Author Archives: Angela Folkestad

I’ve appreciated the opportunity to share educational information and insights on the concrete pavement industry with the readers of the Colorado Public Works Journal over the last 10 years.  From concrete pavement construction best practices to concrete overlay performance and low carbon concrete, we have explored a wide variety of different topics.

University Boulevard in Denver – constructed in 1984 and still performing with the original concrete surface over 40 years later

Concrete pavement continues to serve the taxpayers of Colorado as roads are stretched well beyond their design lives and carry levels of traffic that weren’t anticipated 30 to 50 years ago.  I expect that our current focus on materials and construction practices that make concrete more durable will also result in today’s concrete pavements carrying the load well beyond our expectations.

While budgets continue to be a challenge for agencies of all sizes, investing in long term solutions like concrete pavement must be part of the strategy for managing assets and maintaining transportation infrastructure.  We can’t build ourselves out of the current poor conditions on Colorado’s highways with the band aid approach that has been used in recent years.  This cycle of rehabilitation and maintenance is not sustainable and is unnecessarily draining material and financial resources.  Concrete overlays are the permanent and proven solution to many of these challenges.

6” concrete overlay on SH 13 north of Craig – constructed in 2016 as an alternate bid at an initial cost less than the asphalt alternate

This will be my last column as the Executive Director of the Colorado/Wyoming Chapter of ACPA, and I’d like to thank you all for the great interactions we’ve had over the years.  Stay tuned to future columns to hear more from the concrete pavement industry and the next leader of ACPA.

Article published in the Spring 2025 issue of the Colorado Public Works Journal.

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.

Are you facing pavement maintenance challenges with your county road, local street, urban arterial, parking lot, highway, interstate or airport?  If so, there’s most likely a concrete overlay solution available to help you!

You may be asking yourself “How do I get started with a concrete overlay?”  The good news is that there are user-friendly tools available with great guidance to go along with them – and they’re available online and FREE to use.

The Bonded Concrete Overlays of Asphalt-Mechanistic Empirical (BCOA-ME) design program was developed with funding from the FHWA.  Check out the free web-based software:  https://www.engineering.pitt.edu/bcoa-me

The National Concrete Pavement Technology Center (CP Tech Center) has been developing guidance on concrete overlays for years and has two great documents available to reference – the Guide to Concrete Overlays and the Guide to Concrete Overlays of Asphalt Parking Lots.  Those documents and a wealth of additional information are available at:  https://cptechcenter.org/concrete-overlays/

The Denver International Airport (DEN) has constructed concrete overlays on several of their parking lots, with the most recent involving the completion of the Pikes Peak Parking Lot.  DEN has had great success with 5” concrete overlays, and they’re always happy to welcome visitors to witness the construction, including many who visited the site during an open house in August.

From a sustainability perspective, concrete overlays are a great opportunity for reduced GHG emissions during and after initial construction. They efficiently utilize resources and eliminate the need for disposal of existing pavements. Concrete overlays are cost effective and are constructed quickly while simultaneously extending the life of the pavement.  Their longevity is inherently a sustainable approach to construction.

Contact Sarah Dalton (sdalton@pavement.com) to learn more about designing and constructing concrete overlays – and visit a concrete overlay near you. 

Article published in the Fall 2024 edition of the Colorado Public Works Journal.

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.