1,720,993 research outputs found
Investigation of Reactive Electrokinetic Processes for Permeability Reduction in Hardened Cement Paste
No full textThis work examined the feasibility of transporting chemical precursors into hardened cement paste pores using an electric field and causing them to undergo a chemical reaction that results in blocking the pores and reducing permeability. The chemical precursors, silicate and aluminate solutions and sols, were tested with simulated pore fluid solutions to assess production of precipitates within pores. Electrokinetic pore blocking processes were modeled using micropore filters. Permeability tests were used to study the effect of these processes on hardened cement pastes of high water/cement ratio and of both high and low alkali contents. Significant reductions in coefficients of permeability were observed in model filter systems. Similar results were obtained for hardened cement paste. In each case, it was seen that treatment particles entered pore systems and reacted with pore fluid constituents to produce precipitates. The coefficients of permeability for each of these systems were reduced by at least one order of magnitude. It was observed that the system impedance provided an indication of the permeability-reduction effectiveness of a given process. A transport model was developed to determine the viability of a given treatment candidate. This model predicted the extent of penetration achievable by a treatment as a function of competing transport processes (hydraulic pressure flow, electroosmosis, and ionic conduction). Model predictions correlated well with observed cement paste microstructures and permeability measurements. In addition to conducting hydraulic permeability tests, impedance measurements were also used to predict the viability of a given treatment process. An analytical model was developed to correlate impedance measurements to permeability measurements. This model was based on laminar Poiseuille flow mechanics and the definition of ohmic resistivity as applied to a parallel tube flow system. It was found that this model worked well in predicting changes in system permeability as a function of the observed change in system resistivity. The findings of this study indicate that reactive electrophoretic reduction of permeability can be achieved in hardened cement paste in the presence of an opposing hydraulic flow and that the potential influence of a treatment candidate can be predicted with the use of these physical and analytical models.Made available in DSpace on 2015-09-25T21:03:25Z (GMT). No. of bitstreams: 2
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Previous issue date: 2002Embargo set by: Seth Robbins for item 84467
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Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only239 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002
Interactions Between Portland Cements and Carboxylated and Naphthalene-Based Superplasticizers
No full textIn the final part of this study, the relation between the concrete slumps and the paste rheology is established. However, concretes required much less superplasticizer than paste to be dispersed. The differences in the shear history between the concretes and the pastes possibly explain such discrepancies in admixture dosages.Made available in DSpace on 2015-09-25T21:04:16Z (GMT). No. of bitstreams: 2
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3269856.pdf: 13790261 bytes, checksum: c350a36d74e41881480edd87387c5f55 (MD5)
Previous issue date: 2007Embargo set by: Seth Robbins for item 84602
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only426 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The Development of the Strength Index Method and Protocol for Assessing the Use of Solid Waste Materials in Concrete
No full textThe reactivity of the sludge ashes, as measured by the SIM showed that the sludge ashes in this study can be classified as reactive using the 28 day index values. Concrete containing sludge ash generally exhibited less compressive strength and modulus of elasticity when compared to concrete containing 100% portland cement (control) at all test ages. The stress-strain relationship for the BP and CR concretes were not as stiff as the control concrete but DU and LM concretes exhibited equivalent stiffness as the control concrete. All concrete specimens exceeded the minimum freeze-thaw requirements for durable concrete as tested under ASTM C 666. Concrete mixes containing sludge ash passed the toxicity leaching test and provide economic benefits to the producer and user.Made available in DSpace on 2015-09-25T21:05:07Z (GMT). No. of bitstreams: 2
license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5)
9944807.pdf: 8135239 bytes, checksum: c7f641d860ba417f8b7da2dc92262686 (MD5)
Previous issue date: 1999Embargo set by: Seth Robbins for item 84755
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only288 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1999
Synthesis and fracture toughness of macro-defect-free (MDF) cement
Full text linkMacro-defect-free (MDF) cements were developed following work by the research group led by Birchall at ICI during the late 1970s and early 1980s. MDF cement is a cement-polymer composite seen to provide the high stiffness of a hydrated cementitious material with the high tensile strength of a polymer composite. It is usually made using polyvinyl alcohol (PVA) that undergoes some crosslinking with Al(OH)6 released as the cement hydrates. It is processed using high shear, typically in a twin roller mill. The most remarkable property of MDF is its high flexural strength, 200-300 MPa as compared to 5–10 MPa for hardened cement pastes. The inventors attributed the high tensile strength to the processing, which they claimed removed large voids otherwise seen in cementitious materials such as Portland cement concrete, hence the basis for the name. Later studies demonstrated that crosslinking occurs between polymer and hydrating cement and that this crosslinking plays an important role in the achievement of high strength. However, there are few reports on the study of the fracture toughness of MDF. A common test, the two-parameter fracture method, based on the simple premise that a change in specimen compliance can be correlated to the length of the effective crack at the time the critical (i.e., peak) load is reached, is used to measure fracture toughness of MDF. With the theory of linear elastic fracture mechanics (LEFM), the loads and displacement associated with crack propagation in notched beams can be analyzed easily. A typical fracture toughness value of 1.6-1.8 MPa • m1/2 was obtained. Also, a microhardness test is used to measure fracture toughness because it suits the form of the specimens and is a simple and expedient experiment, however, it didn’t generate well-identified cracks.Item withdrawn by Laura Spradlin ([email protected]) on 2014-05-01T15:06:33Z
Item was in collections:
University of Illinois Theses & Dissertations (ID: 1)
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Characterization of calcium-silicate-hydrate and calcium-alumino-silicate-hydrate
Full text linkThe primary objectives of this thesis were to synthesize calcium silicate hydrate
(C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) and characterize their
structures with varying Ca/Si ratios and aluminum content. As a secondary objective,
carbonation behavior in synthesized C-S-H was studied. C-S-H was synthesized in the
lab using two different methods: the double decomposition of calcium nitrate and
sodium silicate solutions, and the direct reaction between calcium oxide and fumed
silica in water. In C-A-S-H the source of aluminum was sodium aluminate or aluminum
nitrate. A variety of phases were present depending on the degree of carbonation of the
C-S-H or C-A-S-H. C-S-H, C-A-S-H, alumina/silica gel, calcite, aragonite, and vaterite
were all observed throughout the course of study. X-ray diffraction (XRD) was the
technique used to identify these phases. XRD was also used to explore the changes in
crystal structure with varying Ca/Si ratios and aluminum content. No significant
changes to the crystal structure were found. The effect of Ca/Si ratio, aluminum
content, and synthesis method were studied on the molecular scale using 29Si and 27Al
nuclear magnetic resonance spectroscopy (NMR). An increasing Ca/Si ratio has the
effect of a shorter alumino-silicate chain length and an increase in aluminum content
increases the alumino-silicate chain length. Aluminum substitution occurred primarily
in the bridging tetrahedron position, but also in the pairing tetrahedron position.
Aluminum uptake was also examined with respect with Ca/Si ratio and was found to
decrease with increasing Ca/Si ratio. The changes in chemical environment of the
iii
aluminum ion with varying Ca/(Si+Al) ratios was also observed by 27Al NMR. It was
found that as the Ca/(Si+Al) ratio increased, the amount of chemical shielding of the
27Al nuclei decreased . Carbonation of C-S-H was also examined and it was found that
the double decomposition synthesis method allows for more rapid carbonation of the CS-
H. The source of increased carbonation rate is the high pH of the solutions.Item withdrawn by Mark Zulauf ([email protected]) on 2013-07-16T18:55:20Z
Item was in collections:
University of Illinois Theses & Dissertations (ID: 1)
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Modeling Alkali -Silica Reaction Using Image Analysis and Finite Element Method
No full textThe microstructure-based model developed in the present study appears to be unique and promising in spite of some difference because the numerical results are in a good agreement with experimental data. It is considered that image analysis and FEM are powerful tools to understand the overall behavior of concrete affected by ASR.Made available in DSpace on 2015-09-25T21:04:45Z (GMT). No. of bitstreams: 2
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Previous issue date: 2009Embargo set by: Seth Robbins for item 84695
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only217 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009
Using Dynamic Rheology to Explore the Microstructure and Stiffening of Cementitious Mixtures
No full textThe cement paste and the wollastonite pastes made from pore solutions extracted from cement pastes both vary with time according to a power-law, and the exponents are approximately the same. Stiffening of cement paste in the first hour appears to be due to increase in ionic strength by hydration.Made available in DSpace on 2015-09-25T21:03:20Z (GMT). No. of bitstreams: 2
license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5)
3030498.pdf: 7489720 bytes, checksum: 0244a7aa02313d8c586db5ef0f1163aa (MD5)
Previous issue date: 2001Embargo set by: Seth Robbins for item 84457
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only199 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2001
Modeling Alkali -Silica Reaction Using Image Analysis and Finite Element Method
No full text217 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.The microstructure-based model developed in the present study appears to be unique and promising in spite of some difference because the numerical results are in a good agreement with experimental data. It is considered that image analysis and FEM are powerful tools to understand the overall behavior of concrete affected by ASR.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD
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