Consumption Of Natural Aggregates Research Articles

Sustainable development of pavement base stabilization using future road base material (FROBM)

Sustainable road construction has emerged as a critical issue in assessing natural resources and urban development. With the rapid expansion of pavement networks to meet growing traffic demands, road base construction relies heavily on the consumption of natural aggregates and Ordinary Portland Cement (OPC) through the cement-treated base (CTB) technique. This practice contributes to the global warming and greenhouse gas (GHG) emissions associated with road construction. This study investigated a novel road base material, Future Road Base Material (FROBM), which emphasizes both eco-friendliness and economic advantages. Fine crushed rock (FCR) served as the parent aggregate and was modified with a chemical binder comprising 4% of the FCR weight. The proposed sustainable cementitious material, functioning as a non-OPC binder, incorporated fly ash and hydrated limestone as pozzolanic materials, along with sodium hydroxide (NaOH) as an alkali additive. An asphalt emulsion (AE) was employed as a special additive to enhance crucial pavement engineering properties. Through life cycle analysis (LCA), the construction activities and material acquisition of each stabilized base technique were evaluated in terms of project costs and carbon footprints. The non-OPC binder offered sufficient compressive strength for a stabilized base course. Furthermore, the addition of AE improved the elastic modulus and modulus of rupture of the non-OPC binder-stabilized mixture. Utilizing a non-OPC binder and AE in the base layer provides advantages in terms of construction cost and environmental impact. Although the costs increased slightly, the GHG emissions were reduced by approximately 30% compared to conventional base materials, with equivalent functionality and service life for road construction. The proposed stabilizing agent reduced the operational processes and demand for natural aggregates compared with the unbound FCR base course. Road-base stabilization using a non-OPC binder and AE represents an innovative approach to mitigate waste in coal mining and power plant industries by transitioning to a cleaner product. The concept of the FROBM serves as a valuable guideline for the development of future sustainable pavement materials.

Effect of Strength and Durability of Sand Cement Brick Containing Recycled Concrete Aggregate and Cold Bottom Ash

Introduction The market price of brick has risen sharply due to the insufficient brick supply. Therefore, implementing RCA as one of the alternative materials for sand replacement is significant. The consumption of natural aggregate (NA) can be reduced by using the RCA. It is a good step to utilize recycled concrete to minimize the problem of excess waste materials. The results of using RCA and CBA as sand replacements contribute to better performance in compressive strength as compared to the normal brick. The density of the brick was also reduced by 4.95% as the RCA and CBA took place in the brick. Besides that, the water absorption was decreased when incorporating RCA and CBA in the cement brick due to less free water in the mix and fewer voids. Aims This study aims to ascertain the performance, strength, and durability characteristics of sand cement bricks incorporated with RCA and CBA as partial replacements for sand. Methods Percentages of 1.5%, 3.0%, 4.5%, and 6.0% of CBA and 15%, 30%, 45%, and 60% of RCA were chosen for partial sand replacement. The brick had dimensions of 215 mm in length, 65 mm in depth and 105 mm in width. Density, compressive force, and water absorption tests were undertaken after each of the three varied ratios of water to cement (1:5, 1:6, and 1:7). Results The finding indicates that with the optimum RCA and CBA replacement and the correct water to cement ratio, the performance of the new brick is better than the normal brick. Conclusion The optimum sand-to-cement ratio is 1:6, according to the overall results of selecting the optimal sand-to-cement ratio by density, compressive strength, and water absorption test. However, the result for the density value shows that the average brick density is inferior to the control brick. For all of the sample bricks, the compressive strength was best at a sand cement ratio of 1:6. However, as each of the samples complies with the British Standard criterion of less or equal to 15% absorption, it was determined that the sand cement brick's capacity for water absorption was sufficient.

Assessment of mechanical and durability properties of FA-GGBS based lightweight geopolymer concrete

The relentless consumption of natural aggregates and cement in concrete due to rapid construction has resulted in the exhaustion of natural resources; consequently, it's vital to create environment friendly building materials and implement sustainable construction methods. The development of geopolymer concrete (GPC) is a step towards the utilization of by-products. This study aims to prepare and assess the durability and mechanical characteristics of fly ash (FA) and ground-granulated blast furnace slag (GGBS)-based lightweight geopolymer concrete (LWGC). Utilizing sintered fly ash aggregate (SFA) in GPC is one such approach that can lower the usage of regular cement and natural aggregates. In the present investigation a total of six GPC mixes were prepared with varying alkaline activator to binder (AA/B) ratios of 0.3–0.8. The results shows that the AA/B ratio and the mechanical characteristics of LWGC samples are inversely related. The mechanical properties exhibits maximum strength at the lowest AA/B ratio. The LWGC achieved the highest compressive strength (CS) of 48.9 MPa, modulus of elasticity (EM) of 27.3 GPa, split tensile strength (STS) of 3.9 MPa, and direct shear strength of 5.4 MPa after 28 days of ambient curing. The oven dry density (OD) ranged from 1722–1805 kg/m3, satisfying the various codal provisions to be considered a lightweight concrete (LWC). The durability study indicates that for structural applications, the performance is satisfactory, especially in acidic conditions. SEM and EDS analyses also infer strong mechanical and durability characteristics. The obtained results suggests that LWGC is a possible material for structural concrete applications.

Characterization and Environmental Evaluation of Recycled Aggregates from Construction and Demolition Waste in Belgrade City Area (Serbia).

Sustainable consumption of construction materials is an important segment of sustainable development goals towards reducing climate change. Since the consumption of natural aggregates raises environmental concerns, there is an increasing demand for use of recycled aggregates (RAs), as it enhances social and environmental benefits and creates a market opportunity. This paper presents the practice of using recycled construction and demolition waste (CDW) in the Belgrade city area (Serbia) as a resource. Two groups of CDW from Vinča landfill site near Belgrade are analyzed: raw material before, and RAs after, construction of a recycling facility on site. Comprehensive characterization is performed (including particle size distribution, density, water and organic pollutants content, various mechanical resistances, flakiness index, etc.) and compilation of samples analyzed and compared to show a holistic overview. The test outputs in both groups show acceptable values and meet required standards, indicating that recycled CDW generated in the Belgrade area can be used as a substitute to natural aggregates. In addition to that, the environmental and economic benefits from this use as a substitute are analyzed and discussed, proving the substantial income from sold Ras and the landscaping benefits, as well as ecological and economic benefits from energy savings.

Study on the curing conditions on the physico-mechanical and environmental performance of phosphogypsum-based artificial aggregates

The considerable accumulation of phosphogypsum (PG) not only occupies land space but also causes environmental pollution, leading to threatening human health. Under the background of the current massive demand for construction concrete, the problem of natural aggregate shortage urgently needs to be solved. In this research, the raw materials of PG, slag, and cement were adopted to prepare PG-based artificial aggregates (PBAAs) by compression methods, which aimed to develop the applications of PG to construction concrete materials. The different curing temperatures and solutions (Na2SO4 and CaSO4·2 H2O) were investigated to explore the effects of curing conditions on the physical properties and ion leaching of PBAAs. The performance of PBAAs from the aspects of compressive strength, pH value, bulk density, softening coefficient, water absorption, and carbonization degree was evaluated. The microscopic morphology analysis and phase, as well as quantitative analysis were conducted by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively, to study the hydration mechanism of PBAAs under different curing conditions. The Avrami model was used to simulate the PG dissolution rate of PBAAs. The results showed that 40 °C was the most favorable temperature for PBAAs and that the dissolution of PG during immersion curing was mainly controlled by ion reactions. The PBAAs cured in saturated Na2SO4 solution raised the pH value of the curing solution. The curing conditions of CaSO4·2 H2O at 40 °C inhibited the dissolution of PG in raw materials, and provided Ca2+ for the formation of ettringite and C-S-H gel, thereby increasing the bulk density, compressive strength, carbonization resistance, and reducing the water absorption rate of PBAAs. Moreover, PBAAs cured in saturated CaSO4·2 H2O and Na2SO4 solutions at 40 °C effectively solidified heavy metals and P elements in PG. This study contributes to developing the replacement of natural aggregates by PBAAs in construction concrete, which can reduce the consumption of natural aggregates and improve the utilization rate of PG.

Experimental Study on the Durability Performance of Sustainable Mortar with Partial Replacement of Natural Aggregates by Fiber-Reinforced Agricultural Waste Walnut Shells

Through the recovery and reuse of agricultural waste, the extraction and consumption of natural aggregates can be reduced to realize the sustainable development of the construction industry. Therefore, this paper utilizes the inexpensive, surplus, clean, and environmentally friendly waste agricultural material walnut shell to partially replace the fine aggregates in mortar to prepare environmentally friendly mortar. Considering the decrease in mortar performance after mixing walnut shells, basalt fibers of different lengths (3 mm, 6 mm, and 9 mm) and different dosages (0.1%, 0.2%, and 0.3%) were mixed in the mortar. The reinforcing effect of basalt fibers on walnut shell mortar was investigated by mechanical property tests, impact resistance tests, and freeze–thaw cycle tests. The damage prediction model was established based on the Weibull model and gray model (GM (1,1) model), and the model accuracy was analyzed. The experimental results showed that after adding basalt fibers, the compressive strength, split tensile strength, and flexural strength of the specimens with a length of 6 mm and a doping amount of 0.2% increased by 13.98%, 48.15%, and 43.75%, respectively, and the fibers effectively improved the defects inside the walnut shell mortar. The R²s in the Weibull model were greater than 87.38%, and the average relative error between the predicted life of the impacts and the measured values was greater than 87.38%. The average relative errors in the GM (1,1) model ranged from 0.81% to 2.19%, and the accuracy analyses were all of the first order.

Valorisation of the Effect of Waste Aluminum Sawdust on Concrete: Durability Characteristics and Environmental Impacts

The aim of this study is to examine the effect of replacing waste aluminum sawdust (AS) with fine aggregate on the strength and durability properties of concrete. For this, concrete mixtures with a cement dosage of 400 kg/m3, water/cement (W/C) ratio of 0.40-0.50-0.60 were prepared. Aluminum sawdust obtained from Elazığ industrial site was added to the concrete mixtures by replacing 0%, 0.5% and 1% fine aggregate by volume. After curing in the curing pool for 28 days, the produced concrete samples were placed in the carbonation tank and exposed to the accelerated carbonation test in three different time periods as the 1st, 3rd and 7th days. Tests of compressive strength, splitting tensile strength, ultrasound transmission velocity, porosity and carbonation depth were performed on concrete samples before and after carbonation. The samples that were exposed to carbonation were compared with the samples that did not undergo carbonation. In addition, the microstructure of AS concrete was investigated using scanning electron microscopic images (SEM). In the microscopic images, larger cracks, openings and interfacial voids were observed in the concrete matrix with the addition of AS. However, due to the formation of ettringite in these gaps and cracks after carbonation, the cavities became smaller. As a result of the experiments, it was observed that the optimum W/C ratio was 40% and the AS amount was 0.5% in the use of AS in concrete. In addition, it was found that the carbonation effect improves the compressive and splitting tensile strength and increases the ultrasound transmission rate. Finally, life cycle assessment (LCA) was conducted to evaluate the environmental impacts of the prepared concrete samples. Considering the large amount of natural aggregate consumption, it is thought that the use of waste materials in concrete will provide environmental and economic benefits.

Mechanical and Environmental Performance of Asphalt Concrete with High Amounts of Recycled Concrete Aggregates (RCA) for Use in Surface Courses of Pavements

Using aggregates from alternative sources has been considerably encouraged in recent decades. Reducing the consumption of natural aggregates from quarries (which have a substantial economic, visual, and environmental impact) is increasingly a concern. These needs have led to the broader use of more sustainable aggregates, increasing the incorporation percentages and extending their use to more demanding pavement layers (e.g., surface). In order to prove the efficiency of recycled concrete aggregates (RCAs) under such conditions, the “CirMat” project was developed. Among other works and tests, an asphalt concrete (AC) incorporating 52.3% RCA was characterized mechanically and environmentally. Empirical properties were evaluated, including the Marshall test (S = 20.2 kN; F = 2.9 mm) and resistance to permanent deformation (WTS = 0.10 mm/103 cycles), as well as a life cycle assessment (LCA), which confirmed that nine indicators were improved (from 1% to 93%). The test samples were taken from mixtures produced in the laboratory and at a plant (after which they were applied on a construction site). Comparing the results with those obtained in a reference AC (with natural aggregates), it was possible to conclude that the performance of the AC with RCAs was very similar. Therefore, the use of these aggregates, at high rates, does not represent additional risks for asphalt mixtures and has lower environmental impacts in most categories.

Physical, strength and acoustic properties of lightweight cement composite with preplaced chemically-treated crumb rubber

The valorisation of waste tyre crumb rubber (CR) as a sustainable construction material can alleviate environmental pollution and save natural aggregate consumption. However, its use in cement composite can result in a significant loss of strength due to weak adhesion and the non-uniform dispersion of CR. To compensate this strength loss, this research aims to investigate the innovative incorporation of chemically treated CR via the preplaced aggregate mixing (PM) method in producing a lightweight cement composite. The CR was treated with different chemicals, namely soaking in potassium permanganate and sulphuric acid solutions. The findings reveal a significant improvement in compressive strength (up to 160%) and water absorption reduction (from 20% to 175%) using the chemically treated CR and PM mixing methods, producing a lightweight cement composite with a density of about 1535 kg/m3. The SEM observation demonstrates the improvement in the CR–paste interface due to the treatment of the CR and the PM mixing methods, and due to the chemical treatment, which improved the wettability of the CR. On the other hand, the sound absorption and noise reduction coefficient of the chemically treated CR lightweight cement composite was almost similar for both the normal mixing (NM) and the PM methods. Overall, the results demonstrate that the CR treatment with sulphuric acid is promising for the PM method to produce a lightweight cement composite.

Axial compression behavior and stress–strain relationship of slurry-wrapping treatment recycled aggregate concrete-filled steel tube short columns

Abstract The utilization of recycled concrete can effectively solve the problems of large accumulations of construction waste and the constant consumption of natural aggregates. Slurry-wrapping modification and concrete-filled steel tubes (CFSTs) are effective approaches to enhance the utilization ratio of recycled concrete. The study involved 4 ordinary CFST columns and 16 slurry-wrapping recycled aggregate concrete-filled steel tube (SRACFST) columns. The variable parameters included the slurry-wrapping recycled aggregate replacement ratio and the section form. The result shows that the ultimate strength of the specimens reached the minimum and maximum at 25 and 100% aggregate replacement ratio. The favorable strength performance of the SRACFST columns is attributed to the dominant positive effect of the slurry-wrapping treatment in reducing matrix porosity over the negative impact of the recycled aggregate’s complex interface transition zone. Due to the hoop factor, the residual bearing ratio peaks at a 25% substitution ratio. Four design standards were used to predict the ultimate strength, with GB50936 and EC4 yielding more accurate estimations, while AISC360-10 and AIJ provided conservative estimations. This study presents the equations of the stress–strain curve for the whole axial compression process, which can be directly applied in the theoretical and numerical analysis of RACFST columns.

Durability assessment of concrete with natural and Linz Donawitz slag as coarse aggregates

Rapid growth of infrastructure has resulted in incessant consumption of natural aggregates in cement concrete leading to its depletion. Efforts have been made to utilize industrial by-products such as steel slag aggregates in concrete as partial replacement for natural aggregates. However, the utilization of Linz Donawitz (LD) slag aggregates in concrete is very limited compared to other slag aggregates. The limited utilization could be attributed to the expansive nature of LD slag aggregates, which may result in durability issues. In this study, the compressive strength and durability characteristics of concrete with 100% LD slag coarse aggregate are investigated considering three different cement types, including Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC) and Portland Slag Cement (PSC) for all the mixtures. LD slag and control concrete were examined for durability by conducting water permeability, electrical resistivity, drying shrinkage, rapid chloride penetration (RCPT) and water absorption tests. X-Ray Diffraction (XRD) analysis along with the microstructural investigations using SEM-EDS was carried out to supplement durability results. The compressive strength results indicated that LD slag concrete depicted higher strength than control concrete and there was a steady increase in strength with curing duration. Interestingly, PSC concrete depicted higher rate of strength gain compared to other cements. Further, LD slag concrete depicted low permeability and water absorption compared to control concrete, where it can be anticipated lower freeze–thaw damage. RCPT results indicated lower penetration of chloride ions representing delayed corrosion of steel in LD slag concrete. Overall, LD slag concrete depicted enhanced durability than control concrete.

Neural networks implementation for the environmental optimisation of the recycled concrete aggregate inclusion in warm mix asphalt

Regarding the traditional Hot Mix Asphalt (HMA), Warm Mix Asphalt (WMA) with Recycled Concrete Aggregate (RCA) contents (WMA-RCA) requires lower production temperatures and diminishes the consumption of natural aggregates (NAs). Nonetheless, these environmental benefits may be counteracted by the higher optimal asphalt binder demanded by the WMA-RCAs. In this regard, this research develops a computational model to optimize the WMA-RCA design. In order to build a sufficiently accurate and adaptable model, it was decided to employ Artificial Neural Networks (ANNs). The ANN implementation was based on the postulates of the statistical learning theory, i.e., preferring to generate learning through low-complexity models. Also, a representative case study of the northern region of Colombia was assessed. In this scenario, the optimal coarse RCA content was 10%, and the sustainability savings were maintained up to an RCA's hauling distance of 200 km.

Creep and drying shrinkage of recycled aggregate concrete containing cement and alkali activated slag produced by water reduction method (WRM) and equivalent mortar volume (EMV)

The utilization of recycled concrete aggregate (RCA) in producing new concrete is an effective way of reducing waste materials and natural aggregate consumption. In this paper, a new mix proportion method called the water reduction method (WRM), for recycled aggregate concrete (RAC) containing coarse and fine recycled aggregate is proposed. The equivalent mortar volume (EMV) method was also used for RAC containing only coarse recycled aggregate. The creep, shrinkage and mechanical properties of the RACs made by the new proposed method and EMV were investigated and compared with natural aggregate concrete. The method was also examined for the predetermined alkali activated slag specimens. The results showed that the new proposed mix proportion method is more reliable than conventional method in terms of mechanical and long-term properties.

Municipal woody biomass waste ash-based cold-bonded artificial lightweight aggregate produced by one-part alkali-activation method

The rapid industrialization process has resulted in the overconsumption of natural aggregates, leading to significant environmental concerns. Additionally, the disposal of municipal woody biomass ash (MWBA) has caused the depletion of land and further environmental pollution. Hence, production of artificial aggregate using MWBA is of great interest, as it reduces the consumption of natural aggregates and landfill area while recycling the MWBA. The main objective of this study is to determine the optimal mix design that can produce artificial aggregates with satisfactory strength and lightweight properties while maximizing the utilization of MWBA. Following that, the effects of different alkaline contents (9%, 12%, 15%) and ground granulated blast-furnace slag (GGBS) contents (0%, 10%, 20%, 30%) on the physical properties of the MWBA-based AAAs were investigated. Additionally, the pore distribution, phase and elemental compositions of the aggregates were examined to ascertain the mechanism of alkali-activation and strength development of the MWBA-based AAAs. The main result showed that at 15% Na2SiO3·5H2O content, increasing the GGBS content from 0% to 30% resulted in an increase in the loose bulk density and crushing strength of MWBA-based AAAs from 817 kg/m3 to 950 kg/m3 and from 0.84 MPa to 2.25 MPa, respectively, while decreasing the water absorption from 24.0% to 12.5%. This is due to the denser matrix observed, attributed to the GGBS addition, which enhances the effect of alkali-activation. Additionally, a new amorphous phase, namely C-A-S-H, was identified. The Si/Al ratio decreased with the GGBS content, resulting in more C-A-S-H gel formation and a denser microstructure with better performance for the AAAs. The novelty of this study is to demonstrate the feasibility of using MWBA in producing AAAs through a cold-bonded one-part alkali activation method. This method presents an alternative to natural aggregates that can be utilized in concrete.

The Use of Recycled Tire Rubber, Crushed Glass, and Crushed Clay Brick in Lightweight Concrete Production: A Review

Worldwide, vast amounts of waste are produced every year and most waste is sent directly to landfills or burnt, which has severe and harmful impacts on the environment. Recycling waste materials is considered the most visible solution to protect the environment. Using scraps in concrete production is a proper method for getting rid of wastes, improving the characteristics of concrete, reducing the consumption of natural aggregates, and can be used as cementitious materials that decrease cement production so that the CO2 that is produced during cement manufacturing decreases. This review paper summarizes the use of recycled waste materials, including rubber tires, crushed glass, and crushed clay brick in concrete, as a fractional replacement of aggregates, cement, etc., to develop eco-friendly lightweight construction materials. It has been concluded that the dry density of sustainable concrete decreased to 4, 21.7, and 31.7% when crushed glass, clay brick, and rubber tire were incorporated into the concrete instead of traditional aggregate, respectively. Waste rubber has good results in sulfate, thermal, and impact resistance, while glass powder and finely crushed clay brick helped to improve mechanical properties by increasing reach by 33% for glass and a slight increase for crushed clay brick, as well as thermal resistance compared to normal concrete. Moreover, due to the low particle density of these waste materials compared to that of normal-weight aggregates, these materials can be utilized efficiently to produce lightweight concrete for structural and non-structural applications such as road engineering, flooring for mounting machinery, highway and rail crash barriers, permeable pavement, interlocking bricks, insulation, filling concrete, and bearing walls.

Evaluation of pavement design input parameters of biaxial and triaxial geogrid stabilized flexible pavements overlying soft subgrades

Stabilization of flexible pavement layers using geogrids to improve the mechanical response of pavement layers is gaining importance over conventional stabilization techniques due to their low cost and superior performance. However, the lack of experimental data on quantifying the design input parameters of stabilized subgrades or granular layers limits the extensive use of geogrids in the field. Evaluation of design input parameters such as modulus improvement factor (MIF) or layer coefficient ratio (LCR) would promote the use of geogrids in the pavement, reducing the consumption of natural aggregates and the overall project cost. This study attempts to evaluate MIF and LCR due to geogrid stabilized soft subgrades considering different scenarios. All possible combinations of stabilization of pavement layers using biaxial and triaxial geogrids were considered. This involved stabilization of (a) the subgrade layer alone, (b) base layer alone, and (c) subgrade, subbase, and base layers. Accordingly, an extensive, systematic experimental program consisting of eighteen large-scale model pavement experiments (LSMPE) were conducted in five categories (designated as Series I through V). The stabilization of subgrade and granular layers was carried out using commercially available biaxial (BX1 and BX2) and triaxial (TX1) geogrids overlying soft and moderate subgrades with California bearing ratio (CBR) equal to 2.5 and 4%. Test results showed that stabilized subgrade prepared with existing and prepared subgrade material in conjunction with geogrid improved the effective CBR to as high as 10.9% from effective CBR = 7% corresponding to existing and prepared subgrade material without geogrid. The design inputs of geogrids (BX1/BX2/TX1) stabilized granular layers resulted in the MIF and LCR values ranging from 1.9 to 2.8 and 1.31 to 1.63, respectively, for the tested configuration considered in the study. Based on the findings of the study, inputs on resilient modulus of pavement layers were recommended for similar reinforcement and subgrade conditions considered.

Influence of Post-Consumer Waste Thermoplastic Elastomers Obtained from Used Car Floor Mats on Concrete Properties

In this paper, the influence of post-consumer thermoplastic elastomer (TPE) additive derived from used car floor mats on the physical and mechanical properties of concrete is presented. Waste elastomer (fractions 0-2 and 2-8 mm) was used as a substitute for sand or fine aggregate in the amount of 2.5, 5.0, 7.5, and 10.0% by weight of cement. For all series, the physical and mechanical properties of concrete (for example, compressive strength, flexural tensile strength, water absorption, density, and frost resistance), as well as its microstructure, were tested. It has been shown that post-consumer elastomer waste from used car floor mats in the amount of 2.5% of cement weight can replace sand and gravel aggregate in concrete without reducing their mechanical strength and without changing their microstructure. The compressive strength (after 28 days) of concretes in which the waste was introduced as a substitute for sand and aggregate was 57.0 and 57.2 MPa, respectively (the strength of the control sample was 57.0 MPa). The use of post-consumer waste in concrete allows for a reduction in the consumption of natural aggregate (the addition of 2.5% of waste material saves natural aggregate approximately 20 kg/m3), which reduces the cost of concrete production and also has a positive impact on the environment (i.e., it saves cost and space in landfills, where currently used car floor mat are deposited).

Effects of various additives on the crumb rubber integrated geopolymer concrete

The use of scrap tyres in construction materials has been promoted to curb the environmental exploitation caused by the open disposal of non-biodegradable waste rubber. Tyre grinds as aggregates in geopolymer concrete (GPC) would increase its sustainability value by reducing the consumption of natural aggregates. Although there is limited literature addressing the damage to GPC characteristics caused by rubber aggregates, this investigation was designed to determine the extent of possible side effects of using crumb rubber (CR) in GPC. Additionally, this investigation aims to address any resulting reduction in strength and durability using additives such as cement and fibres. Geopolymer specimens with CR replacement of fine aggregates by volume (0, 5, 10 and 15%) showed a compressive strength reduction of up to 17% when tested according to ASTM standards. Substituting the total binder by weight with Ordinary Portland cement (OPC) (0%, 5%, 10%, 15%, and 20%) improved the microstructural integrity of the rubberised geopolymer mix with the highest percentage of OPC. Despite producing new and additional binding products (CSH and CASH gels), the GPC surface readily disintegrated under acid exposure. Optimum glass fibres (GF) reinforcement (0.30%) effectively disrupted the GPC pore network, consequently reducing the acid permeability of the matrix. Further addition of steel fibres (SF) enhanced the GPC specimen's compressive and flexural strength. To analyse the cumulative effect of these additives on GPC microstructure, supporting tests such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy were carried out. Although these additives enhanced the overall performance of rubberised geopolymer, it might somewhat reduce its green aspect.

Thermal coating with rigid recycled polyurethane foam as a partial substitute of limestone aggregate

This research presents the results of an experimental study about the effect of the rigid recycled polyurethane foam used as a partial substitute of limestone aggregates in the elaboration of cement-based coating, with the objective of reducing the consumption of natural aggregate by replacing it with a recycled material and reducing the thermal conductivity of the coating. The rigid recycled polyurethane foam was crushed to be used as a partial substitute of the fine limestone aggregate in proportions of 15, 20 and 25% in volume, maintaining a cement:sand ratio of 1:3., and its mechanical, physical and thermal properties were evaluated. The mortar of coating with 20% of substitution of recycled polyurethane foam by limestone aggregate, presented a better physical-mechanical and thermal behavior to a laboratory level; therefore, so it was used in real conditions as an exterior coating in a construction prototype elaborated with a wall of blocks and exposed to environmental conditions for a year. The results demonstrated that the modified coating improved its thermal performance by decreasing the interior temperature of the prototype by around 15% compared to the traditional coating, with a difference of 0 to 1.5 °C low, thus maintaining it for most of the year and with relative humidity without significant changes.

A Numerical Model for the Optimization of Concentrated Suspensions for Sustainable Concrete Proportioning

Concrete has a large environmental impact due to CO2 emissions related to cement manufacturing and the consumption of natural aggregates. More sustainable concretes can be developed, replacing part of the cement with mineral admixtures or natural aggregates with recycled ones. However, recycled materials are less regular than natural ones, and using new deposit changes concrete properties, which necessitates the re-optimization of mixture proportions. For small/medium-size waste deposits, the expensive experimental work needed to adapt concrete formulation containing these particular wastes is not profitable, which prevents from their valorization. The aim of this study is to develop a numerical model to optimize the mixture proportions of concentrated suspensions based on very limited entry data. In the model, spheres of small radii are seeded in the porosity and allowed to swell until reaching a target radius/density. On monosized suspensions, it is shown that the ratio between the number of random displacements to the number of particles varies with density, following a classical viscosity–density relationship, which allows identification of the packing fraction. The model is extended to bidisperse systems, with the viscosity of the whole suspension calculated by combining the viscosities of each granular class. The model is applied to bidisperse systems of size ratios 4:1 and 2:1 with varying proportions of large particles. The optimum proportions identified numerically are compared successfully to experimental results from the literature.