Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

An investigation into aggregate breakage has been carried out using suspensions of uniform polystyrene spheres destabilised by addition of salt or polymer. A controlled flow apparatus was used to expose the suspended aggregates to turbulent pipe flow of variable intensity and duration. Analysis of aggregate size distribution was carried out using the HIAC light obscuration technique.

No description available.

Sustainable resource management and development have been at the forefront of important issues concerning the construction industry for the past several years. Specifically, the use of sustainable building materials and the reuse and recycling of previously used building materials is gaining acceptance and becoming common place in many areas. As one of the most commonly used building materials in the world, concrete, composed of aggregate, sand, cement and water, can be recycled and reused in a variety of applications. Using crushed concrete as fill and subgrade material under roads, sidewalks and foundations has been the most common of these applications. However, research has been ongoing over the past 50 years in many countries including Germany, Canada, Japan, the United States, China, and Australia investigating the use of crushed concrete from demolished old concrete structures to fully or partially replace the virgin aggregate used to produce new concrete for use in building and pavement applications. Producing concrete using recycled concrete aggregates (RCAs) has several advantages, namely, the burden placed on non-renewable aggregate resources may be significantly decreased, the service life and capacity of landfill and waste management facilities can be extended, and the carbon dioxide emissions and traffic congestion associated with the transport of virgin aggregates from remote sites can be reduced. This research is directed at benchmarking typical RCA sources for usage in structural concrete and investigating the inter-relationships between aggregate properties, concrete properties and the bond properties between reinforcing steel and RCA concrete. The experimental program focused on four main areas: aggregate properties testing, development of concrete mixture proportions, concrete fresh and hardened properties testing, and beam-end bond testing. Four coarse aggregate sources were investigated including one virgin or natural aggregate (NA) source, and three RCA sources. Two RCA sources were derived from the crushing of decommissioned building and pavement structures (RCA-1 and RCA-2) while the third source was derived from the crushing of returned ready-mix concrete (RCA-3). A variety of typical and non-typical aggregate tests were performed to provide a basis for correlation with fresh and hardened concrete properties results. A total of 24 concrete mixtures were developed and divided into three separate categories, 1) control, 2) direct replacement, and 3) strength-based mixtures. The control mixtures were proportioned to achieve compressive strengths of 30, 40, 50 and 60MPa with slump values between 75 and 125 mm and served as a basis for comparison with the RCA concrete mixtures. The direct replacement mixtures were developed to investigate the effect that fully replacing (i.e., 100% replacement by volume) virgin coarse aggregate with RCA has on the fresh and hardened properties of the resulting concrete. The strength-based mixtures were developed to investigate the influence of aggregate properties on reinforcement bond in concrete having the same compressive strength. In addition, two separate experimental phases were carried out which had varying compressive strength ranges, different RCA sources, and different suppliers of the same type GU cement. Concrete properties such as slump, compressive strength, splitting tensile strength, modulus of elasticity, Poisson’s ratio, linear coefficient of thermal expansion (LCTE), modulus of rupture and fracture energy were all measured. In total, 48 beam-end specimens were tested that incorporated three bonded lengths (125, 375, and 450 mm) and four concrete compressive strengths (30, 40, 50 and 60 MPa). Based on the results of the aggregate testing it was found that concrete incorporating pre-soaked (i.e., fully saturated) RCA as a 100% replacement for natural aggregate had slump values between 22% and 75%, compressive strengths between 81% and 137%, splitting tensile strengths between 78% and 109%, modulus of elasticity values between 81% and 98%, LCTE values in the same range, flexural strengths between 85% and 136%, and fracture energies between 68% and 118%, of the equivalent control (natural aggregate) concrete mixture. Overall, reductions in bond strength between natural aggregate and RCA concrete ranged between 3 and 21%. The strength of coarse aggregate as quantified by the aggregate crushing value (ACV) was found to be the most significant aggregate property for influencing bond strength. A regression model (based on the beam-end specimens test results) was developed to extrapolate the experimental development lengths as a function of f’c1/4 and ACV. The model, while not intended for use as a design equation, predicted that the required development lengths for the RCA concrete tested as part of this research study were up to 9% longer as compared to the natural aggregate concrete. A detailed flowchart of the various inter-relationships between aggregate properties, concrete properties and reinforced concrete bond properties was compiled based on the results of this research. A comprehensive guideline for use of RCA in concrete was developed based on the findings of this research. It includes a systematic decision tree approach for assessing whether a particular RCA source can be categorized into one of three performance classes. The range of allowable applications of a concrete which incorporates the RCA source as replacement of natural coarse aggregate will depend on the RCA performance class.

Sustainable resource management and development have been at the forefront of important issues concerning the construction industry for the past several years. Specifically, the use of sustainable building materials and the reuse and recycling of previously used building materials is gaining acceptance and becoming common place in many areas. As one of the most commonly used building materials in the world, concrete, composed of aggregate, sand, cement and water, can be recycled and reused in a variety of applications. Using crushed concrete as fill and subgrade material under roads, sidewalks and foundations has been the most common of these applications. However, research has been ongoing over the past 50 years in many countries including Germany, Canada, Japan, the United States, China, and Australia investigating the use of crushed concrete from demolished old concrete structures to fully or partially replace the virgin aggregate used to produce new concrete for use in building and pavement applications. Producing concrete using recycled concrete aggregates (RCAs) has several advantages, namely, the burden placed on non-renewable aggregate resources may be significantly decreased, the service life and capacity of landfill and waste management facilities can be extended, and the carbon dioxide emissions and traffic congestion associated with the transport of virgin aggregates from remote sites can be reduced. This research is directed at benchmarking typical RCA sources for usage in structural concrete and investigating the inter-relationships between aggregate properties, concrete properties and the bond properties between reinforcing steel and RCA concrete. The experimental program focused on four main areas: aggregate properties testing, development of concrete mixture proportions, concrete fresh and hardened properties testing, and beam-end bond testing. Four coarse aggregate sources were investigated including one virgin or natural aggregate (NA) source, and three RCA sources. Two RCA sources were derived from the crushing of decommissioned building and pavement structures (RCA-1 and RCA-2) while the third source was derived from the crushing of returned ready-mix concrete (RCA-3). A variety of typical and non-typical aggregate tests were performed to provide a basis for correlation with fresh and hardened concrete properties results. A total of 24 concrete mixtures were developed and divided into three separate categories, 1) control, 2) direct replacement, and 3) strength-based mixtures. The control mixtures were proportioned to achieve compressive strengths of 30, 40, 50 and 60MPa with slump values between 75 and 125 mm and served as a basis for comparison with the RCA concrete mixtures. The direct replacement mixtures were developed to investigate the effect that fully replacing (i.e., 100% replacement by volume) virgin coarse aggregate with RCA has on the fresh and hardened properties of the resulting concrete. The strength-based mixtures were developed to investigate the influence of aggregate properties on reinforcement bond in concrete having the same compressive strength. In addition, two separate experimental phases were carried out which had varying compressive strength ranges, different RCA sources, and different suppliers of the same type GU cement. Concrete properties such as slump, compressive strength, splitting tensile strength, modulus of elasticity, Poisson’s ratio, linear coefficient of thermal expansion (LCTE), modulus of rupture and fracture energy were all measured. In total, 48 beam-end specimens were tested that incorporated three bonded lengths (125, 375, and 450 mm) and four concrete compressive strengths (30, 40, 50 and 60 MPa). Based on the results of the aggregate testing it was found that concrete incorporating pre-soaked (i.e., fully saturated) RCA as a 100% replacement for natural aggregate had slump values between 22% and 75%, compressive strengths between 81% and 137%, splitting tensile strengths between 78% and 109%, modulus of elasticity values between 81% and 98%, LCTE values in the same range, flexural strengths between 85% and 136%, and fracture energies between 68% and 118%, of the equivalent control (natural aggregate) concrete mixture. Overall, reductions in bond strength between natural aggregate and RCA concrete ranged between 3 and 21%. The strength of coarse aggregate as quantified by the aggregate crushing value (ACV) was found to be the most significant aggregate property for influencing bond strength. A regression model (based on the beam-end specimens test results) was developed to extrapolate the experimental development lengths as a function of f’c1/4 and ACV. The model, while not intended for use as a design equation, predicted that the required development lengths for the RCA concrete tested as part of this research study were up to 9% longer as compared to the natural aggregate concrete. A detailed flowchart of the various inter-relationships between aggregate properties, concrete properties and reinforced concrete bond properties was compiled based on the results of this research. A comprehensive guideline for use of RCA in concrete was developed based on the findings of this research. It includes a systematic decision tree approach for assessing whether a particular RCA source can be categorized into one of three performance classes. The range of allowable applications of a concrete which incorporates the RCA source as replacement of natural coarse aggregate will depend on the RCA performance class.

The structure of the dihydrolipoamide acetyltransferase (E2p) component of the pyruvate dehydrogenase complex from <i>Escherichia coli</i> and its role in catalysis were studied by the combined approaches of protein engineering, limited proteolysis and <SUP>1</SUP>H-n.m.r. spectroscopy. Genetic reconstruction of the E2p component (performed elsewhere) produced a series of mutant complexes assembled around E2p chains which contain only a single lipoyl domain and an associated (alanine+proline)-rich linker region of gradually diminishing lengths (32, 20, 13, 7 and 1 residue(s), respectively, in the pGS110-,pGS156-,pGS186 ,pGS187- and pGS188-encoded complexes). When this region was shortened to 13 residues or less, the system of active-site coupling in the enzyme complex was dramatically impaired, although the individual enzyme activities were unaffected. The role of the (alanine+proline)-rich region in facilitating moment of the lipoyl domains in catalysis was thus established. The (alanine+proline)-rich regions of the wild-type E2p chains had previously been conjectured to be the source of the unexpectedly sharp resonances in the <SUP>1</SUP>H-n.m.r. spectrum of the enzyme complex, and hence to be conformationally mobile. Examination of the genetically restructured complexes by <SUP>1</SUP>H-n.m.r. spectroscopy revealed that the intensity of the sharp peaks in the spectra correlated well with the length of the (alanine+proline)-rich region in each complex. Furthermore, resonances from a single histidine residue engineered into the (alanine+proline)-rich region of a pGS110-encoded E2p chain was clearly visible in the <SUP>1</SUP>H-n.m.r. spectrum of the resulting enzyme complex. These experiments proved unequivocally that the (alanine+proline)-rich regions are conformationally mobile. The <SUP>1</SUP>H-n.m.r. spectra of the mutant complexes with the most severe deletions in the E2p chains differed from those of the wild-type and pGS110-encoded complexes in that they displayed a novel sharp peak which was not initially apparent in the spectra of the parent assemblies. This resonance was tentatively assigned to another, shorter (alanine+proline)-rich sequence in the E2p chain, which separates the dihydrolipoamide dehydrogenase (E3)-binding and inner-core domains in the <i>C</i>-terminal half of the molecule. It is likely therefore that this sequence is also conformationally flexible. Antibodies against a synthetic peptide with the sequence of the long (alanine+proline)-rich region of the pGS110-encoded E2p chain were raised elsewhere. Binding of the Fab fragments of these antibodies to the pGS110-encoded complex was found to inhibit the overall complex activity even though the activities of the three component enzymes were not affected. Antibody binding was shown to prevent both the reductive acetylation of the lipoyl domains at the pyruvate decarboxylase (E1p) active site and the transfer of acetyl groups between adjacent lipoyl domains, demonstrating the role of the (alanine+proline)-rich sequence in the mechanism of substrate transfer between active sites. A detailed study of the conformation of the (alanine+proline)-rich regions was also undertaken. Synthetic peptides were obtained with sequences identical to the central and innermost such regions of the wild-type E2p chain. The conformation of these peptides in aqueous solution was studied by circular dichroism, <SUP>1</SUP>H-n.m.r. and <SUP>13</SUP>C-n.m.r. spectroscopy. Relaxation time and nOe data pointed to an extended conformation for the peptides, a structure enforced by the predominantly <i>trans</i> Ala-Pro peptide bond. The functional consequences of this conformation and the role of these sequences in the structure and the function of the enzyme complex are discussed.

3 pp. / Gypsum can help stabilize aggregate structure in some soils.

Revised; Originally Published 2006 / 5 pp.

The aim of this work was to use simulation as a tool to better understand areas of orthokinetic (shear-induced) aggregation which are still not well understood. These areas include aggregate structure, aggregate strength, breakup and restructuring and combined perikinetic/orthokinetic aggregation. Previous simulation studies were reviewed and it was concluded that the methodology of Chen and Doi (1989) was an appropriate starting point for this study. The modified simulation was validated by comparison with theoretical and experimental results. Orthokinetic aggregates were found to have a fractal structure with an estimated value of 1.65. Scaling exponents, which were shown to be indicative of fractal dimension, of 2.1-2.7 were also obtained. Flexible bonds allowed restructuring to occur which led to an increase in the co-ordination number, scaling exponent, aggregate strength and a reduction in aggregate size. Thus aggregate strength increases with fractal dimension. It was confirmed that both restructuring and breakup/reformation could lead to the formation of small, compact aggregates. The high shear conditions simulated favoured breakup/reformation, while restructuring was expected to dominate with more flexible bonds, possibly at lower shear rates. Taking some account of hydrodynamic interactions by the inclusion of Kirkwood-Riseman theory led to an increase in the compactness of the aggregates and the co-ordination numbers, as well as a decrease in size of the aggregates. The results showed that hydrodynamic interactions can not be ignored. The explanation for the dramatic effects was that particles/microflocs on the outer edges of the aggregates broke off and reformed in a more compact way. Erosion was found to dominate in all cases, thus supporting the theory that erosion dominates at higher fractal dimensions. The shearing range simulated was found to be relatively high (equivalent to &lt200s-1 for particles of 2-5??m), producing relatively small aggregates. Hence it is proposed that under high shear conditions, erosion dominates. It was shown by extension of the DLCA algorithmic restructuring work of Meakin and Jullien (1988, 1989) that the scattering patterns observed in gently sheared aggregating systems are consistent with the interpretation that the shearing causes partial restructuring at large length scales.

Gravel aggregates had been used extensively in the Houston District of Texas Department of Transportation (TxDOT) for continuously reinforced concrete pavements construction for many years. However, some of these pavements have been subject to early age delamination and eventual spalling damage. Therefore, a series of studies funded by TxDOT since the early 1990's has been conducted to gain a better understanding of mechanisms, material properties, and construction practices, and to provide guidelines and recommendations for minimizing early-age delamination in concrete pavements made with gravel aggregates. In this study, a test protocol to measure the bond strength between aggregates and cement mortar was established, and the effects of different material and construction parameters on the bond strength of concrete at early ages using a fractional factorial design were investigated. The significances of each factor to achieve better bonding performance were determined, and the optimum design combination was subsequently chosen and validated. Geometric parameters were proposed to characterize aggregate shape properties relative to bonding performance with the facilitation of the Aggregate Imaging System. A rating system based on utility theory was developed to evaluate the overall contribution of aggregate properties (i.e. physical, geometric, and chemical) to the concrete bonding capability and the feasibility of certain mixture design combinations. As for theoretical representation of the bond strength across the interfacial transition zone, a model of interfacial fracture energy between aggregate and mortar that represents the energy necessary to create a crack along the interface was formulated. This model built the connection between concrete properties at the meso-level (represented by the interfacial fracture energy between aggregate and mortar) and the macro-level (represented by fracture toughness of concrete and significant influencing materials and construction factors). In addition, the moisture effects on stress development of concrete pavements at early ages using field data as inputs were numerically simulated, and a fracture mechanics-based approach was used to predict the occurrence of delamination. A delamination detection protocol for the field was developed to explore the feasibility and potential of utilizing Ground Penetration Radar technology in delamination detection. Research findings from laboratory investigation, field testing, theoretical modeling, and numerical analysis were further validated through field test sections, and the associated framework for delamination guidelines was established.