Properties Of Recycled Aggregate Research Articles

Influence of pore property and alkalinity on the bio-deposition treatment efficiency of recycled aggregates

Microbial induced calcium carbonate precipitation (MICP) technology has been successfully used to enhance the properties of recycled concrete aggregates. However, the complex source and varied physical and chemical properties of recycled aggregates may have influence on the modification efficiency since microbes are often sensitive to the surroundings. In this study, two representative types of recycled aggregates, recycled concrete aggregates (RCA) and recycled brick aggregates (RBA), were subjected to two kinds of MICP treatments, basic MICP treatment and sodium alginate (SA) aided MICP treatment. The absorption and desorption of bacteria in/on aggregates during MICP treatments were quantified. The physical and chemical properties of aggregates after the bio-treatments were tested, and the influence of alkalinity and pore structure of aggregates under various MICP treatment methods on treatment efficiency were detailed investigated. Results indicated that, when the aggregates were subjected to the basic MICP treatment, the treatment efficiency was more remarkable in RBA, because of its high porosity and moderate pH (around 8–9), which facilitated the absorption of bacteria in/on aggregates and urease activity respectively. While under SA-aided MICP treatment, the influence of pore structure and alkalinity of aggregates on the treatment efficiency was not significant compared with that under the basic MICP treatment, especially the mass of CaCO3 on the aggregates. The biogenic CaCO3 generated by SA-aided MICP treatment not only plugged micropores, but also distributed all over the entire surface of the aggregates, resulting in a sufficient repair of microcracks. Meanwhile, the surface repair may reduce the influence of pore structure and pH of aggregates on the precipitation process, thereby reducing the impact of varied physical and chemical properties of aggregates on the treatment efficiency, which was conducive to the widely unified application of SA-aided MICP treatment in the modification of recycled aggregate based on construction solid waste.

Technical and environmental properties of recycled aggregates produced from concrete sludge and excavation materials

This study presents a Re-Con Zero dry washing technology used to produce recycled aggregates from concrete sludge (RCZ) and combined as a feedstock in wet recycling excavation materials (EM) for unbound applications. A two-component admixture i.e, high water absorbing polymer and aluminum sulphate was used in producing RCZ. RCZ0, RCZ50 and RCZ100 were produced with EM within the range 0–100%. Analysis by the Los Angeles (LA) and micro-Deval (MD) test demonstrated RCZ to be of high-quality, hence a clear trend of improved performance as the content increased was observed in the LA and MD values. X-ray diffraction analysis performed on original and pulverized residues (<1.6 mm) showed that feldspar, quartz, phyllosilicates (mica and chlorite) and minor amounts of pyroxene (diopside) were present together with paste minerals such as portlandite and residual clinker, and calcite. Acid solubility results demonstrated the relation to increased paste content as particle size reduced. This observation was more prevalent in < 1.6 mm RCZ fraction which further indicated the significant amount of remained paste after wet treatment. Low levels of the content of chemical species of potential concern were in general found and were mostly complying to Norwegian regulations. Total Cr exceeded the criteria of 100 mg/kg, but the leachable Cr(VI) was not detected which showed that remaining Cr after recycling process was present mostly on the trivalent form. This indicated low leaching of Cr upon carbonation and a decrease in pH.

Changing the soaking method of microbially induced calcium carbonate precipitation technology to improve the reinforcement effect of recycled concrete aggregates

In this study, the effects of the soaking method employed during the concrete reinforcement process on the properties of recycled concrete aggregates (RCAs) with different particle sizes were investigated based on biodeposited calcium carbonate technology. The microstructure and properties of RCAs and the macroscopic properties of recycled aggregate concrete (RAC) before and after the enhancement treatment were studied. The results showed that the presoaked bacterial solution can improve the reinforcement of RCAs, and the best performance of RCAs was obtained after reinforcement by soaking twice (first time, soaking RCAs into nutrient solution after presoaking with the bacterial solution (Method B), the next time soaking RCAs directly into mixed culture solution (Method A)). After immersing twice, the biodeposited calcium carbonate reinforced the defects of RCAs and coated the surface of RCAs. The mechanical properties of RAC were significantly improved owing to the use of the enhanced RCAs, and the RCAs with secondary soaking treatment endowed the concrete with superior mechanical performance.

Modeling the mechanical properties of recycled aggregate concrete using hybrid machine learning algorithms

To explore the complicated functional relationship between key parameters such as the recycled aggregate properties, mix proportion and compressive strength of recycled aggregate concrete (RAC), a complete database involving 607 records from relevant published literature was built. Two standard algorithms (artificial neural network (ANN) and support vector regression (SVR)) and two optimized hybrid models (Particle Swarm Optimization based SVR (PSO-SVR) and grey Wolf optimizer based SVR (GWO-SVR)) were adopted. Furthermore, two interpretable algorithms (Partial Dependence Plot (PDP) and SHapley Additive exPlanations (SHAP)) were utilized to assess the global and local approaches independent of machine learning models, contributing towards decision-making rationales. Results indicated that the coefficient of determination (R2) of ANN, SVR, PSO-SVR and GWO-SVR were 0.7569, 0.5914, 0.8995 and 0.9056 respectively, showing that hybrid models outperformed the conventional models. However, GWO-SVR was the most problematic with overfitting when analyzing its three subsets. The two feature importance analyses revealed cement content, water content, natural fine aggregates, and water absorption as significant characteristics that affect mechanical performance.

Durability Characteristics of Recycled Aggregates for Physical and Chemical Properties of Concrete

In structural concrete, it becomes essential to perform the comprehensive research work for recycled aggregates (RA) in order to check their material properties as well as assess the influence the second-generation concrete quality. This work has the objective to assess and suggest the technical standards to check the performance and behaviour of concrete as compressive strength developed from recycled aggregates. The demolished crushed waste concrete can provide the RAs. Such aggregates are heterogeneous in composition from a quality point of view as being resultant from diverse adhered mortar and materials. Such properties of RAs must be assessed, as these are utilized in concrete; consequently make an effort to further investigate the RAs characteristics that are needed to be implemented in concrete mixes. This paper presents the characteristics of RAs as physical and chemical properties with further examination on the concrete properties prepared with RAs. It also presents the comprehensive strength to show the durability properties in order to set the standard guidelines. The developed nations such as Japan have even laid down standards for RA usage in concrete. Thus, it becomes essential to make guidelines for the material utilization in construction, especially to match with the local Indian conditions.

Coefficient of Thermal Expansion of Concrete Produced with Recycled Concrete Aggregates

This study presents a comparison between the coefficient of thermal expansion (CTE) of concrete produced with natural aggregate and that of concrete produced with recycled concrete aggregate. In order to achieve this, natural aggregate concrete (NAC) specimens were produced, tested, then crushed and sieved in the laboratory to obtain recycled concrete aggregates, which was then used in the production of recycled aggregate concrete (RAC) specimens. The RAC samples were then tested and compared to the NAC samples. The CTE testing was carried out using a AFTC2 CTE measurement system produced by Pine Instrument Company. In addition to CTE testing, the water absorption, specific gravity, and unit weight of the aggregates was determined. A vacuum impregnation procedure was used for the water absorption test. The recycled aggregate properties showed a significantly higher absorption capacity than that of the natural aggregates, while the unit weight and specific gravity of the recycled aggregate were lower than that of the natural aggregates. The average CTE results showed that both the NAC and the RAC samples expanded similarly. The results show that the CTE of RAC depends on the natural aggregate used in the NAC, which was recycled to produce the RAC. Also, there was no significant difference between the average CTE values of the RAC and that of NAC that could discredit the use of recycled aggregate in concrete.

A Comparative Study on Mortar Removal Methods and their Influence on Recycled Aggregate Properties

The adhered mortar attached to recycled aggregate (RA) is one of the main causes of weakening the mechanical properties and durability performance of recycled aggregate concrete (RAC). Therefore, in order to improve the performance of RA and RAC, several methods have been proposed to remove the adhered mortar in RA. However, knowing the adhered mortar content is as important as removing it. This is because concrete mix designs considering the amount of adhered mortar have been proposed and better strength, durability and environmental benefits of these mix designs were reported compared to conventional RAC mix design. Therefore, in this study, the adhered mortar was removed by using two methods of ‘acid treatment’ and ‘chemical and mechanical stress treatment’ for three types of RA, and the test results obtained from each method were comparatively analyzed. The results showed that the adhered mortar contents determined by the two methods were different for the same aggregate, and neither allowed the complete removal of the adhered mortar from RA. It also showed that the test environment of the chemical-mechanical stress method can be harsh enough to damage the original aggregate in RA, and that the acid treatment can cause corrosion of RA depending on the type of aggregate.

Evaluation of Korean recycled aggregates as backfilling underground power system considering particle breakage effect

Attempts have been made to address the strict regulations on eco-friendly construction and recycle aggregate resources, encouraging researchers to consider the utilization of recycled aggregates for the backfilling of underground power systems. It is essential to recognize the physical and thermal characteristics of domestic recycled aggregates for use as backfill materials for underground power conduits in Korea. Herein, the thermal properties of concrete-based recycled aggregates with different grain-size distributions are evaluated, and the particle breakage effect of recycled aggregates is identified through the compaction tests. The thermal properties of the recycled aggregates and the river sand were measured using a transient hot wire method after a standard compaction test. The particle breakage effect was also investigated during the standard compaction test. The thermal resistivities of the recycled aggregates and the river sand showed a similar trend, which were decreased with an increase in the water content at the same dry unit weight. In addition, particle breakage during compaction led to an enhanced compaction effect, reducing the thermal resistivity and increasing the fine particle content. This study shows that the recycled aggregates can be promising backfill materials that substitute natural aggregates when backfilling underground power conduits.

Multi-recycled aggregate concrete towards a sustainable solution – a review

Reduce, reuse and recycle are the important facets of susta-inable construction and environmental recovery. Increase in the construction activity generates huge amount of construction and demolition waste worldwide, and has a potential to be used as concrete coarse aggregate. In the future, where, most of the cities are likely to become concrete jungles, recycling and multi-recycling of concrete becomes all the more important. Also, the precast industry generates large amount of wastes due to discrepancies in quality of materials. Instead of depositing them as landfi lls or rejecting recycled materials, the possibility of reusing them is investigated and the fi nite number of times the recycling can be done, is examined. The present paper ponders on literature works, done by various researchers to check the variation in properties of recycled concrete aggregate, after fi nite number of generations of recycling. The studies on fresh and hardened state properties of recycled aggregate concrete showed a decrease in quality, with respect to mechanical performance of newly made concrete. The recycled concrete aggregate from precast rejects performed equal to natural concrete and even showed slightly higher compressive strength than natural aggregate concrete and can be replaced up to 20% of natural aggregate, to produce the concrete of accepted quality. The third generation recycled concrete aggregate showed almost twice the amount of mortar as that of fi rst generation re-cycled concrete aggregate. It can be seen that the concrete can be recycled only a fi nite number of times. A relationship between strength and durability properties of recycled aggregate concrete of different generations was derived based on multi-linear regres-sion analysis.

Influence of hydraulic jigging of construction and demolition waste recycled aggregate on hardened concrete properties

abstract: Concern with the maintenance of natural resources has increased research about recycled aggregates for concrete production. However, the heterogeneity of recycled aggregates is one of the main constraints for their use in practice, because it can generate variability in concrete properties, hence reducing their final quality. Then, the jigging has been seen as a promising way of improving recycled aggregate quality. This paper aimed to evaluate its use for better application in concrete. A modified jig was used to sort recycled coarse aggregates. Concrete were produced with water/cement ratio from 0.5 and 100% of recycled coarse aggregate. The recycled aggregate properties upgrade were achieved and the results of compressive strength and modulus of elasticity of recycled concrete made with aggregate which were submitted to jigging were increased, indicating a potential application in wide scale.

Various treatment techniques involved to enhance the recycled coarse aggregate in concrete: A review

Due to the scarcity of natural aggregate, the construction and demolition waste are induced in structural concrete. The adhered mortar existing on the exterior of recycled aggregate tends to decrease the recycled aggregate properties. To remove the adhered mortar on recycled aggregate there are many kinds of treatment. In this present study, discussed the different treatment methods they are chemical treatment, mechanical grinding treatment or ball milling method, thermal treatment, chemical, and calcium metasilicate slurry, carbonation and wrapping methods, cement treatment, mineral additives, modified concrete mixer, and mineral admixtures, warm mix asphalt and hydrated lime, CO2 curing technique, silica gel techniques, waste oil, and asphalt emulsion, nanomaterials, super plasticizers, bio-deposition approach, silane-based water repellent, polymer solution. Each treatment method is discussed clearly and results are also discussed for every method. By treating the recycled aggregate with all treatment processes the physical, mechanical, and durability properties are improved when compared to untreated recycled coarse aggregate concrete. All the methods show their improved results from their treatment. Some of the treatment methods are Eco- friendly with the environment and low cost for treatment method.

An assessment of microcracks in the interfacial transition zone of recycled concrete aggregates cured by CO2

The effect of carbonation on the properties of recycled concrete aggregate (RCA) was investigated in this study. RCAs with diameters of 10–20, 20–30 and 30–40 mm were carbonised for 0, 7, 14 and 28 days. Scanning electron microscopy was used to measure the average microcrack width (Wc) in the interfacial transition zone (ITZ) of the aggregate and mortar in RCA, and the dependencies amongst Wc in the ITZ area and the mechanical properties of recycled aggregate concrete (RAC) were assessed. Experimental results show that carbonation treatment modifies the ITZ microstructure. Wc rapidly and slowly decreases during the early and later stages of CO2 curing, respectively. Wc of ITZ after 28 days of CO2 curing corresponds to 14.1–16.9% of that without CO2 curing. The small aggregate and large specific surface area can facilitate the absorption of additional CO2 by using RCA during carbonation and accelerate the decrease in Wc. Moreover, the mechanical properties of RAC (e.g. compressive strength and modulus of elasticity) increase with the decrease in Wc.

Virtual Revision on Compressive Srength of Conventional Concrete and Recycled Aggregate Concrete Consisting Treated Recycled Aggregate

Use of reused aggregate in concrete can be useful for the ecological protection and economical terms. The application of recycled has been started in many construction projects. Paper hear says the basic properties of recycled concrete aggregate. It similarly relates the properties with natural aggregate, similarly the properties of recycled aggregates concrete were also determined and explained here. For the concrete grades of M25 and M30, the recycled aggregate concrete is produced by changing the natural aggregate, by recycled aggregate in conventional concrete with 5%, 10% and 15% of weight of natural aggregates. Experimental studies were carried out on influence of recycled aggregate treatment and comparison of strength properties of conventional cement concrete and recycled aggregate concrete at the curing of 7days and 28 days. They are two types of treatments under the considerations for recycled aggregates are Abrasion of recycled aggregate and chemical immersion.

Properties of recycled aggregate concrete prepared with scattering-filling coarse aggregate process

RAC produced with crushed recycled aggregate (RA) is regarded as an environmental friendly material, while its high water demand, high mortar content and low modulus have restricted its application. Scattering-filling coarse aggregate (SFCA) process was applied to prepare the recycled aggregate concrete with promoted performance. With the reference of conventional concrete and the scattering-filling natural aggregate (SFNA) concrete, the influences of ratio, type, size and moisture state of RA on mechanical and durable properties of scattering-filling recycled aggregate (SFRA) concrete were investigated. The results indicate that SFCA process could improve the compressive strength, elastic modulus, and reduce the drying shrinkage and chloride penetration. The frost resistance of SFRA is comparable with the conventional concrete. With 10–20 mm scattering-filling aggregate of RA, SFCA concretes get more significant improvement on elastic modulus and anti-permeability; Higher water content of RA worsen the performance of recycled aggregate concrete (RAC) for water in the RA weakening ITZ; Furthermore, image processing analysis and microhardness indicated that SFCA process improve the properties by increasing the homogeneity of aggregate distribution and improving ITZ between the aggregate and cement paste in RAC. SFCA process provides an economic method to produce high-quality recycled aggregate concrete and an efficiently approach to the utilization of recycled concrete aggregate from Construction and Demolition waste.

Mechanical Properties and ITZ Microstructure of Recycled Aggregate Concrete Using Carbonated Recycled Coarse Aggregate

The effect of carbonation treatment and mixing method on the mechanical properties and interfacial transition zone (ITZ) properties of recycled aggregate concrete (RAC) was investigated. Properties of recycled concrete aggregate (RCA) were tested firstly. Then, five types of concretes were made and slump of fresh concrete was measured immediately after mixing. Compressive strength and splitting tensile strength of hardened concrete were measured at 28 d. Meanwhile, the microstructure of RAC was analyzed by backscattered electron (BSE) image. It was found that the water absorption ratio of carbonated recycled concrete aggregate (CRCA) was much lower when compared to the untreated RCA. Comparatively, the apparent density of CRCA was not significantly modified. The concrete strength results indicate that the mix CRAC-2 prepared with CRCA by adopting two-stage mixing approach shows the highest compressive strength value compared to the other mixes. The microstructural analysis demonstrate that the mix CRAC-2 has a much denser old ITZ than the untreated RAC because of the chemical reaction between CO2 and the hydration products of RCA. This study confirms that the ITZ microstructure of RAC can be efficiently modified by carbonation treatment of RCA and encourages broadening the application of construction and demolition wastes.

Functional and structural parameters of a paved road section constructed with mixed recycled aggregates from non-selected construction and demolition waste with excavation soil

This paper evaluates the lab and in situ mechanical properties of non-selected mixed recycled aggregates from construction and demolition waste (CDW) used as base and subbase unbound materials. Excavation materials are mixed with CDW to produce recycled mixed aggregates with soil, as well as a finer material referred to as mixed recycled soil. The research was divided into two different stages: a laboratory study characterizing the properties of recycling aggregates and a road test track evaluating the long-term performance of these materials under real traffic and weather conditions. During construction, several density, plate load, and falling weight deflectometer tests were performed to determine the bearing capacity of all layers. A laser profiler was also used to obtained the international roughness index. After the road was opened to traffic, a follow up of deflections and surface roughness was performed during the following seven years.Two different moduli calculation methods were used: back calculation and forward calculation. Both methods shown acceptable values for these recycled materials. Low quality recycled mixed aggregates can be used as substitutes for natural aggregates as unbound layers. The mechanical performance and surface roughness values obtained from the experimental road shown an acceptable behaviour.

Properties of recycled ceramic aggregates specified in WT-1 2014 Aggregates - Technical Requirements

The article presents the results of research on primary recycling properties of ceramic aggregates conducted following the procedures outlined in WT-1 2014 Aggregates - Technical Requirements. The material for the tests was obtained from a company producing sanitary ceramic products. Damaged ceramic products, coming from the factory waste heaps, were transported to the laboratory and crushed. This enabled producing aggregate that was later subjected to tests carried out on the aggregates commonly used in the production of mineral-asphalt mixes applied in making road surfaces. The factors that were examined include the following: the flow rate of fine aggregates (angularity of fine aggregate), fine particles content - methylene blue test, light-weight impurities content, frost resistance, bulk density of grains as well as water absorption determined by pycnometric method. The test results showed that the properties of the recycled aggregates are similar to those included in traditional aggregates used for the production of mineral-asphalt mixes. On the basis of the conducted analyses, the waste ceramic aggregate was recommended for use.

Mechanical and Durability Properties of Recycled Aggregate Concrete: Effect of Recycled Aggregate Properties and Content

AbstractThe use of recycled concrete aggregates as an alternative aggregate material in concrete has been studied over the past two decades. It is now recognized that the recycled aggregate concret...

A Novel Conceptual Approach for Predicting the Mechanical Properties of Recycled Aggregate Concrete

The construction sector is more and more committed to reduce its environmental impacts. One of the key actions undertaken in the last decade deals with the ability of turning construction and demolition waste into new raw materials. For instance, the use of recycled aggregates for producing new concrete was one of the most investigated. Thus, in the last decade, plenty of researches were involved in project on characterising the mechanical behaviour of concrete made with recycled aggregates. However, these projects were mainly experimental in nature and generally led to merely empirical formulations. Conversely, this paper is intended at providing a contribution for predicting the mechanical properties of Recycled Aggregates Concrete (RAC). Particularly, it aims at quantifying the effect of replacing ordinary aggregates with Recycled Concrete Aggregates (RCA) on the resulting compressive strength of RAC. To this end, a conceptual model considering both the relevant physical properties of regular and recycled aggregates, including the attached mortar content, and the hydration reactions of Portland cement paste is proposed. The actual predictive capacity of the proposed model is assessed through an experimental validation against experimental tests carried out on several concrete batches produced with various values for the different keys parameters, such as the nominal water-to-cement ratio, the aggregates replacement ratio and the initial moisture condition of aggregates. Both the experimental data and the theoretical formulations proposed in this paper stem out from the inter-university collaboration developed as part of the EU funded EnCoRe Project (www.encore-fp7.unisa.it).

Study of recycled concrete aggregate quality and its relationship with recycled concrete compressive strength using database analysis

This work studies the physical and mechanical properties of recycled concrete aggregate (recycled aggregate from concrete waste) and their influence in structural recycled concrete compressive strength. For said purpose, a database has been developed with the experimental results of 152 works selected from over 250 international references. The processed database results indicate that the most sensitive properties of recycled aggregate quality are density and absorption. Moreover, the study analyses how the recycled aggregate (both percentage and quality) and the mixing procedure (pre-soaking or adding extra water) influence the recycled concrete strength of different categories (high or low water to cement ratios). When recycled aggregate absorption is low (under 5%), pre-soaking or adding extra water to avoid loss in workability will negatively affect concrete strength (due to the bleeding effect), whereas with high water absorption this does not occur and both of the aforementioned correcting methods can be accurately employed.