Zapata Orduz, Luis E.

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    Rheological and mechanical characterization of portland cement mixes containing micro and nano amorphous silica particles
    (2013) Zapata Orduz, Luis E.; Portela Gauthier, Genock; College of Engineering; Cáceres Fernández, Arsenio; Molina Bas, Omar I.; Marcelo Suárez, O.; Department of Civil Engineering; Díaz, Ruben E.
    In concrete technology, it is common to use fly ash (FA) and micro-SiO2 (SF) as mineral admixtures. This has resulted in improvements in the fresh and hardened states. On the other hand, nano-SiO2 (nS) is industrially produced for diverse applications due to their unique characteristics. Nevertheless, its use in the concrete industry is not yet common and their physical-chemical effects as well as mechanical and durability capacities are subject of interest in recent research. Thus, the current study employed nS, FA, SF and polycarboxylate-type superplasticizer (SP) to determine their rheological characteristics at early age and their macro-mechanical properties in the hardened state. The rheological properties of grouts using the Marsh cone test (MCT) approach showed that mineral admixtures could improve the fluidity. Nevertheless, results also showed that MCT must be interpreted carefully when mineral additions are applied, because nonlinearities of the plastic viscosity could cause distortions in the MCT analyses. On the other hand, the hardened state of mortar samples containing nano/micro-SiO2 at w/b=0.35 was studied. SEM examinations in the ITZ suggested that compressive strengths of nano-SiO2-systems presented densification and filler effects, whereas micro-SiO2-systems only showed filler effects. Nevertheless, the study of concretes containing nS, SF, FA, and SP was more complex and statistical tools (DOE) and artificial neural simulations (ANN) were required. DOE results of compressive and tensile strength indicated that nS-SF binary mixes are the optimal choice to gain strength. However, DOE results also showed lack-of-fit of the second-order. But, the ANN could effectively explain the lack-of-fit inherit in the DOEs. Finally, splitting tensile failures were carried out on concretes to investigate the accuracy of the Weibull models. The estimated Weibull parameters were obtained by using modern advanced nonlinear methodologies. Statistical analysis indicated that some specific combinations of amorphous silica exhibited Weibull modulus higher than the control case. The novelty in these analyses is that despite the importance of the Weibull modulus in reliability analyses of brittle materials, the majority of the studies are on plain concretes. The data is especially scarce for nano-SiO2 on binary, ternary, and/or quaternary concretes mixes.