Modelling of three-point bending test of beams with steel inclusion situated in the middle of the span

The aim of this paper is to present the numerical model of the fracture response of the test specimens with a steel inclusion in the shape of the prisms which length is equal to the specimen’s width. Specially designed fine-grained cement-based matrix specimens of the nominal dimension 40 x 40 x 160mm with inclusion of 8 x 8 x 40mm and central edge notch serves to determine of the influence of the interfacial transition zone on the effective mechanical fracture parameters of composite. The numerical models of three-point bending test of these specimens are created in ATENA software

Study of statistical behaviour of Gumbel model of plain C30/37 and C45/55 class concrete fatigue response

Cílem příspěvku je představit a porovnat hodnoty základních únavových parametrů betonů pevnostních tříd C30/37 a C45/55 získané z cyklických testů těles. Pro popis únavové S−N křivky je v příspěvku použit nelineární regresní model vyvinutý Castillem a kol., založený na Gumbelovu rozdělení pravděpodobnosti. Autoři se v tomto článku zaměřují na analýzu proměnlivosti naměřených hodnot základních únavových parametrů betonů těles z výše uvedených tříd s využitím pravděpodobnostního softwaru FReET.The aim of this paper is to present and compare values of basic fatigue parameters obtained for plain C30/37 and C45/55 class concrete specimens during dynamic tests with consideration of their variability. The Gumbel distribution utilized by Castillo et al. in a nonlinear regression model is applied for standard description of the S−N curve. The authors focus on the analysis of the variability of the values measured for the basic fatigue parameters of the above mentioned classes of concrete specimens using the FReET probabilistic software

Fracture parameters assessment of lightweight concrete with polypropylene fibres via effective crack and work of fracture methods

V příspěvku je ukázán postup určení lomových parametrů kompozitů s rozptýlenou výztuží pomocí aplikace metod efektivní délky trhliny a lomové práce. Postup byl ilustrován vyhodnocením lomových experimentů na tělesech z lehkého betonu s polypropylénovými vlákny.The paper shows the procedure for determining the fracture properties of advanced building composites via application of effective crack and work of fracture methods. The procedure was illustrated by evaluating fracture experiments on specimens of lightweight concrete with polypropylene fibres

X-RAY MICRO-TOMOGRAPHY CHARACTERIZATION OF VOIDS CAUSED BY THREE-POINT BENDING IN SELECTED ALKALI-ACTIVATED ALUMINOSILICATE COMPOSITE

This paper deals with the pilot characterization of a special alkali-activated aluminosilicate composite composed of waste brick powder, brick rubble and a solution of potassium water glass. Fracture tests were conducted on the specimens via three-point bending and fracture parameters were evaluated. Selected specimen was investigated using micro-tomography to supplement the results with visual information about the inner structure of this newly designed material before and after the mechanical loading. Tomographic measurements and image processing were conducted for a qualitative and quantitative assessment of changes in the internal structure with an emphasis on the calculation of porosimetric parameters and visualization of the fracture surface. Fractal dimension of fracture surface was estimated

Strength characteristics of concrete exposed to the elevated temperatures according to the temperature-time curve ISO 834

While exposed to high temperatures caused by fire, the concrete undergoes a sequence of physical and chemical structure changes causing a mechanical degradation. This paper concerns an experimental strength determination of a temperature stressed concrete. The concrete was temperature loaded according to temperature-time curve ISO 834 and left on a top temperature level for 60 minutes afterwards. This temperature heating rise is in accordance with a common fire expansion in a structure. The concrete panels sized 150 × 1300 × 2300 mm were temperature loaded up to 550, 600, 800 a 1000 °C in a horizontal position in gas furnace for fire testing of structure elements in research Centre AdMaS. The temperatures of the gas in the furnace and the panel was measured during the whole experiment by using the thermocouples. After the fire test, the specimens were drilled out using a 100 mm diameter core drill. The compressive strength and splitting tensile strength tests were made and the results were compared to the reference specimen’s test results. The objective results of a commonly used strength class concrete loaded by elevated temperature corresponding to the real fire exposure differ common linear heat exposure test results and are considered being very valuable

Change of Fatigue and Mechanical Fracture Properties of a Cement Composite due to Partial Replacement of Aggregate by Red Ceramic Waste

Fine-grained cement-based composites used in civil engineering and construction industry are usually made of cement-based matrix and natural aggregate (such as sand, gravel, crushed stone, etc.). Red ceramic waste aggregate is considered as a perspective replacement of a part of natural aggregate in modern environmentally oriented building materials. Fine-grained cement composite with natural aggregate partially replaced by ceramic waste aggregate usually show different mechanical fracture characteristics from ordinary fine-grained concrete. The specimens were tested at six different ages. This was the reason for conducting the research programme. Altogether, 6 fine-grained cement mixtures with various proportions of natural and red ceramic waste aggregate were prepared. The aim of this paper is to present and compare mechanical fracture properties obtained from static and fatigue tests. Bulk density, flexural and compressive cube strength, fracture toughness and fatigue properties (S−N − Wöhler curve) were of special interest. All of these tests are important for a practical application of concrete with ceramic aggregate for structures. All the results were statistically analysed and they showed that the fatigue and mechanical fracture properties were improved or at least kept up with the increasing levels of red ceramic waste aggregate. Environmental impact of application in construction industry of composites in question is discussed

Effect of carbon nanotubes on the mechanical fracture properties of fly ash geopolymer

Fly ash geopolymer is amorphous aluminosilicate material which is considered as alternative to Portland cement concrete. One of the limiting factors of its utilization is an increased shrinkage and related deterioration of fracture properties. This paper reports on a study of the application of multi-walled carbon nanotubes (MWCNTs) to improve the fracture properties of fly ash geopolymer. The amount of MWCNTs added varied in the range of 0.05–0.2% of the mass of fly ash. Mechanical fracture properties were determined via evaluation of three-point bending fracture tests. Specimen response during fracture tests was also monitored by means of acoustic emission, and this method was also used for the determination of cracking tendency occurring during the hardening process. Results show that the addition of MWCNTs increases the elastic modulus and compressive strength of fly ash geopolymer. However, basic fracture parameters (fracture toughness, fracture energy) firstly decreased with very small addition of MWCNTs and were regained or slightly exceeded the reference values with higher amount of MWCNTs

Fracture parameters of concrete after exposure to high temperatures: pilot tests

Experimental concrete panels were after an appropriate aging time loaded by high temperatures (550, 600, 800 and 1000 °C) in a furnace intended for fire tests of building materials. These panels were heated according to the standard temperature-time curve according to EN 1991-1-2. One of panels was a reference without temperature load. Test specimens were obtained as cores drilled out from panels after performing fire tests. The cylindrical specimens were provided with a central chevron type notch and subsequently tested in three-point bending fracture test. The load versus displacement (deflection in the middle of span) diagrams were recorded during testing and basic fracture parameters were subsequently evaluated

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