In a technique for widening prestressed concrete (PC) deck slabs, the connection between the old and new deck slabs is crossed by reinforcement and subjected to external prestressing force. A total of six PC deck slabs under a concentrated load were tested to evaluate the effect of the initial prestressing level, concrete strength of the new deck slab, and surface roughness of the interface. A three-dimensional FEM analysis was also conducted to complement the experimental results. The results showed that all PC deck slabs failed in a brittle manner when shear cracks developed at the interface between the old and new deck slabs. Thus, the effective area of the interface for the PC deck slabs under a concentrated load is proposed in this study. Furthermore, by using the value of the effective area instead of the total area of the interface, it has been confirmed that predicted shear capacities obtained from JSCE Specification, AASHTO, and fib Model Code 2010 provided a good lower limit for the experimental ultimate capacities.
This paper investigates the compressive strength development of blast furnace slag (BFS) blended mortar mixtures incorporating various mineral admixtures, namely BFS, limestone powder (LSP), and gypsum (CS). BFS replacement ratios of 15, 20, and 25 wt.%; LSP replacement ratios of 2, 3, 4, and 5 wt.%; and a CS replacement ratio of 2 wt.% are employed to improve the strength of BFS blended mortar mixtures. The hydration reaction and products resulting from the use of cement, BFS, and mineral admixtures are quantitatively examined with respect to the XRD/Rietveld method in order to investigate the relationship between the produced hydrates and the strength. Experimental investigation reveals that the mortar mixture with BFS 15 wt.%, LSP 4 wt.%, and CS 2 wt.% exhibits similar compressive strength to an ordinary Portland cement mortar mixture. In addition, the strength is found to be decreased as the BFS replacement ratio increases. At a BFS replacement ratio above 20 wt.%, LSP affects the strength improvement of BFS cement and CS affects the initial strength improvement of BFS cement.
A method for estimating the rebar force crossing a crack under model I loading in RC beams using the crack mouth opening displacement (CMOD) is proposed based on fracture mechanics accounting for bond slip at rebar-concrete interface. In the method, a CMOD is regarded as a consequence of the combined action of applied loads, rebar bridging forces and the bond slip. The CMOD due to these three contributors are estimated through an integral transformation based on fracture mechanics and a bond slip model. Since the CMOD due to bond slip is included, the tension stiffness effect is considered implicitly. Theoretically, the rebar force is estimated through the proposed method and the inverse analysis of COD profile using the same noisy synthetic COD profile. The smaller error of the proposed method in most cases demonstrates its reliability. The proposed method is further investigated through estimating the rebar force of an RC beam subjected to four-point bending load in laboratory, where acceptable accuracy is achieved. Conclusively, as the proposed method is dedicated to rebar force estimation of an RC member using CMOD, it provides a potential NDT&E approach for existing structures where the COD profile cannot be measured.
Railway track components often suffer from high aggressive loading and vibrating conditions of railway environment. In this study, the idea of improving structural material which can effectively absorb vibration energy is introduced to use for making railway sleeper. The environment-friendly concrete using crumb waste rubber tyres (425 and 75 Micron) as Micro-filler is presented. Six different types of concrete were designed and produced in accordance to British standard. Two experiments were conducted, which comprised of compressive strength and vibration testing, when the concrete has age of 7 and 28 days. The results illustrated that micro-crumb rubber concrete (CRC) can achieve the strength over 55 MPa (Complying with the requirement to design concrete sleeper) while maintaining the damping property at the excellent level. It was found that damping ratio of CRC is higher than plain concrete about 42%. These fundamental insights will encourage an innovative material application guideline for rail track engineers and managers in maintenance and construction of railway tracks and their components.
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