Moon Won

Dynamic Stress Response of Concrete Pavements to Moving Tandem-Axle Loads

The dynamic stress response of concrete pavements subjected to moving tandem-axle loads of constant amplitude and harmonic and arbitrary variations was investigated. The concrete pavement was modeled using a plate of infinite extent on a viscoelastic foundation. Formulations were developed in the transformed field domain using (a) a double Fourier transform in space and moving space for moving loads of constant amplitude and for the steady-state response to moving harmonic loads and (b) a triple Fourier transform in time, space, and moving space for moving loads of arbitrary variation. The effects of viscous damping, velocity, load frequency, and phase between front- and rear-axle loads on the maximum stress and the stress distribution were analyzed. Without viscous damping, the effects of velocity and frequency, within practical ranges, on the stresses are negligible; however, with viscous damping, those effects are significant. Since materials used in various pavement layers possess damping characteristics, wheel load stresses can vary considerably because of velocity and load frequency. The increase in wheel load variations and corresponding concrete stresses can be significant if the roughness of the pavement surface is not controlled. The difference in the phase angles between front- and rear-axle loads can considerably increase the maximum stress; therefore, the use of tandem-axle loads and dynamic analyses is necessary to obtain the accurate stresses because the phase effect cannot be obtained with single-axle loads or static analyses.

Three-Dimensional Analysis of Continuously Reinforced Concrete Pavements

Continuously reinforced concrete pavement (CRCP) performance depends primarily on early-age cracks that result from changes in temperature and drying shrinkage. Presented is the behavior of the CRCP due to the temperature change obtained by using a three-dimensional finite element model. The nonlinear effects of the bond-slip between concrete and steel and between concrete and base have been studied. Modeling for the curling effect and for the viscoelastic material characteristics also has been considered. The results from the two-dimensional and three-dimensional models have been compared to verify the possibility of using a two-dimensional model. From this study, it was found that crack width and concrete stress are dependent on the transverse steel arrangement near the edge (longitudinal joint), but they are almost independent in the interior of the slab. The tensile stress occurring at the top of the edge on the transverse steel location can be higher than that occurring at the top of the slab center. This represents the possibility of forming a transverse crack from the edge on the transverse steel location. The twodimensional model with the plane stress element gives results very close to those of the three-dimensional model, except near the edge.

Mechanistic Modeling of Continuously ReinforcedConcrete Pavement

The use of continuously reinforced concrete pavement (CRCP) has increased in recent years in urban areas of Texas because CRCP provides a long-lasting pavement requiring little maintenance. A computer program, known as CRCP-10, has been developed using finite element formulations, transformed field domain analysis, and probability theories to analyze the behavior of CRCP. This mechanistic model predicts the crack spacing distribution and time histories of mean crack spacing/width and of longitudinal steel stress. The CRCP-10 computer program considers nonlinear variations of temperature and drying shrinkage through the depth of the concrete slab, curling and warping effects, concrete creep effect, nonlinear bond-slip between concrete and steel bars, changes in material properties with time, and moving dynamic tandem-axle loads. This paper presents details of the mechanistic modeling of CRCP and applications of CRCP-10 to various problems.

Effects of Creep and Built-In Curling on Stress Development of Portland Cement Concrete Pavement under Environmental Loadings

An adequate evaluation of stress developments in concrete is essential to ensure well-performing and long-lasting portland cement concrete (PCC) pavement designs and construction. In this study, the effects of creep and built-in curling (BIC) on the stress history of PCC pavements under environmental loadings were investigated primarily through a series of field tests and numerical data interpretations. To identify the stress-dependent strain component within the in situ measured total strain, a nonstress cylinder (NC) was employed in the field tests. The identified stress-dependent strains from the field tests were converted to stresses using a step-by-step numerical method. To investigate the effect of creep on stress developments, stress histories were computed in two different ways—one with elastic analysis and the other with viscoelastic analysis—and then their difference (stress relaxation) over time was evaluated. The finding indicated that creep may be a key element in the evaluation of long-term stresses and, in turn, the design and analysis of PCC pavements. Furthermore, this study examined the impacts of BIC on the residual stresses of PCC pavements. The result showed that BIC may affect the early-age stress development, but it has little influence on the long-term environmental stress state.

Continuously Reinforced Concrete Pavement: Identification of Distress Mechanisms and Improvement of Mechanistic–Empirical Design Procedures

In 2005, the Texas Department of Transportation initiated a rigid pavement database to collect information in preparation for the calibration and potential implementation of the Mechanistic–Empirical Pavement Design Guide (MEPDG) for continuously reinforced concrete pavement (CRCP). Twenty-seven sections, each 300 m (1,000 ft) long, were selected throughout the state. Deflection testing was conducted with a falling weight deflectometer. The information collected included load transfer efficiency (LTE) at small, medium, and large crack spacing for two different seasons, summer and winter. Also collected were crack-spacing information and slab deflections. LTE values for all the cracks were higher than 90% regardless of slab thickness, pavement age, crack spacing, or season. Mechanisms of primary distresses in CRCP were investigated. The investigation tentatively revealed that many distresses identified and recorded as punch-outs in Texas were not actually caused by structural deficiency. Rather, most of the distresses were caused by imperfections in design details, construction or material quality issues, or both. Horizontal cracking appears to be the major cause of distresses in CRCP in Texas. The interactions between longitudinal steel and concrete in response to dynamic wheel loading applications appear to be the cause of horizontal cracking. From the findings, mechanistic–empirical (ME) CRCP design procedures and a calibration function were developed. Because the accuracy of any ME design procedure depends to a great extent on the reasonableness of the transfer function, further efforts will be made to improve that function.

Effects of Supplementary Cementing Materials on the Setting Time and Early Strength of Concrete

The substitution of a portion of cement in concrete with supplementary cementing materials (SCM), which include ground granulated blast furnace slag (GGBFS), fly ash, and silica fume, frequently results in delayed setting and low early strength. When SCM-containing concrete is placed during cold weather and/or contains certain chemical admixtures, these problems can intensify and can seriously impact the performance of a pavement. This project investigated the setting time, early strength gain, maturity, bleeding, and plastic shrinkage cracking of several concrete pavement mixtures containing SCM under different temperature conditions (mimicking summer, spring, and winter weather). The data were used to develop guidelines for identifying slow-setting mixtures and preventing their use in pavements.

Performance of Continuously Reinforced Concrete Pavement Containing Recycled Concrete Aggregate

This paper presents the performance of continuously reinforced concrete pavement (CRCP) constructed in 1995 that utilized recycled concrete aggregate (RCA) as both coarse and fine aggregates. The project is Houston on a section of IH-10 between Loop 610 W and IH-45. In this project, no virgin aggregates were used. Concerns were raised regarding the performance of CRCP containing RCA. Detailed study was conducted to evaluate concrete material properties containing RCA. The properties of recycled aggregate measured in this study compared with virgin aggregate are consistent with those reported elsewhere: low specific gravity, higher water absorption, sulfate soundness loss, LA abrasion loss, and thermal coefficient. Little variation was observed in the paving operation due to the use of 100 % recycled coarse and fine aggregates. The moisture control of recycled aggregate, especially fine aggregate, is critical in producing consistent and workable concrete. The short-term and long-term performance of the reconstructed CRCP has been excellent, with tight crack widths and little spalling. Between concrete with virgin aggregates and concrete with recycled aggregates, there is no significant difference in thermal coefficient and permeability; however, there are significant differences in modulus of elasticity, compressive and indirect tensile strength, and water absorption. The low modulus of RCA concrete and good bond between recycled coarse aggregates and new mortar appear to be the key ingredients for good pavement performance. After more than 10 years of service under heavy traffic, the CRCP section containing 100% RCA is still providing excellent performance with no single structural distress.

Mechanism of Transverse Crack Development in Continuously Reinforced Concrete Pavement at Early Ages

The transverse crack in continuously reinforced concrete pavement (CRCP), more specifically transverse crack spacing and crack widths, has been cited as one of the most important pavement structural responses determining CRCP performance. Efforts have been made to predict crack spacing and crack widths for given environmental conditions and traffic loading, pavement structure, and material properties, with the primary objective of developing rational CRCP designs. However, that most transverse cracks develop at or near transverse steel implies substantial interactions between transverse steel and other factors causing transverse cracks. These interactions have not been fully incorporated in the theoretical models developed so far to predict transverse crack spacing and crack widths in CRCP. This study investigated the interactions between transverse steel and other factors and identified the mechanisms of transverse crack development at or near the transverse steel. Drying shrinkage and temperature drop in concrete cause concrete volume contractions in all directions (not just transverse and longitudinal, but vertical directions as well). Interactions between concrete volume contraction vertically and transverse steel cause larger concrete tensile stresses at or near transverse steel than at other areas and cause a higher probability of transverse cracks near transverse steel. Traditionally, subgrade drag theory has been used in the design of transverse steel even though current practice is to place just enough transverse steel to support longitudinal steel during concrete placement. If transverse cracks have such substantial effects on CRCP performance as currently thought, interactions between transverse steel and other factors should be considered in the design of optimum transverse steel.

Results of Repairs on Texas Longitudinal Joints and Cracks

Longitudinal joint separations are often observed in concrete pavements. An innovative repair procedure was developed in this study for slot stitching in faulted or separated longitudinal joints. It involves with three stages: (1) low pressure grout to restore support under slabs that exhibited signs of pumping and faulting (2) the slot stitching method of retrofitting tie bars, to restore lateral restraint and load transfer across longitudinal joints, and (3) latex modified concrete overlay to restore proper elevation to slabs that had faulted. This paper discusses the results and lesson learned from the first implementation project on US Highway 75 near Sherman, Texas.

The Application and Early-Age Behaviors of Continuously Reinforced Bonded Concrete Overlay of Distressed Jointed Concrete Pavements

Considerable efforts and money are spent to maintain and repair the distressed jointed concrete pavement (JCP) sections by providing partial-/full-depth repair, under sealing, and patching; however, a lot of distresses reoccur frequently. For severe distresses, overlay was constructed on the JCP. Resurfacing with a bonded concrete overlay (BCO) over the existing pavement to form a monolithic structure has proven to be a cost-effective rehabilitation strategy. Continuously reinforced concrete pavement (CRCP) bonded overlay was constructed for the rehabilitation of a 2000 ft long JCP section on U.S.75 in Sherman, Texas, United States which had been subjected to numerous rehabilitations to construct the guidelines of the CRCP bonded overlay. The pavement design and concrete mix design selected are discussed and introduced in this article. In order to reduce the reflective cracking at the location of the JCP joints, geotextile was placed at the joint location before the overlay construction. For the study on the function of the geotextile, the geotextile was not placed at 20 JCP joints for the comparison. One week after the BCO construction, the investigation for the CRCP cracking was carried out at three stages. The investigated results revealed that the cracks at the transverse steel location are much more than those between the transverse steel. Falling weight deflectometer testing was run on the pavement surface before and after the overlay construction to measure the deflection behavior of the pavement. The performance of the overlay shows that the bonded CRCP is appropriate for the JCP resurfacing.