Cotto Ramos, Anamarie

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    Sequential experimentation and multi-criteria analysis for structural concrete mixtures using fly ash, silica nanoparticles, and plastic aggregates
    (2023-11-15) Cotto Ramos, Anamarie; Torres García, Wandaliz; College of Engineering; Cáceres Fernández, Arsenio; Dávila Padilla, Saylisse; Acosta Costa, Felipe J.; Department of Civil Engineering; Sánchez Quintero, Dilsom
    This study explored the use of plastic aggregate and supplementary cementitious materials (SCMs) as an alternative to natural aggregates and Portland cement (PC) in concrete production with structural properties (compressive strength ≥ 17 MPa). The goal was to reduce the environmental impact of concrete production while maintaining its mechanical properties at a minimum cost. To optimize these alternative concrete mixtures, the study conducted a series of experimental mixture designs incorporating silica nanoparticles (nS), fly ash (FA), and plastic. A screening experiment was conducted to replace coarse aggregate with plastic wholly and partially, considering all concrete mixture components, two process variables, and various constraints. Sequential experiments investigated the use of SCMs and plastic aggregates to replace both fine and coarse aggregates. Then, prediction models were fitted using Ordinary Least Squares with Stepwise (OLS-SW) and Gaussian processes (GP) followed by an iterative model-based validation process to extract feasible solutions. Finally, characterization tests were performed to understand how the incorporation of SCMs and plastic aggregates affects the mechanical properties of concrete. Results indicated that replacing coarse aggregate with plastic was more viable than replacing fine aggregate. The best prediction model was obtained using GP, having a Mean Absolute Error (MAE) of 2.8 MPa, while the MAE of OLS-SW was 3.4 MPa. The last iteration of the methodology reduced the necessary nS percentage in the optimal mixture, reducing the mixture costs compared with the first iteration from $296.00 to $258.00 for a cubic meter of concrete mixture. An optimal concrete mixture containing 1% nS and 17.7% FA by cementitious material weight and 34.7% plastic by coarse aggregate volume achieved structural strength (19 MPa) at 7 days. Permeability test results indicated that concrete samples containing plastic and SCMs were less permeable (i.e., more durable) than those without these materials. The modulus of elasticity is approximately 44% less than that of mixtures made without plastic and SCMs, making them more ductile. Splitting test results determined a tensile strength of 5.8 MPa (25% of 7-day compressive strength). Lastly, 56-day compressive strength tests carried out on concrete samples subjected to high temperatures (300 °C) determined that this temperature minimally decreased the concrete compressive strength, maintaining its structural strength.