Emulsions are used as tack coats to bond asphalt concrete layers and as a bonding agent for aggregates in chip seals. The rate of emulsion application is critical to the performance of both tack coats and chip seals. It has been demonstrated that field EARs can be highly variable, which is not captured using current measures for quality control (QC). Comprehensive QC of emulsion application should include provisions for assessment of (1) transverse variability in EARs, (2) the quantity of emulsion absorbed by the paving surface to enable proper adjustment of the target EAR during construction, and (3) longitudinal variability in EARs along the length of paving.
The Tack Lifter was developed as a simple and efficient means for in-situ measurements of applied EARs and "effective" EARs, neglecting emulsion absorbed by the paving surface to improve QC measures. The Tack Lifter consists of a weight device, frame, and absorbent sheet. Following emulsion application by a distributor, the frame is applied to the surface of interest to seal the test area. The absorbent sheet is inserted into the frame and the weighted device is applied. Emulsion is absorbed into the sheet. The weight of emulsion combined with the sheet area is used to obtain a spot check of EAR. Tests can be applied directly to the paving surface provide a measure of effective EAR. Alternatively, tests can be applied to pans placed on the paving surface prior to emulsion application to provide a measure of the applied EAR. The difference between applied and effective EARs measured by the Tack Lifter allows for quantifying the rate by which a pavement absorbs applied emulsion. For maximum efficiency in measuring applied EARs in the field, elevated plates and a peel were developed. Elevated plates are placed on the roadway's lane center prior to arrival of the distributor. After emulsion application, elevated plates can be easily and efficiently removed from the roadway for Tack Lifter testing to minimize delays in construction operations. A comprehensive laboratory and field experimental program has been employed to develop and evaluate the Tack Lifter, which enabled development of a proposed practice for comprehensive QC of EARs.
Based on laboratory and field experiments, a proposed practice for QC of EARs has been developed. The practice includes three procedures: (1) ASTM D 2995 Test Method B for quality control of transverse variability in EARs each day prior to construction. (2) Tack Lifter tests applied in the wheel path to flat, steel pans and the paving surface on a test pavement section prior to construction and where significant changes in surface conditions are noted to allow for quantifying the rate by which the pavement absorbs emulsion and guide adjustment of the target EAR, (3) Tack Lifter tests conducted on elevated plates following removal from the roadway every 0.5 miles along the length of paving or where changes in grade or curvature are noted for assessment of longitudinal variability in applied EARs.
