Evaluation of Restraint Stresses and Cracking in Early-age Concrete with the Rigid Cracking Frame

Abstract

Early-age cracking problems are common in a wide variety of concrete structures, ranging from bridge decks and piers, to pavements used for highways and airport runways. Numerous surveys conducted by state and federal agencies reveal that concrete bridges throughout the United States suffer from problems associated with early-age cracking. Although early-age cracking is a growing dilemma, advanced investigations into this issue have just recently begun in the US. The primary objective of this thesis is to develop a test method to assess the cracking tendency of concrete mixtures. The research presented in this thesis explores the use of temperature-controlled, rigid cracking frames that have been developed in Germany. A test method to measure early-age, restraint stress development has been developed and a laboratory testing program has been initiated. The laboratory testing program was designed to evaluate the effects of fresh concrete temperature, aggregate type, and cementitious materials on the early-age, restraint stress development of concrete. The laboratory testing program revealed that the rigid cracking frame provides a detailed account of the early-age stress development thus allowing assessment of early-age cracking risk. This risk can be assessed by comparing the stress development to the strength development. The behavior of two rigid cracking frames was also investigated. One cracking frame was manufactured in Munich, Germany and the other cracking frame was manufactured near Opelika, Alabama USA. Comparative testing of the cracking frames revealed that the frame manufactured in Alabama performed comparably to the frame manufactured in Germany.