The visual inspection of a building or structure is one of the first steps of an investigation, before which a desktop study to obtain drawings or any other information may be appropriate. A desktop study will enable the survey to be planned in advance, drawing prepared and the survey undertaken using a standard system for recording and measuring of the concrete defects.
Visual inspection is one of the most versatile and powerful tools to evaluate the condition of a concrete structure. Visual inspection can provide detailed information that may lead to positive identification of the cause of patent distress. Its effectiveness depends on the knowledge and experience of the inspection team and knowledge of structural design, concrete technology, and likely construction methods. This will help the findings obtained from the visual survey of a concrete structure to be fully appreciated, whether it is a floor slab or motorway bridge.
Other than obviously an experienced eye, a camera measuring instrument and note book are required to record defect type and size. Binoculars may be needed if close access cannot be afforded. Optical magnification may allow a more detailed view of local areas of distress. A very useful tool for crack inspection is a small hand-held magnifier with a built-in measuring scale.
A detailed survey should record every defect seen on the concrete surface. The aim of the visual survey is to determine how extensive the defects are and the likely cause of defects. A visual survey is normally only one part of a full concrete condition survey, where testing is used to confirm the cause of patent deterioration and investigate evidence for latent defects.
We have extensive knowledge of investigating, testing and surveying a wide range of reinforced concrete structures and buildings, including bridges, tunnels, coastal defences, historic buildings, multi-storey car parks, high-rise buildings, system built dwellings, swimming pools, industrial facilities and office buildings.
Understanding the design, material characteristics and deterioration processes affecting a particular reinforced concrete building or structure is essential in diagnosing the causation and extent of defects affecting a structure. This enables a durable and cost effective concrete repair to be instigated and decisions made with regard to life-costing. We provide in-depth reports detailing our findings and also provide advice on the most appropriate repair strategies and systems.
Undertaking a sufficient and appropriate concrete survey is a requirement of BS EN 1504, Products and systems for the protection and repair of concrete structures. We are associate members of the Concrete Repair Association.
Some of the testing and survey techniques we can employ in the assessment of existing concrete structures include:
- Measured defect survey which can be used to provide a Bill of quantities for repair in accordance with the CRA Standard Method of Measurement
- Delamination Survey to assess sub-surface cracking due to reinforcement corrosion
- Covermeter survey to assess concrete cover to reinforcement
- Carbonation testing to assess concrete alkalinity and likelihood of de-passivation of reinforcement
- Concrete sampling to determine presence of cast-in chlorides, chloride contamination and to determine chloride profile
- Concrete core sampling for inspection purposes or for compressive strength determination or petrographic examination
- Half-cell potential surveys
- Resistivity measurement
- Corrosion assessments, visual, measured and using surface analysis techniques
- Analysis of hardened concrete for chloride, sulphate and cement content
- Assessment of cement type and High Alumina Cement identification
- Use of Ferroscan and Proceq survey instruments to determine reinforcement provision or large scale assessment of concrete cover to reinforcement
- Assessment of fire and mechanical damage using petrographic examination
Determination of aggregate type, quality, alkali aggregate reaction (ASR) sulphate attack using petrographic examination
Concrete cover to the steel reinforcement in a structure or building ensures that the steel is maintained at a sufficient depth into the concrete to be well away from the effects of carbonation or chloride ingress.
Electromagnetic devices, also known as “Covermeters”, are used for the non-destructive measurement of steel reinforcement concrete cover in structures. The presence of reinforcement in concrete can be detected by the influence that the reinforcement has on the electromagnetic field induced by the Covermeter.
We also use the Profometer PM-650, an advanced Covermeter for the precise and non-destructive measurement of concrete cover and rebar diameters and the detection of rebar locations using the eddy current principle with pulse induction as the measuring method.
Covermeter surveys form part of most concrete condition surveys of buildings or structures. Covermeter surveys can also locate main and secondary reinforcement to determine bar sizes, bar spacing, to determine minimum cover and cover variability across an element.
The position of reinforcing steel and prestressing strands is sometimes also required to avoid them during core sampling or other tests which may be affected by their presence (concrete resistivity).
The use of covermeters is described in British Standard 1881: 204: 1988.
Delaminations are not usually visible on the concrete surface, but wet stains or nearby spalling concrete may indicate areas where delamination is likely. Sounding is a simple and effective method to identify and locate delamination below the concrete surface by striking the surface of a concrete section with a hammer or steel bar to detect planes of delamination. On horizontal surfaces, such as bridge or car park decks, a metal rod can be used to sound the surface or alternatively, various types of chain drag can be used. The chain drag technique is believed to be less accurate than simple hammer or rod soundings. ASTM D 4580 recommends the sounding procedures to detect delaminations in pavements and slabs.
A change in sound near the area of the delamination indicates the presence of delamination. The surface over a defective area emits a hollow or drum sound. A sound area that is not delaminated emits a ringing noise. Some force may be necessary to sound concrete for delamination where the cover to the steel is greater than about 40–50mm. Although a club hammer will locate laminations accurately at this depth, sounding concrete beyond 100mm can be ineffective in picking up deep laminations.
The survey may require the removal or coring though some of the delaminated sections to determine the depth of the delamination and the condition of the reinforcement steel.
Industrial Rope Access is a proven method of achieving safe access at height or in areas of difficult access. It was initially developed from techniques used in caving. Rope access is now used for various tasks ranging from high-rise window and facade cleaning and general maintenance to repair, testing and inspection work.
Our IRATA trained staff regularly use industrial rope access techniques to undertake the following works:
- Condition surveys and testing
- Structural surveys
- Defect inspections
- Make safe surveys
- Water ingress assessments
- Window inspections
- Concrete sampling
- Cladding inspection and sampling