: 32-38
Lviv Polytechnic National University, Department of Building Production
Lviv Polytechnic National University, Department of building production
Lviv Polytechnic National University, Department of construction production

Exposure to elevated temperatures has detrimental effects on the properties of concretes based on the Portland cement, leading to irreversible changes, up to total failure. One of solutions to improve resistance of structures after exposure to high temperatures may be the use of cement-based materials modified at the nanoscale. The influence of complex nanomodification with polycarboxylate ether superplasticizer, ultra- and nanofine mineral additives and volume fiber-reinforcement by thermal stability basalt fibers on the behavior of Portland cementing materials exposed to elevated temperatures was investigated. After 1 and 7 days of curing period the concrete specimens were exposed to elevated temperatures of 105, 200, 400 and 600 °C typical for fire environment. The mass loss, flexural and compressive strength, porosity, shrinkage, water adsorption of the specimens exposed to the elevated temperatures were determined. The nanomodified Portland cementing materials are characterized by high strength at early and later age, exhibit enhanced stability of mechanical properties when exposed to temperatures in a range of 105 to 600 °C. The compressive strength of nanomodified concrete after 1 and 7 days of hardening at normal conditions and exposed to temperatures from 400 °C is increased to 89.8 and 107.4 MPa respectively. The adding of thermal stability basalt fibers is provided additional strength increase of nanomodified fiber-reinforced concrete. The possibility of obtaining nanomodified rapid hardening Portland cementing materials with high thermal resistance is provided by water demand reducing, system particle packing optimization, increasing cement matrix density, stimulating nucleation processes in the intergranular space, acceleration of hydration process and pozzolanic reaction, three-dimensional reinforcement of structure. Lower water/cement ratio and higher degree of water binding into hydration products decreases the total porosity, shrinkage and the rate of shrinkage of the nanomodified fiber-reinforced concrete by providing the rigidity increasing of the solid matrix to resist deformation.

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