As most producers who have been working with SCC know, many variables affect workability, set time, and potential bleeding. One respondent mentioned that he found some of these characteristics affected by temperature while others were not.
Another forum member indicated that he's been studying this production question in the field with a variety of SCC applications. He has focused his work on attempting to determine the ôpot lifeö of this concrete within a concrete temperature range of 60-95 degrees Fahrenheit. He reported that he did not notice an optimum temperature to produce the best characteristics. From his standpoint, temperature has little effect. It seems to be more a question of ingredients such as cement chemistry or set retarders (or accelerators for that matter), transport vehicle efficiency, and plant mixing method.
Another respondent offered a similar observation. He said that he has experimented with SCC mixes in the same concrete temperature range. He found that temperature change had a negligible effect on bleed or flow but may have lengthened the set time compared with that of mixes created with traditional concrete admixtures. (It should be pointed out that this producer was using an admixture that does not require an additional viscosity-modifying admixture.)
Jim Wamelink, a technician from Axim who participated in the online discussion, agreed with the producers who responded that temperature was not a major issue. "SCC workability characteristics such as flow or spread are reliant on your concrete grading, air content, water content, and mixing efficiency of your mixerùto mention just a few," Wamelink wrote.
He suggests that if an SCC mix design results in excessive bleeding, the mix design may not be optimal. "In fact, your bleeding should be minimal because the performance of polycarboxylates [superplasticizer chemistry used for SCC] allows for a lower water-cement ratio while improving flow and maintaining flowability," wrote Wamelink.
He went on to write that, "It is our opinion that a producer can achieve a low variability in spread by developing/designing a proper SCC mix incorporating a super based on polycarboxylates and executing a tight QC plan regardless of the temperature."
It's clear that many producers will continue to have a number of questions about this exciting material. It's a field that will be heavily studied over the next several years. One forum participant suggested that someone could write a book on this subject.
Although we aren't aware of a book on the subject, it's nice to know there is a good deal of information available. Connie Field, the librarian at the Portland Cement Association, wrote to participants that she's compiled a 6-page bibliography of articles and reports on SCC. She wrote: "I'd be happy to e-mail you. If you or anyone else is interested, contact me at firstname.lastname@example.org."
Another important source for information will be the new subcommittee developed at ASTM. At a Dec. 2, 2001 meeting, committee members approved the formation of C09.47 on Self-Consolidating Concrete and Fred Kinney of Essroc was named subcommittee chairman. For more information, contact Jim Olshefsky, ASTM's staff manager of C09, Concrete and Concrete Aggregates, at email@example.com.