Compressive Strength Of Recycled Concrete Research Articles

Influence of Accelerated Carbonation on the Performance of Recycled Concrete Containing Fly Ash, Recycled Coarse Aggregate, and Fine Aggregate.

In order to improve the quality of solid waste utilization, this study simultaneously used recycled coarse aggregate and recycled fine aggregate to prepare recycled aggregate concrete, with fly ash partially replacing cement as a binder. After the particle gradation of recycled aggregate was artificially adjusted into continuous gradation, the effects of accelerated carbonation on the performance and microstructure of recycled concrete were studied. The microstructural change was analyzed using mercury intrusion porosimetry and scanning electron microscopy-energy dispersive spectroscopy. Additionally, the environmental benefits of the recycled concrete were evaluated based on carbon emissions using the life cycle assessment method. The experimental results indicate that accelerated carbonation can increase the compressive strength of recycled concrete by up to 13%, and its microstructure becomes more compact after carbonation. The carbon emissions are reduced by more than 13% after using 20% fly ash, contributing to sustainable development. Additionally, the optimal replacement rate of recycled fine aggregate should be controlled to under 15% when both recycled coarse and fine aggregates are used.

Test of Mechanical Properties of Composite Recycled Concrete After Medium and High Temperature

Compressive strength is one of the important indexes to test the mechanical properties of concrete. The compressive strength of recycled composite concrete after high temperature is studied by single factor experimental analysis and double factor experimental analysis. Combined with variance analysis, the influence of replacement rate of recycled aggregate, volume incorporation amount of polypropylene fiber and volume incorporation amount of nani CaCO3 on compressive strength of recycled concrete after high temperature was systematically studied. The results show that when the replacement rate of recycled aggregate is 50%, the volume incorporation amount of polypropylene fiber is 0.08%, and nani CaCO3 is 1.2%, the compressive strength of composite recycled concrete reaches the maximum value. Nano CaCO3 is the most significant factor affecting the compressive strength of recycled concrete after high temperature. The significant influencing factors are the incorporation amount of polypropylene fiber and the replacement rate of recycled aggregate.

Determining the optimal gradation of mixed recycled aggregate containing coal gangue brick aggregate

Aggregate grading design is the foundation of concrete mix proportion design. Existing aggregate grading design methods are based on the tightest accumulation theory of homogeneous natural aggregates. However, this method has not been applied to mixed recycled aggregate (MRA) containing coal gangue brick aggregate (CGBA) (hereinafter referred to as MRA) due to significant differences in physical and mechanical properties. In this study, we subjected five types of MRA (initial particle size: 19–26.5 mm) to confined crushing, sieving, and grading composition analysis, then configured recycled concrete. We investigated the determination method of the optimal gradation of MRA, summarized the composition, particle distribution characteristics, and fractal characterization of the optimal gradation. This study focused on analyzing the factors that affect the compressive strength of recycled concrete, as well as examining the mix proportion design method. The results reveal that the optimal gradation of MRA can be determined using the five-stage loading method for approach minimum porosity. Our analysis of MRA gradation suggests that the mix proportion design of recycled concrete should be determined by considering the porosity of optimal gradation and the surplus volume coefficient of slurry. Finally, we determined that the water-binder (W/B) ratio is the primary factor that affects the compressive strength, while the CGBA’s intrinsic strength has a minimal impact. The replacement ratio of CGBA primarily affects the porosity of MRA and the W/B ratio, indirectly reducing recycled concrete’s compressive strength. Based on our findings, we recommend that the replacement ratio of CGBA should not exceed 50%. This study can promote the recycling of recycled concrete containing CGBA.

Effects of recycled micro-powders mixing methods on the properties of recycled concrete

Recycled micro-powders were introduced into recycled concrete by adhering them to the surface of recycled aggregate, and a systematic comparison was conducted with recycled concrete prepared with the recycled micro-powder admixture to examine the effects of the mixing modes of recycled micro-powders on the workability and mechanical properties of recycled concrete. In addition, the microhardness test, the hydration products, and the hydrated microstructure were used to investigate its mechanism. The results indicated that recycled micro-powders as a cement admixture decreased the fluidity and compressive strength of recycled concrete. However, the incorporation of recycled micro-powders attached to recycled aggregates improved the fluidity of recycled concrete and obtained a higher compressive strength; in particular, the 28d and 56d compressive strengths increased by 3.66 % and 7.28 %, respectively, compared to those of ordinary recycled concrete. When the incorporation amounts of recycled micro-powders into recycled concrete were identical, the recycled concrete exhibited a denser microstructure and higher microhardness in the interface transition zone when the recycled micro-powders were adhered to the recycled aggregate.

Mechanical performance of recycled aggregate concrete in green civil engineering: Review

The use of recycled aggregate concrete can save natural resources and reduce environmental pollution, which has been widely concerned in recent years. The physical and mechanical properties of recycled aggregate concrete (RAC) are studied based on the literature on waste concrete coarse aggregate (RCCA) and waste brick coarse aggregate (RBCA) published around the world in the last 40 years, in order to understand and study the performance of common RAC. The common characteristics (water absorption, density, and crushing value) of two recycled aggregates with the same particle size were compared. The effects of effective water–cement ratio (e–W/C), aggregate cement ratio (A/C), and recycled aggregate content on the compressive properties of recycled concrete are explained, and the microstructure of recycled concrete is explored. The influence of recycled aggregate content on its elastic modulus (Ec) and the correlation between Ec and the compressive strength of recycled concrete are also investigated. Finally, prospects were made for two types of RAC for further research by scholars.

PENGARUH SERBUK CANGKANG TELUR TERHADAP SIFAT MEKANIS BETON DAUR ULANG

In Indonesia, normal concrete construction is commonly used in the construction process. Excessive concrete waste is usually uncontrolled. Laboratory concrete testing waste can also accumulate and disturb the ecosystem and reduce the aesthetic value of a place. There have been many studies using recycled aggregate from concrete waste. Meanwhile, eggs are one of the foods frequently consumed by Indonesian. Eggshells are certainly becoming waste. According to data from the Indonesia Statistics (2019), chicken egg production in Indonesia reached 4,688,120 tons. Eggshell contains about 94% calcium carbonate with a weight of 5.5 grams. Meanwhile, calcium carbonate is the main constituent of Portland cement, accounting for 70% of other constituents. Based on the reasons above, this study was conducted to determine the effect of chicken eggshell powder as a partial replacement for cement on the mechanical properties of concrete with recycled coarse aggregate. The variations in the use of chicken eggshells in the concrete samples were 0%, 2.5%, 5%, 7.5%, and 10% of the weight of cement. To determine the mechanical properties of the concrete, compressive and splitting tensile tests were conducted using a cylindrical test specimen with a size of 10 x 20 cm. It is expected that the use of chicken eggshell powder can increase the compressive strength of recycled concrete. Based on the test results, the compressive strength of the concrete composition with 2.5% eggshell powder showed the greatest increase compared to the other compositions. This is supported by the UPV test, which showed the same result. The largest increase in splitting tensile strength was also found in the 2.5% composition. Meanwhile, good homogeneity levels were obtained in the concrete, based on the UPV test results on the test specimens at the age of 28 days.

Effect of parent concrete strength on recycled concrete performance

The reuse of concrete waste as a secondary aggregate could be an efficient solution for sustainable development and long-term environmental protection. However, the variable quality of waste concrete, especially with various compressive strengths, can have a negative effect on the final compressive strength of recycled concrete. In this approach, the major goal of this research is to study the effect of parent concrete qualities on the performance of recycled concrete. To accomplish this task, three grades of different compressive strengths (10 to 15) MPa, (20 to 25) MPa, and (30 to 40) MPa have been analyzed in an experimental test program, in which an unknown compressive strength is introduced as well. The experimental mix use 40% of secondary aggregates (both course and fine) and 60% of natural aggregates. This led to the decreasing of the compressive strength of the test concrete between 14% and 23.7% compared to the normal concrete. This loss was improved by adding an amount of cement equivalent to 4% of the weight of the recycled aggregate used. The achieved results prove that the strength properties of the parent concrete have a limited effect on the compressive strength of the recycled concrete. Additionally, low compressive strength parent concrete, when crushed, generates a high amount of fine aggregate and large percentage of recycled coarse aggregates with less attached mortar, and presents the same compressive strength as an excellent parent concrete.

Improvement of recycled aggregate properties through a combined method of mechanical grinding and microbial-induced carbonate precipitation

Due to the shortage of natural aggregates, recycled aggregates are gaining great attention in civil engineering. However, recycled aggregates have lower apparent density and higher water absorption and crushing index as compared to natural aggregates. To enhance the properties of recycled mixed aggregates (RMAs), three different treatment routes were adopted in this work: mechanical grinding, microbial-induced carbonate precipitation (MICP), and a combined method of mechanical grinding and MICP. The apparent density, water absorption, and crushing index of RMAs were examined before and after each treatment, and the slump, apparent density, and compressive strength of recycled concretes (RCs) with treated and untreated RMAs were then investigated. In addition, the micro-mechanism of property improvement due to these treatments was analyzed by scanning electron microscopy (SEM). Experimental results revealed that the combined method, in comparison to the other two methods used separately, led to higher apparent density and lower water absorption and crushing index of RMAs. Moreover, RCs treated with the combined method exhibited greater slump, higher apparent density, and superior compressive strength than untreated RCs. Furtherly, compared with commonly used RA treatment methods presented in recent publications, the proposed combined method shows better influence on compressive strength of RCs.

Correlation of porosity and properties of recycled fine aggregate concrete with fly ash

In this paper, we presented the experimental discussion of samples of recycled aggregate concrete with replacement of natural fine aggregate by recycled fine aggregate. Three mix kinds were produced and, for each of these three kinds, two levels of water to blinder ratio were used with 0%, 10% and 20% of FA. The result of the tests of drying shrinkage and compressive strength of recycled concrete were used for comparison with tests of mercury intrusion porosimetry (MIP), in which the cumulative pore volume and different intervals of pore volume were studied at ages of 28 and 91 days. Correlation graph of compressive strength and cumulative pore volume might be predicted with given W/B, days and FA of the concrete or none given and drying shrinkage might be predicted with given FA.

Evaluating compressive strength of concrete made with recycled concrete aggregates using machine learning approach

To reduce the environmental impact of construction and demolition waste of concrete, recycled concrete aggregate (RCA) has been widely utilized in concrete. The compressive strength of recycled concrete is one of the most important parameters governing the quality of concrete. The compressive strength is determined from the compression test, which requires a huge amount of materials as well as consumes cost and time. Thus, to solve those limitations, this study focused on evaluating the compressive strength of concrete made from RCA using different single and hybrid models of machine learning. Six machine learning models including Gradient Boosting (GB), Extreme Gradient Boosting (XGB), Support Vector Regression (SVR), and three hybrid models of those single models with Particle Swarm Optimization (PSO) namely GB_PSO, XGB_PSO, and SVR_PSO were used to estimate the compressive strength of recycled concrete. The input variables for modeling consisted of cement content, water content, aggregate content, natural aggregate content, recycle concrete aggregate content, sand content, water absorption rates of natural aggregate and RCA. The results of this study show that hybrid models performed better than single models in terms of prediction accuracy. The results indicated that the GB_PSO has the highest prediction accuracy with R = 0.9356, RMSE = 5.5604 MPa, and MAE = 4.2882 MPa. The results of feature importance analysis and partial dependence plots (PDP) analysis revealed that the most important variable effect on compressive strength of concrete made with RAC is cement content, whatever performance strategies of concrete made with RAC. From the results of PDP, the quantity of each material can be computed easily for the designed compressive strength. In the end, this study provides a systematic evaluation of the compressive strength prediction of recycled concrete and has a significant contribution to literature and practice.

Study on Application of Recycled Red Brick Aggregate to Concrete Block

Construction waste in Our country has a good recycling system, can carry out the production of various recycled building materials. In order to understand the availability of red brick in construction waste, the effect of the content of red brick in recycled aggregate on the physical properties and strength of recycled concrete is discussed to explore whether recycled concrete containing red brick is suitable for application in masonry blocks. The results show that there is no significant correlation between the content of red brick and the compressive strength of recycled concrete, while the slurry strength is positively correlated with the compressive strength of recycled concrete. The strength of recycled concrete can be improved by reducing the water-cement ratio. However, reducing the water-cement ratio will reduce the workability of concrete, which needs to be compensated by adding water-reducing agent. According to the experimental results of unit weight, water absorption, ultrasonic wave velocity and resistance properties of recycled concrete, the content of red brick can improve the porosity of recycled concrete and have a negative effect on durability. The overall experimental results are verified by the relevant specifications, and the recycled concrete containing red brick is suitable for class N block and meets the relevant requirements of the specifications.

The Influence of Fly Ash on the Compressive Strength of Recycled Concrete Utilizing Coarse Aggregates from Demolition Works

The compressive strength of recycled concrete with coarse aggregates with and without fly ash was studied in this paper. The recycled concrete was designed to have a compressive strength of Rn=15Mpa. The ratio of conventional aggregates and recycled coarse aggregates was 50-50. Fifteen samples for each recycled concrete aggregate had been cast and were tested 7, 14, and 28 days after curing. The experimental results indicate that the strength development of the two recycled concrete mixes is relatively uniform. Fly ash increased the compressive strength of recycled concrete by 11% for 7-day aged samples. The recycled concrete with fly ash had 7% less compressive strength than the concrete consisting of natural aggregates.

Mechanical Properties of Vitrified Micro Bubbles Recycled Concrete Mixed with Calcined Diatomite

In order to prepare vitrified micro bubbles recycled concrete that meets the requirements of strength, the basic mechanical properties of recycled concrete with different vitrified micro bubbles were tested by adding calcined diatomite. The results show that: Calcined diatomite can fill the macroscopic cracks existing in the recycled coarse aggregate and effectively improve the performance of concrete and enhance the compressive strength of recycled concrete; With the increase of the amount of vitrified micro bubbles, the apparent density, compressive strength, splitting tensile strength and elastic modulus of recycled concrete all show a downward trend. When the amount of vitrified micro bubbles is 100% and the amount of calcined diatomite is 3%, the cubic compressive strength of recycled concrete can reach 32.36Mpa and the apparent density is only 1945kg/m3. Based on the experimental analysis, a linear relationship between cubic compressive strength fcu and axial compressive strength fc of vitrified micro bubbles recycled concrete is presented.

Synergistic effects of fly ash and hooked steel fibers on strength and durability properties of high strength recycled aggregate concrete

To deal with the rising environmental issues, more attention is now being given to recycled-aggregate concrete to partly meet the demands of the construction industry. However, recycled concrete is inferior in mechanical and durability performance compared to its counterpart natural-aggregate concrete. In this study, an effective approach is presented to improve the strength and durability performance of recycled concrete using supplementary materials, namely fly ash and hooked steel fiber. Low calcium refined fly ash was used at 0%, 15%, and 30% by mass replacement of cement with three different doses of steel fiber (0%, 0.5% and 1%). Mixes were evaluated based on results of several strength (compressive strength, splitting-tensile strength, and flexural strength) and durability tests (water absorption, acid attack resistance, and chloride-ion penetration). The results showed that incorporating both steel fiber and fly ash in recycled concrete significantly improves its mechanical performance and the proposed concrete can be markedly upgraded. The strength testing revealed that a synergistic effect of 15% fly ash and 1% steel fiber upgraded the flexural, splitting-tensile, and compressive strength of recycled concrete by 73–78%, 39–50%, and 13–23%, respectively. Fly ash minimized the negative effects of both recycled coarse aggregates and steel fiber incorporation on water and chloride-ion permeability resistance of concrete. Additionally, both fly ash and steel fiber were remarkably useful in increasing the acid attack resistance of concrete.

Statistical Approach for the Design of Structural Self-Compacting Concrete with Fine Recycled Concrete Aggregate

The compressive strength of recycled concrete is acknowledged to be largely conditioned by the incorporation ratio of Recycled Concrete Aggregate (RCA), although that ratio needs to be carefully assessed to optimize the design of structural applications. In this study, Self-Compacting Concrete (SCC) mixes containing 100% coarse RCA and variable amounts, between 0% and 100%, of fine RCA were manufactured and their compressive strengths were tested in the laboratory for a statistical analysis of their strength variations, which exhibited robustness and normality according to the common statistical procedures. The results of the confidence intervals, the one-factor ANalysis Of VAriance (ANOVA), and the Kruskal–Wallis test showed that an increase in fine RCA content did not necessarily result in a significant decrease in strength, although the addition of fine RCA delayed the development of the final strength. The statistical models presented in this research can be used to define the optimum incorporation ratio that would produce the highest compressive strength. Furthermore, the multiple regression models offered accurate estimations of compressive strength, considering the interaction between the incorporation ratio of fine RCA and the curing age of concrete that the two-factor ANOVA revealed. Lastly, the probability distribution predictions, obtained through a log-likelihood analysis, fitted the results better than the predictions based on current standards, which clearly underestimated the compressive strength of SCC manufactured with fine RCA and require adjustment to take full advantage of these recycled materials. This analysis could be carried out on any type of waste and concrete, which would allow one to evaluate the same aspects as in this research and ensure that the use of recycled concrete maximizes both sustainability and strength.

Acoustic Emission Characteristics and Damage Mechanisms Investigation of Basalt Fiber Concrete with Recycled Aggregate.

This paper presents the compression failure process of basalt fiber concrete with recycled aggregate and analyzes the main factors of basalt fiber and recycled aggregate affecting the compressive strength of recycled concrete. The damage mechanism of recycled aggregate concrete is analyzed by the acoustic emission technique. With the method of acoustic emission (AE) b-value analysis, the evolution and failure process of recycled concrete from the initial defect microcrack formation to the macroscopic crack is studied. Based on the AE clustering analysis method, the damage state of recycled concrete under load grade is investigated. Finally, the failure mode of recycled concrete is explored according to the RA-AF correlation method. The results show that when the concrete reaches the curing age, the strength grade of basalt fiber regenerated coarse aggregate concrete is the highest. The basalt fiber increases the strength of regenerated fine concrete by 4.5% and the strength of coarse concrete by 5%, and reduces the strength of fully recycled aggregate concrete by 6.7%. The b-value divides concrete into three stages: initial damage, stable development of internal damage, and internal damage. The variation of AE energy, count, and event number is related to AE activity and crack growth rate. Matrix cracking is the main damage state of concrete, which is greatly affected by the strength of cement mortar. The load grade of fiber cracking in fully recycled aggregate, recycled fine aggregate, and recycled coarse aggregate concrete is 65, 90, and 85%, respectively. Basalt fiber increases the tensile failure event point of recycled concrete and delays the cracking of recycled concrete under compression. When the load grades of fully recycled fiber, recycled fine aggregate fiber, and recycled coarse aggregate fiber concrete are 65–95, 90–100, and 85–100%, respectively, the tensile failure activity increases.

Study on key micromechanics of recycled concrete based on compound random aggregate model

A compound random aggregate program of recycled concrete is developed based on the concrete damage plasticity constitutive mode using computer language. Bifacial mesoscopic models of the recycled concrete are studied with ABAQUS finite element analysis software. The mesoscopic performance of the recycled concrete are studied as follows: uniaxial compression strength, strain change, damage process, stress state, and so on. The influence factors of the mesoscopic mechanical properties of recycled concrete are analyzed. The analysis results show that there are concentration problems of tensile and shear stress in the internal and external interface area of the recycled concrete under the action of uniaxial compression load. The concentration of the tensile stress and shear stress may result in the damage failure of recycled concrete. The initial damage appears the first in weaker interfacial area, after that the damage is developed towards the mortar area. The recycled concrete compressive strength is greatly influenced by the new hardened mortar strength and old hardened mortar strength, and the influence of the interfacial area and the outer surface area is small. The mechanical properties of the recycled concrete are weakened due to the old hardened mortar.

Effect of nano metakaolin on compressive strength of recycled concrete

In order to solve the problem of waste concrete caused by demolition of old buildings, nano metakaolin was added into recycled aggregate concrete to form nano metakaolin recycled concrete. The cube compressive strength test was carried out on it, and the influence of nano metakaolin replacing ordinary Portland cement on compressive strength of recycled concrete was further studied. In this study, the internal microstructure of recycled concrete was observed by scanning electron microscope, aiming at revealing the mechanism of nano metakaolin to improve the performance of recycled concrete. BET multi-point method and BJH method were used to test the specific surface area and total pore volume of recycled concrete. The characteristics of pore size distribution were analyzed also. The results showed that when the replacement rate of recycled coarse aggregate was constant, the 28d compressive strength gradually increased with the increase of nano metakaolin content, but the increase trend was gradually slowed down. When the replacement rate of recycled aggregate were 30% and 50%, and the content of nano metakaolin was 5%, the compressive strength value each were the largest, and the increase of the compressive strength values were 17.0% and 8.0%, respectively. The compressive strength of fully recycled aggregate concrete increased most obviously, and the 28d compressive strength of fully recycled concrete with 7% nano metakaolin increased by 27.1%. There were pores in the recycled concrete with pore sizes of 3.5–4 nm mainly. The total pore volume of recycled concrete decreased after adding nano metakaolin, and the refinement of internal pore enhanced the structure compactness. The strength of recycled concrete with different substitution rates could be increased due to the incorporation of nano metakaolin. Furthermore, when the replacement rate of recycled aggregate was 30%, added 5% nano metakaolin could not only fill the micropore and microcrack of recycled aggregate itself, improve the contact surface of new and old mortar, but also fill the micropores inside the new mortar, so that the compressive strength of recycled concrete exceeded that of ordinary concrete.

Cyclic bond property of steel reinforced recycled concrete (SRRC) composite structure

For the composite structures consisting of the steel profile and recycled concrete, the interfacial bond property between steel and concrete is the most critical factor for the collaborative work. In order to study the interfacial bond property of steel reinforced recycled concrete (SRRC) structures, seven SRRC specimens were fabricated and then tested cyclically. The influences of replacement ratio of recycled aggregate and compressive strength of recycled concrete on the bond behavior of this combination were assessed by looking at failure patterns, hysteretic performance, backbone curves, characteristic loads and corresponding slip, bond strength degradation, and degradation mechanism. Test results showed that the replacement ratio of recycled aggregate dominates the onset of slip between steel and recycled concrete. The obvious pinching phenomenon appears on the hysteresis curves, indicating apparent slip characteristics between the steel profile and recycled concrete. As the chemical cementing force gradually loses effectiveness, the bond strength mainly relies on the friction to maintain the stress balance after the interfacial bond layer gradually crushes. Based on the experimental results, a simplified bond-slip model was proposed and divided into four parts, i.e. intact, hardening, degradation and failure stages, and the degradation mechanism corresponding to each segment was then analyzed in detail.

Effect of Quality and Replacement Rate on the Double Recycled Aggregate Concrete

Recycled aggregate can be used as a substitute for natural aggregate to produce good regenerated concrete, so the text use recycled coarse aggregate and recycled fine aggregate to substitute for natural aggregate with different replacement rates preparing double recycled aggregate concrete, and researching the effect of the quality and replacement rate of recycled aggregate on the mechanical properties of recycled aggregate systematically. The results show that the compressive strength of double recycled aggregate concrete is increased gradually with the improvement of the quality of recycled aggregate, and the effect from weak to strong is class I, class II and class III. On the other hand, the compressive strength of double recycled aggregate concrete is decreased gradually with the increase of the replacement rate of recycled aggregate, and the maximum reduction is up to 57.2%. Therefore, the simultaneous use of recycled coarse aggregate and recycled fine aggregate have an effect of “double weakening” on the compressive strength of recycled concrete, and it can be applied to the concrete products of low strength grade.