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S. Lupica Spagnolo and B. Daniotti
4.2 Exposure of Test Samples to Accelerated Ageing Cycles
After having carried out the characterisation survey at time zero, the sample was
exposed to the designed accelerated ageing cycles: as envisaged in the preliminary
stage and in the preparation of the experimental set-up, the sample was subjected
to two cycles of accelerated ageing in a climatic chamber, each consisting of ten
repetitions of the winter sub-cycle (rain followed by a freezing phase at −20 °C,
then by a warm winter phase at 30 °C) and 25 repetitions of the thermal shock
summer sub-cycle (dry heat at 80 °C followed by rain).
At each time step, the climatic chamber was opened, the photographic survey
was carried out on the surface of the test sample and the colorimetric measurement
was taken in order to verify any variations in colour. Moreover, the flowmeter trend
was constantly monitored, as well as the profile of the flowing section temperatures
during the accelerated ageing.
5 Results
The surface temperature on the cast stone showed smaller variations in absolute
values than the natural stone, demonstrating the fact that the thermal conductivity
of the artificial stone was less than the natural stone one. This means that when the
outside temperature drops, the surface temperature of the cast stone decreases less
than the natural stone, and conversely, when the outside temperature rises, the surface
of the artificial stone is not as hot as the natural stone.
This evidence is attributable to the fact that the thermal conductivity of the cast
stone is smaller than the natural stone; this is a characteristic that causes the surface
temperature variations to be smaller in the artificial stone compared to the ones that
are found in the natural stone. This is regardless of the fact that the adhesive mortar
used for the joints of the cast section itself has thermal properties better than the in
the mortar used for natural stone.
Through flowmeter measures, moreover, it was possible to determine the trend of
the thermal resistance over time, comparing the initial values detected on two of the
sample sections at the door with the measured values as a result of the two steps of
accelerated ageing in the laboratory.
For the measurement of thermal resistance, the method of progressive averages
described in ISO 9869-1:2014 was used. Considered as 100 the initial value detected
at time zero for both types of coating at the door of the sample, the following trend
of the performance decay over time is showed in the following figure.
From the following graph, it is clear that after a decay in thermal resistance of the
same amount of both the sample portions (mainly due to the increase of moisture
content associated with exposure to rain), at time “t 2 ”, both parts demonstrated
mitigation of the initial performance decay. Of the two, the section coated with cast
stone showed better thermal behaviour as a result of the accelerated ageing (Fig. 4).
S. Lupica Spagnolo and B. Daniotti
4.2 Exposure of Test Samples to Accelerated Ageing Cycles
After having carried out the characterisation survey at time zero, the sample was
exposed to the designed accelerated ageing cycles: as envisaged in the preliminary
stage and in the preparation of the experimental set-up, the sample was subjected
to two cycles of accelerated ageing in a climatic chamber, each consisting of ten
repetitions of the winter sub-cycle (rain followed by a freezing phase at −20 °C,
then by a warm winter phase at 30 °C) and 25 repetitions of the thermal shock
summer sub-cycle (dry heat at 80 °C followed by rain).
At each time step, the climatic chamber was opened, the photographic survey
was carried out on the surface of the test sample and the colorimetric measurement
was taken in order to verify any variations in colour. Moreover, the flowmeter trend
was constantly monitored, as well as the profile of the flowing section temperatures
during the accelerated ageing.
5 Results
The surface temperature on the cast stone showed smaller variations in absolute
values than the natural stone, demonstrating the fact that the thermal conductivity
of the artificial stone was less than the natural stone one. This means that when the
outside temperature drops, the surface temperature of the cast stone decreases less
than the natural stone, and conversely, when the outside temperature rises, the surface
of the artificial stone is not as hot as the natural stone.
This evidence is attributable to the fact that the thermal conductivity of the cast
stone is smaller than the natural stone; this is a characteristic that causes the surface
temperature variations to be smaller in the artificial stone compared to the ones that
are found in the natural stone. This is regardless of the fact that the adhesive mortar
used for the joints of the cast section itself has thermal properties better than the in
the mortar used for natural stone.
Through flowmeter measures, moreover, it was possible to determine the trend of
the thermal resistance over time, comparing the initial values detected on two of the
sample sections at the door with the measured values as a result of the two steps of
accelerated ageing in the laboratory.
For the measurement of thermal resistance, the method of progressive averages
described in ISO 9869-1:2014 was used. Considered as 100 the initial value detected
at time zero for both types of coating at the door of the sample, the following trend
of the performance decay over time is showed in the following figure.
From the following graph, it is clear that after a decay in thermal resistance of the
same amount of both the sample portions (mainly due to the increase of moisture
content associated with exposure to rain), at time “t 2 ”, both parts demonstrated
mitigation of the initial performance decay. Of the two, the section coated with cast
stone showed better thermal behaviour as a result of the accelerated ageing (Fig. 4).