Mechanical properties of basalt: a study on compressive loading at different strain rates using SHPB

This article focuses on the mechanical properties of basalt in compressive loading at different strain-rates. The study employs advanced instrumentation for the evaluation of the results in dynamic conditions, while standard uni-axial loading device is used for evaluation in quasi-static conditions. Basalt specimens were subjected to four different loading-rates from 200–600 s−1 on which the stress-strain dependence was evaluated together with DIC analysis of crack initiation and disintegration process. Understanding the mechanical properties of basalt can provide insights for engineers and designers in creating structures that are durable and able to withstand different loading conditions. The findings of this study can have implications for a wide range of industries, including aerospace, automotive, and construction, among others

Effect of petrographic composition and chemistry of aggregate on the local and general fracture response of cementitious composites

This paper concerns the results of research into the influence of the composition of rock inclusions on the fracture response of cement-based composite specimens. Specially designed specimens of the nominal dimensions 40 × 40 × 160 mm with inclusions in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth of 12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, and marble – were tested in the three-point bending configuration. Fracture surfaces were examined via scanning electron microscopy and local response in the vicinity of rock inclusions was characterized via the nanoindentation technique. The aim of this paper is to analyse the influence of the chemical/petrographic composition of rock inclusions on the effective mechanical fracture parameters of cement-based composites, as well as on the microstructural mechanical parameters of the interfacial transition zone. The results of this research indicate the significant dependence of the effective fracture parameters on the petrographic and related chemical composition of the rock inclusions

Mechanical properties of basalt: a study on compressive loading at different strain rates using SHPB

This article focuses on the mechanical properties of basalt in compressive loading at different strain-rates. The study employs advanced instrumentation for the evaluation of the results in dynamic conditions, while standard uni-axial loading device is used for evaluation in quasi-static conditions. Basalt specimens were subjected to four different loading-rates from 200–600 s−1 on which the stress-strain dependence was evaluated together with DIC analysis of crack initiation and disintegration process. Understanding the mechanical properties of basalt can provide insights for engineers and designers in creating structures that are durable and able to withstand different loading conditions. The findings of this study can have implications for a wide range of industries, including aerospace, automotive, and construction, among others

Visualization of the Evolution of the Fracture Process Zone in Sandstone by Transmission Computed Radiography

The article deals with the use of computed X-ray radiography to visualize the development of the fracture process zone in the rock samples. For radiographic observations during the three-point bending loading, glauconitic sandstone from the Řeka quarry (sometimes also referred to as Godula sandstone) was used. The chevron-notched cylindrical specimens with the diameter of 29 mm and 120 mm nominal length were prepared from the sandstone blocks. These specimens were subjected to the Chevron Bend (CB) test carried out in accordance with the ISRM suggested methodology; the span was 94 mm. The evolution of the fracture process zone was continuously scanned using X-ray radiography during the realized Mode I fracture toughness tests (FTT). The scanning was conducted using an industrial X-ray micro-tomographic inspection system equipped with a flat panel X-ray detector of 4,000 × 4,000 pixels and micro-focus X-ray source with reflection target, which are very suitable for obtaining highly detailed radiographic images during the FTT tests. Three-point bending tests were carried out using an in-house designed table-top loading device, construction of which allows precise control of the loading during testing. Continuous X-ray examination and subsequent radiographic image analysis enable investigation of the crack initiation and the process zone development during FTT and represents a useful tool for a better understanding of failure behavior of the rock material during the loading process.The article deals with the use of computed X-ray radiography to visualize the development of the fracture process zone in the rock samples. For radiographic observations during the three-point bending loading, glauconitic sandstone from the Řeka quarry (sometimes also referred to as Godula sandstone) was used. The chevron-notched cylindrical specimens with the diameter of 29 mm and 120 mm nominal length were prepared from the sandstone blocks. These specimens were subjected to the Chevron Bend (CB) test carried out in accordance with the ISRM suggested methodology; the span was 94 mm. The evolution of the fracture process zone was continuously scanned using X-ray radiography during the realized Mode I fracture toughness tests (FTT). The scanning was conducted using an industrial X-ray micro-tomographic inspection system equipped with a flat panel X-ray detector of 4,000 × 4,000 pixels and micro-focus X-ray source with reflection target, which are very suitable for obtaining highly detailed radiographic images during the FTT tests. Three-point bending tests were carried out using an in-house designed table-top loading device, construction of which allows precise control of the loading during testing. Continuous X-ray examination and subsequent radiographic image analysis enable investigation of the crack initiation and the process zone development during FTT and represents a useful tool for a better understanding of failure behavior of the rock material during the loading process

INSTRUMENTATION OF FOUR-POINT BENDING TEST DURING 4D COMPUTED TOMOGRAPHY

High-resolution time-lapse micro-focus X-ray computed tomography is an effective method for investigation of deformation processes on volumetric basis including fracture propagation characteristics of non-homogeneous materials subjected to mechanical loading. This experimental method requires implementation of specifically designed loading devices to X-ray imaging setups. In case of bending tests, our background research showed that no commercial solution allowing for reliable investigation of so called fracture process zone in quasi-brittle materials is currently available. Thus, this paper is focused on description of recently developed in-situ four-point bending loading device and its instrumentation for testing of quasi-brittle materials. Proof of concept together with the pilot experiments were successfully performed in a CT scanner TORATOM. Based on results of the pilot experiments, we demonstrate that crack development and propagation in a quasi-brittle material can be successfully observed in 3D using high resolution 4D micro-CT under loading

Identification of phase composition of binders from alkali-activated mixtures of granulated blast furnace slag and fly ash

The prepared alkali-activated binders (AAB) and composites using suitable latent hydraulic raw materials represent an alternative to materials based on Portland cements. This paper deals with ways how to influence the functional parameters of AAB by setting up mixtures of granulated blast furnace slag (GBFS) and fly ash with selected chemical compositions. In this way the course of hydration process is modified and the phase composition of products of alkali activation is changed as well as their final properties. The amorphous character of the hydration products makes evaluation of the phase composition of hardened AAB difficult and significantly limits the number of experimental techniques suitable to characterise their phase composition. It was observed that measuring the pH of water extracts obtained from the alkali-activated mixtures can give supplementary information about the process of hardening of alkali-activated mixtures of GBFS and fly ash.Web of Science581887

Influence of rock inclusion composition on the fracture response of cement-based composite specimens

This paper concerns the results of research into the influence of the composition of rock inclusions on the fracture response of cement-based composite specimens. Specially designed specimens of the nominal dimensions 40 × 40 × 160 mm with inclusions in the shape of prisms with nominal dimensions of 8 × 8 × 40 mm were provided with an initial central edge notch with a depth of 12 mm. These specimens, which were made of fine-grained cement-based composite with different types of rock inclusion – amphibolite, basalt, granite, and marble – were tested in the three-point bending configuration. Fracture surfaces were examined via scanning electron microscopy and local response in the vicinity of rock inclusions was characterized via the nanoindentation technique. The aim of this paper is to analyse the influence of the chemical/petrographic composition of rock inclusions on the effective mechanical fracture parameters of cement-based composites, as well as on the microstructural mechanical parameters of the interfacial transition zone. The results of this research indicate the significant dependence of the effective fracture parameters on the petrographic and related chemical composition of the rock inclusions

Safety and Efficacy of Dolutegravir in Treatment-Experienced Subjects With Raltegravir-Resistant HIV Type 1 Infection: 24-Week Results of the VIKING Study

Background. Dolutegravir (DTG; S/GSK1349572), a human immunodeficiency virus type 1 (HIV-1) integrase inhibitor, has limited cross-resistance to raltegravir (RAL) and elvitegravir in vitro. This phase IIb study assessed the activity of DTG in HIV-1–infected subjects with genotypic evidence of RAL resistance.Methods. Subjects received DTG 50 mg once daily (cohort I) or 50 mg twice daily (cohort II) while continuing a failing regimen (without RAL) through day 10, after which the background regimen was optimized, when feasible, for cohort I, and at least 1 fully active drug was mandated for cohort II. The primary efficacy end point was the proportion of subjects on day 11 in whom the plasma HIV-1 RNA load decreased by ≥0.7 log10 copies/mL from baseline or was <400 copies/mL.Results. A rapid antiviral response was observed. More subjects achieved the primary end point in cohort II (23 of 24 [96%]), compared with cohort I (21 of 27 [78%]) at day 11. At week 24, 41% and 75% of subjects had an HIV-1 RNA load of <50 copies/mL in cohorts I and II, respectively. Further integrase genotypic evolution was uncommon. Dolutegravir had a good, similar safety profile with each dosing regimen.Conclusion. Dolutegravir 50 mg twice daily with an optimized background provided greater and more durable benefit than the once-daily regimen. These data are the first clinical demonstration of the activity of any integrase inhibitor in subjects with HIV-1 resistant to RAL