scholarly journals A Mechanical Treatment Method for Recycled Aggregates and Its Effect on Recycled Aggregate-Based Concrete

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2186
Author(s):  
Pericles Savva ◽  
Socrates Ioannou ◽  
Konstantina Oikonomopoulou ◽  
Demetris Nicolaides ◽  
Michael Frixos Petrou
Keyword(s):  
Mechanical Treatment ◽  
Mechanical Performance ◽  
Treatment Method ◽  
Performance Characteristics ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Cement Matrix ◽  
Quality Aspects ◽  
Comparable Performance ◽  
And Performance

Recycle concrete aggregates (RCA) consist of natural aggregates and remnant mortar adhered to their surface. The amount, size, and morphology of the adherent remainder paste influences quality aspects of RCA, such as their bonding potential with new cement matrix in an RCA-based concrete, as well as the concrete’s overall rheological and performance characteristics. The objective of this research was to study the effect of reducing the adhered mortar in RCA, by means of a mechanical treatment method, on the performance of concrete containing RCA at different percentages. The treatment process was conducted within a concrete mixer truck drum at specific time intervals, the effect of which was determined by means of image analysis, mass loss recordings, and circularity determinations. The effect of size of treated and field RCA, as well as replacement percentages on mechanical performance and durability of high and normal strength concrete mixes, were also investigated. It was concluded that the optimal treatment duration where no further significant removal of adhered paste occurred thereon was 3 h, and concrete mixes containing 3 h treated RCA exhibited comparable performance characteristics to those of the reference concrete mix.

Microstructural Features of Recycled Aggregate Concrete: From Non-Structural to High-Performance Concrete

2019 ◽  
Vol 25 (3) ◽  
pp. 601-616 ◽  
Author(s):  
Diogo Pedro ◽  
Mafalda Guedes ◽  
Jorge de Brito ◽  
Luís Evangelista
Keyword(s):  
High Performance ◽  
Mechanical Performance ◽  
High Performance Concrete ◽  
Concrete Strength ◽  
High Strength ◽  
Recycled Concrete ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Sequential Approach

AbstractThe use of concrete-recycled aggregates to produce high-performance concrete is limited by insufficient correlation between resulting microstructure and its influence on mechanical performance reproducibility. This work addresses this issue in a sequential approach: concrete microstructure was systematically analyzed and characterized by scanning electron microscopy and results were correlated with concrete compressive strength and water absorption ability. The influence of replacing natural aggregates (NA) with recycled concrete aggregates (RCA), with different source concrete strength levels, of silica fume (SF) addition and of mixing procedure was tested. The results show that the developed microstructure depends on the concrete composition and is conditioned by the distinct nature of NA, recycled aggregates from high-strength source concrete, and recycled aggregates from low-strength source concrete. SF was only effective at concrete densification when a two-stage mixing approach was used. The highest achieved strength in concrete with 100% incorporation of RCA was 97.3 MPa, comparable to that of conventional high-strength concrete with NA. This shows that incorporation of significant amounts of RCA replacing NA in concrete is not only a realistic approach to current environmental goals, but also a viable route for the production of high-performance concrete.

scholarly journals Mechanical Properties and Durability of Polypropylene and Steel Fiber-Reinforced Recycled Aggregates Concrete (FRRAC): A Review

2020 ◽  
Vol 12 (22) ◽  
pp. 9509
Author(s):  
Peng Zhang ◽  
Yonghui Yang ◽  
Juan Wang ◽  
Shaowei Hu ◽  
Meiju Jiao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Steel Fiber ◽  
Mechanical Performance ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Chloride Permeability ◽  
High Durability ◽  
The Matrix ◽  
Research Findings ◽  
Fiber Materials

With the development of concrete engineering, a large amount of construction, demolition, excavation waste (CDEW) has been produced. The treated CDEW can be used as recycled aggregate to replace natural aggregate, which can not only reduce environmental pollution and construction-related resource waste caused by CDEW, but also save natural resources. However, the mechanical properties and durability of Recycled Aggregates Concrete (RAC) are generally worse than that of ordinary concrete. Various fiber or mineral materials are usually used in RAC to improve the mechanical properties and durability of the matrix. In RAC, polypropylene (PP) fiber and steel fiber (SF) are two kinds most commonly used fiber materials, which can enhance the strength and toughness of RAC and compensate the defects of RAC to some extent. In this paper, the literature on PP fiber- and SF-reinforced RAC (FRRAC) is reviewed, with a focus on the consistence, mechanical performance (compressive strength, tensile strength, stress–strain relationship, elastic modulus, and shear strength), durability (water absorption, chloride permeability, carbonation, freeze–thaw cycling, and shrinkage), and microstructure. The research findings regarding FRRAC were analyzed and compared. The results showed that adding mineral additives and fiber in RAC had a good synergistic effect, which made FRRAC have good mechanical properties, high durability and high temperature resistance, and several application prospects. The information and summary presented in this paper exhibit new knowledge and information on the application of FRRAC.

scholarly journals The Influence of Heat and Mechanical Treatment of Concrete Rubble on the Properties of Recycled Aggregate Concrete

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 367 ◽  
Author(s):  
Edyta Pawluczuk ◽  
Katarzyna Kalinowska-Wichrowska ◽  
Michał Bołtryk ◽  
José Jiménez ◽  
José Fernández
Keyword(s):  
Mechanical Treatment ◽  
Fine Fraction ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Building Structures ◽  
Aggregate Concrete ◽  
Appropriate Treatment ◽  
Research Experiment ◽  
Concrete Recycling

Concrete is a building material commonly used for ages. Therefore, in the result of repairs or demolition of building structures, large amounts of concrete rubble are created, which requires appropriate management. The aim of the realized research was to determine the influence of heat and mechanical treatment of concrete rubble on the properties of recycled aggregate concrete. The research experiment included 12 series, with three variables: X1—roasting temperature (300, 600, 900 °C), X2—time of mechanical treatment (5, 10, 15 min), X3—content of coarse recycled aggregates (20, 40, 60% by volume). Two additional series containing recycled aggregate without treatment and natural aggregate were also prepared. Established properties of individual aggregates have confirmed a positive effect of thermo-mechanical treatment. Then, based on the results of compressive strength, flexural strength, Young’s modulus, volumetric density, water absorption, water permeability and capillarity, the most favourable parameters of heat and mechanical treatment of concrete were determined. The test results showed that appropriate treatment of concrete rubble allows to obtain high-quality coarse aggregate and valuable fine fraction. This was also confirmed by the macro- and microscopic observations of the aggregate and separated cement paste. Works realized on the concrete recycling method resulted in obtaining a patent PAT.229887.

scholarly journals Mechanical Properties of Basalt-Based Recycled Aggregate Concrete for Jeju Island

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5429
Author(s):  
Hong-Beom Choi ◽  
Jin-O Park ◽  
Tae-Hyun Kim ◽  
Kyeo-Re Lee
Keyword(s):  
Mechanical Performance ◽  
Drying Shrinkage ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Superior Performance ◽  
Recycled Aggregates ◽  
Replacement Ratio ◽  
Volume Percentage ◽  
Air Content

Recycled aggregate is essential to protect Jeju Island’s natural environment, but waste concrete, including porous basalt, is a factor that lowers the quality of recycled aggregate. Therefore, an experiment was conducted to analyze the properties of concrete application of basalt-based recycled aggregate (B-RA) through quality improvement. The absorption of the B-RA ranged from 3–5%; restricting its absorption to less than 3% was challenging owing to its porosity and irregular shape. However, the increase in the solid volume percentage of the concrete when replacing 25 or 50% of fresh basalt aggregate with recycled basalt aggregate improved the mechanical performance of the concrete, especially at 25%, for which a compressive strength of 55.9 MPa and modulus of elasticity of 25.9 GPa exceeded those of concrete with fresh basalt aggregate. Moreover, increasing the replacement ratio of the fresh basalt with recycled aggregate reduced the slump and decreased the air content, consequently increasing the concrete drying shrinkage. However, the replacement of fresh basalt aggregate with recycled basalt aggregate unaltered the mechanical performance of the concrete. The results indicate that efficient use of recycled aggregates can yield superior performance to that of fresh basalt, irrespective of aggregate quality.

scholarly journals Mechanical Performance of Concrete Made with Recycled Aggregates from Concrete Pavements

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Yancong Zhang ◽  
Lingling Gao ◽  
Wei Bian
Keyword(s):  
Tensile Strength ◽  
Compressive Strength ◽  
Fly Ash ◽  
Mechanical Performance ◽  
Inhibitory Effect ◽  
Recycled Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Concrete Pavements ◽  
Flexural Tensile Strength

This research aims at analysing the mechanical performance of concrete with recycled aggregates from concrete pavements. First, the characteristics of various natural and recycled aggregates used in the concrete were thoroughly analysed. The composition of the recycled aggregates was determined and several physical and chemical tests of the aggregates were performed. In order to evaluate the mechanical performance of recycled concrete, cube compressive strength and flexural tensile strength tests were performed. The effect of recycled aggregates on the strength of recycled concrete is related to the strength of recycled aggregates, the strength of natural aggregates, and the strength of old concrete. The strength of recycled concrete decreases with increasing water-cement ratio. However, due to the water absorption of the recycled aggregate, it has a certain inhibitory effect on the strength reduction. As the replacement rate of recycled aggregates increases, the optimal sand ratio decreases. The sand ratio is controlled between 32% and 38%, which is ideal for recycled concrete. With the increase of fly ash content, the 7 d strength of recycled concrete has decreased to some extent, but the 28 d strength has been slightly improved. In addition, for compressive strength and flexural tensile strength, the optimal content of fly ash is different.

scholarly journals Feasibility of Utilizing Recycled Aggregate Concrete for Revetment Construction of the Lower Yellow River

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4237 ◽  
Author(s):  
Pan Feng ◽  
Honglei Chang ◽  
Guodong Xu ◽  
Qiaoling Liu ◽  
Zuquan Jin ◽  
...  
Keyword(s):  
Mechanical Performance ◽  
Yellow River ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Fine Aggregate ◽  
Micro Hardness ◽  
Aggregate Concrete ◽  
Lower Yellow River ◽  
The Lower Yellow River

To explore the feasibility of utilizing recycled aggregate concrete (RAC) in revetment construction of the lower Yellow River, a series of mix proportions with local recycled aggregates (RA) were designed to evaluate its mechanical properties and durability. The morphology and micro-hardness of the interface transition zone (ITZ) were also characterized to explain the performance of RAC. Based on the compressive strength data of 13 groups of mixtures, which is larger than 30 MPa, and with the RA substitution rate not less than 50%, the RAC containing 50% recycled fine aggregate (RFA) (HDX50), 70% RFA (HDX70), and 50% recycled coarse aggregate (RCA) (HDC50) were selected. The experiment results suggest that the mechanical performance, frost resistance, and carbonation resistance of the selected RAC is generally poorer than that of natural aggregate concrete (NAC), but can meet the performance requirement of concrete for the revetment construction of the lower Yellow River. The comprehensive performance of these three mixtures ranks as: HDX50 > HDX70 > HDC50. When considering the RA substitution ratio as a priority, HDX70 would be the best choice and can be applied in the revetment engineering. A number of defects are observed on the surface of RA with old pastes attached. Furthermore, the ITZs formed around RA are loose and with low micro-hardness, which is deemed to be the dominating reasons leading to the weaker performance of RAC than that of NAC.

scholarly journals Mechanical Performance of Bio-Based FRP-Confined Recycled Aggregate Concrete under Uniaxial Compression

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1778
Author(s):  
Elhem Ghorbel ◽  
Mariem Limaiem ◽  
George Wardeh
Keyword(s):  
Mechanical Performance ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Fiber Reinforced ◽  
Traditional System ◽  
Concrete Mixtures ◽  
Compressive Performance ◽  
Natural Aggregates ◽  
Frp Confinement

This research investigates the effectiveness of bio-sourced flax fiber-reinforced polymer in comparison with a traditional system based on carbon fiber-reinforced epoxy polymer in order to confine recycled aggregate concretes. The experimental investigation was conducted on two series of concrete including three mixtures with 30%, 50%, and 100% of recycled aggregates and a reference concrete made with natural aggregates. The concrete mixtures were intended for a frost environment where an air-entraining agent was added to the mixture of the second series to achieve 4% air content. The first part of the present work is experimental and aimed to characterize the compressive performance of confined materials. The results indicated that bio-sourced composites are efficient in strengthening recycled aggregates concrete, especially the air-entrained one. It was also found that the compressive strength and the strain enhancement obtained from FRP confinement are little affected by the replacement ratio. The second part was dedicated to the analytical modeling of mechanical properties and stress–strain curves under compression. With the most adequate ultimate strength and strain prediction relationships, the full behavior of FRP-confined concrete can be predicted using the model developed by Ghorbel et al. to account for the presence of recycled aggregates in concrete mixtures.

scholarly journals Effect of Recycled Aggregates on Strength and performance of Recylced Aggregate Concrete

2020 ◽  
Vol 184 ◽  
pp. 01085
Author(s):  
Dr.V. Mallikarjuna Reddy ◽  
M. Manikanta Sai Swaroop
Keyword(s):  
Coarse Aggregate ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Fine Aggregate ◽  
Aggregate Concrete ◽  
Recycled Coarse Aggregate ◽  
Recycled Fine Aggregate ◽  
The Difference ◽  
And Performance

This study is taken up to utilise the recycled coarse aggregate and recycled fine aggregate as replacement of natural aggregate in concrete mix. It is required to find the percentage of recycled coarse aggragate and recycled fine aggregate, as the strength of concrete can not be achieved by using higher percentaged. The purpose of study is to compare between recycled coarse aggregate and recycled fine aggregate with natural coarse aggregate and sand in terms of specific gravity, water absorption, particle size distribution. Further, this stydy will also consider the difference between the performance of Recycled Aggregate Concrete for different percentages of recycled coarse aggregate and recycled fine aggregate i.e for 0%, 10%, 15%, 20%, 25%, 30%, 35% replacement. The present study is an experimental investigation on the behaviour of recycled aggregate concrete (coarse& fine aggregates) with respect to the strength and performance.

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