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Some agencies limit the slag (ground-granulated blast-furnace slag) replacement of portland cement in some instances. In other cases, minimum slag replacements are specified. Therefore, there is a need to be able to quantify the slag content to show conformance with specifications. The two methods proposed here are (1) X-ray diffraction (XRD) of ignited mixtures and (2) optical microscopy on thin sections. The XRD method involves ignition of the mortar fraction of concrete at 950 to 1050°C to devitrify the unreacted slag. The resulting crystalline melilite component is then compared to that in an ignited sample of slag from the same source.
The optical method involves preparation of thin sections of the concrete and point counting to obtain the number of unhydrated slag grains. These are compared to a set of calibration standard sections. The optical technique can also be used for estimating fly ash content and similarly, grain mounts have been used to detect the presence of both fly ash and slag substitution in portland cements.
The paper describes both these techniques in detail and discusses limitations. When properly calibrated, either technique can be used to estimate the slag replacement level to approximately ±10%. As well, several case histories are described where these procedures have proved to be extremely useful.
Manager, Ministry of Transportation of Ontario, Soils and Aggregates Section, Toronto, Ontario
Professor, University of Toronto, Toronto, Ontario
Stock #: CCA10337J