1.Definition
Slow bonding prestressed steel strand is a new prestressing technology between bonded and unbonded prestressing, which eliminates the materials and equipment needed for the common bonded system to form holes and grouting, and simplifies the construction process. At the same time, with the late solidification and hardening of retarder, the prestressed tendons have a gripping effect, which effectively solves the fatigue problem of prestressed tendons and anchors in the unbonded prestressed system, and makes the application field of prestressed system more broad
2. Steel strand specifications:
1×7 diameter 15.2mm, 17.8mm gauge steel strand and 1×19 diameter 17.8mm, 21.8mm, 28.6mm gauge steel strand.
Steel strand strength: 1860MPa~2400MPa levels
3. Retarding adhesive
Retarding adhesive is the core of retarding prestressed steel strand, which has the characteristics of corrosion resistance and high strength after curing. The curing strength is greater than 50Mpa. The tensioning period has 60 days, 90 days, 120 days, 240 days and other specifications, and the curing period has 180 days, 270 days, 360 days, 720 days and other specifications. The tensioning period and curing period can be adjusted according to the engineering characteristics.
Under normal circumstances, each project corresponds to a retarding adhesive formula according to the duration and temperature characteristics of the area. The duration is different, the temperature is different in the region, and the formula is different.
During the tensioning period, the gently bonded prestressed steel strand can be freely tensioned and the friction coefficient is small. After the tensioning period, the friction coefficient increases and is not suitable for tensioning. Therefore, the gently bonded prestressed steel strand must be tensioned within the tensioning period.
4. outsourcing sheath
The outer sheath is corrosion resistant. It mainly plays the role of forming protection in the process of preparation, transportation and construction of gently bonded prestressed steel strand. The rib height of the outer sheath is the key parameter. The rib height of 15.2 slowly bonded prestressed steel strand shall not be less than 1.2mm, the rib height of 17.8 slowly bonded prestressed steel strand shall not be less than 1.5mm, and the rib height of 21.8 slowly bonded prestressed steel strand shall not be less than 1.8mm. Rib height directly affects the bonding and anchoring performance. The outer sheath should be ribbed in appearance, and the inner surface must also have ribbed grooves after it is peeled.
