كفاءة الاعتاب الخرسانية المسلحة الحاوية على SIFCON و المدعمة بـاستخدام CFRP

Flexural Behavior of Reinforced Concrete Beams Containing SIFCON and Strengthened by CFRP Sheets

Abatract

Mortar infiltrated within the fibers (SIFCON) is one of the new usages of concrete, which has become more important for the success of its use as a way to reinforce and repair old structures and modernize them, or as a result of increased loads resulting from design errors.
Hybrid concrete (Sifcon) is distinguished by its very ductile substance and excellent energy absorption capacity. Additionally, it has great impact resistance and explosive loading. The resulting hybrid concrete matrix functions as a composite member to distribute loads and absorb shocks on the structural member due to the high values of elasticity and potential energy of the steel fibers.
The present study aims to investigate experimentally the behaviors of reinforced concrete beams containing SIFCON and strengthened by Carbon Fiber Reinforced Polymer sheet (CFRP) at their bottom flexural faces. Fourteen specimens of reinforced concrete beams, divided into five groups were made and tested according to the percentage of steel fiber, thickness of SIFCON layer and CFRP sheets presence.
The results of the experimental program showed that the percentage of steel fiber has an impact on the compressive strength of SIFCON, as increasing the percentage of steel fiber from 0 % to 6% has increased the compressive strengths from (30 to 77%) in comparison with the control specimen at the age 28 days, respectively.
Moreover, it was proved that the percentage of steel fiber has a significant effect on the splitting tensile strength (fct). The splitting tensile strengths increased by approximately (160% to 417%) for the added steel fiber percentages from 0% to 6% relative to the reference specimen for age 28 days, respectively.
The experimental results also revealed that the percentage of steel fiber has an impact on the ultimate flexural force of SIFCON, for the increase of the percentage of steel fiber increased the ultimate flexural force by about (16 and 30%) for the added steel fiber percentage of 4 and 6% concerning the reference specimen of 2% for SIFCON specimens with a thickness of 30mm respectively. At the same time, the increase of the percentage of steel fiber increased the ultimate flexural force concerning the reference specimen of 2% for SIFCON specimens with a thickness of 20mm respectively.
It is worth mentioning that the ductility index is greatly affected by the percentage of added steel fibers and the thickness of the SIFCON layer in the presence of CFRP. And, in this regard, failure is controlled by debonding of the SIFCON layer, which makes it close to failure in the absence of CFRP. This indicates that the CFRP fixation length is insufficient to raise the ductility index. It has been demonstrated that adding more CFRP sheets increases stiffness. Similarly increasing the percentage of steel fibers increases the stiffness, and likewise, increasing the SIFCON layer thickness from 20 to 30 mm increases the stiffness by a small amount.