Today's cement and concrete specifications are based on the 1948 work,” Long-Time Study of Cement Performance in Concrete”. While the 1948 study established early specifications, modern cements differ significantly from their 20th century counterpart’s due to market-driven needs for rapid strength gain, reduction in CO2 emission, and increased use of non-cementitious materials. Moreover, the performance of the aggregate can depend, in part, on the properties of the cement. It is increasingly difficult to extrapolate these early specification criteria to modern cements. This project will provide the industry with valid data to replace the 1948 study and foster new cement specifications. Predictive statistical models will be developed using cements from the Cement and Concrete Reference Laboratory (CCRL) proficiency test data and complementing this information with internally generated materials characterization and performance data. The resulting predictive models and cement specification limits will be validated and promoted within ASTM.
Objective - To develop and promote new ASTM standard test methods and ASTM specification limits for cement and concrete materials based upon a comprehensive assessment of mineralogical, chemical and textural properties.
What is the new technical idea? Current cement specifications are based on materials from the mid-20th century. It is increasingly difficult to apply existing criteria to modern cements because of phase-related specification limits based upon inherently biased estimates of composition and particle fineness, using outdated (70 years old) methodologies. The collective biases of these measurement technologies, simple linear models, and changes in modern cements mineralogical and physical characteristics make the historic relationships between material properties and performance tenuous. Meanwhile, aggregate constitutes up to 70 % of the concrete’s volume, and aggregate selection is important because it affects concrete performance. Despite aggregate selection based on empirical expansion measurements related to alkali-silica reactivity (ASR) and a petrographic analysis, there are still cases of failure due to ASR. This project will provide methodologies to base the selection on detailed characterization of the aggregates, including mineralogy and microstructure and their influences on ASR potential. This information is necessary to establish methodologies and database of materials properties that could be used for new engineered material selections, forming the basis for new screening practices and standard specification limits.
This project will address two constituents of concrete: the cement and the aggregates. To examine the cement, a large volume of cement performance data available from the Cement and Concrete Reference Laboratory (CCRL) proficiency program will be utilized. This program includes results from ASTM standard tests for 38 chemical and physical test results on over 100 cements from over 200 laboratories. These same cements were used in the concrete testing program, comprised of eight tests from over 300 laboratories. Using direct measurements of cement phase and texture characteristics by X-ray diffraction, electron microscopy, and laser diffraction, these cements will be analyzed to identify all crystalline phases and polymorphs, and the results correlated to performance from the CCRL data. These results will provide more comprehensive and accurate estimates of compositional and textural characteristics of cements compared to the currently applied Bogue method in cement specifications. These data form the basis for robust predictive statistical models, with priority placed in developing statistical models for heat of hydration, setting time and sulfate resistance.
Aggregates are typically characterized by sieve size distribution and general rock classification (limestone vs. granite). This limited classification scheme has restricted the development of relationships between material characteristics and performance in key areas, including alkali-aggregate reaction (AAR). Guides and standardized test methods for a detailed characterization of aggregate mineralogy will provide a more comprehensive assessment of aggregate characteristics for durability. Ultimately, a priori characterization of the aggregates will permit a more accurate prediction of their potential performance in various concrete mixtures.
What is the research plan? Project efforts are focused on the following three areas: 1) testing for cement performance in sulfate environments, 3) data management for cements and aggregates and 4) development of statistical models relating physical and mineralogical characteristics to performance.