Influence of Passive Reinforcement on Creep and Shrinkage of Concrete: Long-Term Observations

Abstract

Due to time-dependent concrete deformations, a gradual stress transfer occurs between concrete and steel in most concrete structures. In partially prestressed concrete members where restrained concrete deformation may cause significant tensile stresses to develop, this is of particular interest. In the 1970s, a long term research project was started to study this effect. Sixteen concrete prisms were manufactured in 1979 with dimensions of 140 x 150 x 4,000 mm. They differed in applied compressive stress level (σ = 0; 5; 10 or 15 N/mm 2) and passive reinforcement amount (ρ respectively 0; 1.5; 3 and 6%). Unbonded strands were used to apply, at 28 days, compressive force. The prisms were placed at 20 ± 1°C and 60 ± 3% R.H. in an air conditioned room. To determine stress redistribution due to passive reinforcement restraining effect on concrete shrinkage and creep deformation, measurement was carried out during more than 25 years. The creep and shrinkage model given in the CEB-FIP Mode Code 1990 forms the basis of an analysis, which will be compared with deformation measurement results given in this article.