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Long Term Performance of Concrete Project

Summary:

Sustainable concrete construction design for durability requires performance-based metrics of expected durability and service life prediction. Implementation of both design for durability and performance-based standards and specifications is limited by: 1) the lack of rapid, science-based, simple test methods for characterizing transport properties and degradation resistance of concrete, 2) a lack of understanding of the influence of concrete cracking on long term performance, and 3) a lack of innovation in approaches to producing durable concrete. This project will address these deficiencies in a comprehensive and timely manner by the end of FY2014.

Description:

Objective: To facilitate the realization of performance-based standards and design for durability as accepted components of the concrete specification and design process, by meeting the critical measurement science needs to design, predict, and achieve the targeted long term service life performance of concrete by 2014.

What is the new technical idea? 

The concrete industry initiated a move to performance-based standards and design for durability in 2002 with its Prescriptive to Performance (P2P) initiative, spearheaded by the National Ready Mixed Concrete Association (NRMCA).[1] Implementation on even a limited scale has not been achieved due to the lack of critical performance metrics for characterizing durability and the nonexistence of a durability design code.[2] This project is taking a three-pronged approach to accelerate the realization of design for durability and performance-based standards and specifications: 1) champion standardization of needed test methods to assess the transport properties and degradation resistance of concrete and its component materials, 2) develop a fundamental understanding of the influence of cracking on transport properties and durability that is necessary to support and extend existing service life models, and 3) demonstrate the NIST VERDiCT technology, an innovative new paradigm for producing durable concrete mixtures with increased service life. This approach will provide the tools necessary to design and evaluate new and existing concrete structures, helping to lay the foundation for the comprehensive development of performance-based standards. To achieve maximum impact, these efforts will be focused on producing end-user deliverables (standards, specifications, demonstration projects, and hardcopy and web-based guidance documents) through strategic partnerships and opportunistic leveraging of previous and ongoing efforts.

What is the research plan?  

As the project enters its third and final year, efforts will be highly focused on achieving tangible and industry-critical results. Each of the three major focus areas of the project will be brought to fruition, providing the industry with 1) new measurement methods for transport properties for performance characterization and service life prediction, 2) a quantitative understanding of the impact of transverse cracking on concrete service life and the robustness of various strategies for increasing said service life, and 3) a demonstration of innovative approaches to increasing concrete service life under a variety of common degradation scenarios.

The operation center for the first objective will continue to be the ASTM C09 Concrete and ASTM C01 Cement committees and their various subcommittees. In ASTM C09.66, ongoing standardization activities being championed by project personnel include new standards for concrete’s drying rate and electrical resistivity (the latter using a four-point probe). Draft standards for each of these have been completed, including the critical task of establishing initial precision and bias statements. Balloting is ongoing in FY13 at the subcommittee level and it is envisioned (hoped) that during the last year of this project, both will be approved as new standards by the main ASTM C09 committee. This push towards final acceptance will be facilitated by Dr. Snyder’s anticipated new role as the chair of ASTM C09.66 beginning in June 2013.

Another ongoing standardization activity concerns a new mini-bar test method for evaluating the sulfate resistance of cement paste specimens (originally developed by Ferraris et al. in a project funded by the Portland Cement Association, it is significantly faster than the existing ASTM C1012 mortar bar test). While the specimen configuration (mold, pins, etc.) was optimized in FY13, it was also discovered that using a simple 7 d room temperature curing period for systems with and without supplementary cementitious materials (SCMs) did not provide a proper indication of the SCMs’ improved performance. Thus, in FY14, an appropriate curing procedure for providing a fair comparison of a wide variety of cementitious binders will be developed, validated, and incorporated into a new revision of the draft standard that will then be considered by the ASTM C01.29 Sulfate Resistance subcommittee.

Regarding the influence of cracking on concrete service life, efforts during the first two years of this three-year project have focused on the development and validation of a two-dimensional model for the influence of transverse cracking (above the concrete reinforcement) on concrete service life. These results have been documented in both an award-winning conference paper and an archival journal paper. In FY14, following up on further simulations conducted late in FY13, this new modeling approach will be applied to the practical issue of the robustness of various existing strategies for increasing concrete service life. While many approaches are employed in practice, including high performance concrete, increased cover depths, epoxy-coated reinforcement, corrosion inhibitors, and sealants, the robustness of these approaches with respect to transverse cracking is unknown. The two-dimensional model will be applied to predict the reduction in expected service life for each of these strategies when transverse cracks are present in a field structure. This practical performance information will be disseminated to the concrete community via publication in an archival journal.

The third goal of this project has been to demonstrate innovative approaches to increasing concrete service life under the most common degradation scenarios (corrosion, sulfate attack, etc.). In FY13, NIST results were published indicating the substantial benefits of both internal curing and viscosity modifiers (VERDiCT) for decreasing expansion due to sulfate attack of mortar bar specimens. As both of these approaches have been previously demonstrated to offer performance benefits by reducing chloride ingress in corrosive environments, the sulfate attack study has extended the range of application of these new paradigms for producing durable concrete. FY14 efforts in this area will focus on further dissemination and promotion of these technologies to the concrete construction industry, including the development by the project leader of an ACI Educational Activities Committee (EAC) webinar, in both English and Spanish, highlighting the recently released ACI (co-authored by NIST personnel) report on internally cured concrete; this activity is in response to a direct request to the project leader by the EAC.

 

[1] Bickley, J.A., Hooton, R.D., and Hover, K.C., “Preparation of a Performance-Based Specification for Cast-in-Place Concrete,” RMC Research & Education Foundation, Phase 1 Final Report, 2006.

Obla, K.H., and Lobo, C.L., “Experimental Case Study Demonstrating Advantages of Performance Specifications,” RMC Research & Education Foundation, 32 pp, 2006.

Hover, K.C., Bickley, J.A., and Hooton, R.D., “Guide to Specifying Concrete Performance,” RMC Research & Education Foundation, 39 pp, 2008.

[2] ACI ITG-8R-10 “Report on Performance-Based Requirements for Concrete,” American Concrete Institute, Dec. 2010.

 

Major Accomplishments:

Recent Results:

Technology Transfer Outcomes in FY13

  • NIST-proposed changes approved by ASTM forASTM C1585-13 Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic-Cement Concretes.
  • American Concrete Institute (ACI) published ACI (308-213)R-13---Report on Internally Cured Concrete using Prewetted Absorptive Lightweight Aggregate, co-authored by project PI. Internal curing is of great benefit to both the early-age and long term performance of concrete structures.

Major Product: A suite of standard test methods critical for a complete and comprehensive characterization of the transport properties of concrete with respect to the service life prediction and quality control requirements of the construction community.<

Simulating the influence of a surface crack&nbsp; on road salt penetration into a concrete&nbsp; pavement (from the top down)
Simulating the influence of a surface crack on road salt penetration into a concrete pavement (from the top down). This image (14 mm wide, 45 mm high) shows road salt concentrations.

Start Date:

October 1, 2011

Lead Organizational Unit:

el

Staff:

Project Leader: Dale P. Bentz

Contact

General Information:
Dale P. Bentz, Project Leader
301-975-5865 Telephone

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