In Colorado, concrete placement can be challenging. This is especially true during the summer months when high temperatures and low humidity make it even more difficult. The CO/WY Chapter- ACPA would like to remind everyone of a few best practices for successfully placing concrete pavements and flatwork during the summer season.
Concrete Delivery
Keep the mixing temperatures as low as possible during placement and ensure they do not exceed 90 degrees. Mixing water has the largest impact of reducing concrete temperature, using chillers or ice at the plant can help greatly.
It is acceptable to add water on the job site, but this should only be done when each truck first arrives on site. Always ensure that the maximum water/cementitious ratio is not exceeded, as this will negatively impact both strength and long-term durability.
Make sure the ordered mix design includes an effective water reducer to achieve workability during placement without adding excessive water. For longer haul distances or when low slump mixes are needed for slipform operations, hydration stabilizers can provide a few extra minutes of workability before initial set is reached.
Subgrade
Before placing concrete, base materials should always be wet, but there should be no standing water. Dry materials will absorb water out of the mix. When placing concrete on top of asphalt, the base temperatures should never exceed 120 degrees.
Finishing Aids
In hot weather, the concrete is going to set up faster which can make finishing more challenging. Water should NEVER be applied and worked into the surface as that will lead to scaling in the future. ACPA recommends using finishing aids when necessary, however, there is only one type that is currently acceptable. Finishing aids should be colloidal silica based, as these products are designed to be worked into the surface and contribute to the long-term durability of the concrete. Most other types of products marketed as finishing aids are either evaporation retarders or primarily water and will damage the surface when worked in.
Curing
In Colorado’s dry climate, curing compound is essential when placing concrete in high temperatures and windy conditions. The purpose of curing compound is to prevent water, necessary for hydration, from evaporating out of the concrete. The compound must be applied evenly to all exposed concrete surfaces as soon as possible after finishing, within a maximum of 10 minutes during summer months. Failing to cure promptly can lead to shrinkage cracks, reduced strength, and a weakened surface.
Concrete can be successfully placed year-round in Colorado when proper precautions are taken and best practices are followed. CO/WY Chapter- ACPA is always available to help. If you have questions or would like to schedule a customized training course for your company or agency, please reach out to Sarah Dalton (sdalton@pavement.com).
Article Published in the Summer 2024 edition of the Colorado Public Works Journal.
