Novel Pyrrhotite Detection Method in Concrete Aggregate
Navy SBIR 2016.3 - Topic N163-137
NAVFAC - Mr. Daniel Zarate - [email protected]
Opens: September 26, 2016 - Closes: October 26, 2016

N163-137

TITLE: Novel Pyrrhotite Detection Method in Concrete Aggregate

 

TECHNOLOGY AREA(S): Materials/Processes, Sensors

ACQUISITION PROGRAM: NAVFAC Secondary Program of Record:  Facilities Sustainment, Restoration and Modernization, and NAVFAC Criteria, Non-ACAT

OBJECTIVE: The objective of this SBIR topic is to develop a portable device or test kit for analyzing the presence of “pyrrhotite” in damaged concrete structures, as well as loose aggregate before it is mixed into fresh concrete. The ultimate goal of this technology is the prevention of costly repairs and replacement of concrete structures still in their early life cycle.

DESCRIPTION: The concrete industry is increasingly recognizing the extent of structural damage caused by a deleterious presence of “pyrrhotite” mineral in concrete aggregate. Current diagnostics to detect pyrrhotite require petrographic analysis of samples in a laboratory, a costly and time consuming process. There is a need for development of a novel and portable method for detecting and quantifying the presence of pyrrhotite in aggregate and concrete while in the field.

The Navy is a large consumer of cement and aggregate for its many construction and repair projects of piers, pilings, wharves, runways, and buildings.  NAVFAC is responsible for new construction and sustainment of these facilities.  This responsibility includes design, construction, maintenance and repair services for all concrete facilities. Additionally, the NAVFAC Criteria Office is responsible for technical adequacy of all Navy shore facilities design, construction and maintenance criteria.  Pyrrhotite-related concrete corrosion may be a significant cost factor in Navy facilities sustainment, restoration, and new construction.

The Navy has issued numerous reports and guidance on Alkaline Aggregate Reaction, or AAR, and specifically ASR – Alkaline Silica Reaction in concrete, where “reactive” aggregate containing certain forms of silica combines with alkali hydroxide in the hydrated cement to form an expanding gel that breaks the concrete.  NAVFAC’s guidance on pavements and marine concrete also mention the importance of limiting sulfate content in concrete. Although the effects of sulfate attacks in concrete have been appreciated for decades, the connection to pyrite and pyrrhotite minerals has only recently (late 1990s onward) been reported and researched in-depth. This may be due to current concrete technologies greatly advancing over the past decades. Today’s formulations include a number of ingredients (admixtures) to enhance both the fresh and the hardened concrete’s properties. These advanced formulations may contribute to the recent increase in pyrrhotite-related concrete failures.

Pyrrhotite is a naturally occurring iron sulfide mineral in the particular chemical form Fe(1-x)S , where x = 0 to 0.125. If pyrrhotite is present in the concrete, then water and oxygen, already present in the hydrated cement, will foster a chemical reaction that produces expansive by-products. Numerous recent news reports of pyrrhotite-caused structural damage are emerging from the U.S., Canada, Europe, and other locations around the world, indicating the problem may be much more widespread than previously thought by the construction industry. As a timely example, the mineral has been blamed for widespread foundation cracking in thousands of homes in Quebec, Canada. Officials estimate that 4000+ homes are affected. The Prime Minister has indicated the Quebec Province is spending over $30 Million to mitigate the problem, according to the Canadian Press.

Various remedial measures for pyrrhotite related concrete corrosion have been proposed, but the long term effectiveness of such in-place remediation has not been established. For housing foundations, as an example, the only method of remediation which can guarantee a permanent solution is removal of the pyritiferous material.

A portable device or test kit would be of great benefit for analyzing the presence of pyrrhotite in existing concrete structures suspected of having pyrrhotite-related damage, as well as in aggregate received at the job-site prior to mixing. If successful, this technology would prevent concrete formulations that are “doomed to failure” from being utilized in the DoD’s, and ultimately commercial, myriad of concrete facilities.

GUIDELINES FOR NEW TECHNOLOGY:
1. Capable of operating in an outdoor field environment.
2. Capable of holding calibration for 8+ hours of continuous operation.
3. Device accuracy should provide at least one order of magnitude linearity, and be within ±5% of known values, in a range of 0.1 to 10% by weight pyrrhotite.
4. Capable of consistent, repeatable measurement even with concentration variation over the desired range.
5. Capable of directly reading and/or “swabbing” the aggregate or solid concrete sample.
6. Capable of operation in an expeditionary environment.  Such an environment for the military would include a lack of sheltering infrastructure with limited access to a reliable source of electricity and possible intemperate weather.  Marine waterfront locations would further suffer from the presence of salt spray.  Therefore, minimum environmental goals include operability in:
• Temperatures of -10 to +35-degree Celsius
• Humidity levels of 5 to 95% RH
• Water–proof electronics housing.
7. Sized for portability by one person, i.e. a maximum of 22-lbs for all components.
8. Results provided real-time or near-real-time, with a total cycle time (sampling input to result output) goal of 5-minutes per sample.
9. System availability and reliability of 1000-hours of operation.
10. Minimal external requirements, i.e. kit should include any needed chemicals, compressed air or vacuum source, and include battery operation, in addition to 110-VAC power, if electricity is needed.

PHASE I: Determine feasibility for the development of a novel pyrrhotite detection method for efficacy in a laboratory environment, utilizing known standardized levels of the mineral in both loose aggregate and in formed concrete to assess accuracy. Development of the pyrrhotite detection method must show feasibility for eventual portability and field use.

PHASE II: Based on the results of Phase I, develop and demonstrate a bread-board pyrrhotite detection device with natural aggregate and concrete samples, and compare to independent laboratory analyses provide by the government.  Assemble a full scale demo system to validate operation. Demo will be tested at a Navy facility with suspected pyrrhotite-related concrete degradation in order to prove performance.

Phase II Option, if awarded, will be used to advance the design to improve accuracy, reliability, and/or reduced system size.

PHASE III DUAL USE APPLICATIONS: Based on the results of Phase II, the small business will commercialize the device in combination with Navy-relevant concrete construction and repair projects.  Private Sector Commercial Potential: The device would have wide application across both military and commercial sectors for checking aggregate lots prior to concrete mixing and for on-site failure / forensic analysis during repair projects.

REFERENCES:

1. Hawkins, Brian A., Implications of Pyrite Oxidation for Engineering Works, Springer International Publishing, Switzerland, 2014.

2. “Mineral to Blame in Cracking Foundations”, Durability & Design Magazine, May 11, 2016.

3. Tulis, Ralph H., “Cracked Foundations Need Study by a State Task Force http://ctviewpoints.org/2015/10/08/cracked-foundations-need-study-by-a-state-task-force/ October 8, 2015.

4. “Feds to Spend $30 Million in Quebec on Mineral Problem”, Canadian Press Release, April 2016.   http://globalnews.ca/news/2622979/ottawa-to-spend-30-million-on-helping-quebec-homeowners-who-have-pyrrhotite/

5. “Pyrite Problem – Exploring the Implications of Sulfur in Geological Materials for Civil Engineering”, http://www.pyriteproblem.com

KEYWORDS: pyrrhotite, pyrite, framboid, microcrystal, concrete, sulfate, aggregate, oxidation, sulfide

 

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