Preventing ASR/DEF in New Concrete: Final Report

Abstract

The state of Texas has been widely impacted by materials-related distress in various transportation structures. This distress has been mainly attributed to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) and has been commonly referred to by the Texas Department of Transportation (TxDOT) as “premature concrete deterioration.” In response to these problems, TxDOT has aggressively sought to prevent cases in new concrete structures by implementing new ASR specifications (initially as TxDOT Special Provision to Item 421). The specifications, and updates since, require contractors to address ASR through prescriptive options (e.g., 20–35 percent Class F fly ash) or performance testing. The research detailed in this report was performed in support of this new specification, with the intention of improving upon the initial specification efforts and increasing the service life of transportation applications. This report summarizes the overall findings of TxDOT Project 0-4085, “Preventing ASR and DEF in New Concrete.” This research project was 4 1/2 years in duration, with an emphasis on both laboratory and field evaluations. The work was performed at the Concrete Durability Center (CDC) at The University of Texas at Austin (UT Austin). The main objectives and goals of this project can be summarized as follows: 1. Understand the underlying mechanisms behind ASR and/or DEF; 2. Review available test methods for aggregate reactivity and for preventive measures and recommend test method(s) to prevent ASR and/or DEF in new concrete; 3. Develop specification and guidelines to prevent ASR and/or DEF in new concrete; 4. Identify and implement strategies for preventing ASR and/or DEF, with emphasis on prudent use of supplementary cementing materials (SCMs); 5. Develop protocol for evaluating the cause, extent, and future potential for damage owing to ASR and/or DEF in existing concrete structures; 6. Transfer knowledge and experience gained from this project to TxDOT practice to increase the service life of transportation structures.