SURFACE FREE ENERGY OF HIGH PERFORMANCE CONCRETE WITH ADDITION OF POLYPROPYLENE FIBERS

The study of the physical and mechanical properties of high performance concrete with polypropylene fiber was presented in the paper. Its basic characteristics and physical strength were defined, i.e.: absorbability, density, open porosity, compressive strength, splitting tensile strength, flexural tensile strength and modulus of elasticity. The use of polypropylene fibers results in different wetting and adhesion properties of high performance concrete. The wetting properties of the concretes were determined by measuring the contact angle of their surfaces using two measuring liquids: water and glycerin. Measurements were carried out three times: at the time of application of drops after 0, 5 and 40 minutes. On this basis, the total surface free energy (SFE) was determined. The SFE polar and dispersion components were defined using the Owens-Wendt method. By analyzing the examination results, it can be noticed that the contact angle values depend on the type of concrete. The results of contact angle measurements proved that all the glycerine contact angles (theta(g)) were higher than the water contact angles (theta(w)), and they decreased in the course of time. The highest contact angle was shown for concrete without fibers both at the beginning of the tests and after 40 minutes. The smallest contact angle with water was obtained by the concrete with the smallest addition of fibers. The biggest SFE difference was observed for the lowest fiber content of 0.5%. This is due to the physical characteristics of this concrete. The concrete with the 0.5% addition of fibers is characterized by the highest porosity, absorptivity, and the lowest density among the tested concretes. This indicates increased wettability and increased adhesion properties. Based on the SEM study, the microstructure and distribution of cracks and pores in high performance fiber reinforced concretes were shown.