Reactive Powder Concrete Containing Basalt Fibers: Strength, Abrasion and Porosity.

The paper presents the test results of basalt fiber impact on a compressive and flexural strength, resistance to abrasion and porosity of Reactive Powder Concrete (RPC). The reasons for testing were interesting mechanical properties of basalt fibers, the significant tensile strength and flexural strength, and in particular the resistance to high temperatures, as well as a relatively small number of RPC tests performed with those fibers and different opinions regarding the impact of those fibers on concrete strength. The composition of the concrete mix was optimized to obtain the highest packing density of particles in the composite, based on the optimum particle size distribution curve acc. to Funk. Admixture of basalt fibers was used in quantity 2, 3, 6, 8 and 10 kg/m3, length 12 mm and diameter 18 µm. A low water-to-binder ratio, i.e., from 0.24, was obtained through application of a polycarboxylate-based superplasticizer. The introduction of up to 10 kg/m3 of basalt fibers to RPC mix was proved to be possible, while keeping the same w/c ratio equal to 0.24, with a slight loss of workability of the concrete mix as the content of fibers increased. It was found that the increase of the fiber content in RPC to 10 kg/m3, despite the w/c ratio was kept the same, caused reduction of the concrete compressive strength by 18.2%, 7.8% and 13.6%, after 2, 7, and 28 days respectively. Whereas, the flexural strength of RPC increased gradually (maximum by 15.9%), along with the fiber quantity increase up to 6 kg/m3, and then it reduced (maximum by 17.7%), as the fiber content in the concrete was further increased. The reduction of RPC compressive strength, along with the increase in basalt fibers content, leads to the increase of the total porosity, as well as the change in pore volume distribution. The reduction of RPC abrasion resistance was demonstrated along with the increase of basalt fibers content, which was explained by the compressive strength reduction of that concrete. A linear relation between the RPC abrasion resistance and the compressive strength involves a high determination coefficient equal to 0.97.

Mechanical Testing of Composite Steel and Reactive Powder Concrete Structural Element.

Reactive powder concrete (RPC), typically with higher compressive strength, is particularly attractive to structural engineers to apply them in infrastructures for enhancing their resistance under severe environments and loads. The main objective of the initial study presented in the paper was to investigate the behavior of two types of these new cementitious materials differing in the nature of microfibers. The RPC mixes were reinforced with steel and then with basalt microfibers. To evaluate the structural performance of developed unconventional materials, properties were investigated experimentally and compared with the control normal concrete mix. Mechanical tests indicated that dispersing fine fibers for making RPC, a mean compressive strength of 198.3 MPa and flexural strength 52.6 MPa or 23.2 MPa, respectively, were developed after 28 days of standard curing at ambient temperatures. In composite structures consisting of steel girders and a concrete slab, it is necessary to prevent the relative slip at the steel and concrete interface using shear connectors. The very high RPC strength enabled a material saving, weight-reduced application of precast construction, and particularly effective joint to steel beams. The investigation of such shear connection efficiency, in the case of the higher strength concrete deck, using standard push-out test specimens was executed. Finite element numerical models were developed. The outputs of the studies are presented in the paper.

Experimental Research on Concrete Beams Reinforced with High Ductility Steel Bars and Strengthened with a Reactive Powder Concrete Layer in the Compression Zone.

The article describes four-point bending tests of three reinforced concrete beams with identical cross-sections, spans, and high-ductility steel reinforcement systems. Two beams were strengthened in the compressed section with a thin layer of reactive powder concrete (RPC) bonded with evenly spaced stirrups. Their remaining sections, and the third reference beam, were made of ordinary concrete. Measurements of their deflections, strains and axis curvature; ultrasonic tests; and a photogrammetric analysis of the beams are the main results of the study. For one of the beams with the RPC, the load was increased in one stage. For the two remaining beams, the load was applied in four stages, increasing the maximum load from stage to stage in order to allow the analysis of the damage evolution before reaching the bending resistance. The most important effect observed was the stable behaviour of the strengthened beams in the post-critical state, as opposed to the reference beam, which had about two to three times less energy-absorbing capacity in this range. Moreover, thanks to the use of the RPC layer, the process of concrete cover delamination in the compression zone was significantly reduced, the high ductility of the rebars was fully utilized during the formation of plastic hinges, and the bending capacity was increased by approximately 12%.