The paper deals with the monitoring of the structural changes of fine-grained cement-based composites in the early-age using acoustic emission method. After mixing, the cement-based materials exhibit continuous time-dependent structural changes which lead to the changes in the mechanical properties due to the chemical and physical processes. The events which are emitted due to the internal structure formation were detected using the acoustic emission techniques. A number of AE events are released due to the formation of new crystalline phases and due to microcracking in the material structure during the setting and hardening. The aim of the performed experiments was to extend the knowledge in the field of the early-age material characteristics and in the field of the internal structure formation of the cement-based materials. The results from temperature measurement show that mixture with microsilica has more slowly raised the internal temperature than mixture without microsilica. The results from acoustic emission measurement show that mixture with microsilica has lower activity of acoustic emission than mixture without microsilica during first six hours from measurement start.
Authors:S. Menecier, S. Valette, P. Denoirjean, and P. Lefort
greater weight gains, as on Fig. 7 c. Between this zone and the wüstite, a lot of small pores appeared, while microcracks went through the wüstite layer.
From the same weight gain of 3–4 mg cm −2 , some dark spots appeared at the surface of the
Authors:J. Tulliani, G. Pagès, G. Fantozzi, and L. Montanaro
By using a wet chemical route, pure calcium hexaluminate (CA6) was yielded, significantly lowering the reaction temperature and shortening the synthesis time if compared to usual industrial
procedures. owever, dilatometric studies performed on compacts made of the as-prepared powder, just after pre-heating at 450C,
has shown a superposition between sintering shrinkage and expansion related to CA2 formation, an intermediate phase formed during calcination and phase evolution to CA6. oupling of such opposite phenomena led to microcracking of the material, mainly if the heating rates (10C min-1) were high. However, lower heating rates (1-5C min-1) could quite avoid microcracking but also limit densification.
Authors:L. Pérez-Maqueda, V. Balek, J. Poyato, J. Šubrt, M. Beneŝ, V. Ramírez-Valle, I. Buntseva, I. Beckman, and J. Pérez-Rodríguez
Thermal behavior of talc samples (from locality Puebla de Lillo, Spain) were characterized by emanation thermal analysis (ETA),
DTA and TG. The ETA, based on the measurement of radon release rate from samples, revealed a closing up of surface micro-cracks
and annealing of microstructure irregularities of the talc samples on heating in the range 200–500°C.
For ground talc sample a crystallization of non-crystalline phase formed by grinding, into orthorhombic enstatite was characterized
as a decrease of radon mobility in the range 785–825°C and by a DTA exothermal effect with the maximum at 830°C. ETA results
characterized the microstructure development of the talc samples on heating and served to evaluate their radon mobility and
transport properties on heating and cooling. Transport properties of the talc samples were evaluated by using ETA experimental
data measured during heating to 600 and 1300°C, respectively, and subsequent cooling to room temperature.
In this study we introduce new rock physical models which describe the pressure dependence of seismic velocity and quality factor. The models are based on the idea (accepted in the literature) that microcracks in rocks are opened and closed under the change of pressure. The models were applied to acoustic P wave velocity data measured on core samples originated from oil-drilling wells (27 samples) and also seismic velocity and quality factor data sets published in international literature. During the measurements the pulse transmission and the spectral ratio techniques were used. Measurements were carried out at various incremental pressures and parameters of the models were determined by linearized inversion methods. The calculated data matched accurately with measured data proving that the new rock physical models apply well in practice.
The paper provides information on the mechanical properties of granitic rocks that were subjected to heat. Two types of granitic rocks were tested under laboratory conditions at temperatures of 23 °C, 300 °C and 600 °C. The granitic rock from Bátaapáti (Mórágy Granite) is a pinkish leucocratic monzogranitic type while the second type is grey granite from Mauthausen (Austria). The samples were placed in furnace and temperature raised to 300 °C. Other set of samples were heated to 600 °C. Mechanical tests were performed on non-heated and heated samples and the test results were compared. Heating to 300 °C caused a slight increase in the uniaxial compressive strength and in indirect tensile strength, with reference to the samples kept at 23 °C. A drastic drop in both values was observed when samples were heated to 600 °C. The density of the samples did not show a major change up to 300 °C. On the contrary, a decrease in ultrasonic pulse velocity was observed, with an additional significant loss when samples subjected to 600 °C were compared to the reference samples of 23 °C. This decrease can be related to the initiation of micro-cracks. With increasing temperature the Young modulus of both granites was reduced.
The use of thermal analysis in studying ancient mortars in English cathedrals is explained. Thermal analysis can be used to
investigate both mortar and stone in dated structures. Analysis of ancient mortars show that though recarbonated, they remain
soft, yielding to structural deformations. The use of hard (cement mortar) in modern renovation can result in micro-cracking
in the stone and subsequent chemical attack from the atmosphere. Contrary to the literature, data developed in the present
study suggests that most medieval mortars have reached a near total state of recarbonation.
The effect of talc as an artificial nucleating agent in different concentrations on the crystallization of polypropylene (PP) has been studied. It is considered that the induction time should be taken into account in the Avrami evaluation of isothermal crystallization. From a study of nucleated PP samples prepared in different ways, it has been proved that the nucleating effect of talc slightly decreases with increasing time spent by the sample in the state of the polymer melt. It has been shown that crystallization of non-nucleated polypropylene strongly depends on the material of the sample pan. It has been established that dilatometry cannot be used to study the isothermal crystallization of nucleated polypropylene, since microcracks appear in the sample, partly compensating the volume decrease due to the crystallization process.
Authors:Dorottya Kovács, Gergely Dabi, and Balázs Vásárhelyi
designing underground facilities. Rock mechanics suggests that most mechanical parameters are related to the inherent microcrack system of the rock ( Kemeny and Cook 1991 ).
Retrieval of relevant data for the characterization of fracture geometry is
Authors:Gergely Dabi, Ferenc Tóth, and Félix Schubert
Fluid inclusion planes (FIPs) are fossilized mode I microcracks, formed perpendicular to the σ 3 direction in minerals, which can be mechanically considered isotropic during brittle deformation, e.g., in quartz