Civil Engineering Reference
In-Depth Information
by one unit of cement mass. The author developed a procedure for estimating
the f
eco
, the compressive strength which gives the highest efficiency for a
given set of materials. isaia et al. (2003) also adopted the strength developed
by 1 kg of Portland cement as an indicator. however, these authors did
not count supplementary cementitious materials (pozzolans) as cement.
nowadays, this procedure is not consistent with the global scarcity of such
high-energy products. The economic efficiency of a concrete mix design
was defined by Aïtcin (2000) as the cost of 1 MPa, or 1 year of service life
of the concrete structure. This is a very advanced concept and service life
is rather complicated to forecast and might depend on factors that are not
in the scope of the concrete producer.
our proposition (Damineli et al. 2010) is to adapt a concept that is
almost universally adopted by the ready-mix concrete industry to measure
its efficiency: the amount of cement per 1 MPa of compressive strength at
28 days. This has several advantages: the concept and range of resulting
values are familiar to potential users and very simple to estimate, so it
is easy to develop a benchmark of current performance. however, since
the aim was to access the efficiency of use of scarce energy-intensive
material, the amount of 'cement' was replaced by an equal amount of
binder, by removing the amount of limestone filler from the calculation.
Therefore, we define binder intensity (
bi
cs
) as the amount of binder (
B
, in
kg m
-
³) needed to provide 1 mPa of compressive strength (
CS
) at a given
age:
bi
cs
=
B
CS
Since the Co
2
footprint of cement and even aggregate are available in many
countries, we also proposed a Co
2
intensity of concrete (
ci
cs
), defined as
the amount of Co
2
(C, in kg.m
-
³) released to provide 1mPa of compressive
strength.
bi
cs
=
C
CS
Using the same concept, all series of indicators can be easily defined, even
the expected service life, were possible and relevant. actually, the concept is
to change the functional unit of concrete from one cubic meter to a relevant
performance indicator, such as compressive strength or bending strength.
a benchmark on both
bi
and
ci
is presented in Fig. 2.3. This includes
laboratory data from Brazil, plus another 28 countries, as well as data from
two ready-mix concrete companies in São Paulo. it is worth mentioning that
all the datasets overlap. It is also visible that there are significant differences
in the binder efficiency for any given strength, evidencing the potential to
increase eco-efficiency. From the available data it seems that a minimum
bi
