Скачать или смотреть Modification to ASTM C157 to Measure Early-Age Deformation of Concrete Specimens

Presented by Muzai Feng, University of Kansas; and Eman Khalid Ibrahim, Rouzbeh Khajehdehi, James D. Lafikes, Matthew O’Reilly, and David Darwin, University of Kansas

A modified test method (based on ASTM C157) to capture the deformation of concrete specimens prior to the usual one-day demolding time specified in the current ASTM standard is described. Many technologies have emerged to reduce shrinkage cracking, including shrinkage-reducing admixtures (SRA) and shrinkage-compensating admixtures (SCA). SCAs in particular function by causing early-age expansion to compensate for subsequent drying shrinkage. Due to the nature of the chemical reaction(s) associated with SCAs, a significant amount of the expansion takes place within the first day after casting. Because ASTM C157 requires demolding 23½ ± ½ hours after casting, the test cannot capture deformations that occur during the first day, and as a result, the early-age expansion caused by SCAs cannot be measured. The presentation describes the development of a low-cost modified test method that captures early-age expansion, including techniques for handling the specimens. Test results for mixtures with and without SCAs and SRAs are presented. With the proposed test method, deformation of concrete specimens can be monitored as early as five hours after casting, allowing for a more accurate evaluation of concrete mixtures after final set. The results demonstrate that the conventional ASTM C157 procedures provide accurate results for concretes that do not undergo early-age expansion but that the modified procedure is needed to evaluate concretes that do.