Post-tensioning is the founding specialist activity of Grouting Services and is a method of reinforcing (strengthening) concrete or other materials with high-strength steel multi-strands or bars, typically referred to as tendons. We have been actively involved in multi-strand and bar stressing for over 30 years and operate the internationally accepted VSL and OVM multi-strand post-tensioning system.
The multi-strand system is characterized by standard tendon units using either 12.7mm (0.5") or 15.2mm (0.6") diameter strands, round corrugated ducts (steel or plastic) and a selection of anchorages. Bonded and unbonded tendons are available. Simultaneous stressing of all strands in a tendon is undertaken using a centre hole jack and secured using wedge grips. The free space inside the corrugated duct is pressure filled using a cementitous grout.
For post-tensioned slabs, the compression force is applied after pouring concrete. A rectangular galvanised duct is profiled using bar chairs and steel strand (12.7mm typically) pushed through the duct, and anchored at each end prior to pouring the concrete. Once the concrete has achieved the required strength, the tendons are stressed by hydraulic jacks. When the tendons have been extended to the design specifications, they are wedged in position to maintain tension after the jacks are removed. The duct is then grouted to provide bond between the pre-stressing steel and concrete, and provide corrosion protection. Unbonded systems are also available.
A range of bar diameters is available for the bar system that vary from 26mm to 75mm diameter and these can either be continuously or partially threaded. Stressing is undertaken using a centre hole jack, and a steel bearing plate and locking nut is used to anchor the end of the bar. Threaded couplings can be used to join the bars. Duct and grouting requirements follow those for multi-strand tendons.
Typical applications include office and apartment buildings, parking structures, slabs-on-ground, suspended slabs, bridges, piers & piles, sports stadiums, rock and soil anchors, and water-tanks. Grouting Services offers a full design and construct service for both suspended slabs and slabs on grade and in addition has significant local experience in bridges (longitudinal and transverse), reservoirs, sports stadium, and ground anchors.