BACKGROUND. Laboratory testing and long-term field experience have shown that highway concrete must be properly air-entrained if it is to resist the action of freezing and thawing, particularly in wet climates. Experience has also shown that the effectiveness of air entrainment in providing resistance to freezing and thawing depends on the characteristics of the air void system. These characteristics are influenced by the materials used in producing concrete (e.g., cement type and composition, supplementary cementitious materials, air-entraining and other admixtures, and aggregate size); the practices for proportioning, mixing, and placing concrete; and field conditions. However in some situations, air entrainment has shown adverse effects on other concrete properties (e.g., strength).
Laboratory methods are currently available for characterizing the air void system in hardened concrete and for evaluating the freeze-thaw resistance of concrete. However, the parameters associated with this characterization and the results of these laboratory tests do not always reflect the observed field performance nor do they consider the possible effects on other concrete properties. There is a need to identify the characteristics of the air void system that relate to field performance and develop improved test methods for evaluating the freeze-thaw resistance of highway concrete. Ideally, these methods would evaluate the concrete mixture immediately before placement to allow adjustment of mixture if necessary. This information will help highway agencies prepare specifications for concrete procurement that will provide the air-void characteristics and freeze-thaw resistance needed for enhanced durability and thus ensure longevity of highway structures and pavements.
OBJECTIVES. The objectives of this research are to (1) identify the characteristics of the entrained air void system required for freeze-thaw durability of highway concrete, (2) identify/develop new or modified test methods for measuring these characteristics, and (3) identify/develop new or modified test methods for evaluating freeze-thaw durability.
Accomplishment of these objectives will require at least the following tasks.
Phase I: (1) Review literature, ongoing research findings, and current practices relevant to the characterization of the air void system of highway concrete, the laboratory and field evaluation of freeze-thaw durability, and the effects of entrained air void characteristics on freeze-thaw durability in various highway applications with consideration to other concrete properties (e.g., effect of air void clustering and air content on strength). This information may be assembled from published and unpublished reports, contacts with academia, transportation agencies, industry organization, and other sources. (2) Evaluate the characteristics and methods currently used in the United States and other countries for measuring and evaluating the air void system of fresh or hardened concrete and determining freeze-thaw durability. Discuss the merits and deficiencies of these characteristics and methods, and recommend potential characteristics and methods for use in field quality control and laboratory evaluations, for further evaluation in Phase II. (3) Develop a research plan for an experimental investigation, to be executed in Phase II, to evaluate the potential characteristics and methods identified in Task 2 for (1) determining the characteristics of the air void system of highway concrete required for freeze-thaw durability, (2) developing and demonstrating test methods for measuring these characteristics, and (3) developing and demonstrating test methods for use in predicting freeze-thaw durability of different highway applications and exposures. (4) Prepare an interim report that documents the research performed in Tasks 1 through 3. Following review of the interim report by the NCHRP, the research team will be required to make a presentation to the project panel. Work on Phase II of the project will not begin until the interim report is approved and the Phase II work plan is authorized by the NCHRP. The decision on proceeding with Phase II will be based on the contractor’s documented justification of the updated work plan.
Phase II: (5) Execute the plan approved in Task 4. Based on the results of this work recommend (1) the characteristics of the air void system required for freeze-thaw durability of highway concrete applications, (2) new or modified test method(s) for measuring these characteristics, and (3) new or modified test methods for evaluating freeze-thaw durability. (6) Develop protocols for the test method(s) recommended in Task 5, in AASHTO format. (7) Identify issues affecting implementation of the proposed test methods, propose possible actions to address these issues, and provide a brief description of each proposed action. (8).Prepare a final deliverable that documents the entire research effort.
STATUS: Research in progress..