4.3. Experimental results and discussion
The two types of lightweight concrete samples were tested in
parallel. A continuous data acquisition was carried out during the
test (in-between 10 min intervals (n)). That acquired data comprised
the values of the heat flow across the corn cob concrete
sample (q01(n) and q02(n), measured by the two used heat flux sensors
placed on this sample) and the values of the heat flow across
the expanded clay concrete sample (q1(n) and q2(n), measured by
the two used heat flux sensors placed on this sample). It also included
the interior and the exterior temperatures (Ti(n) and
Te(n)), and the relative humidity. Fig. 7 depicts graphically the
above mentioned registered data.
In this case, almost 48 h were necessary (DT stabilizing, Fig. 7)
to stabilize the interior temperature at 20 C of the confined room.
Meanwhile, the exterior temperature had shown its natural and
expected swing in a day time (e.g. DTnight and DTday, Fig. 7). For
that period of the year, in the north region of Portugal, the exterior
temperature was always lower than the interior temperature.
Therefore, adequate thermal gradients were guaranteed (e.g. details
I and II, Fig. 7).
According to [14], the thermal transmission coefficient (U) can
be quantified by:
UðntotalÞ ¼
Pntotal
n¼1 qðnÞ
Pntotal
n¼1 ðTiðnÞ TeðnÞÞ
ð1Þ
where U is the thermal transmission coefficient, q(n) is the heat
flow across the sample at the moment n, Ti(n) and Te(n) are the interior
and the exterior temperature at the moment n, respectively;
ntotal is the total number of moments in which the data were
registered.
Taking into account that two heat flux sensors were used by
each sample, corresponding to q1(n) and q2(n), it was possible to
estimate two thermal transmission coefficients for each sample,