Jan Fořt

Service Life Assessment of Historical Building Envelopes Constructed Using Different Types of Sandstone: A Computational Analysis Based on Experimental Input Data

Service life assessment of three historical building envelopes constructed using different types of sandstone is presented. At first, experimental measurements of material parameters of sandstones are performed to provide the necessary input data for a subsequent computational analysis. In the second step, the moisture and temperature fields across the studied envelopes are calculated for a representative period of time. The computations are performed using dynamic climatic data as the boundary conditions on the exterior side of building envelope. The climatic data for three characteristic localities are experimentally determined by the Czech Hydrometeorological Institute and contain hourly values of temperature, relative humidity, rainfalls, wind velocity and direction, and sun radiation. Using the measured durability properties of the analyzed sandstones and the calculated numbers of freeze/thaw cycles under different climatic conditions, the service life of the investigated building envelopes is assessed. The obtained results show that the climatic conditions can play a very significant role in the service life assessment of historical buildings, even in the conditions of such a small country as the Czech Republic. In addition, the investigations reveal the importance of the material characteristics of sandstones, in particular the hygric properties, on their service life in a structure.

Effect of temperature on water vapor transport properties

The temperature effect on water vapor transport properties of calcium silicate is studied, together with the influence of sample thickness. For material characterization purposes, the bulk density, matrix density, and total open porosity are measured at first. Sorption and desorption isotherms are measured using dynamic vapor sorption device in order to characterize the water vapor storage in researched material. The sorption process is analyzed for original material samples as well as for finely ground samples in order to evaluate the effect of inner porous space on water vapor storage. The steady state cup method is used for determination of water vapor transport properties, whereas the measurements are performed at several temperatures and for three different sample thicknesses. The obtained data show an important effect of temperature on water vapor transport and storage in studied material. The results also indicate a substantial influence of sample thickness on the calculated water vapor transmission properties.

UHPFRC at high temperatures – Simultaneous thermal analysis and thermodilatometry

Simultaneous Thermal Analysis (STA) and Thermodilatometry Analysis (TDA) are done to reveal the structural and chemical changes in UHPFRC during its high-temperature load. Based on the measured results, several physical and chemical processes that studied material underwent at high-temperatures are recognized. In the temperature interval from 25 to 300 °C, the liberation of physically bound water from pores and the dehydration reaction of C-S-H take place. Additionally, AFt and AFm phases dehydrate at 110 – 156 °C. Endothermic peat at 460 °C corresponds to the portlandite decomposition. At 575 °C, the α → β transformation of quartz is found. This reaction is accompanied by a sharp endothermic heat flow peak and a volume expansion, whereas no change of mass is measured. In the temperature interval 580-800 °C, the calcite and C-S-H gels decomposition is monitored. At the temperature above 800 °C, there is one significant exothermal peak corresponding to a crystallization of wollastonite. In summary, STA and...

The Effect of Elevated Temperature on High Performance Fiber Reinforced Concrete

High performance fiber reinforced concrete (HPFRC) became very popular material due to its high strength, elastic modulus, corrosion and fire resistance. However, detail description of HPFRC behaviour is necessary for its application and an effective building design and development. Here, also the fire safety of buildings must be considered. Therefore, the effect of elevated temperature on HPFRC is studied in the paper. For the reference material, experimental assessment of basic physical and mechanical properties is done. Then, the HPFRC samples are exposed to the temperatures of 600 and 800 °C respectively, and the effect of a high temperature exposure on material structure is examined. It is found that the applied high temperature loading significantly increases material porosity due to the physical, chemical and combined damage of material inner structure, and negatively affects also the pore size distribution.

Reuse of Waste Ceramic Powder with a High Content of Amorphous Phases as Partial Replacement of Portland Cement

A possible use of waste ceramic powder as a partial replacement of Portland cement in blended binders is studied. For the ceramic powder, originating from the contemporary hollow bricks production, the measurement of chemical composition is done using XRF and XRD analysis. The particle size distribution of ceramics and cement is accessed on the laser diffraction principle. The blended binders containing ceramic powder in an amount of 8, 16, 24, 32, and 40% of mass of cement are used for the preparation of cement pastes which are then characterized using the measurement of basic physical properties and mechanical properties. Experimental results show that an application of 16% waste ceramics in the blended binder provides sufficient mechanical properties of the paste. This makes good prerequisites for future research that will be focused on the development of new types of cement-based composites with incorporated ceramic waste powder.

Residual Mechanical Properties of Hybrid Fiber Reinforced HPC Exposed to High Temperatures

The effect of high temperature load on mechanical properties and porosity of a newly designed Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is studied. The hybrid reinforcement of UHPFRC is based on a mixture of polypropylene and steel fibers. In order to identify influence of high temperature exposure on UHPFRC, its residual mechanical parameters such as compressive strength, flexural strength and Young’s modulus of elasticity are accessed. Moreover, residual bulk density, matrix density and total open porosity are examined and related to the monitored structural changes. Simultaneous Thermal Analysis (STA) is employed in order to describe transformation processes during high temperature loading. The conducted tests provide practical information for controlled regulation of water vapor transport in a low permeable cementitious composite in order to decrease risk of spalling.

Applicability of contemporary ceramic bricks for the reconstruction of historical masonry

Two historical ceramic bricks originating from the beginning of 20th century and a contemporary poorly burnt ceramic brick are studied, in order to assess a possible application of current bricks in the renewal of historical masonry. For the researched materials, basic physical, mechanical and hygric properties are analyzed. Among the basic physical properties, determination of bulk density, matrix density, total open porosity and pore size distribution is done. The mechanical performance is characterized by compressive strength and Young’s modulus. The moisture transport properties that represent crucial parameters for the durability of tested materials are described by water absorption coefficient and sorptivity, whereas the measurements are done for the penetration of pure water, as well as 1M NaCl water solution. The obtained data indicate that the studied currently produced ceramic brick can be successfully used at the reconstruction of historical buildings.

Thermal Behaviour of New Type of Plaster with PCM Admixture

In order to decrease the energy consumption of buildings and keep the high thermal comfort of the indoor environment, new types of plasters modified by phase change material (PCM) are developed and experimentally tested. For evaluation of the contribution of PCM admixture to plasters properties, the reference plaster is studied as well. The basic characterization of the tested plasters is done using the measurement of their bulk density, matrix density a total open porosity. For the dry plasters mixtures, the particle size distribution is accessed on laser diffraction principle. Investigation of thermal properties as main parameters affecting the thermal performance of researched materials is done by differential scanning calorimetry (DSC) and transient impulse method. The obtained results proved increased heat storage capacity of the newly developed plasters with incorporated PCM admixture.

Characterization of Cement Pastes Containing Natural Zeolite as a Pozzolanic Admixture

A possible use of natural zeolite originating from a mining area in South Slovakia as a pozzolanic material suitable for the partial cement replacement in composite production is studied. Measurement of chemical composition of natural zeolite is performed using XRF analysis. The particle size distribution of zeolite and dry paste mixtures is accessed on laser diffraction principle. For the tested pastes, basic physical properties and mechanical properties are determined. The obtained results indicate a good potential for the application of natural zeolite in the composite mix design.

Residual Material Properties of High Strength Fibre Reinforced Concrete Exposed to Elevated Temperatures

This paper is focused on the research of material characteristics of high performance concrete reinforced with a combination of steel and hybrid fibers exposed to the extreme temperatures. In the performed experiments it was examined several types of mixtures (HPFRC, UHPFRC) exposed to the extreme temperatures up to 200-1200 °C. Outside residual parameters of each examined mixtures (tensile bending strength, compression strength, fracture parameters) was investigated the dependence of porosity of the matrix, sample damage and chemical analysis of samples exposed to extreme temperatures, to the resulting mechanical parameters. Part of the initial results of the research described base material and physical properties of the examined mixes and shows the effect of high temperatures on these properties. The results presented in the current paper are the basis for further research and the preparation of numerical models for the design of HPC exposed to extreme temperatures.