At a recent concrete conference a representative from FHWA made a statement that really hit home on why we should be using Performance Engineered Mixtures (PEM).  He stated PEMs are the most significant field-level advancement in 40 years in the concrete pavement industry.  That’s an entire career for many.  That’s my entire lifetime.  The South Dakota Department of Transportation and the South Dakota Chapter of the ACPA have provided funding to be one of the champion states for PEM.  We recognize need for a more durable, long-life concrete pavement is necessary in South Dakota as stresses from the freeze-thaw environment and the de-icers that come along with the environment have created the need for the concrete pavement industry to deter these harsh chemicals.  As a champion state of PEM, the SDDOT has been using PEM for several years now on many concrete pavement projects with much success.  Contractors using the mixes have found them to be a more workable concrete, especially in slip-form paving applications.

Some of the highlights of the SDDOT “Special Provision for Contractor Furnished Mix Design for PCC Pavement” include:

1. A Quality Control approach allowing the Contractors to be responsible for the performance, production, and composition of their concrete mix designs.
2. A well graded aggregate gradation in the mix design allowing the mix to be more workable with less paste.
3. The inclusion of 20% to 25% fly ash in the minimum 575 lb/cy cementitious content in the mix.  Fly ash is proven to mitigate alkali silica reaction (ASR) and deter reactions to deicing chemicals.
4. Establishing a maximum water/cementitious ratio in the mix.  Lower w/c ratios provide a less permeable concrete providing another mitigation against deicers.

Our concrete pavement specifications have not been keeping pace with advancements in science and innovation within the concrete pavement industry.  These mixes bring us into the 21st century in the industry.  The link below more thoroughly summarizes PEM and their benefits.  If you have any questions regarding implementing these into your concrete pavement project, please contact your local ACPA chapter or the CP Tech Center. 

PEM MAP brief April 2017

Article originally published in the Spring-Summer 2016 edition of the Colorado Public Works Journal

As noted in the May 2014 “Guide to Concrete Overlays” published by the National Concrete Pavement Technology Center (CP Tech Center), shrinking budgets and ever-increasing traffic volumes have necessitated the immediate need for engineering strategies to preserve and maintain the nation’s roadways. One such approach is an unbonded concrete overlay.

Unbonded concrete overlays are used to restore structural capacity to existing pavements ranging from moderately to significantly deteriorated. The term “unbonded” simply means that bonding between the overlay and the underlying pavement is not needed to achieve desired performance. Thus, the overlay performs as new pavement and the existing pavement provides a stable base.

Source: “Guide to Concrete Overlays: Sustainable Solutions for Resurfacing and Rehabilitating Existing Pavements” (www.cptechcenter.org)

There are several benefits of using unbonded concrete overlays, including the solution’s cost-effectiveness. According to the CP Tech Center, “dollar for dollar, they are one of the most effective long-term pavement preservation and major rehabilitation options for existing pavements.” Other benefits of unbonded concrete overlays include their quick construction, ease of maintenance, and sustainability assets.

In general, unbonded resurfacing is highly reliable, offering longer design life than road rehabilitation with asphalt. It has been used successfully by several states, providing on average more than 30 years of good-to-excellent performance, according to the CP Tech Center.

Innovative methods of construction are continuously being explored, and Route D south of Kansas City, MO was the first in the nation to use a fabric bond breaker in 2008. The 3.7 mile long unbonded overlay was constructed in 50 days with a 5” minimum concrete thickness and 6’ x 6’ jointing on a 24’ wide road carrying 9,300 ADT (5% trucks). The new surface has now been serving the traveling public for 8 years, and a 2015 visual distress survey demonstrated that it is performing extremely well

The South Dakota Chapter of ACPA can provide further education on material considerations for long-lasting concrete overlays, and will gladly review potential projects to identify which option(s) are best for your situation. For more information, please contact us.