Rachel Detwiler, Construction Technology Laboratories, Inc. and Shri Bhidé, Portland Cement Association
Greater emphasis is being placed on constructing public infrastructure, in particular bridges, using the best available technology to ensure that the resulting structures return the greatest benefit to the public at the lowest life-cycle cost. High performance concrete (HPC) has the potential both to provide extended service life and to reduce the number or size of load-carrying members, thereby increasing the return on the taxpayer’s investment in the nation’s infrastructure. The specific meaning of “high performance” depends on the concrete properties under consideration, and may or may not include strength. The Federal Highway Administration has proposed a definition for high performance concrete that enumerates several distinct categories of performance criteria for strength and durability. Based on this, many states have developed their own provisions for use with HPC because no national standard is available. To aid state highway departments and other bridge owners in effectively using high performance concrete, the Portland Cement Association plans to release Guide Specification for High Performance Concrete for Bridges in mid 2004.
The Guide Specification is intended to serve as an aid for developing specifications for high performance concrete for individual projects in all 50 states. The Guide Specification includes 11 performance criteria for high performance concrete: six durability criteria – resistance to abrasion, chloride penetration, freeze-thaw damage, scaling, sulfate attack, and alkali-silica reactivity; one workability criterion – consistency of concrete mixture; and four strength criteria – compressive strength, modulus of elasticity, creep, and shrinkage. The designer or specifier must select the criteria that are important for the specific application.
The intended user of the Guide Specification is an engineer or contractor working directly or indirectly for a state department of transportation, local highway authority, or other bridge owner. The user should be familiar with the characteristics of local materials and be aware of local durability concerns that may necessitate special measures to prevent premature deterioration of the concrete. The Guide Specification alerts the user to the types of questions that should be answered regarding local materials and exposure conditions. It is intended to be modified as needed to suit local conditions.
The Guide Specification is accompanied by a detailed commentary that provides explanatory notes, guidance for selecting appropriate performance criteria, and details about how to achieve the desired properties. It also discusses potential conflicts between criteria, such as high early strength and minimization of cracking. The intent is to provide guidance to both the engineer and contractor as to the measures that should be taken to accomplish the desired performance.
Further Information
For additional details, contact the authors at [email protected] or 847-972-9100 and [email protected] or 847-972-3148.