Mechanical behaviour of thermally activated building structures

This paper focuses on two low-energy systems - thermo-active building systems and energy foundations - both of which use concrete elements that are already required for structural reasons but which simultaneously work as heat exchangers. The aim of this work was to study the mechanical behaviour of these concrete elements due to the inclusion of polyethylene pipe heat exchangers cast directly into the concrete core and the influence of fluids flowing inside at a moderate temperature. Cylindrical and cubic specimens of two types of concrete (H-25 and H-30) were manufactured in order to study the influence of temperature through compression and pull-out tests and the influence of the embedded pipes in different positions using compression tests. The mechanical properties were found to decrease with an increase in temperature in both concrete types, with a sharper decline in the H-30 specimens. The pipe layout reduced the mechanical resistance of the structural elements regardless of the type of concrete used, with the most damaging position being perpendicular to the load. It is concluded that thermo-active reinforced concrete elements perform best when the polyethylene pipes are placed parallel to the load and the temperature of fluid in the pipes is lower than 70 degrees C.