Horizontal/Subsurface Infrastructure & Transportation

We have been using 25% Type F Fly Ash as a cementitious replacement factor for all concrete pavements in our area. The results have been great with respect to early strength development, ultimate strength achieved, mitigation of ASR and (we think) increased abrasion resistance. The industry is in a panic about future supplies. If anybody has direct experience with using slag cement, silica fume or metakaoline for any/all reasons listed, please share. - #SCM Seeker

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Michael Elwardany
Raleigh NC

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Great and very timely question Michael. I look forward to monitoring the chatter that this may generate.

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Richard Boudreau P.E., M.ASCE
Civil Engineer
Boudreau Eng Inc
Norcross GA
(404) 388-1137
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I would need to know if it meets FAA specs as to Alkalinity. This lack of meeting the FAA spec. is the reason for most paving concrete failures. The aggregate has to meet spec also. But one thing at a time.

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Robert Hinton P.E., M.ASCE
Consultant
Tulsa OK
(918)637-6513
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GGBFS, or Granulated ground blast furnace slab has most of the attributes of flyash, except for the enhanced early strength.  It increases durability, reduces ASR, reduces permeability and enhances ultimate strength, but does have a slower strength gain than flyash.  ACI recognizes it's benefits for increased durability through reduced ASR and increased ultimate strength.  Here in the mid-Atlantic area, slag has almost entirely replaced flyash in ready mixed concrete, and slag cement blends are very common in low permeability grout mixes.

However, with the significant reduction in iron and virgin steel production in North America, slag's availability may be in jeopardy within a decade or so.

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Paul Blakita
QA/QC Engineer
Maryland
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Tom Adams can help you:

Thomas Adams, P.E., P.Eng

TAdams@...

(775) 219-9403

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Ed Hendrick, PE, GE, RG, CEG
Principal Geotechnical Engineer
ACE Quality Control
Roseville, California
(916) 742-5096
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ISG Resource/Engineering, in Kennesaw, Georgia may be able to help you (770) 424-1900. They are an in-house engineering subsidiary of a Headwaters Incorporated. I have not had contact with them in several years, but they have a long history in the fly ash industry, and in the past they did R&D on the use of several types of industrial by-products in construction materials. They had several experienced experts on staff, and Dr. Minkara would be a good resource.

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Christopher Davis P.E. (GA, AL, NC), M.ASCE
Owner
CD Technical Services
Harrison TN
(423)413-9297
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Original Message:
Sent: 02-23-2017 16:59
From: Curtis Hendrick
Subject: Type F Fly Ash

Tom Adams can help you:

Thomas Adams, P.E., P.Eng

TAdams@...

(775) 219-9403

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Ed Hendrick, PE, GE, RG, CEG
Principal Geotechnical Engineer
ACE Quality Control
Roseville, California
(916) 742-5096
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I agree with the concern about future supplies of fly ash and slag cement.  Environmental regulations are moving the power industry away from coal fired power plants.  The demise of the domestic steel industry means slag cement will come from steel furnaces offshore.   Other SCMs, such as silica fume and volcanic ash may be used in some locals and some applications.  For more information you should consult the American Concrete Institute's Manual of Concrete  Practice.  ACI 325.9R-15 Chapter 4 has a brief discussion of SCMs commonly use in pavements. 

Over the past ten years or so FHWA has sponsored a great deal of research into prevention and mitigation of ASR.  The specifications and guidance documents can be found on the FHWA website.

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Jon Mullarky P.E., F.ASCE, FACI
Chester MD
(410) 604-3502
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Some of our fly ash sources in North Texas are going away due to EPA requirements to inject activated carbon into the flue gas stream in order to remove mercury.  Type C ash is more common here but that may change as supplies dry up and air standards change.

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James Anderson P.E., M.ASCE
Project Engineer
North Richland Hills TX
(817) 485-6408
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We used 100% class F fly ash as cementious replacement and we achieve strength more than 80MPa. But I am also very suspicious about future of fly ash based GPC. Because in India also government is reducing use of coal. So I also think that fly ash based GPC has no future now.