Non-Destructive Testing on Concrete
Non-destructive tests are the first investigation method to check the actual conditions of a structure, whether under construction or existing. As also indicated by the new anti-seismic legislation, the use of non-destructive investigation methods dramatically reduces the number of specimens needed for laboratory analysis, resulting in benefits not only in terms of the time needed to complete the investigation, but also from an economic viewpoint.

Rebound Hammer Sclerometer Tests
The mechanical sclerometer rebound hammer - the "original Schmidt hammer" invented by Ernst Schmidt in the early 1960s and produced by the Swiss company Proceq - was one of the first instruments designed for concrete testing and is still recognised as the reference standard for fast diagnosis of a reinforced concrete structure. The rebound value (R) measured on site with the rebound hammer sclerometer test is closely related to the compressive strength value of the concrete obtained from breaking tests on specimens in the laboratory. The digital rebound hammer sclerometer represented the next step, with the introduction of the digital readout, data storage and statistical calculation, facilitating data reporting by the specialist professional. More than 50 years after the debut of the "original Schmidt hammer", it was the same Swiss company, Proceq that took another definitive step forward with the new integrated digital Proceq SilverSchmidt rebound hammer sclerometer. Its revolutionary measuring system, greater precision in the result and the practical, intuitive user interface make it an instrument that truly stands out. Thanks to its measuring range extended from 10 to 100 N/mm2, this revolutionary instrument can work on both standard and HPC concrete, providing direct, immediate results, regardless of the testing angle.

Locating Reinforcement
The mapping of the reinforcing bars is crucial not only for monitoring the condition of the structure, but also for the subsequent rebound hammer test sclerometric and ultrasonic investigations. As established by legislation, in fact, the rebound hammer sclerometric test is not valid if carried out near reinforcing bars, whose presence has a significant effect, distorting the compressive strength value of the concrete. Modern cover meters rebar locators use the induced current (Eddy current) technique, i.e. they measure the variation of the electromagnetic field induced by the presence of the reinforcing bar in articles made using reinforced concrete. By analysing the intensity of the signal, it is possible to reach a very precise definition of the thickness of the concrete cover and calculate with a good approximation also of the diameter of the rebar, without drilling or demolishing.

Ultrasonic Investigations
The propagation speed of the ultrasonic pulse in a medium depends on its density and its elastic properties, which in turn are closely linked to the quality and strength of the material itself. Ultrasonic investigations therefore make it possible to determine the characteristics of the concrete: uniformity of the material, presence of cavities or honeycombs, identifying damage caused by fire or frost, modulus of elasticity, strength of the material. In analysing reinforced concrete hardened as a result of surface carbonation phenomena, it is useful to perform measurements using the SONREB (SONic + REBound) method: ultrasounds + rebound test sclerometer) which gives a precise correlation between the two methods. Using this combined method, the influence of the particle size of the aggregates, the dosage, the type of cement and any additives used for casting the concrete is reduced compared to a simple ultrasonic investigation. Moreover, the SONREB method cancels out the effect that the moisture content and degree of curing of the concrete may have on the results of the analyses.

Corrosion of the Reinforcement
Although the reinforcement bars in reinforced concrete are immersed in the cement matrix, they may be subject to corrosion. This occurs when, following the carbonation process triggered by the diffusion of carbon dioxide inside the cement paste, there is a reduction in the pH which creates the ideal environment for corrosion of the reinforcing bars. The corrosion of the reinforcing bars involves the following degrading phenomena: the reduction of the resistant cross-section of the rebar bar with a consequent reduction in its load-bearing and fatigue strength; the cracking of the concrete cover with consequent expulsion when the tensions generated in the concrete due to the expansive phenomena accompanying the formation of rust exceed the tensile strength of the material. The expulsion of the concrete cover naturally causes the complete exposure of the bars to the aggressive effects of the environment, which are therefore accelerated. The phenomenon can be evaluated and monitored over time using sensors able to measure - in a totally non-destructive manner - the difference in electrical potential generated between the reinforcement and the surface of the reinforced concrete, indicating the areas where the gradient of potential is indicative of corrosion. Resistive methods using a Wenner probe are also used to supplement this type of investigation.

Extraction Test for Anchors and Eyebolts
Extraction testers are specific instruments for measuring the clamping strength of bolts and anchors. The extraction test is carried out by tightening the adapter to the element to be extracted (for example an anchor) and starting the traction manoeuvre. When the anchor starts to slip off, the pressure gauge will indicate the force applied to overcome the sealing strength.

Adhesion Test
The Pull-Off technique allows the measurement of the tensile strength of a given material or the determination of the adhesion strength between two different materials (typically the adhesion value of mortars and plasters on the walls). The test consists of fixing a circular aluminium element to the surface of the material to be tested using specific two-component resins and, after having isolated the test surface, with an incision made using a dedicated core barrel, removing it using a special instrumented extractor, measuring the last tensile strength value.

Tests on foundation piles:

CHUM
The ¨Cross Hole Ultrasonic Monitor¨ CHUM uses the sonic ¨cross-hole¨ (CSL) method to make an accurate, high-resolution assessment of deep foundations. An ultrasonic wave is sent from a transmitter to a receiver, moved along the entire length of the pile inside pipes ¨embedded¨ inside it during casting. The wave velocity and its energy are strongly influenced by the quality of the cement itself. Other methods supported by CHUM are ¨Single Hole Ultrasonic Testing¨ (SHUT) and tomography (2D and 3D).

Pet – Pile Echo Test
The Pile Echo Test is another measuring method used in assessing structural integrity in the load-bearing elements of a building. This method of measurement is based on the measurement of a wave reflected inside the pile. The wave generated manually using a hammer propagates inside the structural element; and, using the measuring sensor to analyse, analysing the spectrum of the emitted signal, it is possible to determine the length of the pile being examined and see whether it is intact.

Humidity and Temperature Test
The presence of humidity within a structure is often among the first direct causes or the trigger for many forms of degradation. Proper assessment of humidity is also essential for all those involved in laying coverings of any kind, as well as woodworking. The range of instruments distributed by PASI aims to satisfy any requirement with specific instruments for each individual application or modular and expandable ones. Humidity meters (hygrometers and moisture meters) are pocket instruments that enable immediate assessment of the water content inside a structure quickly and in a completely non-destructive manner on all types of material (plaster, concrete, brick, wood). Systems are also offered for continuous measurement of environmental parameters, suitable for monitoring any kind of internal environment.

Thermography
Thermography is a remote sensing technique, performed by acquiring images in the infrared range. A thermographic camera is an instrument able to measure the temperatures of the bodies analysed by measuring the intensity of infrared radiation emitted by the body in question. Below is a list of possible applications of thermography: - Construction: searching for leaks in the plumbing system, checking for roof seepage, displaying energy losses to plan actions aimed at improvement, identifying structural defects, identifying thermal bridges, preventing plaster detachment, identifying dangerous condensation spots with mould, checking the adherence of facade elements, preventive electrical maintenance on low, medium and high voltages: identifying hot spots in cabinets, circuits, electrical systems, terminal blocks, fuses, motor windings and consequently preventing dangerous overheating and fires. - Restoration of cultural heritage: identifying traces of previous remediations restorations, identifying possible detachment points on frescoes, determining the wall texture and previous cladding. In the field of restoration, thermography allows very precise analysis of what can be found under the layer of plaster and means that the intervention can be planned more carefully. - Fire Brigade and Civil Protection (fire detection and prevention): detecting gas leaks, determining the point of ignition of the fire, detecting hot spots on stacked flammable materials. - Preventive mechanical maintenance. - Checking valves and pipes.

PASI - Model 4,5 Hz -Horizontal Geophones for MASW Surveys

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