Optimizing the COTE of Concrete by Blending High and Low COTE Aggregates to Meet TxDOT Limit

Abstract

The coefficient of thermal expansion (COTE) is an important concrete property that characterizes the dimensional change of concrete subjected to temperature change. In jointed concrete pavements (JCP), expansion joints are used to accommodate length changes due to temperature variations. However, for continuously reinforced concrete pavements (CRCP) with high COTE aggregates, there are no expansion joints to accommodate the length changes. In Texas some districts with high volumes of CRCP, such as Houston, Dallas, and Forth Worth, experience a high degree of transverse cracking, horizontal cracking, and punchouts due to the environmental loading in high COTE concrete CRCP. Very recently the Texas Department of Transportation (TxDOT) imposed a limit on COTE as an acceptance criterion for pavement concrete aggregates. Houston and Beaumont do not have low COTE aggregate sources in the vicinity, and to meet the current TxDOT requirement these two districts have to haul aggregates from long distances. This will not only increase the transportation cost but also limit the use of locally available good quality aggregates, which has high COTE. COTE of concrete can be reduced by blending high and low COTE aggregates. This research study used three high COTE aggregate sources from different strategic locations in Texas suggested by TxDOT; they were each blended with low COTE limestone aggregate at different replacement ratios. Results showed that concrete COTE can be reduced by blending low COTE aggregates with high COTE aggregates. The COTE of concrete decreases linearly with an increase in limestone replacement. These findings will help TxDOT use the local high COTE aggregate sources by blending with imported low COTE aggregates. Aggregate producers with high COTE aggregates can also determine the degree of replacement necessary for their aggregates to be accepted in a TxDOT CRCP paving projects.