Tomáš Plachý

Effect of Pva Modification on Properties of Cement Composites

Polymers are used for modification of the cement-based composites and others building materials since the thirties of 20th century. Based on the conclusions of recent studies, it is assumed that even water soluble polymers could be used as an admixture for such modification. Currently, there exist and are exploited several possibilities for polymer modification of mortars, wood-based products or bituminous asphalts. Various options differ in the way of modification, which can be basically applied to the entire volume or just a surface, but also in the form of the polymer used – either in the form of solution or fibers. The aim of our study was to investigate the influence of volume modification by the water soluble polymers, such as polyvinyl alcohol (PVA), on the properties of cement paste and find an optimum additive. It turned out that the addition of PVA solution into fresh cement paste results in an increase of porosity and therefore a stiffness and compressive strength reduction. On the other hand, the bending strength of PVA-rich specimens was significantly higher and their water absorption decreased, which may consequently result in enhanced frost resistance.

Minimum-Weight Truss Reinforcement of a Composite Beam to Increase the Free-Vibrations Fundamental Eigenfrequency

In this contribution, we design a minimum-weight truss reinforcement of a thin-walled composite beam, such that the fundamental free-vibrations eigenfrequency of the beam is increased to a specific value. The reinforcement structure is designed using techniques of topology optimization and produced using additive manufacturing, in order to achieve economical design and minimize manual interventions in the fabrication process. Finally, an experimental validation of theoretical outcomes is performed on an additively manufactured prototype.

Influence of increasing amount of recycled concrete powder on mechanical properties of cement paste

This paper deals with using fine recycled concrete powder in cement composites as micro-filler and partial cement replacement. Binder properties of recycled concrete powder are given by exposed non-hydrated cement grains, which can hydrate again and in small amount replace cement or improve some mechanical properties. Concrete powder used in the experiments was obtained from old railway sleepers. Infrastructure offer more sources of old concrete and they can be recycled directly on building site and used again. Experimental part of this paper focuses on influence of increasing amount of concrete powder on mechanical properties of cement paste. Bulk density, shrinkage, dynamic Youngs modulus, compression and flexural strength are observed during research. This will help to determine limiting amount of concrete powder when decrease of mechanical properties outweighs the benefits of cement replacement. The shrinkage, dynamic Youngs modulus and flexural strength of samples with 20 to 30 wt. % of concrete powder are comparable with reference cement paste or even better. Negative effect of concrete powder mainly influenced the compression strength. Only a 10 % cement replacement reduced compression strength by about 25 % and further decrease was almost linear.

Utilization of the waste from the marble industry for application in transport infrastructure: mechanical properties of cement pastes

This article is focused on the mechanical testing of cement-based samples containing a micronized waste marble powder used as replacement of standard binders. Tested materials consisted of cement CEM I 42.5 R (Radotin, Czech Republic) and three different amounts of the marbles (25, 50 and 70 wt. %). Standard bending and compressive tests of the prismatic samples having dimensions equal to 40 × 40 × 160 mm were done in order to reveal an influence of marble amount on flexural and compressive strength, respectively. Moreover, the dynamic modulus of elasticity and dynamic shear modulus were examined and compared after 7 and 28 days of mixture curing.

Numerical and Experimental Modal Analysis of Laminated Glass Beams

This paper presents a numerical and experimental modal analysis of laminated glass beams, i.e. a multilayer composite structure made of glass panes bonded to an interlayer foil. These polymer foils provide shear coupling of glass layers, damping of vibrations, and play a key role in post-breakage performance. In this contribution, three-layer beams with ethylene-vinyl acetate interlayer are investigated. Using a finite element discretization and the Newton method, we solve numerically a complex eigenvalue problem which is nonlinear due to the frequency/temperature-sensitive viscoelastic behavior of the interlayer. In our experimental investigations, a roving hammer test was carried out to identify the mode shapes, natural frequencies, and modal damping. The validation shows that there is a good agreement between the numerical predictions and experimental data in natural frequencies. However, the errors in loss factors can be high, because these values are very sensitive to the material properties of polymer, frequency, temperature, and boundary conditions. These effects are discussed in the concluding part of our study.

Relationship between Compressive Strength and Young's Modulus of Cement Paste with Recycled Concrete Powder

This article deals with utilization of recycled concrete in form of high-speed milled powder into cement based materials. Recycled concrete powder in that form is used as microfiller and cement replacement. This article contains results of mechanical properties of the cement pastes with different amount of recycled concrete powder. The mechanical properties as the compressive strength, flexural strength, dynamic Youngs and share moduli are observed during 409 days. According to results can be assumed that recycled concrete powder can be used as microfiller and cement replacement under 30 wt. % of total amount. Especially the results of compressive strength are comparable with reference sample. But there are some abnormalities in long term development of the strength that need to be explained.

Mechanical Properties of Cement Composites Reinforced by Carbon Microfibers: Compressive and Bending Strength

The paper deals with comparison of chosen mechanical properties of cement composites reinforced by carbon microfibers. There are tested three mixtures, which are different in their composition. Each sample was tested by destructive methods to determine their mechanical and physical properties. The main object of experiments was verification of an influence of individual components in concrete mixture on mixture cohesion with a surface of carbon fibers. Evaluation of results and use of the best concrete mixture for experimental testing like a change of mechanical and physical properties is the second object of this paper.

Development of Mechanical Properties of Cement Based Composites with Recycled Concrete Aggregate

This article deals with the usage of recycled concrete, which arises from demolitions of concrete structures. The aim is to find out what amount of recycled concrete as a binder influences final mechanical properties of the concrete. It was found that the gradual replacement of cement with recycled concrete causes reduction of the dynamic Young’s modulus and decreases the size of the increase in strength during the first 28 days. Overall, it is confirmed that recycled concrete may be used for concrete structures with regard to their purpose, importance and applicability.

Diagnostics of an Existing Cable-Stayed Bridge by Means of the Dynamic Load Test

The cable-stayed bridge at the inner ring road in Prague in the Czech Republic was put into operation in 1997. In 2008 a crack was found in the bridge structure area where the end beam was connected with the upper deck of the box section and where the bridge expansion joint system was anchored. The basic objective of diagnostic works, which were started immediately after the finding of the crack, was obtaining the basis for bridge structure modifications, among other things, to prevent formation of similar damages in the future. A series of diagnostic methods was used for determination of the bridge actual state and the real static and dynamic bridge behavior. One of these methods was the dynamic load test. It was focused on an examination of the bridge forced vibration which was caused by dynamic effects of a usual traffic flow. An arrangement of the test was not quite usual because the experiment was concentrated on dynamic behaviour of bridge support areas especially. The abutment area, the pylon area and the area of a pillar with the bearing with a tensile structural element were observed on the investigated bridge. The dynamic load test was performed in two stages. The first stage was focused on investigation of bridge dynamic behaviour in original structural conditions and on obtaining the basis for design of bridge adjustments. The second stage was realized after bridge reconstruction in December 2012 and verified the effectiveness of bridge modifications.