Concrete can be placed in the winter without issue, and it’s done regularly for both pavements and flatwork. There are a few keys to creating deicer resistant concrete that need to be followed:
- Require 20% Class F fly ash. This is the most important component since using Supplementary Cementitious Materials (SCMs) greatly decreases the permeability of the pavement. Minimizing deicer penetration into the pavement reduces the potential for calcium oxychloride reactions. SCMs are also important for increasing sulfate resistance.
- Reduce cementitious paste content. Utilizing a Performance Engineered Mixture (PEM) approach to concrete mixture development includes optimizing aggregate gradations and reducing paste content. It provides another avenue to reduce permeability and increase concrete durability, all while lowering the environmental impact. Guidance on PEM strategies can be found at https://www.cptechcenter.org/performance-engineered-mixtures-pem/
- Maximum w/cm ratio of 0.42. Ideally, flatwork should be held to a maximum water-cementitious ratio (w/cm) of 0.42 for durability in our climate. Many specs allow up to 0.45, including any water added onsite, and that limit should never be exceeded. Permeability increases and strength decreases with high w/cm ratios. ACPA recommends not exceeding in the field the w/cm ratio used in the lab to develop the mix design.
- Follow best practices for finishing. Working water into the surface and overfinishing are usually contributors when scaling happens. Working water in raises the w/cm ratio of the surface, which weakens it. Overfinishing works the air out of the concrete surface, decreasing the ability for the concrete to resist the damage caused by freeze-thaw cycles.
- Consider a cure-seal product when deicers will be applied within 30 days. This is a type of curing compound that has a penetrating surface sealer built in. Even with low permeability mixes it takes several weeks for the concrete to develop deicer resistance. These products are applied like any other cure but keep water and chemicals out while the mix is developing strength. Cure-seal products should meet ASTM C1315, Type I or II, Class A.
The Municipal Government Pavement Engineers Council (MGPEC) has developed concrete specifications that include most of these approaches. Check out Items 30-33 on their website at https://mgpec.org/mgpec-specifications.html.
For additional assistance with any of your concrete pavement questions, please contact Angela Folkestad at afolkestad@pavement.com.
Article published in the Fall/Winter 2024 edition of the Colorado Public Works Journal.
