| dc.description.abstract | Electrical resistivity, a property of the concrete that represents its resistivity to the
passing of electric current, is important in terms of corrosion of reinforced concrete
and, therefore, of the durability of the structures of reinforced concrete. The use of
mineral additives in concrete matrices has been shown to be effective both in reducing
the environmental impact caused by cement production and waste disposal and in
improving properties related to the durability of structures. In this study, the
performance of concrete with partial replacement of Portland cement by sludge ash
from water treatment plant (WTPSA) and ground limestone before electrical resistivity
was investigated. The definition of the mixtures followed a statistical design of the
CCRD type, with WTPSA levels varying from 0% to 30%, concentrations of limestone
between 0% and 15% and minimum and maximum water/binder (w/b) ratios of 0.35
and 0.65, in addition to a reference mix, with no mineral additions, with ratios of 0.35;
0.50 and 0.65. The assessment of the influence of variables in studies on electrical
resistivity, through the response surface methodology, was carried out for the 7th, 14th,
28th, 56th and 91st days. The evolution of the electrical conductivity and potential of
Hydrogen (pH) over time were also analyzed on the 7th, 28th and 91st days. The
WTPSA, which was calcined in a muffle kiln at 700 ° C and ground in a ball mill for 1
h, became a mineral addition with high pozzolanic activity when in ternary mixtures
with Portland cement and ground limestone. Better electrical resistivity results were
obtained limestone content around 7.5% since the early ages. As for WTPSA, its
content ranged from 0% in the early ages to 30% in older ages. The increase in its
effect at each test age is an indication that WTPSA had an influence on the concrete
microstructure. The reduction of electrical resistivity with increasing w/b ratio was
greater at each age, being the factor with the greatest influence after 91 days. In time,
both electrical resistivity, pH, and electrical conductivity decreased in all mixtures.
According to the limits indicated by the CEB 192, low or negligible corrosion risk was
reached with high levels of replacement of WTPSA and limestone in the mixtures.
Moreover, for each relation w/b ratio, the greatest electrical resistivities were those of
the mixtures with high levels of WTPSA and limestone in the proportion 2:1.
Replacement of Portland cement by 15% of WTPSA and 7.5% of limestone proved to
be efficient in reducing the risk of corrosion for both the environmental aggression
classes defined by the NBR 12655 (ABNT, 2015) and on equal mechanical resistivity
with concretes with no mineral additions. Additionally, a cement saving of more than
100 kg/m3 was observed for these same substitution contents in relation to their
mixtures of the same compressive strength value. | |
