New Field Testing Procedure For Measuring Residual Stress in Plain Concrete Pavements and Structures

Residual stresses in rigid pavements diminish a pavement's ability to sustain its designed load. When capacity is reduced by residual stress, a pavement is vulnerable to premature failure necessitating costly repairs or replacement. A test method for measuring residual stresses has already been developed for steel wherein a small hole is drilled adjacent to an affixed surface strain gage (ASTM E837 2008). Based on the geometry of the test procedure, the change in strain reading is correlated to a residual stress in the steel material. While rigid pavements are as detrimentally affected by the formation of residual stresses as steel, no similar testing method exists for concrete. Recent research conducted by the Federal Aviation Administration's (FAA???s) National Airport Pavement Test Facility (NAPTF) investigated the strain relaxation of cantilevered concrete beams when a blind-depth hole using core drilling is made in the vicinity of an affixed strain gage. Initial findings indicated that the testing procedure partially quantified the residual stresses. Research at the University of Illinois at Urbana-Champaign (UIUC) improved the testing procedure using cantilevered concrete beams by instead sawing a linear notch near one end of the strain gage and sawing two linear notches near both ends of the strain gage. Results for the doubly notched concrete beam proved to be a much improved method for measuring residual stresses when compared to the core-drilled test procedure. The current project further improved test procedures and completed additional lab and field testing on in-situ plain concrete pavements. The test procedure was altered in order to observe the strain relaxation in three directions while four saw cuts are made surrounding the strain rosette. When this area of concrete had been appropriately isolated from load-induced stresses, simple calculations determine the residual stress of the material. Three dimensional Finite Element Model (FEM) analyses of these tests further corroborates the findings suggesting that the residual stresses in plain concrete pavements can be reliably measured

Casimir self-energy of a \delta-\delta' sphere

We extend previous work on the vacuum energy of a massless scalar field in the presence of singular potentials. We consider a single sphere denoted by the so-called "delta-delta prime" interaction. Contrary to the Dirac delta potential, we find a nontrivial one-parameter family of potentials such that the regularization procedure gives an unambiguous result for the Casimir self-energy. The procedure employed is based on the zeta function regularization and the cancellation of the heat kernel coefficient a_2. The results obtained are in agreement with particular cases, such as the Dirac delta or Robin and Dirichlet boundary conditions

XMM-Newton and Deep Optical Observations of the OTELO fields: the Groth-Westphal Strip

OTELO (OSIRIS Tunable Emission Line Object Survey) will be carried out with the OSIRIS instrument at the 10 m GTC telescope at La Palma, and is aimed to be the deepest and richest survey of emission line objects to date. The deep narrow-band optical data from OSIRIS will be complemented by means of additional observations that include: (i) an exploratory broad-band survey that is already being carried out in the optical domain, (ii) FIR and sub-mm observations to be carried with the Herschel space telescope and the GTM, and (iii) deep X-Ray observations from XMM-Newton and Chandra.Here we present a preliminary analysis of public EPIC data of one of the OTELO targets,the Groth-Westphal strip, gathered from the XMM-Newton Science Archive (XSA). EPIC images are combined with optical BVRI data from our broadband survey carried out with the 4.2m WHT at La Palma. Distance-independent diagnostics (involving X/O ratio, hardness ratios, B/T ratio) are tested.Comment: 2 pages, 2 figures, uses graphicx package. To appear in proceedings of "The X-Ray Universe 2005", San Lorenzo del Escorial, Spain, September 26-30, 200

Freeze-thaw environment of precast concrete crossties and effect of vibration on fresh materials

High performance concrete is typically designed to achieve high strength and low permeability. These suppositions lead practitioners to install high performance concrete in outdoor environments assured that members will remain durable over scores of years. One such outdoor environment is in railroad lines where timber ties (alternatively known as crossties or sleepers) are being replaced with high performance concrete crossties. Additionally, concrete crossties are being installed in burgeoning high speed rail networks across the United States of America. It has been observed, however, that these high performance concrete crossties are subject to multiple deterioration mechanisms including freeze-thaw damage. This early degradation in critical transportation infrastructure necessitates a better understanding of the durability of high performance concrete in wet, wintry climates. In particular, the concrete crossties have been found to degrade at the rail seat area where the crosstie is physically joined to the rail. Among several failure mechanisms, including abrasion and hydraulic pressure cracking, it is hypothesized that the dense configuration of the rail line, pad, clips, and crosstie leads to pooling of water at the underside of the pad. This stagnant water sits atop the concrete crosstie at the rail seat area and can permeate into the material leading to scaling and freezing-thawing damage in colder climates. In this study, the resiliency of high performance concrete crossties against freezing-thawing damage is assessed in a collaborative effort with researchers at Kansas State University and the University of Illinois at Urbana-Champaign. In this dissertation, specifically, the extent of internal moisture and temperature fluctuations of instrumented crossties installed in ballast is examined. Half-space approximations are applied to predict the fluctuation of internal conditions as affected by external environmental conditions. Additionally, this dissertation also examines the stability of chemically entrained air bubbles in fresh concrete when the fresh material is subjected to varying time and degree of vibration. The propagation and attenuation of the vibratory peak acceleration as a function of distance from the vibrating source and the volume content of aggregate is studied and compared against the extent of air loss and aggregate segregation as evidenced in polished, 2-dimensional sections. Summarily, the mutual instances of critical moisture saturation and freezing temperatures in concrete crossties are experimentally measured and predicted. The predictive models are modified to create a concrete crosstie freeze-thaw susceptibility index based on historical weather data. This susceptibility index better informs owners of concrete crosstie infrastructure of environmental design criteria for freezing-thawing damage potential. The vibratory experimental results lend insight into rheological phenomenon that can to enhanced guidelines for the consolidation of non-conventional concrete that optimizes compaction while mitigating the loss of entrained air and aggregate segregation. Taken together, these two research thrusts enhance the civil engineering community’s understanding of the durability and resiliency of high performance concrete exposed to cold climates

Vanishing chromosomal inversion clines in Drosophila subobscura from Chile: Is behavioral thermoregulation to blame?

Chromosomal inversion clines paralleling the long-standing ones in native Palearctic populations of Drosophila subobscura evolved swiftly after this species invaded the Americas in the late 1970s and early 1980s. However, the new clines did not consistently continue to converge on the Old World baseline. Our recent survey of Chilean populations of D. subobscura shows that inversion clines have faded or even changed sign with latitude. Here, we investigate the hypothesis that this fading of inversion clines might be due to the Bogert effect, namely, that flies' thermoregulatory behavior has eventually compensated for environmental variation in temperature, thus buffering selection on thermal-related traits. We show that latitudinal divergence in thermal preference (T-p) has evolved in Chile for females, with higher-latitude flies having a lower mean T-p. Plastic responses in T-p also lessen latitudinal thermal variation because flies developed at colder temperatures prefer warmer microclimates. Our results are consistent with the idea that active behavioral thermoregulation might buffer environmental variation and reduce the potential effect of thermal selection on other traits as chromosomal arrangements

Colloids in light fields: particle dynamics in random and periodic energy landscapes

The dynamics of colloidal particles in potential energy landscapes have mainly been investigated theoretically. In contrast, here we discuss the experimental realization of potential energy landscapes with the help of light fields and the observation of the particle dynamics by video microscopy. The experimentally observed dynamics in periodic and random potentials are compared to simulation and theoretical results in terms of, e.g. the mean-squared displacement, the time-dependent diffusion coefficient or the non-Gaussian parameter. The dynamics are initially diffusive followed by intermediate subdiffusive behaviour which again becomes diffusive at long times. How pronounced and extended the different regimes are, depends on the specific conditions, in particular the shape of the potential as well as its roughness or amplitude but also the particle concentration. Here we focus on dilute systems, but the dynamics of interacting systems in external potentials, and thus the interplay between particle-particle and particle-potential interactions, is also mentioned briefly. Furthermore, the observed dynamics of dilute systems resemble the dynamics of concentrated systems close to their glass transition, with which it is compared. The effect of certain potential energy landscapes on the dynamics of individual particles appears similar to the effect of interparticle interactions in the absence of an external potential