InstroTek Solution
CoreLok® found by every study to be the most precise method for measurement of open graded asphalt mixes.
Specific gravity (density) is the single most specified parameter in the construction industry. Asphalt samples are routinely tested by the water displacement method for determination of sample bulk specific gravity (density). The volume of water displaced by the sample and the weight can be used to calculate the density of the sample. The Saturated Surface Dry (SSD) technique, ASTM D2726 and AASHTO T166, is used for testing the asphalt sample bulk density. This method works well for dense graded mixes with minimal to no surface texture (voids). However, there are four major problems when using the water displacement method on samples with rough surfaces and open graded mixes.
1. Samples compacted in the laboratory have voids that can be divided into two categories. The first category of voids is the "artificial surface voids" produced by the existing compaction devices used in the laboratory (i.e. Gyratory Compactor, Marshall Hammer, etc.). The second category of voids is the "legitimate voids" which are inherent in the particular mix design and are critical in the durability of asphalt mixture. Volume determined by the SSD method does not account for the "artificial surface voids" and the "legitimate voids". Samples tested by the SSD method will indicate lower than actual volume, higher than actual density and lower air voids calculation.
2. Samples with more than 7% air voids can have a significant amount of interconnecting voids which allows water to simply drain through during water displacement. This effect results in lower volume determination and higher than actual density measurements.
3. Field samples are generally different in surface texture and void content than the laboratory prepared samples. The SSD method can produce different specific gravity results for these two sample types for a given mix.
4. Due to varying degree of water infiltration and drainage, operator experience and technique becomes critical in achieving repeatable and accurate density results.
For accurate density measurements, it is imperative that samples be sealed to account for these effects.
Corelok® was developed by the scientist and engineers at InstroTek to address the critical industry problem of measuring open graded and absorptive samples. To achieve the most accurate density results, the polymer bags were developed based on extensive research on the sealing material composition, bag dimensions and the degree of polymer penetration into the surface voids. To achieve the "true" sample density the "artificial surface voids" and the "legitimate voids" have to be accounted for during the sealing process. The Corelok® settings are calibrated at the factory to allow for the optimum polymer penetration into the voids and the most accurate density results. The CoreLok® results are accurate and do not depend on material type or mix specific calibrations.