PSI - Issue 17

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

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

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3.2.4. Concrete residual expansivity The potential for further expansion of the concrete due to ASR was determined on cylindrical specimens obtained from the cores and using the ASR accelerating conditions specified in RILEM Recommended Test Method AAR-3 (Nixon & Sims, 2016). This test was performed to eight specimens, one from each location, all having 99 mm in diameter and 198 mm in length. The residual expansion of the concrete, in regard to DEF, was assessed according to LPC Method no. 67 (Pavoine & Divet, 2009) on 7 specimens, covering all locations, except location L8 (a structural element with low thickness). The specimens had also a diameter of 99 mm and a length of 198 mm. 3.2.5. Mechanical testing The mechanical testing was made to assess the concrete general condition and to compare its characteristics in the different sites in the underpass deck, serving also as an indicator of the existence of deleterious internal swelling phenomena. The concrete compressive and tensile splitting strengths were determined according to the standards NP EN 12504-1 (IPQ, 2009) and NP EN 12390-6 (IPQ, 2011), respectively. The former was carried out on specimens having a diameter of 99 mm and a length/diameter ratio between 1.0 and 2.0, whilst the latter used cylindrical specimens having a diameter of 99 mm and a length/diameter ratio of 2.0. The stiffness damage test was performed according to a LNEC internal procedure, which derives from the test method originally devised by Crouch, in 1987 (Crouch, 1987; Wood & Crouch, 1987), and further studied by Chrisp et al . (Chrisp, Crouch, et al., 1989; Chrisp, Wood, et al., 1989; Chrisp, et al., 1993), and comprises the test parameters set in LNEC Specification E 397 (LNEC, 1993c) and in the standard NP EN 12390-13 (IPQ, 2014). The compressive strength and stiffness damage tests were performed to “as received specimens” and to specimens that were subject to the concrete residual expansivity tests (“ASR test ed specimens ” and “DEF test ed specimens ” ). The petrographic examination revealed that the coarse aggregate is composed mainly of hydrothermally altered silica rich volcanic rocks (rhyolites and dacites) but it also comprises some chert, quartzite and greywacke; hence, the coarse aggregate has potentially alkali-reactive constituents ( e.g. , microcrystalline silica, deformed-strained quartz; and, due to the genesis of these lithotypes, probably high-temperature silica polymorphs - cristobalite and tridymite). Moreover, the coarse aggregate contains constituents that may release alkalis into the concrete pore solution ( e.g. , alkaline feldspars and micas). The fine aggregate, constituted mainly by quartzites, has also alkali-reactive constituents ( e.g. , deformed-strained quartz). Signs of expansive reactions, like aggregates with borders alteration, fissures in the aggregate, in the paste and in the paste/aggregate interface, as well as neoformation products, were observed in most samples. The microstructural characterisation by SEM/EDS confirmed the presence of products from the expansive reactions in all samples, but mainly those resulting from ASR. 4.2. Chemical analysis The alkali content values obtained for the concrete (acid soluble alkali content – 4.6 kg/m 3 ; and hot water soluble alkali content – 4.4 kg/m 3 ) are compatible with compositions incorporating aggregates having alkaline minerals, thus corroborating the findings from the petrographic examination. The concrete alkali content surpasses the limit recommended in LNEC Specification E 461 (LNEC, 2007b), 3.5 kg/m 3 , to avoid the deleterious development of ASR; this may represent a condition highly favourable for ASR to occur given the potential for and existing alkali-silica reaction signs already observed in the structure, provided that sufficient moisture and reactive silica are available for the reaction to progress further. The cement sulphate contents obtained (4.7 % or 4.0 % if 300 kg or 350 kg of cement per cubic meter of concrete are considered) are above the 3.5 % SO 3 limit established in LNEC Specification E 461 (LNEC, 2007b), for a cement having a C 3 A content higher than 5 %; hence, the evaluated concrete might be susceptible to the deleterious devolvement of DEF if it was exposed to high temperatures during curing and sufficient moisture is available. 4. Results and discussion 4.1. Petrographic and microstructural examination