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Early-Age Performance of Concrete Project

Summary:

Successfully delivering the desired early-age performance of concrete, upon which long-term prediction of sustainable performance depends, requires careful selection of mutually compatible constituent materials, understanding and using the rheological properties of concrete to assure flow and pumping performance, and proper curing of the concrete, all guided by accurate prediction of in-use concrete performance. This project will remove major technical barriers to successful delivery of the desired early-age performance of concrete. One major thrust of this effort is to identify the factors governing the interactions of fly ash with cement and to subsequently develop the measurement science and technology to characterize those factors. This new measurement capability will include quantitative X-ray diffraction, X-ray fluorescence, and optical emission spectroscopy methods for characterizing the composition of cement and pozzolans, and it will lead to the development of new standards and practices for high-volume fly ash binders. A second major thrust is to assure the accurate utilization of concrete flow properties by developing standard reference materials and accurate models that support the standardized use of commercial concrete rheometers.

Description:

Objective: By FY2014, to enable industry to deliver the desired early-age performance of concrete by developing the measurement science basis for new standards for characterizing and classifying the interactions of fly ash with portland cement, and developing a suite of standard reference materials, standards, and models for calibrating concrete rheometers.

What is the new technical idea? Unexpected behavior of current concrete mixtures often can be attributed to unanticipated interactions during construction or during the strength-gaining phase of the chemical reactions. The desired early-age performance of concrete can be reliably achieved only by: (1) carefully selecting mutually compatible constituent materials, including cement, industrial by-product materials like fly ash, sand, gravel, and chemical admixtures; (2) properly quantifying the rheological properties of concrete to assure flow and pumping performance; and (3) properly curing in-place concrete (this item was completed in an earlier project). To base these three aspects of assured delivery on sound engineering principles, they must be guided by accurate predictions of in-service concrete performance. The first two of these areas will be addressed in this project. Chemical interactions between pozzolans and portland cement can lead to unreliable setting and strength development. This project will identify the factors that affect these interactions through the new technical idea of simultaneously monitoring the chemistry of the solution phase, which mediates the chemical reactions, and the evolution of solid phases responsible for strength development. This new technical approach will lead to suite of tests that can be the basis for new standards and practices to guide the reliable selection and use of high-volume fly ash components. Furthermore, assuring the early-age workability of fresh concrete will be accomplished by the new technical idea of combining multi-scale computer simulation of concrete flow with the delivery of new Standard Reference Materials (SRMs) with reproducible flow properties. This combination of simulation and SRMs will provide the capability of calibrating industry rheometers and establishing critical links between rheometer output and flow properties.   The experiments will validate the models, and provide the data required to promulgate new standards.

What is the research plan?  The research plan is divided in two main thrusts: 1) characterize and model the interaction of of fly ash and cement, and 2) develop mortar and concrete rheology standard reference materials and standards using a combination of experiment and rheological models.

X-ray diffraction (XRD), X-ray fluorescence (XRF), field emission scanning electron microscopy FE-SEM), isothermal calorimetry, and optical spectroscopic analysis of leachate solutions will be used to track the chemical and structural development in cement + fly ash paste microstructures. The goal is to identify a critical set of fly ash material parameters that will enable forecasting of undesirable interactions in proposed mixes that lead to delayed setting or poor strength development, and to identify the relative reactivity of its constituent mineral and glassy phases. Improved fly ash characterization that is relevant to its compatibility with cement binders is a measurement capability gap in materials characterizations identified at a 2010 FHWA workshop[1]. Bulk chemical component proportions are principal classification criteria in ASTM C618, which may be traced back to ASTM C114. However, no archival basis exists for either the qualification criteria for C114 or for the analysis of pozzolans. Establishing the precision and bias of quantitative XRF analysis on hydraulic cements is prerequisite to evaluating this analytical method’s performance on fly ash and other pozzolans.

The measurement methods and simulation tools that will be developed will apply directly to concrete binders containing crushed waste glass, which is a potential industrial by-product material that is available in quantities comparable to the annual usage of fly ash in concrete. This will be the subject of a new project in FY15.

Rheometer response is sensitive to the flow geometry and operating principles of the instrument, and the response often is not related directly to any one rheological property of the mixture. Therefore, rheometer behavior must interpreted using a combination of accurate simulations and standard reference materials (NIST term is SRMs). Rheometers based on vane geometry are the most commonly used rheometer geometry used in industry, so the unique NIST capability of accurately simulating flow in a realistic vane rheometer will be essential for interpreting the rheological parameters obtained from these instruments as they are used in the industry. Building upon the recent development of SRM 2492 for cement paste rheology, the mortar SRM will be finalized in FY14 and the concrete SRM will be produced and validated using a combination of modeling and experimental measurements. The “sand” and “gravel” for the mortar and concrete SRMs is comprised of small and large glass beads. Inter-laboratory studies will be organized to ensure industry impact in collaboration with the American Concrete Institute (ACI) Technical Committee 238 the CRÈME consortium and to ensure that this approach is in line with the roadmap developed in the workshop conducted at NIST [2] and is converging toward this integrated vision of future construction. 

[1] Steps Needed in the Research & Development of New Specifications for the Proper Inclusion of Fly Ash into Concrete Mixes for Highway Pavements and Other Transportation Structures. Summary Report of the Fly Ash Workshop Held at Turner-Fairbank Highway Research Center, September 29-30, 2010. 

[2] Ferraris C.F., Martys N.S., “Measurement Science Roadmap for Workability of Cementitious Materials, Workshop Summary Report”, NIST TN 1704, March 2011

Major Accomplishments:

Technology Transfer Outcomes in FY13

  • All materials for a new Standard Reference Material for mortar rheology were provided to Measurement Service Division for packaging.
  • Precision and accuracy qualification criteria on XRF analysis for two different methods using portland cements was provided to the ASTM C01.23 subcommittee. This is an essential step to ensure that a standard test method “X-ray Fluorescence Analysis of Hydraulic Cement“ will be accepted by ASTM and used by all cement manufacturers.
Impacts: 

 FY12:

  • ASTM C1738-11a Standard Practice for High-Shear Mixing of Hydraulic Cement Pastes, which is already widely accepted by both research laboratories and industry.
  • ASTM C1749 - 12 Standard Guide for Measurement of the Rheological Properties of Hydraulic Cementious Paste Using a Rotational Rheometer
Major Products: The major products from this project are two standard test methods for cement paste rheological characterization, two SRMs in the series of SRMs for rheological properties for granular materials (mortar and concrete, based on SRM 2492), the precision, bias and qualification criteria for a new standard test “Standard Test method for X-ray fluorescence analysis of portland cement”, and a test protocol for real-time monitoring of cement and cement-blend hydration based on the new knowledge generated by a combination of advanced experimental methods.
cementitious material workshop cover

Start Date:

October 1, 2011

Lead Organizational Unit:

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Staff:

Project Leader: Dr. Chiara F. Ferraris

 

Contact

General Information:
Dr. Chiara F. Ferraris, Project Manager
301-975-6711 Telephone

100 Bureau Drive, M/S 8615
Gaithersburg, MD 20899-8615