Non-destructive Evaluation of Concrete using Electrical Resistivity and Ultrasonic Wave Propagation

With the intent to investigate the relationship between concrete physical properties and non-destructive evaluation techniques (NDE), several experiments were performed. Specimens were made at varying geometries using a range of different concrete mixes under several different curing conditions. These specimens were subjected to a combination of electrical resistivity and ultrasonic wave propagation measurements. One part of this study investigated determining the orientation of steel fibers using electrical resistivity. This resulted in the fabrication of a four-probe square device with the potential capabilities of determining fiber orientation. The other part of this research applied ultrasonic wave propagation via through-transmission along with electrical resistivity via the uniaxial method. The results from this uncovered an exponential relationship between the pulse wave velocity and formation factor for saturated specimens. With the formation factor’s relationship to strength and microstructural properties, this relationship may lead to predicting strength and pore structure using relationships to a simple ultrasonic property

Dynamic characterization of high performance materials for application to cultural heritage

Natural hazards, such as earthquakes, can compromise the integrity of the cultural heritage with potentially devastating effects. The reduction of the seismic vulnerability of the cultural heritage constitutes a question of maximum importance especially in countries where vast cultural heritage combines with a medium or high seismic risk, such as in Italy. From the second half of the last century, the scientific community edited a number of important documents and charts for the conservation, reinforcement and restoration of the cultural heritage. The aim is to mitigate the seismic vulnerability of the cultural heritage. This research focused on high performance materials for applications aimed to structural and seismic protection of cultural heritage, with a special focus on historical masonry structures. In particular, the final aim is to define a self-diagnosis strategy for fibres, yarns and ties in view of efficient, non-invasive and reversible interventions on cultural heritage buildings. In order to set up the scene, the present thesis starts by introducing the reader to the seismic protection of cultural heritage thorough an extensive review on high performance materials, strengthening techniques and systems, taking care to highlight real world applications and limitations of their use. The second step of this work concerns in the mechanical and rheological characterization of high performance material fibres. The materials investigated are essentially Kevlar® 29 (para-aramid), Carbon and Silicon Carbide. To reach this goal, an extensive experimental testing campaign was conducted on fibres and yarns in accordance with specific protocols. A further step was defining appropriate damage indices for different materials, with a special focus on Kevlar® 29. Within the same research programme, a novel testing machine was also designed in cooperation with the Laboratory of Electronic Measurements of the Politecnico di Torino. A prototype-testing machine for dynamic testing on high resistance fibres was built using recycled materials and components. A distinctive feature of this machine is that it can apply to the sample any kind of dynamic excitation (random, impulse, harmonic etc.). A second testing campaign concerned the durability of Kevlar® 29 fibres, which are known to be sensitive to long-term exposure to UV radiation. Accordingly, for this campaign, the samples were artificially damaged by using UV lamps. The analysis of the resonance profiles allowed for the extraction of parameters such as the elastic moduli, quality factors, and non-linear coefficient for a set of fibres. In particular, non-linearity parameters derived from the Krylov-Bogoliubov method demonstrated to be consistent with the damage affecting the fibres. The final chapter of the dissertation concerns a new concept for a tie endowed with self-diagnosis properties, which are obtained by integrating a low cost testing device into the tie model. The self-diagnosis properties system of existing structures has an important role in the preservation of the cultural heritage because the best therapy is preventive maintenance. Specifically, the para-aramid tie system proposed for the reinforcement of historic building constitutes a non-invasive, reversible and repeatable intervention, as required by the main guidelines on preservation of cultural heritage

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Making Bombs for Peaceful Purposes: How Explosive Processes Render Lignocellulosic Biomass More Amenable to Biological Digestion

Experiments were performed to investigate the effects of shock waves – generated by explosive processes – on enhancing enzymatic digestibility of corn stover for conversion into biofuels, chemicals, or animal feed. Following an alkaline chemical pretreatment process, shock treatment was performed, which increased digestibility. Digestibility was assessed at a standard enzyme loading of 46.7 mg protein/g glucan. Without shock, the enzymatic conversion was 0.80 g glucan digested/g glucan fed. With shock, the enzyme loading is reduced by ~2× while maintaining a constant conversion. Shotgun shells and hydrogen detonation produced identical digestibility increases; however, hydrogen detonation eliminated the need to magnetically remove contaminants introduced from shotgun shells. Contrary to initial hypotheses, varying vessel geometry (depth = 1–3 ft, diameter = 4–8 in) or process conditions (peak pressure = 2.07–12.1 MPa, and solids concentration = 5–10%) had an insignificant impact on shock treatment efficacy within the experimental domain tested. Instead, the pressurization rate is the key parameter when scaling the shock treatment process. Specifically, the shotgun shell blast (108,000 MPa/s) and hydrogen detonation (4,160,000 MPa/s) generate pressure quickly enough to enhance digestibility; in contrast, the propane deflagration (37.2 MPa/s) did not. Therefore, process scaling is extremely simple, because a vessel that contains gas detonations should suffice. A slurry pump enables rapid cycling of the 20-L shock tube to already function at a commercially relevant scale. The maximum benefit of shock treatment has yet to be determined. Subsequent experiments performed with plasma discharge and solid explosives failed to increase digestibility, at the conditions employed; but, liquid-phase shock waves may be more effective

Temperature preference of chicks

The objectives of this investigation were: 1. To determine the temperature preferences of chicks when exposed to a heat gradient composed of radiant and sensible heat, 2. To determine if chicks have temperature preferences that are related to age when exposed to a heat gradient composed of radiant and sensible heat. 3. To determine if chicks have temperature preferences that are related to sex when exposed to a heat gradient composed of radiant and sensible heat

Photothermal experiments on condensed phase samples of agricultural interest : optical and thermal characterization

A rapidly increasing number of photothermal (PT) techniques has had a considerable impact on agriculture and environmental sciences in the last decade. It was the purpose of the work described here to develop and apply new PT techniques in this specific field of research.Chapter I is a general introduction with an overview of PT techniques used in this research. Two different photoacoustic (PA) techniques used for optical characterization of a variety of condensed phase samples are discussed in chapters 2 and 3. The possibilities for thermal characterization of samples are described in chapter 4.In chapter 2 classical PA spectroscopy with microphone detection was used to obtain spectra in the visible region (350-700 nm) of powdered (light scattering) food samples such as flours, coffee and spices (chapter 2.1). The outcome of these experiments suggest the feasibility of PA spectroscopy for quality control in the food-processing industry. Another PA cell was designed (chapter 2.2) and used in the IR region (10 μm). The final PA experiment was concerned with study of various carboxylic acids, alcohols and alkanes at 3.39 μm (chapter 2.3).The feasibility of optothermal window (OW) method, an elegant approach to determine the optical absorption coefficient of condensed phase samples is described in chapter 3. The method was not only extended to 9-11 μm but also proved capable of investigating opaque samples (liquids and gel) which are otherwise not amenable to conventional IR spectroscopies.The content of trans fatty acids in several margarine samples was measured with the OW technique and its performance compared to that of GLC, GLC + TLC and FTIR. The data obtained with the different methods were generally in a good agreement. The improved OW cell resulting in substantial reduction of the background signal, was then used to study extra virgin olive oil (chapter 3.2) adulterated by known adulterants (sunflower oil (4.5%) and safflower oil (6%)). The achieved limit of detection (LOD) was comparable to those reported in literature for other techniques (FTIR-ATR, GLC, HPLC and mass spectroscopy).Many biological samples contain water that itself exhibits a strong absorption in IR. Quantitative measurements on such specimens are all but trivial. The new OW sensor was shown capable of direct and quantitative measurements (chapter 3.3 and 3.4) of lactose, corn starch and sulfate in water. The performance of the OW method was slightly inferior to that of FTIR. On the other hand, unlike the OW method, FTIR-ATR could only provide quantitative results for corn starch samples. As to the study of sulfate in water, the limit of detection (I mmolL -1) achieved with the OW method is one order of magnitude better than that of ATR.In the fourth and last chapter, two different PT techniques (photopyroelectric method and photothermal beam deflection) were used for thermal characterization of a candy (a model for a glassy sugar system) and different packaging materials. The thermal diffusivity of a candy at room temperature found by PPE and PTBD was 14.7 x10 -8and 12.0 x10 -8m 2S -1respectively. In addition, the PPE technique in the standard configuration, was used to measure temperature dependence of the thermal diffusivity in the -30°C to 70°C temperature range. The glass-rubber transition, underwent by the sample in this temperature range was observed and compared to the results obtained by differential scanning calorimetry (DISC).The PPE technique was also used to obtain the temperature behaviour of thermal diffusivity of low density polyethylene and polyvinylchloride foils (used for packaging purposes). Such behavior was found dependent on the thermal history of the sample. The "untreated' foils exhibit values for thermal diffusivity that were consistently lower (7-20%) than those obtained for the same samples when heated to 70°C. The increase in thermal diffusivity is associated with structural changes (i.e. glass transitions) taking place in the material during thermal annealing. Additional measurements by differential scanning calorimetry (DSC) confirmed the validity of PPE results. It was shown that the PPE method is more sensitive than the standard DSC in detecting changes in thermal parameters.Finally, the PPE method allows one in principle to obtain the temperature behavior of all static and dynamic thermal parameters provided one of the remaining thermal parameters (thermal conductivety, thermal effusivity and volume specific heat) is available at a given temperature.OutlookResults of a research described in this thesis show the feasibility of PT techniques for applications to a wide range of condensed phase samples. The methods used here constitute only a part of techniques developed and used in our laboratory. The low-cost and compact OW device is easy to handle and moreover offers the possibility for on-line studies of optically opaque and thermally thick samples that are normally not accessible by other techniques. It is anticipated that development of infrared diode lasers will increase the potential of the OW method because desired wavelengths characterized by the highest spectral contrast will become available. The sensitivity of the OW method was shown comparable to that of FTIR and therefore additional developments might eventually make the OW approach a candidate technique for quantitative analysis throughout the entire infrared region. The analytical potential of PT schemes becomes more obvious when they are used as detectors in combination with separation techniques such as GLC, HPLC or capillary electrophoresis.The potential of photopyroelectric technique was demonstrated by obtaining thermal diffusivity values for different kind of samples. The PPE method is able to provide data on aging effect, structural stability and crystaline polymorphism. The technique is fast, sensitive and reproducible, requires small amounts of sample for analysis while providing more information than existing, classical methods used currently in thermal research. The only drawback of PPE is the necessity for good thermal contact between sample and sensor. When one is interested to obtain thermal diffusivity data in a non-contact manner the photothermal beam deflection (zero crossing method) is a valuable tool. Accurate (5% error determination of thermal diffusivity is achievable due to intrinsically low errors in measurement of frequency and of zero crossing position.In conclusion, based on the results of the work described here, one can anticipate that in the years to come the PT methods, alone or combined with existing techniques, will most likely play a more important role for variety of applications in agricultural and environmental sciences