of the Net Inferior Value and Rank the Tarong is in fourth rank, The Gladstone is in first rank, The Port Augusta is in Second rank, The Collie is in third rank.

Strategies and solutions to green concrete construction material

Strategies and solutions to green concrete construction material

Optimizing Mix Proportion of Geopolymer Concrete with Steel Sludge - A Sustainable Approach

As the construction industry is moving towards sustainable infrastructure, the need for green construction materials has gained importance in current scenario. Geopolymer concrete is considered to be an alternate to conventional concrete with cement as cement production is considered to emit more greenhouse gases into the atmosphere. This work has still raised the sustainable part of the geopolymer concrete by using steel sludge generated from automobile industry as partial replacement for fine aggregate. The experimental results were designed using fractional factorial design. The results were analysed for statistical integrity with ANOVA. It has been observed that the maximum compressive strength achieved with steel sludge up to 30% replacement is 48 Mpa with flexural strength of 5.16 Mpa and split tensile strength of 4.6 Mpa. Optimisation was done to find the proportion that gives maximum strength and it was ascertained with experimental validation. XRD and SEM analysis were carried out for studying the microstructure and reaction products formed in the process.

Effects of pretreated recycled fine aggregates on the mechanical properties and microstructure of alkali-activated mortar

Compared with traditional cement-based binders, alkali-activated binders can be improved upon combination with recycled aggregates to produce a promising and new green construction material. However, during this process, a pretreatment method is needed to alleviate the negative impact of recycled aggregates on the properties of alkali-activated materials. In this study, fly ash (FA), ground granulated blast furnace slag (GGBFS) and recycled powder (RP) were used as precursors, and recycled fine aggregates (RFAs) were used to replace natural fine aggregates (NFAs) to prepare recycled alkali-activated mortar (RAAM). Various RFA replacement ratios (0, 25%, 50% and 100%), pretreatment methods (calcination temperature and carbonation time) and alkaline moduli (0.8, 0.95, 1.1 and 1.25) were investigated. The effects of these parameters on the fresh and hardened properties, chemical composition and microstructure of RAAM were investigated. The results showed that the mechanical properties of RAAM gradually decreased with an increasing RFA replacement ratio due to the poor physical properties of RFA and its poor matrix binding. Two pretreatment methods (optimal calcination at 400 °C and carbonation at 6 h) were effective in improving the properties of RFA and thus the mechanical properties of RAAM. Calcination removed the adhered mortar from RFA and thus improved the mechanical properties of RAAM. Carbonation of RFA enhanced the quality of the attached mortar, which strengthened the RFA and provided better mechanical properties. In addition, microstructural analyses showed that RAAM prepared from pretreated RFA had a dense microstructure and a low critical pore size.

Specimen size effect on compressive and splitting tensile strengths of sustainable geopolymeric recycled aggregate concrete: Experimental and theoretical analysis

The use of industrial solid wastes (e.g., slag, fly ash) and recycled concrete aggregate (RA) to manufacture geopolymeric recycled aggregate concrete (GRAC) has been proved as a sustainable and environment-friendly approach for the concrete industry, and has received an extensive prospect. Understanding the specimen size effect of GRAC is fundamental and essential in the entire design and analysis of concrete components and structures. This paper presents an experimental study on the specimen size effect on compressive and splitting tensile strengths of GRAC, with the influence of RA replacement ratio and water-to-binder (w/b) ratio emphasized. A total of 168 GRAC cubes with four different specimen sizes (70.7, 100, 150 and 200 mm) are tested. The results show that the compressive and splitting tensile strengths of GRAC decrease with increasing RA contents due to the increased amount of defects, with the decreasing amplitudes of about 4%–30.4% for compressive strength and 2.96%–34.91% for splitting tensile strength, respectively, except that their size effect becomes more apparent. While the strengths and specimen size effect degrees of GRAC all decrease with the increase of w/b ratio. Based on Weibull's, Bazant's and Capinteri's size effect laws (SELs), analytical models for SELs of compressive and splitting tensile strengths of GRAC are respectively established. The comparison results indicate that the Bazant's SEL is more suitable for the cubic compressive strength of GRAC, while the splitting tensile strength using Weibull's statistical SEL achieves the most accurate prediction results. Moreover, conversion factors are suggested for the transformation of the compressive and splitting tensile strength measurements of GRAC. Finally, a life cycle assessment method is conducted to evaluate the carbon emission potential of GRAC, which is proven to be a green and low-carbon construction material with an over 60% carbon reduction compared to cement-based plain concrete.