Advanced Materials Research Vol. 1124

Abstract: The paper deals with development of cementitious binders that would be able to efficiently immobilize toxic elements contained in various types of wastes. The basic component of the proposed binders are clinkers with phosphorus incorporated into the structure of clinker silicates, mixtures of cement with ash containing hydroxylapatite and belite-rich clinkers activated with sulfate anions. The prepared binders were mixed with water doped with various toxic elements; after a defined period of cement stone hydration the test beams were subjected to long-term testing of leachability of individual toxic elements. The research methods involved besides leaching tests also optical and electron microscopy.

Abstract: Calcium aluminate cement CAC is able to increase strength of green body distintly. Influence of typical ceramic dispersants – sodium hexametaphosphate SHMP, sodium carbonate SC and sodium silicate (water glass) SWG – on the rheological properties (viscosity) of calcium aluminate cement – kaolin slurries with different ratio between CAC and kaolin was determined. In all cases sodium carbonate is the most effective dispersant but deflocculation is not very intensive – decrease of torque during the rotational viscometer test was not higher than 15 % (from 68,8 N.mm to 58.3 N.mm for ratio 1:1 of CAC:kaolin suspension when 0,06 %-wt of sodium carbonate was used).

Abstract: The paper summarizes the results of water vapour resistance factors of three commonly used compositions for wall finishing (basic adhesive diffusion mortar; basic adhesive diffusion mortar + silicate plaster; basic adhesive diffusion mortar + acrylic plaster). The border conditions of the measuring (temperature, relative humidity and barometric air pressure) and their impacts on the results are discussed as well.

Abstract: Heat flow development during initial hydration of fresh pastes based on mixtures of pure clinker phases C₃S and C₃A with metakaolin was investigated by means of isothermal calorimetry. Phase composition development was examined by "in situ" X-ray diffraction technique. Obtained results from calorimetric measurements and X-ray diffraction were correlated with recent studies in field of hydration of cementitious systems. The effect of co-sintering of clinker phases on early hydration was characterized by isothermal calorimetry.

Abstract: This paper describes effort to reduce amount of gypsum in raw mixture for burning of Portland cement. Substitution of this material was realized by FBC ash. From these modified raw mixtures the clinkers were burnt, which were milled into cement then. These cements were subjected to basic technological tests.

Abstract: Alkali-activated slag (AAS) based binders can have similar or even better properties in terms of mechanical performance, durability and chemical resistance than ordinary Portland cement (PC), but AAS binders also show some drawbacks, especially high shrinkage and poor rheology. Improvement of these features in the case of PC binder is well established, but a lot of conventional admixtures like superplasticizers do not work in AAS. The influence of shrinkage reducing admixture (SRA) and airentraining admixture (AEA) on mechanical properties, workability and shrinkage was investigated in this study. These admixtures were used in the different dosages in the range of 0–2.0% (by mass of slag). With increasing content of both admixtures compressive and flexural strength decreased. Similar effect was observed for workability. On the other hand, promising results in respect of shrinkage reduction were obtained particularly for SRA, where its 1.0% dose reduced drying shrinkage of the reference mortar by more than 70%. Only slight shrinkage reduction was observed for 0.50% of AEA.

Abstract: Production of SCC concrete involves using a higher amount of fine particles consisting primarily of using increased amounts of cement and one or more admixtures. Due to the economic performance of Portland cements, recently looking for ways to lower the environmental and economic burdens. The first production of SCC concrete production was recommended only cements CEM I. Now, the standards EN 206 specify such a requirement and therefore attempt to use cement CEM II and higher amount of admixtures. This paper points out the possibility of using blended cement CEM II in combination with admixtures and particular monitors rheological properties of fresh SCC concrete.

Abstract: The effect of multi-wall carbon nanotubes and nanoSiO₂ content on physico-mechanical properties of glass microspheres-epoxy resin composite, designed for blast energy absorbing applications, was evaluated experimentally. Specific porous lightweight foam with high volume fraction of microspheres (70 vol.%) was prepared and modified by 1 to 5 vol.% of multi-wall carbon nanotubes and nanosilica (nanoSiO₂). Two types of microsperes with different wall thickness and strength were used. The quality of dispersion of nanoparticles was evaluated in relation to the mixing procedure using scanning electron microscope observation. The compressive and flexural strength tests were conducted at quasi-static load. The mixtures containing nanosilica exhibited an increasing trend in both flexural and compressive strength with increasing nanoparticle content up to 4 vol.%. The addition of carbon nanotubes also increased flexural strength (again up to 4 vol%, crossing this concentration, the significant drop was observed), whereas the compressive strength was affected at lower level. Nanoparticle modification is more effective in the foams with higher thickness and thus strength. The evaluation of test results showed that the properties of glass/epoxy foams can be tailored by adding nanoscale fillers.

Abstract: The paper is focused on the mechanical fracture properties of hardened cement mortars in which Portland cement is partially replaced by reactive admixtures. These properties are evaluated in relation to the mortars’ microstructure through the size and content of pores. The cement in the mortars was partially replaced by a diatomite that contains amorphous SiO₂. The three-point bending fracture tests were performed on beams with a central edge notch. The investigated mechanical fracture properties of the aforementioned cement-based composites included flexural strength, compressive strength, elasticity modulus, effective fracture toughness and specific fracture energy.