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This paper presents the results of tests on high performance concrete (HPC) prepared and cured at various ambient temperatures, ranging from 12 ∘C to 30 ∘C (the compressive strength and concrete mix density were also tested at 40 ∘C). Special attention was paid to maintaining the assumed temperature of the mixture components during its preparation and maintaining the assumed curing temperature. The properties of a fresh concrete mixture (consistency, air content, density) and properties of hardened concrete (density, water absorption, depth of water penetration under pressure, compressive strength, and freeze–thaw durability of hardened concrete) were studied. It has been shown that increased temperature (30 ∘C) has a significant effect on loss of workability. The studies used the concrete slump test, the flow table test, and the Vebe test. A decrease in the slump and flow diameter and an increase in the Vebe time were observed. It has been shown that an increase in concrete curing temperature causes an increase in early compressive strength. After 3 days of curing, compared with concrete curing at 20 ∘C, an 18% increase in compressive strength was observed at 40 ∘C, while concrete curing at 12 ∘C had a compressive strength which was 11% lower. An increase in temperature lowers the compressive strength after a period longer than 28 days. After two years of curing, concrete curing at 12 ∘C achieved a compressive strength 13% higher than that of concrete curing at 40 ∘C. Freeze–thaw performance tests of HPC in the presence of NaCl demonstrated that this concrete showed high freeze–thaw resistance and de-icing materials (surface scaling of this concrete is minimal) regardless of the temperature of the curing process, from 12 ∘C to 30 ∘C.

The paper presents the effect of the powders obtained from egg-shells and limestone on the rheological properties of cement pastes. Both powders were added to Portland cement CEM I 42.5 R, 30% by mass. The higher yield stress and plastic viscosity of the cement pastes prepared with the addition of eggshell powder, compared to the cement pastes made with limestone powder, were explained by the influence of the eggshell membrane and its chemical structure. The membrane, which absorbs water and expands in the cement paste, is causing an increase in rheological parameters. The membrane, which absorbs water and swells in the cement paste, causes an increase in viscosity and thixotropy compared to the neat cement slurry and slurry with limestone meal added as a result of particle bonding.

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This paper presents test results of the impact of chemical admixtures used in the underwater concrete technology, i.e. a superplasticizer (SP), an anti-wash admixture (AWA) and SiO2 nano- particles (NP) on the cement hydration process, rheological properties and the setting time. The impact of admixtures was tested in combination and separately, with the use of microcalimetry, X-ray diffraction (XRD) and rheology. It was demonstrated that AWA and SP admixtures caused a delay of the hydration process, while the impact of SP was much greater. The above statement was also confirmed by results of rheological tests. Combined application of AWA, SP and NP causes even a larger delay of the hydration process and the increase of paste rheological parameters, with the impact of the superplasticizer particularly visible.