Influence of moisture-curing reaction on the mechanical properties of one-component polyurethane mixtures

One-component, moisture-curing polyurethane mixture is a potential cold repair material for pavement because of its simple application method and excellent road performance. However, a large amount of CO2 is produced in the moisture-curing reaction of polyurethane, which destroys the mixture’s interlocked-denseness structure and reduces its mechanical properties. In this paper, a one-component polyurethane mixture with AC-13 gradation was prepared, and the mixture used the one-component polyurethane synthesized with diphenylmethane diisocyanate and polyether polyol as the binder. The Marshall stability of the mixture was tested according to polyurethane content, temperature, air humidity, and number of compactions. Results showed that polyurethane content, moisture-curing rate of the polyurethane mixture, and mixture air-void content are key factors affecting the Marshall stability of a polyurethane mixture. When the polyurethane content was 5.5%, the polyurethane mixture had the highest mechanical strength. As the content of polyurethane increased, more CO2 accumulated in the mixture and the mixture strength decreased. When the polyurethane content was increased by 1.5%, the Marshall stability of the mixture was reduced by 41.8%. The increase of temperature and air humidity accelerated the moisture-curing rate of polyurethane, accelerating the production of CO2, and reducing the Marshall stability of the mixture. When the temperature rose from 0 to 60 °C and the air relative humidity increased from 30 to 90%, the expansion rate of the mixture increased by 247.55% and 40.08%, respectively, while the Marshall stability decreased by 17.8% and 11.16%, respectively. At appropriate polyurethane content and curing conditions, a higher number of compactions enhanced the interlocked-denseness structure of the mixture, which improved the Marshall stability. As the number of compactions increased from 40 to 70, the air-void content of the polyurethane mixture was reduced by 44.99%, and the Marshall stability was increased by 157.36%. This paper serves as a reference study for the application of one-component, moisture-curing polyurethane mixtures.