The article deals with the selection of a suitable additives in cement composite material for the production of a masonry block. The blocks contains recycled concrete which replacing 40% cement. The recyclate comes from concrete drainage gutters. Based on previous measurements, two hardening accelerators and one superplasticizer were selected. To determine the effect of these additives on the recycled cement composite, pairs of samples sets were produced, of which one set contains concrete recyclate and the other one does not contain it. The dynamic modulus of elasticity and the dynamic shear modulus were measured by the resonance method at the age of samples 1, 7, 14, 21 and 28 days, and by an ultrasound method at 28 days of age. Then was measured compressive strength. All values were compared with the values measured on the reference samples.

The surface treatment of polypropylene microfibers by plasma processing in oxygen and argon was studied with the motivation to increase their cohesion with the cement matrix. By plasma treatment, it is possible to modify the surface of the microfibers mechanically, chemically or with a combination of both. The microfibers were modified using the reactive ion etching plasma system. The surface of the microfibers was modified by oxygen and argon plasma. The wettability of the microfibers was measured using the Packed Cell method. Furthermore, the weight of the microfibers before and after plasma modification was measured. Finally, the surface of the modified microfibers was examined by scanning electron microscopy. Almost all modifications of the microfiber surfaces were able to increase their wettability with water. The wettability of the oxygen plasma treated microfibers increased on average by about 11%, the wettability of the argon plasma treated microfibers increased on average by about 6% compared to the fibers without modification. The mechanical effect of plasma treatment was proven only for microfibers modified by oxygen plasma.

No abstract

The article deals with the selection of a suitable hardening accelerator for cement composite material for mass production of masonry blocks. The blocks contain cement and finely ground recycled concrete in ratio 1:1. Three different hardening accelerators in different quantity were tested for possibility of fast removing formwork. The dynamic modulus of elasticity was measured by non-destructive resonance method to determine the initial strengths. The modulus of elasticity was measured 7 and 12 hours after sample production to determine the increase in initial strength. Subsequently, the modulus of elasticity was measured at 1, 7, 14, 21 and 28 days after production of the test specimens. The resulting moduli of elasticity were compared with reference samples.

Abstract. A modulus of elasticity was determined for eight differently foamed cement paste samples. Samples were loaded in the laboratory by a hydraulic press. The force acting on the sample was read directly from the laboratory press. Digital Image Correlation (DIC) analysis were used to draw deformations. Before loading pressure test was applied a random contrast pattern to the samples. Samples were captured by the camera in a one-second interval during the loading pressure test. The images were edited in the Adobe Photoshop Lightroom and then evaluated using Ncorr software. The result is a vertical and horizontal shift field. On the basis of the results obtained, it was possible to calculate the modulus of elasticity of each sample.