Correlation of Moisture Loss and Strength Gain in Chip Seals

Abstract

One of the most subjective decisions made during chip seal construction concerns when to allow brooms and traffic on the newly placed surface. If traffic is allowed too early, damage to the surface and to vehicles may occur. If the chip seal is opened too late, traffic is disrupted and motorists are inconvenienced. The curing of asphalt emulsions in the field is related to many factors, all affecting how fast the asphalt emulsion cures. Three laboratory test methods that measure adhesive strength gain as a function of moisture loss are presented. Two of the methods were sweep tests, one performed according to ASTM D7000 and the other according to a modified method. The third test used frosted marbles to measure adhesive strength gain. Results of all tests were similar and indicated that strength in emulsion residues increased as the total moisture in the system was reduced. This finding is important because the moisture content is independent of the mechanism reducing it. Therefore, prediction of strength gain should be possible by measurement of the moisture loss of a given chip seal system. The time required to obtain that strength gain varies in seals because of differences in emulsion, aggregate, interaction factors, weather, ambient temperature, and other environmental factors. Test results indicated that as moisture loss approached 75% to 90%, strength gain was significantly enhanced.

Investigating the Laboratory Performance of Crumb-Rubber-Modified and High-Float Polymer-Modified Asphalt Emulsions in Chip Sealing

“…Yet, it is recognized that several researchers have questioned whether the sweep test can be reliably used as an indicator of chip seal performance ( 19 , 30 ). Nevertheless, based on the reviewed literature, the sweep test is still considered as one of the most popular test methods to investigate the aggregate loss performance of chip seals, given its low cost and the ease of the test procedure ( 17 , 18 , 31 ). In the current study, the sweep test was performed according to ASTM D7000 by replicating the sweeping action of a broom exerting force on the aggregate in the laboratory using a nylon brush.…”

Quantifying Asphalt Emulsion-Based Chip Seal Curing Times Using Electrical Resistance Measurements

“…The chemical reactions between the aggregate As the water evaporates, the asphalt particles move closer together and begin to flocculate (James, 2006). At this early stage of the curing process, a considerable amount of water may have evaporated, but no appreciable mechanical strength has yet developed (Howard, Shuler, Jordan, Hemsley, & McGlumphy, 2011).…”

“…Shuler and others Shuler, 2011) have reported a strong relationship between the moisture content and binder strength in a chip seal system. Howard et al (2011) measured chip seal binder adhesive strength gain as a function of moisture loss using three laboratory test methods: the sweep test (ASTM D7000, 2011), modified sweep test, and frosted marble test. Although all three tests are different, the results were similar and indicated that the strength in emulsion residue increases as the total moisture in the system is reduced, as shown in Figure 2.6.…”

“…The trends in the NRI as a function of MCR data are in agreement with strength gain as a function of moisture loss patterns found in the literature. Howard et al (2011) correlated the binder strength gain and moisture loss by conducting frosted marble tests (FMTs). FMTs are used in an attempt to quantify binder adhesive behavior and identify when chip seals are ready to accept uncontrolled traffic and brooming operations.…”

“…The FMT is conducted using a tray that consists of 15 glass etched marbles that are torqued after curing in a 135 uF environmental chamber. Howard et al (2011) reported that during the early stage of the curing process, high levels of initial moisture loss can be measured, but appreciable mechanical properties do not develop. As the material approaches the critical moisture content range, relatively moderate strength improvement is attained.…”