Recycled concrete research is one of the hot points at home and abroad currently. Whether the recycled concrete can be used in construction or not depends on its strength. Mixture ratio is an important factor deciding strength, while in which, the water cement ratio is one crucial parameter. So the calculation of unit water use in recycled concrete becomes an important research topic. The form of mixed coarse aggregate adding natural sand has already been studied by authors, the calculating formula for increasing water use has been put forward, but the calculation in other else case of aggregate combination form is not discussed. In this paper, the calculation for unit water use in recycled concrete in this case is discussed in detail, which can be used as a reference for designing the recycled concrete mixture ratio.
In some tunnels of railway lines located in water-rich region, due to the long-term water leakage and erosion, the foundation of railway lines showed large uneven settlement deformation, so the above concrete roadbed slabs also experienced uneven settlement accordingly. The smoothness of railway tracks diminished, and the speed of passing trains had to be limited to ensure safety. To restore the smoothness of the tracks, a dedicated polymer injection technology for quick uplift rehabilitation of uneven settlement concrete roadbed slabs was studied on site just within the specified daily skylight time (about 3 hours every day) of the railway lines. A hydrophobic polymer with low-viscosity, quick-setting and high-strength properties was used for injecting, filling and uplifting the concrete slabs in water-rich foundations. The high-precision electronic levels were adopted to monitor rising height of the tracks in real time. After rehabilitation, the filling quality of polymer injection under roadbed slabs was examined using Φ50 mm core samples and the strength of hardened polymer was verified by compressive strength test. Results indicated that the polymer could uplift the concrete roadbed slabs effectively and restore the smoothness of railway tracks accurately even in the water-rich environment. The research can provide some valuable references for quick rehabilitation of uneven settlement concrete roadbed slabs in water-rich tunnels.
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