Setting Behavior of Concrete Cured at Fluctuating Temperatures (05-2205)
Samuel Wade, Auburn University
Jeffrey Nixon, Auburn University
Anton Karel Schindler, Auburn University
Michael G Barker, University of Wyoming

Given knowledge of the time to initial set, contractors can effectively plan measures to finish, texture, and saw cut concrete pavements on time. The time at which final set occurs is important because it indicates when the concrete strength and stiffness development will start. The primary objective of the study described in this paper is the evaluation of the effects of fluctuating temperatures on the setting times of concrete mixtures made with different water-to-cement ratios, supplementary cementing materials (SCMs), and SCM dosages. Initial and final set times of the concrete were determined with penetration resistance testing (ASTM C 403). Concrete was batched at hot, cold, and control temperatures. The wet-sieved mortar samples were placed in hot and cold water baths that cycled over 24-hours between temperature ranges of 32 to 41°C (90 to 106°F) and 4 to 13°C (40 to 55°F), respectively. The control samples were cured at temperatures between 20 and 24°C (68 and 75°F). Results show that Class F fly ash will slightly retard setting and GGBF slag will slightly accelerate setting. The use of Class C fly ash significantly increases setting times. This retardation increases with an increase in the Class C fly ash replacement dosage. The results also indicate that the equivalent age maturity method may be used to predict setting of concrete samples cured under fluctuating temperatures even if they have different water-to-cement ratios, SCMs, and SCM dosages. A practical implementation approach to predicting setting during construction is proposed.