Measurement Science to Assure the Performance of Green Concretes Project

Summary

An effective strategy for making a more "green" concrete is to replace the portland cement (the binding component with large energy and CO₂ footprints) with industrial by-products (IBP) such as fly ash, blast furnace slag, and waste glass. Major questions exist, however, in assuring the performance of these concretes, as evidenced by the fact that the industry-average portland cement replacement in ready-mix concrete was only 18% in 2008, despite the availability of tens of millions of tons of IBP materials that end up in landfills each year. This project will overcome the measurement science barriers to increasing the percentage of IBP in concrete by providing the industry with the metrics and guidance for the design, construction, and durability of green concrete. This work, done in partnership with concrete specifiers, producers, contractors, and owners, will provide the knowledge base to confidently use these more sustainable concretes.

Description

Objective: To develop and deliver the measurement science identified by industry for assuring the performance of Industrial-by-Product (IBP) low-carbon footprint concretes with up to 50% by mass of the cement replaced by IBPs by 2015.

What is the new technical idea? The industry average cement replacement cannot increase significantly without new measurement science to ensure the performance of concretes made with up to 50% IBP materials. This is because the chemistry of an IBP material begins to dominate the chemistry of the portland cement, which can impact the constructability and durability of these blended systems. Because the chemical behavior of IBP materials is not fully understood, variations in the IBP material properties from multiple sources, or even from a single source, can have unanticipated consequences, and correcting for these changes becomes particularly challenging. Furthermore, too little is known about the relative robustness of these blended concrete materials during construction and while in service, and whether the current standard tests accurately reflect the performance of these blended systems.

NIST will design, develop, and operate a Green Concrete Performance Laboratory (GCPL) that is unique in the world. This facility will allow precise measurement and control of external and internal factors (e.g., environment, chemistry) that affect concretes containing up to 50% IBP materials so that standard tests and industry best practice guides can be developed that account for the unique properties of these materials.

NIST will also partner with industry stakeholders to develop a Best Practices Guide for the design and use of concretes containing up to 50% IBP materials. The guide will assist designers, producers, contractors, and specifiers, and it will be revised annually to incorporate new advances, both at NIST and elsewhere.

What is the research plan? NIST has partnered with industry to identify and prioritize the measurement science barriers that prevent the development, specification, and acceptance of blended cement concretes with high cement replacement levels. This partnership included participation from industry, federal agencies, and NGOs representing owners, specifiers, producers, and contractors. Partnership feedback was then used to create a roadmap for developing and delivering the measurement science to assure the performance of concretes made with up to 50% IBP.

There were four critical measurement science needs identified in roadmap. The first is an industry guide for volumetric-based mixture designs because the density of IBP materials are typically more than 10% less than that of portland cement. The second is improved standardized specifications for those IBP materials like fly ash that contain both crystalline minerals and glassy phases, as the current test methods do not provide critical information related to the performance of these materials. The third is a field test to predict the setting time because unanticipated fluctuations in material properties or the weather can result in excessive setting times, which can incur significant construction costs and can erode confidence in the specification and use of Green Concretes. The fourth is improved standard test methods for the deicer scaling performance of Green Concrete because some of the existing limits on portland cement replacement are based on tests that did not use modern concrete mixtures nor the types of deicer chemicals that are typically used today.

To meet these roadmap goals, NIST will develop a Green Concrete Performance Laboratory (GCPL) to support quality assurance testing for constructability and durability. The facilities will enable quantitative performance tests of concrete and its constituent materials, along with performance tests for its paste and mortar fractions. The laboratory will also include facilities for controlling the exposure environment and the means for monitoring both the material and its environment. In addition to the activities within the GCPL, NIST will seek opportunities to collaborate on complementary work at partnering organizations.

A critical component to assuring success is communicating results to the entire concrete construction industry. NIST will develop guides that practicing engineers can use to rapidly develop and evaluate new blended cement concretes. NIST will also work with the industrial partners in this project to develop and promulgate new test methods and standardized guides.

Major Accomplishments

Outcomes:

• The workshop report, "Measurement Science Needs for the Expanded Use of Green Concrete," (NIST Technical Note 1783) was featured in a NIST TechBeat article, and has resulted in a phone interview by a writer for Kiplinger magazine.
• ACI Committee 211 is in the process of publishing a technical note on a mixture proportioning method that will include both mass-based and volume-based proportioning options.
• Publication through WERB: Farnam, Y., Bentz, D., Sakulich, A., Flynn, D., and Weiss, J., "Measuring Freeze and Thaw Damage in Mortars Containing Deicing Salt Using a Low Temperature Guarded Comparative Longitudinal Calorimeter and Acoustic Emission (AE-LGCC)," that reports on a new experimental technique allows the simultaneous monitoring of phase changes and damage within a freezing/thawing specimen and should be useful for examining performance of green mixtures.