A family of versatile, cement particle-dispersing admixtures is rapidly changing concrete plant and field practice, with promises of labor and energy savings, safer working conditions, and better results. Those admixtures are known as third generation superplasticizers or, to chemists and the quality control crowd, “polycarboxylate-type” agents. For cast-in-place construction and precast fabrication, these superplasticizers can impart to mixes a) more rapid strength development than conventional concrete; b) a fluid consistency measured not by slump but spread; c) an ability to migrate throughout forms such that little or no vibration is required; and d) a tendency to produce finished surfaces of superior uniformity and smoothness.

Third generation superplasticizer-bearing mixes took center stage last month in Chicago at the 1st North American Conference on Design and Use of Self-Consolidating Concrete (SCC). With the presentation of nearly 70 papers, the two-day event examined how SCC, a product typically formulated with polycarboxylate agents and carefully graded aggregate, is revolutionizing U.S. and Canadian concrete. Presentations included “U.S. Regulatory Work on SCC,” from Axim Concrete Technologies Manager of Technical Services Martin Vachon and Master Builders Manager of Concrete Technology Joe Daczko. They offered technical and market highlights showing how the industry is preparing SCC for mainstream use:

Standardization

The American Concrete Institute, American Society for Testing and Materials and Precast/Prestressed Concrete Institute (PCI) have adopted “consolidating” for SCC, versus “compacting.” The designation was prompted partly at the behest of retired Corps of Engineers/Vicksburg staffer Bryant Mather.

Leading the way in standardization is PCI, whose producers enjoy more latitude in choosing mix designs and placement methods than their counterparts in other concrete segments. The institute has charged a 20-member Fast Team with developing interim SCC guidelines to be published in the first half of 2003. Among criteria factoring into those guidelines are specifications J.W. Peters developed for Soldier Field, featured on this month's cover and pages 20-22.

At ASTM, a 44-member Subcommittee on Self-Consolidating Concrete (C09.47), formed in June 2001 under Committee C 9, has targeted a third-quarter 2003 balloting for SCC test methods. They will define SCC as a mix 1) fluid enough to fill forms with external energy; 2) one remaining homogenous during and after placement; and 3) flowable through dense reinforcement, if needed. C09.47 members plan to harmonize their definition of concrete mix densification with that of ACI, whose Subcommittee 236B met in October with an eye toward issuing an emerging technology report on SCC next year, followed by a more comprehensive state-of-the-art report.

Market acceptance

With double tee girders at the forefront of applications, precast/prestressed concrete has been the main driver of SCC in North America. An Axim survey found that 30 percent of PCI members are using SCC at a daily rate equivalent to about 5,000 yd. A sampling of 23 National Ready Mixed Concrete Association members yielded 22 responses indicating SCC testing or occasional production. Based on that and other data, “U.S. Regulatory” authors estimate this year's ready mixed SCC output at about 100,000 yd. or less.

The conference was organized by the Center for Advanced Cement-Based Materials in Evanston, Ill., with sponsors ACI, PCI, Portland Cement Association and six of the top ten global players in admixtures and cement. Through frequent news items, technical reports and case histories, we will join these organizations and companies in helping spread the word on SCC.

e-mail: dmarsh@primediabusiness.com