NDT Concrete Testing and Investigation
Non-destructive concrete testing: UPV, half-cell potential, carbonation, chloride and cover surveys to assess condition. London and the South East.
Assessing Concrete Condition Without Destructive Investigation
NDT (non-destructive testing) concrete investigation uses a range of instruments and techniques to assess the condition, integrity and durability of concrete structures without the need for coring, breaking out or other destructive methods. The results inform structural assessments, maintenance strategies, repair specifications and life-cycle planning.
Concrete deteriorates over time through carbonation, chloride ingress, corrosion of embedded reinforcement, cracking and loss of cover. NDT surveys allow engineers to quantify the extent and severity of deterioration across a structure — identifying high-risk zones, prioritising repairs and avoiding unnecessary intervention in areas that remain sound.
ACUO carries out NDT concrete testing across London and the South East for structural engineers, building surveyors, asset managers, local authorities and contractors. All surveys are carried out by Gary Stringer, a GPR NDT Civil Engineer with over 20 years of experience.
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NDT Concrete Testing Techniques
ACUO deploys the following NDT techniques, individually or in combination, depending on the condition assessment objectives.
UPV Surveys — Ultrasonic Pulse Velocity
Concrete integrityUltrasonic pulse velocity (UPV) testing measures the speed of an ultrasonic pulse through concrete. Low velocity readings indicate cracking, voids, delamination or poor-quality concrete. UPV surveys are used to map concrete quality across a structure, identify zones of deterioration and assess the uniformity of concrete placement.
UPV surveys- Mapping concrete quality and uniformity across slabs, walls and columns
- Detecting internal cracking, voids and delamination
- Assessing fire-damaged or chemically attacked concrete
- Monitoring concrete quality during construction
Half-Cell Potential Surveys — Corrosion Assessment
Reinforcement corrosionHalf-cell potential (HCP) surveys measure the electrochemical potential of embedded reinforcement to assess the probability of active corrosion. The survey produces a contour map of potential readings across the concrete surface, identifying zones where corrosion is active, probable or unlikely. HCP surveys are typically combined with cover surveys and carbonation or chloride testing to provide a complete corrosion risk assessment.
Corrosion surveys- Assessing corrosion risk in car parks, bridges and marine structures
- Identifying zones of active corrosion before repair works
- Informing cathodic protection design
- Condition assessment of post-tensioned and reinforced concrete structures
Carbonation Testing
Durability assessmentCarbonation is the process by which atmospheric CO₂ reacts with the alkaline cement paste in concrete, reducing the pH and destroying the passive layer that protects embedded reinforcement from corrosion. Carbonation depth is measured by applying a phenolphthalein indicator to freshly broken or drilled concrete surfaces. The depth of carbonation is compared with the cover depth to assess the risk of reinforcement corrosion.
Corrosion surveys- Assessing residual service life of concrete structures
- Informing repair and maintenance strategies
- Pre-purchase and condition surveys of older concrete buildings
- Combined with cover surveys to assess corrosion risk
Chloride Testing
Durability assessmentChloride ions — from de-icing salts, marine exposure or contaminated aggregates — penetrate concrete and initiate corrosion of embedded reinforcement at concentrations above a threshold level. Chloride content is determined by chemical analysis of concrete dust samples drilled at incremental depths. The chloride profile is used to assess the risk of corrosion initiation and to predict the remaining service life of the structure.
Corrosion surveys- Car parks exposed to de-icing salts
- Marine and coastal structures
- Bridges and highway structures
- Structures with a history of corrosion-related cracking or spalling
Rebar Detection and Cover Surveys
Reinforcement mappingCover surveys measure the depth of concrete cover over embedded reinforcement using GPR and electromagnetic covermeters. Insufficient cover is one of the primary causes of premature corrosion. Cover surveys are used to assess compliance with design requirements, identify zones of low cover and inform repair specifications. GPR surveys additionally locate rebar positions, spacing and estimated bar diameter.
Rebar detection- Cover compliance surveys on new and existing structures
- Identifying zones of low cover before repair works
- Reinforcement mapping before coring, drilling or cutting
- Combined with HCP and carbonation surveys for full corrosion risk assessment
Structural Investigation
Condition assessmentWhere NDT testing identifies significant deterioration, a broader structural investigation may be required to characterise the extent of damage, identify the cause and inform a repair or strengthening strategy. ACUO carries out structural investigations combining NDT survey data with visual inspection, crack mapping and material testing to produce a comprehensive condition assessment report.
Structural investigation- Post-damage assessment following fire, flood or impact
- Condition assessment of structures showing signs of distress
- Pre-purchase surveys of concrete structures
- Informing repair, refurbishment or demolition decisions
When is NDT Concrete Testing Required?
Visible cracking, spalling or staining
Surface cracking, rust staining, spalling concrete or delamination are signs of active deterioration. NDT testing quantifies the extent and identifies the cause.
Pre-purchase or pre-lease surveys
Buyers, lenders and tenants commission NDT surveys to understand the condition of concrete structures before committing to a transaction.
Planned refurbishment or change of use
Before structural alteration, extension or change of use, an NDT condition survey establishes the baseline condition and informs the structural design.
Asset management and maintenance planning
Periodic NDT surveys allow asset managers to track deterioration over time, prioritise maintenance spend and plan ahead for major repairs.
Insurance and liability investigations
Insurers, loss adjusters and solicitors commission NDT surveys to establish the condition of a structure at a point in time and to attribute cause of damage.
Post-construction quality assurance
NDT testing verifies concrete quality, cover depths and reinforcement placement on new structures before handover.
What You Receive
- Written condition assessment report with findings, interpretation and recommendations
- Contour maps and annotated drawings showing test results across the structure
- Photographic record of test locations, surface condition and any visible defects
- Raw data tables for all test readings
- Comparison against relevant standards and threshold values
- Recommendations for further investigation, repair or monitoring where appropriate
Reports issued within 24–48 hours of survey as standard.
Frequently Asked Questions
- What is the difference between NDT and destructive testing?
- Non-destructive testing (NDT) assesses the condition of a structure without causing damage. Destructive testing — such as coring, breaking out or load testing — physically damages the structure to obtain samples or data. NDT is preferred where the structure must remain in service, where access is limited, or where the cost and disruption of destructive testing is not justified. In practice, NDT and limited destructive testing are often combined: NDT surveys identify high-risk zones, and targeted destructive sampling is carried out only where needed.
- Can NDT testing be carried out while a building is occupied?
- Yes. Most NDT concrete testing techniques are non-invasive and generate minimal noise, dust or disruption. UPV testing, half-cell potential surveys and GPR cover surveys can all be carried out in occupied buildings. Carbonation and chloride testing require drilling small-diameter holes to obtain dust samples, which generates some dust and noise but is far less disruptive than coring or breaking out.
- How long does an NDT concrete survey take?
- Survey duration depends on the size of the structure, the number of techniques deployed and the level of detail required. A targeted survey of a specific element — a single slab or wall — may take 2–4 hours. A comprehensive condition survey of a multi-storey car park or large building may take one or more days. We will advise on expected duration when you enquire.
- Do you carry out the laboratory analysis for carbonation and chloride testing?
- Carbonation depth testing is carried out on site using a phenolphthalein indicator. Chloride content analysis requires laboratory testing of concrete dust samples. We collect the samples on site and arrange laboratory analysis through an accredited testing laboratory. Results are included in the survey report.
- What areas do you cover?
- We cover London, Kent, Surrey, Essex, Hertfordshire, Berkshire and the wider South East as standard. We also carry out surveys UK-wide for the right project. Call 07340 549892 to discuss your location.
UPV Surveys
Ultrasonic pulse velocity testing to assess concrete quality and detect cracking.
Learn moreCorrosion Surveys
Half-cell potential mapping and carbonation testing to assess reinforcement corrosion.
Learn moreStructural Investigation
Evidence-based defect surveys combining visual inspection and NDT.
Learn moreConstructionline Gold
Verified supply chain accreditation
SSIP Accredited
Health & safety pre-qualification
20+ Years Experience
Structural NDT specialists since 2003
Typical 24-Hour Response
Fast turnaround on quotes and bookings
Need a survey?
Call 07340 549892 or get a quote within 24 hours.