Recycled Coarse Aggregate Research Articles

The prediction of compressive strength for recycled coarse aggregate concrete in cold region

Concrete in cold environments may suffer from frost damage, which effects the hydration reaction and early strength development of cement. This study aims to test the early strength development of recycled coarse aggregate concrete in cold region using an assisted heating method. Based on Nurse-Saul and Hansen-Pedersen maturity calculation methods, the early strength of recycled and natural coarse aggregate concrete is fitted and predicted using exponential and logarithmic type functions. The results showed that active heating and thermal insulation can ensure early concrete hydration. The temperature of recycled coarse aggregate concrete was slightly higher than that of natural concrete, while its strength was slightly lower. The early strength development of natural and recycled coarse aggregate concrete correlated more with the logarithmic type function. The prediction error of natural and recycled coarse aggregate concrete is basically within 10% for the first 14 days of compressive strength.

Effect of recycled crushed glass and recycled coarse aggregate on the properties of self-compacting concrete

This research was developed to use recycled coarse aggregate (RCA) and recycled crushed glass (RCG) to produce self-compacting concrete (SCC) mixtures. Natural coarse aggregate (NCA) was replaced by RCA from 0% to 100%, and natural fine aggregate (NFA) was replaced by RCG from 0% to 20%. Slump flow with T500 time, L-box, and V-funnel tests were done to ascertain the workability properties of SCC mixtures. The mechanical properties studied were compressive, flexural, and splitting tensile strength at 28 and 56 days. Ultrasonic pulse velocities (UPV) were also measured for the SCC mixtures at 28 and 56 days. Ten shear-critical beams with different shear span-to-depth (a/d) ratios were also cast and tested under 4-point bending. Cracking load, failure load, load-midspan deflection curves, and deflection corresponding to ultimate load were observed. The recommendations of the American Concrete Institute (ACI 318–14 and ACI 318–19), Eurocode (EC2), and Japanese Society of Civil Engineers (JSCE) for shear design were also evaluated on a database of 222 beams cast with SCC and recycled aggregate concrete (RAC) along with the beams tested in the presented study. Results indicate that the workability and mechanical properties were reduced when the replacement level of RCA was increased. The use of RCG as a replacement for NFA enhanced the workability properties and mechanical properties at the age of 56 days. The replacement of NCA with RCA slightly reduced the shear capacity and stiffness of the RC beams. However, the shear capacity and stiffness of RC beams improved when NFA was replaced with RCG. The design provisions of ACI 318–19 yielded accurate estimates of shear capacity compared to JCSE, EC 2, and ACI 318–14.

Experimental investigation on the seismic behavior of TRAC frame column with RCA treated by the silica fume cement paste

AbstractThe physical properties of recycled coarse aggregate (RCA) can be strengthened by pre‐soaking them in silica fume cement paste, thereby improving the mechanical properties of recycled concrete. To evaluate whether treated recycled coarse aggregate (TRCA), which is obtained by pre‐soaking in silica fume cement paste, can be applied to structural elements, considering the axial compression ratio and volumetric stirrup ratio, TRCA concrete (TRAC) frame column specimens and natural aggregate concrete (NAC) column specimens were prepared. Subsequently, a cyclic loading test was conducted on the specimens. The failure mode, hysteresis loop, skeleton curve, ductility, and energy dissipation capacity of the specimens were analyzed and compared. The results showed that compared with NAC specimens, the bearing capacities of the TRAC specimens were slightly higher. The seismic behavior of the TRAC frame columns achieved performance level similar to that of the NAC structural members at low axial compression ratios. This indicates that the RCA treatment of pre‐soaking in silica fume cement paste is effective, and TRAC can be used as loading‐bearing structural concrete.

Comparative Study between Recycled Fine and Coarse Aggregate Used in Roller Compacted Concrete Pavement

To decrease the impact on the environment of building waste, the recycled aggregate may be used in various sustainable engineering applications, such as roller compacted concrete pavement (RCCP). This research examined how using recycled aggregate as a partial replacement for natural aggregate as coarse or fine affected the mechanical properties of roller-compacted concrete pavement. The recycled aggregate was crushed and sieved to coarse and fine aggregate before being used in the roller-compacted concrete pavement. Compressive strength, splitting tensile strength, and flexural strength were all evaluated after the samples were prepared at 28 and 90 days of curing. According to the study's findings, the partial replacement of coarse or fine aggregate with recycled aggregate by (10, 15 and 20%) by volume resulted in decreasing the mechanical properties and increasing the absorption and porosity of RCCP due to the contaminated cement paste on the surface of RCA when compared to the reference mix made with natural aggregate. Because the recycled aggregate contains un-hydrated cement particles, the results have improved after 90 days.

Treated recycled coarse aggregate concrete: A new mixture proportioning method based on packing densities

In this paper, recycled coarse and fine aggregate collected from concrete rubble are treated with acid to remove the adhered cement mortar on the aggregates. These treated recycled aggregates both in fine and coarse aggregates are used to prepare concrete with water-cement ratio of 0.55 based on newly developed mix design method using packing densities. In this study two different recycled coarse aggregate sizes of 10 mm (40 % by mass fraction) and 20 mm (60 % by mass fraction) are used for various replacement levels of natural aggregates. The ratios of aggregates mixture of CA20, CA10 and FA are 38.4:25.6:36.0 by mass. For various packing densities, the recycled aggregates content is evaluated. Quantities for recycled aggregate concrete mixes made with 100 % recycled fine aggregate (RFA) and various replacement percentages of recycled coarse aggregate (RCA) for 0.55 w/c ratio are arrived at. Workability of concrete made with 100 % RFA in terms of slump (mm) can be enhanced by adding 5 % GGBS by mass of cement. Compressive strengths of concrete made with 0 to 100 % replacement of treated recycled fine and coarse aggregate ranges from 27.21 to 19.05 MPa. But when cement or silica fume is added to the recycled aggregate concrete then the compressive strengths are comparable to that of concrete made with natural aggregates.

Effect of heavy-weight recycled materials on radiation shielding and properties of high-strength concrete with CEM III

This research aims to study the effect of replacing up to 100% of recycled coarse aggregates with heavyweight aggregates. In addition to the effect of adding heavyweight aggregate slag on the efficiency of shielding against radiation and on the mechanical physical properties and elevated temperature of heavyweight high-strength concrete (HWHSC). In this investigation, HWHSC mixtures incorporate lead slag (LS), copper slag (CS), and steel slag (SS) as coarse aggregate. Recycled heavyweight coarse aggregates are added to concrete mixtures at volume ratios of 0%, 25%, 50%, 75%, and 100%. Slump test, compressive strength, flexural strength, tensile strength, elastic modulus, and bulk density tests were carried out. Three different gamma-ray energies at 137Cs 662, 60Co 1173, and 60Co 1332 (keV) sources were used to evaluate the mass attenuation coefficient, linear attenuation coefficient, half and tenth-value layer, and mean free path. To evaluate the impact of elevated temperature on density, compressive strength, and radiation shielding properties, concrete mixtures were exposed to 22 °C, 300 °C, 500 °C, and 800 °C. Compared to basalt-based concrete, heavy-weight concrete (HWC) incorporating LS, CS, and SS coarse aggregate has a significantly higher density. The results show a good effect of recycled heavyweight coarse aggregates on fresh, mechanical, and radiation-shielding properties. The density of the developed high-strength concrete (HSC) mixes ranges between 2400 and 3370 kg/m3, and the increase in recycled heavyweight coarse aggregates replacement ratio up to 75% increased all mechanical characteristics of HWC mixtures. Using LS as a replacement of basalt by 75% resulted in the highest compressive strength, splitting tensile strength, flexural strength, and elastic modulus of 105.8 MPa, 14.2 MPa, 19.5 MPa, and 45.76 GPa, respectively. Compared to basalt, LS, CS, and SS eliminate the impact of elevated temperatures on HSHWC strength. The best radiation protection properties were achieved with the complete replacement of basalt by LS.

Physicomechanical Properties and Characterization of Gold Ore Tailings and the Utilization in Manufacturing of Geopolymer Concrete with Class F Fly Ash and Recycled Coarse Aggregates

Physicomechanical Properties and Characterization of Gold Ore Tailings and the Utilization in Manufacturing of Geopolymer Concrete with Class F Fly Ash and Recycled Coarse Aggregates

Optimization on the mix design method of self-compacting concrete with recycled coarse aggregate based on paste rheological threshold theory and material packing characteristics

This study aims to use the mixture design method to optimize self-compacting concrete (SCC) and manufacture SCC with excellent workability using recycled coarse aggregate (RCA) and a ternary cementitious system. The influences of incorporated RCA on the rheological thresholds of SCC with a fixed content of fly ash (FA) and blast furnace slag (BFS) are investigated based on paste rheological threshold theory and material packing characteristics. The original rheological model is improved by introducing the volume of adhesive mortar and modifying the equivalent packing density and mortar film thickness. The improved model is incorporated into the original theoretical system to apply the optimized mix design method to SCC. Moreover, experiments are conducted with different volumes of water, water-powder ratios and RCA replacement levels to verify the applicability of the optimized method. The results indicate that the proposed models can accurately predict the yield strength threshold and plastic viscosity threshold of fresh SCC. Furthermore, compared to the original model, predictions are 53% more accurate with the modified model.

Shear strength assessment of reinforced recycled aggregate concrete beams without stirrups using soft computing techniques

This paper presents a study to predict the shear strength of reinforced recycled aggregate concrete beams without stirrups using soft computing techniques. The methodology involves the development of a Multi-Objective Genetic Algorithm Evolutionary Polynomial Regression (MOGA-EPR) and Gene Expression Programming (GEP) models. The input variables considered are the longitudinal reinforcement ratio, recycled coarse aggregate ratio, beam cross-section dimensions, and concrete compressive strength. Data collected from the literature were used to train and validate the models. The results showed that the MOGA-EPR and GEP models can accurately predict the shear strength of beams without stirrups. The models also performed better than equations from the codes and literature. This study provides an alternative approach to accurately predict the shear strength of reinforced recycled aggregate concrete beams without stirrups.

Frost Durability of Self-Compacting Concrete Prepared with Aeolian Sand and Recycled Coarse Aggregate.

Aeolian sand (AS) and recycled coarse aggregate (RCA) can be reasonably utilized as green materials for concrete modification. The paucity of natural sand and gravel in the construction industry is anticipated to be remedied by the use of these two eco-friendly concrete ingredients. This is incredibly important for environmental protection. Study on the damage law of self-compacting concrete with the addition of AS and RCA (ARSCC) under severely cold conditions is of great significance for the promotion and implementation of this material. In this study, 12 groups of ARSCC specimens were prepared for freeze-thaw cycle experiments, with AS substitution rates of 0, 20%, 40%, and 60% as well as RCA replacement rates of 0, 25%, and 50%. Then, the degradation mechanism of ARSCC freeze-thaw damage was discussed from both macroscopic and microscopic perspectives via mass loss rate (Wn), relative dynamic modulus of elasticity (Pn), bubble spacing factor, and SEM analysis. Finally, the response surface method was utilized to determine the damage variable. A freeze-thaw damage model for ARSCC was developed based on the Weibull distribution and Grey theories. The results showed that the Pn could reflect the evolution law of the internal structure of ARSCC. Appropriate addition of AS to fill the large, harmful pores in RCA would inhibit freeze-thaw damage of ARSCC. The optimum substitution rates of AS and RCA were determined to be 20-40% and 25-50%, respectively. In addition, the values obtained from theoretical damage modeling and experiments were in good agreement. The acquired damage model had the potential to predict ARSCC damage under freeze-thaw cycles.

Analysis on the mechanical properties of recycled concrete

Recycled concrete consists of cement, water and aggregates as conventional concrete; however, the difference is that the former includes a certain percentage of recycled aggregates to achieve environmental friendliness and economic efficiency. This article would focus on the existed application of recycled coarse (RCA) and fine (RFA) aggregate in concrete manufacturing and observe the material properties, such as compressive strength, shear strength, and slump value with different proportion of recycled aggregate mixed during fabrication. Based on sample results from existed experiments, for different amount of recycled coarse aggregate applied for concrete making, the material property would be varied and the appropriate amount of recycled coarse aggregate applied is around 50% for aggregate proportion (could be different for different type of RCA applied). In RFA section, two main resources of RFA are introduced, which are the wasted bricks and concrete. By investigating related research articles, the conclusion of wasted concrete is better than wasted bricks in making RFA is obtained. Several researches are included in RFA replacement experiments, and the conclusion of RFA replacement is that the proportion should be less than 20% in fine aggregate part. Also, intermediate materials such as fly ash, slag powder and silica fume should be applied to guarantee the cohesive property of concrete product. This article illustrates the hurdles and benefits of recycled aggregate application in current stage, and the prospects of recycled aggregates application in concrete products can be more predictable by analyzing the available experiments

Punching Behaviour of Flat Slab Using Recycled Aggregate

Recently, researchers have shown an interest in researching recycling aggregates from old concrete and using them in new construction as a means of protecting the environment and natural resources. This thesis includes an experimental investigation into the punching shear behaviour of continuously supported slabs of concrete with natural and recycled coarse aggregate. In the Laboratory at the MS Ramaiah Institute of Technology the tests on punching shear behaviour of inner slab-column connections in flat plates. ''Natural and recycled'' aggregates were used in six two-way slab models. The slabs were made to only fail while being used as a punching shear. Three specimens of recycled aggregate concrete (RAC) slabs and three specimens of natural aggregate concrete (NAC) slabs were used in the experimental study. Simply supported on four edges, all of the slabs were tested using a central patch load. In order to attain a 25 MPa concrete strength after 28 days, the IS mix design technique was used. For each aggregate size of 12.5mm (Downsize), five concrete mix proportions were used with (0%, 25%, 50%, 75%, and 100%) replacement of natural coarse aggregate with recycled coarse aggregate. Then, casting with a size of 1000 × 1000 × 100 mm was tried with 0% and the highest of the other four (75%). The test findings were then compared with the experimental data and the Codal Provisions for the Accuracy of Ultimate load.

Performance of steel–concrete composite walls with recycled aggregate concrete under low-velocity lateral impact loading

This paper investigates the impact-resistant behaviours of steel–concrete (SC) composite walls experimentally and numerically, which consist of two outer steel plates and infilled recycled aggregate concrete (RAC). Totally eight SC walls were designed and fabricated with different coarse recycled aggregate (CRA) content and steel plate thicknesses. Drop-hammer impact testing was first performed to obtain the failure mode, impact force and deformation. Test results indicated that the impact resistance behaviour of SC walls enhanced considerably with a decrease in CRA content. The tie bars combined with studs were effective to avoid the separation of steel plate from the concrete core. Afterwards, the finite element (FE) models were developed and calibrated, and then used to obtain more information on the full-range motion response, development of stress and strain, and energy absorption. In addition, the influences of different parameters, including the CRA content, material strength, steel plate ratio, tie-bar spacing, impact energy and axial load ratio on the impact resistance performance were assessed. Finally, the displacement response of SC composite walls with RAC was predicted using single-degree of freedom (SDOF) approach.

Impact of Steel Fiber Volume Fraction and Morphology on the Strength of Recycled Aggregate Concrete

Steel-fiber-reinforced recycled coarse aggregate concrete (SFRCAC) has great potential for use in structural members due to environmental and economic reasons. A comparison of SF’s reinforcing effect on the strength of RCAC with natural recycled coarse aggregate concrete (NCAC) was conducted through experiments and analysis. Three types of steel fiber—milling (MF), shear-wave (SWF), and both-end hooked (BF)—were used. The SF volume fraction (Vf) was taken as 0, 0.5%, 1.0%, 1.5%, and 2%. The results show that SF has a similar reinforcing effect on NCAC and RCAC. The reinforcing effect of SF on the strength of RCAC is relevant to the strength of the RCAC matrix. The suitable content range of SF is from 0.5% to 1.5% in terms of the reinforcement effects on the compressive strength (ffcu) and splitting tensile strength (ffts) of RCAC. SF with a higher aspect ratio (AR) has a better reinforcing effect on the splitting tensile strength (ffts) and flexural strength (fftm) of RCAC. The equations of ffts/fts and fftm/ftm with the characteristic parameters of steel fiber (λf) were put forward to accurately determine the dosage of SF.

Research on axial compressive behavior of steel-fiber-reinforced recycled concrete-filled square steel tube slender columns

This paper presents an experimental and analytical study of the axial behavior of steel-fiber-reinforced concrete-filled square steel tube slender columns. A total of 25 axially compressive column specimens are manufactured to investigate the effects of the mass replacement percentage of recycled coarse aggregates (Rp), tube wall thickness (Ts), length-to-width ratio of columns (Lc), and steel fiber content (Vsf) on the performance of slender columns. The results show that the effects of Lc and Ts on the compressive behavior of the column specimens are significant owing to changes in the confinement effect and instability. In terms of the bearing capacity, the compressive strength increases by 12.45%–23.19% as Ts increases from 3 to 5 mm but decreases by 4.35%–10.65% as Lc increases from 6 to 12. However, the incorporation of steel fibers improves the post-peak load mechanical behavior of the slender columns by performing anchoring and bridging effects, and when Vsf reaches 1.2%, it tends to compensate for the reduction caused by changes in Lc and Ts. The synergistic action of the column specimens under axial compression is quantified based on an energy consumption indicator. In addition, predictions of the bearing capacity of the slender columns specified in the Eurocode 4, GB 50936-2014, and Han model are compared and discussed. An incremental iteration model is proposed, and the predicted values are similar to the experiment results with reasonable safety margins.

A mix design method for self-compacting recycled aggregate concrete targeting slump-flow and compressive strength

If waste concrete and excavated engineering soil can be recycled into self-compacting concrete, it could not only alleviate the shortage of natural resources but also realize the sustainable development of self-compacting concrete technology. Therefore, a novel method is proposed for designing self-compacting recycled aggregate concrete (SCRAC) mix. The method is developed by target slump-flow and target compressive strength, avoiding tedious adjustments and laboratory re-testing at the concrete level. The proposed method first determines the contents of natural and recycled coarse aggregate based on the target slump-flow and those of natural and recycled sand are then obtained. Then, the required effective water-cement ratio is calculated based on the target compressive strength. The required admixture content is determined based on the paste rheology. Eleven mixtures designed in this manner were cast and tested. The tested variables included the target slump-flow, target compressive strength, replacement ratio of recycled coarse aggregate (RCA) and recycled sand (RS) from the excavated engineering soil, and coarse aggregate size. The results showed that the proposed method was applicable to SCRAC with a 600–800 mm target slump-flow, 40–60 MPa target compressive strength, 0–100% RCA, 0 and 100% RS, and 5–10, 5–16, and 5–20 mm coarse aggregate sizes. Finally, SCRAC using the RCA and punching residues was successfully fabricated to further verify the feasibility of the proposed method. The proposed method provides design guidance for self-compacting concrete containing RCA and RS obtained from excavated engineering soil.

Flexural and bond-slip responses of reinforced concrete beams containing recycled coarse aggregate and polypropylene plastic

Reusing non-biodegradable plastic waste and recycled concrete as a substitute for natural aggregates can help alleviate the pressure on natural resources. Therefore, this study aims to incorporate polypropylene plastic aggregate (PPA) and recycled coarse aggregate (RCA) in concrete mixtures. The PPA is used as a partial replacement of RCA in reinforced concrete (RC) beams. The flexural responses and bond behaviors of RCA based PPA concrete (RPC) beams are investigated. The main variables are PPA percentages (0, 5, and 10%) and shear span to effective depth ratios (a/d = 2.13, 1.52, 1.07). Nine 1100 mm long RC beams are fabricated for bending tests, and nine 350 mm long RC beams are cast for pull-out tests. Results indicate that the ultimate moment capacity is increased by up to 28.6% for 5% PPA content depending on the beam depths, and for 10% PPA content, it is decreased by up to 15%. Ductility and toughness are increased by up to 11.7% and 113.6%, depending on the PPA contents and beam depths. Bond strength is increased by up to 16.6% for 5% PPA content and then decreased for 10% PPA by up to 37.5% depending on different beam depths. It is recommended that 5% PPA be used in concrete to improve the overall performance of the RPC beams.

Durability of concrete incorporating recycled coarse aggregates: carbonation and service life prediction under chloride-induced corrosion

The use of recycled aggregates (RA) is growing due to the environmental problems associated with extracting natural aggregates (NA) and the disposal of construction and demolition waste (CDW). However, the service-life prediction of recycled coarse aggregate concretes remains incipient. Thus, this study aimed to evaluate the effects of different replacement contents of NA by RA (25, 50, and 75 wt%) on physical (water absorption, porosity, and bulk density), mechanical properties (compressive strength and modulus of elasticity), microstructure (evaluated by X-ray microtomography), accelerated carbonation, and chloride penetration of concrete. A service life prediction analysis of RA concretes was conducted based on the chloride profile obtained and considering the application of different concrete surface treatments. The RA contents evaluated increased the carbonation and chloride diffusion coefficients by 75.7% and 43.0%, respectively, compared to the reference concrete. Nevertheless, reductions of approximately 50% on the critical chloride concentration depth of RA concretes are estimated considering the application of acrylic-based surface treatment. Therefore, applying surface treatments is promising to increase RA concretes' durability and service life, contributing to its wide use and dissemination feasibility.

Development of an axial constitutive model for square steel tube–alkali-activated slag recycled concrete columns

Alkali-activated slag recycled concrete (ASRC) can reduce cement consumption and utilize construction waste. Although, it has poor mechanical properties, a square steel tube can significantly improve its mechanical performance. Therefore, this study conducted axial compression tests on square steel tube-ASRC column (SST-ASRCC) considering the effects of recycled coarse aggregate (RCA) and steel fibre (SF). Subsequently, the bearing capacity, peak compressive strain, and load–strain models of SST-ASRCCs based on the analysis of existing models were established. The results provide an experimental basis and theoretical support for the promotion of SST-ASRCCs in practical engineering.

Simulation-Based Analysis of Micro-Damage to Recycled Concrete-Containing Brick Coarse Aggregates

To achieve sustainable development during urbanization, construction waste is recycled for use as an aggregate in recycled concrete (RC). To determine the influence of the brick content in coarse recycled aggregates on the damage sustained by the resultant RC, the RC was first divided into seven phases: natural crushed stone, old gravel inside waste concrete, bricks, new mortar, old mortar on waste concrete surfaces, and new and old interface transition zones. The Monte Carlo method was then applied to establish a two-dimensional random aggregate model of the RC made with coarse brick aggregates. The ABAQUS software package was used to simulate a uniaxial compression test, the results of which were combined with those of a macro-test to determine the internal damage change rule of brick-containing RC. The stress–strain curves obtained from the simulation coincided well with that of the macroscopic tests. As the brick content increased, the damage zone inside the specimen and the number of microcracks increased. The stress concentration area decreased, as indicated by a lower compressive strength in the macro-test. The results indicate that higher brick contents in RC yield more initial damage inside the concrete and a lower compressive strength.