Self-compacting Recycled Concrete Research Articles

Axial compressive and long-term shrinkage behaviors of self-compacting recycled concrete reinforced with recycled glass fiber

Self-compacting recycled concrete (SCC) has properties of significant shrinkage deformation and early cracking, which limits its wide application in civil engineering applications. Waste fiber addition offers an effective solution to these challenges. This research focuses on waste glass fiber and explored the impact of various parameters on the performance of recycled glass fiber-reinforced self-compacting recycled aggregate concrete (RGF-SCRC). Incorporating waste glass fiber effectively inhibits the long-term shrinkage rate of RGF-SCRC and improves its axial compressive strength, with the improvement of 2.2∼15.3 % in axial compressive strength and a reduction of 17.9∼66.5 % in the long-term shrinkage rate. However, excessive fiber addition shows an negatively effect on the performance of RGF-SCRC. The optimum addition was concluded as 7.5 kg/m³. On the other hand, the waste alkali-resistant glass fiber showed a higher improvement than waste glass fiber. Moreover, microstructure analysis reveals that the waste fibers could be uniformly dispersed within the investigated specimen, effectively bridging gaps and significantly enhancing the concrete’s strength and toughness. Furthermore, the number of large pores and overall porosity were reduced, resulting in greater compactness, improved axial compressive strength, and reduced long-term shrinkage of RGF-SCRC. After 180 days of curing, the porosity of the specimens significantly decreased when compared to the 28 day curing specimens. Based on experimental results, the axial compression stress-strain relationship and long-term shrinkage curves of RGF-SCRC were fitted and modified, and proposed an axial compression constitutive relationship and a long-term shrinkage theoretical analysis model which are applicable to RGF-SCRC. The models' correctness was verified by comparing them with experimental results. These research outcomes offer valuable insights for the future practical implementation of RGF-SCRC.

Evaluation of rheological properties of sustainable self-compacting recycled aggregate concrete produced by two-stage mixing approach

The rheological properties such as static yield stress (τ0s), dynamic yield stress (τ0d), and plastic viscosity (μ) play an important role in controlling the fresh state activities of self-compacting concrete (SCC). In the present investigation, these rheological parameters of self-compacting recycled aggregate concrete (SCRAC) prepared by two-stage mixing approach (TSMA) are determined as a function of recycled coarse aggregate (RCA) percentage. Five types of samples are prepared for this purpose: M1 (0% RCA), M2 (25% RCA), M3 (50% RCA), M4 (75% RCA), and M5 (100% RCA). The static yield stress is determined by a well-accepted static yield stress formula; whereas, the dynamic yield stress and plastic viscosity are determined by Reiner-Riwlin theory in conjunction with the Bingham and modified Bingham models. The values of τ0s, τ0d, and μ are observed to increase with the increase in RCA%. This is due to the increase in internal friction between the particles. However, the influence is less in the proposed TSMA. Various conventional fresh properties of SCC of the same mixes are evaluated and the correlations between the conventional fresh properties and rheological properties have been established. Finally, the compressive strength of the samples is reported and a plausible model is developed to elucidate the mechanism based on the various characterizations including X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM). The study found that the proposed TSMA is an effective approach for improving the rheological and mechanical properties of SCRAC.

The effect of the freeze-thaw cycle and alkali-silica reaction on self-compacting recycled concrete

This article investigates the durability of recycled self-compacting concrete in relation to its resistance against freeze-thaw cycles and alkali-silica reactions. It explores the properties of fresh concrete, investigates the impact of various additives, and evaluates key factors such as spalling, weight loss, compressive strength, expansion rate, and ultrasonic properties in hardened concrete samples incorporating different levels of recycled aggregates. The findings illustrate the feasibility of achieving self-compacting recycled concrete by increasing the use of superplasticizers and adding 10% beach sand. Furthermore, incorporating 10% micro-silica and 7.5% wollastonite in the recycled mix enhances the strength of all samples, with the 25% recycled material sample demonstrating the highest strength and durability. Despite a decrease in strength and increased expansion as recycling percentages and freeze-thaw cycles rise, the recycled samples maintain acceptable durability. Additionally, this study employs the R programming language to elucidate the relationship between compressive strength and modulus of elasticity, offering valuable insights into recycled concrete performance and behavior.

Study on the calcium dissolution of self-compacting recycled concrete

Considering the effects of the replacement rate of recycled coarse aggregate (RCA), content of fly ash (FA), and solution temperature, the accelerated calcium dissolution test of self-compacting recycled concrete (SCRC) was simulated by using ammonium chloride solution. The results show that the physical properties (the mass loss ratio and the dissolution depth) and the strength degradation of SCRC increase with the increase of the replacement rate of RCA and solution temperature. With the increasing content of FA, the physical properties decrease approximately linearly, while the strength degradation first decreases and then increases. For the SCRC with 50% RCA and a dissolution age of 56 days, the dissolution depth of SCRC with the FA contents of 10%, 20%, and 30% decreased by 3.85%, 10.00%, and 15.56% respectively compared with that of SCRC without FA, and the degradation rate of compressive strength also decreased by 11.60%, 25.91%, and 15.01%, respectively. The peak stress of the stress-strain curve of SCRC under axial compression is negatively correlated with the dissolution age, replacement rate of RCA, and solution temperature, while the peak strain is positively correlated with these variables. When the dissolution age is more than 28 days, the calcium silicate hydrate (C-S-H) gels produced by low-volume (10%, 20%) FA after complete hydration lead to an increase in peak stress and a decrease in peak strain of SCRC, while high-volume (30%) FA has the opposite effect due to incomplete hydration. Finally, the performance degradation model of SCRC under calcium dissolution was established.

The rainstorm waterlogging resistance of a novel fiber-reinforced self-compacting recycled pervious concrete after freeze-thaw cycles

The poor permeability of pervious concrete after freeze-thaw (F-T) cycles is a difficult issue in the face of frequent extreme rainstorms, causing urban rainstorm waterlogging problems (stagnant water depth exceeds 150 mm). A novel fiber-reinforced self-compacting recycled pervious concrete (NSPC) with low tortuosity artificial pore channel (APC) is a pervious material with high permeability and strength, and has potential application in pervious pavement at the coupling action of F-T cycles and rainstorm. In this study, the frost resistance, mechanical properties and permeability of C60 NSPC (pore diameter of 3 mm, porosity of 1.13%) with various steel fiber contents (0 vol%, 0.5 vol%, 1 vol%, 1.5 vol% and 2 vol%) were investigated, and then the rainstorm waterlogging resistance of NSPC after 300 F-T cycles was examined under 20-, 50- and 100-year rainstorm. Results showed that the macroscopic destruction of NSPC surface after F-T cycles always started near the APCs, and the existence of APCs aggravated the mass loss and the decrease of the relative dynamic modulus of elasticity. As the increase of steel fiber content, the compressive strength loss of NSPC decreased first and then increased after F-T cycles. The use of steel fiber enhanced the integrality inside the APCs of NSPC and reduced the APC clogging rate, which improved hydraulic-conductivity properties after F-T cycles. After 300 F-T cycles, NSPC with 2% steel fiber achieved an excellent rainstorm waterlogging resistance (stagnant water depth of 0 mm), regardless of the rainstorm return period. Through F-T damage analysis, in order to cope with waterlogging, the maximum FT failure thresholds of NSPC to prevent stagnant water of 50, 70 and 100 mm are 0.097, 0.125 and 0.161 respectively, equivalent to 196, 243 and 264 F-T cycles. This study designed a NSPC that can dissipate stagnant water after F-T cycles, which provided a promising route towards solving urban rainstorm waterlogging.

Rainstorm Resistance of Recycled Pervious Concrete under the Coupling of Fatigue and Freeze–Thaw Cycles

In order to alleviate the increasing serious urban waterlogging problem, the rainstorm resistance of a new self-compacting recycled pervious concrete (NSRPC) under the coupling of freeze–thaw (F-T) and fatigue is studied. The once-in-a-century rainfall was simulated, and the rainstorm resistance of NSRPC was evaluated mainly through the ponding depth and drainage time. In addition, the mechanical properties (compressive strength and flexural strength), mass loss rate and relative dynamic elastic modulus of NSRPC during F-T and fatigue coupling were measured. The microstructure of NSRPC was observed by scanning electron microscopy, and its deterioration mechanism was analyzed. The results show that the fatigue load aggravates the F-T damage of NSRPC in the later stage. With the increase in the number of fatigue cycles, the loss rate of compressive strength and flexural strength of NSRPC increases continuously, and the permeability coefficient decreases first and then increases. With the increase in the number of freeze–thaw and fatigue cycles, the mass loss rate increases gradually, and the relative dynamic elastic modulus decreases gradually. After the coupling of fatigue and F-T cycles, the minimum mass loss of NSRPC is only 2.14%, and the relative dynamic elastic modulus can reach 86.2%. The increase in the number of fatigue cycles promotes the generation and expansion of micro-cracks and provides more channels for water to invade the matrix. Under the action of rainstorm in the 100-year return period, the maximum ponding depth of NSRPC with steel fiber content is 84 mm, and the drainage time is 7.1 min, which meets the needs of secondary highway. This study will provide theoretical basis for improving the service life and drainage capacity of urban drainage pavement in cold areas.

To determine the compressive strength of self-compacting recycled aggregate concrete using artificial neural network (ANN)

Nowadays, special concrete-like self-compacting concrete (SCC) requires sustainability by introducing recycled aggregates as a partial replacement for natural aggregate. Technological development initiatives in the construction sector estimate the 28 days' concrete compressive strength before casting due to faster requirement; one method selected is an artificial neural network. From works of literature, 515 mixed design are collected and utilized for training, validation, and testing data to prepare models. Different applications of SCC require different strengths of concrete. Based on control mix compressive strength, the mix designs are grouped into three families as low, medium, and high strength, apart from a common family. The correlation between input and output variables for three different families is analyzed. ANOVA analyses are done for input parameters. Coefficient of relation (R2) is used for sensitive assessment and results for family I (R2 = 0.9299), family II (R2 = 0.824), family III (R2 = 0.8775), and family IV (R2 = 0.7991). Two further sensitivity analyses indicate that input parameters' influence varies for different families.

Study on the mechanical properties of self-compacting recycled aggregate concrete using CFB slag as fine aggregate

To reveal the influence of CFB slag on the mechanical and expansion properties of self-compacting recycled aggregate concrete (SCRAC), five SCRACs with different CFB slag replacement amounts were made, the cubic compressive strength test, the splitting tensile strength test, the axial compressive strength test, and the dry shrinkage test were carried out. The failure processes and failure forms of SCRAC under compression and tension were observed. The effects of the influence of the CFB slag replacement rate on the basic mechanical properties of SCRAC were analyzed. The conversion relationship between various mechanical indicators of SCRACs was explored. The drying shrinkage performance of SCRAC was tested using the grey theory. The test results indicate that the compressive failure of SCRAC using CFB slag as fine aggregate is similar to that of SCC. The results show that the cubic compressive strength, splitting tensile strength, and axial compressive strength of self-compacting recycled concrete are the highest when the sand replacement ratio of CFB slag is 10%. The proposed conversion relationship between the cubic compressive strength of SCRAC and other mechanical properties indexes has high accuracy. GM (1, N) model and grey correlation analysis were established to analyze the influencing factors of drying shrinkage of SCRAC. The drying shrinkage deformation of SCRAC using CFB slag as fine aggregate has a hyperbola relationship with time, and a lower CFB slag sand replacement rate can compensate for the shrinkage of SCRAC.

The effect of treated recycled steel fibers and slag on the properties of recycled self-compacting concrete

The effect of treated recycled steel fibers and slag on the properties of recycled self-compacting concrete

Combined effect of ground granulated blast-furnace slag and metakaolin on the performance of recycled self-compacting concrete

Combined effect of ground granulated blast-furnace slag and metakaolin on the performance of recycled self-compacting concrete

Evaluation of the rheological properties of self-compacting recycled aggregate concrete

In this paper, the rheological behavior of self-compacting concrete (SCC) containing recycled coarse aggregate (RCA) is presented. For this purpose, RCA is obtained from construction and demolition (C&D) waste and replaced in various proportions in the mixes of SCC. The variation of rheological properties such as shear yield stress and plastic viscosity of SCC are evaluated employing the well-established Bingham and Modified Bingham models. Analyzing the results critically, it is observed that with the increase in RCA percentages, the yield stress and plastic viscosity are increased. The increase in both yield stress and plastic viscosity is due to the presence of adhered mortar on the surface of RCA, which increases the friction among the particles and absorbs water. Finally, the field emission scanning electron microscopy (FESEM) analysis is done to justify the phenomenon.

Effect of recycled concrete aggregate with different degrees of initial alkali–aggregate reaction damage on the mechanical behavior and porosity of self-compacting recycled aggregate concrete

The use of recycled concrete aggregate (RCA) is an effective approach to achieve environmental sustainability. However, the presence of defects due to previous alkali–aggregate reactions (AARs) has caused reluctance toward its use in constructions. This study investigated the application and influence of RCAs with different degrees of initial AAR damage on the mechanical behavior and porosity of self-compacting recycled aggregate concrete (SCRAC). Concrete cubic specimens with different degrees of AAR were produced by soaking the raw materials in a high-alkaline solution. In order to obtain RCAs with different initial AAR durations of 7, 28, 60, and 210 days. The specimens were then crushed using a jaw crusher. The residual reactivity of the RCA produced from concrete affected by the AAR was detected using the accelerated mortar bar test. The rheological properties of the SCRAC with different RCAs were tested. Compressive strength, flexural strength, mercury intrusion porosimetry, and scanning electron microscopy tests were conducted to analyze the effects of RCAs with different degrees of initial AAR damage on the mechanical properties and porosity of the SCRAC. The results show that the RCA can maximally strengthen the compressive strength of the SCRAC after 60 days of alkali immersion at a replacement rate of 30 %. Furthermore, a prediction model considering the filling effect for calculating the influence of RCAs with initial AAR damage on the compressive strength of the SCRAC was proposed. For practical engineering applications, the AAR can strengthen RCAs and improve the utilization rate of RCA, which is beneficial for the sustainable development of the environment.

Durability behaviour of high-volume fly ash self-compacting recycled aggregate concrete

This study presents utilisation of high-volume fly ash (HVFA) in the design of self-compacting concrete (SCC) containing alternative aggregate particles. Class F fly ash was used in a binary blend of Portland cement at a fixed dosage of 50% by weight of powder, and natural coarse and fine aggregates were replaced with coarse and fine recycled concrete aggregates (RCAs), respectively, at replacement levels of 0, 50 and 100% by volume. The durability properties of the SCC mixes were studied using the rapid chloride penetration test, initial surface absorption test and capillary suction test. The results of the study showed that the concrete mix made with replacement of natural coarse aggregates with 50% coarse RCAs, the concrete mix made replacement of natural fine aggregates with 50% fine RCAs and the concrete mix made with replacement of both natural coarse and fine aggregates with the respective RCAs at 50% replacement levels had satisfactory performance without compromising their fresh and hardened-state properties. Furthermore, the incorporation of HVFA in SCCs improved the hardened-state properties at later ages of curing due to the secondary pozzolanic reaction.

Frost resistance of fiber-reinforced self-compacting recycled concrete

Abstract Freeze–thaw damage and the lack of aggregate resources have become two major problems facing the construction industry. The use of recycled aggregate to produce recycled concrete has good social and economic value. In this study, the author used recycled coarse aggregate as a substitute for stone to mix recycled concrete. In order to enhance the performance of concrete, a microwave heating modification process was introduced and 0.10% volume fraction of polypropylene fiber (PPF) was added. The effect of microwave heating modification on the frost resistance of fiber-reinforced self-compacting recycled concrete was studied. The results show that with the increase in the number of freeze–thaw cycles, the degree of denudation and deterioration of the three groups of concrete surfaces becomes more and more serious, the number of surface cracks gradually increases after the concrete is damaged, and the plastic deformation becomes more and more serious, W n gradually increases, E n gradually increases, D n gradually increases, σ 0 gradually decreases, ε 0 gradually increases, ε u gradually increases, E c gradually decreases, and μ gradually decreases. Under the same number of freeze–thaw cycles, the frost resistance of the three groups of concrete is A > C > B. Microwave heating modification improved the frost resistance of group C concrete compared to that of group B concrete. Due to the incorporation of PPF into the concrete, the load did not drop sharply when the load acting on the concrete reached the failure load. The prediction results of the established constitutive model are in good agreement with the experimental results.

Performance keys on self-compacting concrete using recycled aggregate with fly ash by multi-criteria analysis

This study proposes prioritizing of performance for self-compacting concrete (SCC) using recycled aggregate (RA) and/or waste fly ash (FA). A robust framework is created considering six performance keys in technical-environmental-economic performance criteria and analyzed by the three multi-criteria decision-making (MCDM) techniques: TOPSIS, VIKOR, and EDAS. For technical performance, slump flow, flow time, compressive strength, flexural strength, chloride ion penetration coefficient, and the resistance against freeze-thaw cycles and elevated temperature are considered for curing age up to 740 days. While CO₂ emissions and volume of raw materials are evaluated to express the environmental performance. The optimized SCC mixtures suggested by the three MCDM are the ones that combine the use of RA and FA, and the best mixture can be made when 50% RA with 15% FA are utilized. For the optimized SCC, the cost would be 23.9% lower and can offer annual savings of 5.7–8.7 million USD if used in infrastructure projects within developing countries. The proposed framework can be employed for sustainable, economical, and performance based-design applications on the recycled SCC using FA.

Application of silica fume in high-volume fly ash self-compacting recycled aggregate concrete

ABSTRACT Recent advancement in construction practices demands the utilisation of construction materials in a sustainable way which promotes the use of industrial by-products as Supplementary Cementitious Materials (SCMs) and alternative aggregates to protect diminishing natural resources. The present study proposed the utilisation of high-volume fly ash in the production of Self-Compacting Concrete (SCC) made with varying proportions of coarse and fine recycled aggregates. Natural Aggregates (NA) of both coarse and fine type in high-volume fly ash SCC were replaced with the respective type of recycled aggregates at the dosage of 0%, 50% and 100% by volume and their hardened state behaviour was studied in terms of compressive strength, chloride ion permeability, initial rate of water absorption, sorptivity coefficient and sulphate resistance. Results of the investigation recommends uses of Silica Fume (SF) at 10% dosages in ternary blends of cement along with high-volume fly ash for the production of SCC at 50% replacement level of both coarse and fine recycled aggregates, without compromising the hardened state properties of concrete.

To predict the compressive strength of self compacting concrete with recycled aggregates utilizing ensemble machine learning models

This study aims to apply machine learning methods to predict the compression strength of self-compacting recycled aggregate concrete. To obtain this goal, the ensemble methods: Random Forest (RF), K-Nearest Neighbor (KNN), Extremely Randomized Trees (ERT), Extreme Gradient Boosting (XGB), Gradient Boosting (GB), Light Gradient Boosting Machine (LGBM), Category Boosting (CB) and the generalized additive models: Inverse Gaussian (GAM1) and Poisson (GAM2) were applied. For the development of the models, 515 research article samples were collected and divided into three subsets: training (360), validation (77), and testing (78). The SCC components: cement, water, mineral admixture, fine aggregates, coarse aggregates, and superplasticizers were taken as input variables and compression strength as output variables. To determine the ability of the models to project compressive strength, the following metrics were used: R2, RMSE, MAE, and MAPE. The results indicate that the RF (R2 = 0.7128, RMSE = 0.0807, MAE = 0.06) and GB (R2 = 0.6948, RMSE = 0.0832, MAE = 0.0569) models have a strong potential to predict the compressive strength of SCC with recycled aggregates. The sensitivity analysis of the RF model indicates that cement and water are the variables that have the highest impact in predicting the compressive strength, while coarse aggregate has the lowest impact.

Effect of temperature on fatigue behaviour of self-compacting recycled aggregate concrete

The most recommendable frequency range for concrete fatigue tests is between 1 and 15 Hz. It has been clearly established that performing the tests at low frequency (<1 Hz) reduces the fatigue limit because it increases test time and therefore, creep damage. On the other hand, there are not enough studies analysing tests above 15 Hz, which could greatly reduce test time. In this work, three recycled concretes were characterized, starting with the comparison between tests at moderate frequency (10 Hz) with tests at very high frequency (90 Hz). From these tests it was observed that, in all cases, the fatigue limit or fatigue life was notably lower in the case of performing the tests at high frequency. The test results show that, in the case of tests performed over the fatigue limit, the temperature of the specimens rises up to approximately 100 °C, while, in the case of tests performed with strength lower the fatigue limit, the temperature stabilises at around 65 °C. In order to analyse whether the temperature was the cause of the reduction in the fatigue limit, creep tests were carried out at 3 temperatures: 20, 65 and 100 °C, and it was possible to verify that creep damage became significantly greater as temperature was increased, and that this effect was emphasized in those cases where the concretes were made with recycled crushed concrete aggregates.

Bearing Capacity of Recycled Self-Compacting Concrete-Filled Circular Steel Tubular Long Columns Subjected to Axial Load

To investigate the ultimate bearing capacity and deformation of the recycled self-compacting concrete-filled circular steel tubular (RSCCFCST) long columns subjected to axial load, nine specimens with different recycled self-compacting concrete (RSCC) strength grades and slenderness ratios are tested. The experimental results indicate that the lateral deflection dominates the buckling failure of the specimens. The ultimate bearing capacity of the specimens is enhanced gradually as the RSCC strength grade increases but decreases as the slenderness ratio rises. The load-strain curves are linear and basically coincide at the elastic stage. The decrease in the slenderness ratio or increase in the RSCC strength grade contributes to the improvement of the stiffness and ultimate circumferential and axial strains of the columns gradually. Based on the combined tangent modulus theory and bearing capacity of the RSCCFCST short columns, two estimation models are presented to predict the ultimate bearing capacity of the RSCCFCST long columns. Additionally, comparisons between the calculation results of the ultimate strength demonstrate that the prediction models established in this study are more accurate than the other specifications mentioned.

Experimental study on Mechanical Properties of green and environmental friendly self-compacting recycled concrete

By replacing cement with 5% of ground rice husk powder, 4% of corn stalk powder and 30% of fly ash, and replacing natural aggregate with 25% recycled aggregate, the Mechanical Properties of green and environment-friendly self-compacting recycled concrete were studied. The experimental results show that the early strength of the concrete is lower than the common self-compacting concrete. However, the strength of 56 days is up to the design requirement and the volume stability is good. According to the test value of the compressive strength of the concrete block, the curve equation of the relationship between the compressive strength and the age is put forward, and it provides a reference for similar concrete mix proportion design.