Determination of Lime in Hot-Mix Asphalt

Abstract

Lime is added to hot-mix asphalt to mitigate stripping and other modes of moisture damage. No standard forensic test exists for the measurement of the lime content after it has been incorporated in the asphalt. This paper evaluates several methods to quantify the amount of hydrated lime (calcium hydroxide) in asphalt. A rapid analytical technique, Fourier transform infrared spectroscopy, was identified for determining the quality and quantity of lime. It yields qualitative or semiquantitative results from samples as small as 10 mg. No sample preparation is involved, and the binder can be scraped directly from large stones in the hot mix. The analysis can be completed in 30 s and offers the possibility of timely adjustment to the mix. For more accurate quantitative measurement, a second procedure is recommended. Samples are taken from cores with a hammer drill. The lime is separated from the resulting dust by acid extraction, and the calcium level is determined by atomic absorption spectroscopy or ion exchange chromatography. Different methods for removing the binder are discussed.