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.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.