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
[1] De Schutter, G., Taerwe, L.: Degree of hydration based description of mechanical
properties of early-age concrete. Materials and Structures 29 (1996), 335-344
[2] Gutsch, A.-W.: Properties of early-age concrete – experiments and modeling. Materials
and Structures 35 (2002), 76-79.
[3] Schindler, A.K.: Effect of temperature on hydration of cementitious materials. ACI
Materials Journal 101 (2004), 72-81.
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
[4] Lackner, R., Mang, H.A.: Chemoplastic material model for the simulation of early-age
cracking: from the constitutive law to numerical analyses of massive concrete structures.
Cement and Concrete Composites 26 (2004), 551-562
[5] Faria, R., Azenha, M., Figueiras, J.A.: Modelling of concrete at early ages: application to
an externally restrained slab. Cement and Concrete Composites 28 (2006), 572-585.
[6] Briffaut M., Benboudjema F., Torrenti J.-M., Nahas G.: Effects of early-age thermal
behaviour on damage risks in massive concrete structures. European Journal of
Environmental and Civil Engineering 16 (2012), 589-605
[7] Buffo-Lacarrière L., Sellier A., Kolani B.: Application of thermo-hydro-chemo-
mechanical model for early age behaviour of concrete to experimental massive
reinforced structures with strain–restraining system. European Journal of Environmental
and Civil Engineering 18 (2014), 814-827
[8] Gutsch, A.-W., Laube, M., Nothnagel, R.: Crack control in a massive reinforced
concrete foundation slab as concrete sandwich element for a water basin. Proceeding of
the 8
th
International Conference on Creep, Shrinkage and Durability Mechanics of
Concrete and Concrete Structures (CONCREEP 8), Ise-Shima (2008), 647-654
[9] Gutsch, A.-W., Laube, M.: Crack control for the massive structures of the new central
railway station in Berlin, Germany. Proceedings of the International Workshop on
Control of Cracking in Early Age Concrete, Sendai (2000), 377-384
[10] Krauß, M., Rostásy, F. S., Budelmann, H.: Probabilistic concept for the validation of the
effectiveness of countermeasures against early age cracking in massive concrete
structures. Proceedings - Workshop Crack Risk Assessment of Hardening Concrete
Structures, Trondheim (2005), 34-43
[11] Zeiml, M., Leithner, D., Lackner, R., Mang, H. A.: How do polypropylene fibers
improve the spalling behavior of in-situ concrete? Cement and Concrete Research 36
(2006), 929-942
[12] Carino, N. J.: The maturity method: theory and application. Cement, Concrete and
Aggregates 6 (1984), 61-73
[13] Gutsch, A.-W.: Creep and relaxation of early-age concrete. Creep, Shrinkage and
Durability Mechanics of Concrete and other Quasi-Brittle Materials, Proceedings of the
6
th
International Conference CONCREEP-6@MIT, Cambridge (2001), 619-624
[14] Hermerschmidt, W., Budelmann, H.: Creep of early age concrete under variable stress,
Proceedings of the 10
th
International Conference on Mechanics and Physics of Creep,
Shrinkage, and Durability of Concrete and Concrete Structures (CONCREEP 10),
Vienna (2015), 929-937
for basic creep of concrete. Materials and
Structures 9 (1976), 3-11
[16] Honorio, T., Bary, B., Benboudjema, F.: Factors affecting the thermo-chemo-mechanical
behaviour of massive concrete structures at early-age. Materials and Structures 48
(2015), 1-19.
[17] Eurocode 2: Design of concrete structures – Part 1-1: General rules and rules for
buildings; German version EN 1992-1-1:2004 + AC:2010