Production Of New Concrete Research Articles

FEATURES OF USING CRUSHED CONCRETE AS A COARSE AGGREGATE FOR CONCRETE

Problem statement. According to the results of a study by the Kyiv School of Economics as of June 2023 the total amount of direct documented damage to residential and non-residential infrastructure due to destruction and damage as a result of military actions exceeded $150.5 billion. During the post-war reconstruction Ukraine will face the problem of a large number of buildings and structures that will be subject to partial dismantling and demolition. This process will be accompanied by the generation of a significant amount of construction waste, which traditionally in Ukraine is taken to landfills without recycling. On the other hand, there will be a need for a large quantity of construction materials, the share of which in the construction cost may reach 50 %. To reduce the cost of objects, it is advisable to reuse materials from waste generated after dismantling. Such materials are called recycling. The most obvious option is the use of crushed concrete waste as a coarse aggregate for the production of new concrete. The purpose of the article. Identification of the features of recycled coarse aggregates from concrete waste and concrete with their use, determination of the influence of source concrete on the properties of recycled aggregates. Conclusions. The mesoscopic model of concrete with recycled coarse aggregate has been examined. The analysis of the current research results on both recycled concrete aggregates and concrete with their use showed that, in general, with correct calculations of concrete mix compositions that consider the actual physical and mechanical properties of recycled aggregates, the production of structural concrete is possible. At the same time, crushing methods and the grain composition of such aggregates have a significant influence. In order to standardize the approaches to the research of recycled aggregates, it is necessary to create an appropriate methodology or regulatory framework.

Influence of natural fiber rope wrapping techniques on the compressive response of recycled aggregate concrete circular columns

The utilization of recycled waste in the production of new concrete raises significant concerns regarding the quality of the resulting concrete. One prominent drawback of recycled aggregate concrete (RAC) is its inferior mechanical properties compared to natural aggregate concrete. In this study, we examine the impact of hemp fiber rope (HFR) confinement on improving the compressive stress-strain behavior of RAC, specifically using recycled brick aggregates from fired-clay solid bricks (RAC-FCSB) as a partial substitute for natural coarse aggregates. Furthermore, we explore and compare the effectiveness of HFR confinement in the form of strips versus fully wrapped confinement. To conduct the experiments, a comprehensive framework was developed, involving a total of 32 cylindrical specimens. The parameters of interest included the configuration of HFR confinement (strips or full wrapping), the number of HFR layers, and the inherent strength of the concrete. The results indicate that HFR strips can significantly enhance the compressive stress-strain response. However, their performance falls short when compared to the fully wrapped HFR confinement. Nonetheless, HFR strips were able to enhance the peak compressive stress and strain of RAC-FCSB up to 204% and 190%, respectively. The second part of the study investigated the performance of existing models of HFR confinement in predicting the peak compressive stress and strain of RAC-FCSB. The deficiencies in existing models were highlighted, and new models based on non-linear regression analysis were proposed to accurately predict the peak compressive stress and strain of HFR-confined RAC-FCSB.

Predictive Modeling of Recycled Aggregate Concrete Beam Shear Strength Using Explainable Ensemble Learning Methods

Construction and demolition waste (CDW) together with the pollution caused by the production of new concrete are increasingly becoming a burden on the environment. An appealing strategy from both an ecological and a financial point of view is to use construction and demolition waste in the production of recycled aggregate concrete (RAC). However, past studies have shown that the currently available code provisions can be unconservative in their predictions of the shear strength of RAC beams. The current study develops accurate predictive models for the shear strength of RAC beams based on a dataset of experimental results collected from the literature. The experimental database used in this study consists of full-scale four-point flexural tests. The recycled coarse aggregate (RCA) percentage, compressive strength (fc′), effective depth (d), width of the cross-section (b), ratio of shear span to effective depth (a/d), and ratio of longitudinal reinforcement (ρw) are the input features used in the model training. It is demonstrated that the proposed machine learning models outperform the existing code equations in the prediction of shear strength. State-of-the-art metrics of accuracy, such as the coefficient of determination (R2), mean absolute error, and root mean squared error, have been utilized to quantify the performances of the ensemble machine learning models. The most accurate predictions could be obtained from the XGBoost model, with an R2 score of 0.94 on the test set. Moreover, the impact of different input features on the machine learning model predictions is explained using the SHAP algorithm. Using individual conditional expectation plots, the variation of the model predictions with respect to different input features has been visualized.

Dynamic fractures of concrete made of recycled aggregate or reinforced with fibres

In recent decades, there has been a lot of interest in using construction waste as a source of aggregate for the production of new concrete. Another topic of intense study is the optimal characteristics of reinforcing fibres. However, in contrast to the constant value of the static strength, it is widely known that the dynamic strength of concrete is highly dependent on the strain rate. The wide variety of possible concrete additives further complicates the assessment of the dynamic strength of concrete. Therefore, it is necessary to search for new material parameters that will allow evaluating and comparing the dynamic strength of concrete with various modifications of additivities. In this work, the effects of recycled aggregate and fibres on the fracture critical stress of original, natural aggregate concrete were studied using the incubation time criterion. It was confirmed that by estimating only one additional parameter, the incubation time, which is responsible for the preparatory processes of fracture and is invariant with respect to the history of loading in dynamic and static tests, it is possible to construct the stress/strain rate dependences of the critical stress. The intersections of the theoretical rate dependences of the critical fracture stress under static and dynamic loading considering various percentages of recycled aggregate (from 0% to 100%) and carbon, steel, and synthetic fibres were analysed. The decrease in the dynamic strength of steel- and carbon-fibre-reinforced concretes was interpreted in terms of a change in the incubation time characteristic. The influence of the fibre shape on the strain rate sensitivity of steel- and synthetic-fibre-reinforced concretes was analysed. It is here shown that the incubation time parameter can be considered to be a convenient tool for assessing the influence of recycled aggregate or fibres on the dynamic strength of concrete.

Traffic, environmental and economic optimization of the recycling of concrete waste

The recycling of concrete waste is becoming increasingly important as a contribution to conserving resources and reducing mineral construction waste. Currently, concrete is mainly reused in a subordinate application area (downcycling), such as earthworks or road construction, or disposed (Kreislaufwirtschaft Bau 2021). Due to this, natural raw materials have to be mined for the production of new concrete, although there are processing techniques that allow the use of concrete waste for concrete production.This paper deals with the optimization of plant locations for the recycling of concrete waste. Taking the city of Cologne as an example, the recycling process is balanced with regard to the use of natural resources and CO2 emissions of the freight transport. This makes an important contribution to the conservation of natural resources and to climate protection.

Upgrading of demolition concrete into new construction concrete

In Morocco, buildings, road and urban infrastructure are ageing relatively quickly and often require renovation or demolition work. The large amount of demolition rebus generated is a considerable challenge that will have to be buried or reused. The reuse of these materials is an important aspect of their management, especially as regulations concerning landfill sites are becoming increasingly restrictive. Another challenge facing the construction industry is the reduction of natural aggregate sources due to the high demand for raw materials. The use of demolition concrete as recycled aggregates in new concrete is a promising solution in the current context of sustainable development. However, it should be noted that the properties of recycled aggregate concrete are different from those with natural aggregates, mainly their porosity, density and resistance. These differences are attributed to the cement mortar that adheres to natural aggregate particles, constituting an aggregate in itself.This work aims to study the influence of using a combination of Fine Recycled Aggregates (FRA) and Coarse Recycled Aggregates (CRA), with Natural Aggregates (NA). Since the use of the recycled coarse fraction in the production of new concrete may have revealed good performance in recycled concrete, the use of the recycled fine fraction remains still very limited, due to its absorptive capacity by reference to previous bibliographic studies. In order to improve the quality of Recycled Concrete (RC), this work also seeks to study a new crushing alternative that favours less adhered mortar.

INCORPORATION OF ADMIXTURES IN RECYCLED AGGREGATE CONCRETE: A REVIEW

The huge amount of annual concrete production poses significant harmful environmental impact. The demand for construction and concrete production consequently results in a huge demand for natural aggregate thereby causing great concerns for aggregate availability. Recycling waste concrete which often times end up in landfill is one of the major solutions to reduce its environmental effects. Waste concrete are crushed to desired sizes and used as replacement for natural aggregate to a certain degree in the production of new concrete. A reduction in strength has been reported after various researches with most recommending an optimum replacement percentage of 30% beyond which are decline in strength properties is evident. Thus, it becomes necessary to improve this performance and increase the amount of concrete waste reduction. To produce highperformance concrete, early researchers altered the watercement ration to achieve the desired results. Thereafter, they employed the use of chemical and mineral admixtures alongside specialised production process. In addition to performance improvement, Mineral admixture will function to substitute or reduce the consumption of Portland cement leading to a low impact, less energy consuming building material. This paper reviews the effect of admixtures on the mechanical properties of recycled aggregate concrete and possible areas for future research were identified and recommended.

Test and Evaluation of the Flexural Properties of Reinforced Concrete Beams with 100% Recycled Coarse Aggregate and Manufactured Sand

Although studies have been performed on the recycled aggregate made of waste concrete for the production of new concrete, the new concrete with 100% recycled coarse aggregate and manufactured sand (abbreviated as RAMC) still needs to be researched for structural applications. In this paper, an experimental study was performed on seven groups, including fourteen reinforced RAMC beams under the simply supported four-point loading test, considering the factors of the strength of RAMC and the reinforcement ratio of longitudinal tensile rebars. Based on the test results, the cracking resistance, the bearing capacity, the crack width, the flexural stiffness and the mid-span deflection of reinforced RAMC beams in bending are discussed and examined by using the formulas of conventional reinforced concrete beams. Results show that an obvious effect of reinforcement ratio was present, while less so was that of the strength of RAMC. With the comparison of predicted values by the formulas of conventional reinforced concrete beams, the reinforced RAMC beams decreased cracking resistance by about 20%, increased crack width by about 15% and increased mid-span deflection by about 10%, although the same bearing capacity can be reached. The results directly relate to the lower tensile strength of RAMC which should be further improved.

Novel metaheuristic-based type-2 fuzzy inference system for predicting the compressive strength of recycled aggregate concrete

The use of recycled concrete aggregate (RCA) in the production of new concrete can provide several environmental benefits and reduce the pressure on natural resources. Due to the differences in the properties of RCA and natural aggregate, the properties of recycled aggregate concrete (RAC) (i.e., concrete containing RCA) are different from those of normal concrete. Compressive strength (CS) of the RAC, which is a key parameter in many design codes, can be determined either through expensive and time-taking laboratory-based procedures or using empirical relationships. In this study, two types of hybridized machine learning algorithms (i.e., type-1 fuzzy inference system (T1FIS) and interval type-2fuzzy inference system (IT2FIS)) were used to develop predictive models for the CS of RAC. Moreover, arithmetic optimization algorithm (AOA), as a novel optimization algorithm, was employed to optimize the parameters of FIS models. To develop the CS predictive models, a dataset containing information on 1868 data records was used. The results indicate that the IT2FIS model outperformed the T1FIS model. A comparison of the results of this study with those reported in previous studies also confirms the high accuracy of the IT2FIS model. The findings indicate that concrete age, natural fine aggregate to total natural aggregate ratio, and superplasticizer to binder ratio have positive impacts on the CS, while the remaining input variables have negative influences on the CS. Regarding the intensities of the variables, concrete age, total coarse aggregate to cement ratio, and water to binder ratio are in the first to third orders, respectively.

Prediction of Compressive Strength of General-Use Concrete Mixes with Recycled Concrete Aggregate

This paper presents the mechanical behaviour of concrete mixes made with recycled aggregate by replacing the natural aggregate with crushed concrete from pavement demolition. The purpose of this study was to determine the feasibility of using recycled aggregate from pavement demolition to make new concrete for pavement applications. Considering a control mix without recycled aggregate (RCA0) designed for a compressive strength of 34 MPa, two types of concrete mixes with 50% (RCA50) and 100% (RCA100) replacement percentage of natural coarse aggregate by recycled aggregate were made. The resulting concrete specimens were tested at three different curing ages, 7, 14, and 28 days. The results of this study showed that the compressive and flexural strengths decreased for all two mixes as the recycled aggregate content increased, while the density was slightly affected. A new model based on multiple linear regression analysis of the data from this study and other 14 studies from the literature was developed. The model can be used to predict the compressive strength of general-use concrete mixes with recycled aggregate (20–40 MPa) considering both the recycled aggregate content and the curing age of concrete. A good correlation was found between the compressive strength and the two parameters investigated. Given the predictions of this model, it is recommended not to use more than 30% recycled concrete aggregate in the production of new concrete in order not to affect its strength.

The compressive behaviour of natural and recycled aggregate concrete during and after exposure to elevated temperatures

Applications of recycled concrete aggregate (RCA) in the production of new concrete can help in addressing the growing solid waste challenge and preserving natural aggregate resources from depletion. The behaviour of RCA concrete under different loading scenarios is a well-studied topic at both material and structural levels. However, little attention has been directed at studying the performance of concrete made with RCA at elevated temperatures. Most of the previous studies have focused on the residual mechanical response of coarse RCA concrete after exposure to elevated temperatures. This paper presents an experimental study on the behaviour of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC) during and after exposure to elevated temperatures. The RAC in this study contained both coarse and fine recycled concrete aggregates (CRCA and FRCA) as partial replacements of natural aggregates. The compressive strength of the NAC and RAC were evaluated at ambient temperature (unheated), after exposure to three different temperatures of 150, 300, and 450 °C (residual), at an elevated temperature of 450 °C without preloading (steady state), and during heating while being preloaded with 40% and 70% of the ambient strength (transient). A rate of 2 °C/min was used in all these heating scenarios. The results indicated that concrete with aggregates partially replaced with CRCA and FRCA exhibited good performance at elevated temperatures, and it can be considered comparable to conventional concrete. The results also showed that the compressive strengths measured during elevated temperatures, with or without preloading, were relatively higher than the residual compressive strengths for both RAC and NAC. The total thermal strains were also investigated with Digital Image Correlation. Preloading had an impact on the evolution of the total thermal strains and the occurrence of spalling for the types of concrete that were tested.

Mechanical Properties of Concrete Made of Crushed Concrete Subjected to Different Fire Durations (Dept.C)

The amount of construction and demolition waste has increased considerably over the last few years. The heaviest materials found in construction and demolition waste are rocks, concrete and ceramic residues. Nowadays, almost all demolished concrete has been mostly dumped to landfills. From the viewpoint of environmental preservation and effective utilization of resources, the interest in using recycled materials derived from construction and demolition waste is growing all over the world. Crushing concrete to produce coarse arrregate for the production of new concrete is one common means for achieving a more environment-friendly concrete. This reduces the consumption of the natural resources as well as the consumption of the landfills required for waste concrete. From the durability point of view, the performance of recycled concrete exposed to fire or high temperatures is not a very well-known subject since this property has been widely studied on conventional concretes. Such performance is related to the temperature level reached at the surface and interior of the material, the time of exposure. Also, the concrete's own characteristics such as w/c ratio, type of natural aggregate used. In the experimental work, the fresh properties (slump test) and the hardened properties, (compressive strength, splitting tensile strength, and flexural strength) were carried out. A total of thirty concrete mixes with different cement contents (300, 350, and 400 Kg/m3) at w/c ratio (0.5) were made and the percentag of substitution of natural narse aggregate by the recycled concrete aggregate subjected sto fire temperature 600°C for (1, 2, and 3 hours) was (0%, 25%, 50% and 100%). In the process of mixing, equal consistence among all concrete mixes was achieved. The obtained results indicate that the recycled coarse aggregate subjected to fire can successfully be used for making structural concrete.

Recycled aggregate concrete from large-scale production to sustainable field application

Concrete waste is the most prominent construction and demolition waste generated by the construction industry, which is mainly disposed to landfills. Recycling this waste in the form of recycled concrete aggregates (RCA) and substituting it for natural aggregates in the production of concrete could lead to environmental conservation. A growing body of literature in lab settings has already recognized the importance of utilizing RCA in the production of new concrete. However, intense utilization of RCA in the large-scale industrial production of new concrete (structural and non-structural) is not widely accepted by international standards due to its high porosity, a disparity of source concrete and lack of territorial field studies. In this paper, two full-scale field studies of the foundation system and municipal sidewalk constructed with recycled aggregate concrete (RAC) are presented. In addition to this, the long-term performance of RAC examined for 5 years in terms of in-place compressive strength is reported. Moreover, strength correlations developed specifically for RAC for the estimation of compressive strength based on rebound numbers are discussed. This study shows that RCA has significant potential of using as substitution of natural aggregate in the production of concrete of 25 and 32 MPa compressive strength. Furthermore, RAC shows a higher rate of compressive strength development after 28 days of curing and results in comparable long-term compressive strength to conventional concrete. By providing an insight into the sustainable application of RCA in the production of new concrete, the results of this study can serve as a basis for updating the current standards in Canada.

Seismic Behavior of Reinforced Concrete Members Built with Recycled Aggregate

In connection with rapid urbanization and earthquakes, a huge number of structures have been demolished and generated lots of waste concrete for the last 40 years. Studies on the reclamation of the waste concrete is a pioneer subject for construction sectors in the world. Since the recycling of the waste concrete and reusing of recycled concrete aggregate in the production of new concrete is an important issue for saving of natural resources, economic, sustainable development, significant number of studies have been carried out on this subject. In the scope of this study, a literature review is conducted on the effect of recycled concrete aggregate on mechanical and durability characteristics of small-scale members. Furthermore, structural and seismic performances of full-scale reinforced concrete structural members produced with recycled concrete aggregate are discussed. The test results indicated that the structural members containing recycled aggregate exhibited similar structural performance with their counterparts containing natural aggregates. It was also observed that recycled concrete aggregate did not seem to have an adverse effect on seismic characteristics of the structural members such as ductility.

Durability and Structural Performance of Recycled Aggregate Concrete: a Review

The waste generated from construction and demolition is considered the major waste produced in the world in terms of the volume. This waste can be recycled and reused in the production of new concrete for new construction projects such as roads, buildings and bridges. This can help in reducing the need for new natural materials such as coarse and fine aggregate, reduce the overall construction project cost and enhance the environment, which is gaining more attention and being encouraged by most world countries these days. Recycled aggregate concrete (RAC) is being investigated in research and used in many construction projects over the last 20 years. In this paper, a detailed review of recent research conducted on RAC in terms of concrete durability, characteristics and structural performance under different loading conditions is presented. Finally, conclusions and future trends of research associated with RAC are presented in order to efficiently promote more use of RAC.

Recycled coarse aggregates from pelletized unused concrete for a more sustainable concrete production

A significant amount of the concrete produced worldwide is returned unused to production plants and has the potential to cause serious damage to natural soils and waters.This study proposes the use of a new pelletization process to convert fresh unused concrete into an artificial aggregate, which can be reintroduced into the concrete production cycle. Specifically, the investigation focuses on the properties of two pelletized recycled aggregates (PRAs) derived from two sources of an unsettled cementitious mixture. This research is based on the hypothesis that properties of the returned concrete may affect the characteristics of PRAs.PRAs were evaluated by particle size distribution, particle density, water absorption, resistance to fragmentation, and chemical and mineralogical analysis. Test results confirm that the concrete influences some properties of PRAs, and that PRAs exhibit different properties to those of conventional aggregate. However, it can be reused in place of natural coarse aggregate in the production of new concrete.

Role of lime, fly ash, and slag in cement pastes containing recycled concrete fines

Construction and demolition waste recycling for production of new concrete is usually limited to the use of coarse aggregates, and efficient utilization of fine subsieve fractions remains an unresolved issue. In the presented research, Portland cement pastes containing 50% finely ground recycled concrete, blended with lime, fly ash, or blast furnace slag, were studied. SEM-BSE microscopy, EDX analysis, and porosimetry were employed for investigating their microstructure, individual stages of hydration were detected using calorimetry, shrinkage was optically monitored in the early stages of hardening, the evolution of Young’s modulus was assessed using the resonance method, and strength was determined from destructive tests. The study suggests that recycled concrete fines can be incorporated into cementitious composites in large amounts and even improve their properties, especially when blended with fly ash or blast furnace slag. Substitution of Portland cement in the studied pastes by recycled concrete led to a compressive strength deterioration, but also a reduction of shrinkage, and an increase of the tensile strength in bending by up to 26%.

Suitability Investigation of Recycled Concrete Aggregates for Concrete Production: An Experimental Case Study

In developing countries, construction and demolition waste (CDW) is disposed to landfill, causing social, environmental, and economic crises. In these nations, CDW exponentially increase due to their rapid economic growth, industrialization, and urbanization. This paper aims to examine the possibility of recycling concrete waste for production of new concrete in Ethiopia. Physical and mechanical characteristics of recycled concrete aggregate (RCA) acquired from concrete waste are thoroughly examined. Though the RCA exhibited relatively lesser performance compared with the natural coarse aggregate (NCA), it reveals the same properties as of normal-weight aggregates in several instances. The performance of concrete specimens which employ RCA up to 20% is evaluated from workability, strength, and permeability aspects. The utilization of RCA slightly affects the workability and the water permeability properties of the concretes. Replacement of 10% of the NCA by the RCA enhances the compressive strength of the hardened concrete by 8%. The difference between the splitting tensile strength of the concretes which employ RCA and conventional aggregates is trivial. Generally, this work demonstrates the practicability of concrete waste recycling to produce new concrete or construction materials in Ethiopian context.

Performance of mortar prepared with recycled concrete aggregate enhanced by CO2 and pozzolan slurry

One of the most promising strategies to manage the large volume of construction and demolition (C&D) waste is recycling and utilizing it for the production of new concrete. However, recycled concrete aggregate (RCA) derived from C&D waste possesses relatively higher porosity and water absorption capability, which often limits its wild utilization. In this study, pozzolan slurry (includes silica fume, nano-SiO2, and fly ash slurries) and CO2 treatments as enhancement methods for RCA were investigated. Test results showed that CO2 treatment was more effective in reducing water absorption and enhancing fluidity, whereas pozzolan slurry treatment could decrease fluidity. Mortars prepared with treated RCA exhibited better mechanical strength and higher resistance towards carbonation and chloride-ion diffusion than those with untreated RCA. Both pozzolan slurry and CO2 treatments enhanced not only the properties of RCA, but also the old and new interfacial transition zones (ITZs) as demonstrated in the measured micro-hardness and SEM observation.

Concrete based on recycled aggregates – Recycling and environmental analysis: A case study of paris’ region

The use of recycled concrete aggregates as an alternative source of coarse aggregates for the production of new concrete can help to solve the problem of depleting natural resources and that of growing waste disposal crisis. However, their recycling could decrease the concrete performance, particularly for low grade recycled aggregates (RA). To compensate for this decrease, cement content can be adjusted and hence, the environmental interest of RA has to be assessed. This study aims at assessing the environmental footprint of recycled aggregate concrete (RAC), compared to natural aggregate one (NAC), considering the grade of used RA and the aggregates’ delivery distance, at the scale of Paris’ region.From the strength point of view, the use of RA induces a decrease of RAC performance, which is proportional to their content. This decrease can be compensated for by increasing cement content. For 50% of RA dosage, 16% of additional cement is necessary to achieve the compressive strength of NAC, when low-grade-RA are used (RA_1). Recycling high grade RA (RA_2 and RA_3), affects slightly RAC compressive strength and 3% of additional cement are enough to compensate for its decrease. Pre-saturating these RA, reduces by 35% the amount of additional cement.From an environmental point of view, recycled aggregates can be an alternative for natural ones and the environmental footprint of RAC can be limited by using high grade RA. Furthermore, the delivery distance of NA is the key parameter in assessing the environmental impacts of RAC, compared to NAC. Results showed that global warming indicator impact is greater for NAC, compared to RAC with 50% of RA, provided that NA delivery distance exceeds 50km, which is the case in Paris’ region. With 20% of substitution rate, high-grade RA improve all environmental impacts of RAC, except Waste, compared to NAC.