Investigation of mechanical properties of red pine needle fiber reinforced self-compacting ultra high performance concrete

With the increasing effects of global warming, the use of natural materials in engineering studies is increasing. In engineering construction, on the other hand, the use of natural fibers as concrete additives in order to reduce carbon emissions and protect the green environment is the focus of the studies. It is possible to increase ductility with the use of fiber in self-compacting ultra high performance concrete. The use of natural fibers provides an environmentally friendly approach. Therefore, in this study, the effect of red pine needles on the mechanical properties of self-compacting ultra high performance concrete was investigated. Pine needles were divided into 30, 40 and 50 mm length. The red pine needles were purified from organic matter with alkaline solution. It was added into the self-compacting ultra high performance concrete at the rates of 0.25%, 0.50%, 0.75% and 1.00% by volume. Slump-flow test, v-funnel test, compressive strength test, flexural strength test, freeze-thaw test, sulfate attack test were applied to examine the mechanical properties of the samples. In the sample with a length of 30 mm and a fiber content of 0.50%, the slump-flow test results decreased from 738 mm to 723 mm compared to the reference sample. According to the V-funnel test results, the closest results to the reference sample were obtained. The sample with a length of 30 mm and a fiber content of 0.50% provided a 15.6% increase in the 28-day compressive strength. On the other hand, the flexural strength increased from 8.60 MPa to 22.46 MPa according to the reference sample. In the sulfate attack test and freeze-thaw test, the closest results to the reference sample were obtained with the 30 mm length sample with 0.50% fiber content. With the results obtained, it was seen that the use of pine needles as a natural fiber in self-compacting concrete was appropriate.