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2014WinShotcreteEMag

Letters to the Editor C150 restrictions/requirements, with the intention of allowing in the aftermarket of preblenders. Preblending operations the producer to widen the scope of potential materials and seldom have the capability of grinding limestone to the ultra- thereby formulate new cements with unique characteristics fine levels necessary to achieve the results shown in literature. and/or performance greater than the “parent” C150 cement. This is a main concern and must be considered. More recently, these same specifications (C595 and C1157) Jonathan E. Dongell have again been “relaxed” or “broadened” to allow producers Director of Research and Development to use greater additions of fillers/fines (both terms are used Pebble Technologies, Scottsdale, AZ in the literature and specifications) through optimization of the limestone and cement combination, to be “on-par” with the parent cement. The fact is, most literature and testing have shown that the usage of greater amounts of limestone addition, requires the “optimization” of fineness of the cement and limestone to achieve a quality of product that is “on- par” with that of the parent cement. If optimization results in a finer lime- stone cement that is equivalent to or better than the coarser parent cement while simultaneously allowing for a “greener” product, then it would be preferable in many instances. However, if we disagree on this point, then the alternative is to say we are knowingly producing an inferior product by adding limestone. Obviously, this is not the intent of the latest changes to the C1157 and C595 specifications. However, until these specifications are written in a way that assures the consumer that limestone (calcium carbonate) addi- tions are not simply “diluting,” or creating a lesser-quality product, then we have work to do. Mr. Tennis states, “Type IL PLCs are produced to meet specification ASTM C595 or AASHTO M 240 and, thus, be competitive in performance with existing cements.” Yet, no requirement in either specification requires the blended cement to be competitive in performance with existing cements. The only requirement is that the cement meets the minimum stan- dards set in the specification. Therefore, until these specifications address this issue; as I stated, and Mr. Tennis concurs, testing of limestone cements should be done to ensure satisfactory performance in the application for which it is intended. Finally, I agree with Mr. Tennis’s argu- ment that limestone ultimately grinds finer than the cement when added at the time of grinding clinker and gypsum; however, this does not necessarily occur Shotcrete • Winter 2014 13


2014WinShotcreteEMag
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