Interest in the use of high-range water-reducing (HRWR) admixtures, also known as superplasticizers, for concrete is increasing. These admixtures can markedly improve the workability of concrete mixtures. They also have the potential for producing very high strength, durable portland cement concrete by reducing the amount of water used while still allowing conventional placement methods.
Research indicates that these admixtures may affect entrained-air void systems. Air void spacing factors below 0.008 in. seem to correlate with expected satisfactory "freeze-thaw" resistance as predicted by laboratory tests. However, higher spacing factors often found in concrete placed using HRWR admixtures may or may not produce laboratory results predicting poor durability. Because of the poor correlation between air void characteristics of concretes containing HRWR admixtures and laboratory durability test results, a question arises concerning the relationship of air void characteristics and durability. There are also concerns about the influence of other concrete properties on durability and the ability of current freeze-thaw testing procedures to adequately measure durability in the laboratory as a predictor of field performance.
Therefore, research should be conducted to improve laboratory testing procedures for evaluating freeze-thaw durability and to better understand the parameters that influence the durability of concretes containing HRWR admixtures. The major concern is the testing of concretes with low water-cement ratios containing HRWR admixtures so that the benefits of high strength and decreased permeability can be realized.
The objectives of this research were to: (1) investigate the significance of various concrete properties, such as air-void characteristics, on the durability of high strength concretes (compressive strength greater than 4,000 psi) containing high-range water-reducing (HRWR) admixtures, and (2) compare and assess the variability of durability factors calculated from various methods of testing concretes for freezing and thawing durability.
Research is complete. A summary was published as NCHRP Research Results Digest 208.