Title: Air Void System and Frost Resistance of Concrete Containing Superplasticizers
Author(s): L. R. Roberts and P. Scheiner
Publication: Symposium Paper
Appears on pages(s): 189-214
Keywords: admixtures; air-entrained concretes; air entrainment;
bubbles; compressive strength; concrete durability; freeze-thaw
durability; mix proportioning; naphthalene compounds; plasticizers;
Previous workers have shown that the air-void system in air-entrained concrete containing a superplasticizer tends toward larger bubbles. This effect leads to spacing factors larger than the 0.2 mm normally accepted as a requirement for durability. Nevertheless, concretes containing such admixtures generally have been found to be frost-resistant. The present work is an attempt to understand the reasons for durability when the accepted 0.2 mm spacing factor requirement is not met. The distribution of air-void sizes in air-en-trained concretes made with and without a naphthalene sulfonate type superplasticizer were examined, using a new microprocessor-based Rosiwal linear traverse apparatus. The individual chord intercepts available with this system were fitted to a zeroth-order logarithmic distribution function, and the parameters of the fitted function were related to frost resistance as tested for by ASTM: C 666, procedure A. Concretes containing the superplasticizer were frost-resistant, despite spacing factors in excess of 0.2 mm. The most frequently encountered chord lengths in superplasticizer-con-taining concrete did not change relative to equal slump refer-ence concrete.