Vázquez-Rivera, Natalia I.

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    Statistical optimization of pervious concrete pavement containing fly ash and engineered iron oxide nanoparticles for runoff quality and quantity controls
    (2014) Vázquez-Rivera, Natalia I.; Hwang, Sangchul; College of Engineering; Molina Bas, Omar I.; Bogere, Moses; Department of Civil Engineering; Sundaram, Paul
    Portland cement pervious concrete (PCPC) usage has increased due to its potential to reduce storm water runoff and related pollution. Partial Portland cement substitution by fly ash (FA) in concrete production has the advantages of reducing cost, carbon dioxide production associated with Portland cement production and burden of solid waste management. In this regard, a cementitious paste was characterized and a PCPC mixture was optimized by Response Surface Methodology. Also the PCPC was tested for phosphorus removal capacity. As part of the characterization of cementitious paste, spread percentage and setting time were measured. The addition of engineered iron oxide nanoparticles coated with surfactant (ENPFe-surf) increased both the spread percentage and setting time. Also the ENPFe-surf addition slightly increased weight gain when exposed to sulfuric acid, but slightly decreased weight loss when exposed to acetic acid. It is possible that ENPFe-surf facilitates the production of calcium silicate hydrate (C-S-H gel), iron-substituted monosulfate hydrate, or iron-substituted ettringite. The specimens exposed to sulfuric acid had higher compressive strength values compared to those exposed to acetic acid for 90 days. A two-level central composite factorial design was used to investigate the effects of water to powder ratio (W/P, 0.34-0.40), percentage of cement substitution by FA (FA/B, 0.1-0.4) and ENPFe-surf to powder ratio (ENP/B, 0.03-0.05) on compressive strength, permeability, void content and hardened density of pervious concrete. Limestone gravels passing through 9.5-mm sieve but retained on 4.75-mm sieve were used. The results showed compressive strength, permeability, void content and hardened density in the ranges of 2.5-13.5 MPa, 5.3-17.4 mm/sec, 12-22 % and 2120-2360 kg/m3, respectively. W/B and FA/B had significant impacts on all the properties of PCPC studied, whereas ENP/B produced significance only for the compressive strength. Optimal region was found for the desired PC parameters at W/B 34%, FA/B 15% and ENP/B 5%. The PCPC was capable of removing phosphorus by adsorption and/or precipitation. The PCPC specimens with ENPFe-surf had greater removal capacity so it is believe that it facilitated phosphate removal. There was 7% and 10% difference between the first-order phosphorus removal constant obtained for PCPC specimens with or without ENPFe-surf. Similarly, there was between 6% to 10% difference for the Freundlich isotherm Kf coefficients obtained for control samples compared to the sample that had FA and ENPFe-surf added. The dissolution of calcium hydroxide from PCPC was believed to facilitate phosphorus precipitation probably as amorphous calcium phosphorus or hydroxyapatite. Fenton regeneration increased permeability of bioclogged PCPC specimens. ENPFe-surf addition did not play a role in Fenton oxidation. Instead, iron species containing FA were believed to work as the iron catalyst for Fenton oxidation. Compressive strength was not negatively affected despite string oxidation reaction during Fenton regeneration.