Comparative Durability and Corrosion Resistance of Low Carbon, Chromium Microcomposite Steel – 100 Year Modeling

By AZoM

Table of Contents

Introduction
Basis of Durability Design
     Reinforcing Steel Option Assessment
     Concrete Durability Assessment
     Exposure Conditions
     Service Life Modeling
Bridge Model
Definition of Service Life
Prediction Methods
     Demonstrated Effectiveness
     Modeling of the Deterioration Process
     Laboratory Testing
MMFX 2 Concrete Reinforcing Steel Bars
Conclusion
About MMFX Technologies

Introduction

MMFX Technologies Corporation had contracted Tourney Consulting Group (TCG) to evaluate the 100 year life cycle cost analysis of MMFX 2 (ASTM A1035/AASHTO MP 18) reinforcing steel in a bridge exposed to marine pile and deicing salts. The aim of this durability assessment is to compare the service life cost of MMFX 2 bars with other types of concrete reinforcing steels and also to establish that MMFX 2 reinforcing steel can meet the 100-year durability design needs.

Basis of Durability Design

The goal of this project is to acquire a 100-year service life without any structural repairs for the standard structures selected. The durability assessment is built on service life modeling of the concrete using a software program, STADIUM. The assessment included the following components:

Reinforcing Steel Option Assessment

The costs and physical properties of reinforcing steel alternatives were analyzed. These alternatives included MMFX 2 ASTM A1035 microcomposite reinforcing bars, standard ASTM A615/A706 black bars, epoxy-coated reinforcing bars ASTM A775, SS2304 ASTM A995 stainless steel reinforcing bars, and galvanized reinforcing bars ASTM A767.

Concrete Durability Assessment

Criteria such as concrete strength and environmental exposure challenges were evaluated by TCG to determine the characteristics of concrete mixture needed for this project. The mixture characteristics were then utilized to find preliminary model input values by utilizing concrete mixtures database, which offers preliminary ion transport properties for use in the STADIUM software.

Exposure Conditions

Local climate conditions and exposure were analyzed and the results were applied to the service life prediction model.

Service Life Modeling

TCG studied the alternative reinforcing steel options, exposure conditions, and concrete durability assessment in STADIUM simulations to develop solutions that will offer 100 years of service life for the structure. Concrete properties without cracks were utilized for the simulation.

Bridge Model

The bridge model represents a typical structure in the Midwest United States where the bridge crosses fresh water and deicing salts are used. The concrete in the bridge is subjected to two main environmental conditions: Deicing zone exposure refers to the area of the bridge subjected to deicing chemicals, which are utilized in winter conditions to keep the bridge open for vehicles; and Immersed or Splash zone exposure is the area of the bridge that remains permanently in the river, or anticipated to be exposed to changing river level.

It should be noted that performance in this zone is mainly related as to how well the concrete is resistant to erosion, sulfate or potential ASR attack, and hence it will not be taken into account in modeling the performance of corrosion resistant reinforcement.

As MMFX 2 has been added to improve the corrosion resistance, the analyses will focus on the concrete deck which is subjected to severe exposure. A schematic of a standard concrete deck, as modeled in the STADIUM program, is shown below.

Figure 1. Typical concrete bridge deck in the Midwest.

Piles at the immersed or splash zone location are severely exposed to marine environments. A characteristic pile in a marine application, as modeled in the STADIUM program, is illustrated below.

Figure 2. Piles in marine application.

Definition of Service Life

The service life objective is defined as 100 years without structural concrete spalling in key structural elements. In this report, service life considers the effect of corrosion of reinforcing steel in the concrete bridge deck as a result of deicing salts and corrosion of the outermost steel in the pile for soil or marine applications.

Over the life of a structure, reinforced concrete undergoes three stages of degradation with respect to corrosion. These stages include corrosion initiation, corrosion propagation, and repair.

Figure 3. Corrosion service life.

Figure 3 shows the degradation for the three stages. For the structures considered in these studies, the end of stage two defines the end of service life.

Prediction Methods

Prediction methods include demonstrated effectiveness, modeling of the deterioration process, and testing. In this report, the methods to assess service life are based on these three methods and comprise understanding and application of the principles of building and materials science.

Demonstrated Effectiveness

In demonstrated effectiveness, historical performance of similar concrete components is used in similar environments to assess the service life of concrete members as well as corrosion protection alternatives in the future.

The historical perspective identifies synergies gained from combined systems, weaknesses in systems, and engineering strategies. However, this method cannot be employed for new materials or construction practices.

Modeling of the Deterioration Process

Modeling the time to corrosion initiation induced by chloride ion contamination was simulated using the STADIUM software program. This tool enables users to assess the expected service life of new concrete mixtures and materials, and can be utilized to model the effect of fluctuating conditions in "what if" scenarios.

Laboratory Testing

Laboratory testing to confirm corrosion resistance criteria and concrete property estimates is important to verify service life predictions. TCG conducted testing to validate the ion and moisture transport property for standard concretes employed in these applications, and studied reinforcing steel testing programs to substantiate model inputs.

MMFX 2 Concrete Reinforcing Steel Bars

MMFX Steel Corporation supplies MMFX 2 steel bars, which are uncoated, high-strength, corrosion-resistant steel-reinforcing products. These products meet ASTM A 1035/A 1035 M specifications and AASHTO Standard Specification MP 18M/MP 18. The combination of manufacturing process and alloy composition provides improved strength and corrosion. The table given below shows the material composition of a typical heat, and also the ASTM and AASHTO specifications.

Table 1. MMFX 2 (ASTM A1035/AASHTO MP 18) material composition.

Figure 4. MMFX 2 Fine grain martensitic structure.

Figure 5. ASTM A 615 Grade 60 showing a perlite grain structure with ferrite present along some grain.

Conclusion

Various technical reports were reviewed for MMFX 2, stainless steel, galvanized, and epoxy-coated reinforcing steels. The STADIUM analysis identified more than 100 years of service life for MMFX 2 microcomposite and stainless steel when utilized with premium concrete for concrete elements subjected to chlorides.

Galvanized steel could meet the 100-year service life requirements, however high concrete cover is required when compared to MFX 2 and stainless steel. Epoxy-coated bars and black steel failed to meet the 100-year requirements.

About MMFX Technologies

MMFX Technologies Corporation, headquartered in Irvine, California, is a material science company focused on commercializing its patented micro- and nanotechnologies that enable the manipulation of steel microstructure to derive optimum product properties. The nanotechnology is protected by six U.S. patents and related filings in approximately 50 countries/regions. Importantly, the patents cover both the manufacturing process and unique microstructure of the steel.

MMFX Technologies Corporation has successfully commercialized its groundbreaking science through the marketing and sale of its high-demand MMFX2 branded products, uncoated concrete reinforcing steels that provide superior strength and corrosion resistance. MMFX2 is marketed and sold through its two operating subsidiaries, as well as Portland, Oregon-based licensee, Cascade Steel Rolling Mills.

This information has been sourced, reviewed and adapted from materials provided by MMFX Technologies Corporation

For more information on this source, please visit MMFX Technologies Corporation.

Date Added: Jun 7, 2013 | Updated: Jun 11, 2013
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