Solid State Phenomena Vol. 325

Abstract: In this study, the utilization of two types of spongilites in various addition in cement mortars has been investigated with the purpose of exploring a new application of this natural pozzolans as cement mortar additives. The influence of the addition of spongilites on the physico-mechanical properties, frost-resistance, and microstructure of cement mortars as a function of time was studied. The results revealed that the rising proportion of spongilites in cement mortars causes increase in water retention of mortars, reduction of their bulk density, increase in porosity of mortars due to the growing predominance of capillary pores maintaining sufficient mortars strengths, and slightly increase in the frost-resistance of mortars. After initial tests, partial replacement of cement in fine-grained cement mortars with hitherto unexploited spongilites seems to be very promising. Based on the achieved results, a 20% cement replacement can be recommended as optimal.

Abstract: The article monitors the effect of length of grinding in the process of homogenization of raw material mixture and soaking on the number of monoclinic phases of alite M1 and M3 in the sample using the Rietveld method. The wet grinding process in the water environment in the planetary mill PULVERISETTE 6 was chosen for the preparation of raw material mixture. Based on previous research in this area, two firing temperatures 1450 and 1550 °C with soaking of 30, 60 and 90 minutes were selected. The results showed the monoclinic phase M1 is more readily formed during coarser grinding, during which large crystals of M1 are formed. On the contrary, the monoclinic phase M3 is formed at a higher firing temperature, at a larger amount nuclei and finer grinding. The results show that the grinding time has an important effect on the rate of formation of monoclinic phases.

Abstract: The storage of the phosphogypsum in stockpiles causes serious environmental problems. In order to avoid them, this by-product should be utilised. Hence, one solution is to employ it as a binding material, so that its structural and binding properties must be satisfactory. Depending on the type of original phosphate rock, the microstructure of phosphogypsum may differ, determining its main physical-mechanical properties. However, research with comparative analyses of the properties of phosphogypsum from different origins is almost inexistent. Therefore, in this study, the microstructure of phosphogypsum from two different sources is analysed: the first type is from Kovdor mine (Russia); the second is a mixture between material from Kirov (Russia) and Casablanca (Morocco) mines. The microstructure of both phosphogypsum types was analysed and compared by applying SEM-DES analysis and by measuring the loss on ignition. In order to obtain high mechanical properties, the material was processed by press-forming. Eventually, the mechanical properties of hardened phosphogypsum of both types were obtained by compression test and then compared.

Abstract: Mortars containing linseed oil as admixture to lime were identified in several mosaics found in Czech Republic. These mosaics were made around 1900 and the composition of their bedding mortar was likely influenced by publication La Mosaïque by E. Gerspach [1], published in Paris, 1880. The recipe for lime mortar with linseed oil and stand oil has been reproduced within the present paper. Four mixes were prepared with varying oil/stand oil content (below, above and according to Gerspach’s recommendation). The primary motivation of mosaic artists to use oil admixture was to keep the mortar’s plasticity for longer time, what is beneficial for the mosaic tesseraes (stones) adjustment. This effect was quantified by help of Vicat apparatus. The influence of oils on mechanical properties and carbonation was evaluated at 28 days. It was found by XRD, that the rate of carbonation is reduced due to the oil presence. It is caused by fact that the oil acts also as water-repealing admixture what reduces the ability of aerial CO₂ to dissolve in pore solution and react with lime. The deformation behavior of material has been modified by oil toward the higher toughness, but lower compressive strength, due to polymeration of oil in mortar.

Abstract: Lime reactivity is the most used identification parameter for lime quality. The reaction may vary in its rate and maximum reached temperature. In this study, the influence of the properties of limestone on the course of the reaction is studied. The samples are thoroughly examined from a geological point of view (geological age and origin, genesis and diagenesis) and their physicochemical properties are described (total porosity, limestone category, chemical analysis, insoluble residue). Different temperatures and isothermal loads were selected to study the effect of the burning process on the lime microstructure. The newly formed CaO is observed by scanning electron microscopy (SEM images). Lime reactivity analysis is performed, and different reaction courses are compared.

Abstract: The decomposition of limestone during the firing process is mainly based on the decarbonation of CaCO₃. In the case of crystalline limestone, it is the decomposition of calcite crystals. In this study, different limestone properties on the course of decarbonation are studied. Therefore, the samples are determined from a geological and physicochemical point of view (geological age and origin, total porosity, limestone category, chemical analyses and insoluble residue). After thorough identification of the samples, various analyses focused on limestone and lime microstructure are performed, such as SEM image analysis or lime reactivity. For these analyses, the samples are burned at different temperatures. The decrepitation amount of limestones during burning process is determined.

Abstract: The main results of the study of the influence of man-made products of the metallurgical industry on the properties and structure of gypsum binder are presented. It has been proved that the introduction of man-made modifiers, metallurgical dust, and slag leads to an increase in the strength properties and electric conductivity of the material, but, over time, the waste efficiency decreases. The use of Portland cement as an activator leads to the formation of amorphous hydration products based on calcium hydrosilicates, which bind calcium sulfate crystals and provide an increase in the physicomechanical characteristics and electric behavior of the gypsum composite.

Abstract: The high-strength concrete is a cement composite reaching high compressive strength, namely, pursuant to the legislation, higher than 60 MPa in the terms of cube compressive strength. The development of high-strength concretes exceeding 100 MPa is still an up-to-date issue and the production of these concretes is still limited only to a prefabrication. Contemporary construction industry and projecting activity have begun to focus on a construction of statically demanding buildings, which can include e.g. high-rise buildings. Such projecting often requires using of the state-of-the-art materials like cement composites with high mechanical parameters for construction of more subtle buildings. Within this article, the procedure of ready-mixed concretes development with the compressive strength around 100 MPa designed according to a project documentation for actual construction of high-rise building with the height up to 160 meters and 46 floors is described, together with the influence of the aggregate on the resulting composite strength.

Abstract: Research results of modified composites which consist of isolated layers with different properties and their practical usages are represented in this article. A structure of the composite material is considered. The structure is combined of few layers; external layers are made of corrosive resistance material with dielectric behavior while the internal part of the composite is made of electrically conductive material with high conductive and mechanical properties. Conductive properties of each layer have been measured as well as their mechanical properties and structure. Also, the features of the joints between layers in terms of structure and properties were defined. More than that, varieties of mixtures and their possible usage are considered. Conductive properties of composite materials and ways of their adjustment have been described as well. For the first time, the measuring scheme of conductive properties for each layer was offered and heat shrinkable tubes and copper electrodes were used for it. Efficiency of modified composites and its behavior when electrical current applied can be measured by using the scheme.

Abstract: Cement hydration is a process during which the setting and hardening of cement stone occur. This process is linked to the significant development of heat of hydration, which is accompanied by volume changes of concrete composite (i.e. shrinkage). Due to this, cracks in a concrete composite can arise and influence not only its durability, mechanical parameters or aesthetics but, in the case of water-tight concretes (e.g. the so-called white boxes), also its function. The extent of volume changes can be influenced not only by the composite structure itself or the selection and amount of cement but also by using suitable active additions, e.g. high-temperature fly ash. As a result, it is possible to reduce the amount of cement required while maintaining identical mechanical parameters of concrete and, at the same time, slow down the progress of heat of hydration during cement hydration. One of the other options to eliminate volume changes in concrete composites is the use of shrinkage-reducing additives (SRA). This article focuses on the SRA influence on volume changes of high-performance concretes and their impact on the development of hydration temperatures and mechanical parameters of composites.