Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

47

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

of the reinforcement. The design of the minimum reinforcement according to the German 

version of Eurocode 2 [17] is mainly affected by the tensile strength at the time of cracking 

that may be derived from the calculated stress evolutions. In the parts of the structure where 

no cracking has to be expected, the minimum reinforcement can be reduced related to the 

calculated stress level. 

To ensure the correctness of the numerical investigations and the reinforcement design, 

monitoring measures for the temperature and strain evolution in the most critical parts will be 

installed in the construction phase. 

 

 

4. Conclusions 

 

In this paper, an application example for the control of early age cracking in a massive tunnel 

structure based on experimental investigations and numerical simulations was presented. 

An experimental program was carried out to characterise the material behaviour of the 

concrete at early ages. This included the testing of the heat of hydration, the evolution of the 

compressive strength, tensile strength and Young’s modulus and the autogenous shrinkage. 

For reasons of fire protection, a special concrete mix with PP-fibres was used. The high fly 

ash content in combination with a low heat slag cement lead to a relatively slow evolution of 

the mechanical properties and a long lasting growth of the compressive strength. The concrete 

showed a significant autogenous shrinkage that was compensated partly by a swelling at the 

beginning of the reaction. 

The experimental results were used as input parameters for numerical simulations of the 

temperature and stress evolution in the tunnel structure. The results of the thermal analyses 

show that the maximum temperature inside the concrete structure goes up to 57°C for the 

assumed boundary conditions. The restrained contraction of the structure due to the intense 

cooling down and the simultaneous shrinkage of the concrete lead to high tensile stresses and 

consequently to a high risk of cracking. 

To ensure the water tightness of the structure these stresses must be taken into account during 

the design of the reinforcement. Because the boundary conditions have been assumed for the 

worst case scenario, a high amount of reinforcement is necessary for crack width control. To 

ensure an economic design, further simulations will be carried out to check if a reduction of 

the reinforcement is possible when the construction process is optimised. This will include 

investigations on the influence of the climate during construction and the sequence of 

construction phases. Additionally, the temperature and strain evolution will be metrologically 

monitored during construction to check the reliability of the numerical results. 

 

 

References 

 

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[3]  Schindler, A.K.: Effect of temperature on hydration of cementitious materials. ACI 

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48

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

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