Effects of Synthetic Air Entraining Agents on Compressive Strength of Portland Cement Concrete – Mechanism of Interaction and Re
CAIT project no.: FHWA NJ 2001 021
Fiscal Year: 1997/1998
Rutgers-CAIT Author(s): Ali Maher
External Author(s): Farhad Ansari, University of Illinois at Chicago, Zhijin Zhang, University of Illinois at Chicago, Allyn Luke, NJIT, Nicholas Vitillo, NJDOT
Sponsor(s): NJDOT, FHWA-USDOT
This document reports the results of a comprehensive study pertaining to the determination of causes and mechanisms resulting in a reduction of strength in concrete mixtures containing Synthetic air entraining admixtures. The study involved experimentation with concrete mixtures containing both the Synthetic and Vinsol resin admixtures. Tests involved determination of air content for fresh concrete and air bubble characteristics including size and distribution for hardened concrete. Compressive strength of concrete samples were determined at ages 7, 14, 28, and 56 days. Petrographic analysis of the hardened samples revealed that the Vinsol resin admixture produces more of the smaller bubbles desirable for protection against frost. However, Synthetic admixtures induce more of the larger air bubbles within the cement paste. This explains the much lower compressive strengths associated with Synthetic air concretes. It is believed that the larger air bubbles are produced due to the inability of the Synthetic air entraining agents to lower the surface tension in the mixture. This will allow the smaller air bubbles to coalesce into larger ones. Based on the results of this study, recommendations were made that follow up research should involve determination of surface tension in such mixtures.