Investigation of Poor Compressive Strength and Performance of A45 Structural Concrete Mixes

Details

• Creators:
  Rotherham, Jill ; Shearer, Christopher R.
• Corporate Creators:
  South Dakota School of Mines and Technology
• Corporate Contributors:
  South Dakota. Department of Transportation ; United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  • Strength of materials
  • Concrete mixing
  • Mix design
  • Structural analysis
  • Cracking
  • Statistical analysis
  • Literature reviews
  • Field tests
  • Data analysis
  • Surveys
  More +
• Publication/ Report Number:
  SD2022-03
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States
• Edition:
  Final Report: April 2022 - June 2025
• Corporate Publisher:
  South Dakota. Department of Transportation
• Abstract:
  In the five years leading up to the 2022 construction season, the South Dakota Department of Transportation (SDDOT) observed an increasing failure rate for their A45 structural concrete mixes, with mixes failing to meet the 4500psi compressive strength requirement. The sources of low compressive strength concrete tests identified by SDDOT were investigated through a literature review, a statistical analysis, a review of historical test data, interviews with concrete technicians, and a survey to concrete suppliers and other state DOTs. The effects of changing water content, air content, materials, curing conditions, and processing variables were assessed on concrete by measuring fresh properties, compressive strength, and bulk resistivity. Furthermore, a forensics and petrographic assessment was performed on cored samples for low strength concrete in the field. Correlations were found between increased air contents and higher ambient temperatures and increased strength failures when analyzing historical data. Interviews with SDDOT technicians found discrepancies between practice and specification in the areas of testing frequency, the transportation and handling of cylinders, and fresh concrete cylinder temperature control. Field testing revealed higher curing temperatures than allowed by specification. A nationwide DOT survey concluded that while there is not a single perceived reason for their low strength issues, specimen handling and extreme temperatures appear to be significant contributors. Experimental results showed that significantly lower compressive strengths were correlated with higher air content, higher curing temperatures, retempering at high temperatures, higher w/cm, and the use of a different coal ash. Changing these variables, especially in combination, resulted in 28-day compressive strengths lower than 4500psi indicating that the current A45 structural concrete specification can result in strength failures. Bulk resistivity of the concrete was less affected by these changing variables. The specifications should be updated to address issues including re-qualifying mix design strengths for higher air contents and incentivizing lower air contents on hot days, better quality control for batch plant and in-field concrete adjustments and fresh concrete curing procedures, changing the acceptance procedure for 28-day strength to require three cylinders, and more strictly enforcing and changing the mix design qualification procedures.
• Format:
  PDF
• Funding:
  311381
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/93354/dot_93354_DS1.pdf
• File Type:
  [PDF - 10.20 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:3990c06229febd10db9f3900f493d2ebc8fea6517fa8dfd2b1ee53a459f27a7ca12c584e9a70ef249b3acff8378a566eb2bb48d6ab3a13fdb78110e554278eed