Characterization of meso-scale mechanical properties of Longmaxi shale using grid microindentation experiments

Mechanical properties,such as the hardness H,Young’s modulus E,creep modulus C,and fracture toughness Kc,are essential parameters in the design of hydraulic fracturing systems for prospective shale gas formations.In this study,a practical methodology is presented for obtaining these properties through microindentation experiments combined with quantitative observations of the mineralogical phases using X-ray diffraction(XRD),scanning electron microscopy(SEM)with backscattered electron(BSE)imaging,and energy-dispersive X-ray spectroscopy(EDS)analyses.We apply this method in the case of three types of Longmaxi shales with different mineralogies(i.e.carbonate-,clay-,and quartz-rich,respectively),which allows us to determine the characteristic indentation depth,hc?8e10 mm,beyond which the mechanical response of the carbonate-rich shale is homogeneous and independent of its complex heterogeneous microstructure.Moreover,exploiting the results of a large number of indentation tests,we demonstrate that the indentation modulus M of the shale increases as a power-law of hardness H,and its creep modulus C increases linearly with H.We also compute the fracture toughness Kc from the indentation data by assuming a perfectly plastic behavior of the sample.Our results are in good agreement with independent measurements of Kc determined by microscratch tests.Finally,further tests on quartz-and clay-rich samples of the Longmaxi shale suggest further variations in the samples’mechanical properties depending on their burial conditions and the mechanical properties of their dominant mineral phases.

Fleet size estimation for spreading operation considering road geometry,weather and traffic

Extreme weather conditions（i, e. snow storm） in winter time have caused significant travel disruptions and increased delay and traffic accidents. Snow plowing and salt spreading are the most common counter-measures for making our roads safer for motorists. To assist highway maintenance authorities with better planning and allocation of winter maintenance re- sources, this study introduces an analytical model to estimate the required number of trucks for spreading operation subjective to pre-specified service time constraints considering road geome- try, weather and traffic. The complexity of the research problem lies in dealing with heteroge- neous road geometry of road sections, truck capacities, spreading patterns, and traffic speeds under different weather conditions and time periods of an event. The proposed model is applied to two maintenance yards with seven road sections in New Jersey （USA）, which demonstrates itself fairly practical to be implemented, considering diverse operational conditions.

Evaluation of pavement skid resistance using high speed texture measurement

Skid resistance is an important parameter for highway designs, construction, management, maintenance and safety. The purpose of this manuscript is to propose the correlation between skid resistance, which is measured as skid resistance trailer, and mean profile depth （MPD） or the macro surface texture, which is measured by vehicle mounted laser, so that highway agencies can predict the skid resistance of pavement without the use of expensive and time consuming skid resistance trailer, which also causes disruption of traffic in use. In this research skid numbers and MPD from 5 new asphalt pavements and 4 old asphalt pavements were collected using a locked wheel skid trailer and a vehicle mounted laser. Using the data collected, a correlation between the skid number （SN40R） collected by locked wheel skid tester and the texture data or MPD collected by a vehicle mounted laser operating at highway speeds was developed. The proposed correlation for new pavements was positive for MPD values less than 0.75 mm to reach a peak SN40R value, then there was a negative correlation as the MPD increases until the MPD value was equal to 1.1 mm and beyond the MPD value of 1.1 mm to the maximum value of 1.4 mm, SN40R value remained almost constant. There were significant data scatter for the MPD value of 0.8 mm. To explain these results, water film thickness during the friction test was calculated and the critical MPD was defined. The effect of sealed water pool on the SN40R was discussed. The test result showed a similar trend for older asphalt pavements, but with lower SN40R values due to the polishing of pavement micro-texture by traffic. Hence, a reduction factor was proposed for older pavements based on cumulative traffic volume for the above correlation to predict the skid resistance of older pavements.

Chromium steel from chromite ore processing residue——A valuable construction material from a waste

As species we humans generate excessive amounts of waste and hence for sustainability we should explore innovative ways to recover them.The primary objective of this study is to demonstrate an efficient and optimum way to recover chromium and iron from chromite ore processing residues(COPR)for the production of chrome steel and stainless steel.In Hudson County,New Jersey,there are more than two million tons of leftover COPR.Part of COPR was used as fill materials for construction sites,which spread the problem to a larger area.With high solubility along with their toxicity leached chromate from COPR is threatening the environment as well as human health.In this research,COPR was thermally treated to recover iron with chromium by applying techniques used in steel manufacturing.An extensive experimental program was performed using a Thermo-Gravimetric Analyzer(TGA)and bench scale tests to thermally treat the processed chromium contaminated soils with carbon and sand at varying temperatures and under reducing environment.The optimum chemical composition of COPR and additives to be used in the melts were evaluated based upon the thermodynamic properties of the mixture to ensure good phase separation,least amounts of iron and chromium oxides in the slag and minimum variability of final product(steel or iron with chromium).The impact of other oxides on the steel making process was evaluated to minimize the adverse impact on the process.The research demonstrated the feasibility of recovering a valuable construction material(chrome steel)from a waste(COPR).