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Improved criteria for the material properties and mix proportions of concrete slabs to enhance the performance of concrete pavements at Incheon international airport (IA) in the Republic of Korea are suggested. Gimpo IA and Gimhae IA were selected for comparison with Incheon IA based on their facility status and annual flight processing capability. After Incheon IA, Gimpo IA and Gimhae IA have the second and third largest annual numbers of flights per unit area of runway, respectively. Criteria for aggregate and mix proportions were chosen for improvement because of durability cracks (the major form of pavement distress at Incheon IA) due to the poor quality of aggregates used and repeated freeze–thaw cycles. Compared with the other airports, the mix specifications of the concrete slab at Incheon IA showed lower contents of cement and liquid admixture, a higher abrasion rate of coarse aggregate and a larger content of fines in the aggregate. Improved criteria were established based on a comparison of results. Concrete specimens were fabricated using the improved criteria and the performance of the concrete pavement was evaluated by testing the air content and freeze–thaw resistance of 12 mixes with different contents of cement, liquid admixture and fines in the aggregate.

The pavement condition index (PCI) is a tool for evaluating pavement performance and is based on the type and severity of surface distress. It is used to determine maintenance times, methods and location priorities. Most previous PCI prediction models have considered only pavement age or traffic volume as a variable, without consideration of other factors that affect pavement distress. In this study, data from 12 airports were analysed using reports published from 1994 to 2013. The airport pavements were divided into homogeneous zones according to their function and structure. For improved management of concrete airport pavements, a non-linear PCI model was developed for the homogeneous zones and tornado diagrams were used to analyse the sensitivity of the PCI according to the independent variables of the model. The results showed that the developed model can predict the PCI of homogeneous zones of concrete airport pavements more reasonably by considering various factors that affect pavement distress.

This study investigated the distress conditions of test sections of concrete pavement that have been used for more than the design life of 20 years. The study was performed using data from a highwa...

In this study, strain gages were installed at the centre, edge, and corner of concrete pavement slabs of Incheon International Airport based on the slab depth, whereas thermometers were positioned ...

A method for designing an airport concrete pavement (ACP) that can withstand environmental loads as well as traffic loads is presented. Information on ACPs for which double dual tandem landing gears were used for design aircrafts was collected and the stresses induced on the slabs when environmental loads and traffic loads were simultaneously applied were predicted with the finite-element analysis program FeaFaa. In addition, a maximum tensile stress regression model of ACP slabs was developed using the statistical analysis program SPSS. When environmental and traffic loads were simultaneously applied, the maximum tensile stress obtained with the finite-element method was significantly different from that obtained using Westergaard's equation of edge loading only in traffic loads. Therefore, the fatigue model in the US Federal Aviation Administration's AC 150/5320-6E design method was corrected to be appropriate for this study. Using the stress regression model developed in this study and the corrected fatigue model, the thickness and joint spacing of existing ACP slabs were redesigned and compared with existing airport pavements. Previously, only the thickness of a slab was designed and the joint spacing was empirically determined. However, from the results of this study, a slab's thickness and joint spacing can be designed mechanistically.

The objective of this study was to verify the effect of fiber grid reinforcement on the long-term performance of asphalt overlay pavements by performing field investigation, laboratory test, and finite element analysis. Crack, rutting, roughness, and other miscellaneous distresses of fiber-grid-reinforced overlay sections and ordinary overlay sections were compared. Pavement conditions of fiber grid overlay sections before and after the overlay were also compared. Cores were obtained from the fiber-grid-reinforced and ordinary sections to measure bonding shear strength between the intermediate and overlay layers. Fracture energy, displacement after yield, and shear stiffness of the cores were also obtained by analyzing the test results. Finite element analysis was performed by using the test results to validate the effect of the fiber grid reinforcement on the long-term performance of asphalt overlay pavements. Rutting and fatigue cracking were predicted for three cases: 1) fiber grid was not used; 2) glass fiber grid was used; and 3) carbon fiber grid was used. The cracking ratio of fiber-grid-reinforced sections was much smaller than that of ordinary sections. The results of field investigation, laboratory test, and finite element analysis showed that the fiber grid reinforcement improved the long-term performance of asphalt overlay pavements. Keywords: Asphalt pavement, Fiber grid reinforcement, Overlay pavement, Finite element analysis, Bonding shear strength

In this study, a remodeling index (RMI) prediction model was developed to determine and prioritize target sections for large-scale repair works of deteriorated expressway concrete pavements in Korea. The unit sections that represent the distribution of the structural condition of entire analyzed sections were selected for jointed concrete pavement (JCP) and continuously reinforced concrete pavement (CRCP), and the RMI of the representative sections was rated by a panel of members. The model that predicts the RMI of aging JCP and CRCP after a few years hereafter was developed using the RMI obtained by the panel rating as a dependent variable, and the pavement conditions, pavement age, traffic volume, and weather conditions of the corresponding sections were considered as independent variables. The RMI sensitivity was analyzed according to each independent variable, and the appropriateness of the RMI prediction model was verified by comparing the RMIs in 2016 predicted in 2014 (future RMI in two years) with those in 2016 predicted in 2016 (present RMI). The entire aging expressway concrete-pavement sections were divided into homogeneous sections of suitable lengths for remodeling works by applying the RMI prediction model to each unit section. The priority for remodeling works was determined among the highly ranked homogeneous sections using the predicted RMI. The actual pavement conditions of a target section in which the remodeling priority had the highest rank were verified.

In this study, a method to identify the representative section (RS) which can represent the pavement conditions of entire aged concrete expressway pavement (CEP) sections for the large-scale remodeling project, was developed based on pavement management system (PMS) data and an optimized approach. To fulfill this objective, various PMS data sets on the target section (TS) of concrete expressway pavement that exceeded 20 years of design life were collected with 100m intervals. Then, the first version of the optimized 100 RSs, which was a reasonable amount of data for analysis of aged CEP condition, was selected based on the different severity levels of surface damage and international roughness index (IRI) data. Secondly, another crucial PMS factor: the alkali-silica reaction (ASR) severity level, was considered and substituted partially in the previously selected 100 RSs to provide additional and reasonable representative characteristics. Finally, the characteristics of the RS were evaluated and verified by considering whether the various distress size rankings of the RS were uniformly distributed within the entire distress size ranking of the total jointed concrete pavement (JCP) and continuously reinforced concrete pavement (CRCP) TS. It was found that the RS selection approach and corresponding criteria proposed in this study, based on the optimization approach, could be successfully used to determine the future large-scale remodeling priority of the old concrete expressway pavements.

This paper presents a methodology to estimate the stress-strain relationship of an unbound aggregate base using linear viscoelastic theory. Current Mechanistic-Empirical (ME) pavement design procedure adopts the resilient modulus concept to explain the behavior of granular materials for flexible pavement design. The resilient modulus is a stress dependent material property of granular materials that is different from strength. Although California Bearing Ratio (CBR) test results (i.e., stress and strain) can be used to estimate the strength of a granular material, it is not possible to estimate the resilient modulus directly. Therefore, it is necessary to estimate stress along with strain changes. The convolution integral enables the stress to be estimated from the given strain changes only if the relaxation modulus is measured. Aggregate specimens prepared from two different sources in Georgia were subjected to the relaxation modulus test. From the test data, the time-dependent stress due to a known strain rate was computed as a convolution integral of the strain. The computed stress-strain relationship was compared with that from the resilient modulus (MR) test. The results indicate that the stress-strain relationships from the MR test and the convolution integral are similar with nearly the same slopes when horizontal stress is assumed to be approximately 45% of vertical stress. This observation supports the use of the proposed methodology by state highway agencies to validate the MR test results for quality control and quality assurance of aggregate base material selection for pavement design and construction.

This study examined the pavement distress data obtained from the field as well as the effects of the soil cover depth, joint position and reinforced slab length on the behaviour of concrete pavement using the finite element method. An ultimate strength model with a similarity of 1/2 was designed and constructed. Finite element analysis incorporating an implicit direct numerical integration scheme was conducted to obtain an optimal design for the pavement structure above a box culvert. An accelerated pavement test was conducted for validation, in which a realistic traffic load was imposed on the pavement model constructed in the laboratory. The strain histories were measured at each section and compared with those of numerical analysis. The optimal joint position and reinforced slab length that can minimise the damage to the pavement structure above a box culvert were also determined.

This paper presents a method for calculating the environmental load that is essential to the mechanistic design of airport concrete pavements, based on the equivalent linear temperature difference (ELTD) between the top and bottom of the slab. To assess its application, the total ELTDs at 17 airports (military and civilian) across the Korean peninsula, representing the full range of regional climates in the country, were calculated according to slab thickness. Based on the results, a multiple regression model was developed. The environmental load can be considered by simply inputting the ambient temperature, relative humidity and slab thickness into the proposed models. The results can be applied worldwide.

This study examined the effect of the materials and age on the coefficient of thermal expansion (CTE) of concrete paving mixtures at 28 and 120 days. Concrete specimens were prepared in the laboratory by varying the mix design variables with different types of aggregate to produce different mixes using Portland cement. The microstructures of the concrete mixtures were also observed by scanning electron microscopy to determine the relationship between the volume change in concrete and the formation of microcracks. Statistical analyses of the experimental data suggested that the CTEs measured at 120 days are significantly lower than those measured at 28 days. An analysis of variance indicated that the mixture with granite results in significantly higher CTE reduction with time than the mixture with dolomite. The larger volume change with a higher CTE may be due to the formation of microcracks in concrete.

Deteriorated roads should be rapidly repaired to minimize traffic congestion when detours are unavailable. Various overlay methods have been developed to achieve effective repairs of aged and deteriorated concrete pavements. To select the most effective type of overlay, it is necessary to analyze and compare the performance of various types of overlay pavement sections. In this study, the performances of Unpretreated Asphalt Overlay (UAO), Pretreated Asphalt Overlay (PAO), and Bonded Concrete Overlay (BCO) sections constructed on Jointed Plain Concrete Pavement (JPCP), Jointed Reinforced Concrete Pavement (JRCP), and Continuously Reinforced Concrete Pavement (CRCP) were analyzed and compared using the U.S. Long-Term Pavement Performance (LTPP) database. Calculations of the Pavement Condition Index (PCI) of overlay sections were performed and predictions and comparisons of their lifespans were made. In addition, correlations between predicted lifespans and related factors were analyzed based on overlay type. It was mainly concluded that the BCO pavement showed the best performance whereas the UAO pavement had the worst performance of the three overlay types.

Low temperature cracking is a very serious distress for asphalt pavements built in Northern U.S. and Canada. As temperature rapidly decreases, thermal stresses develop in the restrained asphalt surface layer and, when the temperature reaches a critical value, cracking occurs. A “simple” solution to overcome this problem is to use a very soft asphalt binder with high relaxation properties, which limits the accumulation of high stress and the formation of cracks. However, these types of binder may lead to significant permanent deformation at high temperature (e.g., rutting) and, therefore, cannot be used for real pavement constructions. In this research, the possibility of obtaining stiffer asphalt binders by adding fine taconite filler available in Minnesota was investigated. Two different types of asphalt binders were selected and from each binder, three different types of asphalt mastics were prepared based on the amount (i.e., level) of taconite particles used as filler: 5%, 10% and 25%. Bending Beam Rheometer (BBR) and Dynamic Shear Rheometer (DSR) tests were performed to evaluate the low and high temperature properties of asphalt binder and corresponding mastics. From these experimental works, creep stiffness, m-value, thermal stress and shear complex modulus were calculated and then graphically and statistically compared. It was observed that asphalt mastic containing 5% taconite filler presents similar properties at low temperature and better performances at high temperature compared to the corresponding asphalt binder. On the other hand, asphalt mastics containing higher amount of taconite fines (10% and 25%) are much more brittle compared to the original binder at low temperature, even though higher rutting resistance was observed at high temperature.

The development of an Artificial Neural Network (ANN) model to estimate subgrade resilient modulus is described in this paper. Nine (9) different sources of subgrade materials locally available in Georgia were subjected to the resilient modulus test with two replicates. The stress state and physical properties on resilient behavior of subgrade soils were successfully correlated with an ANN model developed in this paper. The results demonstrated that the stress state and physical properties of subgrade soil significantly influenced the subgrade resilient modulus, which in turn has a substantial effect on the pavement response predictions that impact pavement design.

To accurately estimate the tensile stress distribution in concrete pavement slabs, their viscoelastic characteristics must be clearly identified, because in a drying concrete slab, creep and stress relaxation occur in a complex manner over a long time. In this study, a restrained ring test was conducted to determine the viscoelastic characteristics of a concrete pavement slab. Finite Element Analysis (FEA) was performed to simulate the restrained ring test using the solidifying viscoelastic properties obtained from the modified elastic-viscoelastic correspondence principle to verify the effect of the viscoelastic material properties. The tensile stress calculated by the viscoelastic analysis was observed to be ∼50% of that obtained from the elastic analysis. The FEA was performed under assumed environmental conditions for the elastic and viscoelastic models of a concrete pavement. Further, the maximum tensile stress based on the viscoelastic model was observed to be 45–55% less than that based on the elastic model owing to stress relaxation. It is concluded that the model that considers the solidifying viscoelastic properties shows better analysis results for tensile stress distribution in a concrete pavement. With better and more accurate estimates of the concrete pavement responses, a pavement that is more structurally sound can be designed.

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.

In many countries, airport pavements are designed according to the Federal Aviation Administration (FAA) Rigid and Flexible Iterative Elastic Layer Design (FAARFIELD) program. FAARFIELD is capable of analyzing airport pavement behavior based on both the layered elastic-based and three-dimensional finite-element-based design methods. Although the FAA design methods accommodate the mechanical principles needed to calculate the slab thickness required for a given aircraft fleet mix, the effect of temperature-induced loading on the concrete pavement behavior is not considered. This paper presents the tensile stress distribution of concrete slabs and the landing gear position where the maximum tensile stress is observed when both load-induced and temperature-induced loads are taken into consideration in the analysis. Based on three-dimensional finite element analyses, it was observed that the distress types and locations coincided with the actual distress types and locations that are typically found in the field when both traffic-induced and temperature-induced loadings were considered in the analysis.

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 bilinearisa...

This research was conducted to assess the effects of temperature segregation in hot-mix asphalt (HMA) paving construction on pavement distress in the early stages of its life cycle. Several paving projects across Nebraska were visited in which sensory devices were used to test how density, moisture content within the asphalt, material surface temperature, internal temperature, wind speed, haul time, and equipment type, contribute to temperature differential. Areas of high temperature differential were identified using an infrared thermal camera. A nonnuclear density device was also used to record how lower temperature asphalt density correlates with a more consistent hot area. The location was marked digitally with a handheld global positioning system to locate points of interest for future site revisits to verify research findings. The research findings indicate that among the investigated variables, truck types and density are highly correlated with temperature differential. Additionally, analysis of data from revisits after one or two freeze-thaw seasons shows that higher temperature differential is significantly correlated with premature distress of paved HMA roads while they are still in new condition. This finding suggests that higher temperature segregation created from paving construction in the zone of freeze-thaw cycles promotes visible surface distress in the very early stage of the pavement life cycle.

Non-uniform moisture distribution through the depth of jointed concrete pavement causes greater shrinkage at the top of the slab than at the bottom. This kind of shrinkage behaviour induces warping and tensile stress in the top surface of the slab. The warping shape changes with concrete age. In this study, an instrumented concrete slab with vibrating wire strain gauges was constructed in the field to investigate strains in the slab. The coefficient of thermal expansion of concrete was tested in the laboratory, and the thermal and shrinkage strains were analysed from the testing data. Furthermore, shrinkage of the concrete slab was predicted via the ACI (American Concrete Institute) 209R-92 Code. Relevant correction factors for the ACI 209R-92 Code were determined by using simultaneous equations for different vertical positions. The shrinkage effects on the pavement slab were converted to thermal effects and the differential shrinkage–equivalent temperature difference (DSETD) was used to quantify the effects of shrinkage on the behaviour of the concrete pavement. A fairly good correlation occurred between the results obtained from the DSETD model and the field test.

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.

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 spec...

In this paper, effects of tire loads and inflation pressures on predicted pavement responses were presented. The objective was to study the effect of increased tire loads and tire inflation pressures on predicted transverse strains and vertical strains at the different pavement layers and material properties. A 3 dimensional (3D) tire contact stresses for 6 different tires were interpolated from the database of the measured tire contact stresses. The shape of measured tire contact stresses is dependent on tire loading conditions. The results show that the predicted values were different near the asphalt concrete (AC) layer by increased tire inflation pressure. Under the increased tire load, the predicted values were different at the base and subgrade layer. From statistical analysis, predicted transverse strains at the bottom of asphalt layer and vertical strains at the top of subgrade are affected by different AC thicknesses, AC moduli, and subgrade moduli.

A parametric study is conducted to investigate the effect of lead rubber bearing (LRB) isolator and ground motion characteristics on the response of seismic isolated bridges. The purpose was to investigate the most favorable parameters of the LRB for minimum earthquake response of the isolated bridge system for different ground motions. The important parameters included are: ground motion characteristic by considering peak ground acceleration to peak ground velocity, PGA/PGV ratio as damage index; characteristic strength, Q d of the LRB isolator normalized by the weight acting on the isolator; flexibility of isolator by varying post yield time period, T d ; and yield stiffness to post yield stiffness, K u /K d ratio. The performance of seismic isolated bridge is measured by the variation of maximum isolator displacement (MID), maximum isolator force (MIF), deck acceleration and pier base shear. For a specified ground motion, smaller MID and MIF are regarded as indicator of better seismic performance. It is found that there exists a particular value of Q d /W, T d and K u /K d for which the MID, MIF, deck acceleration and pier base shear attain the minimum values. Finally the recommendations are made which are useful for the design engineers at the preliminary seismic isolation design of the bridges with LRB isolator for the ground motion having different characteristics.

In order to represent the concrete maturity and strength relationship, different mathematical models have been developed. In practice, there can be implementation of the logarithmic maturity and double logarithmic strength linear relationship for in-place strength gain and time of opening monitoring under variable temperature conditions. Concrete moisture was considered in the existing maturity concept context as a means for concrete strength predictability improvement. There was modification of a moisture modification factor Bazant developed on the basis of Powers' work, and the factor was included in an existing maturity model based on temperature. By using the corrected moisture modification factor, an improved relative strength and maturity relationship was established.

Structures underneath pavements commonly reduce the bearing capacity of the ground because of poor compaction and long-term settlement at sites around these structures. When a load is applied at these sites, the stress on the concrete slab increases and may exceed the design strength, inducing distress and shortening the lifespan of the pavement. In this study, we investigated the transverse cracking of concrete pavement slabs above box culverts in a test road of the Korea Expressway Corporation. Transverse cracking in the slabs was surveyed in both the north- and southbound lanes with different cover depths over the box culverts. To examine the transverse cracking, the jointed concrete pavement of the test road containing the culvert was modeled and analyzed by the finite-element method. Wheel loading was applied after taking into account the self-weight of the pavement and the temperature gradient within the concrete slab. The positions and magnitudes of the maximum tensile stress and the corresponding positions of wheel loading were investigated for each loading combination. In this manner, we identified the optimal joint positions for which the maximum tensile stress in the pavement slab is minimized. We also analyzed the behavior of the pavement in relation to the cover depth and reinforced concrete transition slab length. Accordingly, we proposed an appropriate length for the reinforced concrete transition slab to ensure minimized tensile stress in the pavement slab.

The temperature profiles in a hydrating concrete slab are produced by a two-dimensional finite-element method software tool, TMAC 2 temperature and moisture analysis for curing concrete, as a function of time and ambient boundary conditions described in this paper. To include the effect of the heat of vaporization, heat flux due to evaporation is included in the boundary condition of heat transfer at the slab surface in addition to the effects of surface humidity, effective curing thickness, and surface moisture emissivity on the rate of evaporation. Thermal conductivity is back-calculated using the data collected from laboratory measurements toward the improvement of the modeling of thermal conductivity. Theoretically, the material properties determined in this manner should facilitate accurate tempera- ture prediction. Thus, temperature prediction in hardening concrete pavements under various conditions can be effectively calibrated by improved material characterization. To this end, this paper provides the basis of a calibration protocol.

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.

Evaporation of concrete influences the development of both initial transverse cracking and delamination in the concrete slab. It was suggested that spatting distress might develop in the slab where the initial transverse cracking occurred by theoretical equations and a field investigation. Thus, efforts to prevent the evaporation of concrete using proper curing methods are required to minimize the distresses of the slabs. Effective curing thickness (ECT) concept was used in this paper to evaluate various curing methods used to prevent the evaporation from concrete. Curing effectiveness quantified by the ECT of different types and amounts of curing compound under various curing conditions was investigated based on the results of laboratory tests. According to the test results, the wind speed is inferred to be a significant factor of the magnitude and continuance duration of the curing effectiveness.

Aggregate gradation effects on cracking-related displacements of concrete are investigated in the laboratory using the German cracking frame. Concrete workability was assessed by use of the slump and drop tests for two different concrete mixtures consisting of gap-graded and dense-graded aggregates. Shrinkage strain, cracking frame strain, and concrete strain were measured and used to compare to strength gain and creep development. The measured and calculated strains of the different aggregate gradations were compared each other. Gradation effects on strength and stress development relative to tensile cracking at saw-cut tip were also investigated. Test results revealed that the gap-graded concrete has indicated larger shrinkage and creep strains than dense-grade concrete perhaps because of its higher volume concrete of cement mortars in the mixture.

A concrete slab was constructed at Texas A&M University to investigate environmental effects in terms of temperature and moisture effects on the behavior of jointed plain concrete pavements. The slab behavior was delineated relative to equivalent linear temperature and humidity differences as a function of time. As expected, the trends of these differences were found to relate with the trends of ambient temperature and relative humidity. The slab had daily periods of tensile and compressive strain corresponding to the daily changes in the ambient temperature and relative humidity. Furthermore, the trends in the slab displacements were clearly dependent upon the changes in ambient temperature and slab temperature gradients. Drying shrinkage and creep strains primarily in the vicinity of the top surface appeared to cause an overall shift in the slab movements. This shift manifest in both the strain and vertical displacement of the slab was determined from data collected up to 2 years after placement of the concrete.

A field test program was conducted for the newly placed concrete pavement of US Interstate Highway 10 between March 26th and 28th, 2003. The test section was located between Van Horn and Sierra Blanca in Hudspeth County approximately 130 km east of El Paso, Texas. The main objective of the test was collecting moisture-related data to validate the models of effective curing thickness, evaporation rate, and moisture-based maturity. Effect of moisture loss on drying shrinkage strain was studied using additional test instrumentation.

Hydrating concrete pavement is typically subjected to temperature-induced stresses that drive cracking mechanisms at early concrete ages. Undesired cracking plays a key role in the long-term performance of concrete pavement systems. The loss of support beneath the concrete pavement due to curling caused by temperature changes in the pavement may induce several significant distresses such as punch out pumping, and erosion. The effect of temperature on these distress mechanisms is both significant and intricate. Because thermal conductivity dominates temperature flow in hydrating concrete over time, this material property is back-calculated by transforming governing equation of heat transfer and test data measured in laboratory. Theoretically, the back- calculated thermal conductivity simulates the heat movements in concrete very accurately. Therefore, the back- calculated thermal conductivity can be used to calibrate concrete temperature predicted by models.

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.

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.

Early-age moisture loss from the surface of a concrete pavement may induce undesirable effects that play a factor in long-term performance. Early-age detrimental behavior such as slab curling, warping, delamination, and even plastic shrinkage cracking are affected by the amount of evaporation and the effectiveness of the curing medium. The rate of evaporation is a key item in the monitoring of the quality of the curing. However, most approaches for this are largely empirical and are useful only under laboratory conditions. The effective curing thickness concept is introduced as a method to evaluate the effectiveness of a curing method. The surface relative humidity has the biggest influence on both the effective curing thickness and the rate of evaporation. Thus, prediction of the rate of evaporation of the water from concrete depends on the relative humidity of the surface and is important for evaluation of the curing method. Existing evaporation models, including the American Concrete Institute nomograph, were evaluated for their capabilities in predicting evaporation from curing concrete. Data from a series of laboratory experiments with a modified version of Penman’s evaporation model are also presented.

Cracking of concrete slabs at saw-cut notches under a given combination of weather and slab conditions is a major concern in the early stages of construction. Several factors affect crack initiation such as material strength parameters, the method and quality of curing, slab–subbase stiffness, and concrete shrinkage and creep. Early-age creep and shrinkage also appear to be key factors in stress and crack development at the tip of the saw-cut notch. These two factors were analyzed and characterized by experiments that provide some insight relative to how shrinkage and creep strain affect crack development. These results can be useful in evaluating the behavior of concrete and the development of cracking at saw-cut notches. The German cracking frame was used to provide restraint and the means to initiate cracking at an artificial notch during early-age strength development in the concrete while the concrete was undergoing creep and shrinkage strains. The cracking frame tests were conducted under constant temperature and relative humidity conditions in the laboratory. A fracture mechanics approach was followed to determine concrete strength at the saw-cut notch. It can be concluded that the development of creep strain in the concrete affects the cracking tendency of the concrete. The data seemed to suggest that a greater cracking tendency at the saw-cut notches did not result until after the incremental creep strain in the concrete had diminished sufficiently. The role of creep and shrinkage under field conditions relative to the control of cracking due to saw cutting in newly constructed concrete slabs is also considered indirectly.

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.

Different backcalculation algorithms produce different elastic moduli which are used as a key indicator of structural capacity of concrete pavements. Accordingly, the elastic moduli backcalculated by various backcalculation algorithms have been evaluated using the elastic moduli of cores of concrete pavement layers measured in the laboratory. However, variation in the backcalculated elastic modulus, even within a pavement section, is a significant issue in the concrete pavement evaluation. In the present work, deflections of jointed concrete pavement under a Falling Weight Deflectometer (FWD) loading were measured for 48 h at the KEC (Korea Expressway Corporation) test road. The curling effect on the backcalculated elastic modulus of the concrete slab was investigated using the different temperature gradients and slab curl conditions arising at different measurement times. The elastic moduli of the concrete pavement layers were backcalculated using the measured deflection basins, the AREA method and the method of equivalent thickness (MET). A basic concept to adjust the cyclic variation in the backcalculated elastic modulus due to the slab curling using the temperature difference between the top and bottom of the slab is presented. Measured data of deflection and load transfer efficiency (LTE) of the tested joints verify the curling effect on the backcalculated structural capacity of the concrete pavements.