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A durability investigation has been conducted on the actual tunnels locating at Kunming Section of Chengkun railway line. Appearance of concrete deterioration was recorded by a Nikon camera. In some representative locations, concrete cores were taken from Shot-concrete or bulk concrete with a hand-held coring rig. The eroded residuals and water around the coring site were collected for further investigations in laboratory. XRD and EPMA analyses were conducted to identify the facts of destructive course. Site investigation shows the lining concrete is subjected to a serious deterioration including salt crystallisation, leaking, surface powdered and flaked, etc. Further investigations in laboratory corroborate the major deterioration, i.e. carbonisation, the chemical erosion and physical attack by sulphate ions, etc. Elements distributions declare that carbonisation has notable evolvement of concrete properties and leads to the movements of sulphur and sodium elements. The sulphur migrates from neutralised area to alkaline area while the sodium moves along the opposite direction. EPMA analysis identifies that the aggressive sulphur ions are sourced from the external environment. [ABSTRACT FROM AUTHOR]

An imitative RPC material was acquired, based on the idea of porosity reduction of set material by optimizing the granular size distribution of dry blend. Regularly the blend was composed of cement, fine crushed aggregate, sand and silica fume, and characterized by high silica fume content, a certain of rubber powder and very low water to binder ratio. The binder used was formatted by silica fume, ultra-pulverized fly ash, and ordinary Portland cement. Local natural medium crude sand in I / II grading zone and a crushed limestone fine aggregate with the size range from five to ten mm were also applied here. Rubber powder with fifty meshes was added to replace part of sand for agreeable flexibility. Properties of various reference concrete series were investigated by conducting multiple tests, including the permeability test, the mechanical strength test, the salt solution absorption test, the accelerated sulphate attack test, and etc. The imitative RPC material was proven to be environmental-friendly by the test results, and exhibits favorable mechanical strength, high impermeability, and excellent durability to sulphate attack. [ABSTRACT FROM AUTHOR]