This paper is about application of recently proposed Performance Based Mixture Design (PBMD) for mix proportion design of high strength concrete (HSC) that can satisfy required performances. The PBMD method is a performance oriented concrete mix proportion design procedure easily applicable to any conditions and environments for a possible replacement to the current prescriptive design standards. Based on extensive experimental results obtained for various material and performance parameters of HSC, the application feasibility of the developed PBMD procedure for HSC has been verified. Also, the proposed PBMD procedure has been used to perform application examples to obtain desired target performances of HSC with optimum concrete mixture proportions using locally available materials, local environmental conditions, and available concrete production technologies. The validity and precision of HSC mix proportion design obtained using the PBMD method is verified with the experimental and ACI presented results to check the feasibility for actual design usage.
Reinforced concrete (RC) structures in marine environments are generally affected by harsh marine environmental actions, resulting in early performance degradation mainly due to chloride-induced deterioration. In such conditions, corrosion of rebar progresses rapidly, and also the cross-sectional area of rebar is reduced and consequently structural performance of RC structures will be degraded. In contrast, the surface of concrete structures is often covered with many marine sessile organisms under marine tidal and submerged conditions. These marine sessile organisms have been empirically known to enhance the durability of concrete though the effectiveness is not appropriately evaluated. This paper describes the long-term resistance of concrete with marine sessile organisms to chloride ion penetration in concrete. The effect and its sustainability of marine sessile organisms on chloride ion penetration in concrete were investigated through field exposure test and laboratory test. From the test results, the basal membrane, which is a matrix of marine sessile organisms, adheres to concrete strongly on a long-term basis though some gaps between concrete and the basal membrane can be observed. In addition, experimental results and simplified simulation clarified that the attachment of marine sessile organisms can enhance the long-term resistance of concrete to chloride ion penetration.
Corrosion of reinforcing steel bar is a critical issue in concrete structures. In response, a variety of techniques have been developed for early detection of corrosion phenomena, including nondestructive evaluation (NDE) techniques. Recently, we have reported that continuous acoustic emission (AE) monitoring is applicable to identify the onset of corrosion and the nucleation of corrosion-induced cracks due to the expansion of corrosion products. In order to clarify the kinematics of these AE activities in concrete, cyclic wet and dry tests on reinforced concrete beams were performed. The SiGMA (Simplified Green's functions for Moment tensor Analysis) procedure was applied to AE waveforms to locate micro-cracks and to determine kinematic information about crack types and orientations of corrosion-induced cracks. These results are visually confirmed through comparison with cracking mechanisms observed by a scanning electron micro-graph (SEM).
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