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This work was financially supported by the Ministry of Education and Science – Poland, within the grant number
FD-IL-003, FD-20/IS-6/021, by the Grant Agency of the Czech Technical University in Prague, grant No
SGS20/153/OHK1/3T/11, and by the Technology Agency of the Czech Republic under project No FW03010256.
The study of the physical and mechanical properties of ordinary concrete with hydrophobic additives is presented in the paper. Basic physical and strength characteristics of concrete were determined, i.e. water absorptivity, density, open porosity, compressive strength, flexural tensile strength, and frost resistance. Three concrete mixtures were prepared: concrete without a hydrophobic admixture, concrete with silane (A1), and concrete with tetramethoxysilane (A2). The reference concrete mixture was prepared using Portland cement CEM I 42.5 R, coarse aggregate 2-16 mm, sand, superplasticizer, and batch water. The use of two chemical additives resulted in different wetting properties and frost resistance of the tested concretes. The wetting properties of concrete were determined by measuring the contact angle (CA) of its surfaces using a single measuring liquid, which was in this case distilled water. The smallest water CA (<1°) was obtained for concrete without hydrophobic additive, 110.2° for concrete with the addition of silane, and 98.5° for application of tetramethoxysilane. After 150 freezing/thawing (F/T) cycles, a damage of specimens characterized by significant mass change of 8.3% was observed for concrete with admixture A2 only. In the case of other two concretes, the mass change of samples that underwent F/T cycles, the weight change of reference sample concrete was 1.3% and 0.3% of concrete with A1. The decrease in the compressive strength of concrete admixture A2 was the greatest and was 35% compared to the reference concrete. On the other hand, concrete with silane showed a slight decrease in the compressive strength of about 6%. In the reduction of water ingress, the highest efficiency was observed for admixture A1 that reduced the water absorbability by 27%. The use of tetramethoxysilane had a negative effect on the frost resistance and compressive strength of the concrete.
