Andre de Fortier Smit

Model Mobile Load Simulator Testing at National Center for Asphalt Technology Test Track

One-third-scale model mobile load simulator (MMLS3) testing was conducted at the National Center for Asphalt Technology test track. Dry and wet-heated MMLS3 tests were done on five sections. The rutting performances of the sections under MMLS3 trafficking were compared with that under full-scale truck trafficking (truck test sections). A synthesis of the research included evaluation of results from laboratory tests done on cores taken from the MMLS3 test sections within and outside trafficked wheelpaths. Tests on the cores included wet and dry Hamburg wheel tracking, Superpave® shear tester frequency sweep, and semicircular bending (SCB) strength testing. Investigations included the evaluation of full-scale rutting data, laboratory wheel-tracking test results, and climatic data monitored on the track during full-scale truck trafficking. The project validated the rut prediction approach developed to compare MMLS3 and full-scale rutting performance and indicated that the MMLS3 may be used to estimate full-scale rutting at the track under specific conditions. Distress due to wet trafficking was also quantified as reduction in tensile strength as measured by the SCB. Conclusions were drawn and recommendations made for MMLS3 as well as continued full-scale testing at the track. Comparative full-scale rutting performance of the track sections evaluated may be quantified and ranked by the MMLS3 performance of these sections.

Mechanistic-Empirical IRI Model Accounting for Potential Bias

The roughness prediction models in the International Roughness Index (IRI) currently incorporated into the Mechanistic-Empirical Pavement Design Guide (M-E PDG) have been developed by means of ordinary least squares (OLS). However, some of the variables used in predicting future IRI were previously estimated by means of separate performance models. This could cause bias because of the correlation between the previously estimated distress types and unobserved components on the IRI model. The bias can be corrected by considering additional variables that are correlated with the distress types causing the bias, thus eliminating the correlation to the unobserved terms in the model. Bias in the IRI model can also be generated by unobserved factors not included in the model. If these factors are section-specific, the bias can be removed considering variations in the performance history of different pavement sections. The writers have used updated Long-Term Pavement Performance (LTPP) data consistent with the data set originally used to fit the M-E IRI model for flexible pavements over thick granular bases contained in the M-E PDG. The data were then used in modeling IRI by means of OLS and instrumental variable (IV) regressions analyzing the data as pooled and as a panel data set (by random-effects, fixed-effects, and joint random-effects approach) to check for possible bias in the model. It was found that the current IRI model, as estimated by OLS, exhibits several types of biases attributed to heterogeneity and incorrect assumptions in the modeling process. It was identified that the preferred IRI model was the joint random-effects approach and, therefore, the model parameters were estimated by correcting the omitted-variable bias and simultaneous-equation bias. Estimating the model by accounting for possible bias in the data indicated considerable changes in the effects of different parameters affecting IRI through time, mainly rutting of the pavement structure.

Incorporating Surface Microtexture in the Prediction of Skid Resistance of Flexible Pavements

Monitoring and managing the skid resistance of the highway network is necessary for controlling and reducing the number of road accidents. High-speed measurements of surface texture can be used as a surrogate parameter for controlling a pavements surface friction on the highway network. The two components of surface texture that affect skid resistance are the macrotexture and the microtexture. However, the technologies commonly used for measuring pavement texture at highway speeds account only for the macrotexture. This study explored ways to characterize the microtexture of pavement surfaces with the main objective of quantifying the effect of accounting for both components of the texture on the prediction of skid resistance, as measured by a British pendulum tester. Various methods for characterizing the microtexture were compared to determine which one better predicted surface friction. The study used field measurements of surface texture and friction performed on various in-service flexible pavements. The surface microtexture was characterized by a series of texture parameters calculated in both the spectral and the spatial domains. The impact of incorporating the microtexture on the prediction of the British pendulum number was evaluated through analysis of a series of models specified by each of the proposed parameters. The results of the analysis showed a drastic improvement in predicting the British pendulum value when the authors accounted for both components of the surface texture, as opposed to only the macrotexture. In a comparison of the analyzed methods for characterizing the microtexture, the use of spectral parameters led to the best prediction of the pavement surface friction. A series of recommendations is provided for the calculation of microtexture parameters.

A fully Bayesian before–after analysis of permeable friction course (PFC) pavement wet weather safety

Permeable friction course (PFC), a porous hot-mix asphalt, is typically applied to improve wet weather safety on high-speed roadways in Texas. In order to warrant expensive PFC construction, a statistical evaluation of its safety benefits is essential. Generally, the literature on the effectiveness of porous mixes in reducing wet-weather crashes is limited and often inconclusive. In this study, the safety effectiveness of PFC was evaluated using a fully Bayesian before-after safety analysis. First, two groups of road segments overlaid with PFC and non-PFC material were identified across Texas; the non-PFC or reference road segments selected were similar to their PFC counterparts in terms of site specific features. Second, a negative binomial data generating process was assumed to model the underlying distribution of crash counts of PFC and reference road segments to perform Bayesian inference on the safety effectiveness. A data-augmentation based computationally efficient algorithm was employed for a fully Bayesian estimation. The statistical analysis shows that PFC is not effective in reducing wet weather crashes. It should be noted that the findings of this study are in agreement with the existing literature, although these studies were not based on a fully Bayesian statistical analysis. Our study suggests that the safety effectiveness of PFC road surfaces, or any other safety infrastructure, largely relies on its interrelationship with the road user. The results suggest that the safety infrastructure must be properly used to reap the benefits of the substantial investments.

Evaluation of the Benefits of Diamond Grinding of a Continuously Reinforced Concrete Pavement

This paper discusses a study to evaluate the benefits on a continuously reinforced concrete pavement (CRCP) of diamond grinding used specifically for improving pavement functionality in surface macrotexture, skid resistance, roughness, and noise. The effectiveness of diamond grinding in improving those properties is calculated on the basis of in-field observations. The effect of three preexisting conditions (carpet drag, burlap drag, and transverse tining) on the effectiveness of diamond grinding is also evaluated. The results of the analysis indicate that diamond grinding improved the surface macrotexture by 0.6 mm and skid resistance by about 60%. The surface roughness of the diamond-ground sections was, on average, appreciably reduced, from 124 to 80 in./mi. An average overall reduction in noise level of 3.2 dB(A) was evident. A maximum reduction in the region of the noise frequencies (1,000 to 2,500 Hz) was observed, with a maximum noise reduction of 5.6 dB(A) at 1,600 Hz. The grinding operation produced a relatively uniform surface in relation to these properties despite the varying preexisting conditions across the CRCP.

Economic Analysis of Pavement Preservation Techniques

This paper summarizes the research study conducted to develop and implement a methodological framework, using an economic analysis technique, to evaluate the cost effectiveness of the three different preventive maintenance treatments applied to roadways in Texas: chip seals, microsurfacing, and thin overlays. The analysis is based on a stochastic evaluation of the effective life and cost of more than 14,000 maintenance and rehabilitation projects undertaken from 1994 to 2015. The effect of traffic loads, traffic volume, and roadway type was also evaluated. The life-cycle cost of the preventive maintenance techniques was obtained using a Monte Carlo simulation. Among the principal results, it was found that chip seals are the most cost-effective treatment and present the lowest life-cycle cost variability. The effective life of all three treatments was found to be quite similar. Additionally, it was found that the chip seals and microsurfacing tend to present comparable life-cycle costs when used on heavy traffic roadways.

Assessment of Using Inertial Profilers to Measure Ride Quality on Short Projects

The Texas Department of Transportation (DOT) ride standard specifies two devices for measuring ride quality on pavement projects: the 10-ft (3-m) straightedge and the inertial profiler. According to this specification, inertial profilers measure the ride quality on projects longer than 2,500 ft (762 m). The 10-ft straightedge must be used to survey roughness for projects of less than 2,500 ft. A study was conducted to identify the potential issues associated with the use of inertial profilers and the international roughness index (IRI) algorithm on short projects. A literature review was performed to collect required information about the inertial profiler operation and the IRI algorithm. A field experiment was conducted with an inertial profiler certified by the Texas DOT. The collected data were analyzed to investigate the effect of profiling speed and segment length. The results indicate that inertial profilers can be used to collect profile data on short segments of less than 2,500 ft, but the IRI algorithm should be used on projects longer than 528 ft (161 m), below which the variation between IRI results increases significantly.

Pay Factors Based on Observed Field-Performance Data

AbstractThe fundamental purpose of any construction specification is to ensure the expected long-term performance of the final product. A construction project that fails to meet the required quality level should always result in reduced payment to the contractor in order to recover the future costs that the highway agency will incur for additional maintenance. However, a superior-quality project must be rewarded based on actual savings to the agency that correspond with the improvement in performance due to higher construction quality. Performance-related specification (PRS) incorporates the economic implications associated with superior or inferior pavement construction practices. In general, earlier PRS development studies were based on performance data collected from either pilot pavement construction projects or models built based on experimental pavement sections. This study primarily focuses on constructing a pay adjustment framework utilizing field performance data and actual quality control measur...

Texas IRI Summary (2000 – 2005)

This paper reports the results of statistical analysis done in order to evaluate International Roughness Index (IRI) on Texas roads from 2000 to 2005. Analyses were done on Asphalt Concrete Pavement (ACP), Continuously Reinforced Concrete Pavement (CRCP) and Jointed Concrete Pavement (JCP) roads. IRI results from Interstate Highways (IH), United States (US) Highways, State Highways and Farm to Market (FM) roads with and without surface treatments are reported separately. For FM roads, differences in IRI as measured in the left and right wheelpaths are also reported. Reductions in IRI resulting from overlaying CRCP and JCP concrete pavements are summarized. Statistical analyses indicate that the mean IRI data as measured in the left and right wheelpaths of roads using automated inertial profilers are log-normally distributed. The riding quality of roads in Texas has improved over the last five years partly because of the introduction of new ride quality specifications. IRI as measured in the right wheelpath is consistently higher than that measured in the left - in particular for FM roads with surface treatments suggesting non-traffic related influences on these roads. ACP generally have the lowest IRI values (highest ride quality) followed by CRCP and then JCP. Results of the analyses are used to recommend research strategies to improve the ride quality of Texas roadways. Findings suggest that significant improvements in the overall ride quality of the Texas roadway network can be achieved by focusing efforts on FM roads with surface treatments and overlaying JCP.

TRIAXIAL TESTING OF ELASTOPLASTIC MATERIALS TOWARD SCALED-DOWN ACCELERATED PAVEMENT TESTING

Small-scale testing of pavement materials provides an alternative means for preliminary indicator or ranking tests before, or in place of, expensive full-scale Accelerated Pavement Testing. To carry out scaled tests effectively, dimensional analysis considerations must be met. This implies that the laws of similitude require observation. In particular, scaled-down pavement layers must be subjected to the same stresses and strains as the full-scale pavement under equivalent loading. In addition, the material properties of the scaled-down layer must be equivalent to the full-scale materials. Research was carried out into the scaling down of different materials, including untreated and emulsion-modified granular materials. Various tests, including static and dynamic triaxial tests, were performed on the materials at full scale and at small scale (1: 10). The test results are discussed with a comparison between the full-scale and scaled-down material properties. Conclusions were drawn concerning the appropriateness of scaling down elastoplastic materials, the requirements of the laws of similitude, the main factors that require consideration for scaling, the need for additional research, and the direction that this research should pursue.