VSL structural diagnostics
and monitoring systems

Specialist services in structural investigation, assessment, testing and monitoring

  • Nhat Tan Bridge - Focus: Monitoring
    VSL’s monitoring equipment forms the ‘nervous system’ of Vietnam’s longest cable-stayed bridge.
    Vietnam - 2015 read more

    Nhat Tan Bridge - Focus: Monitoring

  • Riata Parking Garage
    Saving a structurally deficient parking structure by replacing the post-tensioning.
    USA - 2008 read more

    Riata Parking Garage

  • Rach Mieu Bridge - Focus: Monitoring
    VSL’ s contract for monitoring and the provision of technical assistance for a major cable-stayed bridge.
    Vietnam - 2007 read more

    Rach Mieu Bridge - Focus: Monitoring

  • Industrial Ring Road - Focus: Monitoring
    Load cells have been installed to monitor the load on a single strand within a stay cable.
    Thailand - 2005 read more

    Industrial Ring Road - Focus: Monitoring


Rehabilitation, strengthening and protection of concrete structures all require thorough investigations, clearly defined procedures, expert execution and systematic quality control. Through its wide range of construction and engineering services, VSL provides engineers, contractors, consultants and owners with the specialist advice they need. VSL’s experienced specialists can inspect and assess civil engineering works, buildings, bridges and industrial structures both to determine present condition and to initiate any measures found necessary for restoration to full service condition. In many cases, the team of VSL experts will also undertake the project management for the rehabilitation work, liaising with the contractor and/or owner.

VSL offers a wide range of specialist services in each of the main areas of structural investigation, repair, strengthening and protection for bridges, office buildings, residences, industrial buildings, factories, warehouses and historic structures.

VSL’s products and services

VSL provides services in structural diagnostics and the monitoring of concrete structures:

  • Inspection, assessment and diagnosis of structural deterioration
  • Assessment of the causes, risks and consequences involved
  • Use of state-of-the-art equipment and inspection techniques to detect defects before any significant damage can occur
  • Monitoring schemes, including definition and design, implementation, operation and interpretation.

Advantages of VSL’s services

  • The experience of an international specialist, to anticipate and analyse structural deterioration
  • State-of-the-art systems and technologies to remedy defects
  • Provision of integrated turnkey services worldwide within the VSL network

Contributing to sustainable solutions


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Precise assessment of critical potential damage at an early stage allows adequate preventive measures to be implemented before the damage become too costly to repair or before the state of the structure’s deterioration demands demolition.


Repairs and regular preventive actions serve to extend the life span of a structure, which leads to financial savings and reduced wastage of materials.

How it works

There are many inspection and assessment methods and these are usually divided into destructive and non-destructive. Within these two categories, VSL provides a full range of services:

Non-destructive methods

Visual inspection/ mapping
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Visual inspection provides information about the general condition of the structure and involves mapping of the observed concrete distress (eg cracking, spalling and delamination).

Visual inspection/mapping
Acoustic impact survey

Acoustic impact testing of a concrete structure involves mechanical sounding of accessible concrete surfaces with a hammer while listening for audible changes in tone. A metallic ring means that the concrete is sound while hollow ‘drummy’ areas are identified as unsound. Unsound areas are then typically marked on the exposed concrete surface with marking paint or a lumber crayon.

The locations that have been sounded are usually documented on condition survey drawings to assist in estimating construction repair costs.

Ferroscan pachometer survey
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Ferroscan pachometer surveys are used to determine the diameter, orientation, spacing and depth of embedded reinforcing bars. Reinforcing steel configurations detected during the survey can then be compared to the designed reinforcing details.

The technique also indicates ‘clear’ areas where concrete core samples can be taken without risking cutting into the steel reinforcement during the extraction process.

Ferroscan pachometer survey
Schmidt/rebound hammer test
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The Schimdt/rebound hammer test provides a quick assessment tool to ascertain the quality of the concrete in situ for correlation with a programme of taking samples. The test is performed in accordance with the ASTM C-805 standard method for rebound testing of concrete hardness. This non-destructive testing can be used to determine the consistency of the concrete throughout large concrete structures.

Schmidt/rebound hammer test
Ultrasound Pulse Velocity (UPV) testing
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Ultrasound Pulse Velocity (UPV)

Testing using the ASTM C-597 Ultrasonic Pulse Velocity (UPV) technique employs low-frequency mechanical energy for rapid evaluation of the relative quality and compressive strength of hardened concrete. The test method is based on the physical laws of elastic stress wave propagation in solids. A repeated pulse is generated and applied to one face of the test object by means of a transmitting piezoelectric transducer. The pulses pass through the concrete member and are detected at the opposite boundary by a receiving transducer. Relative quality and homogeneity of concrete is evaluated by statistical comparison of pulse velocities measured at grid points established on a concrete structure. Relatively low measured pulse velocities may indicate low concrete strength and reveal the presence of defects such as cracks, deficient concrete consolidation or voids.

Ground Penetrating Radar scanning

Ground Penetrating Radar (GPR) scanning is a quick, easy, safe and effective way to locate buried obstructions (eg rebar, tension cables, conduits and voids) in concrete structures prior to drilling, cutting or coring.

Impact echo test

The impact echo test involves applying a short-duration stress pulse to the concrete surface. The pulse from the impact is reflected back from defects and external boundaries to the receiver. It is an effective method for detecting large voids or delamination in plate-like structures where these defects are parallel to the test surface.

Half-cell potential survey
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This survey involves measuring the electrical potential of an embedded reinforcing bar relative to a reference half-cell placed on the concrete surface. The comparison is used to indicate the likelihood of corrosion activity.

Half Cell Potential Survey

Destructive methods

Destructive methods require the collection of samples, including concrete cores taken using wet rotary diamond core drilling techniques and concrete powder samples obtained by using rotary hammer drill powder extraction. Once samples have been extracted, the holes are patched with shrinkage-compensating repair mortar.

The following laboratory tests may then be conducted on the extracted samples:

Carbonation depth

Carbonation depths are determined using a modified phenolphthalein pH indicator solution sprayed onto freshly fractured concrete surfaces. Visual observation of the resultant sprayed surface colour tints indicates the existing concrete environment and current susceptibility to corrosion activity.

Chloride ion content of hardened concrete

Chemical extraction test results determine the chloride ion level within the concrete. The detected level is an indicator of the potential electrochemical corrosion process of the metal embedded within the concrete mass.

Compressive strength testing
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Core Sample Extraction

Test results provide strength values and are an indicator as to the relative quality of the concrete.

Structural appraisal and diagnosis

Structural remedial work demands thorough diagnosis of damage and deterioration as well as a full assessment of the causes, risks and consequences involved. VSL employs state-of-the-art equipment and special inspection techniques to detect any defects in concrete, reinforced concrete and prestressed concrete structures before any significant damage can occur. Close cooperation with material testing institutes and structural designers together with the use of the latest investigation techniques enables VSL to prepare precise and comprehensive reports, covering topics such as:

  • Inspection and surveillance of concrete structures
  • Condition evaluation of concrete structures
  • Root-cause analysis
  • Design of repair strategies
  • Order-of-magnitude costing

Plant Condition Management System™

Plant Condition Management System™

The Plant Condition Management System™ (PCMS®) is a multi-phase approach developed to address deteriorating civil infrastructure proactively before the occurrence of any safety-related incidents, diminished structural integrity or reduction in industrial capacity/production. An interdisciplinary team of VSL personnel uses the LQQ (Locate, Qualify and Quantify) method to conduct a condition survey to determine areas of concern, highlighting safety, structural and durability issues. VSL evaluates the cause of any concrete distress that is readily apparent, establishes repair priorities, provides conceptual recommendations and produces order-of-magnitude costs for the associated repairs.

Condition evaluation survey

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Condition evaluation, Sungei Damuan Bridge Brunei Darussalam, 2006)

A condition evaluation survey is a detailed assessment of a deteriorated concrete structure and is used by VSL to evaluate the causes of existing distress in reinforced concrete and to provide conceptual repair recommendations and an order-of-magnitude repair cost. The basic tools used in the survey include:

Non destructive methods:
  • Visual inspection/mapping
  • Acoustic impact survey
  • Ferroscan pachometer survey
  • Schmidt/rebound hammer test
  • Ultrasonic Pulse Velocity (UPV) testing
  • Ground Penetrating Radar (GPR) scanning
  • Impact echo test
  • Half-cell potential survey
Destructive methods:
  • Carbonation/pH test
  • Rapid chloride ion test
  • Compressive strength test

DeMon: VSL’s full-service monitoring package

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Monitoring of the cable-stayed Peldar Bridge, Columbia, 2002

DeMon is a combination of services provided by VSL to bring the data from the monitoring (instrumentation and inspection) of the structure to the desk of the owner and the designer in the simplest way. It consists of ‘back end’ and ‘front end’ modules. The back end, DeMon Site, is a software package installed on site to collect and filter the data from any type of sensor. The front end, DeMon Server, is a secure web server for processing the data and allowing authorised people to access their project data in real time from anywhere. Added services such as real-time alarms and back analysis can also be included. p>Reports can be generated by the DeMon system for distribution as electronic or printed documentation between all the interested parties.

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