Post-tensioning Systems

The development of the CARES certification scheme for the supply and installation of post-tensioning systems and its acceptance by the post-tensioning industry played a key part in the Highways Agency lifting its moratorium on grouted post-tensioned bridges in September 1996. CARES certification enables companies to comply with the major specifiers' quality requirements and enable them to bid for major post-tensioning contracts.

CARES is able to certificate PT contractors that install PT systems, producers of post-tensioning anchors, producers of grout, producers and stockists of prestressing strand and companies that undertake remedial grouting of post-tensioned tendons:

Approval for supply and installation of post-tensioning systems:

CARES Appendix PT 1. The Supply and Installation of Post-tensioning Systems in Concrete Structures, is for major structures with a high durability requirement such as The Concrete Society Technical Report 72 (TR72) type contracts and is for internal and external systems. Under this scheme an approved specialist contractor must supply and install, stress and grout (where required) the post-tensioning system.

CARES Appendix PT 2. The Supply and or Installation of Post-tensioning Systems in Concrete Structures (Excluding Highways Structures), is for general structures such as concrete frames, floor slabs and containment structures. This scheme allows an approved specialist producer to supply post-tensioning systems and another approved specialist to install, stress and grout (where required) the post-tensioning system.

CARES Appendix PT 4. The Supply and or Installation of Bar Post-tensioning Systems in Concrete Structures. Under this scheme a specialist approved contractor/subcontractor must supply, install and stress the post-tensioning system and an approved specialist contractor must pressure grout (where required) the system.

Remedial grouting

CARES Appendix PT 5. Void grouting of Post-tensioning Systems in Concrete Structures. This scheme requires an approved specialist to investigate ducts with voids;locate voids and ascertain the void characteristics and disposition and regrout the voids.

Training Requirements

CARES Appendix PT9. Training of PT operatives is a key part of the CARES Scheme. CARES requires PT companies to provide the training for PT supervisors and operatives and assess the effectiveness of the training. Once personnel have reached a satisfactory level, evidence of achievement is to be sent to CARES which then issues identity cards which must be worn on site. PT ID cards are issued to approved firms for their PT personnel. Approved firms should apply to CARES' office for the cards by submitting the application form (available from CARES office) together with a JPG photo and PT training record for the personnel required.

Approval of post-tensioning kits:

CARES Appendix PT 3. The Production and Supply of Prestressing Anchorages for Post-tensioning systems. This scheme requires an approved specialist producer to supply post-tensioning systems that comply with the performance requirements of ETAG013.

Post-tensioning System Components

The scheme includes the use of CARES approved feedstock rod for high tensile wire and strand, prestressing bar to BS448, wire and strand to BS5896 and pre-bagged grout to BS EN 445, 6 and 7:

PT 6. Feedstock rod for high tensile wire and strand.

PT 7. Prestressing bar which ensures high tensile steel prestressing bars comply with BS 4486.

PT 8. Wire and strand which ensures that high tensile prestressing wire and strand comply with BS5896.

PT 10. Prebagged grout complying with the requirements of BS EN 445, 446 and 447.

PT 11. Stocking and distribution of BS5896 products for the reinforcement of concrete.

PT 12. Wire and strand which ensures that high tensile prestressing wire and strand comply with AS/NZS4672.

Site Quality Requirements

The supplier must have a quality system that complies with CARES requirements and BS EN ISO 9001. The supplier's quality system must cover system production, key on-site and off-site activities as appropriate.

CARES Model Specification for Bonded and Unbonded Post-tensioned Concrete Floors

There are a number of documents that deal with various aspects of post-tensioning of flat slabs, however none comprehensively deals with the technical aspects of post-tensioning in building construction. Consequently CARES has produced a model specification as a guide to specification writers. This is freely available in PDF format from : Model specification for bonded and unbonded Post-tensioned Concrete Floors.

CARES Approved Post-tensioning Contractors

The CARES certification scheme allows two stage certification as a concession to companies which do not have suitable post-tensioning contracts which could be assessed for certification purposes. This facility avoids the need for companies to wait until they have secured a contract before applying for certification and reduces the potential for disparate and anti-competitive bidding.

Specification

The suggested wording for inclusion in a specification for a post-tensioning contractor is:

"Only firms that have achieved full certification under the CARES Certification Scheme for the Supply and Installation of Post-tensioning Systems in Concrete Structures shall be permitted to bid for or undertake contracts to supply and install post-tensioning systems.

However, in exceptional circumstances, where through the lack of a suitable contract, full certification cannot be obtained, a firm will be required to have obtained the letter of pre-certification, in accordance with Section 4, paragraph 4.7 a) of the CARES Certification Scheme."

Certification Documents

The scheme requirements are defined in the CARES' Post-tensioning Scheme Manual. Check the contents and status