In a recent newsletter, I described the five most onerous prescriptive requirements for a concrete mix, according to NRMCA’s Research and Engineering Standards Committee—things like maximum water-cement ratio, minimum cement content, and aggregate grading. Producers want to avoid these requirements, preferring concrete that meets performance specifications. But Pat Harrison and Jerry Holland with Structural Services Inc. objected, asking that mix designs for exposed slabs-on-ground and other important exposed slabs be excluded from this conversation until viable performance testing is identified. “In our experience,” they wrote, “adjusting the type and amount of SCMs allowed (if any), or reasonable minimum cement contents required, are necessary to achieve repeatable results for varying aggregates and placing environments. The quality of the paste has an enormous impact on the finisher’s ability to produce a uniformly densified, durable surface with a sustainable aesthetic that is easily maintained under a variety of conditions in service. We have been asking since 2004 for applicable performance-based measurements, other than 28-day compressive strength and slump, with no response. Without valid measurements, would it not be better to work together to improve prescriptive specifications that the engineering, contracting, and supplier communities could agree upon?” Read more or comment.
Three Things
The Hanley Wood Commercial Construction Group (which includes Concrete Construction, Public Works, and The Concrete Producer) has announced the 2015 Triad Award. This annual award will honor outstanding publicly owned concrete projects that demonstrate three attributes innovation, sustainability, and leadership (the Triad). This year, we are focusing on projects employing portland-limestone cement (PLC), especially in infrastructure construction. The winning project and two runners-up will be featured in each of the sponsoring magazines as well as at a World of Concrete Luncheon and Forum on Feb. 5. Although the award will be given to a project, we will specifically recognize the project team, including the owner, contractor, and concrete supplier. To learn more, go to www.triadaward.com.
Ready-Mix Rumble
Our editorial staff recently had the chance to visit an Ozinga ready-mix concrete plant near downtown Chicago—one of the larger concrete producers in the area. Trucks, running on compressed natural gas, were pulling in to get filled with concrete (and CNG) and departing in an endless stream. Out on the Chicago River, giant excavators unloaded barges filled with cement and aggregate and smaller front-end loaders fed hoppers and conveyors. It’s good to be reminded sometimes of how this stuff is made. Watch the video.
