RESUMO
The science of adding natural fibers to concrete results in an engineering material that is environmentally friendly and has the potential of promoting sustainable development in the construction industry. However, the challenge in adding natural fibers to concrete is that, they are hydrophilic in nature and this affects the bonding between the fibers and the concrete. To avert this problem three different fiber treatment methods namely, chemical, thermal and hybrid treatment methods were conducted on the sisal fibers to investigate the effect of the fiber treatment methods on the mechanical properties of sisal fiber reinforced concrete. The treated fibers were mixed with concrete with percentage fiber content of 0.5 %, 1.0 %, 1.5 % and 2 % and their compressive strength, tensile strength and flexural strength were tested. The experimental results showed that all the treatment methods considered led to an improvement in the tensile strength of the sisal fiber reinforced concrete. The compressive strength was also improved by the thermal and hybrid treatment methods, however, the chemical treatment method led to a reduction in the compressive strength. With regard to the flexural strength, all the treatment methods considered led to a reduction in the flexural strength when compared to the concrete without fibers.
RESUMO
In the present era of technology, the design of structural deep concrete beams is highly modernized through the use of computer-aided tools. However, theories for such design are the paramount aspects to be understood particularly when the beam has openings. To improve the mechanical properties of the deep beam with openings, recycled tyre steel fibres are required. To estimate the bond strength of the fibre-concrete interface, the concrete shrinkage strains for fibre lengths 30, 50 and 60 mm with a content of 0.5% were considered. To mitigate the conservativeness of some available shear models and improve the design of deep beams, the simplified shear equation model was developed. The model was established using a simplified compressive stress block, forces in steel reinforcement and shear stress at the fibre-concrete interface. The combined effect of opening height and length was also considered in the model. The results show that incorporating fibres in concrete increase the shear performance of deep concrete beams with openings due to high strains in the shear zone indicating high loads being transferred. For instance, beam BS2 had a strain of 0.0153 in the lower load path compared to 5.6 × 10-5 for beam BC2 There was a good correlation between measured and proposed shear capacities with t-test values of 0.46, 0.996 and 0.003 for beams without fibres, and with fibres and mesh respectively. Results also showed the model shear equation performed better compared to other equations with mean absolute error (MAE) and coefficient of variation (COV) of 9.3 and 18.9%, respectively for the control beams with openings. The model also showed a mean absolute error (MAE) and coefficient of variation (COV) of 11.6 and 7.4%, respectively for the beams with fibres. The COV and MAE for the proposed model were small than those in the database, therefore, the proposed model can provide the precise design of deep concrete beams with openings and fibres.
