Industrialised, Integrated, Intelligent sustainable Construction - I3con

SUSTAINABLE CONSTRUCTION HANDBOOK 2
cannot be used for real time decision making. Wireless temperature sensors would make on-line
assessment of the temperature conditions possible in a real time environment and the building site
engineers could use it to make actual decisions. For precast concrete products the elements are moved
around from the casting facility to temporary storage, to the building site and finally to its final
position in a building. Hence, precast concrete is often subject to various curing conditions and the
need for continuous monitoring may be helpful for certain products.
Moisture monitoring in concrete. Another important aspect of concrete production is the moisture
content. During hydration the cement reacts chemically with the mixing water but even after complete
hydration there is still say 110 litres of water per m 3 in the concrete pore system (Grasley et al. 2006).
If the concrete is applied into a slab on grade and the floor material is a moisture sensitive material,
e.g. wood or glued plastic flooring the relative humidity in the concrete should not exceed say 85 %-
RH. Otherwise the glue looses its adherence and the basis for growth of fungi is there, increasing the
risk of poor and unhealthy indoor climate.
For conventional concrete for houses this means, that there is an excess amount of water of
approximately 30 litres/m 3 , that needs drying out before flooring is applied. During the cold season
concrete drying is a very slow and lengthy process, requiring a lot of energy for heating and
ventilation. Drying out of concrete will often require 2-3 months with controlled drying climate, i.e.
moderate temperatures and fairly dry air.
It is a big challenge to plan this process into a tight construction schedule. Furthermore, a building site
is always subject to rain and other sources of water during construction that may hinder the drying out
process further (Figure 8).
Figure 8. Ponds of rain water on a concrete slab delay the drying out of the concrete
In Denmark the floor contractor is obliged to document that the moisture, level in terms of relative
humidity in the concrete pores, is below the threshold value before the flooring is applied.
Conventional measuring of relative humidity in a floor slab is often destructive and time consuming
as described below:
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• A RH sensor is placed in a drilled hole so that the relative humidity is registered in half
thickness of the slab. The sensor should be left in the hole for at least a day in order to obtain
moisture equilibrium. Then the operator has to return the next day to take a reading. At a
building site it is not safe to leave expensive and delicate equipment such as a RH sensor in
place for several hours. Also the readings may be sensitive to temperature variations.