###### Abstract  
The prestressed concrete cylinder pipe (PCCP) suffers from cracks and degrades due to the prestress loss which is induced by wire breakage. Reinforcement with external prestressed strands is an option to return the deteriorating pipe's ability to withstand internal pressures. This reinforcement contributes to actively compensating for the prestress loss caused by broken wires at an economic price. The crack propagation in the core is constrained by the strands. Moreover, the high tensile strength of strands does not decrease with an increase in the bending angle. It is also unnecessary to dewater the pipes during construction. To evaluate the reinforcement effect, a prototype test of a PCCP was performed in an assembled apparatus. The apparatus was mainly constituted by two PCCPs whose internal diameter is 2000 mm. The status of each component of the pipe was measured by resistance strain gauges in three sections along the axial direction at inverted (360\({}^{\circ}\)), crown (180\({}^{\circ}\)), and spring-line (90\({}^{\circ}\), 270\({}^{\circ}\)) orientations. The maximum width of the cracks in the outer concrete core at spring-line reduced from 1.2 to 0.1 mm after strengthening. The cracks of the core concrete changed slightly when the internal water pressure increased to the design pressure of 0.9 MPa. The strengthened pipe was capable of sustaining the design internal water pressure and the water tightness property was in a good state. The strains of the steel strands were all below the tensile strain level. The reinforcement of the PCCP with external prestressed steel strands is able to meet the strengthen requirement of the test. p 1 2018 9 149 10.3390/app9010149 1  
PCCPs installed in China has accumulated to 18,000 km within the past two decades [3; 4] (by the end of 2015). A PCCP suffers from cracks and delamination of the mortar coating, corrosion and fractures of prestressing wires, longitudinal cracks in the concrete core and leakage of cylinders due to various factors such as overload, external corrosive environment, hydrogen embrittlement and water pressure fluctuation. PCCP failures may lead to a catastrophic loss without warning due to the pipes' dimension and high internal water pressure [5]. To return the deteriorating pipe's ability to withstand the internal pressures, a series of studies involving the replacement, internal reinforcement (steel cylinder relining, steel cylinder slip-lining, carbon fiber reinforced polymer (CFRP) reinforcement), external reinforcement (CFRP tendons, prestressed steel strands) and other methods were conducted by [PERSON] [6], [PERSON] [7], [PERSON] [8], [PERSON] [9], [PERSON] [10; 11], [PERSON] [12] and [PERSON] [13]. The significant advantage of the external reinforcement is that it is unnecessary to take the deteriorating pipes out of service. Moreover, it is able to actively compensate for the prestress loss caused by the broken prestressing wires [7]. The steel strand is able to fully exert the characteristics of the prestressed steel strand, such as a high tensile strength, and does not decrease with an increase in the bending angle. The well-known large-scale application of the external prestressed strands is the Great Man-Made River pipelines in Libya [14]. The GMR represents around 4000 km of pipes and most of them are 4.20 m internal diameter. In 1999, GMR faced some pipe bursts due to a highly corrosive environment. The authority immediately organized a way to proceed with repair of critical pipes with additional external post tensioning. The typical cycle for one pipe repair is 6 days (plus 2 days for a special pipe) in this project. Some operations can be fulfilled simultaneously to shorten the time cycle during the peak period. The significant advantage of this reinforcement is that it is unnecessary to take the deteriorating pipes out of service. This is significant for the water supply and other associated social issues. This reinforcement technology is a cost-effective way to ensure long-term service of the pipes with broken wires.