Soto Pérez, Linoshka

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    Optimization of pervious concrete incorporating coal fly ash, iron-oxide nanoparticles and water reducing admixtures and its application for the removal of nutrients and fecal coliforms
    (2015-05) Soto Pérez, Linoshka; Hwang, Sangchul; College of Engineering; Molina Bas, Omar I.; Bogere, Moses N.; Department of Civil Engineering; Cortés, José
    Physicomechanical characteristics and durability of the cement pastes containing fly ash (FA) and iron-oxide nanoparticles (NI) showed that workability was reduced with the FA addition, although it was counterbalanced when NI was added. FA substitution enhanced the durability of the hardened pastes by gaining weight and compressive strength when exposed to tap water. However, in acid solutions, the FA substitution produced a negative effect on the durability of the hardened pastes. In comparison, the addition of NI alone increased the compressive strength of the hardened pastes exposed to acid solutions. Concrete is the most widely used engineering construction material. There are different cement mixtures with special properties and chemical compositions that are made to specifications for specific applications. Concrete properties such as strength and durability mostly depend on its internal microstructure, which can be modified and improved by adding mineral admixtures and other additives. Several experiments were conducted to assess the physicomechanical and durability properties of cement pastes containing different additives, optimize the combination of different mixture components and, make a reactive Portland cement pervious concrete (PCPC) and evaluate its mechanical and hydrological capabilities, as well as the FC inactivation and nutrients removal from water. Different curing periods during the development of compressive strength of the cement pastes with FA and NI as admixtures showed that lower compressive strength (CS) was achieved with the increase of FA at early periods of curing. On the other hand, the CS was improved after 90 days of curing. The NI only contribute to the CS at late curing ages. The effect of cement type on the spread percentage (SP) and the compressive strength at 28 days of curing was also evaluated in the cement pastes. The optimum mix ratio of two cement types was obtained for a desired SP and the maximum possible CS. The addition of NI to the mixtures did not play a significant role in the development of the CS at 28 days of curing. The optimum variable settings for the Type IP cement were at 35.1 % W/B, 28.5% FA/B and 1.6% NI/B, while for the Type GU cement the settings were obtained at 35.1% W/B, 40% FA/B and 0.55% NI/B. Slightly higher predictive compressive strength at 64.72 MPa for the Type GU cement was obtained, while for the Type IP a 62.78 MPa was predicted. Quadratic and interaction effects of the factors resulted in playing a significant role in the development of both of the prediction models of the dependent responses. The effect of aggregate type and grading size on the manufacture of PCPC and its performance permeability and CS were evaluated. Gravels retained in the sieves with smaller opening size were better for the PCPC production since a higher compressive strength was obtained. At the same time the permeability was kept between the ranges established for PCPC by the American Concrete Institute. Partial clogging due to the drainage of the binder materials was observed for some of the specimens due to an excess in the W/B ratios and the reduction of FA/B in the PCPC. A green pervious concrete surface (GPCS) capable of removing contaminants from water was developed in a four factor, two level central composite design to investigate the main, quadratic and interaction effects of the independent variables on the permeability and compressive strength. The increment of W/B and the reduction of FA/B independent of the settings of NI/B and WR/B resulted in a decrease of the permeability. The addition of high amounts of FA/B required a large addition NI/B in order to achieve a compressive strength higher than 20.7 MPa, while lower additions of FA/B were found to require less amount of NI/B to achieve similar CS’s. Phosphorus and FC removals were achieved at a high pH, with average values for FC inactivation of 74.2, 67.9 and 95.4% at 2 hour contact time, and for phosphorus removal of 92.6, 84.6 and 100% for Opt A, Opt B and Control, respectively. The increase of contact time improved the nitrate reduction, achieving removals up to up to 79.0, 48.8 and 54.3% by the Opt A, Opt B and Control, respectively. Weight increment in all GPCS’s was observed when exposed to either water or sulfuric acid, although the increment was more noticeable for the specimens placed in water. On the contrary, GPCS placed in the acetic acid solution resulted in a rapid weight loss from the beginning of the experiment. The simultaneous addition of FA and NI resulted in a higher compressive strength for the GPCS even after the exposure to acids.