SME’s consulting engineers and certified technicians provide NDT services on a wide range of materials and projects to provide reliable information used for inspection, construction and repair. 

SME specializes in the restoration and rehabilitation of existing concrete and masonry structures, systems and components. A critical need in these endeavors is knowledge of present conditions and existing material properties. SME’s experts use a wide variety of destructive and nondestructive testing (NDT) equipment and processes to assist in economically and effectively evaluating these materials, their properties and the system’s internal components. Often, several techniques are used in combination to improve accuracy and determine information for structural restoration. SME’s NDT services include: 

Impulse Penetrating Radar (IPR)

The IPR testing uses advanced pulse radar technology similar to ground penetrating radar, but uses higher frequencies to achieve clearer data for processing.  It emits pulses into the scanned surface and records echoes from objects with contrasting dielectric constants, creating images from the echoes.  The IPR technology and procedures were developed specifically for the assessment of concrete to evaluate uniformity and soundness, and to identify internal distress planes or conditions.  Scanning is performed in lines and grids to locate internal items.  In addition, three-dimensional positioning of both magnetic and nonmagnetic embedded materials can be shown after processing scanning data.  The concrete is scanned up to 18” to 24” in depth.  The data obtained has limitations due to equipment limits and the uniformity of the materials being scanned.  The diameter of reinforcing bars cannot be determined by IPR scanning.  

Testing for:
Location & depth of embedded materials, both magnetic & nonmagnetic
Reinforcing steel splice lengths
Depth and extent of delaminations, cold joints, cracks and honeycombing
Thickness of scanned material
Location of energized electrical power cables
Bonding quality of internal interfaces
Presence of voids within sample and/or below slab
Determination of layered system profile
 

Ground Penetrating Radar (GPR)

The GPR testing system uses advanced pulse radar technology at a low frequency to provide deep penetration into scanned surfaces.  It is frequently used to locate buried utilities, underground storage tanks, and other buried items.  Other applications where the deeper reach of the lower frequency signal include locating voids under concrete slabs or under mat foundations.  Scanning is typically performed in lines but may also be performed in grids to provide mapped information relative to the object being scanned.  
Testing for:
Location and depth of embedded materials, both magnetic and nonmagnetic
Depth and extent of voids below concrete slabs
 

Impact Echo Velocity (IE)

The IE testing method is designed to determine the internal condition and thickness of concrete, masonry, stone and timber.  Only one surface needs to be accessible for the impact hammer head and receiver.  It uses an instrumented hammer or an impactor to generate compression waves which are sensed by an accelerometer receiver after being reflected from an internal discontinuity or the bottom surface of the tested member.  The compression waves are measured and the hammer input and receiver output are recorded.  This data is converted to frequency by the digital analyzer for calculations of the transfer and coherence functions, and the automatic power spectrum of the receiver.  These functions are used to determine the depth of reflectors with the spectral responses corresponding to bond conditions between placements.

Testing for:
Delaminations
Honeycombing
Thickness
Cracks parallel to the impacted surface
Voids within the tested material
Bonding quality of internal interfaces
 

Ultrasonic Pulse Velocity (UPV)

The UPV testing method is designed to identify and map flaws in concrete, masonry, stone and timber.  It uses the transmission of compression waves (“P” waves) through the tested material to evaluate the material’s physical properties.  Sources and receivers that are used to generate the signals are specialized piezoceramic transducers that have resonant frequencies ranging from 50 to 150 kHz, which is electrically pulsed to generate sound waves that travel through the material.  The compression wave velocity at internal flaws is slower than in sound material.  The transducers are placed at predetermined grid locations and use three modes of transmission, direct, semi-direct, and indirect, to perform the survey.  Combined with IE testing, estimates of compressive strength can also be determined. 

 Testing for:

  •  Delaminations
  • Honeycombing & voids
  • Cracks

Spectral Analysis of Surface Waves (SASW)

The SASW testing method uses the characteristics of ultrasonic surface waves (“S” waves) to identify material conditions and properties at various depths of the tested element, by determining variations in the material stiffness (shear wave velocity) versus depth.  The SASW procedure is applicable on concrete, asphalt, masonry, stone and timber.  It requires an accessible surface for two receivers spaced at a distance equal to 1.5 to 2 times the investigated depth.  The surface is struck with a hammer at a distance away from the receivers and the surface wave velocity is recorded by the spectral analyzer, showing the velocity versus depth.  It is most often used to determine the depth of cracks in concrete that are visible at the surface of the concrete. 

 Testing for:

  • Surface-opening crack depth measurement
  • Thickness
  • Evaluation of fire, freeze-thaw and alkali-silica damage in concrete
  • Evaluation of epoxy-injected cracks

 

Slab Impulse Response (SIR)

The SIR system is designed to identify subgrade voids below slabs-on-grade that are less than two-feet thick.  It uses a vibration transducer (geophone) and an instrumented hammer.  The vibration response of the tested surface to the impact is measured with the velocity geophone to produce the mobility plots of the tested surface.  Low and comparatively smooth mobility is an indicator of good subgrade support conditions.  Irregular and higher amplitude mobility indicates a less stiff slab-subgrade support system, and poor support conditions (voids).  
The SIR method cannot identify the actual depth or thickness of possible voids, but can determine the lateral extent of voids.  The SIR method can also be used on concrete structures to quickly locate areas with delaminations or voids in the concrete.  SIR can be performed on reinforced and non-reinforced concrete slabs as well as asphalt or asphalt overlays on slabs.  

Testing for:
Voids below slabs and tunnel linings (also below culvert inverts)
Soft, weak subgrade support
Delaminations
 

Windsor Probe

This testing is used to estimate the compressive strength of in-place, hardened concrete.  It is performed by penetrating the surface of the concrete with a hardened steel probe with a conical tip.  The probe is driven into the surface with a calibrated standard force from a powder-actuated driver device.  The concrete compressive strength is then estimated based on the depth of the probe penetration in accordance with ASTM C803, “Standard Test Method for Penetration Resistance of Hardened Concrete”.  At each test location, three probes are fired into the surface for measurement with a specially calibrated device.  This test is semi-destructive, as removing the probes from the concrete results in small pop-out holes.  
  
Testing for:
Compressive strength
 

Pin Penetrometer

This testing method is similar to the Windsor probe, but used primarily on mortars and grouts and uses a smaller penetrating probe and actuator.  

Testing for:
• Compressive strength
 

Half-Cell Potential

The half-cell potential test is an electrochemical testing method for indicating whether active corrosion may be occurring in reinforcing steel in concrete structures.  This test method uses a high-resistance voltmeter to measure the potential difference between the reinforcing steel and a copper-copper sulfate reference electrode in contact with the concrete surface.  The potential difference provides an indication of the presence or absence of active corrosion of the reinforcing steel.  This test method does not provide information regarding the actual rate of corrosion, but rather it indicates where active corrosion may be occurring with our without visual signs of distress.  Most often performed on concrete slabs, the testing is performed in a grid pattern to map areas of potential.  Access to the reinforcing steel must be made for the electrical connection, and the internal reinforcing must be fully connected throughout the test area.  Half-cell results less than -0.20 volts indicates a 10% probability of corrosion occurring.  Values between -0.20 and -0.35 volts indicates uncertain corrosion activity.  Potential values greater than -0.35 volts indicates a 90% probability of corrosion occurring.  

Testing for:
Internal corrosion to reinforcing steel
 

Infrared Thermography (IR)

This testing method detects infrared energy emitted from objects.  IR uses a special camera that is able to detect this spectrum of energy and convert it to a temperature differential and process a visual image of the temperature distribution.  IR is most widely used in building enclosure assessment to locate heat loss and air gaps, but is also being used for other structures to locate subsurface anomalies, such as delaminations.  IR can corroborate results from IPR and acoustical sounding procedures or be used where these methods are not as practical.  

Testing for:
Subsurface delaminations and cracking in concrete elements such as slabs, decks, pier columns, cap beams and walls
Locating heating / cooling grids in concrete floors
Verifying carbon fiber reinforcement adhesion
Locating leaks in piping within or below concrete slabs
 

Pachometer (R-Meter)

This testing method uses a hand-held probe to identify ferrous embedment (reinforcement) in concrete and masonry by sweeping the surface of the placement and using magnetic and electrical pulses.  The unit processes the returned signal to determine the depth to the surface of the reinforcement; however the size of the embedded reinforcement cannot be determined with this method.  The user can mark the reinforcement locations on the surface to determine spacing.  Typically only the first layer of embedded reinforcing steel can be detected.

Testing for:
Location of reinforcing steel in concrete
 

Schmidt Rebound Hammer

The Schmidt rebound hammer employs a hardened steel, spring-loaded hammer which impacts the concrete surface with a standard, calibrated force.  The placement hardness is determined by the rebound of the hammer which is correlated with known compressive strength (from test cylinders or core samples).  

Testing for: 
Concrete hardness and compressive strength

 

Bond Strength By Pull-Off Method

Tensile strength of concrete surfaces and the bond strength of repair and overlay materials can be determined using this pull-off test.  This method adheres a dolly to the concrete or coating material and applies a tensile force until failure.  This test is semi-destructive.  

Testing for: 
Bond strength of repair materials

 

Pull-Out Resistance Load Test

Adhesive and expansion anchors, lane ties and reinforcing dowel bars are required to resist a specified tension load based on the substrate quality, adhesion to substrate, installation procedures and the anchor’s mechanical properties.  A hydraulic jack system is used to test the embedded item to required test load or to failure.

Testing for: 
Pull-out resistance of embedded elements
 

Maturity Testing

The actual compressive strength of the concrete in the placement is frequently different than indicated with test cylinders because the placement is more massive and due to differences in environmental conditions, especially temperature.  The concrete maturity method uses the temperature of the concrete and the length of time the concrete has been in place to determine a time-temperature factor (TTF).  The strength of the concrete that has been properly placed, consolidated, and cured is a function of its age and temperature history.  This relationship is determined prior to construction by obtaining time, temperature and compressive strength data for a test batch of concrete for each mix design.  The temperature of the concrete in place is determined using radiofrequency identification (RFID) tags or tags with external probes.  The tags store data obtained at predetermined intervals to create a history of the temperature of the concrete.  

Maturity testing can be used to quickly and repeatedly determine the compressive strength of the in-place concrete.  Using maturity testing can potentially prevent delays to the project, and could improve the schedule of the project.  The maturity testing equipment can also monitor the curing temperatures of the concrete to verify the contractor has adequately protected the concrete from the hot or cold environmental conditions.

Testing for: 
Compressive strength
Curing temperature monitoring
 

Timber Resistograph

The Timber Resistograph testing method is based on the measurement of the drilling resistance.  A drilling needle (3mm diameter) is inserted into the timber under a constant drive force by the apparatus.  While drilling, the energy needed to penetrate the timber is measured relative to the needle depth in the timber.  The data is processed and plotted as the drilling progresses.  The test provides information about the internal condition and composition of the timber, such as decayed zones and splits, by showing variations in the drilling resistance versus the drilling depth.  A chart of drilling resistance versus depth is produced during the test.  

Testing for:
Internal deterioration
Depth of deterioration

 

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