Replacement Of Natural Aggregates Research Articles

USE OF WASTE PLASTIC WITH BACTERIAL COATING AS A SUSTAINABLE BUILDING MATERIAL IN CONCRETE

The use of plastic is increasing day by day, although steps were taken to reduce its consumption. The suitability of recycled plastics shredded as coarse aggregate in concrete and its advantages are discussed here. Tests were conducted to determine the properties of plastic aggregate density, specific gravity and aggregate crushing value. As 100% replacement of natural coarse aggregate (NCA) with shredded plastic is not feasible, partial replacement at various percentage were examined. Higher compressive strength was found with 5% NCA replaced concrete.

Copper heap leach residue aggregates in concrete: Properties and performance

This study assesses the feasibility of using copper heap leach residue (CHLR) as a sustainable alternative to natural aggregates in concrete production. The CHLR possesses flaky-angular shape grains with rough surface texture and microcracks, crystalline silica of 51.6 %, 6.1 mg/g silt-clay with a median particle size of 4.3 mm, and it becomes suitable for the partial replacement of natural fine and coarse aggregates after removing 4.2 mg/g fines through 60-minute wash. Concrete containing 25–75 % CHLR aggregates met design slump and air content of 125±25 mm and 2±0.5 %, respectively, while also demonstrating a negligible 2.9 % reduction in fresh density and 2.8 % increase in compaction factor. Concrete containing 50 % CHLR as a partial replacement of natural coarse and fine aggregates achieved compressive strengths of 47.3 MPa and 45.1 MPa at 28 days, while the compressive strength of control mix was 46.7 MPa. The mechanical properties significantly declined at 75 % CHLR incorporated concretes. The BSE-EDS analysis highlighted improved interfacial transition zone for CHLR aggregates with minimal microcracks at early age compared to the natural aggregates but developed interfacial transition zone microcracks with prolonged curing leading to a decline in mechanical strength development.

Optimal utilization of low-quality construction waste and industrial byproducts in sustainable recycled concrete

Construction and demolition waste (CDW) contains abundant low-quality recycled brick aggregates (RBA) that can potentially substitute natural aggregates (NA) in concrete production. However, recycled brick aggregate concrete (RBAC) shows inferior mechanical and durability performance compared to natural aggregate concrete (NAC), posing barriers to RBAC widespread adoption. This study investigates the combined influence of supplementary cementitious materials (SCMs) derived from industrial byproducts and hooked-end steel fibers (HSF) on properties of concrete with 0%, 50% and 100% RBAs from CDW as replacement for natural coarse aggregates (NCA). Addition of 0.5% HSF and 20%, 10%, and 30% fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBS) as cement replacement, respectively, were considered. Effect of different SCMs and HSF on compressive strength, splitting tensile strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption (WA), freeze-thaw (FT) and acid attack resistance of concrete were studied. Results indicated that individual incorporation of HSF showed more contribution towards mechanical performance while combined incorporation of SCMs and HSF enhanced both mechanical and durability properties, along with reduction of up to 15.6% in embodied carbon of RBAC. Microstructural examination showed pore refinement and interfacial transition zone densification in RBAC with SCMs and HSF. This study demonstrates that sustainable RBAC with excellent mechanical and durability requirements could be produced using demolished brick waste and industrial byproducts.

Strength characterization and sustainability assessment of coal bottom ash concrete.

Coal bottom ash (CBA) which is waste and environment contaminant has been used in grinded and raw form as replacement of Portland cement (PC) and natural fine aggregates (NFA) in concrete. The combined effect of grinding period (GP) (2-10h), grinded CBA (GCBA) (10-30%), and raw CBA (0-50%) on strength and microstructural characteristics was investigated and optimized along with its sustainability assessment. An enhancement in strength parameters with an increase in GP and replacement of PC and NFA with GCBA and CBA respectively was observed. The microstructural techniques like XRD, SEM, EDS, and FTIR also correlate with the aforementioned behavior. Mathematical models for strength parameters are well fitted and in good agreement with experimental and predicted values. Multi-objective optimization suggested 6.38h grinding, 24.21% GCBA, and 32.96% CBA as the optimum values. CBA-based optimized mix resulted in 19.79% and 22.6% lower carbon footprints and eco-cost than the control mix.

Numerical analysis of shear critical BFRP-reinforced concrete beams containing basalt fibers

Simulation models were developed for concrete beams reinforced with basalt fibers (BF) and basalt fiber-reinforced polymer (BFRP) bars. Experiments were conducted on physical concrete beams to validate predictions of the numerical models. The effect of replacement of natural aggregates (NA) by recycled concrete aggregates (RCA) and the inclusion of BF on shear response of BFRP-reinforced concrete beams was then investigated numerically. The shear capacity of the beam models with 30–100% RCA decreased by 10–28 % relative to that of a control beam model with NA. The inclusion of BF at a volume fraction (vf) of 0.5 % to beam models with 30 % and 60 % RCA fully restored the shear capacity of the control model. At 100 % RCA, a maximum of 93 % of the shear capacity of the control model was restored at vf= 1.5 %. Research findings would assist practitioners in proper modeling of BFRP-reinforced concrete beams containing nonmetallic fibers.

Utilizing bottom ash from municipal solid waste incineration as a sustainable replacement for natural aggregates in epoxy mortar production: a feasibility study

Utilizing bottom ash from municipal solid waste incineration as a sustainable replacement for natural aggregates in epoxy mortar production: a feasibility study

Effects of Over-burnt Bricks on Gradation, Water Absorption and Specific Gravity of Aggregates, Workability and Compressive Strength of Concrete

Demand of bricks is increasing day by day by the requirement of new structures. Due to manufacturing of bricks, over-burnt bricks are also made. Generally over-burnt bricks are the waste materials which is generally used for dumping purpose and sometime it is thrown in useful land that create social and environmental problems. Therefore, this material should be properly treated, recycled and used in concrete as coarse aggregate. In this research work, six (06) batches were made with 1:2:4 mix and 0.5 water cement ratio. Each batch consists of five (05) samples. Six (06) batches were made with 0%, 20%, 40%, 60%, 80% and 100% replacement of natural coarse aggregates with over-burnt bricks aggregates. The outcome of study reveals that the gradation of both the aggregates shows same pattern and the trend of curve was almost similar, with minor difference in range values over a sieve. The water absorption of over-burnt bricks aggregates was more than the water absorption of natural coarse aggregates and the specific gravity of over-burnt bricks aggregates was less than the specific gravity of natural coarse aggregates. The result of slump test shows that there was continuous decrease in workability of concrete mix, as replacement of over-burnt bricks aggregates increased. 30 concrete cubes of (6” x 6” x 6”) size were prepared and cured for 28 days followed by compressive strength. The result shows that the concrete derived from over-burnt bricks aggregates attained lower compressive strength than the regular concrete. However, the values obtained from over-burnt bricks aggregates are still acceptable, especially for reasonable levels of the replacement ratio up-to 60%. This concrete can be used in new constructions, but it is proposed to be initially utilized in low load areas.

Influence of recycled coarse aggregate on properties of fly ash and slag-based geopolymer concrete cured under oven and ambient temperature

Purpose The purpose of this paper is to investigate the effect of the replacement of natural coarse aggregate (NCA) with different percentages of recycled coarse aggregate (RCA) on properties of low calcium fly ash (FA)-based geopolymer concrete (GPC) cured at oven temperature. Further, this paper aims to study the effect of partial replacement of FA by ground granulated blast slag (GGBS) in GPC made with both NCA and RCA cured under ambient temperature curing. Design/methodology/approach M25 grade of ordinary Portland cement (OPC) concrete was designed according to IS: 10262-2019 with 100% NCA as control concrete. Since no standard guidelines are available in the literature for GPC, the same mix proportion was adopted for the GPC by replacing the OPC with 100% FA and W/C ratio by alkalinity/binder ratio. All FA-based GPC mixes were prepared with 12 M of sodium hydroxide (NaOH) and an alkalinity ratio, i.e. sodium hydroxide to sodium silicate (NaOH:Na2SiO3) of 1:1.5, subjected to 90°C temperature for 48 h of curing. The NCA were replaced with 50% and 100% RCA in both OPC and GPC mixes. Further, FA was partially replaced with 15% GGBS in GPC made with the above percentages of NCA and RCA, and they were given ambient temperature curing with the same molarity of NaOH and alkalinity ratio. Findings The workability, compressive strength, split tensile strength, flexural strength, water absorption, density, volume of voids and rebound hammer value of all the mixes were studied. Further, the relationship between compressive strength and other mechanical properties of GPC mixes were established and compared with the well-established relationships available for conventional concrete. From the experimental results, it is found that the compressive strength of GPC under ambient curing condition at 28 days with 100% NCA, 50% RCA and 100% RCA were, respectively, 14.8%, 12.85% and 17.76% higher than those of OPC concrete. Further, it is found that 85% FA and 15% GGBS-based GPC with RCA under ambient curing shown superior performance than OPC concrete and FA-based GPC cured under oven curing. Research limitations/implications The scope of the present paper is limited to replace the FA by 15% GGBS. Further, only 50% and 100% RCA are used in place of natural aggregate. However, in future study, the replacement of FA by different amounts of GGBS (20%, 25%, 30% and 35%) may be tried to decide the optimum utilisation of GGBS so that the applications of GPC can be widely used in cast in situ applications, i.e. under ambient curing condition. Further, in the present study, the natural aggregate is replaced with only 50% and 100% RCA in GPC. However, further investigations may be carried out by considering different percentages between 50 and 100 with the optimum compositions of FA and GGBS to enhance the use of RCA in GPC applications. The present study is further limited to only the mechanical properties and a few other properties of GPC. For wider use of GPC under ambient curing conditions, the structural performance of GPC needs to be understood. Therefore, the structural performance of GPC subjected to different loadings under ambient curing with RCA to be investigated in future study. Originality/value The replacement percentage of natural aggregate by RCA may be further enhanced to 50% in GPC under ambient curing condition without compromising on the mechanical properties of concrete. This may be a good alternative for OPC and natural aggregate to reduce pollution and leads sustainability in the construction.

Investigation of tensile strength performance of green concrete incorporating steel slag

This study examined the compressive and tensile strength performance of steel slag-containing concrete composites in a sulphate environment. Steel slag sourced locally was mechanically crushed and sieved into aggregates ranging in size from 20 to 1 mm. The control concrete of grade 20 and other five (5) batches of concrete with 10 to 50% steel slag at a step of 10% as replacement for natural coarse aggregate were produced. The physical properties of the aggregate specimens (steel slag and granite) were evaluated in the laboratory, as well as the concrete workability and the 7- and 28-day compressive and tensile strengths after exposure to 50 g/l of magnesium and sodium for 7 and 28 days. According to the results, the concrete workability decreased as the steel slag content increases. The 20 N/mm2 desire strength with rise in compressive and split tensile strengths as the steel slag contents increased from 0 to 50% after curing in water for 28 days. The concrete compressive and tensile strengths improved with steel slag content ranging from 0 to 40% but decreased with increase in steel slag content from 30 to 50% after exposure to Na2SO4 for 28 days. For the concrete exposed to MgSO4, the compressive and split tensile strengths increased when the steel slag content increased from 0 to 40% before it decreased with further increase in steel slag from 40 to 50% after 28 days. The experimental findings revealed that up to 40% steel slag is sufficient as replacement for natural coarse aggregate in concrete work exposed to aggressive sulphate climate. Thus, for improved compressive and tensile performance, the optimum of 40% steel slag is suggested as replacement for natural coarse aggregate substitution for healthier sulphate attack resistance.

Dynamic compressive behaviors of polyethylene terephthalate fiber reinforced recycled aggregate concrete

AbstractPolyethylene terephthalate (PET) fibers are green, environmentally friendly materials. They mainly come from recycled plastic bottles and other products. The addition of PET fibers to recycled aggregate concrete (RAC) has the potential to reduce concrete damage and increase specimen toughness. In this study, the influences of recycled coarse aggregate (RCA) replacement ratio and fiber volume ratio on the impact response of PET fiber reinforced RAC at various strain rates were experimentally investigated. It was found that the compressive strength, critical strain, and toughness grew with the increasing strain rate, followed by the aggravation of the concrete damage. Owing to the strain rate effect, the failure mode of concrete specimen at a high strain rate was different from that under a quasi‐static loading. This led to the reduction of differences in the dynamic compressive strength between the natural and recycled aggregate concrete at a high strain rate. Although the replacement of natural coarse aggregates with RCAs resulted in the decrease in the dynamic compressive strength, it increased the critical strain of the specimen. To reduce the brittleness of concrete materials, flexible fibers, PET fibers were added into the concrete matrix. It was found that the addition of PET fibers increased the critical strain and significantly reduced concrete damage. The empirical equations were proposed to describe the rate‐dependent dynamic compressive strength, critical strain, and toughness based on experimental data.

Impact of Recycled Concrete and Brick Aggregates on the Flexural and Bond Performance of Reinforced Concrete

The construction industry strongly relies on concrete and clay bricks for various applications. The escalating demand for these materials, driven by rapid population growth, has led to resource depletion and increased construction and demolition waste (CDW). Recycling CDW into construction materials, particularly in the form of recycled concrete aggregates (RCAs) and recycled brick aggregates (RBAs), has emerged as a promising solution. This study deals with the structural performance of concrete incorporating RCAs and RBAs. The experimental program encompasses material characterization, concrete mix design, and several tests to assess density, compressive strength, bond behavior, and flexural properties. The results indicate that the replacement of fine natural aggregate (NA) with fine RCAs or RBAs has a negligible impact on density, while the partial replacement of coarse NAs with RAs yields modest reductions in compressive strength. Notably, the bond strength between steel rebar and concrete is influenced by the type and content of RA, with specimens containing RCAs exhibiting a higher bond strength than those with RBAs. Empirical models used to predict bond strength generally align with experimental results, with conservative predictions by some models, such as ACI 318, and overestimation by others, such as models proposed by AS-3600 and CEB-FIB. The flexural tests of beams highlight the variation in stiffness and load-bearing capacity with the proportion of NAs replaced by RAs. While beams with 50% NA replacement demonstrate comparable performance to control beams, those with 100% RA replacement exhibit lower cracking and yielding stiffness. Cracking patterns in beams with RAs differ from control beams, with RA-containing beams showing more cracks and an altered crack distribution. The findings underscore the feasibility of using recycled aggregates in construction, with partial NA replacement offering a balance between sustainable material usage and desired structural properties.

POSSIBILITIES FOR CONSERVING NATURAL RESOURCES AND THE ENVIRONMENT THROUGH THE USE OF RECYCLED WASTE AGGREGATES AS A SUBSTITUTE FOR NATURAL AGGREGATES IN CEMENTITIOUS COMPOSITES

The conservation of the environment and the protection of natural resources are urgent and current challenges. The objective of this experimental investigation was to evaluate the potential use of aggregates derived from recycled glass waste, blast furnace slag, recycled brick waste aggregates and recycled electronic waste aggregates (textolite) as replacements for natural aggregates in cement-based composites. The experimental tests aimed to investigate how the replacement of natural aggregates with recycled waste aggregates affects various physico-mechanical parameters, including density, compressive strength, flexural strength, abrasion resistance and capillary water absorption. This investigation also included detailed microstructural analysis using optical microscopy, SEM, EDX and XRD techniques. The aim of the research was to explore the potential for soil conservation by reducing the amount of waste to be disposed of, and at the same time to conserve natural resources by identifying alternatives using recycled materials, thereby contributing to the implementation of the circular economy concept. The results of the research confirmed this potential; however, depending on the nature of the recycled aggregates, there are influences on the physico-mechanical performance of the cement composite that can be seen at the microstructural level.

Mechanical and Microstructural Investigation of Geopolymer Concrete Incorporating Recycled Waste Plastic Aggregate.

The effective use of waste materials is one of the key drivers in ensuring sustainability within the construction industry. This paper investigates the viability and efficacy of sustainably incorporating a polylactic acid-type plastic (WP) as a 10 mm natural coarse aggregate (NA) replacement in geopolymer concrete. Two types of concrete (ordinary Portland cement-OPC and geopolymer) were produced for completeness using a concrete formulation ratio of 1:2:3. The ordinary concrete binder control was prepared using 100% OPC at a water/binder ratio of 0.55, while the geopolymer concrete control used an optimum alkaline activator/precursor-A/P ratio (0.5) and sodium silicate to sodium hydroxide-SS/SH volume ratio (1.2/0.8). Using the same binder quantity as the control, four concrete batches were developed by replacing 10 mm NA with WP at 30 and 70 wt% for ordinary and geopolymer concrete. The mechanical performance of the developed concrete was assessed according to their appropriate standards, while a microstructural investigation was employed after 28 days of curing to identify any morphological changes and hydrated phases. The results illustrate the viability of incorporating WP in geopolymer concrete production at up to 70 wt% replacement despite some negative impacts on concrete performance. From a mechanical perspective, geopolymer concrete indicated a 46.7-58.3% strength development superiority over ordinary concrete with or without WP. The sample composition and texture quantified using automated scanning electron microscopy indicated that adding WP reduced the presence of pores within the microstructure of both concrete types. However, this was detrimental to the ordinary concrete due to the low interfacial zone (ITZ) between calcium silicate hydrate (CSH) gel and WP, resulting in the formation of cracks.

Finite element method for sustainable and resilient structures made with bar and fiber -reinforced EAFS concrete

Structural engineers have to address the climate change challenge by designing sustainable and resilient structures. At this juncture, Electric Arc Furnace Slags (EAFS), a steel-industry waste, are used in replacement of natural aggregates to enhance concrete properties. Moreover, steel and synthetic fibers are added to improve the postcracking behavior while the traditional bar reinforcement enhances the tensile performance. This makes EAFS concrete substantially ductile compared to normal concrete, which contributes to a higher structural resiliency, and hence minimizes functionality disruptions. However the use of fiber and bar -reinforced EAFS concrete in structures is still limited due to the uncertainties introduced by EAFS and fibers. This justify the development of advanced modeling techniques (ie. Finite element Analysis, FEA), which can be used to predict the behavior of EAFS concrete structures at the designing stage. This work build up from the extensive work of the coauthors in the testing of EAFS concrete and, more recently, in the developed FEA of fiber-reinforced EAFS concrete. In this paper the modeling of bar reinforcement is added to the FEA to study the behavior of structural elements made with fiber-reinforced EAFS concrete. The presented FEA is validated through full-scale experiments (four-point flexural test), which shows that the presented FEA is appropriate. The presented numerical model enables to study phenomena difficult to study from experiments or in-situ such as the cracking. It is worth noting that the addition of steel fibers reduced the crack mouth opening displacement in 29.3% and the depth of the cracks in 12.7% in the presented EAFS concrete.

Upcycling of End-of-Life-Vehicle (ELV) plastics as a replacement for natural fine aggregate in concrete

End-of-life vehicle (ELV) plastics pose technical challenges in conventional recycling due to their diverse polymer compositions. Consequently, landfilling remains the prevailing disposal method. This study explores an innovative approach by upcycling ELV plastics as a substitute for natural sand in concrete. The study investigates the physical, mechanical and economic performance of ELV plastic-containing concrete. Plastic aggregates were prepared from real-world ELV plastics, featuring particle sizes below 4.75 mm, with over 90 % falling within the range of 1.18–4.75 mm. The research involves replacing natural sand with ELV plastics at varying volumes (0 %, 15 %, 25 %, 35 %, and 40 %) and examines the effect of sand replacement on various concrete properties. The results suggest that as the replacement ratio increases, the workability, density, and strength of concrete decrease. However, the 28-day compressive strength of concrete at the maximum replacement rate of 40 % was found to be 39 MPa, which suffices for certain non-structural strength applications, such as traffic routes, shared-use paths, local streets and curbs. In addition, compared to previous studies using mixed commodity plastics, ELV plastics lead to significantly lower strength reductions at high replacement ratios. Scanning Electron Microscopy (SEM) analysis reveals a distinctive rough and fibrous aggregate morphology, which enhances physical binding and provides bridging effects within the concrete matrix, potentially mitigating strength loss. Moreover, the economic analysis highlights a significant potential to commercialize ELV plastics for concrete applications. This study demonstrates that ELV plastics can be effectively used at high replacement rates (up to 40 % by volume) in non-structural applications.

Sustainable Structural Lightweight Concrete with Recycled Polyethylene Terephthalate Waste Aggregate

Plastic is a widely consumed material with a high decomposition time, occupying significant space in landfills and dumps. Thus, strategies to reuse plastic waste are imperative for environmental benefit. Plastic waste is a promising eco-friendly building material for cement-based composites due to its reduced specific gravity and thermal conductivity. However, this waste reduces the composites’ mechanical strength. This work aims to produce and evaluate lightweight concretes made with only lightweight aggregates and mostly recycled plastic aggregates. Initially, an optimized dosage approach for lightweight concrete is presented. The mixture proportion of the lightweight concrete was based on the performance of mortars with the complete replacement of natural aggregate by recycled polyethylene terephthalate (PET) aggregates. The PET aggregates showed irregular shapes, impairing workability and providing lightweight concretes with around 18% water absorption and 21% void index. However, the concretes presented significantly low-unit weight, approximately 1200 kg/m3. This work presented a structural lightweight concrete (ACI 213-R) using only lightweight aggregates and mostly plastic waste aggregate, with a compressive strength of up to 17.6 MPa, a unit weight of 1282 kg/m3, and an efficiency factor of 12.3 MPa·cm3/g. The study shows that with an optimum dosage, reusing plastic waste in concrete is a viable alternative contributing to environmental sustainability.

Experimental investigation of eco-friendly fiber-reinforced concrete using recycled and natural fibers, integrated with recycled aggregates

This study investigates the integration of recycled and natural fibers with recycled concrete aggregates to develop environmentally friendly fiber-reinforced concrete (FRC), with a primary aim of maintaining or enhancing its properties. Four concrete mixtures, namely plain concrete (C-Plain), recycled steel fiber-reinforced concrete (C-RSF), recycled plastic fiber-reinforced concrete (C-RPF), and kenaf fiber-reinforced concrete (C-KF), were formulated and analyzed for their fresh, hardened, and durability characteristics. A 50% replacement of natural coarse aggregates’ weight with recycled concrete aggregates (RCA) was implemented. By standardizing fiber volume fractions at 1.0% for all FRC mixtures, the study evaluated properties such as workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, modulus of elasticity, post-cracking flexural performance, modulus of rupture, flexural toughness, splitting tensile strength, and freeze-thaw resistance after 100 and 300 cycles. Testing involved three specimens for each parameter at 7 and 28 days. The results indicated positive effects on post-cracking flexural performance, modulus of rupture, flexural toughness, splitting tensile strength, and durability with the incorporation of recycled and natural fibers. Notably, C-RSF demonstrated the highest compressive strength (46.63 MPa), flexural toughness (64.35 kN-mm), and modulus of rupture (7.46 MPa) compared to other FRC composites. Additionally, it exhibited minimal weight loss (2.18% and 3.07%) after freeze-thaw cycles, indicating exceptional durability. C-RSF exhibited superior performance, while C-KF showed enhancement slightly below that of C-RSF. Although not reaching the level of C-RSF, C-RPF positively influenced concrete performance. Compressive response either maintained performance or exhibited marginal reduction. The findings carry significant implications for developing environmentally conscious construction materials with enhanced mechanical and durability properties, thereby advancing sustainable construction practices.

Mechanical Properties of Rubberised Geopolymer Concrete.

The environmental impact of non-biodegradable rubber waste can be severe if they are buried in moist landfill soils or remain unused forever. This study deals with a sustainable approach for reusing discarded tires in construction materials. Replacing ordinary Portland cement (OPC) with an environmentally friendly geopolymer binder and integrating crumb rubber into pre-treated or non-treated geopolymer concrete as a partial replacement of natural aggregate is a great alternative to utilise tire waste and reduce CO2 emissions. Considering this, two sets of geopolymer concrete (GPC) mixes were manufactured, referred to as core mixes. Fine aggregates of the core geopolymer mixes were partially replaced with pre-treated and non-treated rubber crumbs to produce crumb rubber geopolymer concrete (CRGPC). The mechanical properties, such as compressive strength, stress-strain relationship, and elastic modulus of a rubberised geopolymer concrete of the reference GPC mix and the CRGPC were examined thoroughly to determine the performance of the products. Also, the mechanical properties of the CRGPC were compared with the existing material models. The result shows that the compressive strength and modulus of elasticity of CRGPC decrease with the increase of rubber content; for instance, a 33% reduction of the compressive strength is observed when 25% natural fine aggregate is replaced with crumb rubber. However, the strength and elasticity reduction can be minimised using pre-treated rubber particles. Based on the experimental results, stress-strain models for GPC and CRGPC are developed and proposed. The proposed models can accurately predict the properties of GPC and CRGPC.

Enhancing Thermal Efficiency in Water Storage Tanks Using Pigmented Recycled Concrete.

The present work investigated the manufacture of elements such as water tanks from recycled concrete for applications where industries require water heating. This proposal leverages precast rejects for recycled concrete and incorporates colouring pigments. It is expected to contribute to the circularity of construction materials (due to the total replacement of natural aggregates by recycled aggregates) as well as to energy and emissions savings, which are attributed to improved thermal performance driven by the thermal behaviour that the coloration pigment gives to the manufactured concrete elements. To assess the efficacy of the proposed solution, on the one hand, mechanical tests were carried out in tensile, compression and modulus of elasticity, which showed a suitable concrete dosage for HA-30 structural concrete. Simultaneously, in search for a material that would increase the internal temperature of the tanks, thermal tests were carried out in a controlled laboratory environment on samples with different percentages of pigment, and an optimum concentration of 1% was obtained. It was also found that the thermal conductivity remained almost unaffected. Finally, two water tank prototypes were manufactured and tested under real environmental conditions: one with the optimised pigment concentration solution and other (the reference tank) without pigment. The results revealed that the colourised tank with the optimal concentration resulted in an average water temperature increase of 2 °C with respect to the reference tank. Finally, the economic and environmental benefits of this temperature increase were studied for industrial processes requiring water heating with a potential saving of 8625 kWh per month.

Self-sensing properties of cementless ultra-high performance concrete (UHPC) with slag aggregates

This research addresses the environmental impact of traditional cement-based construction materials and explores sustainable alternatives. The study aims to explore the mechanical properties, flowability, setting time, and self-sensing performance of cementless ultra-high performance concrete (UHPC) by utilizing the electrical properties of electric arc furnace slag (EAF slag) as a replacement for natural aggregates, along with alkali-activated slag as the binding material. Comparative analyses are conducted between cementless UHPC with EAF slag and silica sands, as well as the impact of incorporating carbon fiber. The study reveals that cementless UHPC with EAF slag exhibits improved fluidity and slightly increased setting time compared to UHPC with silica sands, attributed to the spherical shape and ball bearing effect of EAF slag. While the compressive and tensile strength of cementless UHPC with EAF slag is slightly lower than that of UHPC with silica sands, it still meets UHPC standards with strengths of 150 MPa and 8 MPa, respectively. Nonlinear curve fitting accurately quantifies the self-sensing performance, yielding precise simulation results. Importantly, EAF slag-based UHPC exhibits superior self-sensing capabilities, outperforming carbon fiber incorporation. Unlike UHPC with silica sands, which generates substantial noise even with carbon fiber, EAF slag-based UHPC demonstrates effective self-sensing with minimal noise, even in the absence of carbon fiber. This study expands the understanding of self-sensing performance in cementless UHPC by effectively utilizing EAF slag as a replacement for natural aggregates. The results suggest that the valorization of EAF slag has the potential to enhance sustainability and the self-sensing capabilities of cementless UHPC.