The compressive strength of steel fibre reinforced concrete obtained by testing cubes and cylinders

There are two most popular approaches to determining the compressive strength of concrete: testing cubes, testing cylinders. The use of different samples gives different results, which are intended to characterize one parameter of the material compressive strength. The article discusses a general approach to determining the compressive strength of cylinders and cubes. The analysis of the factors influencing the transition coefficients when testing the cylinder samples with the ratio of height to diameter is less than 2. The results of testing cubes and cylinders for compression made of fiber-reinforced concrete are presented

Nanoindentation of cement stone samples

The preliminary results of the studied cement samples were obtained by the nanoindentation method. It was revealed that the elastic modulus M increases in samples that contain a complex additive containing nanosized particles. The effect is also observed with the introduction of an additive containing only one type of nanoparticles (nanosilica sol SiO2 or carbon nanomaterial MCNT). The selection of the parameters of the nanoindentation method, which ensured the obtaining of the final consistent results, was performed. These results are presented by histograms of the distribution of nanoindentation points in modulus of elasticity M and hardness H and distributions in M and H in the horizontal XY plane perpendicular to the motion of the nanoindentor. The results obtained indicate that there is a change in the nanostructure of the C – S – H gel, which is compared with an increase in strength, Young’s moduli and shear, upon the introduction of SiO2 nanoparticles and MCNT nanoparticles

Fracture toughness of carbon nanotubes modified cement based materials

С. А. Жданок, Е. Н. Полонина, Е. А. Садовская, С. Н. Леонович. ВЯЗКОСТЬ РАЗРУШЕНИЯ ЦЕМЕНТНЫХ МАТЕРИАЛОВ, МОДИФИЦИРОВАННЫХ УГЛЕРОДНЫМИ НАНОТРУБКАМИIn order to increase the fracture toughness of concrete, dispersed fiber reinforcement is increasingly used in practice. The initiation of crack initiation occurs at the nanoscale in the cement matrix. Thus, the use of nano-reinforcement with dispersed nanoparticles can have a positive effect on the fracture toughness of the cement composite. It is proposed to consider carbon nanotubes (CNTs) as such nanofibers. This article discusses the possibility of using nanocarbon tubes as elements for restraining the development of cracks at the nanoscale in cement composite. The results of testing nanomodified cement stone for strength indicators, fracture toughness indicators, results of nanoindentation, ultrasonic sounding and infrared spectroscopy are presented. A structural model of a cement stone dispersed-reinforced with nanocarbon tubes is considered