Concrete, a cornerstone of modern infrastructure, has weathered the test of time since its first use. The age-old issue of “salt scaling” has continued to haunt our urban landscapes, presenting a persistent challenge. Surface distress, often caused by a blend of factors, has proven elusive to pinpoint and address. However, the year 2023 has witnessed an unusual surge in problems related to surface distress, urging a reexamination of this matter writes Peter Taylor in a MAP brief for the National Concrete Consortium.
Several factors are likely contributing to the recent uptick in surface distress. Firstly, contemporary portland limestone cements now incorporate up to 15% interground limestone. While this shift should not directly impact concrete’s vulnerability to distress, it may indirectly influence water demand, bleeding, and setting time, potentially heightening the risk of scaling.
Secondly, the harsh 2022-2023 winter subjected Des Moines to 18% more freeze-thaw cycles compared to 2006-2007. Thirdly, the workforce turnover, accentuated by the challenges of the COVID-19 pandemic, might have eroded field finishing skills. Significantly, most of the issues seem to afflict hand-placed concrete, which often possesses a higher water-to-cementitious materials (w/cm) ratio, a greater likelihood of retempering, and more variability in finishing practices compared to slipformed sections. Damage is particularly prominent near edge drains or wheel paths, where salt concentrations tend to be higher.
Minimizing the Risk of Surface Distress
To mitigate the risk of premature surface distress, a series of guidelines and actions are recommended on the tech brief. These measures include enforcing a maximum final w/cm ratio of 0.45, with a target of 0.42, limiting the utilization of supplementary cementitious materials, ensuring appropriate air void spacing, timing finishing operations after the cessation of bleeding, applying high-quality pigmented curing compounds to maintain pavement reflectivity, and avoiding early salt application, especially magnesium chloride (MgCl2) and calcium chloride (CaCl2). Implementing these preventative measures can significantly enhance the resilience and longevity of concrete surfaces.
Read the full report here.