Crushed Concrete Aggregate Research Articles

Preliminary assessment of the secondary setting of Portland cement in recycled crushed concrete incorporated in cold recycled road base mixes with foamed bitumen

The recycled crushed concrete (RCC) unlike the natural aggregates, has a residue of the unhydrated Portland cement (PC) covering the aggregate grains, which may result in a secondary cementation process after its application in a road base. The paper presents the results of exploratory research on the phenomenon of the secondary setting of Portland cement in recycled crushed concrete aggregates in cold-recycled mixes with foamed bitumen (FB). The tests were performed using two mixtures, i.e. Mix-FBREF reference mixture without the addition of RCC, and Mix-FBRCC research mix containing 25% of RCC. The composition of mineral mixtures with foamed bitumen was designed using typical recycled materials, used as a part of the road repair works of pavements, i.e. Reclaimed Asphalt Pavement (RAP), Reclaimed Aggregates (RA) and new aggregates (NA). All mineral materials used in the tests met the requirements in terms of suitability for the foamed bitumen cold-recycled mixtures, intended for basecourse. The total amount of the bituminous binder in the Mix-FB mix was 5.5%. To assess the phenomenon of the secondary setting of Portland cement contained in the recycled concrete, tests were conducted to evaluate the increase of the unconfined compressive strength (UCS) in time of the material. The strength of UCS samples of Mix-FBREF and MixFBRCC mixtures was determined after 3, 4, 7, 14 and 28 days of conditioning. The tests showed that the value of the analysed parameter in the reference mixture increased by about 180 kPa with time, whereas for the mixture containing the concrete recycled aggregate the difference was virtually unnoticeable (only by 6 kPa). The obtained test results were subjected to the statistical analysis, which showed that for each of the considered sample conditioning periods, no statistically significant differences between the strength values of unconfined compression of the tested mixtures were found. The presence of bituminous binder in basecourse cold-recycled mixtures, (old, with RAP and new, in foamed form) yields the bituminous binding dominant over the effects of PC binding, therefore minimizing the effects of the secondary Portland cement setting.

Corrosion risk assessment of structural concrete with coarse crushed concrete aggregate

Crushed concrete aggregates (CCA) are an increasingly popular replacement for natural aggregates (NA) in structural concrete due to industry demands for more recycled, low carbon footprint and responsibly sourced materials. There is uncertainty regarding chloride-ion ingress, which can ultimately cause deterioration of reinforced concrete. This is reflected in European and British concrete design standards, which currently exclude CCA in chloride environments. Structural concretes with up to 60% coarse CCA (and CEM I, CEM II/B-V and CEM III/A binders) were exposed to aggressive chloride environments and monitored with electrochemical techniques and subsequent destructive testing to determine their risk of corrosion initiation. The results showed that CEM II/B-V and CEM III/A concretes with up to 60% coarse CCA outperformed the control CEM I concrete with 100% NA, and had a lower risk of corrosion initiation. It is recommended that further monitoring is required over longer periods to determine the corrosion-initiation risk. Supplementary cementitious materials had a beneficial effect on the chloride-ion ingress resistance, significantly increased the predicted time to corrosion initiation beyond the 50-year design life and largely outweighed any observed detrimental effects from an increased coarse CCA content, suggesting that limitations imposed by existing design standards are conservative.

Assessment of the physical characteristics and stormwater effluent quality of permeable pavement systems containing recycled materials

This paper evaluates the physical characteristics of two recycled materials and the pollutant removal efficiencies of four 0.2 m2 tanked permeable pavement rigs in the laboratory, that contained either natural aggregates or these recycled materials in the sub-base. The selected recycled materials were Crushed Concrete Aggregates (CCA) and Cement-bounded Expanded Polystyrene beads (C-EPS) whilst the natural aggregates were basalt and quartzite. Natural stormwater runoff was used as influent. Effluent was collected for analysis after 7–10 mins of discharge. Influent and effluent were analysed for pH, Chemical Oxygen Demand (COD), Dissolved Oxygen (DO), Electroconductivity (EC), turbidity, Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Nitrate-Nitrogen (NO3-N), reactive phosphorous () and sulphates (). Both CCA and C-EPS had suitable physical properties for use as sub-base materials in PPS. However, C-EPS is recommended for use in pavements with light to no traffic because of its relatively low compressive strength. In terms of pollutant removal efficiencies, significant differences (p < 0.01) were found in pH, EC, TDS, DO, and across all rigs whereas no significant differences (p > 0.05) were found with respect to TSS, turbidity, COD and NO3-N. Effluent from rigs containing CCA and C-EPS saw significant increases in pH, EC and TDS measurements whilst improvements in DO, TSS, turbidity, COD, and were observed. All mean values except pH were, however, within the Maximum Permissible Levels (MPLs) of water pollutants discharged into the environment according to the Trinidad and Tobago Environmental Management Authority (EMA) or the United States Environmental Protection Agency (US EPA). In this regard, the CCA and C-EPS performed satisfactorily as sub-base materials in the permeable pavement rigs. It is noted, however, that further analysis is recommended through leaching tests on the recycled materials.

Eco-Friendly Recycled Aggregate Concrete

This article aims to study the mechanical properties of concrete containing the recycled and crushed aggregate instead of normal aggregate separately, and reinforced with volumetric ratios equal to (0.25,0.5,0.75,1,1.25 and 1.5)% of plastic fibers, which produced by cutting the plastic water bottles as a partial replacement from volume of coarse aggregate. Preliminary results showed that the compressive strength of recycled aggregate concrete(RAC) increased with increasing the waste plastic fibers (PET) more than the observed values of crushed aggregate concrete(CAC), while the results showed that the splitting tensile strength of concrete samples containing recycled aggregate have a higher splitting tensile strength than those containing the crushed aggregate. On the other hand, it was noted that the increasing in the proportions of PET from (0.25-1) % showed an increase in compressive and splitting tensile strength, but after the ratio of PET used equal to (1% ), it was observed a decreasing in both of compressive and splitting tensile strength.

A critical assessment of the compressive behavior of reinforced recycled aggregate concrete columns

This paper presents a critical assessment of the compressive behavior of reinforced recycled aggregate concrete (RRAC) columns. Previous research has demonstrated that recycled aggregate concrete (RAC), manufactured using crushed concrete aggregates obtained from construction and demolition waste, can be a feasible and environmentally friendly alternative to conventional concrete for the use in structural applications. Currently, very limited information is available in the literature about the methods to be used for designing RC elements manufactured with recycled concrete aggregates. With the aim of extending the available experimental data, a fiber section based nonlinear finite element (FE) model was developed so as to provide in-depth insights into the compressive behavior of RRAC columns. First, a comparison between simulation results of the compressive behavior of RRAC columns and available experimental results were made to validate the FE model. Then, using the validated FE model, a parametric study was performed to investigate the effects of different recycled concrete aggregate (RCA) contents, volumetric ratio and yield strength of longitudinal steel reinforcement, and spacing and yield strength of transverse steel reinforcement on the compressive behavior and load capacity of RRAC columns. Finally, based on the limited available experimental database, a grey correlation analysis was used to evaluate the parametric sensitivity of the compressive behavior of RRAC columns. The experimental and numerical investigations demonstrate that the method used for considering the additional water absorption of RCAs in manufacturing RAC has a significant influence on the compressive load capacity of RRAC columns and that the influence of the RCA content on the compressive load capacity of RRAC columns is lower when compared with other important parameters but this effect should not be ignored in modeling the behavior of RRAC columns.

Crushed concrete in road structures – two decades of experience

Since the early 1990s, crushed concrete aggregate (CCA)/recycled concrete aggregate has been successfully used in Finnish road constructions. The aim of this paper is to analyse the long-term behaviour of CCA and to compare CCA with conventional mineral aggregates in road structures. The analysed trial sections consist of the road and highway pavements where CCA has been used in the base and subbase layers. The first studied Finnish trial section was constructed in 1995, which has enabled nearly two decades of follow-up studies. In total, five follow-up trial sections were studied. E-modulus of pavement layers was determined using the deflection data from falling weight deflectometer measurements. The studies revealed excellent long-term behaviour in the CCA build pavements and validated the suitability of chosen design parameters in previous guidelines. In this study, the sections consisting of maximum 50 mm particles of CCA in the base or subbase layer gained 10–25% larger bearing capacity in 13–15 years after construction than the reference pavements that were constructed with crushed rock. The increase of the CCA stiffness was faster in the first years after construction and in the 2–5 years little or insignificant increase in such stiffness could be observed.

Performance of Recycled Aggregate Concrete after Washing Treatment of Aggregates

Retrieval and reuse of crushed concrete aggregates (CCA) in the concrete industry is a common practice that has gained popularity due to environmental concerns that identify the saturation of landfill areas as a harmful and costly by-product of construction, and has therefore become a necessity for a sustainable, more well-coordinated effort towards improving concrete preparation. This research examines a natural method of CCA-washing that aims to effectively segregate contaminants from healthy material by allowing CCAs to sit outdoors for a period of time thus being subjected to several rain-washing cycles. Eleven mixes were prepared, a control mix with 100% natural/virgin concrete aggregates (NCA/VCA) and ten mixes with CCA content varying between 10-100% replacement. Findings showed that even up to 100% substitution a remarkable reduction of only 15% in compressive strength was observed, with no significant change or effect on the consistency; thus conferring potentially significant sustainability implications.

Performance of Recycled Aggregate Concrete after Washing Treatment of Aggregates

Retrieval and reuse of crushed concrete aggregates (CCA) in the concrete industry is a common practice that has gained popularity due to environmental concerns that identify the saturation of landfill areas as a harmful and costly by-product of construction, and has therefore become a necessity for a sustainable, more well-coordinated effort towards improving concrete preparation. This research examines a natural method of CCA-washing that aims to effectively segregate contaminants from healthy material by allowing CCAs to sit outdoors for a period of time thus being subjected to several rain-washing cycles. Eleven mixes were prepared, a control mix with 100% natural/virgin concrete aggregates (NCA/VCA) and ten mixes with CCA content varying between 10-100% replacement. Findings showed that even up to 100% substitution a remarkable reduction of only 15% in compressive strength was observed, with no significant change or effect on the consistency; thus conferring potentially significant sustainability implications.

Durability performance of sustainable structural concrete: Effect of coarse crushed concrete aggregate on rapid chloride migration and accelerated corrosion

The increasing use of crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA), has led to research into the effects of coarse CCA in higher value structural applications. Concerns exist regarding the effect on chloride ion ingress which ultimately can cause deterioration of reinforced concrete. This concern is reflected in existing European and British concrete design standards as limitations prevent their use in environments where chlorides may be present. The rapid chloride migration coefficient and rate of accelerated corrosion of structural CEM I and CEM III/A CCA concretes was measured to determine the effect on chloride ion ingress. Three sources of coarse CCA were evaluated; results show that coarse CCA generally had a detrimental effect on the chloride ion ingress of structural concrete. However, these effects can be mitigated by the inclusion of GGBS to produce structural CEM III/A concretes, thus allowing higher proportions of coarse CCA. It is recommended that the GGBS and coarse CCA content be limited to 50% and 60% respectively as this reduces the risk of a significant detrimental effect on chloride ion ingress. The results also suggest that the limitations in existing European and British standards are conservative and sustainable structural CEM III/A concrete with the inclusion of coarse CCA could be a viable option for future responsibly sourced projects, provided that a reliable and consistent source of CCA can be obtained. This is a positive outcome for the wider implementation of coarse CCA into structural concrete applications.

Durability performance of sustainable structural concrete: Effect of coarse crushed concrete aggregate on microstructure and water ingress

The use of crushed concrete aggregate (CCA), formerly referred to as recycled concrete aggregate (RCA) is increasing, particularly with a recent push towards sustainable sourcing of materials. Further research is required to understand the effect of coarse CCA on the mechanical properties and durability performance of structural concrete. The electrical resistivity, water absorption by capillary action and SEM analysis of CEM I and CEM III/A concretes were investigated to determine the effects on concrete microstructure and water ingress, together with compliance of characteristic (fc,cube) and target mean compressive strengths. The results show that for the three coarse CCA sources tested, the inclusion of coarse CCA generally has a detrimental effect on the microstructure and water ingress of structural concrete. These can be largely overcome through the incorporation of GGBS to produce CEM III/A concretes, allowing higher proportions of coarse CCA to be incorporated. We conclude that the GGBS and coarse CCA content be limited to 50% and 60% respectively, as this reduces the risk of a significant reduction of compressive cube strength and durability performance. The findings suggest that sustainable structural CEM III/A concrete can be a viable option for future responsibly sourced projects, provided that a reliable and consistent source of CCA can be obtained. This is a positive and significant outcome for the wider implementation of coarse CCA into structural concrete applications.

Measurement of particle size distribution and specific surface area for crushed concrete aggregate fines

Different methods for measuring particle size distribution (PSD) and specific surface area of crushed aggregate fines (⩽250μm), produced by high-speed vertical shaft impact (VSI) crushing of rock types from different quarries in Norway, have been investigated. Among all the methods studied, X-ray sedimentation is preferred because it has adequate resolution and requires fewer and more reliable input parameters. This combination makes it suitable for practical applications at hard rock quarries. X-ray microcomputed tomography (μCT) combined with spherical harmonic analysis was applied to estimate the actual error introduced when PSD measurements were used to calculate the specific surface area of the VSI crushed rock fines. The μCT results, to the limit of their resolution, show that the error in the calculated surface area caused by assuming spherical particles (a common assumption in PSD measurements) is of unexpectedly similar magnitude (−20% to −30%) over the entire investigated particle size range, which was approximately 3–200μm. This finding is important, because it simplifies relative surface area determination and is thought to be quite general, since the crushed aggregate fines investigated were produced from 10 rock types that had a wide range of mineralogies.

Comparison of 2-D and 3-D shape analysis of concrete aggregate fines from VSI crushing

The shape of concrete aggregate fine particles (fines), with particle sizes between 3μm and 250μm, produced by high-speed vertical shaft impact (VSI) crushing of 10 different rock types from quarries in Norway, has been studied by both dynamic image analysis (DIA), which is a two-dimensional (2-D) method, and X-ray computed microtomography (μCT) coupled with spherical harmonic (SH) analysis, which is a three-dimensional (3-D) method. The 3-D μCT results serve as a check on the 2-D DIA results. The intent was to evaluate the applicability of the 2-D DIA method to extract shape parameters that could represent the actual 3-D shape of the VSI crushed concrete aggregate particles. The results show that the 2-D DIA method has problems correctly measuring the shape of particles smaller than about 40μm due to too large of a pixel size and possibly some particle flocculation. The findings of this paper show, however, that if a large enough number of particles are analysed by the 2-D DIA method, a good but limited indication of the actual 3-D shape of the irregular crushed aggregate fines larger than 40μm can be acquired and used for simple quality control in hard rock quarries.

Three dimensional shape analysis of concrete aggregate fines produced by VSI crushing

We studied the 3-D shape of concrete aggregate fines with particle sizes between 3μm and 250μm produced by high-speed vertical shaft impact (VSI) crushing of rock types from 10 different quarries representing a wide range of local Norwegian geology with respect to mineralogy and mechanical properties. This included igneous (intrusive and extrusive), metamorphic, and sedimentary rocks that were both mono- and multi-mineralic. VSI crushing seems to be able to generate concrete aggregate fines of very similar equidimensional mean shape characteristics for the whole analysed size range, independent of the mineralogical composition of the rocks included in the study. The effect on normalising the average particle shape was somewhat lower for the particle size range smaller than about 15μm, where there seems to be a greater influence of the crystallographic structure of the individual minerals. Particles of the rock type containing the highest mica content (5.5%, by mass) had the least equidimensional shape. The most equidimensional shape in a given particle size range was found for both limestone rock types that were analysed. A new shape parameter, the micro-Flakiness Index (μFI), has been proposed to characterize the shape of the fine crushed concrete aggregate particles to enable practical use of shape parameters.

NEAR ZERO WASTE USING RECYCLED OF CRUSHED CONCRETE AGGREGATE IN ASPHALT MIXTURES

In asphalt mixtures aggregate generally represents the largest proportion of asphalt concrete mixture. It accounts for 92 to 96 percent of asphalt concrete mixtures by weight or approximately 75 to 85% by volume. Using these large quantities of aggregates in asphalt mixtures affect the natural resources. So recycling of crushed concrete could be a solution to this problem. The use of recycled crushed concrete in asphalt mixtures can prevent the accumulation of waste material and primary production costs as well as environmental pollution. In this research the basic properties of natural aggregate and recycled aggregate were evaluated. In asphalt concrete mixtures natural aggregate replaced with recycled aggregate in deferent percentage namely 10%, 20%, 30%, 40% and 50%. The mechanical characteristics of the mixtures were evaluated by Marshall Stiffness and indirect tensile strength to choose the optimum recycled aggregate replacement ratio. The results indicated that using recycled aggregate in asphalt concrete mixtures have good impact in environment protection and economics. Up to 20% of recycled of crushed concrete aggregate can be used in asphalt concrete mixtures. The mixtures with recycled of crushed concrete aggregate have low stiffens and stability so it should be used at low traffic area.

Recycling of CDW and Steel Slag in Drainage Layers of Transport Infrastructures

Using waste as a civil engineering construction material represents an important environmental and economic advantage. In this context, it was studied the durability and permeability of a crushed concrete recycled aggregate (CCCDW), processed from construction and demolition waste (CDW), and an inert steel aggregate for construction (ISAC), processed from electric arc furnace (EAF) steel slag, with the aim to evaluate the technical feasibility of their recycling in the drainage layers of transport infrastructures. The durability of recycled materials was studied using the slake-durability test (SDT) proposed by International Society for Rock Mechanics (ISRM). In order to test the behaviour of the material in mechanical conditions more adverse than those specified in the ISRM method, more 600 rotation cycles than those foreseen in the original method were applied. As a complement to SDT tests, macro- and micropetrographic observations as well as physical characterizations of two recycled materials, both before and after SDT tests, were performed. Regarding the hydraulic behaviour of the recycled materials, constant-head permeability tests were carried out on specimens prepared from grain-size fractions in the ranges 0.25-2.0 mm and 2.0-20.0 mm. In the study was compared the behaviour of two recycled materials with two reference natural materials, a basalt and a limestone. The results obtained show, for the conditions tested, the technical feasibility of their recycling in the mentioned applications.

Flexural load tests of full-scale recycled aggregates concrete structures

In order to study the behaviour of concrete structures made with coarse crushed concrete aggregates recycled from discarded elements from the precasting industry, extensive testing was performed in four full-scale structures with varying recycled aggregate (RA) ratios. This paper describes and analyses the results of vertical load tests on each slab of these double-floor structures. The Young’s modulus (E) of the concrete mixes was estimated by finite element model calibration using deflection data from the tests. The response pattern of the various structures was the same and the aggregates used had a small influence on E, even smaller than the execution conditions. One of the concrete mixes included a superplasticizer (SP) and this product more than offset the loss of stiffness due to RA use. To the authors’ best knowledge this is the first study ever concerning the behaviour of full-scale recycled aggregate concrete (RAC) structures subjected to vertical loading and the behaviour of slabs with significant replacement of conventional aggregates by RA.

Natural aggregate totally replacement by mechanically treated concrete waste

Abstract This paper presents the results obtained from the research focused on the utilization of crushed concrete waste aggregates as a partial or full replacement of 4/8 and 8/16 mm natural aggregates fraction in concrete strength class C 16/20. Main concrete characteristics such as workability, density and compressive strength were studied. Compressive strength testing intervals for samples with recycled concrete aggregates were 2, 7, 14 and 28 days. The amount of water in the mixtures was indicative. For mixture resulting consistency required slump grade S3 was followed. Average density of all samples is in the range of 2250 kg/m3 to 2350 kg/m3. The highest compressive strength after 28 days of curing, 34.68 MPa, reached sample, which contained 100% of recycled material in 4/8 mm fraction and 60% of recycled aggregates in 8/16 mm fraction. This achieved value was only slightly different from the compressive strength 34.41 MPa of the reference sample.

Shrinkage cracking of cement treated demolition waste as a road base

This paper presents the shrinkage cracking characteristics of cement treated demolition waste as a road base layer, which was produced by using recycled crushed concrete and masonry aggregates from construction and demolition waste (CDW). The developed method to estimate the crack pattern was based on the structural properties of cement treated demolition waste measured in the laboratory and the average climatic conditions recorded in the Netherlands. The influences of four mixture variables (masonry content, moisture content, cement content and degree of compaction) on the crack pattern were investigated. Results show that the proposed estimation model can predict the crack pattern of cement treated demolition waste comparable to the crack spacing observed in the field. The masonry variation in CDW is a key factor to determine its shrinkage cracking characteristics.

Strength and stiffness of compacted crushed concrete aggregate

A comprehensive series of drained triaxial compression tests were performed on crushed concrete aggregate (CCA) moist as compacted. When compared to ordinary natural well-graded gravelly soils, the peak strength and stiffness increase more significantly with dry density, while the effect of the degree of saturation during compaction is much less significant. In a range of confining pressure of 30–600kPa, the strength and stiffness of well-compacted CCA is similar to, or, in some cases even higher than, typical selected high-class backfill materials (e.g., well-graded gravelly soil of crushed quarry hard rock). The strength and stiffness of CCA with a maximum particle size Dmax=37.5mm obtained from a typical concrete crushing plant are noticeably lower than CCA sieved to Dmax=19mm compacted using the same energy. However, when compacted to the same dry density, the original CCA exhibits the strength and stiffness higher than the sieved CCA. Effects of the strength of original concrete on the strength and stiffness of compacted CCA are insignificant, while the strength and stiffness of compacted CCA are, respectively, noticeably higher than, or similar to, the original concrete aggregate (i.e., natural gravelly soil) compacted using the same energy. All these results indicate that well-compacted CCA can be used as the backfill material for important civil engineering soil structures requiring a high stability while allowing a limited amount of deformation.

Use of recycled crushed concrete and Secudrain in capillary barriers for slope stabilization

A capillary barrier is a two-layer cover system having distinct hydraulic properties to minimize water infiltration into the underlying soil by utilizing unsaturated soil mechanics principles. In this study, a capillary barrier system was designed as a cover system for a residual soil slope to maintain stability of the slope by minimizing infiltration during heavy rainfalls in the tropics. The capillary barrier system (CBS) was constructed using fine sand as the fine-grained layer and recycled crushed concrete aggregates as the coarse-grained layer. The coarse-grained layer is commonly constructed using gravels or granite chips. However, due to scarcity of aggregates and in consideration of environmental sustainability, recycled crushed concrete aggregates were used as the coarse-grained layer in this project. The suitability of recycled crushed concrete aggregates as a material within the coarse-grained layer of a CBS is subject to the hydraulic property requirement. For comparison, another CBS was constructed using fine sand as the fine-grained layer and a geosynthetic (Secudrain) as the coarse-grained layer. The performance of each constructed CBS on the residual soil slope was monitored using tensiometers installed at different depths — from 0.6 to 1.8 m below the slope surface — and a rainfall gauge mounted on the slope. An adjacent original slope without the CBS was also instrumented using tensiometers and piezometers to investigate the performance and effectiveness of the CBS in reducing rainwater infiltration and maintaining negative pore-water pressures in the slope. Real-time monitoring systems were developed to examine pore-water pressure, rainfall, and groundwater level in the slopes over a 1 year period. Characteristics of pore-water pressure distributions in the residual soil slope under a CBS with recycled crushed concrete aggregates and in the original slope during typical rainfalls are highlighted and compared. The measurement results show that the CBS was effective in minimizing rainwater infiltration and therefore, maintaining stability of the slope.