| dc.description.abstract | There are constant searches for alternatives to reduce the environmental impact in
the production of in consumables, like concrete, that is actually a pollutant. Mineral
additions have been investigated as partial substitutions for cement in concrete
because other than taking advantage of industrial residues, that many times don t
have a specific distinction and are degrading in the ambiental view, they can offer
better material durability characteristics, as proved in previous studies. In Brazil, a big
rice producer, millions of tons of rice husk are produced, where part is utilized for
energy production in thermoelectric plants. The rice husk ash, result of the burning of
the husk, has been the font of studies as a partial substitution of cement in concrete.
There are still very few studies that make a comparison of the viability influence of
the utilization of rice husk ash with different levels of carbon graphitic (light and dark
grey), obtained by controlled burnings, a durable characteristic in concretes. In this
work, mixtures containing different levels of light and dark RHA were investigated in
concrete structural performance through water capillary absorption, following the
NBR 9779:1995 and apparent electrical resistivity, conforming to the four electrode
method (Wenner). Additionally, an analysis was made of the axial compressive
strength in accordance with the NBR 5739:2007. For this, eight compound mixtures
were tested and investigated in relation to their w/wc 0,35, 0,50 e 0,65: one
composited of 100% Portland cement, REF, three with substitution of cement by light
RHA in levels of 10%, 20% and 30%, namely 10 LRHA, 20 LRHA, 30 LRHA,
respectively, and another three with the same levels of dark RHA replace cement,
identified as 10 DRHA, 20 DRHA and 30 DRHA, respectively, and a mixture with
10% of silica fume, 10 SF, to compare results. The increase in cure time and in the
purport of the substitution of cement by RHA resulted in better performance as to the
investigated properties. In equality of w/wc relations, the compressive strength values
were, in general, similar, indifferent to the level of carbon graphitic of the RHA. The
composite mixture with DRHA presented better performance with regards to capillary
absorption, even though it was overcome by the mixture with SF. In relation to
electrical resistivity, the composed mixture of 30% LRHA presented better
performance in all analysis times. | |
