Characteristics and pozzolanic attributes of opaline sandstones of the Serra de Itaqueri, São Paulo, Brazil

Abstract

Opaline sandstones of the Itaqueri Formation are considered natural pozzolans because their reaction with cement yields pozzolanic reactivity indexes in the range of 79% and 90%, which is much higher than the lower limit of 75% established by Brazilian standards (ABNT, 1992a). These rocks have been found during exploration campaigns in the region of Itaqueri da Serra - São Paulo State, Brazil. Analytical work revealed their intrinsic mineralogical attributes that, in addition to lithostratigraphic and tectonic characteristics, give important prospection guidelines for opal mineralization in the Paraná Basin. This paper discusses the classification of natural pozzolans according to their origin and emphasizes the importance of the Itaqueri Formation as a metallotect for pozzolanic deposits. The strategies for prospection of natural pozzolans are also examined, as well as the analytical techniques that pre-qualify and quantify these materials, such as X-ray diffraction that depicts the neoformation of C-S-H resulting from the chemical reaction between Ca (OH)2 paste and opaline sandstone after 7-day curing. The technological and mainly environmental and economical benefits of using pozzolans in cement blending are analyzed and compared here. There is the emission of up to 0.44 t of CO2 per ton of calcinated limestone and savings of approximately 20% are gained in the production of blended Portland cement.