The Shinmiya Bridge was completed in October 1988 in Ishikawa, Japan. This was the first prestressed concrete bridge in Japan, and the world, to utilize carbon-fiber-reinforced plastic (Carbon Fiber Composite Cable, CFCC) tendons in its main girders to counteract salt damage. To investigate and clarify the serviceability and durability of the main girders after a long period of service in a corrosive environment, two full-scale PC test girders were fabricated and placed next to the main girders in the same conditions at the time of the original construction from 1988. One of them was used for a destructive test in 1994. In this study, another test specimen exposed to a severe environment for 30 years was subjected to a destructive bending test and CFCCs taken out from the test girder were analyzed via mechanical and chemical tests. The suitability of the CFCC and durability of the main girder were confirmed. In addition, a numerical model was proposed to predict the behavior of a main PC girder using a finite element analysis program called DIANA. The influences of the input data from the experiment, the decrease in material properties, and the bond-slip model were studied in the simulation.
We investigated the microstructure and shrinkage behavior of autoclaved aerated concrete (AAC) from several manufacturers in Vietnam comparing with Japanese AAC. Three types of Vietnamese AAC and one type of Japanese AAC were used for powder X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, and shrinkage tests. The experimental results show that the main hydration products of AAC that used fly ash as silica materials is semicrystalline calcium silicate hydrate, while the ones of others are tobermorite; but the tobermorite crystals of AACs from some manufacturers in Vietnam are disordered structures and lack of interlocking among tobermorite crystals. The pore size distribution of all Vietnamese AAC are single peak, whereas Japanese AAC is bimodal. The pore distribution characteristics of AACs significantly influenced their shrinkage behavior and the shrinkage of Vietnamese AAC is higher than that of Japanese AAC at intermediate relative humidity (RH). The capillary tension is the principle shrinkage mechanism for AAC materials at high RH (above about 65%) to cause local minimum shrinkage of Japanese AAC at high RHs, while the change in surface free energy is dominant at low RH conditions.
In this paper, various engineering properties of both fresh and hardened concrete with various limestone and calcined clay contents are investigated. Two concrete grades were considered: 50 MPa or 30 MPa average 28 days compressive strength. A low grade calcined clay was used with about 50% amorphous phase.
A reduction in concrete workability was observed with the increase in General Purpose (GP) cement substitution. Superplasticiser was required to obtain a slump equivalent to that of reference GP cement concrete. With 15% GP cement replacement rate, the 28 days compressive strength achieved was superior to that of reference grade 50 MPa concrete, reaching 58 MPa. However, the average 28 days compressive strength reduced significantly with 30% and 45% GP cement replacement, reaching about 35 MPa. Considering concretes with similar 28-day compressive strength, results showed that the 7-day compressive strength was only marginally affected by the limestone and calcined clay substitu-tion. Mercury intrusion porosimetry results revealed that incorporating calcined clay and limestone led to significant refinement of the porosity: increase in the quantity of pores inferior to 0.01µm and reduction in the quantity of coarse pores (with size > 0.1 µm).
This study investigates structural behavior of shear connectors in glass fiber-reinforced polymer (GFRP)-concrete composite bridge deck slabs. Five kinds of push-out specimens with GFRP shear connectors were prepared and tested. The failure modes of the specimens were observed, and the load-slip curves were obtained. The effects of rib shapes, presence of holes, and existence of transverse rebars on failure mode, shear resistance, and ductility were investigated. Results showed that (1) the shear resistance and ductility of T-type rib shear connectors were greater than those of flat plate shear connectors. (2) Shear resistance and ductility were significantly improved by holes. (3) The transverse rebar has a significant influence on the failure mode. The concrete slabs in the specimens without a transverse rebar failed. Similarly, the GFRP shear connector in the specimens with a transverse rebar collapsed. (4) All of the specimens showed a similar failure mode caused by the shearing failure of the connectors in the root when the transverse rebar was applied. Furthermore, the shear resistance and ductility of GFRP shear connectors decreased as the number of transverse rebars increased. Empirical equations were proposed to predict the shear resistance and validated with the test data.
This work determines the replacement ratio of fly ash of 25% in SBR-modified cement mortars based on the past re-search, including SBR emulsion (SBR-E) and SBR powder (SBR-P). In addition to the Japanese guidelines for the repair material, the past researches related to polymer-modified cement mortars are also used to determine an appropriate mix proportion of the patch repair material for deteriorated RC building structures. According to the experimental re-sults in this work, it can be observed that increasing the S/W ratio of SBR is useful to improve the flexural bonding strength effectively; however, the compressive, flexural and tensile strength of cement mortars decreases. Besides of the mechanical strength, the workability and economy are considered to determine the S/W ratio of 10% of SBR-P for cement mortars with fly ash. Additionally, according to the regression results, its corresponding compressive, flexural, tensile and flexural bonding strengths are 36.5, 9.68, 3.35 and 2.8 MPa, respectively. For most of RC buildings with an age of over 30 years in Taiwan, since their average testing compressive strength is around 20 MPa, the suggested mix proportion of SBR-modified cement mortars with fly ash can provide enough performances for the patch repair.
This paper investigates the behaviour of concrete failing under high stress levels and subjected to different types of loading. The aim of this investigation is to clarify the development of linear and nonlinear creep strains and how they relate to material damage and eventual failure. This research is supported on the results of a new experimental programme performed on concrete cylinders tested in uniaxial compression under varying strain and stress rates. The results of this programme allow investigating the influence of the loading history on the material response in terms both of its strength and deformation capacity. On this basis, a failure criterion related to the inelastic strain capacity of concrete is defined. Such failure criterion, showing consistent agreement for all types of loading histories, allows calculating in a simple manner the reduction of the strength for a long-term loading situation and also its associated deformation capacity. On that basis, a comprehensive method for predicting failure of concrete under different long-term loading patterns is proposed and validated.
PC tendon is a vital component for strength of prestressed concrete structure. However, there is no warning sign when it is degraded or damaged, because of its invisibility from outside. Vibration-based method is one of the technique for damage detection due to simplicity. However, the extensively used method such as modal-based analysis is still insensitive to such damages. Recently, phase space-based analysis, a novel method for damage detection, was adopted in Civil engineering and a new index called Change of Phase Space Topology (CPST) has been developed. It is effective in identifying the damage existence regardless a known of damage location. Therefore, this paper adopted such technique to investigate damages of PC tendon. A pretension concrete girder with artificial PC tendon damages was used in experiment and it was excited by two vibration tests; free vibration and impact hammer test. The CPST values and the results from modal-based analysis were investigated and compared. The index shows increasing trend with increasing of damage levels. Moreover, it is more sensitive to the PC tendon damages than the results from modal-based analysis. This implies that CPST might be an effective index to detect the damages of PC tendon.
The demand for safe reuse of material from aged concrete structures is increasing. This report describes a technology for concrete demolition and surface concrete scraping for reuse of the material based on high voltage pulse discharge (HVPD) while immersed in water. The technological advantages of the new method compared with conventional methods are explained. The principle of concrete demolition using HVPD, experimental results on actual concrete structures (with and without steel reinforcement), and the influences of the immersion water are reported. A method of immersing a vertical surface (concrete wall) in water is described. Finally, the concept of mass reduction of radioactive concrete waste is discussed.