Engineers for state departments of transportation (DOT) throughout the United States have used fly ash and ground granulated blast-furnace slag (slag cement) as a partial replacement for portland cement in concrete production for many years. However, the main thrust of their usage has been to comply with the Resource Conservation and Recovery Act (RCRA) mandate for the use of by-product materials in federally funded projects. Few attempts have been made to optimize the use of fly ash or slag cement to produce concrete mixtures that meet specific performance objectives. Instead, the strategy has always been to produce concrete mixtures that exhibit performance similar to mixtures employing only portland cement. With the growing availability of slag cement and silica fume, and the limited supply of fly ash in some markets, the selection of materials for any given job has become more complicated. Supplementary cementitious materials (SCMs) have the potential to dramatically improve the overall performance and lower the long-term (life-cycle) cost of concrete. However, this assumes that the various materials have been used properly. Some believe that the introduction of fly ash and slag cement, as a cement replacement in concrete, has resulted in the following problems: · Rapid slump loss · Unstable air content or inability to retain air · Uncontrolled cracking with late season paving · Unfriendly or hard to work mixtures · Inability to predict workability and set time in early or late season construction · Scaling in mixtures containing high dosages of SCMs Closer inspection of the list and the technical literature suggests that the root issues appear to be related to constructability, ambient weather problems, proportioning of cementitious materials, and materials variability problems. However, some detailed discussion with appropriate materials vendors is needed to clarify the reasons for the real or perceived problems and to design solutions that optimize multiple cementitious systems for transportation concrete. There are currently several ongoing research projects in this area. The Pennsylvania DOT and an industrial consortium have been working with Pennsylvania State University on optimizing performance in bridge deck concrete, using both binary and ternary blends of SCM (4). The Texas DOT has conducted detailed studies on optimizing fly ash and portland cement combinations for selected performance characteristics (5). On a national level, the FHWA initiated a major project (Task 64) that will help simplify job-specific mix design when multiple sources of materials are available. Also, the NCHRP has two projects that are currently in progress that deal with SCMs. The first project is entitled "Supplementary Cementitious Materials to Enhance Durability of Concrete Bridge Decks (project 18-08A)." The second project is entitled "Improved Specifications and Protocols for Acceptance Tests on Processing Additions in Cement Manufacturing (project 18-11)."

The goal of this project is to provide the quantitative information needed to make sound engineering judgments pertaining to the selection and use of supplementary cementitious materials in conjunction with portland or blended cement. This will lead to a more effective utilization of supplementary materials and/or blended cements enhancing the life-cycle performance and cost of transportation pavements and structures. The efforts of this project will be directed at producing test results that support the following specific goals: · Provide quantitative guidance for ternary mixtures that can be used to enhance the performance of structural and pavement concrete · Provide a solution to the cold weather issues that are currently restricting the use of blended cements and/or supplementary cementitious materials · Identify how to best use ternary mixes when rapid strength gain is needed · Develop performance-based specifications for concrete used in transportation pavements and structures

The purpose of this research project is to make a comprehensive study of how SCMs can be used to improve the performance of concrete mixtures. This is an enormous task because the study must incorporate both portland cements and blended cements. In addition, it is desirable to include several samples of each type of supplementary cementitious materials (fly ash, slag, and silica fume in this instance) so that the material variability issue can also be addressed. Several different sources of portland cement and blended cement also need to be included in the experimental program. This causes the experimental matrix to grow rapidly, and, hence, the proposed project will be conducted in three different phases. In addition, a brief literature study will be conducted to close some of the knowledge gaps that exist in the research plan. The literature study will include making contact with state DOTs that have already utilized ternary mixtures in field work (for example, Ohio DOT, New York DOT, Pennsylvania DOT, Iowa DOT) to discuss practical concerns about field applications. The effort expended in the three different phases will not be uniform. Most of the effort (and monetary resources) will be directed at Phases 2 and 3. The thrust of this project is to get to the field concrete studies. Phase 1 will simply serve as a filter to identify materials combinations that will not perform adequately. The first phase will consist of laboratory experiments that study the influence of various proportions of cement, slag, silica fume, and fly ash on specific properties of mortar specimens. The Phase 1 testing program will use a wide range of different materials and many different dosage levels. Test results will be evaluated to locate potential optimums in the various test responses. Chemical admixtures (water reducers) will be included in this phase of the study to compare how setting and strength gain behavior of the mixtures varies with chemical admixture dosage and SCM dosage. All of the materials used in the study will be subjected to bulk chemical and physical testing in accordance with the appropriate ASTM or AASHTO specifications. In addition, X-ray diffraction and thermal analysis will be used to determine the minerals present in the bulk samples and selected paste specimens. Glass content of the various SCMs and blended cements will also be estimated using X-ray diffraction. The second phase will use the information obtained from Phase 1 to select a reasonable range of materials and dosages for use in laboratory concrete mixtures. Again, the thrust of the experimentation is to replicate optimum mixtures that were obtained from Phase 1 of the laboratory study. The materials used in both phases will be identical so that the mortar test results can be directly compared to the test results obtained from concrete test specimens. This comparison is needed so that the research project provides information pertaining to the selection of appropriate quality control tests. It would be very desirable to find out that quality control testing could be conducted on mortar specimens rather than on full-scale concrete specimens. The third phase will be a field demonstration phase where contractors and states will have on-site technical support for using ternary mixes. The PCC Center's mobile research laboratory will participate in at least one project for each participant state.

Commitment request (12 states): $75,000 over 5 years @$15,000 per year