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Title:Use phase performances of photocatalytic cements
Author(s):Baral, Aniruddha
Advisor(s):Roesler, Jeffery R.
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Photocatalytic concrete
Photocatalytic cement
Titanium dioxide
Nano titanium dioxide (TiO2)
Use phase sustainability
Calcium Sulfoaluminate-Belite cement
White cement
Life cycle assessment
Nitrogen oxide (NOx) Removal
Glass aggregate
Abstract:Photocatalytic concrete containing nano TiO2 particles has generated interest in the 21st century for their air pollutant removal and self-cleaning performance on civil infrastructure components. In this research, photocatalytic cement pastes were evaluated for NOx removal in a laboratory photoreactor while the self-cleaning performance of photocatalytic mortar specimens were assessed though Rhodamine B (RhB) degradation. The self-cleaning and NOx removal capacity of Calcium Sulfoaluminate Belite (CSAB) cement relative to Ordinary Portland Cement (OPC) was compared. Finally, a use phase Life Cycle Assessment (LCA) was performed for concrete overlay made of either gray or white cement with or without titanium dioxide (TiO2) considering vehicular pollutant removal, Urban Heat Island (UHI) effect, and building energy consumption. Overall, NOx removal of photocatalytic CSAB was lower than white photocatalytic cement by 43% and 28% for noncarbonated and carbonated samples, respectively. Replacing both types of cement by fly ash decreased NOx removal in the non-carbonated state, but helped to reduce the adverse effect of carbonation. Based on XRD measurements, CSAB samples carbonated more than the OPC samples. CaCO3 content in white OPC and CSAB samples decreased with increase in TiO2 content and decrease in w/b. Carbonation of photocatalytic CSAB samples contained Calcite and Aragonite as the major phases and Vaterite as the minor CaCO3 phases, whereas carbonated white OPC samples had Calcite and Vaterite as the major CaCO3 phases without any Aragonite. The activation energy of the photocatalytic samples were lower than activation energy of pure nano TiO2 used in the specimens, which indicated the possibility of local defects in the TiO2 present in the paste. All photocatalytic paste sample in the presence of photons with energy just below the activation energy showed exponential decay (Urbach tail) in absorbance with decrease in photon energy, which is generally observed in semiconductors containing defects. Observance of Urbach tail of absorption confirmed the presence of local defects in TiO2 present in photocatalytic paste. The slope of the Tauc plot, which relates absorbance and photon energy, was used to represent the photoconductance of the samples. Carbonated samples had a higher slope than the noncarbonated samples indicating a higher photoconductance in the carbonated samples. The self-cleaning efficiency of all the photocatalytic mortar mixes increased with fine glass aggregate and TiO2 content, but the effect was less significant for mortar with CSAB compared to OPC. Replacement of cement with class F fly ash drastically decreased self-cleaning efficiency. It was hypothesized that decrease in pH of pore solution with fly ash replacement of OPC caused the decline in self-cleaning efficiency. An experiment to study RhB degradation with pH showed that the rate of RhB degradation increases with alkalinity. RhB can photocatalytically degrade through two mechanisms: N-de-ethylation and cleavage of chromophore structure depending on the reaction surface characteristics. N-de-ethylation of RhB involves successive removal of the ethyl groups in RhB, whereas cleavage of the chromophore structure involves removal of the conjugated chromophore structure in RhB. Some of the RhB on the mortar surface was degraded by N-de-ethylation path regardless of the cement and aggregate used. Overall, increasing TiO2 (anatase) content increased RhB degradation through N-de-ethylation. In the use phase LCA study, the NOx removal of white photocatalytic cement was set higher than gray photocatalytic cement based on photoreactor results and the albedo of white cement was significantly higher for white cement over gray cement. Given these properties as input to the LCA, white cement concrete overlays had five times less Global Warming Potential (GWP) than gray cement and produced a net decrease in indoor energy consumption of 9.5 kWh per capita per year compared to gray cement. The environmental impacts of concrete overlay with different binder combinations were converted into ten Normalized Environmental Impact Parameters (NEIPs) and a single-score Net Environmental Impact (NEI) with gray cement without TiO2 as the control case. Addition of TiO2 in concrete decreased acidification, ecotoxicity, eutrophication, human health degradation factors, smog formation and respiratory effects, whereas using white cement instead of gray cement decreased all ten NEIPs and NEIs. The most substantial reduction in NEI was for white cement with TiO2 with NEI at -1.16×〖10〗^(-2) and the least reduction was for gray cement with TiO2 with NEI at -5.35×〖10〗^(-4).
Issue Date:2017-12-15
Rights Information:Copyright 2017 Aniruddha Baral
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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