Review and Summary of Pre-Wet Methods and Procedures

Shi, Xianming; Bergner, Dave; Du, Sen; Keep, Dale; Reed, Cheryl · 2021 · ROSA P / Minnesota. Department of Transportation. Clear Roads Pooled Fund

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Summary

This report synthesizes current practices, equipment, and materials for pre-wetting in winter road maintenance (WRM), addressing the need to optimize operations amid budget constraints and environmental regulations. Pre-wetting involves applying liquid deicers, such as brines, to solid materials like salt or abrasives prior to road application. The study aims to compile best practices from literature, practitioner surveys, case studies, and manufacturer outreach to provide guidance for agencies seeking to improve efficiency and reduce material waste. The research methodology comprised five tasks: a comprehensive literature review of national and international sources; an online survey of 34 respondents from 25 U.S. states and Canada; interviews and case studies of nine transportation agencies; and outreach to six equipment manufacturers. This multi-source approach captured diverse operational experiences, equipment specifications, and field-tested procedures. Key findings indicate that pre-wetting significantly improves material retention and ice-melting performance. Field tests showed that 80% of pre-wetted salt remained on the road after traffic exposure, compared to only 15% for dry salt. Pre-wetting reduces bounce-and-scatter losses, accelerates brine formation, and allows agencies to achieve desired levels of service more quickly. Typical salt savings range from 25% to 30%, while pre-wetted abrasives can reduce material application by up to 50%. Effective liquid-to-solid application rates are 8–12 gallons per ton, with 8–16 gallons per ton considered reasonable for enhancing ice-melting capacity. Higher rates (30–50 gallons per ton) are feasible for trucks equipped with slurry pumps. Salt brine (23 wt.%) is the most common pre-wetting liquid, though magnesium chloride and calcium chloride are preferred in lower temperatures. Beet juice is increasingly used as a performance enhancer. Equipment trends show a shift from electric to hydraulic pumps to support higher flow rates, and the adoption of zero-velocity spreaders, which can reduce salt use by 70% and cut bare-pavement time in half. The report concludes that while pre-wetting offers substantial operational and economic benefits, current practices rely heavily on trial-and-error rather than systematic scientific investigation. Significant knowledge gaps remain regarding the quantitative cost-benefit analysis of pre-wetting and the optimization of application rates under varying climatic and traffic conditions. The authors recommend future research involving statistically valid field tests to determine optimal liquid-to-solid ratios and evaluate the impact of different equipment configurations on material longevity, friction improvement, and corrosion reduction.

Key finding

Pre-wetted salt demonstrated 80% retention on pavement surfaces after traffic passage compared to only 15% for dry salt, while typical operations reported 25–30% savings in total salt requirements.

Methodology

mixed_methods

Sample size: 34

Provenance

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Topics

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• road surface friction