Key Engineering Materials Vol. 677

Abstract: Influence of exposure to microwave (MW) radiation of concrete with paraffin addition was presented. Specimens were exposed to MW after 7 and 28 days from casting. The exposure times were: 20 minutes and 40 minutes. Concretes were made with 1 and 3% addition of paraffin of the volume of concrete mixture. As a reference served concrete with no paraffin addition and concrete containing paraffin but not treated with MW. Paraffin was added in two forms: as a powder (fine paraffin) and as a granules (coarse paraffin). Influence of radiation on compressive and tensile splitting strength was tested as well as its impact on sorptivity and free water absorption. Exposure to MW radiation lowered the mean values of concrete compressive and tensile splitting strength maximum of about 24%. Sorptivity test results showed no general tendency and free water absorption has decreased maximum about 20%.

Abstract: Ternary gypsum-binders with different types of pozzolan were stored in the water and in the air. Brick powder, microsilica and blast slag were used as a pozzolan admixture. The quantity of the pozzolan in the mixture was determined from the amount of the amorphous phase in the pozzolan. Mixtures with pozzolans do not lose strength when stored in the water. Porosimetry shows that the product of the pozzolanic reaction started to develop.

Abstract: Bitumen modified by polyphosphoric acid (PPA), as well as in combination with polymers and is widely used for production of road bitumen, which correspond to high standards. Therefore, the aim of this work is to study the influence of the properties of the polyphosphoric acid with different contents of phosphorous oxide (P₂O₅) and a derivative of them based additives esters of polyphosphoric acid and synthetic phospholipids DAD-KT, developed by "Selena".The influence of these additives on the change of adhesive, cohesive properties of bitumen, as well as on the properties of asphalt concrete to change of the limits of the crushing stress, water saturation and long waterproof. The use of additives had a positive effect on the adhesion of bitumen with mineral material. The index of cohesion increased with the addition of DAD-KT, more than 80%. This is due to the presence in its structure of the polymer.In connection with the increase of adhesion and cohesion of asphalts modified polyphosphoric acid, asphalt concrete prepared with these binders should be characterized by the increased values of water, heat and frost resistance and resistance to rutting.Study of the influence of additives on the physico-mechanical characteristics of asphalt concrete shows a positive effect on the properties of the latter. So the strength of asphalt concrete at 20 °C has risen on average by 10 % relative to the initial bitumen without additives, the strength at 50 °C by 15 %, the strength at 0 °C decreased by 8-12 %, the water saturation decreased by 30-40 %, indicating that the decrease in porosity of asphalt concrete and increase the durability of asphalt to seasonal temperature changes. In turn, the resistance increased by 5-8 % relative to the bitumen without additives. Long resistant with additives also increased which can be explained by the improvement of adhesion of bitumen with mineral materials of asphalt concrete. So the resistance after 15 days of the original bitumen and bitumen with additives decreased by 15 and an average 5 %, respectively, after 30 days at 25 and 7 % respectively. It can be concluded that in the modification of bitumen polyphosphoric acid, and in particular the addition of DAD-KT, there has been a significant improvement in the properties of bitumen and asphalt concrete. Therefore, it is possible to expect the improvement of the quality of the road pavement made of asphalt, with the use of additives containing polyphosphoric acid, in particular - DAD-KT.

Abstract: 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.

Abstract: This paper describes influence of exposure to high temperatures on material properties of cement paste with addition of fly ash. The properties of cement pastes are significant to the assumption behaviour of concrete and concrete structures. In the cement paste containing fly ash, the effect of high temperature up to 600 ° C causes the changes of content in physically bound water and the change in the material structure. The results of research indicate changes that are reflected in the material properties of the cement paste as compressive strength, tensile strength in bending.

Abstract: Durability of concrete is a crucial parameter with respect to lifetime of concrete structures, nevertheless it is very complex issue. There is number of methodologies to predict final durability of concrete and substantial part of them is based on the accelerated tests in severe conditions or environment. Present paper deals with the experimental study of the influence of concrete composition on the resistance to sulfate environment. Metakaolin replacement of Portland cement was incorporated in the studied mixtures which were subjected to various sulfate containing solutions. Final resistance was evaluated by means of loss of mass and compressive strength. Performed experimental program confirmed positive influence of metakaolin replacement up to 30 % by cement weight, however higher doses reduced workability. All studied mixtures with metakaolin addition exhibited improved resistance to acid environment.

Abstract: Thermal energy storage represents an important aspect of building energy conservation. Unfortunately, modern buildings with lightweight building envelopes not provide sufficient heat storage capacity and indoor overheating is a common problem, mostly solved by high performance air conditioning that leads to the higher electricity consumption. Here, Phase Change Materials (PCMs) that allow significant heat storage or release when undergo phase transition can find use. On this account, a detailed testing of a new type of cement-lime plaster modified by PCM admixture with respect to the temperature change rate is presented in the paper. The studied material is based on commercial dry plaster mixture that is modified by microencapsulated polymer PCM admixture. For characterization of the developed material, measurement of basic physical and mechanical properties is done. Within the DSC analysis, the researched material is exposed to the temperature loading ranging from 0 °C to 40 °C, with the temperature change rate of 1, 5 and 10 °C/min respectively. On the basis of DSC tests, temperature of phase change and its corresponding enthalpy are determined. The obtained data show the effect of heating and cooling mode on materials performance in the form of a significant shift of DSC curves. This effect is evaluated and applicability of incorporated PCM admixture for the use in thermal energy storage plasters is discussed.

Abstract: This paper deals with heat of hydration in a concrete structure at the early age. The influence of temperature on development of hydration heat in the concrete structure is implemented through a fuzzy-logic model of the degree of hydration. The transient heat transfer problem was solved as a three-dimensional finite element simulation. The whole process of calculation is implemented in MATLAB Environment. The result of this work provides temperature distribution in the structure for each time step, the maximum temperature in the structure, and the time when it occurs.

Abstract: A range of testing methods were used to study the potential structural changes as a result of the effects of high temperatures on lightweight types of concrete developed above all for fire resistant structures. One such test for monitoring changes in concrete structures is the non-stationary determination of the coefficient of thermal conductivity using the hot wire method. The matrix structure progressively collapses as a result of the effects of high temperatures on the concrete structure ́s surface because erosion takes place of the matrix and aggregate porous structures. The degradation of the porosity of the concrete results in the deterioration of its thermal insulating properties. This paper assesses the dependence of the thermal conductivity coefficient of lightweight concretes on temperature and determines the potential occurrence of structural changes in the lightweight concrete matrix. The results were verified using other methods to determine the concrete ́s resistance to thermal load.

Abstract: This work deals with determination of location of micro fibers positions in fiber-reinforced concrete. The digital images of sectioned cement-paste samples with dimension equal to 40 × 40 mm were used as an information source about the monofilaments positions. Properly acquired digital image of high resolution allows to determinate the number of fibers in samples cross sections and relate theirs coordinates to any point. Optical microscope Carl Zeiss Axio Zoom.V16 with camera and software allowing individual shots composition of examined samples surface was used to obtain these parameters. Cement pastes reinforced with PET (polyethylene terephthalate) micro fibers having diameter equal to 0.4 mm were studied. The total number and the fibers distribution along the height and width of the sample cross section were examined.