Jin-Sun Lim

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.

Development of Performance Criteria for Korean Pavement Warranty Specification

Existing road pavement specifications require that contractors meet only certain material and construction conditions regardless of pavement life. However, performance-based warranty specifications guarantee preservation of the product and designate responsibility for repair of defects to contractors. The warranty contracts and specifications for pavements used since the 1960s in Europe have been adopted in several states of the United States based on state-specific needs, and they have also been used in construction projects. In this study, the performance criteria of warranty specifications in Europe and the United States were investigated to develop performance criteria appropriate for Korea. Automated pavement survey equipment was used to inspect and evaluate indicators of pavement performance with regard to certain performance criteria. Each area of pavement was divided into 2-km sections, which were then subdivided into four 500-m segments. Among the numerous possible indicators, cracking, rutting, international roughness index (IRI), and surface defects (e.g., raveling, bleeding, and microcracking) were selected as performance indicators of asphalt pavement, whereas cracking, IRI, spalling, and D-cracking were selected for concrete pavement. Pavement management system (PMS) data from expressways and national highways were collected and analyzed at a 95th percentile confidence level to determine threshold values of the performance indicators. Warranty periods were also determined for newly constructed asphalt and concrete pavements, as well as asphalt overlay pavement. Remedial actions for the performance indicators were also suggested. Performance indicators and threshold values were evaluated by examining the asphalt overlay sections of national highways constructed between 2005 and 2007. As a result, conclusions were drawn about reasonable performance criteria appropriate for Korea.

Laboratory Testing of Material Properties of Asphalt Binder Containing Wasted Vinyl

PURPOSES: In this study, various laboratory tests were performed to investigate the suitability of wasted vinyl as a modifier of asphalt binder. METHODS: Based on the ASTM specification, variations in material properties of asphalt binder such as penetration, flash point, softening point, ductility, penetration index (PI), and performance grade (PG) with vinyl content were tested and analyzed. RESULTS: Lavoratory tests revealed that penetration and ductility of the asphalt binder increased with the vinyl content. The flash point, softening point, and PI decreased, and PG changed from 64-22 to 70-22 with increase of the vinyl content. CONCLUSIONS: Wasted vinyl modified the material properties of the asphalt binder. However, the asphalt binder with vinyl content over 6.0% was unsuitable as a pavement material.

Development of Mechanistic-empirical Joint Spacing Design Method for Concrete Pavements

Tensile stress occurs and random crack develops in concrete pavement slab when it contracts by variation of temperature and humidity. The tensile stress decreases and the random crack is minimized by sawcutting the slab and inducing the crack with regular spacing. The random crack, joint damage, decrease of load transfer efficiency are caused by too wide joint spacing while too narrow joint spacing leads to increase of construction cost and decrease of comfort. A mechanistic-empirical joint spacing design method for the concrete pavement was developed in this study. Structurally and environmentally weakest sections were found among the sections showing good performance, and design strengths were determined by finite element analysis on the sections. The joint width for which the load transfer efficiency is suddenly lowered was determined as allowable joint with referring to existing research results. The maximum joint spacing for which the maximum tensile stress calculated by the finite element analysis did not exceed the design strength were found. And the maximum joint width expected by the maximum joint spacing were compared to the allowable joint width. The new method developed in this study was applied to two zones of Hamyang-Woolsan Expressway being designed. The same joint spacing as a test section constructed by 8.0m of joint spacing wider than usual was calculated by the design method. Very low cracking measured at 6 years after opening of the test section verified the design method developed in this study.