The aim of this work is to study the concrete behaviour of thermo-active slabs and foundations due to the inclusion of embedded pipes in which fluids circulate at low temperatures

Cobo Escamilla, Alfonso

González Rodrigo, Sonsoles

Martínez Pérez, Inmaculada

Pereda, Luis de

Prieto Barrio, Maria Isabel

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Effect of thermal mass activation on concrete mechanical properties of building structures

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III International Congress on Construction and Building Research 
Escuela Técnica Superior de Edificación 
Universidad Politécnica de Madrid 
Avda. de Juan de Herrera, 6 28040 Madrid, Spain 
14
th
 -16
th
 of December 2015 
 
 
EFFECT OF THERMAL MASS ACTIVATION ON CONCRETE MECHANICAL 
PROPERTIES OF BUILDING STRUCTURES  
Martínez, Inmaculada (1), Cobo, Alfonso (2), Prieto, María Isabel (2), De Pereda, Luis (3), 
González, Sonsoles (1) 
(1) Departamento de Construcciones arquitectónicas y su control. Escuela Técnica Superior de Edificación. 
Universidad Politécnica de Madrid. i.martinez@upm.es  
(2) Departamento de Tecnología de la Edificación. Escuela Técnica Superior de Edificación. UPM                               
(3) Director de proyectos de ENRES, Sistemas Energéticos Sostenibles. 
Keywords: Energy efficiency in building; Thermo Active Building Systems; Heat exchangers; Concrete. 
 
1. Introduction – Net Zero-Energy buildings (NZEBs) [1] collaborate to solve the constant 
concerns about energy supply constraints, decreasing energy resources, increasing energy 
costs and the rising impact of greenhouse gases on word climate. Thermo-active building 
systems [2], as low exergy systems, are defined as heating or cooling systems that allow the 
use of low valuated energy, which is delivered by sustainable energy sources, as geothermal 
energy, i.e., using building foundations as heat exchangers with the soil. (Figure 1) 
The effect of thermal activation on the mechanical behaviour of 
these concrete building structures can be analysed on three 
levels, the effect on the ground [3], on the foundation [4], and on 
the structural slabs [5]. The impact of thermal loads on the 
mechanical response of the ground and on the behaviour of 
energy foundations has been studied, but thermo active slabs 
studies [6] already performed are focused in estimate the 
thermal comfort and energy consumption.   
The aim of this work is to study the concrete behaviour of 
thermo-active slabs and foundations due to the inclusion of 
embedded pipes in which fluids circulate at low temperatures. 
 
2. Methods – In order to assess the effects of an increase in temperature and its influence 
on the mechanical behaviour of concrete, compressive strengths and the anchoring 
resistance of steel bars in concrete were studied. 52 specimens made from two different 
types of concrete, H-25 and H-30, were produced and subjected to four different 
temperatures, 20ªC, 40ºC, 70ºC and 100ºC. Half of them were formed in cylindrical moulds 
100 mm dia. and 200 mm height, and they were used to evaluate concrete compressive 
strength. The other 26 specimens were prepared in cubic moulds, 100 x 100 x 100 cm3, with 
a 10 mm dia. central reinforcement to carry out pull-out test.  
To evaluate the influence of the inclusion of pipes, a further 
54 specimens were made from two different types of 
concrete, H-25 and H-30: 24 specimens were prepared in 
cylindrical moulds (Figure 2) and 30 in cubic moulds. These 
specimens with 24 mm dia. polyethylene pipes embedded at 
different positions were tested to compression.  
 
3. Results and Discussion – In order to compare the results obtained in the tests from 
different points of view, the most representative values were selected and calculated from 
the data obtained in the compression tests, these are maximum strength max, maximum 
strain max, ultimate strain u, maximum strain energy Emax  and ultimate strain energy Eu. At 
Figure 1 Thermo-active building 
system. ENERES 
20º a 25ºC
10º a 30ºC
18º a 30ºC
Figure 2 Cylindrical specimens with 24 mm 
dia. Polyethylene pipes embedded in 
different positions tested to compressive 
strength. 
  
 
 
 
 
 
 
 
III International Congress on Construction and Building Research 
Escuela Técnica Superior de Edificación 
Universidad Politécnica de Madrid 
Avda. de Juan de Herrera, 6 28040 Madrid, Spain 
14
th
 -16
th
 of December 2015 
 
 
the same time, values obtained from the pull-out tests were pull-out strength FR, maximum 
displacement max, ultimate displacement u, maximum strain Emax, ultimate strain energy Eu.  
The correlation between the strength loss, the temperature and the position of the pipes, for 
concrete H-25 and H-30, is shown in table 1. As can be seen, strength losses increase as 
temperature increases, both in the compression test and in the pull-out test, producing stress 
losses of around 20% when concrete H-25 reaches 70°C and concrete H-30 reaches100°C. 
In the pull-out test, the strength loss values are greater at lower temperature, reaching values 
above 20°C in the two types of concrete for 70°C temperature. The introduction of 
polyurethane pipes reduces concrete strength in both cylindrical and cubic specimens, with 
losses over 20% when the pipe is in a horizontal position, i.e. perpendicular to the load.  
 
 
3. Conclusions - The expected degradation in the temperature ranges in which these 
thermo-active building structures operate (as a high-temperature cooling system, 16-20ºC, 
and a low-temperature heating system, 25-30ºC) is very small regarding existing behaviour 
studies of concrete subjected to high temperatures [7], however it is necessary to quantify 
this degradation for their safe design. 
From the results obtained in the test can be drawn that an increase in temperature 
diminishes its mechanical properties, regardless of the type of concrete, and the inclusion of 
polyethylene pipes embedded in concrete specimens reduces their mechanical properties, 
this reduction being more pronounced for a pipe laid perpendicular to the application of load.  
It can be concluded that thermo-active concrete structures perform best when the 
polyethylene pipes are placed parallel to the load and, regarding the temperature of fluids, it 
can be affirmed that the concrete mechanical properties are not jeopardized with strength 
losses of more than 20%, because the fluid temperature is always below 70ºC. 
References 
[1] Energy Efficiency Directive 2012/27/EU of the European Parliament and of the Council. 25 October 2012.  
[2] Basecq V., Michaux G., Inard C., and Blondeau P., (2013) Short-term storage systems of thermal energy for 
buildings: a review. Advances in Building Energy Research 7(1): 66–119. 
[3] Brandl, H., (2006), Energy foundations and other thermo-active ground structures. Geotechnique 56: 3-44. 
[4]  Laloui L and Di Donna A (2013) Energy geostructures. Innovation in underground engineering. ISTE Ltd, 
Great Britain. 
[5] Lim J.H., Song J.H., Song S.Y., (2014). Development of operational guidelines for thermally activated 
building system according to heating and cooling load characteristics. Applied Energy, ISSN 0306-2619, 
Volumen 126, pp. 123 – 135. 
[6] Kalz D, Pfafferott J and Koenigsdorff R (2012). Operating experience with Thermo-Active Building Systems 
(TABS). Bauphysik / Building Physics 34(2): 66–75. 
[7] Schneider U (1983). Behavior of concrete at high temperatures. RILEM-Committee 44-PTH. 
 
Compression 
test 
Pull-out test 
 
Compression 
test 
Compression 
test  
Cylindrical Cubic Cylindrical Cubic 
Temperature 
(ºC) 
Strength loss  
(%) 
Strength loss  
(%) 
Concrete 
type 
Strength loss  
(%) 
Strength loss  
(%) 
Pipe position 
20 
0,00 0,00 H-25 0,00 0,00 
Pipeless 
0,00 0,00 H-30 0,00 0,00 
40 
5,35 12,01 H-25 5,17 12,76 Vertical 
centered 5,70 17,91 H-30 9,43 6,37 
70 
19,05 24,15 H-25 13,45 ------ Vertical 
decentered 11,16 31,00 H-30 10,50 ------ 
100 
24,40 37,37 H-25 21,27 23,33 Horizontal 
centered 22,74 47,05 H-30 27,85 16,20 
Table 1 Strength loss in concretes H-25 and H-30, for different concrete temperatures and pipe position. 
(Losses exceeding 20% strength are marked) 
 


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Effect of thermal mass activation on concrete mechanical properties of building structures

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