Development of Performance-Based Tests for Nontraditional Road Additives

Nontraditional road additives (chemical stabilizers and dust palliatives) are applied to unsealed roads to reduce dust levels and gravel loss and improve riding quality and all-weather passability. However, the level of research conducted on additives and documentation derived from it are often unsatisfactory. A review of studies revealed that similar procedures were followed, which entailed routine laboratory tests on a locally available material, followed by a field test during which the period of effectiveness was assessed. No documented test methods exist specifically for these additives. Researchers tend to adapt methods developed for cementitious and asphaltic additives or compare before- and after-treatment results on standard indicator tests. Results rarely correlate with field performance, necessitating construction of full-scale experiments before making a decision on applying the additives on a wider scale. Invariably, a new experiment must be constructed each time conditions such as material, traffic, and climate change. A series of performance-based laboratory tests for nontraditional road additives has been developed, and results have been compared with performance in full-scale experiments. Results are compared with untreated controls or traditional stabilizers. The tests have been incorporated into a research protocol as well as a fit-for-purpose certification system for road additives. They are sensitive enough to assess performance at different application rates and to compare the performance of different additives on the same material. Tentative limits for decision making have been developed on the basis of comparisons of test results with performance on full-scale sections.