Concrete testing & assessment

Concrete remains one of the world’s most trusted construction materials and is frequently designed into critical structures with very long functional life expected, up to 100 year design life not being uncommon.

ALS brings an unparalleled capability in assisting clients in the process of understanding the condition of concrete structures through our ability to combine:

• Engineering Expertise; with
• Market leading suite of destructive and non-destructive field and laboratory tests.

ALS provides a range of destructive and non-destructive tests to characterise critical concrete properties. These include:

Concrete Contamination Ingress Modelling

Concrete structures are particularly susceptible to carbonation, chloride and sulphate compounds which can affect the structural strength of concrete and lead to preferential corrosion attack of reinforcing bar and mesh. ALS laboratories provide a full suite of testing to analyse the nature and extension of contamination including.

• Phenolphthalein testing to assess change in alkalinity and the extent of carbonation and acidic ingress
• Metallographic sectioning to examine for structural changes
• Scanning Electron Microscope (SEM) for detailed microstructure and compositional analysis.

Concrete Compressive Strength Assessment including Schmidt Hammer Testing

The compressive strength of concrete as cured is critical to its structural integrity. ALS provides:

• Destructive Testing to AS 1012 involves extraction and crushing of a concrete core to determine compressive strength.
• Non-destructive testing using the Schmidt hammer technique may be undertaken when destructive testing is not practical.

Schmidt rebound hammer measures the “Q value’’ at the insitu concrete surface which is then converted via a calibration curve to determine the indicative concrete strength about the concrete surface.

Spectral Analysis of Surface Waves (SASW)

SASW is a multifaceted technology that is used to determine changes in material density such as:

• honeycombing
• cracking
• delamination
• voiding or
• localised weakening

of the concrete matrix. It is particularly useful across joints and cracks and can be used on multiple materials such as epoxy joints and grouted tendons.

The instrument comprises two transducers to create a multi frequency sound impulse is concrete by striking. This generates a series of surface waves (Raleigh waves) that are analysed to determine changes in material density within the concrete matrix (typically 50 to 500mm depth) based on the speed and spectral shape of waves.

Impact Echo Testing

Impact Echo testing is used to identify:

• Element thickness and the presence/depth of defects such as delamination, voiding and cracking.

The instrument introduces a sound impulse into the component which is analysed to determine the presence/depth of defects. This will have a range of approximately 500mm. Readings may be taken continuously to allow for the retrieval of data to comprehensively identify cavities and voids in the item under test.

Ground Penetrating Radar

Ground Penetrating Radar (GPR) is a highly adaptable method that can be used over large areas of concrete (or other matrix such as epoxy, soil, bitumen etc) to map the internal steel reinforcement, identify voiding and/or quantify the likelihood of corrosion to the internal steel reinforcement.

A concrete distress survey is typically undertaken over extended areas where there is suspected corrosion or other defects. GPR uses electromagnetic radiation to measure changes in the concrete dielectric to determine the location of reinforcing and corrosion. Results can be mapped in 2D or 3D and are often analysed in accordance with ASTM D 6087-08 to provide guidance on the quantification of the extent of corroded material.

Sonic Echo/Impulse Response (SEIR)

SEIR is used to understand the condition of in-situ piles, walls and deep foundations and can identify cracking, bulbing, necking, inclusions of overall length of the pile. Additional details pertaining to the quality of the placed concrete can also be determined via assessment of the overall speed of the sound through the material.

The method involves a wave being generated by an impulse hammer and travelling down the shaft or pile until a change in impedance is encountered.

Cross Hole Sonic Logging

Cross hole sonic logging is employed by ALS to assess the integrity of deep foundation elements such as concrete drilled shafts, auger cast piles, slurry walls or any mass concrete pour where QA is a priority.

It has been particularly refined for identifying the location of defects such as voiding, cracking and honeycombing in any material that can support transmission of ultrasonic waves above or below the waterline.

Ultrasonic Pulse Velocity (UPV) survey

UPV testing provides crucial information about the integrity of the concrete structure and is typically used to identify the presence of voiding, cracking, honeycombing and sound concrete. It is particularly useful for rapid testing of concrete ‘insitu’ provided there is suitable access for the source and receiver across the sample area being tested.

The method involves an ultrasonic pulse being generated at one side of the test piece. Pulse velocity is compared across all points tested with defective areas typically exhibiting a lower pulse velocity.