Experimental study on mechanical properties and impact on components for existing concrete of different service life
To study mechanical properties and impact on components for existing concrete of different service life, uniaxial compression tests for existing un-carbonated concrete serviced 10, 20, 40 years respectively were carried out, and 14 complete stress-strain curves were obtained. Test results showed that The mechanical properties on elastic modulus, ductility, peak strain, ultimate strain and transverse deformation of existing un-carbonated concrete decreased to different degrees, as the service year increased. Changing laws of these parameters and the influence on the bearing capacity and deformation capacity for components with the increase of concrete service life were generalized, which was expected to provide theoretical basis for strengthening and rebuilding design and evaluating the service life of existing concrete structures.
Effect of strength and age on the stress–strain curves of concrete specimens
Abstract Many researchers have rigorously studied the nonlinear behavior of the stress–strain relationship of concrete using mathematical curves. Currently, most empirical expressions for the stress–strain relationship, however, have been focused on hardened concrete and are unable to completely represent the behavior of concrete at an early age. A broad understanding of the behavior of concrete from early age to old age is important in evaluating the durability and service life of concrete structures. In this paper, the effect of five different strength levels and various ages from 12 h to 28 days on the compressive stress–strain curve was observed experimentally and analytically. Tests were carried out on ∅ 100×200 mm cylindrical specimens cured in a standard moist room at a temperature of 20±3 °C. An analytical expression of the stress–strain curve with strength and age was developed using regression analyses on experimental results. For verification of the proposed model equation, the equation was compared to the experimental data and existing model equations. The result shows that the proposed model equation is not only compatible with the experimental data but also describes satisfactorily the effect of strength and age on the stress–strain curve.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.