Environmental Engineering Reference
In-Depth Information
2.2 Experimental method
2.2.1 Mixture design
several mixture batches were cast and tested using
the selected materials. The addition of natural poz-
zolanic aggregate (aPn) to the 0-5 mm size frac-
tion as a substitute for 10% cement by volume was
analyzed in order to improve the mechanical prop-
erties of the blends. The aPe, aeV and the aPn
have a high absorption coefficient. steiger & hurd
(1978) observed that when the concrete density
increased 1% due to water absorption, the thermal
conductivity of concrete decreased up to 5%. The
consequences of adding Thermocal TM as a substi-
tute for Portlant cement in 10%, 20% and 30% by
volume were also analyzed in order to improve the
absorption coefficient.
The Test Plan was divided into two stages, and
the results were then compared to the manufacture
or reference mixture ( Table 9 ) , which was taken
from a precast concrete manufacturing industry
located in Gran canaria. in stage 1 the initial
mixture was adjusted, and the influence of the
compaction method and the water-cement ratio in
eight mixtures was analyzed.
in order to correlate the data obtained in manu-
factured in the block machine, a vibrocompacting
device was designed and built. The machine was
used to mould and vibrocompact the 30 × 30 cm
square plaque shaped specimens of different
widths, as well as to compact the 40 × 40 × 160 mm
prismatic specimens. This device was also used dur-
ing the stage 2 of the test plan. The main conclu-
sions of this stage 1 are that the vibrocompacting
method is the most appropriate for reproducing in
the laboratory a lightweight concrete with similar
characteristics as the reference lightweight con-
crete, and that a 1.2 W/c ratio is the most appro-
priate to produce in the laboratory lightweight
concrete mixtures with similar density character-
istics as the reference lightweight concrete. Fifteen
batches of lightweight concrete were analyzed dur-
ing stage 2 after having incorporated the different
selected materials by weight and by volume. The
water: cement ratio was 1.2 and the compaction
was made using the vibrocompacting machine.
2.2.2 Specimens preparation
Twenty three blends (23) and 435 specimens
were cast altogether, making a total of 1753 tests.
Between 12 and 18 specimens (40 × 40 × 160 mm)
were cast for the density and capillary absorption
tests, and three (3) 300 × 300 mm plaque shaped
specimens with widths varying from 50 mm to
70 mm were used in the density, water absorption
and thermal conductivity tests. For each mixture
the specimens were cast and cured in laboratory
conditions until the moment of testing (7 and
28 days). after the curing, the specimens were
tested in laboratory conditions in accordance with
Une en 772-11:2001, Une en 12350-6:2006,
Une en 12390-7:2001 and Une en 12664:2001
regulations. The specimens were produced in a
vibromoulding machine designed to reproduce the
same vibration conditions of a block machine.
3
ResUlTs anD DiscUssion
3.1 Density
Figures 1 and 2 show that as we add new mate-
rials to the mixture by weight, the density values
decrease about 7% in the 4 × 4 × 16 cm specimens
as compared to those obtained for the same batches
in the 30 × 30 × 5 cm specimens.
The +10%aPe 0-6 mm batch showed the
greatest percent difference in density in 28 days: a
reduction of 20.83% in the 4 × 4 × 16 cm specimens
and of 12.80% in the 30 × 30 × 5 cm specimens.
To replace 100% by weight of the aeV 0-12 mm
fraction with the 0-8 mm fraction did not entail
a significant reduction in density. only in the
4 × 4 × 16 cm specimens a slight decrease of about
5% was observed.
Figures 3 and 4 show that the influence of
the specimens' size on these batches by volume
results in 6% decrease in the density values of the
4 × 4 × 16 cm specimens, as compared to those
obtained for the same batches in the 30 × 30 × 5 cm
specimens. in the 4 × 4 × 16 cm specimens, the
+30%aPe 0-6 mm batch obtained a greater per-
cent difference in density in 28 days, with a reduc-
tion of 21.41%.
however, in the 30 × 30 × 5 cm specimens it was
the 90%ceM 10%TheR batch that obtained a
greater percent difference in density in 28 days with
a decrease of 19.13%.
Table
9.
lightweight
concrete
manufacture
(or
reference) batch from the manufacture of Bhic.
Materials
kg/m 3
3.2 Capillary water absorption
With regard to the capillary Water absorption
coefficient in weight batches, in Figures 5 and 6
we realize that in the standard batch, such as the
100%aeV 0-12 mm (W/c = 1.2), the absorp-
cement ceM ii/a-P 32.5
240
Water
96
natural yellow sand 0-4 mm
400
Volcanic lapilli aggregate 0-12 mm
1700
W/c ratio
0.4
 
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