Evaluation of transfer length in pretensioned geopolymer concrete beams

[EN] The emergence of geopolymer concrete (GC) is making a positive contribution to environmental sustainability in construction. However, GC has not been extensively used in prestressed structures, so the applicability of design provisions remains unverified. In particular, the use of strands in GC structures requires the determination of their transfer lengths. This paper evaluates the transfer lengths of 12.7 and 15.2 mm Grade 270 (1860 MPa) steel strands in beams cast with three different grades (30, 50 and 70 MPa). Initial prestress of 0.65-0.75fpu was applied and gradually released. The transfer lengths were measured by applying the 95 % Average Maximum Strain Method. The strain field at one beam end was also obtained using Digital Image Correlation, which provided a new way to analyze the Hoyer effect. The tests showed that the transfer length was closely related to concrete compressive strength at release, prestress level and strand diameter. Moreover, the transfer length values in GC members were similar compared to ordinary concrete members for grades 50 and 70 MPa concrete and shorter for 30 MPa GC members. Prediction results from several international design codes and existing equations were obtained, which are close or conservative compared to the experimental results.