PSI - Issue 37

João Custódio et al. / Procedia Structural Integrity 37 (2022) 644–651 João Custódio et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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4.2. Maximum temperature attained in concrete – estimate vs experimental The average recorded temperatures at the locations described in section §3.1 are presented in Fig. 4. The reported age of these records, in this figure, is related to the time when the concrete first contacted the probe. The time of environmental records is related to the contact of concrete to the probes located at a depth of 1.1 m.

0 10 20 30 40 50 60 70 80

P_1,1m P_0,6m P_0,1m Environment

Temperature, ºC

0

50

100

150

Time after contact with the probe, hours

Fig. 4. Temperature evolution at the tested structural element as well as the ambient temperature around the viaduct deck.

The maximum temperatures recorded at each location inside the concrete deck are presented in Table 4, the table also presents the fresh concrete temperature at the time it was poured-in-place. Table 4. Temperature of concrete (ºC). Temperature Probe at 1.1 m Probe at 0.6 m Probe at 0.1 m Maximum temperature attained during concrete cure 68.9 66.2 56.2 Concrete temperature when cast-in-place 24.4 25.2 23.9 The fresh concrete temperature was high, considering the environmental temperature, due to the cement temperature which reached about 70 ºC inside the silo at the concrete batching plant. As a result, it can be stated that, according to Portuguese regulations (LNEC, 2021) and from these temperature records, there is a high risk of deleterious occurrence of ISR in this concrete. According to LNEC Specification E 461 (LNEC, 2021), this type of structure is categorised into risk category R3 and, since it contains massive concrete elements, the level of precaution against ISR to be selected is the P3. In this prevention level, it is necessary to limit the temperature range to 65 ºC during the hydration process (preventive measure M1); if this is not possible then a non-deleteriously reactive concrete mixture must be used (preventive measure M5) and one of the following preventive measures must be used: M2 – limit concrete alkali content and limit binder aluminate and sulphate contents; M3 – reduce moisture ingress to maintain the concrete in a sufficiently dry state to prevent deleterious expansion; or M4 – limit the calcium hydroxide content (e.g. through the use of type II additions of demonstrated effectiveness). The estimation of the maximum temperature attained during concrete curing was made applying the method proposed in the IFSTTAR technical guide GTI5 (Ifsttar, 2018). This method requires the values of Q 41,EN196-9 and Q 120,EN196-9 which, as seen above, are the heat of hydration values, expressed in joules per gram of cement and obtained after 41 and 120 hours after the water contacted the cement, determined according to the NP EN 196-9 (IPQ, 2010). Using Q 41,EN196-9 and Q 120,EN196-9 values of 314 and 331 J/g (Table 3), respectively, to the concrete mixture indicated in Table 2, a relation between the 2 and 28 days compressive strength of concrete of 0.6, and to the worst case scenario of the deck section, i.e. , a depth of 1.1 m (Figure 1); the maximum estimated temperature, reached by a concrete applied at a temperature of 24.4 ºC, would be 70.7 ºC. Therefore, there is a good agreement for the temperature estimate made with the IFSTTAR method (70.7 ºC), when using the cement heat of hydration values determined with the semi-adiabatic method, and the actual temperature attained in the structural element (68.9 ºC), a difference of roughly 3 %.