Paper and Presentation by Moon Won Title from ASCP 4th Concrete Pavements 2017
The performance of continuously reinforced concrete pavement (CRCP) has been excellent in Texas, and in 2001, the Texas Department of Transportation (TxDOT) made it a policy to use CRCP when a rigid pavement system is selected for projects. One of the pre-requisites for good pavement performance is optimum design. Over the years, TxDOT tried various CRCP designs, with the prime objective of obtaining desirable transverse crack spacing. Most of the transverse cracks in CRCP develop primarily due to environmental loading (temperature and moisture variations), with the effect of wheel loading on transverse crack development being minor. Since longitudinal steel amount, concrete temperature and concrete properties, especially coefficient of thermal expansion (CTE), affect the cracking behaviour of CRCP, CRCP designs tried over the years in Texas have variations in those three factors. However, the interactions among those three variables are quite complicated, and an approach based on purely theoretical modelling and analysis has substantial limitations. To overcome these limitations, TxDOT investigated the behaviour and performance of CRCP sections built with various designs, constructed test sections with various combinations of longitudinal steel and concretes with different CTE values, and conducted follow-up investigations of the behaviour and performance of these test sections.
TxDOT’s rather exhaustive efforts to improve CRCP designs revealed several major findings; first, contrary to the general belief that transverse crack spacing has significant effects on CRCP performance, keeping cracks tight had a pronounced effect on CRCP performance. Keeping cracks tight in CRCP requires a larger amount of longitudinal steel, which results in smaller crack spacing that quite often is less than the minimum limit value specified in the AASHTO Pavement Design Guide. Another significant finding is that coarse aggregate type has significant effects on major spalling and shallow delaminations. A research study that was completed in 2014 revealed that CTE of concrete is a major factor for the development of those two distresses (Ryu, et al, 2012), and TxDOT now limits CTE of concrete to 9.9 x 10-6/°C. The latest TxDOT CRCP Design Standards that were developed in 2013 incorporated all the findings made up to that point, and present the most effective CRCP designs.