Julie M. Vandenbossche

Performance, Analysis, and Repair of Ultrathin and Thin Whitetopping at Minnesota Road Research Facility

Thin and ultrathin whitetopping overlays are becoming a more common method of pavement rehabilitation. It is important to gain information on the types of distresses that occur in the overlays and effective repair techniques. In 1997 the Minnesota Department of Transportation constructed several thin and ultrathin whitetopping test cells at the Minnesota Road Research (Mn/ROAD) facility. Typical distresses included corner breaks, transverse cracks, and reflective cracks. The finite element program ISLAB2000 was used to investigate stress patterns and their relation to the distresses. Different techniques for repairing ultrathin whitetopping were investigated. Various techniques were also used to deter reflective cracking, including various bond-breaking materials and full-depth sawing at strategic locations along the longitudinal joint to prevent cracks from propagating into adjacent panels at misaligned transverse joints. Four of the six sections had present serviceability indexes (PSIs) greater than 3.5 before the repairs, showing that a good level of performance has been maintained after 4.7 million equivalent single-axle loads. The two sections that exhibited the largest drop in PSI were the overlays with 1.2- × 1.2-m (4- × 4-ft) panels. The repairs made in sections containing these panels have brought the PSI back up to an acceptable level (PSI > 3). The thin and ultrathin whitetopping test sections at Mn/ROAD have shown that whitetopping is a viable rehabilitation alternative for asphalt pavements. The importance of choosing an optimum panel size was exhibited. It has also been shown that when necessary, it is easy to repair ultrathin whitetopping sections. Various techniques for repairing each type of distress have been summarized.

Performance of Rigid Pavements Containing Recycled Concrete Aggregates

State highway agencies in Connecticut, Kansas, Minnesota, Wisconsin, and Wyoming have successfully designed and constructed rigid pavements containing recycled concrete aggregate (RCA). Success has been attributed in part to the minimization of old mortar content in the RCA during recycling processes, thereby controlling the total mortar content of the new portland cement concrete (PCC) mixture, or to the achievement of higher-than-expected compressive strengths through adjustments in mix proportions, or both. There was no clear correlation between mortar content and cracking distresses in field investigations, although one project did exhibit significantly more slab cracking in the recycled pavement than in the corresponding control pavement. The increased cracking may have been due to the large differences in total mortar content between the recycled and control sections. In general, the recycled PCC pavements considered in this study have performed comparably with their conventional PCC pavement counterparts, including the recycled pavements that incorporated RCA derived from concrete affected by D-cracking and alkali-silica reactivity (ASR). There is, however, evidence of small amounts of localized recurrent ASR in the recycled Wyoming pavement. Whether this reactivity will eventually develop into widespread distress remains to be seen.

Comparison of measured vs. predicted performance of jointed plain concrete pavements using the Mechanistic–Empirical Pavement Design Guideline

This research evaluates the ability of the Mechanistic–Empirical Pavement Design Guide (MEPDG) to accurately predict the performance of jointed plain concrete pavements (JPCPs). This is accomplished by comparing predicted performances with observed performances for the in-service mainline test cells at Mn/ROAD. These comparisons indicate that MEPDG performance predictions for JPCP are most accurate when the default (constant) built-in equivalent temperature difference of − 5.5°C is used instead of a site-dependent value. It appears that significant portions of the error of estimation can be explained by the sensitivity of the performance models to variability in hardened concrete properties (modulus of rupture, modulus of elasticity and coefficient of thermal expansion) and pavement structural features (slab thickness, joint spacing, subbase type and bond condition). Predictions of slab cracking were found to be highly sensitive to these parameters. In addition, the MEPDG cracking model seemed not to fit local cracking observations for the Minnesota test cells. New calibration factors are needed to more accurately predict Minnesota JPCP slab cracking. This study also included comparisons of predicted service lives for the Mn/ROAD test cells using different design methodologies and as-built input parameters. In most cases considered, the MEPDG predicted longer service lives than did the 1993 AASHTO procedure. The MEDPG also predicted longer service lives than the PCA procedure for the 5-year cells but shorter service lives for the 10-year cells. This infers that, when holding service life constant, the MEPDG generally results in thinner concrete pavement sections than the 1993 AASHTO procedure.

Quantifying built-in construction gradients and early-age slab deformation caused by environmental loads in a jointed plain concrete pavement

Construction curling and warping produces a built-in gradient, which takes place as the result of changes in temperature and moisture that occur prior to the hardening of Portland cement concrete (PCC) pavements. The slab remains flat in the presence of this gradient because the plastic concrete has not developed sufficient stiffness to generate stress or strain. The new Guide for the Design of New and Rehabilitated Pavement Structures has shown the importance of quantifying the built-in gradient. In this study, the magnitude of the built-in gradient was quantified along with the early-age response of the slab to environmental loads. It was found that the equivalent linear temperature gradient at the time of set was < 0.09°C/cm (0.55°F/in.). The largest built-in curvature measured along the diagonal for the restrained and unrestrained slabs was 0.0000124 1/m (0.0000408 1/ft) and 0.0000138 1/m (0.0000454 1/ft), respectively. The increase in curvature with an increase in equivalent linear temperature gradient for the unrestrained slabs was 7% higher than the restrained slabs. The profiles also indicated that the slab edges are, at times, completely unsupported.

Effects of Temperature and Moisture Gradients on Slab Deformation for Jointed Plain Concrete Pavements

Slab curvature, which represents the response of concrete pavement slabs to environmental loads, influences the location and magnitude of critical slab stresses and affects long-term pavement performance. The purpose of this study was to measure the changes in temperature and moisture profiles in a newly constructed concrete pavement and to determine both the overall deformed shapes of the slabs as well as the relative contributions of built-in and transient environmental effects over time. Data were collected from an instrumented jointed plain concrete pavement (JPCP) over a 2-year period. Slab curvatures were computed or predicted using measurements of temperature and moisture conditions in the slab, static strain measurements, and pavement surface profile measurements. It was found that the additional restraint provided by the dowel and tie bars does not appear to significantly reduce slab curvature resulting from daily temperature fluctuations or from reversible drying shrinkage. It does have a substa...

A Solitary Wave-Based Sensor to Monitor the Setting of Fresh Concrete

We present a proof-of-principle study about the use of a sensor for the nondestructive monitoring of strength development in hydrating concrete. The nondestructive evaluation technique is based on the propagation of highly nonlinear solitary waves (HNSWs), which are non-dispersive mechanical waves that can form and travel in highly nonlinear systems, such as one-dimensional particle chains. A built-in transducer is adopted to excite and detect the HNSWs. The waves are partially reflected at the transducer/concrete interface and partially transmitted into the concrete. The time-of-flight and the amplitude of the waves reflected at the interface are measured and analyzed with respect to the hydration time, and correlated to the initial and final set times established by the penetration test (ASTM C 403). The results show that certain features of the HNSWs change as the concrete curing progresses indicating that it has the potential of being an efficient, cost-effective tool for monitoring strengths/stiffness development.

Bonded Whitetopping Overlay Design Considerations for Prevention of Reflection Cracking, Joint Sealing, and the Use of Dowel Bars

Hundreds of bonded portland cement concrete (PCC) overlays of hot-mix asphalt (HMA) pavements are being constructed in the United States and around the world. Increasing interest in this rehabilitation method has led to a need to define further the most common forms of distresses, quantify the extent of influence of design parameters on performance, and develop rational design guidelines. This study evaluates the performance of in-service pavements to establish criteria for when reflection cracks might develop. Reflection cracking is dictated by the thickness of the PCC overlay and HMA layer, panel size, climatic conditions, and accumulated vehicle loads. When the relative stiffness of the PCC overlay and HMA layer (defined during the coldest month of the year) falls below the critical value one, reflection cracking develops. The rate of development is a function of the load-related stress in the overlay. The performance analysis of the in-service pavements also verify the benefits of joint sealing and the use of small diameter dowel bars for high volume roadway applications.

Redefining the Failure Mode for Thin and Ultrathin Whitetopping with 1.8- × 1.8-m Joint Spacing

Bonded whitetopping is a thin concrete overlay on a distressed asphalt pavement. The existing design procedures for bonded whitetopping assume the failure mode is a function of the overlay thickness. It has been traditionally assumed that the failure mode for thin whitetopping [overlay thickness greater than 102 mm (4 in.) but less than 152 mm (6 in.)] is transverse cracking, and the failure mode for ultrathin white-topping [overlay thickness between 51 mm (2 in.) and 102 mm (4 in.)] is corner cracking. However, the performance of in-service whitetopping overlays indicates that the actual failure mode is dictated more by slab size than by overlay thickness. For both thin and ultrathin whitetopping with 1.8-m (6-ft) joint spacing, cracks initiate at the bottom of the overlay at the intersection of the transverse joint and the wheelpath and propagate longitudinally. At times, these cracks will continue to propagate in the longitudinal direction and intersect the adjacent transverse joint; at other times, they will turn on a diagonal and propagate toward the lane–shoulder joint. To verify this failure mechanism observed in the field further, a three-dimensional finite element model subjected to environmental and wheel loads was developed. The results support the proposed failure mode, showing that the critical tensile stress is indeed in the wheelpath and at the bottom of the portland cement concrete overlay. This type of failure results in a longitudinal crack.

PERFORMANCE ANALYSIS OF ULTRATHIN WHITETOPPING INTERSECTIONS ON US-169: ELK RIVER, MINNESOTA

The Minnesota Department of Transportation constructed an ultrathin whitetopping (UTW) project at three consecutive intersections on US-169 at Elk River, Minnesota, to gain more experience with both the design and the performance of UTW. Distinct cracking patterns developed within each test section. The UTW test sections with a 1.2- ×1.2-m (4- ×4-ft) joint pattern included corner breaks and transverse cracks. Corner breaks were the primary distress in the test section with a 1.8- ×1.8-m (6- ×6-ft) joint pattern, although very little cracking was exhibited. The Minnesota Road Research Facility UTW test sections on I-94 allow comparisons of the same UTW design on hot-mix asphalt (HMA) pavements with different structural capacities to be made. The strain and deflection measurements emphasize the importance of the support provided by the HMA layer. A reduction in this support occurs when the temperature of the HMA is increased or when the HMA begins to ravel. During evaluations of whether UTW is a viable rehabilitation alternative, cores should be pulled from the pavement to determine if the asphalt is stripping and if the asphalt layer has adequate thickness. UTW can be successfully placed on as little as 76 mm (3 in.) of asphalt, if the quality of the asphalt is good. The cores should also reveal whether the asphalt layer is of uniform thickness and whether stripping and raveling have occurred. If the asphalt layer is of uniform thickness and stripping and raveling have not occurred, UTW is a good option for use in the rehabilitation of asphalt pavements.

Evaluating the continuously reinforced concrete pavement performance models of the mechanistic-empirical pavement design guide

The reasonableness of the models in the Mechanistic-empirical Pavement Design Guide (MEPDG) used to predict the performance of the continuously reinforced concrete pavements (CRCPs) was evaluated in this study. The MEPDG punchout, crack width and spacing and load transfer efficiency (LTE) models were evaluated through a factorial sensitivity study. The input matrix was defined to reflect ‘real-world’ design situations. It was found that, contrary to the 1993 American Association of State Highways and Transportation Officials (AASHTO) Design Guide, crack width must be below 0.5 mm to maintain adequate performance. Additionally, based on the performance predictions from the MEPDG, a crack spacing of less than 1.8 m ensures a crack width of less than 0.5 mm, which is another contradiction with the approach in the 1993 Guide.