Substitution Of Natural Aggregates Research Articles

Characterization of Stone Waste Sludge and Preliminary Investigation on Green Materials Based on Traditional Lime Putty for Sustainable Construction

Very large quantities of stone waste sludge are disposed in exhausted quarries and have a very low reuse rate to date. The paper considers the possibility of using these types of industrial waste in partial substitution of natural aggregates for the production of lime-based plasters. Traditional materials based on lime, the only material with a carbon neutrality life cycle, have considerable potential for use as components of green materials for plastering and finishing building surfaces in both new construction and historic heritage conservation. The paper presents the preliminary results of a research activity aimed at developing pre-packaged products based on Traditional Lime Putty (TLP) by partially replacing natural aggregates with Stone Waste Sludge (SWS), with a low rate of recovery from the Apricena limestone production district in Apulia. The mineralogical and chemical analysis carried out using XRD (X-Ray Diffraction), TG-DTA (Thermo Gravimetry-Differential Thermal Analysis), and hydrochloric acid attack test showed that the SWS consisted of 98.4 % CaCO3 by mass. The particle sizes measured by laser diffraction technique are below 22.5 μm for the 92% mass of the sample. The high fineness of the stone waste was confirmed by the Blaine-specific surface method, which equals to 9273.79 cm2/gr. The behavior of three fresh mixtures for prepacked coarse plaster, fine plaster, and finishing plaster with 12.90%, 17.94%, and 18.90 by mass of SWS, respectively, was evaluated by spreading test and applicability tests on a perforated ceramic slab. The finishing plaster has the highest consistency value of 235 mm, while the fine plaster and the coarse plaster have values of 205 mm and 155 mm, respectively. The coarse plaster is suitable for use as base plaster (arriccio) or second layer rendering (tonachino) up to a thickness of approximately 1 cm. Both the fine plaster and finishing plasters can be used for the surfaces finishing with the application of layers of a few millimeters thick.

Second Life for Recycled Concrete and Other Construction and Demolition Waste in Mortars for Masonry: Full Scope of Material Properties, Performance, and Environmental Aspects

This review presents the scope of current efforts to utilize recycled construction and demolition waste in mortars for masonry. More than 100 articles are divided into groups pertaining to the type of mortar, different binder systems, the type of construction and demolition waste (CDW), and its utilization specifics. Cement-based mortars dominate this research domain, whereas recycled concrete is the main material employed to replace virgin aggregates, followed by recycled masonry and recycled mixed waste aggregates. Such application in cement-based mortars could increase water demand by 20–34% and reduce strength by 11–50%, with recycled concrete aggregates being the most favorable. Natural aggregate substitution is disadvantageous in strong mortars, whereas weaker ones, such as lime-based mortars, could benefit from this incorporation. The extent of this topic also suggests possibilities for different recycled material use cases in mortars for masonry, although the available literature is largely insufficient to infer meaningful trends. Nonetheless, the most relevant knowledge synthesized in this review offers promising and environment-conscious utilization pathways for recycled concrete and other construction and demolition waste, which brings opportunities for further research on their use in mortars for masonry and industrial-scale applications.

Recycling of RAP (Reclaimed Asphalt Pavement) as aggregate for structural concrete: experimental study on physical and mechanical properties

The replacement of natural aggregate in concrete with artificial and/or recycled one has recently gained attention as meaningful strategy to reduce the environmental impact of structural concrete and promote circular economy principles. This study investigated the possibility to use Reclaimed Asphalt Pavement (RAP), in the “as received conditions”, as a partial or complete substitution of natural aggregate for structural concrete. RAP aggregate was firstly characterized in terms of grain size distribution, density, assessment of fines, chloride content, moisture content and water absorption. Subsequently, a total of twenty-four concrete mixes were designed, considering two cement types, two w/c ratios and several aggregate substitution percentages. For each mix, properties at the fresh and hardened state were investigated, such as workability, density and total open porosity, compressive strength, dynamic modulus of elasticity, and electrical resistivity. Results showed that RAP has a good potential to be used in reinforced concrete, provided that different water absorption and moisture content are considered in the mix design. RAP concrete was characterized by a lower density and increased total open porosity; however, an accurate tailoring of the concrete recipe could compensate the strength loss for several applications. Other properties, such as electrical resistivity and the relationship between dynamic modulus of elasticity and compressive strength did not result significantly altered by the presence of RAP.

Avaliação tecnológica de argamassa de revestimento produzida com vermiculita expandida

The construction industry is associated with a high consumption of non-renewable resources, such as sand, in addition to the energy demand involved in the construction processes and the use of buildings. In the search for new technologies for traditional building materials, cement mortars have been modified by replacing sand with lightweight aggregates, such as expanded vermiculite. The aim of the present study is, therefore, to analyze the flexural tensile strength of rendering mortars produced with a 1:1:6 mix ratio by volume, with 10% and 20% substitution of natural aggregate by expanded vermiculite, comparing them with a reference mixture. The experimental phase consisted of the characterization of aggregates, preparation of mortars, tests in the fresh state, and flexural tensile strength tests. Overall, the replacement of sand with expanded vermiculite increased the flexural tensile strength, enhanced the fresh-state bulk density, and reduced the consistency index. Known for contributing to improvements in thermal and acoustic insulation, reducing structural weight, among other effects, the use of vermiculite in mortars demonstrated potential based on the results, as it did not significantly impair the mechanical behavior of the mixtures.

Sustainable utilization of mine wastes in mortar production as a part of aggregates: a case study on calcareous wastes of Angoran lead and zinc mine.

This study investigated the feasibility of large-scale utilizing calcareous wastes (CW) of Angoran lead and zinc mine as aggregates in mortar production with the maximum possible substitution of natural aggregates. The main goal was to produce mortar (concrete with fine aggregates as fine as sand or smaller) from Angoran mine's calcareous wastes for maintenance in its underground spaces.Compared to concrete, suchmortars with better fluidity can enter narrow spacesmore easily.In addition,it can be usedto build various structures around the mine. Therefore, multiple samples were prepared by replacing 0% (as the control sample), 20%, 40%, 60%, 80%, and 100% of natural aggregates with CW. Subsequently, compressive strength, flexural strength, water absorption, slump, and TCLP tests were conducted on these samples. The results revealed that the mortar sample with 80% CW exhibited significantly higher compressive strength at 3, 14, 28, and 56days compared to both the control sample and other samples. Specifically, the compressive strength of this sample reached 35.5MPa at 56days, representing an 18.4% increase over the control sample. This indicates that the hydration of cement and the growth of C-S-H gel were enhanced. Analysis of the workability and slump of the samples indicated that as the percentage of natural aggregate replaced by CW increased, the fluidity of the mortar slightly decreased. In addition to mechanical properties like compressive strength, environmental aspects like heavy metal stabilization are also very important. So, TCLP tests conducted on the four heavy metals lead, zinc, copper, and cadmium demonstrated that the released amounts of these elements from all the samples were below the EPA standard limits. These findings confirm the effective stabilization of heavy metals in mortar samples. A comparison of SEM images revealed that the mortar sample made with 20% CW (with minimum compressive strength) exhibited a higher presence of ettringite compared to the sample made with 80% CW (with maximum compressive strength) after 28days.

ПЕРСПЕКТИВЫ ИСПОЛЬЗОВАНИЯ ОТХОДОВ СТРОИТЕЛЬНОЙ КЕРАМИКИ ПРИ ПРОИЗВОДСТВЕ СТРОИТЕЛЬНЫХ МАТЕРИАЛОВ

The main technological aspects of the production of building ceramics are given. Based on the analysis of literary sources, a comprehensive assessment of the feasibility of using construction ceramic waste as a secondary raw material for the production of new building materials was carried out. Based on the research of modern scientists, it has been established that the waste from the scrap of building ceramics is suitable for use as an aggregate, partial replacement of cement and a reactive additive in concretes and mortars. When using scrap of con-struction ceramics as an aggregate, it is recommended to limit the substitution of natural aggregate at the level of 20-30%, together using various additives: plasticizing and improving rheotechnological and physico-mechanical properties of concrete. Finely ground waste from brick scrap has pozzolan activity and, when used as a reactive additive or partial replacement of cement in concretes and mortars, up to 20-25% can improve the structure of cement stone, increase strength, reduce macroporosity and penetration of chloride ions, and increase sul-fate resistance. This kind of binder is prone to a later set of strength compared to Portland cement. In addition, the waste of building ceramics can be used in the production of alkali-activated cements and slag-alkali binders, as well as s raw materials for the production of new bricks or the construction of road surface bases. It has been revealed that the production of building materials and products based on con-struction ceramics waste is a promising direction for the development of construction production. It is possible not only to obtain materials of equal quality to products based on natural raw materials, but also with improved characteristics.

Evaluation of asphalt film thickness and heavy metal leaching of oxidizing slag used as an aggregate material in dense-graded asphalt concrete.

Electric-arc-furnace (EAF) steelmaking uses scrap iron and steel as raw materials. Scrap iron and steel originate from complex sources and may contain heavy metal components which can leach into the environment over time due to wear-and-tear. A by-product of the EAF steelmaking process is oxidizing slag, and approximately 1.2 million metric tons is produced every year in Taiwan alone. This study investigated substitution of natural aggregates with oxidizing slag in dense-graded asphalt concrete. We evaluated the water resistance and asphalt film thickness of the oxidizing slag substituted asphalt concrete and further explored the performance of oxidizing slag as paving material. We determined the dissolved and total amounts of heavy metals in the oxidizing slag, comparing these results with current regulatory controls to assess the environmental compatibility of the oxidizing slag. We found that due to the complicated sources of oxidizing slag, the basic properties should be analyzed on a batch-to-batch basis. Furthermore, we recommend trial mixing before upscaling the production of oxidizing slag substituted dense-graded asphalt concrete to confirm the mixing time required to achieve uniformity. The results also show that in comparison to natural aggregates used in asphalt concrete, oxidizing slag exhibits superior performance in terms of increased asphalt film thickness and improved water resistance. Furthermore, oxidizing slag as an aggregate material was associated with decreased heavy metal leaching and reduced environmental pollution. The results of the toxicity characteristic leaching procedure (TCLP) met regulatory requirements. However, the microwave-assisted aqua-regia digestion procedure showed heavy metal concentrations exceeding the monitoring standards for food crops. Considering environmental compatibility, it is recommended that controlling the total amount of heavy metals in oxidizing slag should be included in regulatory requirements. Furthermore, we should prohibit the use of materials such as oxidizing slag and other steel furnace slag in the roadways adjacent to edible crop farmlands.

Effect of Public Fillers on Cement-Stabilized Recycled Mixes of Road Performance: Mechanical Properties, Microstructure, and Durability.

In order to address the challenges of resource utilization posed by construction waste, the substitution of natural aggregate (NA) with public fill (PF) contents was investigated for load reclamation and road grassroots applications. A comprehensive assessment of road performance for the recycled mixture was conducted, focusing on parameters such as unconfined compressive strength, splitting strength, compressive resilience modulus, dry shrinkage, and frost resistance. Additionally, the impact of incorporating PF at various types and replacement ratios on the microstructure of cement-stabilized aggregate (CSA) was analyzed. The results indicated that the unconfined compressive strength of cement-stabilized recycled mixture with varying PF contents meets the base strength requirements for heavy, medium, and light traffic pavement on secondary and sub-secondary roads in China. Notably, the unconfined compressive strength and resilience modulus follow a similar pattern, reaching their peak at a 25% PF content. Microscopic examination reveals that an appropriate PF content leads to the predominant formation of C(N)-A-S-H, hydrotalcite, Ca(OH)2, and CaCO3 as paste reaction products. As the replacement of public fill increases from 0% to 25%, there is a gradual stacking of gel products, which enhances the compactness of the microstructure by cementing together unreacted particles. Consequently, this process reduces dry shrinkage strain and effectively mitigates the formation of reflection cracks. Applying large quantities of public fill to road construction can effectively deal with various waste accumulation problems and produce a novel road material with significant social, economic, and environmental benefits.

The influence of nanosunflower ash and nanowalnut shell ash on sustainable lightweight self-compacting concrete characteristics

The absence of biodegradability exhibited by plastics is a matter of significant concern among environmentalists and scientists on a global scale. Therefore, it is essential to figure out potential pathways for the use of recycled plastics. The prospective applications of its utilisation in concrete are noteworthy. The use of recycled plastic into concrete, either as a partial or complete substitution for natural aggregates, addresses the issue of its proper disposal besides contributing to the preservation of natural aggregate resources. Furthermore, the use of agricultural wastes has been regarded as a very promising waste-based substance in the industry of concrete manufacturing, with the aim of fostering the creation of an environmentally sustainable construction material. This paper illustrates the impact of nano sunflower ash (NSFA) and nano walnut shells ash (NWSA) on durability (compressive strength and density after exposure to 800 °C and sulphate attack), mechanical properties (flexural, splitting tensile and compressive strength) and fresh characteristics (slump flow diameter, T50, V-funnel flow time, L-box height ratio, segregation resistance and density) of lightweight self-compacting concrete (LWSCC). The waste walnut shells and local Iraqi sunflower were calcinated at 700 ± 50 °C for 2 h and milled for 3 h using ball milling for producing NSFA and NWSA. The ball milling succeeded in reducing the particle size lower than 75 nm for NSFA and NWSA. The preparation of seven LWSCC concrete mixes was carried out to obtain a control mix, three mixtures were created using 10%, 20% and 30% NWSA, and the other three mixtures included 10%, 20% and 30% NSFA. The normal weight coarse aggregates were substituted by the plastic waste lightweight coarse aggregate with a ratio of 75%. The fresh LWSCC passing capacity, segregation resistance, and filling capability were evaluated. The hardened characteristics of LWSCC were evaluated by determining the flexural and splitting tensile strength at 7, 14 and 28 days and the compressive strength was measured at 7, 14, 28 and 60 days. Dry density and compressive strength were measured after exposing mixes to a temperature of 800 °C for 3 h and immersed in 10% magnesium sulphate attack. The results demonstrated that the LWSCC mechanical characteristics were reduced when the percentages of NWSA and NSFA increased, except for 10% NWSA substitution ratio which had an increase in splitting tensile strength test and similar flexural strength test to the control mixture. A minor change in mechanical characteristics was observed within the results of LWSCC dry density and compressive strength incorporating various NSFA and NWSA` contents after exposing to temperature 800 °C and immersed in 10% magnesium sulphate attack. Furthermore, according to the findings, it is possible to use a combination of materials consisting of 10–20% NSFA and 10–20% NWSA to produce LWSCC.

Transforming waste into sustainable building materials: Properties and environmental impacts of Geopolymer concrete with recycled concrete aggregates

<p>Industrial by-products such as cementitious materials or aggregates have the potential to mitigate the adverse environmental effects associated with traditional cement manufacture. Geopolymer Concrete (GPC) is more eco-friendly than conventional concrete because it does not require cement. GPC with Recycled concrete aggregates (RCA), Ground granulated blast furnace slag (GGBS), and Fly Ash (FA) reduce raw material use and create sustainable infrastructure. GPC compounds increase workability, slump value above standard concrete, and reduce the amount of water usage. The study examines GPC mechanical properties, durability, and environmental properties with different RCA content. The M30 concrete mix design is established by trial and error utilizing a 0.45 water/binder ratio. GPC with 0%, 10%, 20%, 30%, 40%, and 50% recycled coarse aggregate replaced natural aggregate(NA) by mass. GPC with 50% GGBS provides an early strength of 96% of normal compressive strength on day seven. The compressive, split tension, and flexural strengths exhibit significant improvement with up to a 40% substitution of NA with RA. These results highlight GPC's potential as a sustainable alternative in the construction sector.</p>

Study of the influence of the substitution of natural aggregates by hardened cement aggregates in concrete and the exposure of concrete to a medium enriched with carbon dioxide

The valorization of waste is an excellent way to protect the environment. This study focuses on waste consisting of cement that has hardened before use. The goal of this study is to determine the conditions under which these can be valorized in concrete. These wastes are used as aggregates, referred to as Hardened Cement Aggregates (HCA). First, the density, granulometry, and impact resistance of these aggregates were measured and compared to those of natural aggregates (NTA). The results showed that natural aggregates have a bulk density and specific gravity more than 25% higher than those of HCA. However, this trend reverses when considering mechanical strength. Specifically, the Los Angeles and micro-Deval abrasion coefficients of NA are 10% and 18% lower, respectively, indicating better mechanical resistance than HCA. This difference in performance is attributed to the higher porosity within the structure of HCA. When evaluating the concrete, it was observed that the poor physical and mechanical properties of HCA adversely affected the concrete produced with them (HCAC). Therefore, the subsequent phase of the research aimed to identify conditions that could optimize the properties of HCAC. Samples of HCAC were cured in two different environments: plain water (control) and CO2-enriched water (carbonated environment). The results demonstrated that curing in the carbonated environment significantly improved the mechanical properties of HCAC by over 20%. This increase allowed the concrete to reach a compressive strength of 28 megapascals, which matches the strength of concrete made with natural aggregates (NAC). Consequently, hardened cement aggregates can effectively replace natural aggregates in concrete when used in a carbonated environment.

Eco-Friendly Pavements Manufactured from Mixed Recycled Aggregates Obtained from Construction and Demolition Waste: An Industrial-Scale Validation.

This study aimed to validate that laboratory-scale results could be commercially replicated when manufacturing marketable precast concrete. Construction and demolition waste (CDW) was separated into two (fine and coarse) recycled aggregates (RAs). Precast paver and kerb units were fabricated by partial or total substitution of natural aggregates (NAs) by RAs. The study involved the comprehensive characterisation of raw materials, including particle size distribution, mineral composition, and elemental composition. Paver blocks and kerbs manufactured with up to 50% RAs showed mechanical resistance (T = 3.7 ± 0.2 and B = 5.3 ± 0.6 MPa, respectively), water absorption between 5.3-5.7%, and abrasion resistance (approximately 20.2 mm), which met the standard requirements (UNE-EN 1340:2004 and UNE-EN 1338:2004). Furthermore, industrial-scale precast pavement units demonstrated strength and durability suitable for heavy traffic areas. A reduction of 13% in cement content could maintain the requirements with a partial RA substitution of 25%, offering economic and environmental benefits. Therefore, it is feasible at an industrial level to replace NAs with RAs, promoting durability and technological properties with a positive environmental impact and considerably reducing CO2 emissions by up to 65%. Overall, pavers with RAs manufactured at the laboratory scale met mechanical standards, and the kerb stones showed improvements in abrasion resistance. On an industrial scale, kerb stones and precast blocks with specific substitutions can meet strength, water absorption, and abrasion requirements, allowing a reduction in cement content.

Structural Sustainable Recycled Aggregate Concrete Production Under Environmental Conditions

The use of recycled aggregates (RA) in the concrete industry has become increasingly popular due to the reduction in natural aggregate (NA) consumption and the ability to reuse demolition waste. This research focuses on analyzing the performance of recycled aggregate concrete (RAC) cured with sodium sulfate (Na2SO4). Five different mixtures were created, varying from 0% RA without supplementary cementitious material (SCM), to 0%, 15%, 30%, and 45% substitution of NA with RA and SCM. The slump test was performed on all fresh RAC mixtures, which showed a decrease in slump with an increase in RA content. Both 5% Na2SO4 solution curing at 91 days and standard curing at 7, 28, and 91 days resulted in a reduction in compressive strength and ultrasonic pulse velocity (UPV) as the proportion of RA increased. Compared to standard curing, the compressive strength of specimens cured with 5% Na2SO4 solution at 91 days showed a decrease of approximately 5-7%. The UPV of SCM-based mixes showed 14-28% improvement with respect to normal aggregate concrete (NAC) in normal water curing. Furthermore, the SCM-included specimens have produced less deterioration in Na2SO4 immersion as SCM particles resist the severity of the dominant sulfate environment.

Influence of the Addition of Recycled Aggregates and Polymer Fibers on the Properties of Pervious Concrete.

The aim of the study was to check the possibility of reusing aggregate from recycled concrete waste and rubber granules from car tires as partial substitution of natural aggregate. The main objective was to investigate the effects of recycled waste aggregate modified with polymer fibers on the compressive and flexural strength, modulus of elasticity and permeability of pervious concrete. Fibers with a multifilament structure and length of 54 mm were deliberately used to strengthen the joints among grains (max size 31.5 mm). Eight batches of designed mixes were used in the production of pervious concrete at fixed water/binder ratio of 0.34 with cement content of 350 kg/m3. Results showed that the use of recycled concrete aggregate (8/31.5 mm) with replacement ratio of 50% (by weight of aggregate) improved the mechanical properties of pervious concrete in all analyzed cases. Whereas the replacement of 10% rubber waste aggregate (2/5 mm) by volume of aggregate reduced the compressive strength by a maximum of 11.4%. Addition of 2 kg/m3 of polymer fibers proved the strengthening effect of concrete structure, enhancing the compressive and tensile strengths by a maximum of 23.4% and 25.0%, respectively. The obtained test results demonstrate the possibility of using the recycled waste aggregates in decarbonization process of pervious concrete production, but further laboratory and field performance tests are needed.

Predicting Strength Properties of High-Performance Concrete Modified with Natural Aggregates and Ferroslag under Varied Curing Conditions

High-performance concrete (HPC) is obtained by inclusion of mineral admixtures like silica fumes and fly ash to the normal concrete. Consumption of natural materials such as sand, natural aggregates, and limestone produces environmental degradation. Similarly, industrial by-products such as fly ash, silica fume, and ferro slag need to be safely disposed of without negatively impacting the environment. The problem being addressed in this study is the need to develop high-performance concrete (HPC) that is durable and environmentally friendly. In recent years, the use of natural aggregates and ferro slag as partial replacements for traditional aggregates has gained attention as a sustainable alternative in the production of concrete. However, there is limited research on the effect of these materials on the mechanical and durability properties of HPC under varied curing conditions. In this current research, high-performance concrete of M60 grade with partial substitution of coarse aggregate with ferro slag aggregate was formed as per the recommendations of the American Concrete Institute with the inclusion of fly ash and silica fume. Natural coarse aggregate was partly substituted by ferro slag aggregate in proportions from 0% to 40%. Partial substitution of cement was made with 15% of fly ash and 10% of silica fumes. Specimens of normal concrete mix (MF0) and modified ferro slag aggregate concrete mix (MF20, MF30, and MF40) were prepared and subjected to acid test, sulphate test, and alternate wet and drying tests to assess the compressive strength of the concrete mixes. Central composite design (CCD) of RSM modelling was adopted to recommend a regression model to forecast the compressive strength of concrete under wetting drying test, acid test, and sulphate attack. Further, natural aggregate, ferro slag, and duration of curing were considered as basic variables to suggest the model. Regression models for response data were evaluated using analysis of variance (ANOVA) and Pareto charts. The results show that the mix MF30 (30% substitution of natural aggregate by ferro slag aggregate) had higher compressive strength. The residual compressive strength at 270 days under alternate wetting and drying, acid attack, and sulphate attack was obtained as 62 MPa, 62.50 MPa, and 66.50 MPa, respectively. Similarly, the percentage loss of weight was obtained as 12.92%, 12.22%, and 6.60% for alternate wetting and drying, acid attack, and sulphate attack, respectively. The findings of the analysis of variance (ANOVA) indicate that the most significant factors influencing the variables C S W D , C S A T , and C S S T are natural aggregate, ferro slag, and curing period. The regression models for C S W D , C S A T , and C S S T are extremely significant, as shown by the ANOVA and Pareto chart analyses.

Use of Waste Concrete for Ordinary RCC Structure

The aim of current study was to determine the recycled concrete aggregate (RCA) applicability in the production of concrete mixture for vibropressed concrete rcc structure. The experiments were focused especially on the crushed waste material from the same concrete elements producing plant. For this type of precast elements only some finer fractions can be implemented and the “earth-moist” consistency of fresh mixture is required. The series of samples was prepared in which the mixture of natural aggregates was partially or totally substituted by recycled concrete aggregate. The 0/4 RCA fraction, which is usually rejected in ready mix concrete technology, plays a role of 0/2 sand. The substitution of sand fraction was from 20% to 100% respectively. The substitution of the coarser aggregate fractions by 4/16 RCA was also done. The standard properties of vibropressed elements, such as the degree of densification, the density of material, the compressive and splitting tensile strength and the water absorption capacity according to the relevant standards were determined. The parameters of materials with the natural aggregate substitution by RCA are affected by the ratio of recycled concrete aggregate. In most cases the results do not decline specially from those for reference samples, when only the natural sand (0/2) fraction is substituted by the 0/4 recycled aggregate. As one could expect, as lower the substitution, as better the test results. The partial substitution of natural aggregate by coarser fractions requires experimental verification; over 20%substitution of natural aggregate by 4/8, 8/16 or 0/16 RCA should be excluded.

Use of Waste Concrete for Block, Paver, Brick Production

The aim of current study was to determine the recycled concrete aggregate (RCA) applicability in the production of concrete mixture for vibropressed concrete blocks. The experiments were focused especially on the crushed waste material from the same concrete elements producing plant. For this type of precast elements only some finer fractions can be implemented and the “earth-moist” consistency of fresh mixture is required. The series of samples was prepared in which the mixture of natural aggregates was partially or totally substituted by recycled concrete aggregate. The 0/4 RCA fraction, which is usually rejected in ready mix concrete technology, plays a role of 0/2 sand. The substitution of sand fraction was from 20% to 100% respectively. The substitution of the coarser aggregate fractions by 4/16 RCA was also done. The standard properties of vibropressed elements, such as the degree of densification, the density of material, the compressive and splitting tensile strength and the water absorption capacity according to the relevant standards were determined. The parameters of materials with the natural aggregate substitution by RCA are affected by the ratio of recycled concrete aggregate. In most cases the results do not decline specially from those for reference samples, when only the natural sand (0/2) fraction is substituted by the 0/4 recycled aggregate. As one could expect, as lower the substitution, as better the test results. The partial substitution of natural aggregate by coarser fractions requires experimental verification; over 20%substitution of natural aggregate by 4/8, 8/16 or 0/16 RCA should be excluded.

Study on green concrete replacing natural fine and coarse aggregate by plastic waste – An experimental and machine learning approach

One of the most universally used materials in construction industries is concrete because of its accessibility, affordability, extended lifespan and resistance to damage against unfavourable weather conditions. However, there is a massive depletion of valuable natural resources for the concrete production. Further, plastic consumption as well as waste generation is increasing day by day which is very much challenging to be managed as it is non-biodegradable and creates various environmental pollution. Thus, the usage of plastic waste as a fractional substitution of natural aggregates in construction industry may mitigate the problems. For the present study, nine concrete mixtures of M30 grade concrete containing recycled plastic waste polyethylene (RPE) and plastic waste polyethylene-terephthalate (WPET) were prepared as a fractional volumetric replacement for both natural coarse aggregates (NCA) and fine aggregates (NFA). The replacement levels were 0%, 5 %, 10%, 15%, 20%, 25%, 30%, 35% and 40% keeping constant the water-cement ratio (0.37).The usage of waste plastic aggregates for preparation of concrete were assessed through different fresh and hardened properties like slump, dry density, compressive strength (CS), flexural strength (FS), split tensile strength (STS) and ultrasonic pulse velocity. The test results corroborates that the slump increased with higher percentage replacement of waste plastic aggregate (PA) in concrete. Further, incorporation of WPET and RPE in concrete reduced the dry density by 10.59 % at 40% mix proportion. It is to be mentioned that, the CS decreases with with increase of partial replacement of natural aggregate with waste PA. The ultrasonic pulse velocity (UPV) also decreased with increase of the PA. The test result also depicted that up to 5% replacement the STS value is almost constant, after that it reduces. Further, in case of FS test, the replacement with waste PA concrete by 10%, the FS improved to 19.91%. Furthermore, the data prediction models of slump, CS, FS and STS were developed by artificial neural network. Moreover, the optimization of mix proportion was conducted by factor response optimizer with composite desirability of 0.65.

Influence of Recycled Plastic Incorporation as Coarse Aggregates on Concrete Properties

Plastic waste has increased significantly in recent years as a result of fast population growth and urbanization. Studies on the incorporation of plastic aggregates as a substitution for natural aggregates in concrete are needed to successfully reduce both adverse environmental impact and the depletion of natural resources. The objective of this research was to investigate the use of plastic as a partial substitution for natural coarse aggregates in concrete. For this purpose, seven concrete mixes were produced using 0, 10, 15, and 20% plastic coarse aggregates to replace natural aggregates with and without silica fume of similar replacement levels with cement. Fresh density, workability, compressive strength, splitting tensile strength, stress–strain response, and Poisson’s ratio were observed to study the fresh as well as hardened properties of concrete mixtures. Indoor and outdoor thermal performance and thermo-gravimetric analysis were also investigated. The results revealed that the plastic aggregates’ incorporation improved the workability of concrete; however, it negatively influenced the fresh density and mechanical properties of concrete. The compressive and tensile strengths of plastic aggregate concrete without silica fume were reduced by 32 and 33%, respectively. The reduction in strength could be associated with the smooth texture of plastic aggregates. The addition of silica fume with plastic aggregates resulted in denser concrete and improved mechanical properties. In general, the performance of plastic aggregates as a partial replacement for natural aggregates was satisfactory, which suggests their possible use to produce eco-friendlier concrete.

Performance assessment of recycled aggregate concrete and its variability

AbstractThe use of recycled aggregate improves waste management and is a crucial step toward the sustainable development of the concrete industry. Hence, this paper presents the experimental investigation to determine the mechanical properties of concrete with recycled concrete aggregates as the selective substitution for natural aggregates. The slump was observed to decrease by replacing natural coarse aggregates with recycled concrete aggregates. Compressive strength of about 40 MPa was achieved after 56 days of curing with the utilization of 100% recycled concrete aggregates. Besides, a reduction in the splitting tensile strength of 14% was observed due to the incorporation of recycled concrete aggregates. The statistical techniques use various probability distribution models such as Gamma, Lognormal, Weibull, and Normal distributions. Amongst the considered functions, lognormal and Weibull distributions best represent the experimentally obtained compressive strength of concrete with 100% natural aggregates and 50% recycled concrete aggregates, respectively. However, for concrete with 100% recycled aggregates, Weibull distribution represent compressive strength after 28 days of curing, and lognormal distribution is given the best fit for the compressive after 56 days of curing. In the case of split tensile strength, lognormal distribution provided the best representation after 56 days of curing for all specimens.