The online system successfully measured the air content of SCC.
SCC real-life operations were discussed at the SCC 2008 conference.
Air content measurement
The presenters began their efforts to use the mixer for air content measurement by performing preliminary tests with a lab mixer. They then moved to a full-scale precast plant using normal concrete.
As their results proved, the concept could be used to measure air content. They adopted a more extensive test with SCC at a high-volume precast plant.
During this effort, they measured the air content from 81 batches during two working days. The samples included SCC mixes with and without air-entrainment at several strength targets with varying aggregate combinations for a wide range of products. These included columns, culverts, prestressed beams and double-Tees.
Their online system successfully measured the air content of SCC. The presenters believe this innovation provided their production team several operational advantages, compared to using traditional laboratory air meters. These advantages began with better samples since the entire concrete batch, not just a small sample, is measured. By measuring air the same way, they avoided errors from sample handling.
The increase in product consistency was gained at a relatively small investment. The mixer required no changes, since they only installed a programmable frequency inverter to the electrical system. Testing costs were reduced since all batches were measured with no other extra expenses than the original calibration and occasional off-set adjustment and slightly extended mixing cycle.
But more importantly, operators had a tool with which to make faster adjustments, since all the measured results were immediately stored in a company database to allow quick retrieval.
The presenters indicated that their work on this topic wasn't finished. While their new procedure may help provide tighter control on total air content, it provides little direction on air bubble distribution and sizing. They plan to investigate the possibility of incorporating an air void analyzer.Temperature Variability
Another interesting producer-focused presentation focused on quality concerns caused by temperature variability on SCC's workability. “Production Related Aspects of Self-Compacting Concrete” was an international effort.
The authors were B. Barragán, T. García and L. Agulló, School of Civil Engineering, Universitat Politécnica Catalunya, Spain; R. Zerbino, CONICET-LEMIT, Faculty of Engineering, UNLP, La Plata, Argentina; and R. Gettu, Indian Institute of Technology Madras, Chennai, India.
This team gave a status report on an exhaustive experimental program aimed at evaluating the influence of temperature (from 10° to 40° C), time (up to more than one hour after production) and waiting conditions (stationary or periodically remixed) on SCC properties. They are conducting rheological measurements by using a BML viscometer, and slump-flow and V-funnel tests.