Masoud Ghandehari

Application of Surface Wave Transmission Measurements for Crack Depth Determination in Concrete

It has been established in earlier studies that stress wave attenuation measurements performed on concrete are very sensitive to the presence of damage located along the wave path. In this study, a modified form of this concept is introduced in a self-compensating measurement scheme. Surface wave transmission is obtained, across a range of frequencies, between two sensing points on the surface of a concrete specimen. The obtained signal transmission values are independent of the type of wave transmitter and receiver used. An experimental test series on a range of concrete slabs containing notches and controlled cracks of varying depths is described. The cracks are generated by subjecting the slabs to flexure using a closed-loop loading procedure. The actual depth of each generated crack is determined with the laser-based phase measurement interferometry technique. Self-compensating wave transmission measurements are performed across the discontinuities, (notches, open cracks, and closed cracks) and are shown to be repeatable and sensitive to the presence of notches and even tightly closed cracks. A relationship between the wave transmission and the crack depth normalized with respect to propagating wavelength is noted. This relationship appears to be largely unaffected by the type of concrete and the nature of the discontinuity. The results demonstrate that self-compensating wave transmission measurements show excellent potential for sensitive detection and sizing of surface-breaking cracks in concrete structures.

ESTIMATION OF WATER FLOW THROUGH CRACKED CONCRETE UNDER LOAD

This research studied the relationship between cracking and water permeability of normal-strength concrete under load and compared the experimental results with theoretical models. A feedback-controlled wedge splitting test was used to generate width-controlled cracks. Speckle interferometry was used to record the cracking history. Water permeability of the loaded specimens was evaluated by a low-pressure water permeability test at the designed crack mouth opening displacements (CMODs). Water permeability results were compared with those previously obtained for unloaded specimens for which cracks were induced by a feedback-controlled splitting tension test. The experimental results indicate that water permeability of cracked material significantly increases with increasing crack width. The flow for the same cracking level is repeatable regardless of the procedure used for inducing the cracks. No direct relationship between water flow and crack length was observed, whereas clear relationships existed between CMOD or crack area and flow characteristics. Experimentally measured flow was compared with theoretical models of flow through cracked rocks with parallel walls and a correction factor accounting for the tortuosity of the crack was determined. Calculated flow through cracks induced by a wedge-splitting test provided an acceptable approximation of the measured flow.

meso-Tetraarylporpholactones as high pH sensors.

The ability of meso-tetra(pentafluorophenyl)porpholactone (T(F)PL) and its Pt(II) complex [meso-tetra(pentafluorophenyl)porpholactonato]Pt(II) (T(F)PLPt) to function as optical high pH sensors is described. Under strongly alkaline or high methoxide conditions, their UV-vis spectra undergo dramatic and reversible red-shifts. The dynamic range for the sensor T(F)PLPt in solution is from pH 11.5 to 13.2. Using (1)H, (19)F, and (13)C NMR, UV-vis and IR spectroscopy, mass spectrometry, and the use of model compounds, the molecular origin of this optical shift is deduced to be a nucleophilic attack of OH(-)/MeO(-) on the lactone carbonyl of the chromophore, representing a novel mechanism for porphyrin-based sensors. The sensing compound was solubilized with Cremophor EL for use in aqueous solutions and embedded in polymer matrixes for testing as optical fiber-based optodes and planar sheet optode materials.

Influence of Fiber Dispersion on the Performance of Microfiber Reinforced Cement Composites

Enhanced elastic behavior, pseudo-strain hardening response and toughened post-peak response are the characteristics of high performance fiber reinforced composites. Investigated in this study is the effect of dispersion of fibers on the multiple cracking behavior of fiber reinforced composites. To record the location of crack initiation, sequence of multiple cracking and corresponding cracking stresses, the study used electronic speckle pattern interfometry technique. Microstructural parameters are statistically quantified by the theory of point processes at each crack location. The study calculated the size of the fiber free areas and fiber clumping at the crack cross sections. Also calculated was the fracture toughness of the matrix by using linear elastic fracture mechanics. The study results indicate that the toughness of the composite depends on the fiber clumping at the first crack cross section.

Oxazolochlorins 11: Tuning the dynamic high pH sensing range of [meso-tetraarylporpholactonato]M(II) complexes by variation of the central metal ion, the aryl substituents, and introduction of a β-nitro group

Based on the high pH-sensing ability of [meso-tetrakis(pentafluorophenyl) porpholactonato]-platinum(II), we investigated the influence of the metal (M = Zn(II), Ni(II), Cu(II), Pd(II), Ag(II), Pt(II)), the aryl group (Ar = C6H5, C6F5), and the presence of a β-NO2 group on the pH sensing range. The syntheses of the novel β-nitroporpholactone derivatives are described, and their regiochemistry deduced by spectroscopic and single crystal X-ray diffraction methods. The UV-vis base titration midpoints for all derivatives were determined in an aqueous solution containing a surfactant, showing that the metal has the least influence, thus identifying a cheaper and easier method to prepare porpholactone M complex-based high pH-sensors. The influence of the pentafluorophenyl groups and the β-nitration were comparable with respect to their ability to increase the nucleophilicity of the porpholactone toward hydroxide, but the optical response for the pentafluorophenyl-substituted derivative were stronger. β-Nitration and pentafluorophenyl-substitution had additive effects.

Design and Application of Concrete Tiles Enhanced with Microencapsulated Phase-Change Material

AbstractPhase-change materials (PCMs) have a high heat of fusion compared to that of traditional material, and for this reason, they are able to store and release larger amounts of energy at their transition temperature. The inclusion of PCMs in buildings has attracted much interest worldwide because of their ability to reduce building energy demand and increase indoor comfort. This paper presents the development and testing results of a concrete tile system with microencapsulated PCMs. The concrete tiles were cast for use in a high-performance house built for the Solar Decathlon China 2013 competition. The paper shows that the addition of PCMs reduced the overall compressive and flexural strength properties of the concrete. A more than 25% decrease in compressive strength was observed with the addition of 20% PCM per volume of concrete. However, a significant improvement in the thermal properties of the concrete tile PCMs was measured. The thermal energy storage capability of the PCM-enhanced concrete ti...

Patterns of waste generation: A gradient boosting model for short-term waste prediction in New York City

Historical municipal solid waste (MSW) collection data supplied by the New York City Department of Sanitation (DSNY) was used in conjunction with other datasets related to New York City to forecast municipal solid waste generation across the city. Spatiotemporal tonnage data from the DSNY was combined with external data sets, including the Longitudinal Employer Household Dynamics data, the American Community Survey, the New York City Department of Finances Primary Land Use and Tax Lot Output data, and historical weather data to build a Gradient Boosting Regression Model. The model was trained on historical data from 2005 to 2011 and validation was performed both temporally and spatially. With this model, we are able to accurately (R2>0.88) forecast weekly MSW generation tonnages for each of the 232 geographic sections in NYC across three waste streams of refuse, paper and metal/glass/plastic. Importantly, the model identifies regularity of urban waste generation and is also able to capture very short timescale fluctuations associated to holidays, special events, seasonal variations, and weather related events. This research shows New York Citys waste generation trends and the importance of comprehensive data collection (especially weather patterns) in order to accurately predict waste generation.

Bond-Induced Longitudinal Fracture in Reinforced Concrete

Splitting of concrete caused by pullout of deformed rebars is investigated. The influence of specimen cross section size and geometry on the relationship between the components of stress and relative displacement at the interface is evaluated. Phase measurement interferometry is used for accurate mapping of the splitting cracks. The measured crack profiles, material model, and a fracture criterion are used in a hybrid experimental/ numerical approach to evaluate the unknown normal component of traction at the interface.

In situ sensing of subsurface contamination--part I: near-infrared spectral characterization of alkanes, aromatics, and chlorinated hydrocarbons.

There is an imperative need for a chemical sensor capable of remote, in situ, long-term monitoring of chemical species at sites containing toxic chemical spills, specifically at chemical waste dumps, landfills, and locations with underground storage tanks. In the current research, a series of experiments were conducted measuring the near-infrared optical absorption of alkanes, aromatics, and chlorinated hydrocarbons. A spectral library was then developed to characterize the optical spectra of liquid hydrocarbons. Near-infrared analysis was chosen due to compatibility with optical fibers. The goal was to differentiate between classes of hydrocarbons and to also discriminate between compounds within a class of similar molecular structures. It was observed that unique absorption spectra can be obtained for each hydrocarbon, and this uniqueness can be used to discriminate between hydrocarbons from different families. Statistical analyses, namely, principal component analysis (PCA) and correlation coefficient (Spearman and Pearson methods), were attempted to match absorption spectra from an unknown hydrocarbon with the database with limited success. An algorithm was subsequently written to identify the characteristic peaks of each hydrocarbon that could be used to match data from an unknown chemical species with the database.

People-Centric Cognitive Internet of Things for the Quantitative Analysis of Environmental Exposure

Exposure to air pollution poses a significant risk to human health, particularly to urban dwellers. When correlated with individual health outcomes, high resolution information on human mobility, and the spatial and temporal distribution of the pollutants can lead to a better understanding of the effects of pollution exposure. People-centric sensing is normally carried out by data sharing through a central cloud server. This system architecture is not designed to serve the ever-growing number of high fidelity connected devices, particularly when crowdsourcing urban data on location and environmental conditions. Here, we outline an architecture for a people-centric and cognitive Internet of Things (PIoT) environmental sensing platform, which involves closed loops of interactions among people nodes and physical devices as well as servers and recommendations on device connections by cognitive computing. Taking advantage of smart objects and virtual node technology in PIoT, an algorithm to aggregate on-demand user data from smart devices is proposed. A PIoT prototype sensing system is designed and deployed to measure the space-time distribution of particulate matter in air (PM2.5), and mobility counts, for quantifying personal exposure to air pollution. A case study of particulate matter PM2.5 exposure in New York City is presented to illustrate the potential application of people-centric measurement system and data analysis.