Voliro enhances the testing of concrete structures with its specialized Voliro T inspection drone, incorporating omnidirectional mobility to perform testing with precision and stability across various structures.
Concrete testing methods fall into two categories: destructive and non-destructive testing. Destructive testing assesses the performance limits of a test object or determines the cause of its failure. Methods such as pull-out or flexural tests apply force until the concrete structure sustains damage, measuring its strength and durability. Because of this, destructive testing is primarily used for quality control before construction begins or during forensic investigations of structural failures.
Non-destructive testing (NDT) evaluates the quality, integrity, and strength of concrete structures without causing permanent damage. These methods help identify flaws, discontinuities, and signs of deterioration. Common NDT techniques include ultrasound scans, industrial radiography, magnetic particle inspection, and liquid penetrant testing, among others.
Non-destructive concrete testing allows repeated assessments and condition monitoring throughout an asset’s lifecycle. It provides essential data on mechanical stress, cracking, spalling, and delamination, allowing asset owners to take preventive measures to avoid expensive repairs and regulatory penalties.
When Non-Destructive Testing of Concrete is Required
All commercial, residential, and industrial concrete structures must meet structural safety regulations. Industrial structures subjected to heavy loads must adhere to specific design requirements, such as resistance to fatigue from frequent foot traffic.
Although these regulations differ by country and industry, their core objective remains the same: Owners are responsible for ensuring the reliability and safety of primary structures. These standards exist for good reason. Poor maintenance of concrete structures can lead to catastrophic incidents.
Industrial facilities contain concrete assets such as silos, storage tanks, and kilns, which are vulnerable to deterioration, mechanical stress, abrasion, excessive loads, moisture infiltration, and temperature fluctuations. For example, silos storing moist plant materials generate lactic and acetic acids that react with the cement matrix, gradually weakening the structure until failure occurs.
Industry Standards & Regulations
To prevent such failures, various industry standards and regulations have been established. The recommended frequency of concrete NDT varies depending on factors such as asset type, age, and operational intensity. At a minimum, all concrete assets require thorough inspections every 3 to 5 years. Annual NDT assessments are advisable for aging structures and those with a history of significant damage and subsequent repairs.
Non-Destructive Testing Methods for Concrete Structures
Industry standards outline recommended NDT techniques for concrete structures. Testing must be conducted by certified inspectors using specialized non-destructive concrete testing equipment. Depending on the asset and its operational conditions, inspectors select the most suitable method.
Various inspection techniques detect different defects, such as surface dents, subsurface cracks, scaling, delamination, and stress from excessive loads. This information is gathered using ultrasonic, stress wave, nuclear, thermal, magnetic, and electrical readings.
Ultrasonic Testing
Ultrasonic testing identifies defects by analyzing reflected high-frequency sound waves. By studying ultrasonic pulse trajectories and timing, inspectors can pinpoint the location, size, and severity of delamination, debonding, or cracking.
This method is also useful for measuring concrete thickness to ensure compliance with construction standards. Thickness loss can result from abrasion, freeze-thaw cycles, or fungal and mold colonization, which degrade protective coatings and cause further structural damage.
Although ultrasonic testing provides high-quality data, its application is sometimes limited due to the need for direct contact with the surface. Large industrial assets may require scaffolding or aerial platforms for access unless an industrial inspection drone is used.
Voliro has developed an omnidirectional drone equipped with mountable NDT payloads. Featuring double tilt rotors and an advanced sensing system, the drone can approach objects from multiple angles, conducting wall thickness measurements with an ultrasonic transducer or detecting structural damage with an electromagnetic acoustic transducer (EMAT).
With Voliro drones, inspectors can gather up to 200 readings per hour and inspect 5 to 10 concrete storage tanks daily, reaching difficult areas without the need for scaffolding.
Radiographic Testing
Industrial radiography produces X-ray images of concrete structures, allowing inspectors to analyze density and composition. Gamma rays penetrate several feet of material, highlighting defects such as voids, honeycombing, delamination, and inconsistencies in density, which can lead to structural weaknesses.
This method is also effective for locating reinforcement bars to confirm compliance with design specifications. The International Atomic Energy Agency reportedly endorses radiographic testing for ensuring high-quality standards in nuclear facilities.
However, radiographic testing presents challenges, including the need for portable scanners, additional safety precautions, and protective shielding, making it costly and logistically complex for field use.
Acoustic Emission Testing
Acoustic emission testing detects mechanical vibrations that indicate structural stress. Unlike other NDT techniques, AE not only identifies defects but also evaluates their severity and progression under varying conditions.
AE is particularly useful for assessing load-bearing capacity and detecting microcracking in concrete structures. It also verifies the effectiveness of repairs by measuring emissions before and after reinforcement work.
One key advantage of AE is its reliability across different cement types, admixtures, curing conditions, and temperatures. However, its detection range is limited, requiring unobstructed surface access. In large concrete structures, acoustic signals may weaken before reaching sensors, affecting data accuracy.
Thermal Imaging
Thermal imaging captures temperature variations on the surface of concrete structures, revealing potential defects. Elevated temperatures may indicate mechanical stress or chemical degradation, while cooler areas can signal moisture intrusion or freeze-thaw damage.
This method also detects voids, cracks, and delamination through variations in thermal conductivity. While thermal imaging provides valuable surface-level insights, it is often combined with ultrasonic or penetration resistance testing for more comprehensive analysis.
Penetration Resistance Test
Penetration resistance testing measures the compressive strength of hardened concrete. Using specialized equipment such as ASTM C803-compliant steel probes, inspectors determine strength levels by measuring penetration depth. This method is useful for assessing the structure’s ability to withstand axial loads, wind pressure, and thermal expansion.
However, results may vary in porous or reinforced concrete, making supplementary testing advisable.
Rebound Hammer Test
The rebound hammer test evaluates concrete hardness and compressive strength by measuring the velocity of a hammer’s rebound after impact. A higher rebound number (R-number) indicates greater hardness.
This test helps assess concrete uniformity and detect signs of deterioration, making it a valuable tool for quality control and condition monitoring. However, surface characteristics such as smoothness, carbonation, and moisture levels can affect results, requiring adjustments for accurate measurements.
