Mixed Recycled Aggregates Research Articles

Potential application of by-products from the construction industry and waste from coconuts for concrete road paving blocks: physical and mechanical properties

ABSTRACT This paper analyzes concrete paving blocks (CPB) with mixed recycled aggregates from construction and demolition waste (CDW) as by-products and coconut fibres (CF) as waste, a novelty of these types of blocks, through physical and mechanical characterisation. Then, eighteen mixtures were used to produce rectangular CPB 20 cm × 10 cm × 8 cm (length × width × thickness): three without CDW and CF (with natural aggregate), six with CDW materials (3 replacing natural aggregate by weight in 50%, and other 3 in 75%), three with CF (adding a percentage of 0.1% by concrete weight), and six with CDW materials and CF. Tests, such as visual inspection, water absorption, voids, and compressive strength at 7 and 28 days, were done for blocks CPB with three water/cement ratios of 0.63, 0.73, and 0.83. The results showed that the mixes with different uses of CDW and CF behave better than the equivalent reference mixtures. Then, the study supports the CPB with CDW materials and CF can be used on light motorised trafficked road pavements.

Evaluation of geotechnical, mineralogical and environmental properties of clayey soil stabilized with different industrial by-products: A comparative study

The utilisation of soil stabilization techniques employing binders like lime or cement enables the use of soils that are classified as disposable, thereby reducing the need for landfills and the consumption of natural resources. However, the production of lime and cement results in significant CO2 emissions. Therefore, the application of industrial by-products (IBP) for stabilizing expansive soils presents an opportunity to minimise the use of traditional binders. This study investigates the geotechnical, mechanical, mineralogical, and environmental properties of four IBP (biomass bottom ash, biomass fly ash, steel slag, and mixed recycled aggregate) combined with a silica-based nanomaterial for road layer applications. The technical feasibility of the use of IBP was demonstrated, especially in combination with nanomaterials, allowing a 66 % reduction in the percentage of added lime, obtaining significant improvements with minimal plasticity and swelling index and bearing capacity CBR values higher than 25 %, applying BBA, BFA and SS. An environmental assessment of leachate analysis was performance, showing an immobilization of heavy metals that makes the application of IBP feasible. In addition, a life cycle analysis study showed the environmental benefits of applying IBP, such as a 50 % reduction in CO2 emissions due to the reduction of lime, resulting from the use of these materials, thus promoting more sustainable economic models.

Life-Cycle Assessment and Environmental Costs of Cement-Based Materials Manufactured with Mixed Recycled Aggregate and Biomass Ash.

The development of new building elements, such as concrete and mortar with sustainable materials, which produce a lower carbon footprint, is an achievable milestone in the short term. The need to reduce the environmental impact of the production of cement-based materials is of vital importance. This work focuses on the evaluation of the life-cycle assessment, production costs, mechanical performance, and durability of three mortars and three concrete mixtures in which mixed recycled aggregates (MRAs) and biomass bottom ash from olive waste (oBBA) were included to replace cement and aggregates. Powdered MRA and oBBA were also applied as complementary cementitious materials with a reduced environmental footprint. Chemical and physical tests were performed on the materials, and mechanical performance properties, life-cycle assessment, and life-cycle cost analysis were applied to demonstrate the technical and environmental benefits of using these materials in mortar and concrete mixtures. This research showed that the application of MRA and oBBA produced a small reduction in mechanical strength but a significant benefit in terms of life-cycle population and environmental costs. The results demonstrated that finding long-term mechanical strength decreases between 2.7% and 14% for mortar mixes and between 1.7% and 10.4% for concrete mixes. Although there were small reductions in mechanical performance, the savings in environmental and monetary terms make the feasibility of manufacturing these cement-based materials feasible and interesting for both society and the business world. CO2 emissions are reduced by 25% for mortar mixes and 12% for concrete mixes with recycled materials, and it is possible to reduce the cost per cubic meter of mortar production by 20%, and the savings in the cost of production of a cubic meter of concrete is 13.8%.

Eco-friendly concrete: Combining treated wastewater and recycled aggregates.

The concrete industry is a significant consumer of drinking water and natural aggregates, such as sand and gravel. However, the scarcity of water and aggregate resources and the challenges associated with the disposal of construction and demolition waste prompted the exploration of alternative materials. This study investigates the feasibility of incorporating secondary treated wastewater from UASB reactors followed by trickling filters and mixed recycled aggregates as potential alternatives. To assess the viability of these alternatives, the study considered the replacement of 100% potable water with treated wastewater, as well as varying proportions of recycled gravel (20, 40, 60, 80, and 100%) and recycled sand (10, 20, 30, 40, and 100%). Physical and mechanical properties were negatively affected, but it was possible to reach compressive results over 40 MPa and splitting tensile strength over 4 MPa for almost all mixes. Regarding physical properties, the use of alternative materials caused poorer outcomes for density, water absorption, and air-void ratio. The limited magnitude of these detrimental effects indicates the potential of manufacturing concrete with the addition of combined treated wastewater and recycled aggregate as a viable strategy while enhancing reuse practices.

LCA applied to comparative environmental evaluation of aggregate production from recycled waste materials and virgin sources

Nowadays, all productive sectors, including the construction industry, are facing the challenge of reducing their environmental impact. To achieve this objective, numerous actions are being carried out to access greater levels of environmental and economic sustainability. Techniques as Life Cycle Assessment contribute to quantifying environmental impacts, promoting a circular economy in a sector that consumes a high volume of resources, materials, and energy while generating large amounts of gaseous, liquid, or solid emissions. The present study aims to deepen our understanding of aspects that demonstrate the benefits of using RA instead of natural aggregates. This study not only quantifies the environmental impact but also explores the effects of potential improvements in the productive system and their impact on reducing environmental harm. The Life Cycle Assessment methodology is applied to quantify and compare the environmental impacts generated in the production of a ton of mixed recycled aggregates (MRA) from construction and demolition wastes, based on the data provided by plant managers. This is compared to the environmental impacts generated in the production of one ton of natural aggregates extracted from a quarry. The results revealed that the production of mixed recycled aggregate is more environmentally beneficial, confirming a reduction of 70.66% in environmental impacts during the production of recycled aggregates, in comparison to the natural aggregates extraction. Furthermore, the economic analysis demonstrates the economic advantage since the cost of producing recycled aggregates is over 30% cheaper than natural aggregates, being more competitive even when the transportation distances from the plant to the work sites exceed those of natural aggregates.Graphical

Pathway to Carbon Neutrality in the Cement Industry: CO2 Uptake by Recycled Aggregates from Construction and Demolition Waste

Cementitious materials can capture CO2 through carbonation reaction during their service life and post-demolition. Indeed, construction and demolition waste (CDW) still have some potential for carbonation as they contain concrete and cement-based mortars. This research consists of an experimental programme to evaluate the CO2 capture of recycling aggregates (RAs) from CDW. Two types of CDW were studied, namely mixed recycled aggregates (MRAs) and recycled concrete aggregates (RCAs). The recycled aggregates were submitted to forced and accelerated carbonation at 23 °C, 60% relative humidity and 25% of CO2 concentration. This study contributes to the existing literature by investigating more realistic RA sources that have already absorbed atmospheric CO2 during their service life. From the experimental campaign, the results show that RCAs have higher carbonation potential when compared to MRAs due to the higher cementitious material content (Rc) and to the degree of natural carbonation. The recycled aggregates’ maximum CO2 capture was assessed by thermogravimetric analysis (TGA) at different CO2 exposure times. It was verified that the maximum CO2 capture, respectively, for MRAs and RCAs, occurred after 5 h and 12 h of exposition. In short, CDW captured from 5 wt.% to 35 wt.% of CO2 per tonne of cement paste, which corresponds to 0.6% to 4.1% per tonne of aggregate. It was concluded that the carbonation process of CDW has the potential to sequester from 123 kg to 225 kg of CO2 per tonne of cement paste for MRAs and 52 up to 491 kg of CO2 per tonne of cement paste for RCAs.

Influence of the Properties of Different Types of Recycled Aggregate on the Service Properties and Leaching of Paving Blocks Manufactured at Industrial Scale.

The literature shows that a circular economy can benefit some sectors such as the construction industry. This sector demands huge amounts of raw materials and produces waste when buildings and structures are demolished. This paper explores the possibility of manufacturing at industrial scale paving blocks using different types of construction and demolition wastes as aggregates, without modifying the commonly used industrial conditions. A total of four different recycled aggregates were used in this research. Both natural and recycled aggregates have been characterized. The dosages were optimized (three different formulations). Prefabricated tests have been carried out on the products manufactured in industrial plants and the evolution of mechanical properties over time has been analysed. The results obtained were analysed statistically by applying the principal component analysis (PCA) method. To ensure the security of the elements manufactured, the ionic leaching of the materials used as recycled aggregate and of the elements produced has been tested. The main implications of this research on the construction industry show that the majority of recycled aggregates used could replace 25% of the natural aggregate in manufactured precast concrete, that the properties of the aggregates should be taken into account in the different standards and that all paving blocks manufactured in this study can be considered environmentally safe (no risk of leaching) according to the Netherland Soil Quality Decree. Therefore, it is evident that it is possible to manufacture on an industrial scale paving blocks with mixed recycled aggregates, concrete and ceramic in nature, both with the fine and coarse fractions that meet the requirements of its reference standard UNE-EN 1338 and the Netherland Soil Quality Decree that evaluates environmental risks due to leaching.

Effect of Brick Aggregate Content on Performance of Recycled Construction-Solid-Waste Aggregate.

In road engineering, road construction requires a large amount of natural aggregate; its substitution with recycled construction-solid-waste aggregate not only saves resources but also reduces the burden on the environment. The main components of construction solid waste are concrete blocks and brick slag; the breakability of the latter can affect the performance of mixed recycled aggregate, which hinders the use of construction solid waste in road engineering applications. To analyze the applicability of recycled construction-solid-waste aggregate containing brick slag aggregate in the subgrade layer, the effect of brick aggregate content on the CBR (California bearing ratio) and crushing value of mixed recycled aggregates was evaluated based on laboratory tests, and the field compaction quality of the recycled aggregates was analyzed. The results show that the 9.5-19 mm mixed recycled aggregate samples were crushed to a higher degree during the compaction process. A brick aggregate content less than 40% had little effect on the performance of mixed recycled construction-solid-waste aggregate. It is recommended to use a 22 t road roller for five passes (two weak vibrations + two strong vibrations + one weak vibration) at a speed of 3 km/h in the main compaction stage of the subgrade filling.

Determining the optimal gradation of mixed recycled aggregate containing coal gangue brick aggregate

Aggregate grading design is the foundation of concrete mix proportion design. Existing aggregate grading design methods are based on the tightest accumulation theory of homogeneous natural aggregates. However, this method has not been applied to mixed recycled aggregate (MRA) containing coal gangue brick aggregate (CGBA) (hereinafter referred to as MRA) due to significant differences in physical and mechanical properties. In this study, we subjected five types of MRA (initial particle size: 19–26.5 mm) to confined crushing, sieving, and grading composition analysis, then configured recycled concrete. We investigated the determination method of the optimal gradation of MRA, summarized the composition, particle distribution characteristics, and fractal characterization of the optimal gradation. This study focused on analyzing the factors that affect the compressive strength of recycled concrete, as well as examining the mix proportion design method. The results reveal that the optimal gradation of MRA can be determined using the five-stage loading method for approach minimum porosity. Our analysis of MRA gradation suggests that the mix proportion design of recycled concrete should be determined by considering the porosity of optimal gradation and the surplus volume coefficient of slurry. Finally, we determined that the water-binder (W/B) ratio is the primary factor that affects the compressive strength, while the CGBA’s intrinsic strength has a minimal impact. The replacement ratio of CGBA primarily affects the porosity of MRA and the W/B ratio, indirectly reducing recycled concrete’s compressive strength. Based on our findings, we recommend that the replacement ratio of CGBA should not exceed 50%. This study can promote the recycling of recycled concrete containing CGBA.

Feasibility of Using New Sustainable Mineral Additions for the Manufacture of Eco-Cements.

Due to a continuously developing population, our consumption of one of the most widely used building materials, concrete, has increased. The production of concrete involves the use of cement whose production is one of the main sources of CO2 emissions; therefore, a challenge for today's society is to move towards a circular economy and develop building materials with a reduced environmental footprint. This study evaluates the possibility of using new sustainable supplementary cementitious materials (SCMs) from waste such as recycled concrete aggregates (RCAs) and mixed recycled aggregates (MRAs) from construction and demolition waste, as well as bottom ash from olive biomass (BBA-OL) and eucalyptus biomass ash (BBA-EU) derived from the production of electricity. A micronisation pre-treatment was carried out by mechanical methods to achieve a suitable fineness and increase the SCMs' specific surface area. Subsequently, an advanced characterisation of the new SCMs was carried out, and the acquired properties of the new cements manufactured with 25% cement substitution in the new SCMs were analysed in terms of pozzolanicity, mechanical behaviour, expansion and setting time tests. The results obtained demonstrate the feasibility of using these materials, which present a composition with potentially reactive hydraulic or pozzolanic elements, as well as the physical properties (fineness and grain size) that are ideal for SCMs. This implies the development of new eco-cements with suitable properties for possible use in the construction industry while reducing CO2 emissions and the industry's carbon footprint.

Influence of mixed recycled coarse aggregate on the engineering properties of recycled aggregate concrete

Influence of mixed recycled coarse aggregate on the engineering properties of recycled aggregate concrete

Axial Compression Behavior of Composite Sandwich Panel with Mixed Recycled Coarse Aggregate Concrete

The coarse aggregate produced from the construction and demolished waste of masonry structure is called mixed recycled coarse aggregate (MRA), which is mainly composed of concrete recycled coarse aggregate (CRA) and brick recycled coarse aggregate (BRA). The paper presents the results of an experimental and numerical study of concrete composite sandwich panel made with MRA. The composite sandwich panel with MRA (CSPMRA) were tested under axial compression to investigate the influence of concrete mix proportion, thickness of insulation board and added edge frame on the load-displacement curve, load-strain curve, vertical displacement, ultimate bearing capacity and failure mode of CSPMRA. Results of the experimental and finite element analysis (FEA) were compared with the results based on Chinese code, ACI design equation and other empirical equations developed by researchers which might be applicable to predict the ultimate load of sandwich panels. A semi-empirical equation was proposed to better fit the experimental and the FEA results.

Study on the compressive mechanical properties of mixed recycled aggregate concrete with silane modified

This study used a 10% silane solution to strengthen recycled brick aggregates (RBA). Subsequently, mixed recycled aggregate concrete (MRAC) was prepared by using recycled concrete aggregate (RCA) and RBA modified with silane (Si-RBA). The properties of RBA and RCA were compared. The effects of the Si-RBA/RCA ratio on the failure modes, compressive strengths, and characteristics of the compressive stress strain curves under monotonic loading and cyclic loading were tested. The microstructures of the RBA, Si-RBA, and MRAC were analyzed by scanning electron microscopy (SEM). The test results showed that RBA modified with silane reduced water absorption by 51.61% and improved the crushing index by 14% compared to RBA. When the Si-RBA/RCA ratio changed from 0:10 to 10:0, the failure mode of MRAC transformed from interfacial transition zone (ITZ) failure to aggregated failure, while the compressive strength decreased. The MRAC specimens exhibited similar failure phenomena, regardless of monotonic or cyclic loading. The peak stress and elastic modulus decreased as the Si-RBA/RCA ratio increased, whereas the peak strain showed a fluctuating growth trend, and the plastic strain increased. In addition, SEM images showed that the reaction products of silane filled the pores of the RBA, and the silane solution made the ITZs of the RBA much denser. Based on the test data, a constitutive model for MRAC under monotonic and cyclic loadings was proposed, which showed good accuracy in predicting the response of MRAC under a compressive load.

Optimisation of hybrid eco-efficient mortars with aggregates from construction and demolition waste and olive biomass ash

Materials considered as waste, such as Construction and Demolition Wastes (C&DW) and Biomass Bottom Ash (BBA) are the subject of this study to implement them in cement-based materials. After basic and advanced characterization, as well as leaching studies to assess the environmental impact, they are implemented in mortars as a replacement for standard silica sand. In this way, their mechanical behaviour, durability and micro-properties in hardened state are tested. The feasibility of implementing Mixed Recycled Aggregates (MRA) from C&DW and BBA to replace natural sand in high substitution rates is studied by substituting the wastes alone and in combination. Mortar mixes in which 50% of the aggregate is replaced, reaching more than 80% of the standard mortar strength. Mixtures in which 10% of the aggregate is replaced reaching more than 95% of the standard mortar strength.

Thermo-mechanical treatment as an upcycling strategy for mixed recycled aggregate

The study investigates thermo-mechanical treatment for mixed recycled aggregates (MRA). Six treated aggregates were prepared by heating MRA between 300 °C and 800 °C, followed by 100 abrasion cycles. The thermo-mechanical treatment causes loss in the adhered mortar and improves aggregate crushing, impact and abrasion value up to 700 °C. Concrete prepared with MRA treated at 700 °C, as compared to natural aggregates, shows higher workability (166.67%) and comparable mechanical strength, i.e., compressive (93.72%), flexural (99.94%) and split tensile (97.87%). The sustainability assessment shows that treating MRA with renewable energy can have lower economic costs (89.36%) and carbon emissions (58.05%) than manufacturing natural aggregates.

Study of the relationship between the water binder ratio and strength of mixed recycled aggregate concrete based on brick content

High-value recycling of mixed recycled aggregate (MRA) has attracted the attention of researchers in the worldwide, but its influence on the Bowromi formula is still unclear, which hinders its in concrete. Against this background, this research focuses on the basic physical properties of MRA and the effect of brick content on the properties and microstructure of MRA and mixed recycled aggregate concrete (MRAC) under different water binder ratios (W/B). The results showed that the compressive and splitting tensile strengths of MRAC decreased with an increase in the brick content; however, the splitting tensile strength was more sensitive to changes in the brick content than the compressive strength. In microscopic analysis, it was found that although the addition of the recycled brick aggregate could enhance the internal curing effect of the MRAC, it was still insufficient to compensate for the adverse effects of the pore structure deterioration and original cracks in MRA. Finally, based on the above results, this study provides an effective method to predict the compressive strength of MRAC with different brick contents, and optimizes the Bowromi strength and MRAC strength development formulas. This research result is helpful in promoting MRA applications in the real-world construction projects.

ANÁLISIS DE LA VIABILIDAD TÉCNICA Y MEDIOAMBIENTAL DE LOS MORTEROS DE CEMENTO ELABORADOS CON ÁRIDO RECICLADO MIXTO

The construction industry is one of the main economic drivers of nations, but it is also an industry that generate a large amount of waste that cause a strong negative environmental impact. This research studies the effect of partial or total substitution of natural aggregate by mixed recycled aggregate in the manufacture of cement mortars. To this end, an experimental study was carried out to examine the mechanical properties and evaluate the shrinkage of mortars made with different proportions of mixed recycled aggregate, to subsequently improve these properties by adding reinforcement fibres to the mortars. The results show how from 50% replacement of natural aggregate the technical performance of the mortars is affected, and how basalt fibre is postulated as a suitable reinforcement for these construction materials. In addition, the carbon footprint derived from the manufacturing process of the mixed recycled aggregate has been determined, which is lower than that obtained for natural aggregate.

Characterization of Three Types of Recycled Aggregates from Different Construction and Demolition Waste: An Experimental Study for Waste Management

Achieving sustainable management and efficient use of natural resources stands out as one of the goals included in the Goals for Sustainable Development in the 2030 Agenda. The construction sector is currently far from presenting an efficient model in terms of treating waste generated by it. Variations in the physical and chemical properties of recycled aggregates coming from construction and demolition waste are one of the main reasons of their limited use in the production of construction materials. This research presents a physicochemical characterization of three different types of recycled aggregates coming from different types of waste: concrete, ceramic and mixed. Physical characterization shows that recycled concrete aggregate has better physical properties compared with mixed recycled aggregate and ceramic recycled aggregate, which makes it more suitable for use in masonry mortars and concrete, due to its higher dry density (2210.33 kg/m3), its lower content of fines (5.17%), its lower friability coefficient (24.60%), and its water absorption coefficient (6.70%). Chemical characterization shows that none of the tested recycled aggregates contains traces of harmful chemical agents that exceed the limits established by the reference regulations. Finally, the statistical analysis shows good homogeneity for these raw materials, obtaining low coefficients of variation and values within the recommended in each of the calculated confidence intervals.

Pullout behaviour of polymeric strips embedded in mixed recycled aggregate (MRA) from construction & demolition (C&D) waste – Effect of type of fill and compaction

Recycling and reusing construction and demolition (C&D) waste is the pressing priority, and the use of such non – conventional structural fill in reinforced soil structures (RSS) is gaining momentum. However, the utilisation of mixed recycled aggregate (MRA) from processed C&D waste as structural fill with polymeric strips (PS) and the effect of poorly compacted structural fill on the pullout interaction is not reported. This research presents the viability of using MRA as a structural fill for reinforced soil structures, appraising the physical, mechanical and electrochemical properties of MRA and the pullout behaviour of polymeric strips embedded in MRA at different relative densities in a large-scale pullout box. The results for MRA were compared with those obtained using locally available coarse and fine sands. The test results showed that MRA was alkaline (pH < 9) and had good mechanical properties and shear strength suitable for reinforced soil structures. Pullout testing results exhibited high values of the interface apparent coefficient of friction (μS/GSY) under dense conditions and a 70–80% reduction in loose conditions. The present study reinforces the viability of using MRA as an alternative structural fill with PS and highlights the effect of construction variability on μS/GSY.

Analiza osnovnih mehaničkih svojstava mješavina recikliranog betona s recikliranim krupnozrnatnim agregatom

Three kinds of recycled aggregate concretes (RACs), with six different replacement rates at four ages, are subjected to the standard cube axial compression test to study mechanical properties. Failure modes, compressive strength, stress-strain curves, peak strain, and elastic modulus of RACs are systematically analysed. In addition, three equations are proposed for RACs to describe the relationship between the compressive strength and replacement rate. Comparison between various equations of elastic modulus and test results is presented, and then three most suitable equations are established for three kinds of RACs, including necessary modifications, especially for RAC with mixed recycled aggregates.