Effect of shrinkage reducing admixture on time-dependent pre-stress losses in pre-tensioned beams

الملخص EN

Sixteen large scale pre-stressed concrete beams were tested under monotonic center point loading to determine the effect of shrinkage reducing admixture (SRA) on the time-dependent (TD) pre-stress losses in pre-tensioned beams.

The nominal dimensions of the beam were 4.0 m x 0.20 m x 0.25 m (13 ft.

1.5 in.

x 7.9 In.

x 10 in.).

The beams were reinforced with two straight, seven-wire, low relaxation strands of Grade 270.

The SRA was added at dosage rates of 0 %, 1 % and 2 %.

The beams were instrumented and tested at variable ages ranging from 3 to 945 days.

The flexural cracking load was measured and used to calculate the pre-stress force at the time of testing using principles of mechanics, and thus the pre-stress loss was evaluated at different ages.

The results showed that the addition of SRA significantly reduced the pre-stress loss in the beams, particularly when added at 2 %.

The SRA reduced the TD pre-stress losses by up to 41.9 % and 37.6 % at the ages of 735 and 945 days, respectively.