Aggregate Replacement Ratio Research Articles

Experimental Study on Direct Shear Behavior of New-to-Old Interface for Recycled Aggregate Concrete with Different Replacement Ratios

The large amount of construction waste produced by the construction industry brings severe natural resource consumption and environmental pollution, elevating the awareness of sustainable development. Recycled aggregate concrete, crushed from construction waste, is recognized as an eco-friendly material and the current optimal solution for the environmental problem. The interface shear failure between substrate recycled coarse aggregate concrete (RAC) and overlay natural aggregate concrete becomes vital for structural safety. In order to study the direct shear performance, a total of 19 specimens were designed to carry out the direct shear test with different replacement ratios, interface types and curing ages. The whole process and failure mode were recorded. The relationships between the shear capacity and deformation, ductility, damage evolution, and energy dissipation were evaluated and discussed. The results demonstrate that the RAC component in the interface was the weak line in the shear plane, accelerating the damage evolution. In the early curing stage, the replacement ratio had a slight influence on the shear properties. Increasing the recycled aggregate replacement ratio from 0 to 100% improved the normalized strength ratio by 8.94% and 14.62%, respectively, for curing ages of 3 days and 7 days. A regression equation was proposed to predict the shear strength, accounting for the curing ages. With the increase in the replacement ratio, the ductility and energy dissipation gradually enhanced.

Post-fire flexural buckling and resistances of square recycled aggregate concrete-filled stainless steel tube (RACFSST) columns

The flexural buckling behaviour and residual resistances of square recycled aggregate concrete-filled stainless steel tube (RACFSST) columns after exposure to fire are studied in this paper, based on experiments and numerical modelling. Twelve column specimens, fabricated from concretes with three recycled coarse aggregate replacement ratios (0%, 35% and 70%), were tested after exposure to the ISO 834 standard fire for 0 min (i.e. at ambient temperature), 15 min, 30 min and 45 min. The experimental investigation included heating of specimens, cylinder tests as well as post-fire initial global geometric imperfection measurements, tensile coupon tests and pin-ended column tests. The test setups, procedures and results were fully reported and the ductility indices, lateral deflection distributions and longitudinal strains were discussed and analysed. A numerical investigation was afterwards carried out, where the test results were used to validate thermal and mechanical finite element models; upon validation, parametric studies were conducted to expand the test data bank over a wider range of cross-section dimensions and member lengths. On the basis of the test and numerical data, the relevant design rules for square natural aggregate concrete-filled carbon steel tube columns at ambient temperature, as set out in the European code, Australian/New Zealand standard and American specification, were assessed, using post-fire material properties, for their applicability to square RACFSST columns after exposure to fire. It was found from the assessment results that the three design codes resulted in overall accurate and consistent post-fire flexural buckling resistance predictions but some were unsafe.

Seismic Performance of Recycled-Aggregate-Concrete-Based Shear Walls with Concealed Bracing

Relatively few studies have been conducted on the seismic performance of recycled aggregate concrete (RAC) shear walls with concealed bracing. To promote the development of high-performance green building structures and the application of RAC in structural components, the seismic performance of RAC shear walls under different influencing factors was tested, and low-cycle reversed loading tests were performed on ten RAC shear walls with different shear-to-span ratios. The test parameters included the recycled coarse aggregate (RCA) replacement ratio, the recycled fine aggregate (RFA) replacement ratio, the axial compression ratio, the shear span ratio and whether to set up the concealed bracing. The influence of the above variables on the seismic performance was then assessed. The results revealed that the bearing capacity, ductility, stiffness and energy dissipation capacity of the RAC shear walls decreased in line with an increase in the replacement ratio of the RFA. However, the bearing capacity, energy consumption and stiffness of the RAC shear walls decreased within 10% and the ductility decreased within 15%. The RAC shear walls were able to meet the seismic requirements of the building structure after reasonable design and use. As the axial compression ratio increased, the bearing capacity of the RAC shear walls improved, but their elastic–plastic deformation capacity was reduced. Setting the concealed bracing significantly improved the seismic performance of the RAC shear walls, such that they achieved a seismic performance close to that of the natural aggregate concrete (NAC) shear wall. After setting up the concealed bracing, the load carrying capacity of the RAC shear walls increased by up to 15%, the ductility increased by up to 20% and the energy consumption capacity increased by up to 50%. A mechanical calculation model of the RAC shear wall was then established by considering the effect of recycled aggregate, the calculated results of which were a good match with the test results.

Exploring economic and environmental impacts of recycled aggregate concrete using particle swarm optimization algorithm

Recycled aggregate concrete (RAC) is a sustainable alternative that encounters challenges due to varying sources and processing methods. This study introduces a novel approach to optimize the mix proportions of RAC through machine learning and multi-objective optimization techniques. It identifies the key factors influencing the compressive strength of concrete, aiming to minimize costs and environmental impacts while meeting compressive strength requirements. Six machine learning models were developed based on a database of 522 samples to predict the cubic compressive strength of RAC. Among these, the XGBoost model demonstrated the highest accuracy, establishing a functional relationship between cubic compressive strength and mix proportions, achieving an R2 of 0.965 and a composite performance index of 0.081. Additionally, life cycle cost analysis and life cycle assessment were employed to evaluate both cost and environmental impacts. Using the particle swarm optimization algorithm, the optimization of strength, cost, and environmental impact was conducted, comparing RAC with conventional concrete. The significant factors affecting cubic compressive strength were identified as curing age, water-to-cement ratio, and sand content, contributing 28.6%, 20.6%, and 15.8% to the variation in strength, respectively. Cement content and the fly ash-to-cement ratio were found to significantly influence cost and environmental factors, respectively. Optimal reductions in cost and environmental impact were achieved with a recycled aggregate replacement ratio of 45%–60%, resulting in decreases of up to 18.94% and 41.72%, respectively.

Strength and microstructure of geopolymer recycled brick aggregate concrete after high temperatures

Geopolymer recycled brick aggregate concrete (GRBC), as a new environmentally friendly material, exhibits excellent mechanical performance at ambient temperature, but its properties after exposure to high temperatures are not clear. In this paper, the strength and microstructure of GRBC after high temperatures were investigated and compared with ordinary recycled brick aggregate Portland cement concrete (ORBC) through compressive strength, splitting tensile strength, and microscopic tests. The main parameters varied in the strength tests were temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and recycled brick aggregate (RBA) replacement ratio (0 %, 25 %, 50 %, 75 %, and 100 %). The results indicated that the strength of GRBC decreased less than that of ORBC after high temperatures. The compressive strength retention rate of GRBC after exposure to 800 °C was 0.359−0.456, and the tensile strength retention rate was 0.415−0.442. The strength of GRBC with 50 % RBA replacement ratio was about 0.70 that of the case without RBAs. The microscopic test results showed that the structure of GRBC was denser than that of ORBC, and the interfacial transition zone (ITZ) between matrix and RBAs was less affected by the temperature. The first weak zone after high temperatures was RBA itself for GRBC, but ITZ between matrix and RBAs for ORBC. The X-ray diffraction analysis indicated that the phase composition of GRBC and ORBC after high temperatures was basically similar to that at ambient temperature. The strength of GRBC was mainly provided by the N-A-S-H and C-A-S-H gels, while the strength of ORBC was mainly relied on the C-S-H gel.

Research on the flexural performance of recycled coarse aggregate concrete beams after carbonation

This paper discusses the flexural behavior of carbonated recycled aggregate concrete (RAC) beams through experimental data. We produced fifteen beams, each varying in recycled aggregate replacement ratios: 0 %, 30 %, 50 %, 70 %, and 100 %. Each replacement ratio included three beams, amounting to different levels of carbonation: non-carbonated, partially carbonated, and completely carbonated. Post accelerated carbonation processes; flexural testing was conducted. The findings reveal that beams incorporating varying amounts of recycled coarse aggregates (RCA) but maintaining identical carbonation levels exhibited a minor reduction in the cracking moment, with negligible variations in ultimate flexural strength and deflection. Moreover, beams sharing the same RCA replacement ratio demonstrated increased cracking moment, ultimate flexural strength, and stiffness with advancing carbonation levels, while deflection tended to decrease. Based on these findings, predictive models for cracking moment and ultimate flexural strength of carbonated RAC beams were developed. Comparisons between experimental outcomes and numerical simulations, particularly within the RAC50 group, indicated nearly identical results.

Experimental study on the compressive fatigue performance of nano-silica modified recycled aggregate concrete

This study focused on the compressive fatigue performance of nano-silica (NS) modified recycled aggregate concrete (RAC). 108 prism specimens with varying replacement ratios (i.e., 0 %, 50 %, and 100 %), NS soaking concentrations (i.e., 0 %, 1 %, 2 %, and 3 %), and stress levels Smax (i.e., 0.75, 0.8, 0.85, and 0.90) were designed for compressive fatigue test. The failure process and failure modes for the specimens were observed, the fatigue life curves of NS modified RAC under different design parameters were measured. Moreover, the relationships between different design parameters and fatigue life, fatigue strength were analyzed. The results revealed that the failure modes for specimens with different design parameters were mainly shear failure, conical failure and mixed failure. Fatigue life exhibited significant changes under different stress levels, decreasing notably with increasing stress levels. As the recycled coarse aggregate (RCA) replacement ratio increased, fatigue life demonstrated a decreasing trend. Based on the two-parameter Weibull distribution function, the fatigue life equation considering the influence of variable parameters under different failure probabilities was proposed. When the failure probability was 0.5, the specimen with a NS soaking concentration of 2 % exhibited the highest fatigue strength at the same replacement ratio.

Analysis of Impact Crushing Characteristics of Steel Fiber Reinforced Recycled Aggregate Concrete Based on Fractal Theory

The fractal theory can effectively describe the complexity and multi-scale of concrete under impact load and provide a scientific basis for evaluating concrete’s impact resistance. Therefore, based on the fractal theory, this study carried out the fragmentation size analysis by weighing the quality of SFRRAC fragments, disclosed the distribution characteristics of impact fragmentation size of steel fiber reinforced recycled aggregate concrete (SFRRAC) specimens under different recycled coarse aggregate (RCA) replacement ratio, different steel fiber (SF) contents and different impact pressures. The results indicate that the fractal dimension can describe the degree of fragmentation of the specimen. The greater the fractal dimension, the more the amount of fragmentation of the specimen subjected to impact load, the lesser the fragmentation size, and the greater the degree of fragmentation. Under the impact load, the fractal dimension of SFRRAC is between 1.36 and 2.28. As the impact pressure increases, the energy consumption increases, and the fractal dimension decreases. With the growth in replacement ratio, the fractal dimension gradually increases, and the energy consumption is negatively correlated with the fractal dimension. Along with the growth of SF content, the energy consumption gradually increases, and the fractal dimension continuously decreases. A new metric angle is provided to explore the inherent law between the impact-crushing characteristics of SFRRAC and the dynamic load, thereby offering foundational support for the application of SFRRAC in practical engineering.

The ultimate capacity of geopolymer recycled aggregate concrete filled steel tubular columns: Numerical and theoretical study

Concrete-filled steel tubular (CFST) columns have been extensively used due to their numerous advantages including high load-bearing capacity, stiffness, energy absorption, and ductile failure mode. Human awareness toward environmental problems is increasing and research on geopolymer recycled aggregate concrete (GRAC) has gained much attention as a green and sustainable material. However, there is little experimental and numerical research on the behavior of CFST columns with the GRAC as an infill material with the available design codes not yet modified for addressing the utilization of unconventional concrete mixes, such as the GRAC. This research introduces a critical modification of the ACI code provisions using the nonlinear finite element analysis method (FEA) on the behavior of square GRACFST columns under axial compression where the proposed modification was verified using experimental data from the literature. The influence of the length-to-width ratio, width-to-thickness ratio, geopolymer concrete strength, and the recycled aggregate replacement ratio was investigated. Results show that the outward local buckling was the primary failure mode for both short and slender columns. Considerable improvements were observed in the column's load-bearing capacity, initial stiffness, ductility, and energy absorption by (81.0, 101.9, 46.5, and 87.8)%, respectively, achieved upon increasing the steel tube thickness from 3 mm to 9 mm. However, the increase in length-to-width ratio negatively affects the energy absorption by 39 % while the ductility was reduced up to 20.4 %. The predictability of the AISC360-16, ACI318-19, and BS5400-5 codes on the capacity of GRACFST columns was evaluated where conservative predictions were guaranteed with the closest one recorded for the ACI318-19 code with a 24.5 % overestimation percentage. Finally, a modification was proposed to the ACI code prediction, taking into account the inclusion of recycled aggregate and geopolymer concrete with only a 2 % average error.

Compressive behavior of concrete-filled FRP tubes with FRP solid waste as recycled aggregates: Experimental study and analytical modelling

The disposal and recycling of FRP (Fiber-Reinforced Polymer) solid waste pose significant challenges globally, with a recycling rate of less than 10 %. Current methods of handling FRP solid waste (FSW), including landfill disposal, incineration, chemical treatment, and thermal cracking, face limitations in achieving large-scale recycling and resource utilization. In civil engineering, FRP is widely employed for retrofitting structures and holds promise for new constructions. A new approach has emerged for recycling FSW by using it as aggregates in concrete, offering lower costs and reduced environmental impact. Research on using FSW aggregates in plain concrete shows that optimizing replacement ratios and aggregate shapes can enhance split tensile strength and toughness without significantly lowering compressive strength. To further improve the mechanical performance, this study investigated concrete-filled filament-wound FRP tubes with FSW aggregates (FSW-CFFTs) under axial compression. 35 specimens were tested to evaluate the influence of granular FSW aggregates (i.e., replacement ratio = 0 %, 20 %, 40 %, 60 %, and 80 %) and FRP thickness (i.e., 0 mm, 3 mm, and 5 mm) on their axial compression behavior. The experimental study revealed that: incorporation of FSW aggregates in unconfined concrete cylinders led to a notable decrease in Young's modulus and compressive strength, while concurrently increasing the peak compressive strain; as the replacement ratio of FSW aggregates increased, there was a tendency for the peak stress of FSW-CFFTs to decrease, while their ultimate axial strain tended to increase; compared FSW-CFFTs with unconfined concrete cylinders, the FRP confinement helped to mitigate the reduction ratio in axial compressive strength induced by the inclusion of FSW aggregates in the concrete, particularly at higher FSW aggregate replacement ratios; specimens with a thicker FRP tube exhibited higher secondary stiffness, along with higher strength and larger ultimate compressive strain. The modeling work indicated that accurately predicting axial stress-strain curves requires consideration of the bi-axial stress state of filament-wound FRP tubes.

Performance of the bond between recycled concrete and steel bars subject to transverse stirrup constraints after exposure to high temperatures

This study investigates and assesses the bond performance between steel reinforcement and recycled concrete, subject to the confining effect of transverse stirrups post high-temperature exposure. A series of 24 specimen groups was examined, with variations in parameters including transverse stirrup ratios (0 %, 0.24 %, 0.67 %, 1.34 %), recycled concrete aggregate (RCA) replacement ratios (0 %, 50 %, 100 %), and temperatures (300 °C, 500 °C, 700 °C). Central pull tests were administered to discern the impact of each parameter on the bond integrity of steel-reinforced recycled concrete. The results revealed that high temperatures reduced the thickness of the critical cover, altering the failure mode of the specimen. With rising temperatures, the bond strength of steel-reinforced recycled concrete weakened. Nonetheless, an increase in stirrup ratio served to counteract the detrimental effects of high temperatures. In contrast, a higher RCA replacement ratio exacerbated these effects. For example, specimens with a 1.34 % stirrup ratio showed a 30 % decrease in the adverse impacts of high temperature on bond strength compared to those with no stirrups. A comprehensive computational model, devised from experimental data and theoretical analysis, predicts the bond-slip behavior of steel-reinforced recycled concrete, incorporating the constraint coefficient k, temperature T, and replacement ratio r as pivotal parameters. The model’s predictive curve corresponds closely with the experimental findings, effectively capturing the influence of high temperature, lateral restraint, and RCA replacement ratio on the bond performance of steel-reinforced recycled concrete.

Engineering performances of permeable concrete blocks using oyster shell, bottom ash, and biochar

In this study, permeable concrete blocks using industrial by-products (Oyster shell, bottom ash, and biochar) were developed, and the recycling suitability of the industrial by-products and engineering performances were evaluated. The flexural strength of permeable concrete blocks using by-products decreased as the bottom ash aggregate replacement ratio increased. When using oyster shell and biochar, the 28 days flexural strength was increased, and the development of initial strength was faster. The permeability is about 41.6–102.9 times greater than the Korean standard for permeable concrete block (0.01 cm/s). Oyster shell cement and biochar lowered permeability, and bottom ash aggregate had the effect of increasing permeability. The porosity of each specimen increased as the bottom ash aggregate substitution ratio increased and the replacement ratio of oyster shell cement decreased, and the continuous porosity decreased when biochar was mixed. Comparing the test results with permeable concrete block quality standards of South Korea, the substitution ratio of oyster shell cement can be up to 40 % and that of bottom ash aggregate up to 20 %. By mixing 2 % BC, a permeable concrete block was applicable for sidewalks even the substitution ratio of both oyster shell cement and bottom ash was 40 %.

Axial compression behavior of carbon fiber reinforced polymer confined partially encased recycled concrete columns.

Partially encased concrete (PEC) has better mechanical properties as a structure where steel and concrete work together. Due to the increasing amount of construction waste, recycled aggregate concrete (RAC) is being considered by more people. However, although RAC has more points, the performance is inferior to natural aggregate concrete (NAC). To narrow or address this gap, lightweight, high-strength and corrosion-resistant CFRP can be used, also protecting the steel flange of the PEC structure. Therefore, carbon fiber reinforced polymer (CFRP) confined partially encased recycled coarse aggregate concrete columns were studied in this paper. With respect to different slenderness ratios, recycled coarse aggregate(RCA) replacement ratios, and number of CFRP layers, the performance of the proposed CFRP restrained columns are reported. The RCA replacement ratio is analyzed to be limited negative impact on the bearing capacity, generally within 6%. As for the slenderness ratio, the bearing capacity increased with it. However, wrapping CFRP significantly increased the bearing capacity. Considering the arch factor, a simple formula for calculating the ultimate strength of CFRP-confined partially encased RAC columns is developed based on EC4 and GB50017-2017. By comparison with the experimental values, the error is within 10%.

Experimental and numerical investigation of the bending, shear, and punching shear behavior of recycled aggregate concrete precast/prestressed hollow core slabs

AbstractAlthough it has been shown that using recycled concrete aggregate in new structural concrete is economical and sustainable, the use of this material for such applications is still not widespread. One of the reasons is that manufacturers, designers, engineers, owners, and other market players are not familiar with specifying and utilizing this material—although standards are starting to incorporate provisions for recycled aggregate concrete, successful, practical example projects are needed. The current paper describes the results of a partnership between universities and a precast concrete manufacturer of hollow core slabs. Seven hollow core slabs with volumetric replacement ratios of natural aggregate with recycled aggregate from 0% to 60% were tested to failure in both bending and shear, and then undamaged portions of the slabs were subjected to punching shear until failure. The results showed only mild differences in strength, with different replacement percentages of recycled aggregate under the various loading scenarios. Numerical simulations performed in Abaqus demonstrated the feasibility of analyzing recycled aggregate concrete structural elements and provided important insights into their behavior.

Mechanical behavior of self-compacting recycled concrete reinforced with recycled disposable medical mask fiber

The outbreak of the COVID-19 epidemic has led to a large number of waste disposable medical face masks (DMFMs) worldwide, which seriously pollute the environment and threaten human health. In this paper, waste DMFMs were recycled as mask fiber and mixed into self-compacting recycled aggregates concrete (SCRAC) to form a mask fiber reinforced self-compacting recycled aggregates concrete (FRSCRAC). The effects of recycled coarse aggregate (RCA) replacement ratio, DMFM fiber content, and length on the working and mechanical properties of FRSCRAC were investigated. The results show that the specimens meet the requirements of self-compacting concrete (SCC) in terms of working and mechanical performance, but the RCA and DMFM fiber could reduce the workability of the FRSCRAC, and the higher the amount of RCA and DMFM fiber, the more obvious the reduction. At the same time, the mechanical properties of FRSCRAC increased as the decreasing RCA replacement ratio and growing DMFM fiber content. Compared with specimens without DMFM fiber reinforcement, the compressive strength, split tensile strength, flexural strength, and elastic modulus were increased by 1.3%-9.6%, 1.46%-8.6%, 24.4%-54.69%, and 0.65%-4.73%, respectively. Moreover, the reduction of the DMFM fiber length is favorable to the mechanical properties of FRSCRAC as well. Furthermore, the X-ray CT and scanning electron microscope (SEM-EDS) techniques were applied to analyze the microstructure of typical specimens. The results showed that the DMFM fiber and surrounding mortar could form a multiphase composite, which reduces the porosity and improves interfacial stress transfer efficiency, thus enhancing the mechanical properties of FRSCRAC. In addition, based on the experimental results, the mechanical strength index of FRSCRAC and the calculation formula of its mutual conversion relationship were proposed. The research conclusions of this paper can provide a reference for the application of waste DMFM fibers in FRSCRAC.

Dynamic compressive behaviors of polyethylene terephthalate fiber reinforced recycled aggregate concrete

AbstractPolyethylene terephthalate (PET) fibers are green, environmentally friendly materials. They mainly come from recycled plastic bottles and other products. The addition of PET fibers to recycled aggregate concrete (RAC) has the potential to reduce concrete damage and increase specimen toughness. In this study, the influences of recycled coarse aggregate (RCA) replacement ratio and fiber volume ratio on the impact response of PET fiber reinforced RAC at various strain rates were experimentally investigated. It was found that the compressive strength, critical strain, and toughness grew with the increasing strain rate, followed by the aggravation of the concrete damage. Owing to the strain rate effect, the failure mode of concrete specimen at a high strain rate was different from that under a quasi‐static loading. This led to the reduction of differences in the dynamic compressive strength between the natural and recycled aggregate concrete at a high strain rate. Although the replacement of natural coarse aggregates with RCAs resulted in the decrease in the dynamic compressive strength, it increased the critical strain of the specimen. To reduce the brittleness of concrete materials, flexible fibers, PET fibers were added into the concrete matrix. It was found that the addition of PET fibers increased the critical strain and significantly reduced concrete damage. The empirical equations were proposed to describe the rate‐dependent dynamic compressive strength, critical strain, and toughness based on experimental data.

Experimental study on the triaxial compression mechanical performance of basalt fiber-reinforced recycled aggregate concrete after exposure to high temperature

The use of basalt fiber-reinforced recycled aggregate concrete (BFRRC) can effectively treat waste concrete and reduce the consumption of natural resources. BFRRC is often in complex triaxial compression in engineering applications and may exposure to high temperature conditions. To evaluate the conventional triaxial compression mechanical performance of BFRRC after exposure to high temperature, 324 cylindrical specimens were produced. The specimens were designed and fabricated by varying several experimental parameters: the recycled coarse aggregate replacement ratio, basalt fiber dosage, temperature, and lateral confining pressure. The specimens previously exposed to high temperature were subjected to conventional triaxial compression tests and the effects of various experimental parameters on the mechanical performance indexes of BFRRC were analyzed. The results show that the peak stress and elastic modulus of BFRRC all raise with greater fiber dosage and confining pressure but decrease with higher replacement ratio and temperature. The maximum increase of the peak stress and elastic modulus is 352.45% and 224.59%, respectively. The peak strain of BFRRC has two variation trends of gradual increase and gradual decrease with the replacement ratio rising. And the peak strain gradually grows with the temperature and confining pressure increasing. The fiber dosage, however, does not exert the considerable impact on the peak strain. The maximum increase of the peak strain is 132.22%. The research provides a scientific basis for the triaxial mechanical performance, fire resistance design, and post-disaster assessment of BFRRC, and promotes the popularization and application of BFRRC in building structures.

Seismic performance of ternary composite geopolymer recycled concrete columns: Experimental study and modeling

In order to achieve seismic-resistant structures cast from green building materials, a new kind of column, ternary composite geopolymer concrete with recycled aggregates containing recycled fireclay brick aggregates (GRA-RFBAC) column, was proposed in this paper. The ternary binder material in GRA-RFBAC was produced by the combination of industrial by-products (ground granulated blast furnace slag (GGBS), recycled fireclay brick powder (RFBP), and fly ash (FA)) and alkali-activated solution. Cyclic loading tests of five reinforced GRA-RFBAC columns, each with a shear-to-span ratio of 3.07, were conducted to investigate the seismic performance. The influence of the recycled aggregate containing recycled fireclay brick aggregate (RA-RFBA) replacement ratio, stirrup spacing, and axial compression ratio on the seismic performance of GRA-RFBAC columns was discussed. The results indicated that all specimens showed similar flexural failure modes under cyclic loading. The first cracking of concrete occurred within the drift ratio range of 0.18%–0.41%, the failure drift ratio varied from 3.27% to 4.11%, and the peak load of the specimens ranged from 237.50 kN to 288.87 kN. Although increasing the RA-RFBA replacement ratio led to a decrease in both the bearing capacity and lateral stiffness of the columns, the GRA-RFBAC columns showed comparable or even better seismic performance than Portland cement concrete columns. Moreover, a prediction model for the skeleton curve of GRA-RFBAC columns was proposed and verified by comparing the prediction results with the test results.

Freeze-thaw, chloride penetration and carbonation resistance of natural and recycled aggregate concrete containing rice husk ash as replacement of cement

This study investigated the effect of using rice husk ash (RHA) as replacement of cement (i.e., replacement ratios of 0%, 10%, 20% and 30%) on the durability of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). We examined the freeze-thaw resistance, chloride penetration resistance, and carbonation resistance of NAC and RAC (with 50% recycled coarse aggregate replacement ratio). It was found that during the freeze-thaw process, both NAC and RAC showed an overall weight increase, which was further enhanced by the addition of RHA. Meanwhile, the compressive strength of NAC was reduced more obviously than that of RAC after 100 freeze-thaw cycles. A replacement of 10% cement with RHA resulted in larger reduction in strength loss for NAC (by 36%) compared to RAC (by 4%). As the RHA replacement ratio increased, the chloride penetration resistance of RACs was improved more rapidly than that of NACs, and the difference in the total charge passed between NACs and RACs also decreased considerably. In addition, an increase in the RHA replacement ratio led to an increase in the carbonation coefficient of NAC. Conversely, in the case of RAC, the carbonation coefficient displayed an initial decrease at a 10% RHA replacement ratio, followed by a subsequent upward trend, indicating a positive impact of RHA on preventing carbonation for RAC.

Axial compressive behavior of steel reinforced GGBS-RFBP-FA ternary composite geopolymer recycled fireclay brick aggregates concrete columns

In this study, the axial compressive behaviors of steel reinforced ternary composite geopolymer recycled fireclay brick aggregates concrete columns were investigated. The ternary binder material used in this study was produced by the combination of industrial by-products (i.e., granulated blast furnace slag (GGBS), recycled fireclay brick powder (RFBP), and fly ash (FA)) and alkali-activated solution. A total of 60 square steel reinforced composite columns (with a 200-mm side length and 600-mm height) were tested under axial compression. The tested variables included the mix proportion of ternary composite geopolymer concrete with recycled aggregates containing recycled fireclay brick aggregates (GRA-RFBAC), the recycled coarse aggregate replacement ratios (0%, 30%, 50%, 70%, 100%), the longitudinal reinforcement ratios (1.13%, 2.01%), and the hoop stirrup reinforcement ratios (0.81%, 1.62%). Each group contained three identical samples. The ductility, failure mode, and axial load-bearing capacity of the columns were recorded and analyzed. The experimental results revealed that the damage progression and patterns of steel reinforced GRA-RFBAC columns were similar to those of ordinary Portland cement based recycled concrete columns. The ultimate bearing capacity of steel reinforced GRA-RFBAC columns decreased with an increasing replacement ratio of recycled coarse aggregate and increased with an increasing reinforcement ratio of longitudinal and hoop stirrups. Meanwhile, the stress-strain model of steel reinforced GRA-RFBAC columns under axial compression was proposed based on the experimental results. The present study suggests an efficient and environmental-friendly compression member.