PSI - Issue 17

João Custódio et al. / Procedia Structural Integrity 17 (2019) 80–89 João Custódio et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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4.3. Concrete residual expansivity

The average residual expansion of the concrete cores, from each location, is summarized in Tables 2 and 3. The ASR residual expansion individual test results for all cores ranged from 208x10 -6 to 775x10 -6 , whilst the expansion rate varied between 10x10 -6 /year and 110x10 -6 /year; this indicates a negligible to moderate potential for continued expansion due to ASR (Fasseu, 1997; LCPC, 2010). Concerning DEF, the individual expansion values varied between 0.004 % and 0.122 %, meaning that there is also a negligible to moderate residual concrete expansion potential due to this swelling phenomenon (LCPC, 2010). Table 2. Results of the expansion tests carried out on concrete cores to evaluate the potential for further expansion due to ASR. Location Specimen Approximate depth of extraction (m) Expansion (x10 -6 , 424 days) Expansion rate (x10 -6 /year) † L1 3A 0.61 - 0.81 351 10 L2 7A 0.65 - 0.85 384 50 L3 11A 0.59 - 0.79 263 10 L4 18A 0.55 - 0.75 476 100 L5 22A 0.61 - 0.81 775 90 L6 26A 0.61 - 0.81 511 30 L8 33A 0.05 - 0.25 278 110 L9 39B 0.10 - 0.30 208 20 NOTE: † The expansion rate was calculated for the test period according to (Fasseu, 1997); the values presented correspond to the calculated values rounded to the nearest tenth. Table 3. Results of the expansion tests carried out on concrete cores to evaluate the potential for further expansion due to DEF. Location Specimen Approximate depth of extraction (m) Expansion (%, 364 days) Expansion (x10 -6 , 364 days) L1 4B 0.92 - 1.12 0.044 437 L2 8B 1.11 - 1.31 0.055 548 L3 12B 1.00 - 1.20 0.043 427 L4 19B 0.98 - 1.18 0.028 277 L5 23B 0.98 - 1.18 0.063 632 L6 27B 1.02 - 1.22 0.122 1218 L9 38B 0.64 - 0.84 0.004 40 4.4.1. Compressive strength test Fig. 1a displays the compressive strength determined experimentally for the “as received specimens”, as well as the compressive strength estimates made from the concrete strength class prescribed for the structure. The estimate considers (i) that the concrete used in the structural elements assessed would be a C30/37; (ii) f cm = f ck + 8 = 30 + 8 = 38 MPa; an age coefficient, β, of 1.26 and of 1.43 , calculated according to EC2 (IPQ, 2010), applied to the mean value of concrete cylinder compressive strength at 28 days; (iv) a factor of 0.85 for converting the strength of specimens cast in the laboratory to the strength of cores extracted concrete from the structure, according to EC2 (IPQ, 2010). This calculation results in a compressive strength, for a 17 years old concrete, of 41 MPa (β = 1 .26) and of 46 MPa (β = 1.43). The results show that there is a great variability on the condition of the concrete sampled throughout the deck, with the individual values ranging from 40.3 MPa (location L6) to 57.6 MPa (location L8). When comparing the experimental values with the correspondent estimated values for sound concrete, it is observed that the compressive strength is inside the estimated range; the exception being the values obtained for the concrete sampled in locations L4 and L8, which are higher than the estimated ones. Overall, the sampled concrete exhibits an acceptable compressive strength, and thus it is not possible to infer that concrete degradation has already occurred in service, even though there is visible cracking in the structural elements assessed. Fig. 1b depicts a comparison between the compressive strength determined experimentally for the “as received specimens” with that of the “ASR tested specimens” and “DEF tested specimen s”. The individual values obtained for the “ASR /DEF tested specimens” vary from 29.0 MPa (location L6) up to 68.2 MPa (location L8). The mean compressive strength of the “ASR/DEF tested specimens” (36 MPa , approximate extraction depth = 0.55-1.31 m) was lower than that of the “as received specimens” (46 MPa , approximate extraction depth = 0.10-0.32 m) for the concrete 4.4. Mechanical testing