Freeze-Thaw Durability Requirements for New Concrete Structures in Alabama

Abstract

Concrete is one of the most widely used building materials in Alabama Department of Transportation (ALDOT) infrastructure. Section 501, “Structural Portland Cement Concrete,” of the ALDOT 2026 Standard Specifications for Highway Construction specifies a required total air content range of 2.5 to 6.0% that is intended to ensure that concrete mixtures are protected from freeze-thaw damage. However, the total air content is the sum of both entrapped and entrained air voids and does not provide a measure of the internal spacing of the entrained air voids that protect the concrete from freeze-thaw damage. Given this limitation, a new test method called the Sequential Pressure Method, also known as the Sequential Air Method (SAM), provides an indication of the quality of the air-void system before the concrete hardens. The adequacy of the SAM for use in ALDOT projects along with the sufficiency of ALDOT Section 501’s current required total air content range are evaluated in this project. A literature review and a laboratory testing phase were conducted to determine the mixture proportion factors that influence the freeze-thaw resistance of concrete mixtures. A meta-analysis of literature-derived data was also performed using multivariable linear regression analysis, logistic regression analysis, and classification analysis. The classification analysis was repeated for data obtained from laboratory testing. In the laboratory testing phase, 34 concrete mixtures with water-to-cement ratios of 0.35, 0.40, 0.45, and 0.50 and total air contents of 2.0 to 7.0% were tested. It was found that the current ALDOT required minimum total air content is too low to protect concrete from freeze-thaw damage and the allowable range of total air contents should therefore be increased to 3.5 to 7.0%. It was also found that there is no benefit of using the SAM as opposed to the current total air content test for quality assurance testing to identify non-freeze-thaw durable concrete mixtures in the field. The SAM is therefore not recommended for implementation by ALDOT.