John T Harvey

The Use of Reflective and Permeable Pavements as a Potential Practice for Heat Island Mitigation and Stormwater Management

To help address the built environmental issues of both heat island and stormwater runoff, strategies that make pavements cooler and permeable have been investigated through measurements and modeling of a set of pavement test sections. The investigation included the hydraulic and thermal performance of the pavements. The permeability results showed that permeable interlocking concrete pavers have the highest permeability (or infiltration rate, ~0.5 cm s -1 ). The two permeable asphalt pavements showed the lowest permeability, but still had an infiltration rate of ~0.1 cm s -1 , which is adequate to drain rainwater without generating surface runoff during most typical rain events in central California. An increase in albedo can significantly reduce the daytime high surface temperature in summer. Permeable pavements under wet conditions could give lower surface temperatures than impermeable pavements. The cooling effect highly depends on the availability of moisture near the surface layer and the evaporation rate. The peak cooling effect of watering for the test sections was approximately 15–35?°C on the pavement surface temperature in the early afternoon during summer in central California. The evaporative cooling effect on the pavement surface temperature at 4:00 pm on the third day (25 h after watering) was still 2–7?°C lower compared to that on the second day, without considering the higher air temperature on the third day. A separate and related simulation study performed by the University of California Pavement Research Center (UCPRC) showed that full depth permeable pavements, if designed properly, can carry both light-duty traffic and certain heavy-duty vehicles while retaining the runoff volume captured from an average California storm event. These preliminarily results indicated the technical feasibility of combined reflective and permeable pavements for addressing the built environment issues related to both heat island mitigation and stormwater runoff management.

Permeability measurement and scan imaging to assess clogging of pervious concrete pavements in parking lots.

This paper describes a study that used permeability measurement along with physical and hydrological characteristics of 20 pervious concrete pavements in parking lots throughout California. The permeability was measured at five locations: the main entrance, an area with no traffic, and three separate measurements within a parking space at each parking lot. Hydrological and physical site characteristics such as traffic flow, erosion, vegetation cover, sediments accumulation, maintenance practice, presence of cracking, rainfall, and temperature data were also collected for each parking lot. These data were used to perform detailed statistical analysis to determine factors influencing changes in permeability and hence assessing possible cause of clogging. In addition, seven representative core samples were obtained from four different parking lots with permeability ranging from very low to very high. Porosity profiles produced from CT scanning were used to assess the possible nature and extent of clogging. Results showed that there is a large variation in permeability within each parking lot and between different parking lots. In general, the age of the parking lot is the predominant factor influencing the permeability. Statistical analysis revealed that fine sediment (particles less than 38 μm) mass is also an important influencing factor. Other influencing factors with lower significance included number of days with a temperature greater than 30°C and the amount of vegetation next to the parking lot. The combined scanned image analysis and porosity profile of the cores showed that most clogging occurs near the surface of the pavement. While lower porosity generally appeared to be limited to the upper 25 mm, in some core samples evidence of lower porosity was found up to 100mm below the surface.

Effects of Asphalt Content and Air Void Content on Mix Fatigue and Stiffness

The primary objective of most procedures for asphalt concrete mix design is to find an asphalt content that minimizes the possibility of stability failure while providing adequate fatigue and other durability characteristics. To date, the consequences of asphalt content selection and construction compaction on fatigue performance and flexural stiffness have not been thoroughly investigated and documented with experimental data. The results of laboratory-controlled strain flexural beam testing, (i.e., fatigue life and flexural stiffness) for one aggregate and asphalt cement combination, five asphalt contents, and three air void contents are presented. The results clearly indicate the benefits of a lower air void content on both fatigue life and initial stiffness. Increased asphalt content was found to increase fatigue life and reduce stiffness. Alternative models for predicting fatigue life and initial stiffness using asphalt content, air void content, voids filled with bitumen, and the volume concentrations of asphalt and aggregate were evaluated. Elastic-layer theory was used to simulate the effects of air void content and asphalt content on the fatigue life of several example overlays using the models for stiffness and fatigue life from the laboratory testing. The simulations indicated an increase in predicted pavement fatigue life for lower air void contents and higher asphalt contents. Example simulations of the effects of increased asphalt content and decreased air void content at the bottom of thick overlays indicated a marked increase in predicted fatigue life. It was also concluded that stiffness should not be included in regression for fatigue life models for mix design unless there is a clear understanding of the effects of other variables in the model that correlate with both fatigue life and stiffness.

Selection of Laboratory Test Specimen Dimension for Permanent Deformation of Asphalt Concrete Pavements

Permanent deformation of asphalt concrete pavements is a critical distress mechanism. Efforts are currently being made to understand, analyze, and predict permanent deformation response. To characterize asphalt concrete, laboratory testing is routinely performed. The concept of the representative volume element for determining the minimum specimen dimensions to obtain reliable and repeatable laboratory test data is discussed here. Two conceptual laboratory tests that are currently used to characterize asphalt concrete—the restricted triaxial test and the simple shear test at constant height—are also discussed. The imperfections of both tests are investigated and recommendations for specimen size and the aspect ratio for each of the tests are made.

Comparative field permeability measurement of permeable pavements using ASTM C1701 and NCAT permeameter methods

Fully permeable pavement is gradually gaining support as an alternative best management practice (BMP) for stormwater runoff management. As the use of these pavements increases, a definitive test method is needed to measure hydraulic performance and to evaluate clogging, both for performance studies and for assessment of permeability for construction quality assurance and maintenance needs assessment. Two of the most commonly used permeability measurement tests for porous asphalt and pervious concrete are the National Center for Asphalt Technology (NCAT) permeameter and ASTM C1701, respectively. This study was undertaken to compare measured values for both methods in the field on a variety of permeable pavements used in current practice. The field measurements were performed using six experimental section designs with different permeable pavement surface types including pervious concrete, porous asphalt and permeable interlocking concrete pavers. Multiple measurements were performed at five locations on each pavement test section. The results showed that: (i) silicone gel is a superior sealing material to prevent water leakage compared with conventional plumbing putty; (ii) both methods (NCAT and ASTM) can effectively be used to measure the permeability of all pavement types and the surface material type will not impact the measurement precision; (iii) the permeability values measured with the ASTM method were 50-90% (75% on average) lower than those measured with the NCAT method; (iv) the larger permeameter cylinder diameter used in the ASTM method improved the reliability and reduced the variability of the measured permeability.

Characterization of Truck Traffic in California for Mechanistic-Empirical Design

Truck traffic information is one of the key inputs in the design and analysis of pavement structures. Until relatively recently, truck traffic data typically were aggregated into equivalent repetitions of a standard axle load for pavement design. The mechanistic pavement design procedures being developed for the California Department of Transportation by the University of California Pavement Research Center will make use of axle-load spectra and other more detailed truck traffic information when incremental design and incremental–recursive design approaches are used. It is necessary to develop traffic inputs in different regions in the state to support the new pavement design procedures. With the weigh-in-motion data collected in California, the truck traffic characteristics were studied for developing default traffic inputs. Traffic composition, temporal and spatial distribution of truck volume, traffic growth rate, vehicle speed, and axle-load spectra were analyzed by intensive and unbiased sampling. Cluster analysis was applied to multivariate responses (e.g., axle-load spectrum) to extract the structure of highway sections in terms of traffic characteristics, which ensured the preservation of useful information during analysis.

Calcool: A multi-layer Asphalt Pavement Cooling Tool for Temperature Prediction During Construction

The temperature at which compaction takes place is an important factor in the construction of asphalt concrete pavements. In cold climates, rapidly cooling mats can contribute to poor compaction. Under warm paving and high traffic demand conditions, time of construction is a greater concern, and the compaction schedule should minimize the required time for construction. This research created a computer tool (CalCool), based on theoretical heat transfer considerations, for use by pavement designers and on-site construction crews to predict the pavement temperature during construction and modify designs or compaction procedures accordingly. A model validation study compared CalCool to several construction scenarios. The comparisons were favorable in the single-layer cases, but increased discrepancies were observed Fin the multi-layer cases. Future validation studies are needed to expand the data set beyond the two sites examined in this paper.

Analytically Based Approach to Rutting Prediction

An analytically based (mechanistic-empirical) procedure was conducted to estimate the development of rutting in asphalt pavements as a function of both traffic loading and environment as defined by pavement temperatures. The procedure uses permanent strain determined for a representative asphalt concrete mix as a function of load repetitions, shear stress, and elastic shear strain. It combines multilayer elastic analysis for determining key shear stresses and strains in the asphalt concrete resulting from traffic loading to be used in the permanent strain expression with a time-hardening procedure for the accumulation of permanent strain as a function of both traffic loading and environment. The WesTrack test sections were used to calibrate the methodology, with results of rutting predictions evaluated for four different test sections from that experiment. Based on the results of the regression analyses, an expression can be used to determine coefficients for use in the permanent strain expression that reflect the permanent deformation characteristics of a specific mix as measured in repeated simple shear test at constant height. In addition to the WesTrack examples, results illustrated the use of the approach to predict rutting development in a controlled loading condition at 50°C (122°F) using the heavy vehicle simulator.

Investigation of the Curing Mechanism of Foamed Asphalt Mixes Based on Micromechanics Principles

This study investigated the curing mechanism of foamed asphalt mixes, based on which proposed standard curing procedures that are appropriate for use in project level mix design. Mixes with various asphalt and portland cement contents were subjected to two relatively extreme curing conditions, and multiple types of laboratory tests were performed. It was found that portland cement enhances certain properties of foamed asphalt mixes by strengthening the mineral filler phase, with the curing mechanism similar to that of normal cement treated materials. The curing mechanism of foamed asphalt mastic is primarily related to water evaporation. The bonding between asphalt mastic and aggregate particles cannot fully develop until most of the water retained at the interface evaporates. This bonding, once formed, is only partially damaged by reintroduced water. This mechanism was supported by direct fracture face observations on tested specimens. Two curing methods are proposed as standard procedures for project level mix design. The proposed strategy tests materials under two extreme conditions instead of attempting to precisely replicate field conditions, allowing the engineer to judge whether the tested materials suit the actual range of conditions at a specific project site. Portland cement or other appropriate active filler is recommended to be used in conjunction with foamed asphalt, which has a slow curing rate under most field conditions, to obtain early strength and allow early opening to traffic.

Temperature Sensitivity of Foamed Asphalt Mix Stiffness: Field and Lab Study

Knowledge of the temperature sensitivity of foamed asphalt stiffness is very important in mix and structural design, field non-destructive testing and advanced research. However, this subject has not been studied extensively, especially the effects of the stress state on the temperature sensitivity, which is essential to understand the behavior of weakly bonded granular materials. This paper first presents triaxial resilient modulus testing results of foamed asphalt treated materials with various asphalt contents at various temperatures. General observations are made in terms of the effects of the bulk stress, deviator stress, temperature and their interactions. Based on these observations, the temperature sensitivity coefficient of foamed asphalt stiffness is defined and a simplified model to predict foamed asphalt mix stiffness at any triaxial stress state and temperature is proposed and validated. A procedure to normalize back-calculated resilient modulus to a standard temperature is also presented. The essential step of this procedure is to estimate the temperature sensitivity coefficient based on the field test results at various temperatures. Finally, an example is presented comparing the stiffness of a foamed asphalt material over two years. It was found that the stiffness did not change significantly over the two years period, despite the accumulation of traffic loading.