Low Compressive Strength Test Results? What They Mean and Next Steps…

Compressive strength tests are used for concrete acceptance based on criteria defined in ACI 318 and ACI 301. Tests results not meeting these criteria are referred to as low strengths. This presentation covers the “low strengths” topic in detail and provides answers to questions such as: what is considered a strength test and what is not, what the minimum frequency of testing is, what the acceptance criteria for strength tests are, and how to investigate strength tests not meeting the acceptance requirements. In addition, steps needed by a concrete supplier, in case acceptance criteria are not met, will also be discussed. To better understand discussed concepts, the presentation will use statistical concepts and numerical examples. A list of reading resources will be provided for those interested to study it in more detail. Topics covered in this presentation include:

• Definitions related to strength testing
• Methods of sampling, fabrication, handling and curing strength test specimens
• Acceptance criteria for strength tests
• Interpretation of strength test results not meeting acceptance requirements
• Investigation of non-compliant concrete
• Addressing low strength concrete issues in production

Presented by:

Jerzy Zemajtis, PhD, PE
Executive Director of NEx,
an ACI Center of Excellence for Nonmetallic Building Materials.

Dr. Zemajtis received received his BS and MS in civil engineering from the Technical University of Gdansk, Poland, and his PhD in civil engineering from Virginia Tech. He worked as a Structural Engineer in Virginia Beach, VA, and Vancouver, Canada, as a Civil/Materials Engineer at Construction Technology Laboratories in Chicago, IL, and as Senior Engineer at the Engineering Department of ACI. He is a licensed engineer in Washington and British Columbia.