Examples of NDT Use in Building Diagnostics

Overview

Diagnosis of building deterioration is not a simple task and often entails iterative investigations and therefore costs. However, investigations can be more efficient by applying basic Non-Destructive Test (NDT) methods.

The main benefits of NDT include greater coverage in shorter times, and avoidance of disruption (i.e. noise, cost, time, and restoration work) when assessing concealed elements.

Note that the use of any NDT method should also be balanced with wet technology – that is, the consultant’s eyes and brain working together! This article introduces three case examples to illustrate.

1) Service Riser Leaks – Mould, Magnesite and Spalling

A ground floor Unit developed cupping to the extent that some internal doors could not open and a trip-hazard had developed. Additionally, mould and high humidity made the Unit uninhabitable.

Our investigations combined visual assessment with destructive and NDT methods. The initial visual assessment confirmed corroding steel door jambs, severe rot and mould in particleboard substrate, and a magnesite topping.

We used a Protimeter MMS2 moisture meter for RH and surface temperatures to assess whether there was a dewpoint issue or any cold bridge, rising damp or cavity-related issues. We subsequently coordinated sampling of the magnesite for asbestos testing, and slab cores for chloride and cement contents in order to assess the future corrosion risk.

NDT methods included application of basic GPR to establish the slab thickness and reinforcement size, position, and spacing.

The findings concluded that the reinforcement was generally at low risk of corrosion but was also of an unusual and unexpected detail (i.e. located low in the slab, irregular and wide spacing), except for the higher-risk area at the cantilever of the balcony, and immediately adjacent to the wet areas.

The underlying source of moisture was found to be a series of separate leaks in the sewage service riser from a combination of failed joints and age, compounded by no “fail-safe” detailing at the base of the riser.

Ultimately, substantial remedial works recommended were: 

• Partial upgrade of the sewer riser, 

• Re-configuration of the base of the riser and fail-safe flashing/tanking details, 

• Removal of magnesite from living areas and bedroom 1, 

• Refurbish wet areas, 

• Replace severely corroded door jambs, 

• Replace kitchen, including upgrade to ventilate externally, 

• Spalling repairs, including use of sacrificial anodes, and

• Mould decontamination.

2) Mould and Ventilation – 42 Lot Residential

This Scheme required diagnostic work and strategic advice to address recurring complaints of mould affecting the interior of several Units. The Scheme’s architectural layout meant that natural ventilation could not be achieved.

Investigations carried out were a combination of visual, NDT and direct break out. The visual assessment confirmed areas of high risk and guided subsequent steps. The NDT carried out was a combination of thermal imaging using a FLIR camera to identify elements suspected to be subject to cold bridging, and application of the Protimeter MMS 2 to assess dewpoint conditions.

In some locations, cold bridging exists above sliding door openings due to the structural concrete beams spanning the opening also eliminating any cavity between interior and exterior surfaces.

We also carried out flowmeter assessment of the mechanical ventilation system. This indicated deficiencies in the concealed ducting, since the extraction rates in some Units were much higher that the exhaust rate at the external discharge point.

Subsequently, we carried out destructive investigations including removal of fans but also breaking into the ceiling space to confirm shortcomings in the ducting. We found variance of duct quality throughout this Scheme, which included instances of detachment of ducting, failure of duct joints, and some ducts terminated in ceiling voids with no external vent discharge point.

The remedial scope of work recommended included: 

• Ducting repairs and continuation to discharge vents, 

• Fan upgrades including run-on timers and flow balancing, 

• Where feasible, adding supplementary exhausts, 

• Staged upgrading of flashing details and cleaning out of cavities, and 

• Mould decontamination.

3) NDT for Reuse of Roof Area – 10-storey CBD

This commercial Client needed to assess the structural adequacy of the 40-year-old building due to lease obligations, which anticipated a specific use of the rooftop area.

The rooftop area was to be changed from maintenance loads to a full live load and public use area. This resulted in an increased load of some 4-5 times. Since structural drawings had been lost, investigations would be required to confirm details. Additionally, the building was occupied, meaning destructive investigations would be prohibitive due to disruption, access and make-good costs.

The NDT methods applied included a foundation audit using ground penetrating radar (GPR) and Pile Integrity Testing (PIT) to identify the approximate size and detail of some basement piles, plus GPR and Ultrasonic Pulse Velocity (UPV) to the roof slab and beams and selected columns below.

By applying the above NDT methods, we were able to carry out site investigations in 1 working day compared to several days of destructive investigations.

Ultimately our recommendations included: 

• Providing supplementary structural framing at roof level, 

• Upgrade to numerous columns throughout the building, and 

• Further investigations to verify connection of beams to central cores.

Summary

Proper diagnosis of building deterioration and structural detailing can be made more efficient by appropriate use of NDT methods.