Soto-Toro, Hildélix L.
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Publication Characterization of an optimized hig performance concrete with partial replacement of cement by fly ash and nanosilica(2018) Soto-Toro, Hildélix L.; Suárez, O. Marcelo; College of Engineering; Acosta Costa, Felipe J.; Cáceres, Arsenio; Shafiq, Basir; Department of Civil Engineering; Vega, JoséModern construction industry requires new technologies to comply with increasingly stricter environmental regulations. In particular, cutting back cement demand in concrete fabrication lowers carbon dioxide emissions caused by its production. One solution is cement replacement by other materials with smaller carbon footprints and equivalent cementitious properties, such as fly ash. This industrial waste material in contact with water turns into a cement-like paste. Alas, due to a slower reaction, at early age fly ash decreases the rate of strength gain in concrete. Counteracting such strength loss at early age with the addition of nanostructured silica motivated the present research. Furthermore, since the study of concrete mix with Portland cement, nanosilica, and fly ash can be complex and time-demanding, a statistical design of experiment for mixtures was developed. In this controlled experimental design, the compressive strength was response variable; the levels of Portland cement, fly ash and nanosilica were the independent factors whereas the water-to-binder ratio was kept constant. Five combinations of cement components were prepared for this design. Compressive, flexural and tensile strength results were measured at 7, 28 and 90 days of curing. On mixes with a 3% replacement with nanosilica, a strength development of 82% (of final resistance normalized at 90 days) was attained at 7 days. In addition, a 40% increment of compressive strength and a faster development of such strength were obtained by replacing part of cement with fly ash and nanosilica compared with mixtures containing only fly ash. Absorption and permeability test were conducted to identify properties which can eventually have an effect on concrete durability and other mechanical properties. This thesis reveals that a higher reduction of permeable voids and absorption is feasible in mixes with higher content of fly ash and nanoparticles. Finally, an analysis of the high performance concrete market, costs and concrete performance was used to evaluate costs of the product to, in the near future, develop a commercialization strategy