Strength of sandy and clayey soils cemented with single and double fluid jet grouting

Abstract Innovations in jet grouting technology have primarily focused on the cutting efficiency of the jets, with the aim of creating larger columns and increasing the productivity of construction sites. Relatively little attention has been paid to the consequences of the grouting system on the mechanical properties of the formed material. This paper investigates this aspect by analysing the results of two field trials carried out in both sandy and clayey soils, where single and double fluid jet grouting were simultaneously performed, with varied grout composition and injection parameters. Parallel uniaxial compressive tests on samples cored from the columns show that the material formed with the double system is systematically lower in strength than the material formed using the single fluid system. The mineralogical composition of samples cored from the columns was analysed by performing parallel Scanning Electron Microscopy (SEM), X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA) and Thermo-Gravimetric Analyses (TGA) to determine the reasons for this difference. A lower proportion of cementitious products, an accelerated carbonation of portlandite and a less homogeneous distribution of cement hydration products was found on the surface of the soil particles of the double samples than for the single fluid columns

Terahertz confocal microscopy with a quantum cascade laser source

We report on the implementation of a confocal microscopy system based on a 2.9 THz quantum cascade laser source. Lateral and axial resolutions better than 70 \u3bcm and 400 \u3bcm, respectively, are achieved, with a large contrast enhancement compared to the non-confocal arrangement. The capability of resolving overlapping objects lying on different longitudinal planes is also clearly demonstrated

Assessment of occupational exposure to engineered nanomaterials in research laboratories using personal monitors

Exposure assessment is a key stage in the risk assessment/management of engineered nanomaterials. Although different sampling strategies and instruments have been used to define the occupational exposure to nano-scale materials, currently there is no international consensus regarding measurement strategy, metrics and limit values. In fact, the assessment of individual exposure to engineered nanomaterials remains a critical issue despite recent innovative developments in personal monitors and samplers. Hence, we used several of these instruments to evaluate the workers' personal exposure in a large research laboratory where engineered nanomaterials are produced, handled, and characterized in order to provide input data for nanomaterial exposure assessment strategies and future epidemiological studies. The results obtained using personal monitors showed that the workplace concentrations of engineered nanomaterials (lung deposited surface area and particle number concentrations) were quite low in all the different workplaces monitored, with short spikes during the execution of some specific job tasks. The sampling strategy was been adopted on the basis of an Organisation for Economic Cooperation and Development (OECD) suggestion for a tiered approach and was found to be suitable for determining the individual exposure and for identifying possible sources of emission, even those with very low emission rates. The use of these instruments may lead to a significant improvement not only in the exposure assessment stage but, more generally, in the entire risk assessment and management process

Aggregation and fractal formation of Au and TiO2nanostructures obtained by fs-pulsed laser deposition: experiment and simulation

In the synthesis of nanostructures by pulsed laser deposition (PLD), a crucial role is played by the environmental deposition pressure and the substrate temperature. Due to the high temperature of nanoparticles (NPs) at landing, other factors may determine the structure of the resulting aggregates. Here, Au and TiO2nanostructures are obtained by non-thermal fs-PLD in ambient conditions. On Si(100), only TiO2 NPs form fractals with areas up to ~\ua01 x10^6\ua0nm^2, while on quartz Au NPs also form fractals with areas up to ~\ua05 x10^3\ua0nm^2, a much smaller size with respect to the TiO2 case. The aggregation is described by a simple diffusive model, taking into account isotropic diffusion of the NPs, allowing quantitative simulations of the NPs and fractal area. The results highlight the key role of substrate thermal conductivity in determining the formation of fractals. [Figure not available: see fulltext.]

Terahertz confocal microscopy with a quantum cascade laser source

We report on the implementation of a confocal microscopy system based on a 2.9 THz quantum cascade laser source. Lateral and axial resolutions better than 70 μm and 400 μm, respectively, are achieved, with a large contrast enhancement compared to the non-confocal arrangement. The capability of resolving overlapping objects lying on different longitudinal planes is also clearly demonstrated

Evidence of diffusive fractal aggregation of TiO2 nanoparticles by femtosecond laser ablation at ambient conditions

The specific mechanisms which lead tothe formation of fractal nanostructuresbypulsed laser deposition remain elusive despite intense research efforts, motivated mainly by the technological interest in obtaining tailored nanostructures with simple and scalable production methods. Here we focus on fractal nanostructures of titanium dioxide, TiO2, a strategic material for many applications, obtainedby femtosecond laser ablation atambient conditions.We compare a theoretical model of fractal formation with experimental data. The comparison of theory and experiment confirms that fractal aggregates are formed after landing of the ablated material on the substrate surface by a simple diffusive mechanism. Wemodel the fractal formation through extensive Monte Carlo simulations based ona set of minimal assumptions: TiO2 nanoparticles arrive already formed onthe substrate, then they diffuseinasize/mass independent way and stick irreversibly upon touching, thus forming fractal clusters. Despite its simplicity, our model explains the main features of the fractal structures arising from the complex interaction of large TiO2 nanoparticles with different substrates. Indeed our model is able to reproduce both the fractal dimensions and the area distributions of the nanostructures for different densities of the ablated material. Finally we discuss the role of the thermal conductivity of the substrate and the laser fluence on the properties of the fractal nanostructures. Our results represent an advancement towards controlling the production of fractal nanostructures by pulsed laser deposition

Evidence of diffusive fractal aggregation of TiO2 nanoparticles by femtosecond laser ablation at ambient conditions

The specific mechanisms which lead tothe formation of fractal nanostructuresbypulsed laser deposition remain elusive despite intense research efforts, motivated mainly by the technological interest in obtaining tailored nanostructures with simple and scalable production methods. Here we focus on fractal nanostructures of titanium dioxide, TiO2, a strategic material for many applications, obtainedby femtosecond laser ablation atambient conditions.We compare a theoretical model of fractal formation with experimental data. The comparison of theory and experiment confirms that fractal aggregates are formed after landing of the ablated material on the substrate surface by a simple diffusive mechanism. Wemodel the fractal formation through extensive Monte Carlo simulations based ona set of minimal assumptions: TiO2 nanoparticles arrive already formed onthe substrate, then they diffuseinasize/mass independent way and stick irreversibly upon touching, thus forming fractal clusters. Despite its simplicity, our model explains the main features of the fractal structures arising from the complex interaction of large TiO2 nanoparticles with different substrates. Indeed our model is able to reproduce both the fractal dimensions and the area distributions of the nanostructures for different densities of the ablated material. Finally we discuss the role of the thermal conductivity of the substrate and the laser fluence on the properties of the fractal nanostructures. Our results represent an advancement towards controlling the production of fractal nanostructures by pulsed laser deposition