The Fragmentation of the Tensioned Zone of the Strengthened Reinforced Concrete Beam with Carbon Fiber Composite

The article analyzes the intensification influence of tensioned concrete on carbon fiber composite and concrete joint in a strengthened beam cracking manner. The paper calculates enlarged concrete compressive tensioned strength according to the impregnation of epoxy resin. The article figures out the level of epoxy resin penetration and deals with a microscopic analysis of concrete and carbon fiber composite joint. The presented modified calculation method of the cracking moment evaluates the characteristics of impregnated modified tensioned concrete. Four beams were tested. Two reinforced concrete beams were additionally strengthened with an external carbon fiber composite layer and loaded till failure. In addition, two reinforced beams without external reinforcement were tested. The accomplished experimental research of cracking strengthened beams showed that the calculated cracking moments with evaluated tensioned concrete layer intensification were more similar than the results without evaluation. After failure of strengthened beams, accomplished microscopic analysisof debonded carbon fiber composite layer. A microscopic analysis of concrete and carbon fiber composite joint was performed applying electronic microscope DG-3x. The thickness of the composite layer and modified tensioned concrete layer was measured using Micro Measure V 1.0 computer program. The accomplished microscopic analysis approved theoretical assumptions about epoxy resin penetration and distribution between aggregates. The strengthening of the reinforced concrete beam with carbon fiber composite improved mechanical characteristics of the tensioned concrete layer near concrete and carbon fiber composite joint. During strengthening, epoxy resin penetrates into concrete and fills micro cracks and pores. Thus, epoxy resin provides additional connections with aggregates. The calculated modified concrete tensioned strength and modulus of elasticity was respectively 3,0 and 1,9 times higher than that of ordinary concrete. Changes in concrete strength at the tensioned layer have influence on cracking manner because the ultimate deformation of modified concrete increases. Experimentally determined what evolution of vertical crack starts above the modified tensioned concrete layer at the joint with carbon fiber composite. Peeling the carbon fiber composite layer when the ultimate load level is reached also evolves above the modified tensioned concrete layer. The remained hydrated cement on the surface of the peeled external composite layer proves that shear stresses in the joint of concrete and carbon fiber composite reduced a weaker tensioned layer of concrete.