Visual Inspection of Underwater RCC Structures -Tools and Limitations

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Visual inspection is the most widely used method for inspection of underwater reinforced concrete structures. This technique is economical, and it neither time consuming nor needs expensive and large number of equipments. Not only does visual inspection utilize to specify damages on the surface of the structure but also it is used to specify and find seriously deteriorated positions of the structure. Techniques such as photography, video and the eye of inspectors who dive underwater may be involved in the underwater reinforced concrete structure evaluation. Visual assessment of the underwater concrete structures, limitation of the technique, and required tools used in this method is discussed in the following sections.

Fig.1: Visual Inspection of Underwater Reinforced Concrete Structures

Visual Inspection of Underwater Reinforced Concrete Structures

Following points are discussed regarding visual inspection of underwater RCC structures:

• Visual inspection tools
• Measuring equipments used in under water visual inspection
• Limitation of visual inspection method
• Tactile assessment of underwater reinforced concrete structure

Visual Inspection Tools for Underwater Reinforced Concrete Structures

There are different tools and equipments applied in the visual inspection of underwater reinforced concrete structures. Such tools may include pry bars, hammers, probing bars that might be required for conducting concrete soundings, and picks. Delamination and voids are usually observed in this technique that is why chipping equipments are considerably significant to chip off part of concrete and determine how far the damage has penetrated the concrete. The type of assessment obtained with help of these tools should be used as guidelines for further evaluation and analyzing. Flash lights and clear water mask are substantially important to enhance visibility to achieve better underwater inspection results. This is because such devices can enhance the visibility underwater which is essential while underwater inspection is carried out. It is reported that, both thallium iodide and quartz iodide lamps have been employed in the underwater inspection process successfully.

Measuring Equipments for Visual Inspection of Underwater RCC Structures

There are several simple tools which are used by divers to obtain limited amount of data during the processes of inspecting underwater reinforced concrete structure. These equipments are not expensive and can be used easily without spending much time. Their capacity to determine the degree of deterioration is considerably restricted. Measuring tools can be divided into different groups includes linear measurement, circular measurement, and spall or deformation depth.

Linear Measurement for Visual Inspection

Devices employed for linear measurements while underwater reinforced concrete structure is inspected are provided in Table-1. Table-1: Linear Measurement Tools, their Applications and Accuracies

Device types	Application of the device	Accuracy of measurements
Ruler, Figure-2	Measure crack length and spall width and length	+/- 0.5 mm
Tap measure, Figure-3	Used for measurements of up to 100m	+/- 5 mm
Magnetic tape	Used for circular measurements and employed for maximum of 3m	+/- 1 mm
Scales	Used in combination with photography	+/- 5 mm
Comparator	Measure crack width	+/- 0.025 mm for dry condition but the accuracy is decreased underwater

Fig.2: Ruler

Fig.3: Tape Measure

Circular measurements

The devices used to obtain circular measurement during the process of visual inspection underwater reinforced concrete structure are provided in Table-2. Table-2: Circular Measurement Tools, their Applications and Accuracies

Device types	Application of the device	Accuracy of measurements
Calipers, Figure-4	Take measurements of up to 2 m in diameter	+/- 0.5 mm
Special jigs	Measure member ovality	+/- 5 mm

Fig.4: Caliper

Deformation or Spall Depth Measurements

There are number of devices used in the underwater inspection to measure deformation or spall depth and these tools are provided in Table 3. Table-3: Deformation of Spall Depth Measurement Devices and their Applications and Accuracies

Device types	Application of the device	Accuracy of measurements
Profile gauge	Used to record mirror image of defects on concrete elements	+/- 0.5 mm
Taut wire	Employed for great deformation or spalling regions, in addition to measure out of plumbness of members	+/- 5 mm
Casts	Applied to achieve mirror image of defects and employed to take samples to the surface for visual inspection	---

Limitation of Visual Inspection Method for Underwater RCC Structures

Even though underwater visual inspection is considerably quick to conduct and it is economical but there are conditions that may restrict this inspection technique which involves strong waves that decrease diver capacity, turbid water which decline visibility, and marine growth that cover structural defects if it is not cleaned. Diver skills and experiences largely affect restriction related to the diver. For example, inexperienced diver may not be able carry out good visual inspection due to environmental conditions.

Tactile Assessment of Underwater Reinforced Concrete Structures

Tactile inspection of underwater concrete structure is the application of diver capability other than visibility for instance the sense of feel and touch. This technique is used when the visibility is substantially decreased due to extreme environmental conditions or prior to cleaning of structures which are covered with marine growth. This underwater inspection method requires considerable preparation compared with structural assessment in clean water. The diver needs to familiarize himself with structure, which is intended to be inspected, through drawings of the structure. Great communication between divers and individuals on the surface needs to be considered. Read More: Inspection of Underwater Concrete Structures -Methods, Types and Purpose Methods and Procedure for Repair of Underwater Concrete Structures Anti-Washout Admixture for Underwater Concreting -Types, Advantages and Uses Underwater Concreting Methods- Tremie Method Process and other Techniques