Jin-Hoon Jeong

Early-Age Curling and Warping Behavior: Insights from a Fully Instrumented Test-Slab System

A concrete slab was constructed at Texas A&M University to study temperature, moisture, and creep effects on the curling and warping behavior of jointed concrete pavements under different curing conditions. A saw-cut joint was placed at the mid-slab location, where one half of the slab was cured with a standard curing compound and the other half was mat-cured. The half of the slab under membrane curing was subjected to a larger built-in curling and shrinkage than the half that was mat-cured. Because of differences in the amount of shrinkage and creep between the two curing methods during the hardening process, the two halves of the slab showed different early-age behaviors with respect to strain and vertical displacement. The dowels also affected the early-age behavior of the slab at the saw-cut joint. A linear relationship was found among measured vertical corner displacements, concrete strain, and calculated dowel bending moments. The equivalent temperature differences calculated by ISLAB 2000 present the effects of shrinkage and creep on the curling and warping behavior of the slab.

CHARACTERIZATION OF STIFFNESS PARAMETERS IN DESIGN OF CONTINUOUSLY REINFORCED AND JOINTED PAVEMENTS

Key performance factors related to the deterioration of a joint or crack stiffness in terms of the prediction of faulting or punchout distress are characterized. Over the past decade, several advancements have been made that address various stiffness components that contribute to the transfer of load between adjacent slab segments. An approach is presented that addresses key stiffness components in a rational format in terms of a mechanistic process to address faulting and punchout development. This approach is suitable for both the design and rehabilitation of concrete pavement systems. Components of load transfer are discussed and detailed along with key material parameters relative to a loss of stiffness mechanism triggered by repetitive loading. This discussion leads to a mechanistic erosion model to provide a tie between joint deterioration of the development of voids created by erosive action. This work provides a basis of follow-on efforts to illustrate the sensitivity of key design parameters in an overall design and rehabilitation process.

Use of surface free energy properties to predict moisture damage potential of Asphalt concrete mixture in cyclic loading condition

The synergistic effects of microdamage due to repeated loading in Asphalt-Aggregate system at a high temperature (40°C) and moisture damage analysis based on surface free energy theory are presented in this paper. The introduction of moisture in either a liquid or vapor state during cyclic loading may well be more damaging than simply moisture conditioning an asphalt concrete sample prior to testing. This difference may be due to the presence of a dynamic “network” of adhesive fracture, which potentially provides a channel for moisture movement within the sample. The percentage of the surface area of aggregate that has been exposed to water was used as a significant index to quantify the level of adhesive fracture. This index is calculated with the surface free energies of aggregate and asphalt which are measured by two methods, the universal gas adsorption and the Wilhelmy plate, respectively. The relation between the percentage of the surface area of the aggregate exposed to water and the number of cycles of loading assists in quantifying adhesive fracture in the asphalt-aggregate mixture.

Effects of different calcium salts on calcium carbonate crystal formation by Sporosarcina pasteurii KCTC 3558

We examined the effectiveness of using different calcium salts for bioconsolidation. Four calcium salts were chosen based on their applicability and solubility. Initial experiments demonstrated that the addition of any calcium salt had a negative effect on the urease activity of S. pasteurii. Microscopic examinations elucidated the morphological and structural differences of the calcium carbonate (CaCO3) crystals induced. Calcite and vaterite are the prominent forms of CaCO3 detected according to X-ray diffraction (XRD) analysis. Bioconsolidated sand samples were able to significantly resist water flow through a column compared to the non-treated samples. Also, in a tightness test, the differences in the ability to retain water within columns were observed among the samples tested. Moreover, despite the differences, the calcium salts tested still bound the sand together to form blocks. Our results further explain the influence of multiple factors in crystal formation and sand bioconsolidation effectiveness.

Moisture profiles and shrinkage in early-age concrete pavements

This paper describes the effort placed to apply a series of discrete test and analysis methods as an integrated approach for the estimation of time- and position-dependent humidity changes and shrinkage in early-age concrete. The total moisture loss in concrete is assumed to be a result of autogenous drying and conventional external drying. Autogenous drying or self-desiccation is expressed as a function of the degree of hydration in terms of strength ratio, which can be determined by the maturity and strength relationship. Moisture loss due to external drying is estimated by finite element analysis based on the nonlinear diffusion theory. Estimated humidity reduction is then used to estimate shrinkage potential in the concrete by applying a linear shrinkage coefficient, which may be determined by tests. Time- and position-dependent shrinkage potential will be useful for further stress analysis. Application of the analysis approach is introduced with an example analysis for a 300 mm × 300 mm cylinder specimen tested under 1D drying for the first 7 days since after casting.

Effect of Slab Curling on Movement and Load Transfer Capacity of Saw-Cut Joints

The effect of slab curling on the development of cracking at saw-cut notches and long-term joint movement in the concrete pavement sections of the Korea Highway Corporation test road was investigated in addition to joint deflections and load transfer efficiency (LTE) at the joints. During paving operations, 50 joints were saw-cut immediately after the occurrence of a random crack in the concrete pavement. The location and the time of the uncontrolled cracking were observed by a comparison of the tensile strength of the concrete with the tensile stress developed by the slab curling because of the temperature difference between the top and bottom of the slab. The development of cracking and movement of the saw-cut joints and random cracks were observed over a 2-year period after construction. The relationship between the initial and long-term joint movements is presented. The deflections and LTE at the joints and random cracks were measured by using the falling weight deflectometer 2 years after concrete placement. The effect of slab curling due to a permanent built-in temperature difference on the deflection at the joint is described. In addition, the effect of dowel locking due to the upward slab curling on the load transfer capacity of the joint is presented.

Testing and modelling of friction characteristics between concrete slab and subbase layers

This paper presents the results of an analysis of the interlayer friction characteristics between a concrete slab and various types of subbases, which are commonly used in concrete pavement construction. The interlayer friction characteristics were examined by conducting push-off tests on concrete slabs placed on top of lean concrete, crushed stone, or asphalt subbase, with and without separation membranes, under a range of saturated conditions. Throughout the tests, the friction resistance force and horizontal displacement, along with different types of subbases, were measured during the first application of a load, steady conditions, and saturated conditions. The measured interlayer friction resistance force and horizontal displacement after applying the first load showed results similar to other studies. To incorporate the test results into an analysis, a simple method was developed to estimate the maximum friction resistance force, initial slip displacement, and friction stiffness based on bilinearisation from the field-measured nonlinear friction resistance force, displacement relationship using the energy method. The finite element programs, ABAQUS and EverFE, were incorporated to analyse a concrete pavement. The interlayer friction behaviour was considered both with nonlinear and bilinear models in finite element programs and the interlayer friction characteristics were modelled with connector elements. The maximum tensile stress and horizontal displacement under temperature loading conditions were calculated using analytical models and the results were compared with field data. The results of the bilinear model based on the energy method matched the field data.

Age and Moisture Effects on Thermal Expansion of Concrete Pavement Slabs

A mechanistic-empirical pavement design guide (MEPDG) for portland cement concrete pavement (PCCP) has been developed recently and, within it, the coefficient of thermal expansion (CoTE) of concrete is considered as a crucial variable. Previous research has suggested that the concrete CoTE is affected by the availability of moisture in capillary and gel pores. The capillary pores are filled with hydration products, and their volume decreases at an early age of the concrete. However, the variation of the concrete CoTE due to hydration and moisture has not been quantified completely. The results have varied mainly due to the development of measurement techniques. The age and moisture effects on the CoTE of concrete were investigated by measuring the temperature, humidity, and strain of a cylinder specimen at both the initial and later ages. Drying shrinkage and autogenous shrinkage were considered in the calculation of the CoTE, particularly at early concrete ages. This investigation was facilitated by moving a concrete test specimen periodically from a 60°C environment to a 10°C environment over a 6-month period. Dilatometer testing and composite modeling were also conducted to verify the age and moisture effects on the concrete CoTE. Results show a close resemblance between the CoTEs determined by these different approaches. According to finite-element (FE) analysis, the behavior of the pavement slab was significantly affected by the variation of the concrete CoTE.

Improvement of Fatigue Model of Concrete Pavement Slabs Using Environmental Loading

Concrete slab curls and warps due to the uneven distribution of temperature and moisture and as the result, internal stress develops within the slab. Therefore, environmental loads must be considered in addition to the traffic loads to predict the lifespan of the concrete pavement more accurately. The strength of the concrete slab is gradually decreases to a certain level at which fatigue cracking is generated by the repetitive traffic and environmental loadings. In this study, a new fatigue regression model was developed based on the results from previously performed studies. To verify the model, another laboratory flexural fatigue test program which was not used in the model development, was conducted and compared with the predictions of other existing models. Each fatigue model was applied to analysis logic of cumulative fatigue damage of concrete pavement developed in the study. The sensitivity of cumulative fatigue damage calculated by each model was analyzed for the design factors such as slab thickness, joint spacing, complex modulus of subgrade reaction and the load transfer at joints. As the result, the model developed in this study could reflect environmental loading more reasonably by improving other existing models which consider R, minimum/maximum stress ratio.

Comparative Analysis in Sensitivity of Cumulative Fatigue Damage of Mechanistic-Empirical Concrete Pavement Design Programs

The MEPDG(Mechanistic-Empirical Pavement Design Guide) developed based on the AASHTO Design Guide helps engineers find optimal alternatives by using traffic volume, climate, material property, and pavement structure as its input parameters. However, because technical problems were found in the MEPDG, efforts to improve the program by settling the problems have been continued. Meanwhile, another mechanistic-empirical design program has been developed by the KPRP(Korea Pavement Research Program) in Korea. To develop and improve the Korean design program reasonably, it is necessary to analyze the MEPDG and then compare programs each other. For concrete pavement, fatigue cracking is predicted by using very complicated logic different from other performance indicators. Therefore, in this paper, transfer functions of the fatigue cracking used in the version of 0.5, 1.0, and 1.1 of the MEPDG were analyzed. Sensitivity of the input parameters to the cumulative fatigue damage was compared to each other by the MEPDG version and KPRP.