Consideration of soil temperature in the modelling of early-age mass concrete slab

Modeling the structural behavior of concrete at early ages is one of the most challenging, yet fundamental, tasks for civil engineers working on mass concrete. To obtain a reasonably accurate model, a number of factors should be taken into account. Considerations should include both external influences as well as the changes occurring in the complex structure itself. The modeling of an early-age concrete massive slab requires the proper assignment of initial conditions, including the initial temperature of the analyzed element and the adjacent structures. The temperature distribution in the subsoil is the factor analyzed in this paper. The aim of the study is the determination of the temperature distribution in the ground, which is useful in the process related to the acquisition of the most accurate model of the analyzed structure and reflects the actual conditions in the numerical model. For this purpose, the analytical method described in the literature was applied and subsequently evaluated on the basis of the numerical calculation. The performed calculations allow the estimation of the depth representing the range of the influence of the temperature in the ground and the values of the temperatures corresponding to the successive layers of the subsoil. Moreover, aiming the optimization of the numerical analysis of the massive foundation slab, the legitimacy of such detailed consideration of the temperature development in the underlying subsoil was evaluated by the comparison with the temperature distribution in the slab obtained with simplified consideration of the constant soil temperature.The publication is financed by BKM-547/RB6/2018 resources. Funding provided by the Portuguese Foundation for Science and Technology (FCT) to the Research Project IntegraCrete PTDC/ECM EST/1056/2014 (POCI-01-0145-FEDER-016841), as well to the Research Unit ISISE (POCI-01- 0145-FEDER-007633) is also gratefully acknowledged

Tuning the Elasticity of Cross-Linked Gold Nanoparticle Assemblies

Composite materials of organically stabilized or cross-linked metal nanoparticles represent a versatile material class with manifold potential applications. Numerous studies explored their tunable optical and charge transport properties. However, due to challenging experimental requirements, only a few studies addressed their mechanical properties. Here, we report the first investigation on the tunability of the elastic properties of cross-linked gold nanoparticle (GNP) composites. Thin films consisting of GNPs (diameter 3–4 nm) cross-linked with α,ω-alkanedithiols of different chain length, as well as 1,4-benzenedithiol, were fabricated by spin-coating and transferred onto circular apertures with diameters of ∼100 μm. The mechanical properties of thus-prepared freestanding membranes with thicknesses between 21 and 51 nm were probed using bulge tests with atomic force microscopy (AFM) based deflection readout. We demonstrate that, along with their optical and charge transport characteristics, the elastic modulus of these GNP composites can be adjusted in a range from ∼3.6 to ∼10 GPa by shortening the α,ω-alkanedithiol chain length from 10 to 3 methylene units. These variations in elasticity are attributed to the varying fraction of soft organic matter and to structural differences within the composites. Our results provide a basis for further experimental and theoretical studies, as well as for applications of cross-linked nanoparticle composites in future micro- and nanoelectromechanical (MEMS/NEMS) devices, their design, and modeling

Quantification the filling of microcracks due to Autogenous self-healing in cement paste

Microcracks play vital roles in the prediction of the service life of concrete structure. Because microcracks in concrete structure are the preferential ingression channels for aggressive ions, e.g., chloride, sulphate, etc. However, microcracks have potentials to self-heal autogenously due to the continuous hydration of unhydrated cement, especially when ultra-/ high strength concrete is used. To quantify the autogenous self-healing effects of microcracks in cement paste, our experiment is designed to monitor the self-healing process of microcracks in cement paste continuously by using optical microscope. The healing products are quantified by image analysis with newly implemented software in MATLAB. The results indicate that the microcracks are not filled evenly along the crack length and most healing products are Ca(OH)2, which dissolve partly from the paste matrix and re-nucleate in the microcrack, in addition to its counterpart from the continuous hydration of unhydrated cement. Furthermore, the sample cracked at earlier age shows higher potential to heal, while the sample with smaller crack width experiences greater filling efficiency. The obtained autogenous selfhealing mechanism will be used in the future simulation

Electrostatically Actuated Membranes of Cross-Linked Gold Nanoparticles: Novel Concepts for Electromechanical Gas Sensors

We report the preparation of freestanding membranes of cross-linked gold nanoparticles (GNPs) and demonstrate their application as electromechanical sensors for volatile organic compounds (VOCs). First, we show that the fundamental vibrational mode frequency of electrostatically excited GNP-membranes shifts significantly when exposing them to solvent vapors. We attribute this effect mainly to the reduction of the membranes’ pre-stress. Second, the relief in pre-stress upon analyte sorption can also be detected via quasi-static actuation of the membranes. In this case, the increase of the deflection amplitudes at constant bias voltages can be measured as the sensor signal and correlated to the analyte’s concentration. Additionally, we propose a facile route to the fabrication of such hybrid MEMS/NEMS sensors using layer-by-layer spin-coating and contact printing

Evaluation of the LDPM elastic and fracture parameters by up-scaling procedure

The heterogeneity of the concrete may be considered on different size scales of observation, ranging from the atomistic scale (10-10m), characterized by the behavior of crystalline particles of hydrated Portland cement, to the macroscopic scale (101 m), where concrete has traditionally been considered homogeneous. The multiscale framework we are proposing in this paper is based on the following models: chemical analyses at the cement paste scale; mechanical lattice model at the cement and mortar scales; geometrical aggregate distribution models at the mortar and concrete scales; and the Lattice Discrete Particle Model (LDPM) at the concrete scale. For that purpose, a set of analysis starting from a known set of parameters of the cement paste. This input is utilized to evaluate the mechanical properties of the mortars (cement and sand), and then these properties are used to evaluate the mechanical properties of the mortar-a4 (mortar-s and aggregate smaller then 4mm). The upscaling in the proposed methodology involved the evaluation of the LDPM concrete parameters based on the mortara4 properties. Here we are suggesting a uni-axial tension "numerical experiments" on the mortar-a4 scale to evaluate the elastic and fracture LDPM mechanical parameters

Cross-Linked Gold-Nanoparticle Membrane Resonators as Microelectromechanical Vapor Sensors

We report a novel approach for the detection of volatile compounds employing electrostatically driven drumhead resonators as sensing elements. The resonators are based on freestanding membranes of alkanedithiol cross-linked gold nanoparticles (GNPs), which are able to sorb analytes from the gas phase. Under reduced pressure, the fundamental resonance frequency of a resonator is continuously monitored while the device is exposed to varying partial pressures of toluene, 4-methylpentan-2-one, 1-propanol, and water. The measurements reveal a strong, reversible frequency shift of up to ∼10 kHz, i.e., ∼5% of the fundamental resonance frequency, when exposing the sensor to toluene vapor with a partial pressure of ∼20 Pa. As this strong shift cannot be explained exclusively by the mass uptake in the membrane, our results suggest a significant impact of analyte sorption on the pre-stress of the freestanding GNP membrane. Thus, our findings point to the possibility of designing highly sensitive resonators, which utilize sorption induced changes in the membrane’s pre-stress as primary transduction mechanism

Copy number variations in “classical” obesity candidate genes are not frequently associated with severe early-onset obesity in children

Background: Obesity is genetically heterogeneous and highly heritable, although polymorphisms explain the phenotype in only a small proportion of obese children. We investigated the presence of copy number variations (CNVs) in “classical” genes known to be associated with (monogenic) early-onset obesity in children. Methods: In 194 obese Caucasian children selected for early-onset and severe obesity from our obesity cohort we screened for deletions and/or duplications by multiplex ligation-dependent probe amplification reaction (MLPA). As we found one MLPA probe to interfere with a polymorphism in SIM1 we investigated its association with obesity and other phenotypic traits in our extended cohort of 2305 children. Results: In the selected subset of most severely obese children, we did not find CNV with MLPA in POMC, LEP, LEPR, MC4R, MC3R or MC2R genes. However, one SIM1 probe located at exon 9 gave signals suggestive for SIM1 insufficiency in 52 patients. Polymerase chain reaction (PCR) analysis identified this as a false positive result due to interference with single nucleotide polymorphism (SNP) rs3734354/rs3734355. We, therefore, investigated for associations of this polymorphism with obesity and metabolic traits in our extended cohort. We found rs3734354/rs3734355 to be associated with body mass index-standard deviation score (BMI-SDS) (p = 0.003), but not with parameters of insulin metabolism, blood pressure or food intake. Conclusions: In our modest sample of severely obese children, we were unable to find CNVs in well-established monogenic obesity genes. Nevertheless, we found an association of rs3734354 in SIM1 with obesity of early-onset type in children, although not with obesity-related traits