The current study presents research into the effect of graphene oxide (GO) with a carbon to oxygen ratio of 4:1 on the fluidity, hydration, microstructure, mechanical and physical properties of Portland cement pastes and mortars. The amounts of GO investigated were 0.02%, 0.04%, and 0.06% by weight of cement, while for mortars, an extra composition with 0.1% was also prepared. According to the results, the fluidity of cement paste and mortar increased and the hydration process was slightly retarded with the addition of GO. Despite this, improvements in compressive and flexural strength were established in the mortars containing GO. The maximum effects (~22% and ~6%, respectively) were obtained with the addition of 0.06% GO. The calculation of estimated strength proportional to samples of equal density showed that for mortars cured for 7 days the gain in strength was directly related to the gain in density. For mortar samples cured for 28 days, the estimated strength was found to be significantly higher than that of the reference sample, indicating that besides density there are other factors determining the improvement in strength of mortars modified with GO. The possible structure strengthening mechanisms are discussed.

The use of steel fiber reinforced concrete (SFRC) in structures with high physical-mechanical characteristics allows engineers to reduce the weight and costs of the structures, to simplify the technology of their production, to reduce or completely eliminate the manual labor needed for reinforcement, at the same time increasing reliability and durability. Commonly accepted technology is exploiting randomly distributed in the concrete volume fibers with random each fiber orientation. In structural members subjected to bending, major loads are bearing fibers located close to outer member surfaces. The majority of fibers are slightly loaded. The aim of the present research is to create an SFRC construction with non-homogeneously distributed fibers. We prepared layered SFRC prismatic specimens. Each layer had different amount of short fibers. Specimens were tested by four point bending till the rupture. Material fracture process was modelled based on the single fiber pull-out test results. Modelling results were compared with the experimental curves for beams. Predictions generated by the model were validated by 4PBT of 100 × 100 × 400 mm prisms. Investigation had shown higher load-bearing capacity of layered concrete plates comparing with plate having homogeneously distributed the same amount of fibers. This mechanism is strongly dependent on fiber concentration. A high amount of fibers is leading to new failure mechanisms—pull-out of FRC blocks and decrease of load-bearing capacity. Fracture surface analysis was realized for broken prisms with the goal to analyze fracture process and to improve accuracy of the elaborated model. The general conclusion with regard to modelling results is that the agreement with experimental data is good, numeric modelling results successfully align with the experimental data. Modelling has indicated the existence of additional failure processes besides simple fiber pull-out, which could be expected when fiber concentration exceeds the critical value.