Journal of Advanced Concrete Technology Vol. 15(2017) No. 7

The strain evolution and crack pattern of reinforced concrete attacked by accelerated corrosion have been studied us-ing strain gauges and the digital image correlation (DIC) technique. Results show that there was good consistency be-tween DIC and the classical strain gauges in the strain evolution of corroding reinforced concrete. Moreover, the strain field and crack behaviour of reinforced concrete could be tracked by DIC image pattern intuitively and its stress could also be calculated by DIC quantitatively. However, the micro-deformation of reinforced concrete could not be ob-tained by DIC because of its test accuracy. When reinforced concrete was attacked by accelerated corrosion, the ex-pansion stress was applied to the upper zone of reinforced bar, and the compressive stress was applied to its bottom zone. And the failure model of reinforced concrete was mainly in a brittle manner.

This paper presents the results of an experimental study conducted to evaluate the effect of curing conditions on the properties of normal and high strength concrete (NSC and HSC) with and without pre-wetted lightweight aggregates (LWAs). Cylinder specimens were drilled out from square concrete slabs subjected to four curing regimes (i.e. standard, water, natural and sealed curing) respectively, and then tested to obtain the compressive strength after 60 days. Three discs cut along the height direction of cylinder specimens (top, middle and bottom) were used to orderly measure the ultrasonic pulse velocity (UPV), open porosity, water absorption and splitting tensile strength. Afterwards, the comprehensive evaluation index, i.e. relative curing efficiency (RCE), was proposed based on the testing results above to quantitatively assess the effect of curing conditions on the physical properties of concrete. The experimental results indicat-ed that curing conditions significantly influence the strengths and durability-related properties of NSC and HSC. The linear correlation can be obtained between sorptivity and open porosity of concrete under various curing conditions. Furthermore, in terms of the RCE analysis, the durability-related properties are more sensitive to the curing conditions than strengths for NSC and HSC.

The aim of this study is to investigate the effect of sustained loads on the capacity of large-scale deep beams as a part of underground reinforced concrete, and to conduct parametric studies by numerical methods. The reduced shear ca-pacity under long-term sustained loads is investigated to be associated with the mode of failure, and the higher time-dependency is numerically suggested for deep-beams irrespective of their gain in the short-term static capacity. The main source of the possible decay of shear capacity is analyzed to originate from the creep damage of diagonal compression strut over the web concrete, and a simple expression of the strut-tie analogy is extended to the creep shear rupture of deep beams. Finally, it is concluded that the design safety factor of 1.2~1.3 for shear is appropriate for avoiding the risk of creep failure against long-term sustained loads of about 100 years.

This paper aims to upgrade the poro-mechanical scheme to simulate concrete volume change and damages which are strongly coupled with both alkali silica reaction (ASR) and freeze-thaw cycles (FTC). The interaction of two impacts are modeled by considering ASR gel intrusion and ice formation in micro pores and crack gaps, gel movement and un-frozen water suction into entrained air, gel and water migration through cracks as well as equilibrium and mass conservation of both concrete skeleton and mixed pore substances. For the assessment how the proposed numerical scheme works, sequence of events on ASR and FTC is focused on. It shows that ASR can reduce the FTC expansion for non-air-entrained (non-AE) case, but increase the frost damage for air-entrained (AE) concrete. Similarly, the FTC damaged concrete will have a smaller ASR expansion for non-AE case, but a greater expansion when AE admixture agent is dosed. The simulated behaviors also agree well with past experiments of combined ASR and FTC. Finally, the analysis on short-term strength shows that the ASR damaged concrete has a higher residual compressive strength and ductility rather than FTC damaged one due to viscous ASR gel which stand for broken symmetry of damage fields.