Q: Our lab has developed a self-consolidating concrete (SCC) mix design that we plan to use on a recently awarded project. It will be our first large SCC project. While we have provided the SCC recipe on several small jobs and for this project's test pours, this will be our first attempt to incorporate our SCC product into our operations.

Do you have any suggestions on how to best prepare for incorporating SCC into our ready-mixed concrete operation?

A. Batching SCC in a central mix, ready-mixed concrete operation shouldn't require too many special changes from normal procedures. Many producers have reported that in the process of preparing for SCC, they often fine-tune their standard operating procedures.

Recently, Alberto Casiano, manager of technical services for Empresas Master, a producer in Toa Baja, Puerto Rico, presented a paper at the American Concrete Institute's Fall Convention on this subject.

He described his company's effort to supply SCC to the Eddifico de Estudios Generales de Puerto at Recinto de Rio Piedras, a new school builing. The SCC was poured into forms containing liners. When stripped, they became the key architectural elements of this structure.

Casiano told the group that he made a concerted effort to develop efficient communications with the general contractor. “We wanted to be sure that the contractor knew of SCC's fresh concrete properties, had adapted his placing procedures to meet these properties, and was aware of the overall quality control program we had put in place for the project,” he said.

As full-scale production was about to start, Casiano reviewed his plant operations. To minimize potential problems, he worked with his production team and revised the company's operating procedures. He focused these efforts in two main areas: materials and operations.

Materials
  • Establish separate stockpiles for both the coarse and fine aggregates that will be used in the SCC mix.
  • Inspect those stockpiles daily, looking for any degradation, contamination, or other changes.
  • Schedule weekly samplings of both the coarse and fine aggregates, conducting gradation analysis.
  • Retain a portion of the weekly samples for later comparisons.
  • Test weekly for organic materials in the fine aggregates, using ASTM C40.
  • If the SCC is to be pumped, monitor the pre-wetting process of the coarse aggregate to ensure it is adequately saturated.
Operations
  • Install an amp meter at the plant's mixer, and have a qualified electrician calibrate it.
  • Once calibrated, establish the target reading that represents the completion of the mixing process.
  • Calibrate all moisture probes; record all readings.
  • Check the mixer and the truck's drum for any leftover concrete or wash water.
  • Once the SCC is in the truck mixer, allow the driver enough mixing time, perhaps up to five minutes, to establish a homogenous mix.
  • Require a visual inspection of the mix in the drum, by either the driver or a QC technician.
  • Conduct a spread test on every other load.
  • Recheck the spread test at the jobsite on every other load.
  • Conduct spread and air checks, calculate unit weight, and prepare test cylinders from the middle portion of random loads on each day's pour.
  • Establish a written procedure on how to retemper a load of SCC using the proper high-range water reducer or viscosity-enhancing admixtures at the jobsite.

We invite questions and comments from readers on any aspect of concrete mix design, production, testing, or troubleshooting. You can e-mail your questions toryelton@hanleywood.com.

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