Jan Hurta

Hybrid Alkali Activated Concretes - Conception and Development for Practical Application

Hybrid cements represent a relatively new type of binders which combine some of the advantages of Ordinary Portland Cement (OPC), the application of mineral admixtures and alkali activation. Hybrid cements represent blends containing a low portion of OPC and a high proportion of mineral additions (such as blast furnace slag, fly ash, metakaolin ....). The paper is focused on the study of properties of mortars prepared from hybrid cements. Mortars with hybrid cements were prepared for an evaluation of the effects of the dosage and the composition of alkali activator, the dosage of OPC and the ratio between ground granulated blast furnace slag and fly ash. The results make it possible to optimize the composition of hybrid alkali activated concretes.

Comparison of Properties of Concretes with Different Types and Dosages of Fibers

Concretes with PP fibers 12 mm, construction polymer fibers 25 mm, 3D steel fibers 25 mm, and steel microfibers 12 mm were prepared in dosages 0.5 and 1%. The mechanical properties (compressive strength, bending strength, fracture properties, and modulus elasticity) and the frost resistance of these concretes were tested and they are discussed. The behavior of these concretes is also discussed using graphs load vs. deflection. As bad results of frost resistance are sometimes recorded for concrete with fibers, this property is also evaluated. As was expected, mechanical properties are enhanced with the addition of suitable fibers. Frost resistance is usually comparative with concrete without fibers, but in the case of concrete with 1% of steel fibers, it is reduced.

Concrete deflection measurement using fiber optic distributed strain system

The monitoring of building structures deformations and testing of construction materials resilience are very important processes in the development and production of given materials and structures. Undesirable or excessive deformations of materials are phenomena which are unacceptable in construction, especially in supporting structures. These issues are currently monitored by electromechanical sensor in most cases. It is a classic technique when the sensor measures the material stress at the point of its installation. This paper deals with the concrete deflection measurement using fiber optic distributed strain system. This system uses optical fiere as a sensor and operates at the principle of measurement of Brillouin frequencies. The mechanical stress on the optical fiber causes shift of these frequencies. This change is subsequently converted to stress unit micro-strain. In our experiments, the optical fiber was embedded in concrete along its whole length. The advantage of this system is that the measurement is carrying out along the entire fiber length with spatial resolution around 50 cm, so it is possible continuously measure several thousands of points at the distance of several kilometers.

Measurement of insulation layers using DTS system

Fiber optic distributed temperature sensing systems (DTS) are based on the principle of reflectometer and allow us to measure the temperature along the optical fiber. Optical fiber in these systems is used as a temperature sensor which can measure up to thousands of points simultaneously. DTS sensors use nonlinear phenomenon known as Raman scattering for temperature measurement. The advantages of this system include immunity to electromagnetic radiation, low cost of optical fiber, the possibility of measurement to a distance of 10 km and safe use in flammable or corrosive environments. The small size of optical fiber allows using in applications where the dimensions of the other sensors were problematic. A typical example of the DTS application is the fire detection in tunnels and buildings at risk, detection of water leaks on dikes and dams or monitoring of temperature in mine shafts. This article deals with the measurement of temperature transmission over various insulation layers using the DTS system. One of the problems of temperature transmission is that most of the sensors cannot measure the entire temperature profile but only allows a point measurement. This problem is solved by DTS systems with optical fibers. Optical fiber, due to its small size, can be applied among various insulation layers that were formed by rock wool. Three sensory layers formed by rings of multimode optical tightbuffered fiber with 50/125 micron core/cladding dimension were applied. The layers were linked together allowing a direct comparison of measured temperature. Rows of rings were placed on the margins and one was in the middle. Individual rings were linked together into the horizontal lines. Thus we were able to cover the whole surface of the insulation layers. Measurement was carried out in a closed air-conditioned room for 37 hours. Graphs with the progress of temperature at time and place were compiled from the measured data.

Comparison of Experimental Tests of Foundation Slabs

In civil engineering we solve problems with interaction between the foundation base and the subsoil often. For the determination of stress in foundation structure is needed to determine the influence of the stiffness respectively pliability of subsoil to structural internal forces, and vice versa, how the stiffness of the foundation structure affects the resulting subsidence. In this article I would like to compare subsidence and deformation of several different baseboards.

Numerical Investigation of a Masonry Column Reinforced by the Helical Reinforcement

In recent years numerous advanced materials technologies have appeared in the market or have been developed for use in construction. In civil engineering there are also numerous fields of application for these materials, which can be used for construction of new buildings as well as for reparation and improvement of older structures. In many cases the helical reinforcement is used for the improvement and rehabilitation of masonry structures. This type of reinforcement offers several advantages. It requires only minimal changes of the existing masonry elements and it introduces no visual changes of the rehabilitated structure. In the paper a numerical analysis and an assessment are presented of such a helical reinforcement for the improvement of axially loaded masonry columns.

Measurement of the spectral characteristics of telecommunication fiber emitted at high temperatures

The fiber optic sensors have a great possibilities thanks to its sizes, features and usage possibilities in measurement engineering. Optical fiber is mostly used as a medium for the transfer of information, but if we consider an optical fiber as a sensor then the other usage can be found for example in medicine or biology. If the optical fiber is heated by sufficiently high temperature, the light signal starts to be emitted in the internal structure. This signal has a spectral characteristic, which can be used for evaluation of temperature thanks to quality analysis. The article will describe the evaluation of spectral characteristics for utilizationof optical fiber as fiber optic sensor for very high temperatures.