Evaluation of a Procedure for Determining the Converted Strength of Calcium Aluminate Cement Concrete

摘要

There is renewed interest in North America for the use of calcium aluminate cement (CAC) in infrastructure repair because of its ability to gain strength rapidly even at low temperatures, the ability to customize its fresh workability, and its durability in adverse environments. Conversion of the hydration products of concrete where CAC is the only binder is a well-known phenomenon that is typically accompanied by strength loss, the rate and extent of which is dependent on the temperature history of the concrete, the w/cm, the cement content, and the concrete mixture design. An accelerated method of determining the converted strength of CAC concrete that is convenient for use in the field is presented. This test allows the samples to be cast in the field and left at ambient field temperatures for the first 24 hours; then the specimens are moved to the laboratory and placed in a water bath at 50 degrees C to promote conversion. Robustness testing results are presented for the test method. The effects of the water to cement ratio, the initial (first 24 hours) curing temperature, the length of time before placing the specimens in the 50 degrees C water bath, and the aggregate type are examined. The impact of the low replacement rates (up to 10 %) of finely ground limestone (FGLS) for CAC in concrete mixtures on converted concrete strengths was also studied. Results from testing showed that the majority of mixtures converted 48 hours after submersion in the 50 degrees C water bath; however, differences in the initial curing temperature or aggregate type can delay conversion up to 11 days when specimens are cured following this procedure. Results also indicate that FGLS at replacement rates of 5 % and below in CAC systems may help increase the converted strength observed without reducing initial early strength gain.