Cold Weather Subgrade Stabilization

This paper describes an approach to cold-weather subgrade stabilization. Background information was derived from the open literature, ongoing research and discussions with stakeholders in industry, academia and the government. Traditional subgrade stabilization in road construction is defined herein as the use of unmodified lime, cement or fly ash in soil to improve the strength and overall performance of a pavement system. Many of the non-traditional additives currently on the market have been evaluated in recent years. Broadly, these may be categorized as asphalts, polymers, electrolytes, biochemical additives, FGD gypsum and lime/cement additives. Careful evaluation of each category in turn reveals that the most promising alternative to unmodified lime and cement is modified lime and cement. Specifically, rapidly maturing research in the field of cold weather concreting has demonstrated the ability for cementitious reactions to occur at low and sub-freezing temperatures when modified appropriately. Cementitious reactions are the same principle by which conventional lime and cement impart strength on subgrade soils. Naturally, straightforward research is required to transfer concreting technology to soil stabilization. To that end, an experimental campaign has been conducted. In particular, three chemical additives were selected and procured from the W.R. Grace Company, namely Polarset, Gilco and Daraccel. As a preliminary metric of performance, unconfined compression strength testing was conducted on mixtures with and without the chemical additives. At the levels tested, the range of additives increase the cost of conventional stabilization from approximately 10 to 50%, although subsequent research may lower those values still. The control (unmodified) mixture of soil and cement resulted in an average 1-day strength of 487.1 kPa (70.6 psi) when cured at 2 °C (35.6 °F). For the same mixture at the same curing temperature, the average 1-day strength increased to 1286.9, 1394.5 and 1079.2 kPa (186.5, 202.1 and 156.4 psi) for the Polarset, Gilco and Daraccel additives, respectively. These increased strengths at 2 °C are also approximately double that of the unmodified samples cured at 20 °C. These results are unique in that they represent the first application of cold-weather concreting technology to soil stabilization. While more work remains, these results suggest that the additives are promising.