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2014WinShotcreteEMag

Letters to the Editor I(pages 10 to 12). Portland limestone cement (PLC) provides intended or recommended for use in moderate- or high-sulfateportland cement in concrete applications. They are appropriatefor both wet and dry exposures, although they are not currently magazineShotcretewas excited to see the title of the article “Limestone Cementin Shotcrete” in the Fall 2013 issue of similar performance characteristics to Type I portland cements, exposures. A potential issue with low-temperature sulfate with reduced environmental impact (meeting the goal stated resistance of PLCs (and/or concretes made with limestone in the article). However, I believe that some misimpressions fillers) has been suggested, and the industry is proceeding might result from the article. cautiously in this regard. ASTM C595/AASHTO M 240 notes Type IL PLCs are produced to meet specification ASTM that PLCs are not used in applications requiring sulfate resis- C595 or AASHTO M 240 and, thus, be competitive in perfor- tance while additional research is being conducted. mance with existing cements. The article states that “…current I will echo the author’s recommendation that test panels ASTM standards do not require that limestone fineness be fine be fabricated to ensure that the expected and desired proper- enough to ensure a similar performance to that of the ‘parent ties of the mixture are achieved. Coupled with reviewing mill portland cement’…” This appears to be a criticism of ASTM test reports on the cement and certifications for other shotcrete C595/AASHTO M 240, which define requirements for Type ingredients, this is sound advice for any new material or IL cements with between 5 and 15% limestone. There are good mixture design. I believe that PLCs will provide suitable fresh reasons why no fineness limits for limestone (or other ingredi- and hardened shotcrete properties, including durability, ents) are included in this specification: without significant changes to mixture designs. 1. Requirements for properties such as setting time and strength For additional information on PLCs, I would be happy to will require that appropriate fineness materials be used; supply electronic copies of a relevant PCA research report and 2. Once the materials are interground or blended, there is no literature review, upon request. efficient way to determine or check the fineness or particle- Paul D. Tennis, PhD size distribution of the individual materials; and Manager, Product Standards and Technology 3. Blended cements are often interground, which changes the Portland Cement Association, Skokie, IL fineness substantially, so a limit on the original fineness of the ingredient is meaningless. References available electronically: Limestone as an ingredient in PLC is typically interground Thomas, M. D. A. and Hooton, R. D., “The Durability of Concrete Produced with portland cement clinker and sulfate. Since clinker is sig- with Portland-Limestone Cement: Canadian Studies,” SN3142, Portland Ce- ment Association, Skokie, IL, 2010, 28 pp. nificantly harder than limestone, the limestone tends to prefer- Tennis, P. D.; Thomas, M. D. A.; and. Weiss, W. J., “State-of-the-Art Report entially be ground to a finer size than the nominal cement on Use of Limestone in Cements at Levels of up to 15%,” SN3148, Portland fineness, providing the particle-packing benefits noted in the Cement Association, Skokie, IL, 2011, 78 pp. article. While there are no limits for fineness in ASTM C595/ AASHTO M 240, the Blaine fineness (ASTM C204) and 45 µm sieve fineness (C430) of the finished cement are reported Editorial Response to be unfounded, at least with regard to PLC. Tconcern being put forward is one of “buyer beware.” Thehe intent of my article was not to suggest that limestonecements are not a viable option for many projects. The are usedlimestone fillers andlimestone finesThe terms on all mill test reports, so the concern in the article would appear somewhat loosely in the article as equivalent to limestone as fact is, there is potential for a portland cement to be processed cement ingredients. This may cause confusion for the reader. with limestone in a way that lessens the quality of the “parent” Although each of these materials is similar—essentially cal- portland cement (I use the term “limestone” as ASTM Speci- cium carbonate—it is incorrect to refer to just any mixture of fications/Standards currently use the term, although I agree limestone with cement as “limestone cement.” True limestone with Mr. Tennis that “calcium carbonate content” is what we cements must meet ASTM C595 or AASHTO M 240. need to know). The statement that “overall durability of cement with lime- Again, the intent of my article was actually in support of stone filler decreases with an increase in limestone” is not correct much of Mr. Tennis’s (PCA’s) argument. Limestone cements for PLC. There is a wealth of information on PLCs used in Europe are a viable option; however, current ASTM Specifications/ and other countries demonstrating that durability issues (corro- Standards allow for, at the very least, a bad perception to be sion, chloride penetration, salt attack, freeze/thaw, etc.) are created by potentially allowing (although not intentionally) similar for PLCs and other cements and are primarily a function a lesser quality cement to enter the market. of concrete permeability (water-cement ratio, compaction, and In the past, the ASTM C150 specification for portland paste content) and other factors like adequate strength and air cement, which has more restrictive prescriptive and perfor- void systems. (For example, refer to the article by Thomas et al. mance requirements, has dominated the marketplace. In a in the December 2013 issue of Concrete International.) manner of speaking, the “bar was set” with the C150 speci- ASTM C595/AASHTO M 240 Type IL cements generally fication. Optionally, ASTM C595 and C1157 specifications provide similar strength and durability performance to Type I allow a more “relaxed” or “broadened” option to that of the 12 Shotcrete • Winter 2014


2014WinShotcreteEMag
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