Development of an integrated approach for improving concrete pavement performance: Field testing and analytical studies insights on base quality, concrete materials and pavement design

Date

2022-08

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Abstract

To get the best performance of continuously reinforced concrete pavement (CRCP), the good quality of the base, materials used in the concrete mix, and the concrete pavement steel design play essential roles. Long-term performance of PCC pavement depends, to a large extent, on slab support. However, current quality assurance testing on the preparation and construction of subgrade and base layers is quite deficient, does not reflect the importance of slab support, and needs to be improved. In this study, the viability of deflection testing on stabilized base as a quality assurance testing was investigated. Deflection testing was conducted on top of stabilized base in four construction projects, and deflection data were analyzed to back-calculate subgrade k-values and base modulus. To develop a threshold deflection value on top of stabilized base, mechanistic analysis was conducted to estimate maximum deflections on stabilized base with various levels of modulus of subgrade reaction and base modulus. Deflection-based quality assurance testing for support layers in PCC pavement is a significant departure from traditional quality assurance testing. Also, there are some discrepancies between back-calculated (subgrade k-values and base modulus) and forward analysis (deflections) results, implying technical imperfections at this point. However, the advantages of the proposed protocol for quality assurance testing, including the speed of testing and resulting expanded coverage, outweigh the increase in cost. Implementation of the protocol is expected to improve PCC pavement performance. The performance of continuously reinforced concrete pavement (CRCP) in Texas has been quite satisfactory, primarily thanks to the continuous improvements in design and construction. However, severe spalling has been a major problem, and the Texas Department of Transportation (TxDOT) has sponsored several research projects since 1985 to identify solutions for this serious problem. Even though the research efforts were successful in identifying spalling mechanisms, developing a policy that TxDOT could easily implement has been a challenge. To develop a more practical solution to this problem, TxDOT initiated a research study, and the research efforts consisting of identifying CRCP projects with severe and no spalling, obtaining and conducting materials testing on concrete cores from those projects, analyzing the testing data, and performing theoretical analyses to validate the testing results. Among the material properties evaluated, the coefficient of thermal expansion (CTE) of concrete proved to have the best correlation with spalling. Detailed analyses of mechanistic behavior of concrete conducted with an object-oriented finite element program (OOF2) and commercial finite element program verified the reasonableness of the field-testing results. All concrete cores from CRCP with severe spalling had a CTE larger than 5.5 microstrains/°F, whereas no spalling was observed in concrete with a CTE less than that value. Based on this finding, TxDOT now requires the use of coarse aggregate that will produce concrete with a CTE of less than 5.5 microstrains/°F for CRCP construction. It is expected that this implementation will reduce the spalling in CRCP substantially. Over the years, thicknesses of continuously reinforced concrete pavement (CRCP) have increased to address the increase in truck traffic. Since the percentage of longitudinal reinforcement is fixed at a constant ratio of the concrete cross-sectional area, a thicker slab requires more reinforcement and reduced bar spacing, potentially hindering concrete consolidation. To address this issue, two-mat steel design was implemented in Texas for pavements with thickness of 13 in. or larger. Performance evaluations of thick CRCPs revealed that horizontal cracking developed at the depth of reinforcement where one-mat steel was placed, while no horizontal cracking was observed where two-mat steel was used . Pavement responses with one-mat and two-mat reinforcements with different depths were analyzed by three-dimensional modeling with a finite element analysis (FEA) program for the wide range of environmental loadings. Maximum concrete vertical tensile stresses around longitudinal reinforcement at transverse crack area are a good indicator of horizontal cracking potential; those stresses were evaluated, along with concrete stresses at the top of the slab, which are responsible for top-down transverse cracking. The results show that the two-mat design causes higher concrete stresses at the top of the concrete slab and lower concrete stresses around the longitudinal reinforcement, leading to increased transverse cracks and a reduction in horizontal cracking potential.


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Keywords

Concrete Pavement, Base, Quality Assurance, FWD, Spalling, OOF2, CTE, Aggregate Type, CRCP, Environmental Loading, Horizontal Cracking, One-Mat Design, Reinforcement Design, Thickness of CRCP, Transverse Cracking, Two-Mat Design, 3-D FE Model

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