BEYOND THE COVER METER: AS-BUILT QUALITY CHECK OF A MULTI-STOREY CAR PARK

"Trace delivered a comprehensive understanding of the as-built structure quickly and without disruption to the project. Their methodology provided far greater coverage than originally specified, enabling us to avoid additional intrusive works and maintain programme. The clarity of their reporting and communication made it easy to act on the findings."

Operations Manager, Tier 1 Contractor

TRACE provides holistic solutions to each client’s project. One size does not fit all.

HIGHLIGHTS

• GPR cover readings confirmed against physically exposed reinforcement to within ±1mm accuracy

• Seven levels and seven structural element types investigated non-intrusively

• Reinforcement layout mapped and confirmed against design drawings across all nominated elements

• Construction variations identified and clearly communicated, giving the design team actionable information rather than ambiguity

  
  

BACKGROUND

TRACE was instructed to undertake a non-intrusive survey of a multi-storey car park – from ground to sixth, checking everything from slabs to core walls and comparing it to design drawings.

As part of the contract, the client was tasked with providing quality assurance on rebar cover in accordance with BS 1881: Part 204; a traditional approach to reinforcement verification.

The requirement of meeting the stated standard, in this case BS 1881-204, is something TRACE has encountered many times. TRACE is aware that clients are often contractually obliged to meet specified standards that may be outdated or misrepresented. TRACE proposed an alternative methodology: one that would meet the requirements of the client’s needs, conformed to the standard, but deliver it faster with more accuracy, and without any additional intrusion into the structure.

OBJECTIVES

To verify reinforcement layout, bar spacing, and concrete cover against the design drawings across all nominated structural elements, identifying cover, any construction variations or features.

Providing the design and engineering team with usable results to make structural assessments and inform decision making.

SOLUTIONS

TRACE selected specific GPR systems tailored to the various elements and access conditions across the site.

TRACE’s knowledge and experience in knowing which bit of kit to use in which situation also enabled for rapid data acquisition across large areas at a high resolution.

All data was processed and analysed off-site by TRACE, calibrated against physical measurements taken on site and included collected data against exposed reinforcement at breakout locations.

KEY FINDINGS

Slab, column, shear, core and party wall construction across all seven levels was found to be consistent with the design drawings. Reinforcement layout, cover depths, and additional bars around column heads and shear wall junctions were confirmed and mapped.

A small number of construction variations were noted and clearly communicated to the design team.

The findings established that concrete cover was sufficient for structural bonding but insufficient to protect the reinforcement from sulphate corrosion.

As a result of TRACE’s method and analysis, a protective epoxy floor coating was installed across each level to meet the specification requirements; an informed resolution made possible by the delivery of clear and usable data.

BENEFITS

Rather than discrete compliance checks, the design and engineering team received a dataset they could use directly: overlayed on CAD drawings for every floor, construction details confirmed and anomalies clearly identified.

The result moves beyond compliance checking to something more valuable: a complete, reliable picture of how the structure had been built.