~ Summary ~
Thermography Services UK conducted a detailed thermal imaging inspection of a major UK suspension bridge to assess structural integrity, identify delamination, and detect moisture ingress.
Using high-resolution infrared thermography aligned with ASTM D 4788-03, BS EN 13187:1999, and BRE 176, our survey provided critical insights into early-stage defects. The project helped inform targeted maintenance strategies to enhance longevity and safety.
Introduction
Thermography Services UK was commissioned to complete an advanced thermal imaging report from thermography level 1 inspection data collected by our client of a major suspension bridge, focusing on its under-deck, carriageways, and structural integrity. The report aimed to identify hidden defects such as delamination, spalling, and moisture ingress, which could compromise long-term performance and structural integrity.
Using high-resolution infrared thermography in accordance with ASTM D 4788-03, BS EN 13187:1999, and BRE 176, we were provided with detailed thermograms for analysis and to determine the temperature differentials across critical structural elements.
The survey was conducted in November, under controlled environmental conditions with an ambient air temperature of 8.6°C, ensuring accurate data collection.
Degradation, Spalling, Delamination, Moisture Ingress, Concrete Deterioration
Task & Objective
Thermographic inspections are a vital tool in assessing the structural integrity of bridge components. By detecting temperature variations on surfaces, these inspections can identify anomalies such as delaminations, voids, and moisture ingress, which may compromise the bridge’s future safety and longevity. Below is a summary of findings presented in our thermography level 3 report, organised by specific sections of the bridge:
West Bound Carriageway and Pedestrian Access
During the thermographic inspection of the westbound carriageway and adjacent pedestrian access, a notable circular thermal anomaly was detected, exhibiting a temperature differential (ΔT) of approximately 1.5 to 1.9°C compared to the surrounding concrete. Conducted at 10:00 AM in November, with an ambient temperature of 8.6°C, the conditions were conducive to identifying subsurface irregularities. Such thermal patterns may suggest potential delaminations or voids within the concrete structure. According to ASTM D4788-03, infrared thermography is an effective method for detecting delaminations in concrete bridge decks, as it identifies temperature variations caused by subsurface defects. ref source: cdn.standards.iteh.ai
The presence of this anomaly warrants further investigation to assess the structural integrity of the affected area and to determine the necessity of remedial actions.
Central Reservation
The central reservation was subjected to a comprehensive thermographic survey under the specified environmental conditions. The inspection did not reveal any significant thermal anomalies; the temperature distribution appeared uniform across the surveyed area. This uniformity suggests an absence of subsurface defects such as delaminations or voids within the central reservation. Maintaining consistent thermal profiles is indicative of structural soundness, aligning with the standards outlined in ASTM D4788-03 for bridge deck evaluations. Ref Source: cdn.standards.iteh.ai
Regular monitoring is recommended to ensure the continued integrity of the central reservation, especially considering environmental and load-induced stresses over time.
East Bound Carriageway and Pedestrian Access
The thermographic assessment of the eastbound carriageway and its pedestrian pathway identified several areas exhibiting minor thermal irregularities, with temperature differentials ranging between 0.5 to 1.0°C relative to adjacent regions. While these variations are less pronounced than those observed on the westbound side, they may still indicate early-stage subsurface anomalies, such as moisture ingress or initial delamination. Early detection of such issues is crucial, as it allows for proactive maintenance, potentially extending the lifespan of the infrastructure and ensuring user safety. Adherence to established thermographic inspection standards, such as those detailed in ASTM D4788-03, ensures accurate detection and interpretation of these anomalies. Ref cource: cdn.standards.iteh.ai
It is advisable to conduct targeted investigations in these areas to ascertain the underlying causes and to implement appropriate remedial measures if necessary.
How to Differentiate Delamination and Spalling
| Aspect | Delamination | Spalling |
|---|---|---|
| Location | Subsurface; below the surface layer | Surface-level; visible damage |
| Appearance | Surface may appear intact or slightly cracked | Visible flaking, cracking, or chipping |
| Detection | Requires specialised testing (e.g., thermography) | Easily visible during inspection |
| Cause | Internal stress or corrosion causing separation | Corrosion, freeze-thaw, or impact causing breakage |
| Impact | May lead to spalling if untreated | Directly compromises the surface and load capacity |
Why Differentiation Matters
Structural Integrity:
- Delamination indicates hidden damage that can grow and compromise the concrete over time.
- Spalling often exposes reinforcement, accelerating deterioration if left unaddressed.
Repair Strategies:
- Delamination: Requires epoxy injection, bonding agents, or replacement of affected layers.
- Spalling: Involves surface patching, reinforcement protection, and sometimes full-depth repairs if severe.
