Book Description

Rapid construction practices throughout the concrete industry have brought increasing pressure on specifying agencies to assess the quality of concrete at an earlier age than 7 or 28 days after placement. Currently, the later age is still specified for compression tests of 152 by 304-mm (6 by 12-in.) cylinders of concrete as delivered to the job site in order to determine quality. During the 28-day period, it is not unusual for a multistory building to rise several floors before the strength tests are conducted. This situation is considered by many to be too precarious for construction to proceed on a sound technical basis and with adequate assurance of safety. Furthermore, extensive and costly delays are encountered when 28-day test results are low, since a field investigation may be necessary to verify the load-carrying capacity of the structure. Further delay is certain if concrete must be reinforced or replaced. Conversely, economics dictate that work continue without knowing quality, thus setting the stage for a catastrophic collision between advancing construction technology and the price owners are willing to pay for their capital facilities. Surely, an earlier assessment of concrete quality is absolutely essential.