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Non-Destructive Tests in Civil Engineering

An overview of the main types of Non-Destructive Testing (PND) to understand the importance of constant monitoring of civil infrastructure for risk management and safety.

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  • Non-Destructive Tests in Civil Engineering

Safety and monitoring of facilities

The security of infrastructure

1,500,000 km of roads of which 600,000 km in alarming conditions, 1.5 million bridges of which only 60,000 are monitored, 10,000 between bridges and concrete viaducts at risk of which 1400 without manager, 500 thousand km of water distribution network that in 2019 alone has sent lost 3.45 billion cubic meters, 34,652.8 km of gas pipelines, 1900 km of railway network that crosses hydrogeological risk areas for an area equal to 23700 square km. These are some of the numbers of the Italian public heritage and it is clear from the beginning that it is impossible to talk about civil infrastructure – both public and private – without simultaneously dealing with infrastructure security, culture of conservation and maintenance of existing works that suffer both the condition of obsolescence and the absence of a system of constant monitoring.

Structural monitoring

The theme of structural monitoring is closely connected with the risk management related to the entire life cycle of a civil infrastructure and has recently returned to the limelight of the news and political actions after the collapse of the Morandi Bridge in Genoa. Following this terrible incident, Legislative Decree No. 430/2019 entered into force on 21 November 2019, Morandi Decree, which established a National Computer Archive of Public Works and legislated a system of control of Italian public works throughout their life cycle.

The regulatory development regarding the safety of civil infrastructure has been the engine of a strong push to technological innovation and today the professionals in the sector have more and more advanced tools and technologies able to monitor the status of health of a work and that allow you to plan targeted maintenance and conservation of the same.

The dynamic tests

To date, in the field of non-destructive testing, dynamic testing is used to assess the behaviour of civil infrastructures as fully as possible, throughout the life cycle of the work.

The dynamic tests allow to evaluate and verify the design hypotheses, ensure during testing if the work meets the requirements of safety and reliability, identify in operation if there is structural damage that affects the static structure of a structure. The dynamic method allows to evaluate how a structure reacts to continuous dynamic actions such as loads, accelerations, speeds, vibrations and oscillations.

In essence, the dynamic tests give a general picture of the structural integrity of the work and provide an important parameter for evaluating its degradation and safety.

The Non-Destructive Controls

What are non-destructive tests and what are they for

In this regard, Non-Destructive Controls have a decisive role in structural diagnostics and monitoring of civil works. The Non-destructive Controls are non-invasive techniques and procedures, that is, such as not to compromise the functionality, used for the purpose of evaluating the physical conditions of a material and through which it is possible to detect any discontinuities in the object under assessment.

More generally and with respect to the subject we have discussed so far, Non Destructive Controls are used in the civil sector in order to assess integrity and reliability, improve the design process, identify possible maintenance interventions.

The non-destructive diagnostic techniques

The main non-destructive diagnostic techniques are:

  • Static monitoring and dynamic characterization of civil structures
  • Method Sonreb on concrete structures
  • Georadar study
  • Thermographic study
  • Test of Extraction Pull-out
  • Ultrasonic tomography
  • Ultrasonic welding
  • Radiographs
  • Magnetoscopy
  • Dye penetrant inspection
Non destructive Controls: Material Investigations

The Non-Destructive Tests are therefore all those examinations and reliefs that allow to ascertain, measure structural discontinuities and possible defects, without compromising the integrity of the work under examination. This type of investigation can be carried out on different materials, metallic and non-metallic. One of the most important aspects of structural monitoring, conservation and durability of civil structures, concerns concrete surveys.

The aging and degradation of concrete works is a real emergency in our country and for this reason, in the field of non-destructive tests, concrete tests have a primary role.

In the concrete construction the structural elements undergo the degradation of time and the tests on the material, for example through ultrasound tomography, allow you to inspect the internal structure, identify cavities, gaps, cracks, delaminations, filling inclusions and leaks.

The GPR methodology is also used in concrete structural surveys to monitor uniformity and assess the stability of concrete walls or floors. Another important parameter in the investigations concerning concrete is the assessment of its resistance. For this purpose, pull-out tests are carried out which consist in the extraction of a post plug inserted connected to an oleodynamic jack driven by a hydraulic pump.

Among the tests on masonry are also widely used sonic tests through the propagation of mechanical waves and the measurement of their speed return a qualitative data on the consistency of the masonry, the presence of any discontinuities such as voids or fractures.

Non-Destructive Controls are also used in the investigation of other materials such as wood and rock.

Rock tests are carried out to determine the characteristics of permeability, deformability, resistance and elasticity of the rock; through ultrasonic instruments, digital radiography or GPR methodology, it is possible to detect defects, cracks, cavities, voids and inclusions.

The detection of the state of health and conservation of wooden structures also has a specific field of non-destructive investigation: non-destructive tests on wood allow to measure the resistance, the deformability, bending and other mechanical characteristics of the object under analysis.

Non-destructive tests: load tests

The load test is a Non-Destructive Test that allows to evaluate the behavior of structural elements such as beams, slabs, roofs, wooden structures and roads, railways and viaducts, subjecting them to stresses with loads in operation.

The load test may be carried out in two modes:

  • Through a concentrated load applied by means of an oleodynamic system characterized by hydraulic jacks, extensions and transoms;
  • Through tanks filled with water.
Non-Destructive Controls: Foundation Poles

The control of the foundation poles is also a decisive aspect in the control of the behaviour of the load-bearing structural elements. Surveys of foundation piles may be carried out during the project phase on pilot piles, during testing and during operation.

A common methodology for assessing the quality of foundation poles is the cross-hole, a tomographic technique that uses ultrasound and measures the speed of wave propagation in the investigated object, returning a very accurate and detailed integrity check.

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Non-destructive testing: Georadar and drone surveys

Georadar methodology

Among the most advanced non-destructive investigation methodologies is the georadar methodology. The georadar is an instrument that allows, through the high frequency pulses of electromagnetic waves sent underground, to detect in a non-invasive way any anomalies and to identify structures that are in the subsoil.

For this reason, non-destructive tests using georadar have found application in several fields: in the structural field, for example, to have information on the thickness of the walls or the presence of reinforcements, but also in geology for profiling the ground level, in archaeology for mapping structures and detecting underground finds, in the military to locate tunnels, tunnels and bunkers.

Integrated georadar and drone system

The georadar is a tool that can also be applied on drones: surveys with georadar and drone allow to perform surveys on rough terrain, on ice, rock and fresh water, and efficiently solve all those critical situations of a topographical nature that could endanger the safety of operators. The different types of GPR antennas that can be mounted on the drone ensure efficient investigations and certain results acquired in total safety.

Monitoring and data acquisition in situ tests

In the field of diagnostics and in situ testing, a final aspect to consider is monitoring and data acquisition. The instrumentation currently on the market allows operators in the sector to measure parameters and physical quantities to be stored and monitored in the long or short term. The automation of this aspect of monitoring has huge advantages on the quality of surveys because it guarantees an effective response to the need for increasingly sophisticated and reliable measurements.

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