ECS Lessons Learned
OBSERVATIONS AND LESSONS FROM THE SCHOOL OF EXPERIENCE
After more than 30 years in the industry, we’ve amassed some great takeaways pertaining to the work we do. We felt this key information was important to share, so in 1996, Lessons Learned was created as a mailed piece sent out to our peers. Now, we are pleased to offer Lessons Learned electronically once a month, accessible on this page or delivered directly to your inbox when you sign up.
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It wasn’t that long ago when most concrete produced in this country consisted of just the traditional components: Portland cement, water, coarse aggregate, and sand. The amounts of each may have varied, but the basic ingredients were largely consistent.
The first additions to the basic “recipe” were probably chemical admixtures designed to modify the properties of either the fresh or the hardened concrete. Today there are probably hundreds of different available admixtures that are classified with such functions as air-entraining agents, accelerators, retarders, corrosion inhibitors, water-reducers, and many more.
The next category is the addition of small fibers dispersed throughout the fresh concrete. They are used fairly frequently to enhance the toughness of the hardened concrete and to help control cracking. Available fibers can be made from steel, glass, synthetic, or natural materials.
A third general category of materials that can be added to concrete to enhance the final materials characteristics are grouped under the title of “Supplementary Cementitious Materials” or SCMs. The phrase mineral admixtures was used in the past. Much of the remainder of this Lessons Learned will briefly touch on what SCMs can do to increase the serviceability of the concrete used in a project.
For many years the concrete industry has been incorporating ever increasing amounts of these supplementary cementitious materials into many concrete mixes. Many readers are probably more familiar with some of the actual SCMs rather than the overall term. Most have heard of fly-ash, slag cement, silica fume, or natural pozzolans.
Many of these materials are byproducts of other industrial processes. As an example, slag cement results from a waste product of steel production, while fly ash is a waste product of coal-fired power plants. When either are used as a partial replacement for standard portland cement, their use can be a net gain for the environment. Energy is conserved by decreasing the demand for the Portland cement being replaced, and industrial waste products may not need to be disposed of in landfills.
Additionally, the use of SCMs can result in many beneficial effects in the concrete mixes they are used in.
Let’s use slag cement – also called ground, granulated blast-furnace slag (GGBFS) – as an example. Although its effects will vary with the quantity used and the actual chemical and physical properties of the slag cement, a concrete mix incorporating 30%-50% slag cement as a replacement for a portion of the portland cement can provide many improved concrete characteristics. Workability and long-term strength are generally increased. At the same time, permeability is usually decreased making the hardened concrete more corrosion resistant or otherwise subject to damage from exposure to chemicals or water penetration. The primary disadvantage of using slag cement that we’ve identified is that early strength gain can be slowed. This can be a problem when early-strength is desired for formwork removal or post-tensioning.
Fly ash has many similar positive effects. Workability and long-term strength are typically improved.
A thought we can all take away from this brief discussion is the value of involving a concrete supplier during the design phase of your next project. They have the ability and the tools to help you customize the concrete you will be using on your next project to help optimize the properties of both the fresh and the hardened concrete.
Please feel free to discuss these topics with a knowledgeable ECS representative as you plan for your next project. We hope this Lessons Learned has been of assistance to you.
ECS Group of Companies
The ECS Group of Companies (ECS) is an employee-owned engineering consulting firm with more than 2,000 employees providing geotechnical, construction materials, environmental and facilities consulting services. ECS has grown to over 65 locations and five subsidiaries spread across the Mid-Atlantic, Midwest, Southeast and Southwest. The firm is ranked 69 in Engineering News-Record’s Top 500 Design Firms (April 2020) and 52 in Zweig Group’s 2020 Hot Firms (June 2020).