Summary
The effect of grout properties on the structural behaviour of 18 post-tensioned prestressed concrete beams was investigated. The beams were 6 × 10 in. in cross-section and 10 ft long with an average concrete compressive strength of approximately 8,500 lb/in2. In each beam the prestressing cable consisted of eight 0·2 in. smooth high-tensile wires having a nominal eccentricity of 2 in. All the beams were identical but the properties of the grouts were varied over a wide range. The fluidity (immersion test) varied between 4 and 85 s, the bleeding (“tin-can” method) varied between 0 and 16·9%, the volume change (“tin-can” method) varied between 18 % sedimentation and 11·1 % expansion, and the cylinder compressive strength at 21 days varied between 2,100 and 4,300 lb/in2 Air-entraining agents, plasticizers and expanding agents were used in some of the grouts.
At 28 days the beams were tested to failure by two-point symmetrical loading and the following factors were determined: the ultimate strength; the ratio of steel stress at failure to its ultimate tensile strength (λ); the pattern of cracking (number, spacing and width of cracks).
Evaluation of the results clearly suggests that the structural behaviour of grouted post-tensioned prestressed concrete beams subjected to bending is not significantly affected by extreme variations in the properties of the injected grouts.
