National Concrete Pavement Technology Center

Project description

Natural virgin aggregates (NVAs) have become gradually exhausted across the state of Tennessee. There is a growing need for the Tennessee Department of Transportation (TDOT) to replace NVAs with more sustainable recycled concrete aggregates (RCAs). It is the intention of the project to quantitatively assess various RCAs available in Tennessee and to explore their suitability for TDOT new paving concrete mixes. This report documents the main findings of the project. A total of eight RCAs were collected representing different concrete origins of pavement, returned concrete, and mixed sources including buildings. Their basic properties were evaluated, including size and gradation, specific gravity, absorption, LA abrasion loss, chloride content, and pH value. These properties were observed to vary widely with RCA sources. This report also covers how RCAs affected the performance of concrete. It becomes evident that RCAs from good quality concrete origins such as pavements can be used in new paving concrete when adequately designed and proportioned. They demonstrated similar performance as NVAs. However, RCAs from unknow or mixed sources should be used with cautions as they may have inconsistent quality. Poor quality RCAs reflected by high absorption, high LA abrasion loss, and low specific gravity due to unsound adhered paste are not recommended for paving concrete because they will substantially reduce the strength and durability of concrete. RCAs with nondurable aggregate origins are also unsuitable for paving concrete applications.