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  Test methods for the quality control of fiber reinforced concrete in tunnels and under ground construction

  Fiber reinforced concrete (FRC) is widely used as temporary support and permanent lining in tunnels and other underground constructions as mining projects around the world. In segmental lining for tunnels, adding structural fibers improves the response of the structure during construction, particularly when subjected to the thrust of the jacks during the placement, and also reduces the global costs of the project by reducing the conventional passive reinforcement.In Mexico and Spain, FRC has been successfully used in landmark projects of civil and mining infrastructure. In Spain, for example, FRC was used in the segmental lining of the Metro Line 9 in Barcelona. In Mexico City, it is currently being applied in segmental linings of two tunnels of the deep drainage system (Tunel Emisor Oriente and Tunel Emisor Poniente) and in the extension works of the Metro Line 12, as well as in other underground and mining projects in different cities.Given the intrinsic scatter of the material and the several factors that influence in the distribution of the fibers in the concrete matrix, quality control in production and reception on site are paramount to the manufacturer and the contractor. When using FRC, specifications in project usually refer to the post-cracking behavior either in terms of absorbed energy or residual strengths.Current methods for assessing the post-cracking behavior of FRC include bending tests on small beams, toughness tests in panels and the double punch test. The most extended in tunneling is the bending test on notched beams. However, other tests are already being used as an alternative in tunnel projects for the systematic control due to the high scatter, time and material consumption of the former.The paper presents a review of the main testing methods used in the quality control of underground construction projects that use fibers as reinforcement. Namely, the ASTM C1609 beam test, the ASTM C1550 round panel test, the EN 14488-5 square panel test and the UNE 83515 double punch test or Barcelona test. Besides a thorough analysis of the test procedures, the characterization parameters used as a reference are revised and evaluated as well as their scatter and implications in the quality control. Fiber Reinforced Concrete, Quality Control, Beam Test, Round Panel Test, Square Panel Test, Barcelona Test.

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