Jaroslav Pokorný

Modification of the computational model of coupled heat and moisture transport: The transition between the liquid and gaseous phases of water

An adjustment of the Kunzel´s mathematical model of coupled heat and moisture transport is presented. The balance equation of moisture is rearranged using additional parameters, introduced for a modification of the description of liquid and gaseous moisture transport in the transition zone between the hygroscopic and overhygroscopic moisture ranges. The adjustment is accomplished by a special weighing function to put fast liquid water transfer and slower vapor diffusion into balance in accordance with the real observations. A simple numerical experiment illustrates the advantage of the modification of the model and the results are discussed.

The GUHA-DBS Data Base System

This paper presents the concept of the GUHA-DBS Data Base System intended for the users of the GUHA method and for GUHA procedure programmers. The architecture of the system as a whole is described and the features of its principal components are presented.

Coagulated silica - a-SiO2 admixture in cement paste

Amorphous silica (a-SiO2) in fine-grained form possesses a high pozzolanic activity which makes it a valuable component of blended binders in concrete production. The origin of a-SiO2 applied in cement-based composites is very diverse. SiO2 in amorphous form is present in various amounts in quite a few supplementary cementing materials (SCMs) being used as partial replacement of Portland cement. In this work, the applicability of a commercially produced coagulated silica powder as a partial replacement of Portland cement in cement paste mix design is investigated. Portland cement CEM I 42.5R produced according to the EU standard EN 197-1 is used as a reference binder. Coagulated silica is applied in dosages of 5 and 10 % by mass of cement. The water/binder ratio is kept constant in all the studied pastes. For the applied silica, specific surface area, density, loss on ignition, pozzolanic activity, chemical composition, and SiO2 amorphous phase content are determined. For the developed pastes on the basis...

Application of a-SiO2 Rich Additives in Cement Paste

The effect of a-SiO2 of various origin on the properties of cement paste with incorporated different silica containing materials is experimentally studied in the paper. For the applied a-SiO2 materials, basic physical and chemical properties are accessed, together with their chemical composition. Amount of amorphous phase of SiO2 in particular siliceous materials is determined using XRD analysis. Matrix density, bulk density, total open porosity, compressive and bending strength are measured for all developed pastes with incorporated a-SiO2 containing materials, together with initial and final setting time of fresh mixtures. The obtained data give evidence on a high and fast reaction activity of tested siliceous materials which results in a significant improvement of porosity and mechanical strength of a-SiO2 modified cement pastes.

Thermal properties of light-weight concrete with waste polypropylene aggregate

Thermal properties of a sustainable light-weight concrete incorporating high volume of waste polypropylene as partial substitution of natural aggregate were studied in the paper. Glass fiber reinforced polypropylene (GFPP), a by-product of PP tubes production, partially substituted fine natural silica aggregate in 10, 20, 30, 40, and 50 mass%. In order to quantify the effect of GFPP use on concrete properties, a reference concrete mix without plastic waste was studied as well. For the applied GFPP, bulk density, matrix density, and particle size distribution were measured. Specific attention was paid to thermal transport and storage properties of GFPP that were examined in dependence on compaction time. For the developed light-weight concrete, thermal properties were accessed using transient impulse technique, whereas the measurement was done in dependence on moisture content, from the dry state to fully water saturated state. Additionally, the investigated thermal properties were plotted as function of porosity. The tested light-weight concrete was found to be prospective construction material possessing improved thermal insulation function. Moreover, the reuse of waste plastics in concrete composition was beneficial both from the environmental and financial point of view considering plastics low biodegradability and safe disposal.Thermal properties of a sustainable light-weight concrete incorporating high volume of waste polypropylene as partial substitution of natural aggregate were studied in the paper. Glass fiber reinforced polypropylene (GFPP), a by-product of PP tubes production, partially substituted fine natural silica aggregate in 10, 20, 30, 40, and 50 mass%. In order to quantify the effect of GFPP use on concrete properties, a reference concrete mix without plastic waste was studied as well. For the applied GFPP, bulk density, matrix density, and particle size distribution were measured. Specific attention was paid to thermal transport and storage properties of GFPP that were examined in dependence on compaction time. For the developed light-weight concrete, thermal properties were accessed using transient impulse technique, whereas the measurement was done in dependence on moisture content, from the dry state to fully water saturated state. Additionally, the investigated thermal properties were plotted as function of p...

Influence of various amount of diatomaceous earth used as cement substitute on mechanical properties of cement paste

Active silica containing materials in the sub-micrometer size range are commonly used for modification of strength parameters and durability of cement based composites. In addition, these materials also assist to accelerate cement hydration. In this paper, two types of diatomaceous earths are used as partial cement replacement in composition of cement paste mixtures. For raw binders, basic physical and chemical properties are studied. The chemical composition of tested materials is determined using classical chemical analysis combined with XRD method that allowed assessment of SiO2 amorphous phase content. For all tested mixtures, initial and final setting times are measured. Basic physical and mechanical properties are measured on hardened paste samples cured 28 days in water. Here, bulk density, matrix density, total open porosity, compressive and flexural strength, are measured. Relationship between compressive strength and total open porosity is studied using several empirical models. The obtained res...

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.

Properties of Cement Paste with Incorporated Sodium Silicate

Sodium silicate, usually known as water glass, is researched as material that can potentially find use in composition of cement based matrix in order to improve its porous structure and related physical parameters. The water glass is applied in cement paste mixture in an amount of 5, 10, 15, and 20 mass% of cement. The water dosage is experimentally accessed in order to attain the same workability of particular mixtures. For the applied water glass and cement, the particle size distribution is measured on laser diffraction principle. Pozzolanic activity of water glass is investigated using modified Chapelle test. The particular studied cement pastes are cured 28 days in water and characterized by basic physical and mechanical properties, whereas the results of mechanical resistivity are supported by pore size distribution data accessed by mercury intrusion porosimetry. Althought the particles of applied water glass are coarser than that of cement and did not exhibit pozzolanic activity, their application partially tightened the porous structure of hydrated products and thus contributed to the mechanical strength by means of filler effect. This makes good prerequisites for future research that will be focused on a development of new types of cement-based composites with incorporated sodium silicate used as an modifying admixture.

Engineering properties of composite materials containing waste ceramic dust from advanced hollow brick production as a partial replacement of Portland cement

Waste ceramic dust originating in the advanced hollow brick production is applied as a supplementary cementing material replacing a part of Portland cement in concrete. The measurements of mechanical and fracture-mechanical properties, water vapor and liquid water transport parameters, thermal conductivity, specific heat capacity, and freeze/thaw resistance show that the ceramic dust application does not affect negatively the properties of the analyzed concretes over the whole studied Portland cement replacement range up to 40% by mass. The achievement of such a high limit for the ceramic dust application can be attributed, besides the pozzolanic reaction being initiated already during the time period of 7 to 28 days, to the positive effect of the excess ceramic dust in the mixes with a high volume of uniformly distributed air voids. The part of the ceramic additive which cannot participate in the hydration and pozzolanic reactions due to the lack of available Ca2+ acts, apparently, as fine aggregate partially filling the voids, thus contributing to the compaction of the hardened mixes and compensating, to a certain extent, the factual decrease of the amount of binder.

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.