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1. Introduction
The reinforced concrete has been established over the years as
one of the most used building systems. According to Helene and
Levy (2003) [1], the concrete will have a more promising future in
the coming decades, once its architectural versatility, combined
with increased durability, will enable the implementation and the
development of any project.
For the concrete to achieve the forecasted resistances for the good
functioning, it is necessary that hydration reactions are completed
between cement and water. Therefore, the external temperature
behaves as a catalyst of these reactions, the hotter it is, and the
faster these reactions occur.
According to Shoukry et al. (2010) [2], the temperature, along with
the relative humidity of the air plays a big role in the reactions of
the hydration of the cement paste by affecting the properties of
fresh and hardened concrete.
However, Brazil is comprised of a large territory, encompassing
many kinds of weather conditions, including low temperatures in
certain periods of the year. In the South region, for example, the
weather can be compared to that of other Latin American coun-
tries and the world, where the incidence of low temperatures over
long periods of the year is characterized by a temperate climate.
Yet, the Brazilian norm of project of concrete structures, the ABNT
NBR 6118:2007 [3] does not distinguish between the regions of
the country or external temperatures. Structural designs, and con-
sequently, the execution have been achieved without caution, in
respect to temperature control in the early days of curing, which
may lead to irreversible problems in these structures.
According to Mehta and Monteiro (2008) [4]:
“In this respect, the concrete equates to a child: to become
a healthy adult, the newborn needs special attention in the
first times of growth. However, in both instances, there is
no clear definition of how long this early age period lasts.”
The Portland cement, by reacting with water, forms a paste with
more or less fluidity, depending on the percentage of added water.
In the course of time, this mixture hardens by irreversible reaction
of water with cement, acquiring mechanical strength able to turn it
in an excellent material for structural performance, under the most
diverse exposure environments (Isaia, 2005 [5]).
According to Anka et
al
. (2009) [6], the entire process of hydration
of the cement in concrete is very complex, and can be influenced
by many factors. Among the properties most impact the hydration
process is the initial temperature of the concrete and also the tem-
perature of air.
The tricalcium aluminate (C
3
A), a component of the cement hy-
drates at a rate much quicker than the silicates. Neville (1997) [7]
quotes the reactions of pure C
3
A with water occur in a violent man-
ner and results in an immediate hardening of the cement paste,
also known as instant concrete setting time. In order to prevent
this, gypsum (CaSO.2H
2
O) is added to the clinker manufacturing
process of Portland cement. According to Kirchheim et al. (2010)
[8], an example of the action of the C
3
A can be seen in the execu-
tion of Iberê Camargo museum in Porto Alegre, where it was used
white Portland cement with C
3
A contents above 9%.
The calcium silicates (C
3
S e βC
2
S) are responsible for about 75%
of the constitution of ordinary Portland cement, exerting a dominat-
ing role in determining the characteristics of hardness, also known
as the rate of development of resistance. The hydration of C
3
S and
βC
2
S in the Portland cement produces βC
2
S in a family of the
hydrated calcium silicates, which have similar structures that vary
widely in the relation between calcium and silica in addition to the
chemically combined water content (Mehta and Monteiro, 2008)
[4]. However, the tetracalcium ferroaluminate (C
4
AF) results in hy-
dration products structurally similar to the products of C
3
A, though
the reactivity of C
4
AF is slower (Neville, 1997) [7].
In parallel to the reactions, the heat of hydration of the Portland
cement is generated which can be observed as a thermal energy
resulting from the contact with water. This development of heat oc-
curs quickly from the mixture of Portland cement clinker milled with
water. The hydration of cement is characterized as an exothermic
reaction, that is, a reaction that generates heat, thus the hydration
process is directly related to the amount of heat generated.
Hence, what is expected of the Portland cement is a good cor-
relation between the rate of the cement hydration and the heat
of hydration. Cements with high hydration heat, hydrate faster
compared to cements that generate less heat of hydration (Taylor,
1967) [9]. Kirchheim et al. (2010) [8] add that in certain works use
large amounts of concrete, its thermal conductivity can be low and
with a high heat release due to the hydration reaction, which can
generate cracks through thermal retraction.
According to Mehta and Monteiro (2008) [4] the heat of hydration
can sometimes be unfavorable, for example, in the mass-concrete
structures. And sometimes be favorable, for example, in concrete
work in the winter or in regions of low temperatures when the envi-
ronment temperature may be too low to supply the energy required
for the activation of the initial reactions of hydration. According to
Zhang et al. (2008) [10], there is not a single value of activation
energy for all concrete and their different formulations.
According to Pinto Barbosa et al. (2006) [11], the whole process
of hydration of the cement can be compared starting from an evo-
lutionary rate that depends on the concentration and temperature
of all reagents of the solution. The hydration is accelerated at high
temperatures and reduced at lower temperatures. Kim et al. (2002)
[12] emphasize that concrete subjected to high temperatures at
early ages reach higher early resistance, but reduce the growth
rate of resistance over time. Husem and Gözütok (2004) [13] add
that cures at high temperatures reduce the strength of concrete in-
cluding being applied to conventional molded parts in conventional
concrete and of high performance, which can cause problems in
the future.
When the concrete is in a period of solidification or in the beginning
of hardening, and has interference by low temperatures, these ac-
tions have a tendency to be decelerated or even reversed owing
to the reduction in the rate of hydration of the active components
of the cement (Cánovas, 1988) [14]. As for the heating, the me-
chanical properties of concrete decrease remarkably, resulting in a
decrease in the quality of the concrete structure (Kelestemur and
Demirel, 2010) [15].
According to Shoukry et al. (2010) [2], one must consider in struc-
tural design the variability of the evolution of concrete properties
due to temperature, as this may affect their structural behavior.
The authors demonstrated for a thermal variation of 80 °C (-25 to
55 °C) at 28 days of curing, there is a reduction of 38% and 26% of
the resistance to compression and tension, respectively. However,
the work was conducted in extreme temperature conditions of cur-
69
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 1
V. CECCONELLO | B. TUTIKIAN