Crushed recycled aggregate contains particles with brittle defects such as cracks, pores, and voids. This study presents a method for improving the quality of recycled fine aggregate by selectively removing these defects. Fourteen recycled fine aggregates were manufactured by three types of processors including a jaw crusher, ball mill, and granulator. The influence of the recycled fine aggregate on the flowability and strength of the mortar was evaluated by multivariate analysis. The results showed that flowability was mainly affected by the filling fraction of the recycled fine aggregate and the content of components passing through a 0.075-mm sieve. Both the compressive and flexural strengths of the recycled mortars were unaffected by the filling fraction, but they were affected by the fraction of defects in the aggregate and its surface smoothness. In addition, the results clearly showed that polishing involved in ball mill or granulator processing is effective both for increasing the filling fraction of recycled fine aggregate and reducing the fraction of defects in the aggregate. Moreover, it was determined that the grain surface of grains was more irregular with the granulator than that with the ball mill, resulting in higher strength of the mortar subjected to the granulator. The fracture configuration resulting from flexural stress on the recycled fine aggregate in the mortar differed according to the type of aggregate. Furthermore, the calculated amounts of emitted CO2 and the compressive strength of the recycled mortar showed that the recycled fine aggregate should not be polished excessively.
Non-destructive evaluation of reinforced concrete structures is an increasingly important field in the construction and civil engineering community. A large number of pathologies affecting both the concrete and the reinforced bar inside the concrete are related to the presence of water and its spatial development. In this context, the quantification of both water content and bar diameter is an important part of the diagnosis of concrete. The aim of this paper is to present the results of two important studies undertaken in order to estimate the volumetric water content and bar diameter in concrete structures. The dielectric properties of concrete were studied as a function of volumetric water content. Experimental tests were carried out using an HP impedance analyzer. More than 800 samples of concrete were analyzed and a new relationship between the relative dielectric constant and volumetric water content was obtained. Further experimental tests were carried out by using GPR travel time tomography to study the effectiveness of the new relationship between the relative dielectric constant and volumetric water content. The study was subsequently focused on rebar sizes estimation inside concrete structures. Models were reproduced in the laboratory using a range of rebar sizes from 8 to 22 mm. These models, which represent rebars in a concrete medium, were used to detect rebar’s position and study the rebar sizes as a function of the ratio of the cross polarized to normal polarized electromagnetic wave amplitudes. GPR measurements, using the 1 GHz center frequency antenna, were performed on the model reproduced in the laboratory. The results of the GPR measurements were compared with the results of a simulation forward model, proposing an empirical relationship between rebar sizes and the ratio of the cross polarized to normal polarized electromagnetic wave amplitudes. Furthermore, several experimental tests were carried out by using a GPR to study the effectiveness of the proposed relationship.
This paper represents the behaviors of hybrid cathodic protection (hybrid CP) system in a reinforced concrete column specimen. Cathodic protection (CP) is widely used as a means of protecting corrosion for marine concrete structures such as harbor and offshore facilities. Specifically, hybrid CP, which is the combination both sacrificial anode cathodic protection (SACP) system and impressed current cathodic protection (ICCP) system, can be an optimum way to protect corrosion. Some complex concrete structures as well as harbor constructions are considered to be protected by both systems. Especially, it becomes more complicated to protect corrosion damage of concrete structures in the tidal and splash zones of marine environment. In case of Yellow Sea of the South Korea, the tidal zone reaches to 6-8m. On the condition that this system is well applied in the Yellow Sea, it is expected to show a good CP behavior to solve an underprotection problem, especially in tidal and splash zones. In this study, the hybrid system installed both the ICCP with Timesh anode and the SACP with zinc anode has been adopted to verify the current influence through laboratory experiment. CP potential and current have been investigated, in addition, 4-hour depolarization test has been involved to reveal the effectiveness of hybrid CP.
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