This article explores the applications and advantages of Non-destructive Testing for Water Treatment Plant Rehabilitation projects across Canada. Water and wastewater treatment facilities are critical infrastructures that ensure public health and environmental protection. In Canada, many of these facilities are aging and require regular assessments, and rehabilitation to maintain their structural integrity and functionality. Traditional assessment methods often involve intrusive techniques that can be time-consuming, costly, and sometimes disruptive to operations. Non-Destructive Testing (NDT) and Evaluation offer a suite of advanced methodologies that allow for comprehensive structural assessments while minimizing the damage to the structures. The insight from a well designed NDT-E program can help consultants and asset owners with more effective repair and rehabilitation strategies, and enhancing asset reliability assessment.

Condition Assessment of Water Treatment Plant

Concrete structures in the water and wastewater treatment plants are exposed to aggressive agents such as sewer, excessive moisture, and various mechanical loads. Some structural elements such as roof in digester tanks might be exposed to uplift as a result of gas build up.  Over time, these factors can lead to premature deterioration of concrete structures, corrosion of concrete and steel reinforcement, and other forms of degradation. Regular inspection and structural condition assessment are essential to:

• Identify early signs of deterioration

• Plan maintenance and rehabilitation activities

• Ensure compliance with safety and environmental regulations

• Extend the life span of the facilities

Non-Destructive Testing for Water Treatment Plant Rehabilitation

Traditional condition assessment methods often involve extracting limited number of core samples and other laboratory tests on concrete. While effective, these procedures can be disruptive and may not provide a complete picture of the structure’s health and condition. Furthermore, the location of the core drilling in this method is more of a guess work. In contract, a NDT-based condition assessment program includes a range of techniques that assess different properties and characteristics of concrete. In addition, these methods can provide insight about the integrity of materials and structures without causing damage, making them ideal for asset routine inspection and assessment planning. In the context of water and wastewater treatment facilities, NDT methods are invaluable for evaluating concrete structures, detecting defects, and monitoring changes over time. Key NDT methods applicable to these facilities include:

Ultrasonic Pulse Testing 

Ultrasonic Pulse Test is a family of NDT methods that use Ultrasonic Pulse to study the subsurface condition of the element. Two distinct tests in this category are the Ultrasonic Pulse Velocity (UPV) and Ultrasonic Pulse Echo (UPE). UPV measures the velocity of ultrasonic pulses through concrete to evaluate its quality and homogeneity. In normal practice, the pulse travels between two probes (facing opposite each other, or the direct configuration), however, it some cases, semi-direct and in-direct configurations can also be adapted. The UPV method helps in detecting internal flaws, estimating strength, and assessing the depth of cracks. UPV is a reliable method for monitoring the progression of damage over time, especially in structures affected by chemical reactions like alkali-silica reaction (ASR). Learn more on UPV

On the other hand, UPE Tomography is particularly useful for assessing the thickness and integrity of concrete elements where access is limited to one side, such as tanks, walls, and slabs. It can detect subsurface defects like voids, honeycombing, and delaminations. The test method can provide valuable information on potential sub-surface defects within the concrete elements. Learn more on UPE

Ground Penetrating Radar (GPR)

GPR  is an effective tool in structural assessment of existing building. GPR can provide key information about the steel reinforcement configuration, detecting voids, and mapping the layout of embedded utilities. GPR is non-intrusive and provides rapid assessments, making it ideal for large areas and for planning intrusive investigations. The GPR scans can be studied along UPE scans to create a digital twin of the structural components. Learn more on GPR in Structural Assessment

Surface Electrical Resistivity

This method measures the electrical resistance of concrete surfaces, which correlates with the material’s permeability and potential for corrosion. Lower resistivity indicates higher moisture content and a greater likelihood of corrosion. Surface electrical resistivity is a quick and non-invasive method for assessing the durability of concrete structures.

Advantages of NDT in Rehabilitation Projects

The integration of NDT methods into the assessment and rehabilitation of water and wastewater treatment facilities offers several benefits:

• Comprehensive Assessments: Since the tests are generally non-intrusive, the test program can easily be expanded to larger areas, developing a better picture of the condition of the asset.

• Minimize Interruption and Downtime: As NDT methods are non-intrusive, they allow for assessments without halting operations or causing damage to the structures.

• Enhances Asset Reliability: Regular NDT assessments contribute to the early detection of potential failures, thereby enhancing the safety of the facilities.

Data informed Intrusive Assessment

Conducting a multi modal NDT-E ahead of intrusive assessment has several advantages:

• Guiding Core Sampling: A well structured NDT-E program can help engineers in identifying critical areas for core extraction, ensuring that samples are taken from locations that are most representative of the structure’s condition (either good locations or poor quality areas).

• Complementing Laboratory Analyses: Data from NDT assessments can be correlated with laboratory results to provide a more comprehensive understanding of material properties and degradation mechanisms. In addition, conducting NDT on core samples can provide extremely valuable information prior to conducting intrusive tests (i.e. compression test).

• Monitoring Post-Rehabilitation: After rehabilitation, NDT methods can be used to monitor the effectiveness of repairs and detect any new issues that may arise. Furthermore, NDT methods can be used in the Quality Control and Quality Assurance of new concrete structures or repairs.

Case Studies: NDT in Canadian Treatment Facilities

Across Canada, several water and wastewater treatment facilities have successfully integrated NDT methods into their assessment and rehabilitation processes. For instance:

• Corbett Creek Wastewater Treatment Plant: FPrimeC utilized multi modal NDT-E program to assess the quality and integrity of concrete walls of a digester tank: GPR and UPV was used to assess the condition of concrete tanks, leading to targeted repairs that extended the service life of the structures.

• Markham Main Trunk Sewer: Employed UPV, Schmidt Hammer and surface electrical resistivity measurements to assess the quality and integrity of concrete. Ultrasonic Pulse Echo was used to assess the thickness of concrete lining.

Conclusions

Non-Destructive Testing and Evaluation methods are indispensable tools in the structural assessment and rehabilitation of water and wastewater treatment facilities in Canada. By providing detailed insights into the condition of concrete structures without causing damage, NDT enhances the effectiveness of maintenance strategies, ensures the safety and reliability of critical infrastructure, and contributes to the sustainable management of water resources. As the demand for efficient and non-intrusive assessment methods grows, the integration of NDT into routine evaluations will continue to be a cornerstone of infrastructure management.