ABSTRACT The objectives of this study was to evaluate the effects of using aggregate produced fro... more ABSTRACT The objectives of this study was to evaluate the effects of using aggregate produced from recycled concrete as a replacement for natural (virgin) coarse aggregate in pavement mixtures. All mixtures containing the recycled concrete aggregate (RCA) were designed to meet the requirements of Indiana Department of Transportation (INDOT) specifications. The scope of the study included evaluation and comparison of several properties of RCA and natural aggregates, evaluation and analysis of the effects of RCA on concrete properties, and modification of aggregate gradations and mixture composition in an attempt to improve the properties of RCA concrete. A total of ten different concrete mixture types were produced in the course of this study. These included four different RCA replacement levels (0%, 30%, 50% and 100% by weight of the natural coarse aggregate) and two different cementitious systems (plain system – Type I portland cement only and fly ash system – 80% of Type I portland cement and 20% of ASTM C 618 Class C fly ash). All ten mixtures were first produced in the laboratory (trial batches) and subsequently reproduced in the commercial ready mixed concrete plant. Each mixture produced in the ready mixed plant was used to prepare several types of specimens for laboratory testing. The tests performed on fresh concrete included determination of slump and entrained air content. The mechanical properties of the hardened concrete were assessed by conducting compressive strength, flexural strength, modulus of elasticity and Poisson’s ratio tests. The durability of concrete was assessed using wide array of measurements, including: rapid chloride permeability (RCP), rapid chloride migration (RCM), electrical impedance spectroscopy (EIS), surface resistivity, free shrinkage, water absorption test, freeze-thaw resistance and scaling resistance. The test results indicated that the properties of plain (no fly ash) concrete mixtures with 30% RCA as coarse aggregate were very comparable (in some cases even better) than those of the control concrete (0% RCA). Although mixtures with 50% RCA showed up to 36% reduction in durability and mechanical properties, the test results still met INDOT’s specifications requirements. However, the mechanical properties of plain concretes made with 100% RCA were measurably lower (16- 25%) than those of the control concrete. It should be pointed out, however, that these properties were still above the minimum required by INDOT’s specification, the only exception being the w/cm value that needed to be elevated to 0.47 from the maximum recommended of 0.45. The use of fly ash improved the quality of RCA concrete, especially at later ages. In particular, the properties of concrete with 50% of RCA were similar to the properties of control concrete. Similarly, the properties of mixture with 100% RCA improved when compared to the same mixture without fly ash and the concrete met minimum requirements imposed by INDOT’s specifications. However, when compared to the fly ash concrete with 100% virgin aggregate the mechanical properties of the 100% RCA concrete were up to 19% lower. The results of all tests performed during this study were used to develop several statistical models which can be used to predict selected properties of the RCA concrete, thus reducing the number of laboratory test required to be performed on the actual mixtures. The developed models can be used to predict the following properties: slump, 7-day flexural strength and 56-day bulk resistance. These models were successfully verified using results from several independent (not used in the original model development) mixtures. Once the testing of the original ten types of concrete mixtures was completed, six additional concrete mixtures were produced, each with modified (with respect to original mixtures) gradation of aggregate. These mixtures were used to study if the virgin and RCA aggregates can be combined in different proportions to produce the “optimized blend” which will improve one (or more) concrete characteristics. The test results obtained from the six additional mixtures indicated that modifying the aggregate gradation did not have beneficial effects with respect to either compressive or flexural strength values. Considering limited scope of this study (only one source of RCA aggregate was used) it is recommended that the amount of RCA in plain concrete be limited to 30% and that in the fly ash concrete be limited to 50% to ensure the adequate quality of the pavement concrete.
ABSTRACT Disposal of aged concrete pavements involves great cost and (due to volumes involved) ca... more ABSTRACT Disposal of aged concrete pavements involves great cost and (due to volumes involved) can be detrimental to environment when all of this material is deposited in landfills. It is therefore cost-effective to recycle crushed concrete as coarse aggregates (referred hereafter as RCA) to replace natural aggregates (NA) during construction of new concrete pavements. This approach reduces the need for quarrying of natural aggregates and saves space in the landfills. The main focus of this study was on determining the chloride penetration resistance of pavement concretes containing various levels (0, 30 and 100%) of RCA as a replacement for NA. All concrete mixtures used in this study were designed to meet the fresh properties and flexural strength requirements specified for pavements by the Indiana Department of Transportation (INDOT). The resistance to chloride ion penetration was determined using two electrical migration tests: rapid chloride permeability (RCP) test (as per ASTM C1202) and non-steady state migration test (as per NT BUILD 492). Before the initiation of the RCP test, all specimens were first subjected to 250 mV AC potential scan using Solartron™ 1260 gain-phase impedance analyzer. The impedance spectra (collected over a frequency range of 0.1 Hz to 10 MHz) were used to obtain bulk resistance (Rb) of the concrete. The steady state diffusion coefficients were calculated using RCP test data in Nernst-Plank and empirical equations. The general trends obtained from the chloride penetration resistance results indicate that initial current values from RCP test can be used to predict the performance of concretes containing RCA. Mixtures with 30% RCA performed similar to 0% RCA mixture while the resistance to chloride penetration of concrete with 100% RCA was somewhat reduced.
The main purpose of this research was to evaluate the influence of using air-cooled blast furnace... more The main purpose of this research was to evaluate the influence of using air-cooled blast furnace slag (ACBFS) coarse aggregate as a replacement for natural dolomite coarse aggregate in pavement concrete mixtures. All mixtures containing ACBFS were designed to meet the requirements of Indiana Department of Transportation (INDOT) specifications for pavement concrete. The scope of the study included evaluation and analysis of the effects of ACBFS on concrete properties in the presence of three different types of deicers (CaCl 2, MgCl2 and NaCl). These evaluations were conducted under simulated temperature cycles that represented exposure to freezing-thawing (FT) and wetting-drying (WD) conditions. A total of eight different concrete mixtures were produced in the course of this study. The mixtures were prepared using two types of coarse aggregates, ACBFS and (for comparison with the typical INDOT mixtures) dolomite. Four different binder systems were used, and included the following: (a) plain - 100% portland cement (PC), two types of binary binder systems (b) 20% fly ash (FA) + 80% PC and (c) 25% slag cement (SC) + 75% PC, and a single ternary system (d) 17% FA + 23% SC + 60% PC. Each of the mixture produced was used to prepare several types of specimens for laboratory testing. The test performed on fresh concrete included determination of slump, unit weigh and entrained air content. The mechanical properties of the hardened concrete were assessed by conducting compressive strength and flexural strength tests. The durability of concrete was assessed by periodical measurements of relative dynamic modulus of elasticity (RDME) and monitoring the length changes of the prismatic specimens. The changes in the physical appearance of specimens exposed to either FT or WD conditions were documented at different stages of the exposure cycles. The depth of chloride ion penetration was measured after the completion of exposure period. The combined effects of the deicer/exposure conditions on the microstructure of the concrete were evaluated using scanning electron microscopy (SEM) analysis on the specimens after the completion of the exposure test. The results from this study revealed that ACBFS is a viable option for coarse aggregate in pavement concrete. The usage of fly ash, slag cement and the combination of both as partial replacement of portland cement was found to not only improve concrete’s strength at later age but also to increase concrete durability in the presence of deicers and FT/WD exposure conditions. Among the three types of deicers studied, CaCl2 was found to be the most aggressive in terms of inducing damage to the concrete followed by MgCl2. Thus, it is advised that the use of these deicers on plain concrete pavements should be more strictly monitored and restricted to cases where other deicer cannot provide the required safety of the roadway. Key words: air-cooled blast furnace slag (ACBFS), coarse aggregate, deicers, freezing-thawing (FT), wetting-drying (WD), pavement concrete, durability properties, scanning electron microscopy (SEM), relative dynamic modulus of elasticity (RDME), plain concrete, binary mixtures, ternary mixtures
Transportation Research Record: Journal of the Transportation Research Board, 2015
This study evaluated the effects of substituting natural coarse aggregate (dolomite) with air-coo... more This study evaluated the effects of substituting natural coarse aggregate (dolomite) with air-cooled blast furnace slag (ACBFS) on the strength and durability properties of pavement concretes. The scope of the study included evaluation and analysis of four types of concrete subjected to three deicers [calcium chloride (CaCl2), magnesium chloride (MgCl2), and sodium chloride (NaCl)] while undergoing freeze–thaw (FT) exposure. Of the four types of concrete mixtures, two were prepared with ACBFS and two with natural dolomite as coarse aggregate. For each aggregate type, one mixture was produced with Type 1 portland cement, while the second one was produced with a binder composed of Type 1 cement and Class C fly ash (20% replacement by weight). Fresh properties of concrete tested included slump, unit weight, and total air content, while compressive and flexural strengths were measured for hardened concrete. Durability of concrete exposed to FT was assessed by periodically measuring dyna...
In recent years, the use of recycled concrete aggregate (RCA) obtained from the demolition of exi... more In recent years, the use of recycled concrete aggregate (RCA) obtained from the demolition of existing concrete pavements as a potential replacement for natural aggregate in the production of concrete mixtures for construction of the new pavements is emerging as technically feasible alternative to existing practice of landfill disposal or utilization in the base layers. In this study, the RCA reclaimed from an old concrete pavement was used as replacement for two varieties of quarried dolomitic limestone. The study involved both plain and fly ash concrete mixtures in which the coarse natural aggregate was replaced by RCA at four different weight percentages (0%, 30%, 50%, and 100%). Prior to being used in the production of the concrete mixtures, all aggregates were subjected to several tests, which included determination of absorption, specific gravity, and abrasion resistance. The results of these tests indicated that the RCA had lower specific gravity, higher absorption, and lower...
ABSTRACT The objectives of this study was to evaluate the effects of using aggregate produced fro... more ABSTRACT The objectives of this study was to evaluate the effects of using aggregate produced from recycled concrete as a replacement for natural (virgin) coarse aggregate in pavement mixtures. All mixtures containing the recycled concrete aggregate (RCA) were designed to meet the requirements of Indiana Department of Transportation (INDOT) specifications. The scope of the study included evaluation and comparison of several properties of RCA and natural aggregates, evaluation and analysis of the effects of RCA on concrete properties, and modification of aggregate gradations and mixture composition in an attempt to improve the properties of RCA concrete. A total of ten different concrete mixture types were produced in the course of this study. These included four different RCA replacement levels (0%, 30%, 50% and 100% by weight of the natural coarse aggregate) and two different cementitious systems (plain system – Type I portland cement only and fly ash system – 80% of Type I portland cement and 20% of ASTM C 618 Class C fly ash). All ten mixtures were first produced in the laboratory (trial batches) and subsequently reproduced in the commercial ready mixed concrete plant. Each mixture produced in the ready mixed plant was used to prepare several types of specimens for laboratory testing. The tests performed on fresh concrete included determination of slump and entrained air content. The mechanical properties of the hardened concrete were assessed by conducting compressive strength, flexural strength, modulus of elasticity and Poisson’s ratio tests. The durability of concrete was assessed using wide array of measurements, including: rapid chloride permeability (RCP), rapid chloride migration (RCM), electrical impedance spectroscopy (EIS), surface resistivity, free shrinkage, water absorption test, freeze-thaw resistance and scaling resistance. The test results indicated that the properties of plain (no fly ash) concrete mixtures with 30% RCA as coarse aggregate were very comparable (in some cases even better) than those of the control concrete (0% RCA). Although mixtures with 50% RCA showed up to 36% reduction in durability and mechanical properties, the test results still met INDOT’s specifications requirements. However, the mechanical properties of plain concretes made with 100% RCA were measurably lower (16- 25%) than those of the control concrete. It should be pointed out, however, that these properties were still above the minimum required by INDOT’s specification, the only exception being the w/cm value that needed to be elevated to 0.47 from the maximum recommended of 0.45. The use of fly ash improved the quality of RCA concrete, especially at later ages. In particular, the properties of concrete with 50% of RCA were similar to the properties of control concrete. Similarly, the properties of mixture with 100% RCA improved when compared to the same mixture without fly ash and the concrete met minimum requirements imposed by INDOT’s specifications. However, when compared to the fly ash concrete with 100% virgin aggregate the mechanical properties of the 100% RCA concrete were up to 19% lower. The results of all tests performed during this study were used to develop several statistical models which can be used to predict selected properties of the RCA concrete, thus reducing the number of laboratory test required to be performed on the actual mixtures. The developed models can be used to predict the following properties: slump, 7-day flexural strength and 56-day bulk resistance. These models were successfully verified using results from several independent (not used in the original model development) mixtures. Once the testing of the original ten types of concrete mixtures was completed, six additional concrete mixtures were produced, each with modified (with respect to original mixtures) gradation of aggregate. These mixtures were used to study if the virgin and RCA aggregates can be combined in different proportions to produce the “optimized blend” which will improve one (or more) concrete characteristics. The test results obtained from the six additional mixtures indicated that modifying the aggregate gradation did not have beneficial effects with respect to either compressive or flexural strength values. Considering limited scope of this study (only one source of RCA aggregate was used) it is recommended that the amount of RCA in plain concrete be limited to 30% and that in the fly ash concrete be limited to 50% to ensure the adequate quality of the pavement concrete.
ABSTRACT Disposal of aged concrete pavements involves great cost and (due to volumes involved) ca... more ABSTRACT Disposal of aged concrete pavements involves great cost and (due to volumes involved) can be detrimental to environment when all of this material is deposited in landfills. It is therefore cost-effective to recycle crushed concrete as coarse aggregates (referred hereafter as RCA) to replace natural aggregates (NA) during construction of new concrete pavements. This approach reduces the need for quarrying of natural aggregates and saves space in the landfills. The main focus of this study was on determining the chloride penetration resistance of pavement concretes containing various levels (0, 30 and 100%) of RCA as a replacement for NA. All concrete mixtures used in this study were designed to meet the fresh properties and flexural strength requirements specified for pavements by the Indiana Department of Transportation (INDOT). The resistance to chloride ion penetration was determined using two electrical migration tests: rapid chloride permeability (RCP) test (as per ASTM C1202) and non-steady state migration test (as per NT BUILD 492). Before the initiation of the RCP test, all specimens were first subjected to 250 mV AC potential scan using Solartron™ 1260 gain-phase impedance analyzer. The impedance spectra (collected over a frequency range of 0.1 Hz to 10 MHz) were used to obtain bulk resistance (Rb) of the concrete. The steady state diffusion coefficients were calculated using RCP test data in Nernst-Plank and empirical equations. The general trends obtained from the chloride penetration resistance results indicate that initial current values from RCP test can be used to predict the performance of concretes containing RCA. Mixtures with 30% RCA performed similar to 0% RCA mixture while the resistance to chloride penetration of concrete with 100% RCA was somewhat reduced.
The main purpose of this research was to evaluate the influence of using air-cooled blast furnace... more The main purpose of this research was to evaluate the influence of using air-cooled blast furnace slag (ACBFS) coarse aggregate as a replacement for natural dolomite coarse aggregate in pavement concrete mixtures. All mixtures containing ACBFS were designed to meet the requirements of Indiana Department of Transportation (INDOT) specifications for pavement concrete. The scope of the study included evaluation and analysis of the effects of ACBFS on concrete properties in the presence of three different types of deicers (CaCl 2, MgCl2 and NaCl). These evaluations were conducted under simulated temperature cycles that represented exposure to freezing-thawing (FT) and wetting-drying (WD) conditions. A total of eight different concrete mixtures were produced in the course of this study. The mixtures were prepared using two types of coarse aggregates, ACBFS and (for comparison with the typical INDOT mixtures) dolomite. Four different binder systems were used, and included the following: (a) plain - 100% portland cement (PC), two types of binary binder systems (b) 20% fly ash (FA) + 80% PC and (c) 25% slag cement (SC) + 75% PC, and a single ternary system (d) 17% FA + 23% SC + 60% PC. Each of the mixture produced was used to prepare several types of specimens for laboratory testing. The test performed on fresh concrete included determination of slump, unit weigh and entrained air content. The mechanical properties of the hardened concrete were assessed by conducting compressive strength and flexural strength tests. The durability of concrete was assessed by periodical measurements of relative dynamic modulus of elasticity (RDME) and monitoring the length changes of the prismatic specimens. The changes in the physical appearance of specimens exposed to either FT or WD conditions were documented at different stages of the exposure cycles. The depth of chloride ion penetration was measured after the completion of exposure period. The combined effects of the deicer/exposure conditions on the microstructure of the concrete were evaluated using scanning electron microscopy (SEM) analysis on the specimens after the completion of the exposure test. The results from this study revealed that ACBFS is a viable option for coarse aggregate in pavement concrete. The usage of fly ash, slag cement and the combination of both as partial replacement of portland cement was found to not only improve concrete’s strength at later age but also to increase concrete durability in the presence of deicers and FT/WD exposure conditions. Among the three types of deicers studied, CaCl2 was found to be the most aggressive in terms of inducing damage to the concrete followed by MgCl2. Thus, it is advised that the use of these deicers on plain concrete pavements should be more strictly monitored and restricted to cases where other deicer cannot provide the required safety of the roadway. Key words: air-cooled blast furnace slag (ACBFS), coarse aggregate, deicers, freezing-thawing (FT), wetting-drying (WD), pavement concrete, durability properties, scanning electron microscopy (SEM), relative dynamic modulus of elasticity (RDME), plain concrete, binary mixtures, ternary mixtures
Transportation Research Record: Journal of the Transportation Research Board, 2015
This study evaluated the effects of substituting natural coarse aggregate (dolomite) with air-coo... more This study evaluated the effects of substituting natural coarse aggregate (dolomite) with air-cooled blast furnace slag (ACBFS) on the strength and durability properties of pavement concretes. The scope of the study included evaluation and analysis of four types of concrete subjected to three deicers [calcium chloride (CaCl2), magnesium chloride (MgCl2), and sodium chloride (NaCl)] while undergoing freeze–thaw (FT) exposure. Of the four types of concrete mixtures, two were prepared with ACBFS and two with natural dolomite as coarse aggregate. For each aggregate type, one mixture was produced with Type 1 portland cement, while the second one was produced with a binder composed of Type 1 cement and Class C fly ash (20% replacement by weight). Fresh properties of concrete tested included slump, unit weight, and total air content, while compressive and flexural strengths were measured for hardened concrete. Durability of concrete exposed to FT was assessed by periodically measuring dyna...
In recent years, the use of recycled concrete aggregate (RCA) obtained from the demolition of exi... more In recent years, the use of recycled concrete aggregate (RCA) obtained from the demolition of existing concrete pavements as a potential replacement for natural aggregate in the production of concrete mixtures for construction of the new pavements is emerging as technically feasible alternative to existing practice of landfill disposal or utilization in the base layers. In this study, the RCA reclaimed from an old concrete pavement was used as replacement for two varieties of quarried dolomitic limestone. The study involved both plain and fly ash concrete mixtures in which the coarse natural aggregate was replaced by RCA at four different weight percentages (0%, 30%, 50%, and 100%). Prior to being used in the production of the concrete mixtures, all aggregates were subjected to several tests, which included determination of absorption, specific gravity, and abrasion resistance. The results of these tests indicated that the RCA had lower specific gravity, higher absorption, and lower...
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