High-volume recycled materials for sustainable transportation infrastructure

The objective of this study is to investigate the feasibility of using high performance concrete made with high-volume of recycled materials in transportation infrastructure. The main focus was to develop mixtures for rigid pavement construction. A variety of fine and coarse recycled concrete aggregates (RCA) were investigated. The feasibility of replacing 50% of Portland cement with industrial by-products and supplementary cementitious materials (SCMs) was also evaluated. Experimental program was conducted to quantify the effect of concrete mixture design and RCA characteristics on mechanical properties, drying shrinkage, cracking potential, and durability of concrete. The development of a database and analysis using artificial intelligence was considered to quantify the properties of concrete as a function of RCA characteristics. Results were validated during a field implementation project in Missouri. The project involved the design of the concrete mixtures, the sampling and testing of concrete at the job site, and in-situ monitoring of deformations of rigid pavement section under controlled traffic loading and environmental effect. Testing was also conducted on large-scale reinforced concrete beams cast with selected concrete mixtures to investigate the structural performance of such green materials. In general, satisfactory performance was achieved for the key properties of concrete for infrastructure applications, indicating that concrete with 50% SCM and over 50% coarse RCA can be considered for the production of sustainable and high performance concrete. The 120-day shrinkage of such concrete can be limited to 450 µε, while meeting the design criteria for mechanical properties and durability and exhibiting no cracking under re-strained conditions up to 35 days --Abstract, page iii

Effects of Mixture Proportioning, Curing, and Finishing on Concrete Surface Hardness

With adoption of winter maintenance strategies that typically include incorporation of aggressive deicer chemicals, pavement surfaces in cold regions are exposed to the risk of scaling damage. Reduced ride quality due to surface deterioration can eventually lead into a variety of maintenance and repair programs. Such pavement preservation programs impose significant charges to the owner agencies, while raising concerns regarding the safety issues associated with work zone areas. The present study addresses the correlation between surface hardness and concrete hardened properties. Moreover, factors that influence the concrete performance with respect to surface-abrasion resistance (hardness) were investigated. Of special interest was the relationship between surface hardness and concrete salt-scaling performance. An extensive investigation was carried out to assess the effects of various mixture proportions, curing regimes, andfinishing times on surface hardness of the concrete specimens. In addition, compressive strength, depth-sensing indentation (DSI), and salt scaling tests were used to evaluate the correlation between concrete surface hardness and performance. A scaling quality classification table using abrasion mass loss values was developed. The results reflect further understanding of the relationship between abrasion resistance and salt scaling resistance that can cause defects when more than two cycles of abrasion testing are applied.This article is published as Amini, Kamran, Seyedhamed Sadati, Halil Ceylan, and Peter C. Taylor. "Effects of mixture proportioning, curing, and finishing on concrete surface hardness." ACI Materials Journal 116, no. 2 (2019): 119-126. doi:10.14359/51714457. Copyright © 2019, American Concrete Institute. Posted with permission

Field Performance of Concrete Pavement Incorporating Recycled Concrete Aggregate

This paper reports test results of a field-oriented study carried out to demonstrate the performance of recycled concrete aggregate (RCA) for use in the construction of rigid pavement. Properties of eight concrete mixtures containing RCA were first compared to those of a reference mixture. Two mixtures proportioned with 30% and 40% of coarse RCA along with the reference concrete were then used for field implementation, which involved casting a 300-m long pavement section in St. Louis, Missouri. Samples were taken during slip-form pavement construction. Core samples were extracted at 120 days to determine in-situ properties. Instrumentation was incorporated to monitor the long-term deformation of different pavement sections. Incorporation of 30% and 40% RCA reduced the 91-day compressive strength by 7% and 12%, and the 56-day modulus of elasticity by 22% and 14%, respectively. The 56-day splitting tensile strength and flexural strength values of the two RCA mixtures were similar to those of the reference concrete. Mixtures exhibited similar performance in terms of durability against abrasion, freeze and thaw cycles, and rapid chloride ion permeability. An increase of 100 με in shrinkage was observed for the 40% RCA compared to the reference concrete. However, all field investigated mixtures exhibited similar long-term deformation patterns and magnitudes. In-situ deformation of all pavement sections was limited to 150 με at sensor locations

Effect of Recycled Aggregate Characteristics on Drying Shrinkage of Paving Concrete

The research presented in this paper addresses the effect of coarse recycled concrete aggregate (RCA) on drying shrinkage of concrete designated for transportation infrastructure. Six types of RCA were employed at 30 to 100% replacement rates of virgin coarse aggregate. Two binder systems, including a binary cement with 25% Class C fly ash and a ternary system with 35% fly ash and 15% slag were employed. Three different water-cementitious materials ratios (w/cm) of 0.37, 0.40, and 0.45 were considered. Test results indicate that the use of RCA increased drying shrinkage by up to 110% and 60% after 7 and 90 days of drying, respectively. Correlations with R2 of up to 0.85 were established to determine the shrinkage at 7, 28, 56, and 90 days as a function of aggregate properties, including specific gravity, water absorption, and Los Angeles abrasion resistance of the combined coarse aggregates. The water absorption of the combined coarse aggregate was shown to be a good index to showcase the effect of RCA on shrinkage. Contour graphs were developed to determine the effect of RCA content and its key physical properties on 90-day drying shrinkage of concrete intended for rigid pavement construction. A classification system available in the literature was also used to suggest the maximum allowable replacement rates for use of RCA in a hypothetical case study. Results suggest replacement rates of 100%, 70%, and 50% (% wt.) to limit the 90-day shrinkage to 500 µε when RCA of A-1, A-2, and A-3 Classes are available, respectively

Can Concrete Containing High-Volume Recycled Concrete Aggregate Be Durable?

This paper evaluates the effect of recycled concrete aggregate (RCA) on concrete durability. Six RCA types procured from different sources were employed at 30 to 100% replacement rates by volume of virgin coarse aggregate. One fine RCA was also investigated and was used for up to 40% replacement by volume of virgin sand. In total, 33 mixtures were proportioned with these aggregates in concrete made with a binary or a ternary binder system and a water-cementitious materials ratio (w/cm) of 0.37 to 0.45. The mixtures were investigated for frost durability, electrical resistivity, sorptivity, and abrasion resistance. Test results indicate that concrete made with up to 100% coarse RCA from an air-entrained source can exhibit proper frost durability. No significant reduction (limited to 3%) in frost durability factor was observed when the fine RCA volume was limited to 15% of total sand. Increase in mass loss due to deicing salt scaling was observed in concrete made with 50% of RCA with high (over 4%) deleterious materials content and high mass loss during soundness test. For a given w/cm and binder type, the use of 50% coarse RCA resulted in up to 32% reduction in electrical resistivity. The reduction in w/cm from 0.40 to 0.37 and the use of ternary binder containing 35% Class C fly ash and 15% slag proved to be effective in mitigating the potentially negative impact of RCA on sorptivity and abrasion resistance, compared to concrete made without any RCA with w/cm of 0.40 and binary cement with 25% fly ash

Restrained Shrinkage Cracking of Recycled Aggregate Concrete

The increase in drying shrinkage and decrease in tensile properties of concrete proportioned with recycled concrete aggregate (RCA) can result in a high risk of cracking under restrained conditions. However, the reduction of the modulus of elasticity of such concrete, can lead to greater stress relaxation and reduction in cracking potential. An experimental program was undertaken to evaluate the effect of using RCA at high substitution rates of 50 and 100% (by vol.) on the cracking potential under restrained conditions. Four different types of coarse RCA, two binder types, and water-to-cementitious materials ratio (w/cm) of 0.37 and 0.40 were considered in the study. Mechanical properties, drying shrinkage, and cracking potential using the ring test were investigated. Test results indicated no cracking up to 35 days in the case of the reference mixture and the concrete prepared with 50% RCA replacement. The 28-day stress rate of such mixtures were limited to 0.12 MPa/day. Depending on the RCA type, the incorporation of 100% coarse RCA in a binary system made with 0.40 w/cm increased the 35-day cracking potential to up to 74%, with values of stress rate ranging from 0.25 to 0.34 MPa/day. The mixtures proportioned with 100% RCA developed tensile creep coefficient of 0.34–0.78 at the time of cracking compared to 0.34–0.36 for the reference concrete at the same age. However, greater elastic concrete strain and lower tensile strength resulted in reduced time to cracking at 100% RCA replacement, which was 9.0–11.0 days

Rheological and Hardened Properties of Mortar Incorporating High-Volume Ground Glass Fiber

The present research investigates the performance of mortar prepared with high-volume ground glass fiber (GGF) incorporated as partial replacement of Portland cement. Several binary and ternary mixtures with up to 50% cement substitution were investigated to evaluate rheological properties, heat of hydration, strength development, drying shrinkage, electrical resistivity, and carbonation. The incorporation of up to 50% GGF was found to reduce yield stress by up to 50% compared to control mortar without any GGF. On the other hand, this resulted in up to 100% increase of plastic viscosity of mortar in comparison with the Reference mortar cast with 100% Portland cement. The rate of structural build-up at rest of the tested mortars, that reflects the thixotropic nature of the mortar, decreased from 7.1 to 0.8 Pa/min with cement substitution by 50% of GGF. Reduction in 91-day compressive strength from 34 to 28 MPa was observed with 50% cement substitution by GGF. The coefficient of pozzolanic activity of mortar cast with 10% to 50% GGF ranged from 0.18 to 0.71 at 91 days, compared to mixtures containing 50% cement substitution with Class F fly ash (FA-F), Class C fly ash (FA-C), or blast furnace slag (SL) where the 91-day coefficient of pozzolanic activities were 1.80, 1.46, and 1.21, respectively. The incorporation of 10% to 50% GGF reduced the 91-day drying shrinkage by 0–20%. At 50% GGF replacement, the electrical resistivity was enhanced from 10 to 88 kΩ.cm at 91 days, while the carbonation coefficient increased by about 100%. The incorporation of 15% or 25% GGF in ternary systems containing either FA-C, FA-F, or SL was effective in enhancing compressive strength, with values ranging between 34 and 49 MPa. The best performance was observed in the case of the GGF/FA-C ternary binders, followed by the GGF/SL, and GGF/FA-F systems where 91-day compressive strength gains of up to 45%, 28%, and 10%, respectively, were observed compared to the Reference mixture with 100% Portland cement

Shear Performance of Reinforced Concrete Beams Incorporating Recycled Concrete Aggregate and High-Volume Fly Ash

The study reported in this paper investigates the shear capacity of full-scale reinforced concrete beams fabricated with high volume fly ash and coarse recycled concrete aggregate (RCA). The study involved testing 24 full-scale beams. The beams were fabricated with three different longitudinal reinforcement ratios of 1.27%, 2.03%, and 2.71%. Four concrete mixtures were employed for casting the beams: conventional concrete (CC) without any fly ash or RCA as the reference; fly ash concrete with 50% of Class C fly ash replacement (FA50 beams); RCA concrete with 50% coarse RCA replacement (RCA50 beams); and sustainable concrete (SC) proportioned with 50% Class C fly ash and 50% RCA. In order to evaluate the performance of concrete in shear, the beams were cast without any stirrups in the shear zone. The test results were compared with theoretical models provided by different design codes as well as a shear data base for CC. The experimental results were also compared to analytical approaches based on fracture mechanics as well as the modified compression field theory method. On the average, the SC beams had a 10% lower shear capacity than the CC beams. The average shear capacity of the SC beams was 18% and 16% lower than those of the FA50 and RCA50 beams, respectively

Bond Performance of Sustainable Reinforced Concrete Beams

Proper force transfer between reinforcement and surrounding concrete is one of the most significant factors affecting the structural performance of reinforced concrete. Because of the increasing interest in using fly ash and recycled concrete aggregate (RCA) in structural applications, it is necessary to investigate bond properties of mixtures proportioned with high volume of these materials. The present study investigates bond strength between concrete and reinforcing steel in full-scale beams constructed with various green concrete mixtures, including high-volume fly ash concrete containing 50% Class C fly ash replacement (FA50), concrete with 50% of coarse RCA replacement (RCA50), as well as a so-called sustainable concrete (SC) proportioned with 50% Class C fly ash and 50% RCA. Conventional concrete (CC) made without any fly ash and RCA is employed as the Reference mixture. Data obtained from the testing of 11 full-scale spliced beams are analyzed, including one beam per concrete type (except for RCA50) for investigating the top-bar effect. Experimental results are compared to six different analytical models available in literature. Results are also evaluated based on the bond database of specimens fabricated with RCA developed through literature survey as well as the database proposed by ACI Committee 408 for bond in CC. On average, SC specimens exhibited 15% higher normalized bond strength compared to the Reference beams. Performance of SC mixture was similar to that of RCA50, which were both slightly (6%) lower than that of the FA50 beams in terms of bond strength. No sign of top-bar effect was observed for the FA50 and SC beams

Artificial Intelligence to Investigate Modulus of Elasticity of Recycled Aggregate Concrete

Modulus of elasticity (MOE) is one of the main factors that affect the deformation characteristics and serviceability of concrete in the hardened state. The use of recycled concrete aggregate (RCA) in concrete production can lead to a significant reduction in the MOE. An artificial neural network (ANN) was employed to quantify the effect of coarse RCA on the concrete\u27s MOE. A database summarizing over 480 data series obtained from 52 technical publications was developed and analyzed using ANN. Concrete mixture proportions and aggregate properties were considered input parameters. The rate of reduction in 28-day MOE was considered the output parameter. An additional data set of 43 concrete mixtures obtained from laboratory investigation of concrete with well-known properties was used to validate the established model. Several combinations of input parameters and ANN architectures were considered in the analysis. Results indicated that the performance of the system was acceptable, with a coefficient of correlation ranging from 0.71 to 0.95 for the training, validation, and testing of the model with a mean square error limited to 0.008. The developed model was incorporated for a case study on a typical concrete used for rigid pavement construction. Contour graphs were developed to showcase the effect of up to 100% coarse RCA replacement on the variations in the MOE of concrete made with 0.40 water-cementitious materials ratio (w/cm) and 323 kg/m3 (545 lb/yd 3 ) of a binary cement, designated for rigid pavement construction. The results indicated that depending on the RCA quality, a reduction of 10 to 30% in the MOE of pavement concrete made with 50% RCA can be expected. However, the reduction in the MOE will be limited to 10% when RCA with water absorption limited to 2.5% and an oven-dry specific gravity of over 2500 kg/m3 (156 lb/ft3) is used