Concrete strength assessment

An estimate of the in-situ strength of concrete may be required for several reasons:

  • when an assessment of the in-situ concrete strength is needed during construction
  • when an existing structure is to be modified or redesigned
  • to assess structural adequacy when doubt arises about the compressive strength in the structure due to defective workmanship or deterioration of concrete due to fire or other causes
  • to assess structural adequacy in the case of non-conformity of the compressive strength obtained from standard cube test specimens (or when cube results are not available)

The most contentious issues normally arise when cube results are not available or when they are below specified strength.

Two standards are key to this process:

BS EN 13791:2007, 'Assessment of in-situ compressive strength in structures and pre-cast concrete components'

BS 6089:2010, ‘Assessment of in-situ compressive strength in structures and precast concrete components. Complementary guidance to that given in BS EN 13791'

Between them they cover both direct (cores) and indirect (Rebound Hammer to measure surface hardness, Ultrasonic Pulse Velocity (UPV) of the concrete, Pull out strength) methods for assessing the in-situ compressive strength of concrete. They also provide guidance for establishing the relationships between test results from indirect test methods and the in-situ core strength, and hence the in-situ strength of the concrete in the structure.

Historically, Concrete Society Technical Report 11 (CSTR 11), Concrete core testing for strength, was used in the UK to interpret core strength results but it is no longer regarded as best practice and is superseded in part by BS EN 13791. In places CSTR 11 also conflicts with BS EN 13791. Consequently, aspects of the approach have been adopted within the overall system described in BS 6089.

Core samples tested in the laboratory are used to obtain a ‘Corrected insitu cube strength’

The ‘Corrected insitu cube strength’ is the measured core compressive strength expressed as the strength of an equivalent cube. It is intended to provide a measure of the actual strength of the concrete as it presently exists in the structure with specific allowance in calculation for the geometrical differences between cores and standard cubes. Correction is made for shape, the ratio of length to diameter of the specimen under test and the influence of any embedded reinforcing steel.

Sandberg can offer a full testing and consultancy service comprising

  • Initial review
  • Planning a suitable test programme
  • UKAS accredited core sampling and laboratory testing
  • Full interpretation of results

An important point to remember is that the compressive strength of cores and the in-situ strength will generally be less than that measured on standard test specimens taken from the same batch of concrete. This is due to a range of factors including the degree of compaction and curing in practical site conditions and dependent on the location in the member where in-situ strength is determined

Richard Rogerson

For further information contact: Richard Rogerson, Partner
Direct Tel: 020 7565 7080
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Corporate Profile
Quality of Service
Neil Sandberg
Simon Clarke
David Ellis
Tony Willmott
Richard Rogerson
Mike Eden
Julian French
Chris Morgan
Gavin Mayers
Gregory Moor
Jayne Fagan
Bob Easthope
Ian Hudson
Julie Dell
Simon Morris
Marion Ingle
Mariachiara Faliva
Roger Lucas
Tony Pitman
Daniel Kinnersley
Doug Hunt
Panos Sotiropoulos
Jim Carmichael
Yohann Guellil
Ewan Maclean
Alexander Hollyman
William Newby
Steve Pringle
Rom Gostomski
Kevin Green
Simeon Tulip
John Gallagher
Latest News
Memberships and Associations
Contact us
Building Inspector
NDT/Welding Inspector
Building Inspector / Rope Access
Pension scheme documents
Building Stone
Building Stone
CE Marking Stone
Stone Testing
UKAS Stone Testing
Cement Testing
Chemical Testing
Chloride Testing
Hardened Concrete Analysis
Infrared Spectroscopy
Lead in Paint
Mortar Testing
Rock Salt Testing
Screed Analysis
Water Testing
Construction Materials
Agglomerated stone
Aggregate Testing
Bricks, Blocks, Flags & Pavers
Concrete Testing
Fresh Concrete Testing
Hardened Concrete Testing
Screed Testing
Concrete Petrography
Mundic Concrete
SEM and X-ray
Sulphate Attack
Laboratory Services
Bolt Testing
Metallographic Analysis
Metals and Welding
On-site Material Identification
Scaffold Testing
Tensile Testing
UKAS Testing
Investigation & Inspection
Ground Penetrating Radar (GPR)
GPR Surveys
GPR Principles
Building Investigation
Chimney Flue Location
Concrete Imaging
Concrete Slab Surveys
Ferroscan or GPR
Abseil Inspection
Bedding Mortar
Bridge Inspection
Building Inspection
Cladding Inspection
Concrete Floors
Ferroscan Surveys
Fire Damaged Concrete
GFRC Inspection
HAC Concrete
NDT Weld Inspection
Paint Inspection
Precast Concrete Inspection
Leak Detection
Leak and Defect Location
Waterproof Membranes
Load Testing
Balcony and Barrier Testing
Car Park Barriers
Crowd Barriers
Cladding Systems
Glass Panels
Specialist Testing
Slip Resistance
Steelwork Services
Site Sampling
Safe Working Loads
Steelwork Fire Damage
Building Envelope
Building Fire Safety Audits
Building Regulations
Facades & Roofing
Our Track Record
Thermal Performance
Thermal Training
U-Values and Bridging
Alkali Aggregate Reactivity
Concrete Consultancy
Concrete Durability
Concrete Strength Assessment
Ancient and Modern
Historic Mortars
Expert Services
Expert Witness
Independent Advice
Geomaterials Services
Coastal Engineering
Polymer Consultancy
Odour Analysis
Polymers in Construction
Polymer Failure
Polymer Identification
Polymer Microscopy
Quality Assurance
Contract Administration
Materials and Workmanship
Specialist Services
Damage Assessment
Demolition and Refurbishment
Glass and Glazing
CE Marking
ISO 3834 Services
Metallurgical Failure
Steelwork Consultancy
Stone Consultancy
Building Stone (new projects)
Building Stone (existing structures)
Building Stone (suitability)
Sandberg Consultants