Standard Test Method For Resistance Of Concrete To Rapid Freezing And Thawing

Since 1961 the Research Council has used equipment manufactured by Conrad, Inc. for exposing concrete specimens to rapid cycles of freezing and thawing. In addition, the Materials Division of the Virginia Department of Highways and Transportation sends to the Research Council specimens of concrete mixtures and related materials not previously used in the Department's construction when freezing and thawing tests are required as part of the Department's acceptance procedures. The Council's freezing and thawing procedures are based upon ASTM Designation C666 "Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing", Procedure A (freezing and thawing in water), except that surrounding the specimens is a 2% solution of NaCl rather than water. Prior to exposure, specimens are moist cured for 14 days and air dried for 7 days. Based upon about 17 years of experience in the use of this approach at the Council, the following criteria have been established for judging acceptability. Weight loss, maximum at 300 cycles 7% Surface factor, maximum at 300 cycles 3% Durability factor at 300 cycles 60% A limited evaluation of this procedure was made using NaCl solutions with concentrations of 4%, 3%, 2% and 0% (water). Concretes of three levels of expected durability were tested. Based on these tests the following conclusions were drawn. 1. Freezing and thawing of specimens using the procedures of ASTM C666 as modified to use 2% NaCl solution as the surrounding medium rather than water is more severe and more discriminating than using water as required by the standard method. 2. Minor variations of salt concentration likely to be encountered during the progress of the testing do not significantly affect the results. 3. The period of drying between moist curing and exposure to freezing and thawing in an NaCl solution significantly improves the indicated performance. 4. Based upon ACI recommendations for durable concrete, the Council's current requirements for evaluating freezing and thawing resistance may be too lenient for concrete subjected to severe exposure conditions.

This study, aimed at improving the freeze-thaw resistance of concrete, consists of three parts. Part I evaluates parameters affecting the freeze-thaw durability of concrete. A modification of the existing standard of method for determining the durability factor of concrete specimens is proposed, and a new procedure for fundamental transverse frequency (used in durability factor calculations) has been developed. Part II focuses on developing better methods for identifying nondurable aggregates, and has resulted in a rapid new test based on the hydraulic fracture of aggregates. Part III describes field experiments to evaluate the freeze-thaw resistance of a number of specified concrete mixes and the use of sealants to mitigate D-cracking. Preliminary field performance results are presented.

The procedures used to evaluate the durability of coarse aggregate in concrete by freezing and thawing were determined by a survey. Results indicate that a number of state transportation agencies use freeze-thaw procedures in place of, or in addition to, sulfate soundness and other tests. However, each agency's procedure has unique aspects. ASTM Test Method for Resistance of Concrete to Rapid Freezing and Thawing (C 666) describes the procedures for freeze-thaw cycling and gives partial information on expressing test results, but ASTM has no standard procedure to guide the testing agency in important aspects such as: aggregate grading, aggregate moisture treatment and pretreatment, and concrete mixture proportioning (including cement content, air content of concrete, or curing procedure). The ASTM C 666 method of expressing results for change in length does not permit comparison between different aggregates. The information in this paper is intended to assist ASTM Committee C9 on Concrete and Concrete Aggregates in preparing a practice for evaluation of coarse aggregate in concrete by freezing and thawing.