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.
STRESS-STRAIN CHARACTERISTICS OF HIGH-STRENGTH CONCRETE
The stress-strain relationship and flexural stress distribution for ultimate strength design has been well established from previous work. Generally, normal-weight concretes with strengths ranging from 1,000 psi to 7,500 psi (6.9 MPa to 51.7 MPa) have been investigated. In the present study, flexural characteristics of high-strength concretes were obtained from a series of specimens tested at the Portland Cement Association laboratories. The test series included concrete strengths ranging from 6,500 psi to 14,850 psi (44.8 MPa to 102.4 MPa) for normal-weight concretes and from 3,560 psi to 12,490 psi (24.5 MPa to 86.1 MPa) for lightweight concretes. Concretes containing three different normal-weight aggregates and two different light- weight aggregates were included in the study. Stress-strain curves, flexural constants, and moduli of elasticity are reported for the complete range of concrete strengths. Results of this investigation have been combined with those of other investigators. The data are compared with the latest ACI Building Code revisions pertaining to flexural constants for strength design. /Author/