Recycled Fine Aggregate Research Articles

The Properties of Fine Recycled Aggregate Concrete Containing Recycled Bricks from Construction and Demolition Waste

This paper presents research results of recycled fine aggregate concrete testing. The main aim of this contribution is verification of properties of fine aggregate concrete with partial replacement of fine natural aggregate by recycled masonry aggregate originated from construction and demolition waste. The influence of partial replacement of natural sand to mechanical properties and freeze-thaw resistance is described. The compressive strength and flexural strength were tested at the age of 28 and 60 days and after 25, 50, 75 and 100 freeze-thaw cycles. Partial replacement of natural sand was 0, 25 and 50 % for all these tests. Prismatic specimens were examined.

Influence of high temperature on mechanical properties of concrete containing recycled fine aggregate

This paper presents the results of an experimental study to investigate the influences of high temperatures on the mechanical properties of concrete containing recycled fine aggregate. A total of 150 concrete prisms (100x100x100 mm) are cast and heated under five different temperatures (20oC, 200oC, 400oC, 600oC, 800oC ) for test. The results show that the mass loss, compressive strength, elastic modulus, splitting tensile strength of concrete specimens containing recycled fine aggregate decline significantly as the temperature rise. At the same temperature, the compressive strength, splitting tensile strength, elastic modulus of concrete specimens containing recycled coarse aggregate and recycled fine aggregate (RHC) is lower than that of concrete specimens containing natural coarse aggregate and recycled fine aggregate (RFC). The shape of stress–strain curves of concrete specimens at different temperatures is different, and the shape of that become flatter as the temperature rises. Normal concrete has better energy absorption capacity than concrete containing recycled fine aggregate.

Performance Evaluation of Concrete Manufactured with Precoated Recycled Fine Aggregates Using Supplementary Cementitious Materials

Performance Evaluation of Concrete Manufactured with Precoated Recycled Fine Aggregates Using Supplementary Cementitious Materials

Mechanical behavior of recycled fine aggregate concrete after high temperature

This paper reports mechanical behavior of recycled fine aggregate concretes after high temperatures. It is found that compressive strength of recycled fine aggregate concretes decline significantly as the temperature rises. The elastic modulus of recycled fine aggregate concretes decreases with the increase in temperature, and the decrease is much quicker than the decrease in compressive strength. The split tensile strength of recycled fine aggregate concrete decrease as the temperature rises. Through the regression analysis, the relationship of the mechanical behavior with temperature are proposed, including the compressive behavior, elastic modulus and split tensile strength, which are fitting the test data.

Economical graphene reinforced fly ash cement composite made with recycled aggregates for improved sulphate resistance and mechanical performance

The paper reports the incorporation of graphene into fly ash cement mortars at different doses (% by weight of cement) and evaluation of compressive and flexural strength and resistance to sulphate attack of composites at different hydration times. Fine recycled aggregates (FRA) from have been used as total replacement of fine natural aggregates (FNA) in mortars. Compressive strength and flexural strength results showed that 0.05% graphene produced maximum increase of 8% and 13% respectively with respect to FNA mortar. Excellent resistance to sulphate attack in 0.05% graphene composite could be achieved with minimum loss in compressive strength of 21%.

Cyclic Behavior of Low Rise Concrete Shear Walls Containing Recycled Coarse and Fine Aggregates.

In this study, the cyclic behaviors of low rise concrete shear walls using recycled coarse or fine aggregates were investigated. Eight low rise Recycled Aggregates Concrete (RAC) shear wall specimens were designed and tested under a cyclic loading. The following parameters were varied: replacement percentages of recycled coarse or fine aggregates, reinforcement ratio, axial force ratio and X-shaped rebars brace. The failure characteristics, hysteretic behavior, strength and deformation capacity, strain characteristics and stiffness were studied. Test results showed that the using of the Recycled Coarse Aggregates (RCA) and its replacement ratio had almost no influence on the mechanical behavior of the shear wall; however, the using of Recycled Fine Aggregates (RFA) had a certain influence on the ductility of the shear wall. When the reinforcement ratio increased, the strength and ductility also increased. By increasing the axial force ratio, the strength increased but the ductility decreased significantly. The encased brace had a significant effect on enhancing the RAC shear walls. The experimental maximum strengths were evaluated with existing design codes, it was indicated that the strength evaluation of the low rise RAC shear walls can follow the existing design codes of the conventional concrete shear walls.

Influence of recycled fine aggregate on microstructure and hardened properties of concrete

The objective of this work was to investigate the effect of commercially produced recycled fine aggregate (RFA) on the compressive, tensile and microstructural behaviour of recycled aggregate concrete (RAC). The effect of RFA as a substitute for natural sand at various volume replacement levels (0, 25, 50, 75 and 100%) on the compressive strength, splitting tensile strength and flexural strength of RAC was studied. For 100% replacement of natural fine aggregate (NFA) by RFA, the compressive, splitting tensile and flexural strengths were found to decrease by 13·51, 6·46 and 22·62% respectively. Microstructures of a control concrete and concrete made with RFA (RFAC) were compared, and scanning electron microscopy observations showed that the RFAC contained more unhydrated cement particles and more voids, and its calcium silicate hydrate gel was less dense than that observed in the concrete made with NFA.

Environmental Improvement in Use of Fine Fraction Recycled Aggregates as a Raw Material in Masonry Mortar Fabrication

Background: Great use of raw material and natural resources as well as generation of huge amount of waste make the construction and building sector one of the less sustainable human activities. Objective: The main aim of this research is to study both technical feasibility and environmental sustainability of fine fraction recycled aggregates (RA) use in masonry mortar fabrication. Method. The tests were developed using the binder CEM IV/B (V) 32.5 N and two types of RA: ceramic RA and concrete RA. The substitution percentages were 50%, 75% and 100% and cement-to-aggregate by dry weight proportions were 1:3 and 1:4. Results: Performed tests show that cement-based mortars fabricated with CEM IV/B (V) 32. 5 N can incorporate concrete and ceramic recycled aggregates, using both cement-to-aggregate proportions, complying with the limits established by the Spanish standards. On the other hand, carbon footprint calculation of one of the RA used in the research and a comparative study with natural aggregate (NA) carbon footprint were carried out to analyze environmental sustainability of fine fraction RA. Conclusion. The results show that the amount of kgCo2eq released into the atmosphere as a result of RA fabrication is significantly lower compared with the emissions from NA fabrication, and therefore the use of this type of waste reduces greenhouse gas emissions.

Method for controlling the absorbed water content of recycled fine aggregates by centrifugation

Accurate determination of the absorbed water content of recycled fine aggregates (RFAs) is necessary for proper proportion cement-based mixtures. However, some current standard methods are time consuming and have high operator error. In this paper, we propose an alternative method to control the absorbed water content of RFAs by centrifugation. The rotation speed, centrifugation time, and initial water content are considered as parameters. Ten commercially available RFAs were tested by a single operator with multiple measurements by the centrifugation method, and the results were compared with those obtained by the cone and volumetric flask methods. In addition, the fluidity of the mortar with RFAs and manufactured sand were compared to evaluate the additional water required for saturation. The experimental results indicate that the pre-wetted RFAs can reach the saturated-surface-dry condition after centrifugation at 2000 rpm for 10 min when the centrifugal radius is 6–10 cm, at which the water content can be defined as absorbed water. By comparing the standard deviations with other methods, the absorbed water content can be more accurately and repeatedly controlled by the centrifugation method. The fluidity of the mortar with RFAs including additional water by centrifugation shows a good relationship with that of manufactured sand. Therefore, the centrifugation method can be used to control the absorbed water content of RFAs and applied to mixture design.

Pore-structures and durability of concrete containing pre-coated fine recycled mixed aggregates using pozzolan and polyvinyl alcohol materials

In this study, we coated fine recycled concrete aggregate (FRCA) with fly ash, slag, or polyvinyl alcohol (PVA) (viscosity: 44–50 cps), replaced 25% of the natural fine aggregate in concrete with the coated FRCA, and examined the durability and microscopic properties of the flesh concrete and hardened concrete. We then examined the effects of the various types of coating as well as the thickness on the properties of concrete.Our test results indicate that coating FRCA with fly ash or PVA increases the workability of the fresh concrete, whereas slag coatings slightly reduce the workability. Slag coatings increased the compressive strength, splitting strength, and durability of specimens to a greater degree than do fly ash or PVA coatings, regardless of the water-cement ratio. Furthermore, thicker coatings were shown to produce better results. Scanning electron microscopy images and mercury intrusion porosimetry tests verified that specimens containing FRCA coated with slag resulted in superior engineering properties.

Dynamic Mechanical Properties and Microstructure of Graphene Oxide Nanosheets Reinforced Cement Composites.

This paper presents an experimental investigation on the effect of uniformly dispersed graphene oxide (GO) nanosheets on dynamic mechanical properties of cement based composites prepared with recycled fine aggregate (RFA). Three different amounts of GO, 0.05%, 0.10%, and 0.20% in mass of cement, were used in the experiments. The visual inspections of GO nanosheets were also carried out after ultrasonication by transmission electron microscope (TEM) atomic force microscope (AFM), and Raman to characterize the dispersion effect of graphite oxide. Dynamic mechanical analyzer test showed that the maximum increased amount of loss factor and storage modulus, energy absorption was 125%, 53%, and 200% when compared to the control sample, respectively. The flexural and compressive strengths of GO-mortar increased up to 22% to 41.3% and 16.2% to 16.4% with 0.20 wt % GO at 14 and 28 days, respectively. However the workability decreased by 7.5% to 18.8% with 0.05% and 0.2% GO addition. Microstructural analysis with environmental scanning electron microscopy (ESEM)/backscattered mode (BSEM) showed that the GO-cement composites had a much denser structure and better crystallized hydration products, meanwhile mercury intrusion porosimetry (MIP) testing and image analysis demonstrated that the incorporation of GO in the composites can help in refining capillary pore structure and reducing the air voids content.

Effects of material properties of HFDFRCC Using recycled fine aggregate on shear strength of RC beam

In this study, we performed loading tests on RC beam specimens made of high-fluidity ductile-fiber-reinforced cementitious composites incorporating recycled fine aggregate with different water-binder ratios. We also performed nonlinear finite element analyses to investigate the effects of water-binder ratios and shear reinforcement bars on RC beam shear strength. Additionally, for some factors, we investigated the influence of the presence or absence of shear reinforcement bars on the shear strength of R-HFDFRCC RC beams. We found that fluctuations in the maximum load of the RC beam specimens attributable to differences in the water-binder ratio can generally be predicted if we understand the differences in the material properties (mainly compressive strength, tensile strength and ultimate tensile strain) of the tough, highly fluid cement compound materials incorporating recycled fine aggregate.

Erratum to: Quality improvement of recycled fine aggregate using steel ball with the help of acid treatment

There is a need to promote high-value added utilization of recycled aggregates, considering the aspect of effective use. It should be noted, however, that recycled fine aggregates are generally low in quality due to the presence of cement paste attached to the aggregate surface.

Bonding Behavior of Deformed Steel Rebars in Sustainable Concrete Containing both Fine and Coarse Recycled Aggregates.

In order to assess the bond behavior of deformed steel rebars in recycled-aggregate concrete (RAC) incorporating both fine and coarse recycled aggregate, pull-out tests were carried out in this study on 16-mm diameter deformed steel rebars embedded concentrically in RAC. The concrete was designed using equivalently mixed proportions of both recycled coarse aggregate and recycled fine aggregate. The tests employed five types of recycled aggregate replacement combinations and three types of rebar placement orientation (i.e., vertical bars and two-tiered and three-tiered horizontal bars). Based on the pull-out test results, the maximum bond strength tended to decrease and the slip at the maximum bond strength increased as the average water absorption of the aggregate increased, irrespective of the rebar orientation or placement location within the concrete member. The pull-out test results for the horizontal steel rebars embedded in RAC indicate that the casting position effect could be determined from the mid-depth of the concrete member, irrespective of the member’s height. The normalized bond versus slip relationship between the deformed rebar and the RAC could be predicted using an empirical model based on regression analysis of the experimental data.

Effect of CO2 curing on demolition recycled fine aggregates enhanced by calcium hydroxide pre-soaking

Because of a long storage time, recycled fine aggregates (RFAs) derived from demolition concrete have an extremely low content of carbonatable compounds, which makes it difficult to improve their performance through a regular carbonation process. In this study, we attempted to increase the content of carbonatable compounds in demolition RFAs via calcium hydroxide (CH) pre-soaking for enhancing the carbonation effectiveness. RFAs pre-soaked with CH before carbonation exhibited better properties, including a lower crush value, water absorption, and powder content, as well as a higher strength, than RFAs subjected to carbonation alone. The effect of the carbonation parameters on CO2 curing was examined, and the optimal condition was identified. Experimental results show that the crush value, water absorption, and powder content were significantly reduced by curing the RFAs under the optimal condition (ORFAs). Moreover, the flowability of mortars prepared with ORFAs was improved, and the compressive strength at 28d was increased. The porosity of mortars made prepared using ORFAs was reduced, and the pore structure was refined, as revealed by a mercury intrusion porosity test. The enhancement mechanism was investigated using X-ray diffraction and scanning electron microscopy.

Mechanical Performance Evaluation of Self-Compacting Concrete with Fine and Coarse Recycled Aggregates from the Precast Industry.

This paper intends to evaluate the feasibility of reintroducing recycled concrete aggregates in the precast industry. The mechanical properties of self-compacting concrete (SCC) with incorporation of recycled aggregates (RA) (coarse recycled aggregates (CRA) and fine recycled aggregates (FRA)) from crushed precast elements were evaluated. The goal was to evaluate the ability of producing SCC with a minimum pre-established performance in terms of mechanical strength, incorporating variable ratios of RA (FRA/CRA%: 0/0%, 25/25%, 50/50%, 0/100% and 100/0%) produced from precast source concretes with similar target performances. This replication in SCC was made for two strength classes (45 MPa and 65 MPa), with the intention of obtaining as final result concrete with recycled aggregates whose characteristics are compatible with those of a SCC with natural aggregates in terms of workability and mechanical strength. The results enabled conclusions to be established regarding the SCC’s produced with fine and coarse recycled aggregates from the precast industry, based on its mechanical properties. The properties studied are strongly affected by the type and content of recycled aggregates. The potential demonstrated, mainly in the hardened state, by the joint use of fine and coarse recycled aggregate is emphasized.

Effect of presoak-accelerated carbonation factors on enhancing recycled aggregate mortars

As the low content of calcium-bearing components in demolished recycled fine aggregates (RFA) significantly limits the carbon dioxide (CO2) curing efficiency, the effects of pre-soaking demolished RFA with calcium source solutions before the curing process are presented in this paper. Effects of varied types of calcium source solutions, including calcium hydroxide (CH), calcium chloride (CL) and calcium nitrate (CN) on the curing process are investigated. In addition, the influence of the other two parameters pertaining to curing conditions, namely, the carbon dioxide pressure and curing temperature, on the curing process are also studied. The experimental results show that, after the pre-soaking and curing process, the values of powder content, water absorption and crush value are all decreased for RFA. Furthermore, the compressive strength of mortars at 28 d are increased by as much as 56%. In addition, CN pre-soaking allows the RFA to achieve the lowest water absorption, and CL pre-soaking enables the mortars to obtain the highest compressive strength at 28 d; increasing gas pressure brings about a minor improvement in the properties of RFA and mortars, and curing temperature has complex effects on the carbonation reactions.

Performance and durability of self compacting concrete using recycled concrete aggregates and natural pozzolan

The use of recycled concrete aggregates from rubble and demolition waste in combination with cementitious additions in concrete has several practical, ecological and economic advantages by reducing carbon dioxide emissions, reducing the excessive consumption of natural resources and contributes to a cleaner production of concrete. In this paper, rheological, mechanical and durability properties of self-compacting concrete (SCC) using recycled concrete aggregates and natural pozzolan (PZ) are evaluated. Four concrete mixes were manufactured, by varying the level of substitution by weight of both coarse and fine natural aggregates by fine and coarse recycled aggregates. The substitution levels were fixed at 0%, 50%, 75% and 100%. The cement was also partially replaced by weight from 5% to 25% by natural pozzolan. The performance at the fresh state of SCC was discussed using the following tests (slump test, J-Ring, flow time test V-funnel, L-Box and sieve stability tests). Compressive strength was measured at the ages of 7, 28, 56, 90 and 120 days. Considering the importance of studying the durability of SCC in aggressive environments, the behavior of chloride ions diffusion was analyzed using the Fick’s second law and the loss in mass after immersion in sulfuric acid (H2SO4 was also investigated). The results indicate the possibility of using 50% recycled coarse and fine aggregates for performing self-compacting concrete. The NSCC and RSCC mixtures containing PZ develop a comparable compressive strength to mixtures without PZ at 120 days. The incorporation of 15% and 20% PZ in NSCC and RSCC decreased the penetration depth of chloride ions to 50% and also decreased the mass loss under sulfuric acid attack.

Performance of mortars containing recycled fine aggregate from construction and demolition waste

Waste from construction and demolition accumulates in large quantities in the modern world. Recycled coarse aggregates derived from this waste can replace virgin aggregates used in the production of new concretes but the studies on the effect of using the fine fraction of this waste on the properties of new concrete have not yet led to clear conclusions. The present study evaluated the properties of recycled fine aggregates derived from two recycling plants using two different waste treatment procedures, as well as their effects on the properties of fresh and hardened mortars prepared using these aggregates at two water-to-cement ratios and three replacement ratios. It was found that the recycled aggregates were more porous than the natural aggregates and may have contained some organic matter. Setting times were longer when recycled aggregates replaced natural aggregates and strength and durability were reduced as well. Partial replacement of the fine aggregate is possible if an appropriate compensation of the water to cement ratio is applied.

EFFECT OF RECYCLED MATERIALS ON THE TENSILE BEHAVIOR OF STEEL FIBER-REINFORCED CEMENT COMPOSITE

Conventional cement composite is generally produced with ordinary Portland cement (OPC) as a binder. However, during manufacturing the cement composite, large amount of carbon dioxide (CO2) are emitted. Therefore, fly ash is proposed to be replaced to OPC in order to reduce CO2 emission of cement composites. For reinforcing fibers, micro steel fibers were used. For investigating mechanical properties of steel fiber-reinforced cement composites (SFRCCs), direct tension tests were conducted. The test results showed that fly ash improves tensile strength and ductility of SFRCCs. However, tensile strength of the SFRCC decreased as replacement ratio of recycled fine aggregate increased. The use of recycled materials in FRCC helps to save natural resources and promote sustainability in civil engineering materials.