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The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

Abstract.In the scientific studies the influence of burning regime or composition of formation mix on the final properties of the ceramic bricks is analysed most often. However, drying regime is also of paramount importance in the process of the high quality ceramic production. The formed ceramic samples were dried according to 8 different drying regimes while burning regime was not varied during the investigation. The dried samples were burnt for 24 hours keeping the maximum temperature 1050 o C for 3 hours. Later on these parameters were determined experimentally: density, general shrinkage, compressive strength and rate of ultrasound spread. As the statistical and regression analyses of data were performed, the empirical equations, showing how the selected stages of drying regime influence the physical and mechanical parameters of ceramics, and vice versa, how the selection of the dimensions of the stages of drying regime depends on the desired values of the ceramics properties, were derived.

The investigations of the effect of the Ca(NO 3 ) 2 dosage at different initial curing temperatures on the Portland cement hydration process and the physical and mechanical properties of Portland cement are presented in the paper. The results show that the Ca(NO 3 ) 2 admixture shortens the induction period of the hydration of the cement paste and reduces the maximal hydration temperature of the cement paste. The setting time of the cement paste with Ca(NO 3 ) 2 is about 1 hour shorter for 1 % of Ca(NO 3 ) 2 in the cement paste. At 0 °C and 5 °C, the accelerating effect of the Ca(NO 3 ) 2 admixture is the most pronounced. At lower temperatures (-5 °C, -10 °C), only 3 % of the Ca(NO 3 ) 2 admixture can shorten the initial setting time by about 40 %. The most effective application of Ca(NO 3 ) 2 is achieved at -5 °C. For the 2 day-specimens cured at the lower initial temperatures (-5 °C, -10 °C), the higher Ca(NO 3 ) 2 dosages (2 -3 %) significantly improve the standard strength values of the concrete.

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Abstract. Glass fiber reinforced concrete (GRC) is used for 40 years to create world's most stunning and complex architectural elements due to its high mechanical properties, particularly flexural strength. Yet it is very important to note that any type of glass fibers in the concrete matrix are undergoing complex ageing processes, resulting to significant decrease of initial mechanical characteristics of this composite material under natural weathering conditions. Aspects of GRC durability are mainly dependent from the properties of fibers and interaction between them and concrete matrix. In this article, long term strength retention of this composite material is discussed, existing experimental data of weathering tests presented, and main corrosion mechanisms explained. Lack of knowledge about freeze-thaw resistance of glass fiber reinforced concrete is addressed. Finally, latest attempts of GRC durability improvement are reviewed, such as adding micro fillers, polymers to the concrete matrix and enhancing surface of fibers in Nano scale.

The problem of frost resistance is relevant to facing materials, especially glazed ceramic tiles. Analysing the processes of ceramic tile destruction it is important to take into account the primary destruction symptoms. New estimation of service frost resistance of ceramic tile according to residual surface and residual mass of the tile after a certain number of simulated service cycles is presented in the paper. Applying the new estimation, the forecast of frost resistance under extremely unfavourable service conditions may be performed. As for other ceramic products regarding frost resistance, one of the most important parameters is the reserve of pore volume. .or a rapid estimation of service frost resistance of ceramic tile it is best to use several parameters under multiple correlation with the parameter of service frost resistance.

Portland cement manufacturing significantly contributes to CO 2 emissions into the atmosphere. In order to reduce CO 2 emissions, limestone and slag mineral admixtures are most prospective both technologically and economically in cement production. For such cements, it is important to select a certain type and amount of plasticizer and evaluate what plasticizers influence the heat released during hydration. In order to achieve the objectives of research, viscosity, conductivity, and DSC analyses of cement pastes with A and B plasticizers were performed. This study analyzes the effect of polycarboxylate ester (A) and modified lignosulfonate (B) plasticizers amount on rheological properties and hydration processes of the limestone and slag cement pastes. The use of A additive in contrast to B additive has a long-term effect on viscosity of both cement pastes and is less sensitive to mineral composition. Optimal A additive amount in case of limestone cement is 1.25 % and in case of slag cement is 0.3 %. In limestone cement additive A reduces total heat value by 6 % and additive B by 15 % after 48 h of hydration. In slag cement additive A increases total heat value by 4 % and additive B by 2 % after 48 h of hydration. Exothermal profiles show that in limestone cement additive A extends the EXO maximum time by 25 % and additive B by 40 % in samples after 24 h of hydration. In slag cement additive A extends the EXO maximum time by 37 % and additive B by 25 % in samples after the same time of hydration.