DOI

10.5703/1288284314619

Report Number

FHWA/IN/JTRP-2011/05

Abstract

This project presents an evaluation of seal coat materials and design method. The primary objectives of this research are 1) to evaluate seal coat performance from various combinations of aggregates and emulsions in terms of aggregate loss; 2) to evaluate how the properties of aggregates and emulsions affect seal coat performance; 3) to evaluate current seal coat design methods based on INDOT seal coat practice; and 4) to develop seal coat design software incorporating Indiana practice.

To evaluate the effects of aggregate and emulsion types on aggregate loss performance of seal coat, three emulsions and eight aggregates including CRS-2P, RS-2P, and AE-90S for emulsions and Trap Rock, Sandstone, Blast Furnace Slag, Steel Slag, Limestone, Dolomite, Crushed Gravel (one face), and Crushed Gravel (two faces) were tested utilizing the sweep test and Vialit test. In addition, to explore influential factors (i.e., electrical surface charge interaction, water evaporation change in emulsion, water affinity of aggregate, etc.), the Zeta potential, water content, and X-ray deflection (XRD) tests were also conducted.

According to the Zeta potential test results, the electrical surface charge of an aggregate in emulsions varies with the type of emulsion (i.e., with the pH of the emulsifier). From the water content test, among the emulsions, CRS-2P was the earliest emulsion to have enough bond strength to retain aggregates in open traffic. In addition, aggregate can retard the water evaporation process of emulsions. Based on the XRD test results, Sandstone and Dolomite have the highest and smallest content of SiO2, respectively among the eight aggregates. This means that Sandstone and Limestone have the highest and lowest water affinity (hydrophilic and hydrophobic), respectively.

In the sweep test with Limestone with various curing time, CRS-2P showed superior aggregate loss performance among the emulsions. Comparing the sweep test results to the water contents of emulsions, faster water evaporation presented better aggregate loss performance. This finding indicates that the bond strength of emulsion to retain aggregate can be mainly a function of water evaporation in emulsion. Based on the sweep test at 77 ˚F after 24 hours of curing, CRS-2P performed the best regardless of aggregate type. The Vialit test at a temperature range of 35 °F to -22 F° after 24 hours of curing shows the most aggregate loss at lower testing temperatures. AE-90S had the strongest resistance in losing aggregate among the three emulsions at lower temperatures, which is an opposite trend comparing to the sweep test results. Also, Crushed Gravel with two faces outperformed Crushed Gravbel with one face.

According to statistical analysis results, it was concluded that AE-90S and Crushed Gravel with two faces showed the best performance among the emulsions and aggregates, respectively. In addition the best-performing aggregate-emulsion combinations were AE-90S with most of the aggregates, except for Steel Slag. Thus, the aggregate type in terms of mineral/chemical composition is not a major factor affecting the aggregate loss performance.

To develop a seal coat design, seal coat performance was evaluated for various emulsion (EAR) and aggregate application rates (AAR) by using three different evaluation methods: the IRI, friction, and visual inspection. Based on these performance tests, immediate failure occurring locally during construction due to incorrect application rate (e.g., insufficient aggregate rate) can cause total failure of the seal coat road resulting from a chain reaction. Employing a factor to compensate for AAR discrepancies between target and actual is critical for seal coat survival during construction. This study confirms the irrelevance of seal coat application to IRI values due to the thin coat and the limitation of the IRI measurement (e.g., 250 mm moving average). The friction test results show an adequate skid resistance performance on all seal coat test sections. In addition, friction improvements due to seal coat applications were confirmed within a range of seal coat rates applied in this study. Overall, IRI, friction, and visual inspection did not show distinct differences in seal coat performance in terms of application rates. A methodology in selecting an equipment factor for correcting any difference between a target rate and a measured rate was developed considering reliability and a designed rate using the McLeod equation.

Design software, “INDOT SEAL COAT DESIGN (iSeal)”, was developed as part of the study to aid the seal coat design process and incorporates INDOT seal coat practice. The software was largely based on the McLeod design method which includes factors that the INDOT seal coat specification lacks. Furthermore, an additional factor, an equipment factor, was implemented into the design process to resolve issues due to discrepancies between designed rate and applied rate.

Keywords

Surface Treatment, Seal Coat, Aggregate Loss, Low Temperature, Vialit Test, Sweep Test, Performance-based Design, Application Rate, Equipment Correction Factor, Influence Factor, SPR-3087

SPR Number

3087

Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version

2011