Engineering plastic tubes are economic alternatives for the advanced composite tubing systems. The mechanical behavior of concrete-encased with engineering plastic tube (CFPT) is examined in the present study by testing short-stub CFPT columns under concentric loading. The test parameters include the plastic tube and coarse aggregate/cement ratio (a/c) ratio. Due to the low stiffness of plastic tubes, the cementitious systems have an important role to increase the stiffness of CFPT. For making concrete of consistent strength, a/c ratio is an important criterion since aggregate constitutes more than 70% of concrete. The proportion of this major component of concrete was altered in increments of 0.5 resulting in twelve mixes with a/c ratios from 3 to 8. Due to the limited test data, the mechanical performance of these structures continues to be pursued through experimental methods. The aim of the present study was to investigate experimentally the relationship between the strength of CFPT and a/c ratio which is also affected by variations in other constituent materials. The a/c ratio was the common variable in both control and CFPT specimens. The experimental results show that the ability of the engineering plastic tube in improving the load capacity of CFPT was considerably affected by the a/c ratio increment which yielded a beneficial effect on the tube confinement capacity
