Search Results (4)

Welded tuffs have a wide range of welding degrees and show significant variability in mechanical behavior. However, the detailed influence of welding degree on the meso-mechanical behavior of welded tuffs remains unclear. Based on petrographic and pore-structure analysis, we conducted a series of meso-mechanical experiments on weakly to strongly welded tuffs by utilizing a mesoscale real-time loading-observation-acquisition system. The results indicated that the strongly and weakly welded tuffs showed a small range in mineralogical composition and porosity, while the meso-mechanical behavior exhibited significant variability. Strongly welded tuffs showed lower uniaxial compression strength, weaker mechanical anisotropy, and smaller fracture surface roughness. In contrast, weakly welded tuffs exhibited higher uniaxial compression strength, stronger mechanical anisotropy, and rougher fracture surface roughness. Welded tuffs with strong packing and welding of glass shards tended to have fractures propagating along the maximum principal direction, while those with weak packing and welding of glass shards may have had failure along the alignment of glass shards. The influence of welding degree on the meso-mechanical behavior of welded tuffs probably originates from their diagenesis environments, mainly depending on the combined effect of the pyroclastic properties and pseudo-rhyolitic structure. The findings reveal the meso-mechanical differences of welded tuffs and shed light on improving tuffs for stable and durable construction. Full article

The diagenesis of welded tuffs is a process in which volcanic debris undergoes degassing, compaction, and quenching, and vitreous rheologic, which indicates that the welding occurred in a high-temperature, high-pressure diagenetic environment and that different temperatures and pressures result in different degrees of welding in the welded tuffs, which can also result in differences in the mechanical properties of the rock. In this study, based on petrographic identification, mineral composition analysis, and pore structure characterization, uniaxial compression combined with linear accelerator CT and Brazilian splitting tests was carried out to investigate the influence of the welding degree on the strength and failure modes. The test results showed that although they had almost similar mineral composition and porosity, the uniaxial compression strength and tensile strength of the strongly welded tuffs were greater than that of the weakly welded tuffs. Their failure modes were also different. Fractures in the weakly welded tuffs developed gradually, while the strongly welded tuffs showed a higher brittleness with sudden failure. The results of this study shed light on the influence of the diagenetic environment on the mechanical properties of rock from a geological perspective and can provide a mechanical basis for rockfall risk evaluation in scenic areas of welded tuff. Full article

This paper presents modern copper-matrix composite materials in which volcanic tuff particles are used as a reinforcing phase. The aim of the research was to determine the optimal shares of volcanic tuff additive based on such criteria as softening temperature, relative density, electrical conductivity, and hardness. The properties of the produced and tested composites allowed us to determine the usefulness of this type of material for resistance welding electrodes. To confirm the assumptions made, preliminary investigations of the durability and behavior of electrodes made of the tested material during the processes of welding non-alloy steel sheets were carried out. As a result of the research, it was discovered that the addition of 5% tuff produces the best results in this type of composite. It was found that for the sample with a 5% share of tuff, a high softening point above 600 °C was obtained, high hardness after densification at the level of 62 HRB, and high relative density of approximately 95% and very good conductivity at the level of approximately 45 MS/m. The conducted tests did not show any electrode wear different from the commonly used alloys for resistance welding. Full article

The topic of this study is the archaeometric characterization of mortars from Villa del Pezzolo, a Roman Villa located in Seiano (Napoli-Campania, Italy), dated between the 1st century B.C. and the 3rd century A.D. Mortars were analyzed by means of a multi-analytical approach (polarized optical microscopy, X-ray powder diffraction, scanning electron microscopy and energy-dispersed spectrometry, thermal analyses and mercury intrusion porosimetry) according to existing recommendations. Analytical results evidenced the use of local geomaterials composed of sedimentary and volcanic aggregates in the mix design and confirmed the three distinct building phases identified by archaeologists. Volcanic tuff fragments, identified in the 1st building phase can be ascribed to Campanian Ignimbrite formation, widely cropping out in the Sorrento Peninsula, as confirmed by the presence of glassy shards, partially devitrified and replaced by authigenic feldspar, a typical feature of welded grey ignimbrite lithofacies (WGI). Volcanic aggregates in samples of the 2nd and 3rd building phases show, instead, the presence of leucite-bearing volcanic scoriae and garnet crystal fragments related to Somma-Vesuvius products. Study of these mortars allowed us to: (1) understand the production technologies; (2) highlight use of materials with hydraulic behavior, such as volcanic and fictile fragments; (3) confirm the three building phases from compositional features of mortars and (4) highlight the change over time of the volcanic aggregate for mortars mix-design. Full article