Recycled Aggregate Content Research Articles

Chloride permeability of recycled aggregate concrete under the coupling effect of freezing-thawing, elevated temperature or mechanical damage

Chloride penetration frequently leads to a steel corrosion and reduces the durability of reinforced concrete. Although the previous studies have investigated the chloride permeability of recycled aggregates concrete (RAC), the chloride permeability of RAC with pre-damage received little considerations. Considering that the RAC may be subjected to various exposure environments, this paper focused on exploring the chloride permeability of RAC under the coupling effect of freezing-thawing, elevated temperature or mechanical damage. The freezing-thawing, elevated temperature or applied loading test was first employed to induce initial damage on RAC, and then the chloride diffusivity test was conducted on RAC with various pre-damages. The findings showed that the chloride permeability of RAC increased with increasing recycled coarse aggregate (RCA) content. Exposing to harsh environment, the incorporation of RCA increased the freezing-thawing, elevated temperature or mechanical damage of RAC. The chloride permeability increased with increased initial damage, and a good relation could be observed between them. The incorporation of RCA improved the sensitivity to the chloride permeability of RAC exposed to harsh environment; such as, the chloride diffusion coefficient of RAC with 100% RCA was 51.4% higher than that of the plain concrete without pre-damage, while the results were 233.3% and 62.1% after 75 freezing-thawing cycles and 80% fc.

Experimental Study on Carbonation Behavior of Waste Fiber Recycled Concrete

Based on the rapid carbonization test process of concrete, this paper studies and analyzes the influence of water-cement ratio, recycled aggregate content, fiber length and fiber content on the carbonation rule change of waste fiber recycled concrete. The results show that the depth of carbonization increases with the increase of water-cement ratio. With the increase of the replacement rate of recycled aggregate, the carbonation depth increases. The carbonation depth decreases with the increase of fiber length. As the proportion of waste fiber content increases, the carbonation depth does not change monotonously. The best content is 0.12%.

Performance assessments of open-graded cement stabilized macadam containing recycled aggregate

Increased awareness of sustainability has called for increasing use of construction waste in civil infrastructures. However, the incorporation of construction waste should be well examined without compromising the performance. There are few studies focusing on applying construction waste in pervious concrete. This study was aimed at exploring the feasibility of reusing recycled aggregate from construction waste for open-graded cement stabilized macadam (OGCSM) and evaluating its performance. Various replacement ratios of recycled aggregate ranging from 0% to 100% were designed and studied in the OGCSM. The performance of OGCSM containing recycled aggregate are comprehensively evaluated. Specifically unconfined compressive strength (UCS) test, indirect tensile strength (ITS) test, compression resilience modulus test, dry shrinkage test, frost resistance test, and permeability test were conducted. As the results showed, the UCS, ITS and compression resilience modulus of OGCSM decreased with the increase of replacement ratios of recycled aggregate. Dry shrinkage performance also declined with the increase of recycled aggregate content while permeability performance increased with the increase of recycled aggregate content. The UCS after freeze-thaw cycles declined with the increase of recycled aggregate content and cycles. However, there was no significant correlation between residue strength rate and recycled aggregate content. When the replacement ratio was 30%, the residue strength rate was maximum. Although the performance of OGCSM declined with the increase of recycled aggregate content, it could be potentially used in the base of the highway when the performance of OGCSM containing appropriate amount of recycled aggregate met the requirement of base layer of pavements.

Mechanical properties and freeze-thaw durability of recycled aggregate pervious concrete

Recycled aggregate (RA) was obtained from waste cement concrete brick with the method of crushing and sieving. In order to research the effect of RA content on the properties of pervious concrete, RA was added to replace natural aggregate with equivalent quality method at different levels (25%, 50%, 75% and 100%). The natural aggregate pervious concrete and RA pervious concrete were prepared in the lab. The porosity, permeability, compressive strength, flexural strength and freeze-thaw (F-T) durability of RA pervious concrete were tested. The results indicated that the compressive strength and flexural strength of RA pervious concrete decreased with the increase of RA content. The rapid decreases for compressive strength and flexural strength occurred when the RA content was 25%-75% and 0%-25%, respectively. The porosity and permeability decreased slowly with the increasing RA content. F-T durability of RA pervious concrete was poorer than the natural aggregate pervious concrete. The incorporation levels had negative effect on the F-T durability, but the compressive strength loss of all groups after 25 F-T cycles met the requirement of the national standard. Although the mechanical properties and F-T durability of RA pervious concrete are not satisfied, it can still be used for sidewalks, parks and other light traffic roads.

Properties of high-calcium and low-calcium fly ash combination geopolymer mortar containing recycled aggregate

This study presents the properties of a recycled aggregate geopolymer mortar made with a blend of high-calcium fly ash (HCF) and low-calcium fly ash (LCF). An experimental study was divided into two series. In series I, an effort was made to produce a more durable HCF geopolymer by partially replacing a portion of the HCF with LCF. A mortar with a 50:50 weight blend of HCF and LCF provided a high early strength and showed excellent potential in an acidic environment. In series II, recycled aggregate was used in the LCF-blended HCF geopolymer mortar. The results showed that the compressive strength of the geopolymer mortar decreased with an increase in the recycled aggregate content. The results also indicated that application of the mortar made with recycled aggregate under aggressive conditions should be avoided. However, a mixture with 25% recycled aggregate showed a compressive strength similar to that of the control mixture containing 100% natural aggregate.

Influence of fly ash on the compressive strength of concrete containing recycled aggregate

It is well known that the mechanical properties of concrete containing recycled aggregate (RA) are generally inferior to those of concrete made with natural aggregate. The residual compressive strength of concrete after exposure to high temperature and freeze–thaw cycling was investigated experimentally, and the influence of adding fly ash (FA) was examined. Two hundred and twenty-eight 100 mm cubes were compression-tested to failure. The water/binder (w/b) ratios tested were 0·34, 0·40 and 0·50. The RA replacement levels were 0, 30, 50, 70 and 100%, and the FA replacement levels were 0, 30 and 50%. The high-temperature exposure was 3 h at 400°C. Fifteen cycles of freezing to −18°C and thawing to +5°C were applied. Increasing the w/b ratio or the FA or RA content generally weakened the concrete. FA in the mix minimized to some extent the adverse effect of exposure to high temperature, but the concrete’s freeze–thaw performance was poorer with FA in the mix.

Effects of Recycled Aggregate on Concrete Mix and Exposure to Chloride

Construction and demolition waste has dramatically increased in the last decade, and most of it goes into landfills, increasing the burden on landfill loading and operations. Recycling of concrete is needed from the viewpoints of environmental preservation and effective utilization of resources. Regarding the durability of concrete, chloride diffusion, which is one parameter that reflects the durability of concrete, is tested in this study. Concrete made with different percentages of recycled aggregate (0%–100%, with increments of 10%) is investigated using mechanical and nondestructive testing of mixes consisting of two aggregate particle sizes (1/2″ and 3/8″). In addition, we studied the chloride diffusion of saturated concrete made with different percentages of recycled aggregate. The samples were exposed to sea water with 3% chloride concentration and tested after 2 and 4 weeks of exposure. The results indicate that the density and air content of new concrete decreased with an increase in recycled aggregates content. Compressive strength decreased with the increase in the recycled aggregate content, and a concrete mix with 40% recycled aggregate exhibited the best strength. Concrete mix with 30% recycled aggregate had the lowest chloride penetration after 2 weeks of saturation and performed better than a concrete mix with 100% natural aggregate. Owing to the lower density and higher water absorption of recycled aggregates, chloride ion diffusion increased with increasing recycled aggregate content beyond 2 weeks.

ДЕФОРМИРОВАНИЕ ЦЕНТРАЛЬНО СЖАТЫХ ЖЕЛЕЗОБЕТОННЫХ КОЛОНН ИЗ БЕТОНА С ДОБАВЛЕНИЕМ КРУПНОГО ЗАПОЛНИТЕЛЯ ИЗ БЕТОННОГО ЩЕБНЯ

The article presents results of experimental studies of centrally compressed reinforced concrete columns with the addition of concrete rubble as coarse aggregate. Previous studies shows that recycled concrete in the form of crushed concrete rubble obtained from construction waste is an environmentally friendly alternative to traditional coarse aggregate for the manufacture of load-bearing structures. Currently, the scientific literature has a limited amount of information about the calculation methods to be used for the design of reinforced concrete columns with the addition of concrete rubble as coarse aggregate. In this paper, the experimental data on the physicomechanical properties of concrete available in the foreign and domestic literature are summarized. In addition, the deformation features of reinforced concrete columns are highlighted to substantiate the initial premises, hypotheses and possible limitations when developing methods for calculating centrally and eccentrically compressed elements from the specified concrete. Researches are analyzed related to the effect of different content of recycled concrete aggregate in the concrete, the number of longitudinal steel reinforcement in the cross section of the element and its yield strength, pitch and yield strength of transverse reinforcement on the deformability and bearing capacity of concrete columns with the addition of coarse aggregate from concrete rubble. The use of such concrete for the manufacture of centrally and eccentrically compressed concrete columns leads to an insignificant decrease in their bearing capacity. This indicates the possibility of recycling a significant amount of concrete rubble resulting from the processing of reinforced concrete structures destroyed during the demolition of buildings; it allows to attribute this technology to “green building”.

Physicochemical properties of alkali activated GGBS and fly ash geopolymeric recycled concrete

Reuse of recycled aggregates (RA), which are from construction and demolition wastes, and fly ash and ground granulated blast furnace slag (GGBS), which are from industry by-products, in geopolymeric recycled aggregate concrete (GRAC) could provide a sustainable solution to deal with the increasing construction waste and to reduce the CO2 emission from OPC production. This work aims to investigate the workability, mechanical performance and hydration mechanism of GGBS and fly ash based alkali activated GRAC. In this study, the RA were used to replace different levels (0%, 30%, 50%, 70% and 100%) of natural aggregates, and GGBS and fly ash based geopolymer was used to replace 100% of OPC. A series of slump, setting time, compression, XRD and SEM tests were conducted to evaluate the effects of RA content and water-binder ratio on the physicochemical properties of this green concrete. It is found that the combination of fly ash and GGBS based geopolymer and RA can provide an excellent compression resistance in concrete. The compressive failure of GRAC was dominated by the defects in RA and the ITZ. However, the denser geopolymer matrix could modify these shortages in RA and the ITZ, resulting in that GRAC have better mechanical properties than conventional concrete.

The Influence of Heat and Mechanical Treatment of Concrete Rubble on the Properties of Recycled Aggregate Concrete.

Concrete is a building material commonly used for ages. Therefore, in the result of repairs or demolition of building structures, large amounts of concrete rubble are created, which requires appropriate management. The aim of the realized research was to determine the influence of heat and mechanical treatment of concrete rubble on the properties of recycled aggregate concrete. The research experiment included 12 series, with three variables: X1—roasting temperature (300, 600, 900 °C), X2—time of mechanical treatment (5, 10, 15 min), X3—content of coarse recycled aggregates (20, 40, 60% by volume). Two additional series containing recycled aggregate without treatment and natural aggregate were also prepared. Established properties of individual aggregates have confirmed a positive effect of thermo-mechanical treatment. Then, based on the results of compressive strength, flexural strength, Young’s modulus, volumetric density, water absorption, water permeability and capillarity, the most favourable parameters of heat and mechanical treatment of concrete were determined. The test results showed that appropriate treatment of concrete rubble allows to obtain high-quality coarse aggregate and valuable fine fraction. This was also confirmed by the macro- and microscopic observations of the aggregate and separated cement paste. Works realized on the concrete recycling method resulted in obtaining a patent PAT.229887.

The deterioration law of recycled concrete under the combined effects of freeze-thaw and sulfate attack

The freeze-thaw of the 3% Na2SO4, 5% Na2SO4 and 10% Na2SO4 (mass fraction) solutions and water was tested using the quick freezing method for recycled concrete, with a water-binder ratio of 0.45 and a recycled aggregate content of 30%. The damage-deterioration law of recycled concrete was studied from the aspect of changes in the weight of recycled concrete, relative dynamic elasticity modulus, loss of compressive strength, thickness of the damage depth, and compressive strength of the damaged layer concrete. Combined with scanning electron microscopy, the composite damage mechanism of recycled concrete under sulfate and the freeze-thaw cycles was analyzed. The results revealed that the relative dynamic elasticity modulus of recycled concrete presents three stages: slow declining stage, rapidly declining stage, and accelerated declining stage. Compressive strength exhibited a slow declining stage, and accelerated the loss of two stages. With the increase in freezing and thawing times, the ultrasonic velocity in the damaged layer of recycled concrete decreases, the thickness of the damaged layer increases, the compressive strength of the recycled concrete in the damaged layer decreases, and the damage degree of the recycled concrete increases. The freeze-thaw damage of recycled concrete in the 5% Na2SO4 solution was serious, and the frost resistance was the worst. In the 3% Na2SO4 solution, the degradation degree of recycled concrete in the early stage of the freeze-thaw cycle was smaller than that of water, and the degradation degree of recycled concrete was more than that of water after 200 cycles of freezing and thawing. The deterioration of recycled concrete in the 10% Na2SO4 solution was greater than that of the 3% Na2SO4 solution and water. Through theoretical analysis and experimental data regression, the freeze-thaw damage model of recycled concrete with different sulfate concentration is established.

Creep of recycled aggregate concrete: Experimental database and creep prediction model according to the fib Model Code 2010

Recycled aggregate concrete (RAC) is a promising solution to addressing the sustainability issues raised by concrete production. However, its long-term properties are not fully characterised, especially creep behaviour, which is significant for the design of RAC structures. This study presents the results of a meta-analysis of previously published research on the creep behaviour of recycled aggregate concrete (RAC). The main goal of the study is to formulate an analytic expression for the creep coefficient of RAC as an extension of the fib Model Code 2010 creep prediction model. A database of experimental results on the creep of RAC and companion natural aggregate concrete (NAC), produced with the same effective water-cement ratio, was compiled from available literature and using strict selection criteria. The database is comprised of results from 10 studies, 46 creep curves (14 NAC and 32 RAC) and 233 data points. Compared with companion NAC, RAC displays a larger creep coefficient; the difference between RAC and NAC increases with increasing recycled concrete aggregate (RCA) content and decreases with increasing RAC compressive strength. When predicting the creep coefficient of RAC using the fib Model Code 2010’s creep prediction model, relative to the model’s performance on companion NAC, the creep coefficient of RAC is underestimated. A correction coefficient for the creep coefficient of RAC, ξcc,RAC, is proposed for use with the fib Model Code 2010 model, dependent on RAC compressive strength and RCA replacement ratio.

Mechanical properties of steel fiber reinforced recycled aggregate concrete

This study experimentally investigates the mechanical properties of steel fiber reinforced recycled aggregate concrete (SFRRAC). The smaller strength and ductility of recycled aggregate concrete (RAC), compared to those of natural aggregate concrete (NAC), have restricted its use to mainly non‐structural applications in the construction industry. Such limitations in the mechanical behavior of RAC can be overcome by adding industrial steel fiber (SF). In this study, the split‐tensile strength, the compressive strength, the toughness under compression and the elastic modulus for 25 SFRRAC mixes are experimentally investigated. These 25 mixes were prepared from combinations of five different volume fractions of SF, 0, 0.3, 0.5, 0.7 and 1.0% and five different replacement proportions of natural aggregates (NA) by recycled aggregate (RA), 0, 30, 50, 70 and 100%. From experiments, it was observed that the split‐tensile strength, the compressive strength and the elastic modulus of SFRRAC mixes decreased with RA content; the split‐tensile strength and the toughness under compression increased with SF content. However, there was no clear correlation observed between the SF content and the compressive strength or the elastic modulus. Regression models were established based on the RA and SF contents in the SFRRAC mixes to predict their split‐tensile strength, compressive strength and elastic modulus.

Valorization of marble waste in the manufacture of concrete

The building materials manufacturing industry generates a lot of waste and their landfill has many problems (including the place occupied by the storage sites, the importance of the costs and the impact on the environment). This industry does not pose problems only at the end of the life cycle of these materials. It is imperative to find means of recovery and reuse of these wastes and therefore to propose another alternative to the depletion of aggregate sources. The main objective of this study is to show technically the possibility of using the aggregates from the manufacture of marble as a substitute in hydraulic concrete. The article presents the methodology of study and characterization of marble scrap, as well as the different formulations of concretes; series of tests have been developed, with a constant W / C ratio for a variable recycled aggregate content. The study consists of analyzing the results obtained and its comparison with a control concrete (100% natural aggregates); the rheological properties in the fresh and mechanically hardened state of concretes with different proportions of aggregates from marble waste (25%, 50%, 75%, 100%). The results show that marble waste is ready to be used as substitute material.

Shrinkage of recycled aggregate concrete: experimental database and application of fib Model Code 2010

This paper describes a meta-analysis of previously published studies on the shrinkage strain of recycled aggregate concrete (RAC). The study aims at providing an analytic expression for the shrinkage strain of RAC to be used in conjunction with the existing fib Model Code 2010 shrinkage prediction model. For this purpose, a database of experimental results on the shrinkage of RAC and companion natural aggregate concrete (NAC), produced with the same water-cement ratio, was compiled using strict selection criteria. Results from 19 studies entered into the database, consisting of 125 shrinkage curves (39 NAC and 86 RAC) with a total of 424 data points. A comparison of RAC and companion NAC revealed that, on average, RAC displays a larger shrinkage strain. This difference increases with increasing recycled concrete aggregate (RCA) content and with decreasing compressive strength. Applying the fib Model Code 2010 shrinkage prediction model revealed that, relative to its performance on NAC, the shrinkage strain of RAC is underestimated. Finally, a correction coefficient for the shrinkage strain of RAC, $$\xi _{{\mathrm{cs}},{\mathrm{RAC}}}$$, to be used in conjunction with the fib Model Code 2010 model, was proposed in the form of a bivariate power function with RAC compressive strength and RCA replacement ratio as variables.

Workability and mechanical property of low grade pumping concrete modified by recycled coarse aggregate

In recent years, the construction industry has entered a stage of rapid development in Chinawith more and more construction waste, which has a great negative impact on natural resources and environment. These building wastes can be processed into recycled aggregate by sorting, crushing and processing. This kind of technology can realize the recycling of construction waste [1]. In order to promote the research and application of recycled aggregate concrete, this paper probes into the effect of recycled coarse aggregate (RCA) on the performance of pump concrete. By using the orthogonal test to studied the impact of the amount of fly ash, replacement of RCA and change of sand rate on the mechanical properties of C30 recycled pump concrete (RPC). By adjusting water consumption to ensured RPC pump requirements. The pump concrete prepared by natural coarse aggregate (NCA) was treated as a control group, which was called natural pump concrete (NPC). The experimental results show that the best proportion of RPC, fly ash content, recycled aggregate content, sand rate respectively are 40wt%, 50wt% and 45wt%.

Investigation of 30% recycled coarse aggregate content in sustainable concrete mixes

The improvement of sustainable concrete, by applying recycled coarse aggregates has an important role to ensure the minimization of damages towards environment. The amount of construction waste increases annually. Also modern technology is given a chance to improve recycling usage in sustainable concrete industry. In modern technology world, recycling plays a vital role to protect the natural resources in our planet. This research carries out a thorough investigation of fresh & hardened RCA concrete, the thermal performance (thermal properties & thermal dynamic properties) with 30% recycled coarse aggregate content. It provides a clearer understanding on how it can be applied to improve the usage of 30% RCA content in concrete for sustainable development.

Properties of recycled aggregate concrete prepared with scattering-filling coarse aggregate process

RAC produced with crushed recycled aggregate (RA) is regarded as an environmental friendly material, while its high water demand, high mortar content and low modulus have restricted its application. Scattering-filling coarse aggregate (SFCA) process was applied to prepare the recycled aggregate concrete with promoted performance. With the reference of conventional concrete and the scattering-filling natural aggregate (SFNA) concrete, the influences of ratio, type, size and moisture state of RA on mechanical and durable properties of scattering-filling recycled aggregate (SFRA) concrete were investigated. The results indicate that SFCA process could improve the compressive strength, elastic modulus, and reduce the drying shrinkage and chloride penetration. The frost resistance of SFRA is comparable with the conventional concrete. With 10–20 mm scattering-filling aggregate of RA, SFCA concretes get more significant improvement on elastic modulus and anti-permeability; Higher water content of RA worsen the performance of recycled aggregate concrete (RAC) for water in the RA weakening ITZ; Furthermore, image processing analysis and microhardness indicated that SFCA process improve the properties by increasing the homogeneity of aggregate distribution and improving ITZ between the aggregate and cement paste in RAC. SFCA process provides an economic method to produce high-quality recycled aggregate concrete and an efficiently approach to the utilization of recycled concrete aggregate from Construction and Demolition waste.

Carbonation resistance of self-compacting recycled aggregate concretes with silica fume

The paper presents the results of carbonation resistance of Self-Compacting Concrete (SCC) made with coarse recycled concrete aggregates and fine recycled concrete aggregates. To evaluate the carbonation resistance of SCC mixes, two different groups consisting of nine SCC mixes were prepared. The impact of coarse recycled concrete aggregates and fine recycled concrete aggregates has been quantified based on the observed performance of SCC mixes of Group-I whereas, the influence of Silica Fume (SF) has been observed on the SCC mixes of Group-II. The incorporation of SF in various SCC mixes not only improves the compressive strength, the carbonation resistance is significantly increased. It has also been observed with the scanning electron microscopy analysis that the incorporation of SF in SCC mixes containing different contents of recycled concrete aggregates, resulted in the production of SCC mixes, with higher/comparable performance to that of control SCC mix.

Durability of recycled aggregate concrete – A review

Recycling of waste concrete has become an important issue worldwide due to the continued increase of construction wastes. Also, the growing global construction activities urge to find sustainable resources to replace natural materials for the production of concrete. In the past few decades, many researches have been carried out on the use of recycled aggregate (RA) derived from construction and demolition wastes to produce concrete products. This paper reviews the previous findings on the effects of use of RA on durability of concrete. In general, the amount of adhered mortar and the quality of the original concrete have a significant effect on the properties of resulting concrete. The increase of RA content and w/c ratio results in poorer durability of concrete. In comparison, the negative effect of recycled fine aggregate is more obvious than that of recycled coarse aggregate. The use of pozzolanic materials either for surface coating of RA or intermixed within the concrete are effective and feasible to improve the overall durability of concrete. Recent researches on CO2 treatment indicate that it can enhance the properties of RA and durability of concrete significantly.