Troubleshooting - Concrete Mix Design, Quality Control and Specification - page 268

• Inadequate strength
• Difficulty in pumping/blockage
• Inability to compact
• Unsatisfactory appearance
• Excessive segregation or bleeding
• Inadequate retention of workability
• Failure to set or stiffen sufficiently rapidly
• Presetting cracks or later age cracks
• Excessive cost of imported materials
• Excessive variability
Possible problem sources are
• Unsatisfactory aggregates
• Unsuitable mix design
• Poor testing (including sampling, casting, and curing of specimens)
• Cement or pozzolan quality
• Unsuitable admixtures or admixture usage
Data to request (having relevant past data available on arrival can often
shorten the investigation by a day or more):
• Mix details
• Aggregate gradings
• Delivery dockets
• Concrete test records (including times, temperatures, and specimen
collection details)
• Cement test certificates if available
• Cores and failed test specimens to inspect
Of course it is desirable that records go back to a period before occur-
rence of the problem if possible. Where aggregate testing records seem
inadequate, a rapid visit to the stockpiles is desirable before (further)
change occurs. Segregation of coarse aggregates, silt content of the sand,
and contamination with subgrade material by front-end loader are items to
look for.
12.1 STRENGTH, PUMPABILITY, AND APPEARANCE
12.1.1 Inadequate strength
The typical steps taken when called in to investigate problems may be of
interest. The steps are