PSI - Issue 67
Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000
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Fig. 3. TEM graphs for (a) E5-LFA nano-silica and (b) E5-IC nano-silica.
2.2. Mixing procedures To compare the effect of different nanoparticles (i.e., nano-TiO 2 and nano-silica) on the strength and durability of concretes, a series of OPC concretes (i.e., concretes solely utilizing ordinary portland cement as the cementitious binder) were prepared in the laboratory. The mixture proportions of these concretes are presented in Table 3. There are two types of OPC reference concretes (OPC1 concrete had a w/c = 0.44, and OPC2 had a w/c = 0.45). For OPC1, three levels of addition of nano-TiO 2 addition were used (0%, 0.5% and 1 % by weight of cement). The OPC2 concretes contained different combinations of E5 nano-silica (E5-LFA and EE-IC, E5-LFA, E5-IC) as shown in Table 3. For all the concrete studies, consistent amounts of HRWR (5.3 oz/cwt cement or 331 ml/100 kg cement) and air entrainer (1.5 oz/cwt cement or 94 ml/100 kg cement) were added into the concrete. All materials needed for mixing were preconditioned at room temperature and accurately measured before mixing. Batch weights of the aggregates and water were adjusted as needed to account for the moisture content and absorption of both coarse and fine aggregates. Mixing commenced by introducing both coarse and fine aggregates into the mixer along with a portion of the batch water. Subsequently, these components underwent brief mixing, after which cementitious materials and the remaining portion of the batch water were added into the mixer. When incorporating nano-TiO 2 , the material was introduced into the remaining batch water, with a high-range water reducer (HRWR) already dissolved in it, and manually mixed for a few minutes. Subsequently, this suspension was added to the mixer for the final mixing stage. Air-entraining admixture (AEA) was introduced towards the conclusion of the mixing process. To prepare concrete incorporating nano-silica, the mixing protocol prescribed by the supplier was followed. Initially, 50% to 70% of the water was placed into the mixer before introducing the fine and coarse aggregates. The mixer was then started, and cement, air-entraining admixture (AEA), and high-range water reducer (HRWR) were added sequentially, followed by at least 2-5 minutes of mixing. Subsequently, the nano-silica was blended with the remaining mixing water and carefully added to the mixer using a syringe. The mixing process concluded with an additional 5-6 minutes of mixing. Following the completion of mixing, fresh concrete underwent testing for slump and air content. Subsequently, concrete samples were cast into molds to prepare various specimens required for future tests, followed by a 24-hour storage period in the laboratory, maintained at a temperature of 23°C and relative humidity of 50%. Afterward, the concrete samples were demolded and subjected to curing in saturated lime water at two distinct temperatures: room temperature (23°C) and low temperature (4°C), for the specified durations. The low curing temperature was selected to simulate the temperature conditions in the late fall season in the state of Indiana in the U.S. (where the study was
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