ASTM C-157 Standard Audit for Third-Party Shrinkage Testing Laboratories to Improve the Reliability of Results for Concrete Mixes

Shrinkage of concrete is one of the reasons of concrete cracking in bridge decks. To minimize such cracks, concrete mixes with minimal shrinkage potential is used. This shrinkage potential was evaluated by third party shrinkage testing laboratories as per ASTM C-157 standard. However, significantly different results were obtained from different laboratories for the same mixes. For this reason, it was necessary to do an ASTM C-157 standard audit for third party laboratories to improve the reliability of such results. The Utah Department of Transportation (UDOT) was interested in selecting a shrinkage acceptance value for concrete mixes, and therefore sponsored this research project to better understand the variability and reliability of the results. For this purpose, different laboratories were visited to collect information on existing practices followed and capability of the laboratories to perform such tests. Three laboratories were selected to perform the ASTM C-157 free shrinkage test on concrete specimens. The duration of curing period was kept to 7 days, including the period in molds, due to time constraint. The procedures followed by the labs and the method to obtain and maintain the recommended temperature and relative humidity were noted. In the process, different methods of initial curing and to maintain the recommended temperature and relative humidity were observed. The date at which shrinkage measurements were taken also differed. It was observed that the labs were able to maintain the temperature within the recommended limits for most duration of the test. However, the relative humidity was lower than recommended limits. Moreover, the shrinkage of concrete specimens at 28 days was significantly different. To conclude, the methods used by the laboratories to maintain the required relative humidity were not satisfactory. Different methods of initial curing and to maintain the temperature and relative humidity have significant effect on the shrinkage measurements. To improve the reliability of the results, such differences should be eliminated, and one common accepted method should be followed by all laboratories. This would allow the use of single laboratory, multiple operator precision values recommended in ASTM C-157 standard as a reliability check.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 35p

Subject/Index Terms

Filing Info

  • Accession Number: 01718517
  • Record Type: Publication
  • Report/Paper Numbers: UT-19.07
  • Contract Numbers: 18-8992; 5H08014H
  • Files: NTL, TRIS, ATRI, USDOT, STATEDOT
  • Created Date: Sep 30 2019 10:08AM