As the older infrastructure around the world approaches the end of their service life, the condition assessment of existing concrete structures becomes important to ensure their continued safe structural performance. The overall rehabilitation programme for an infrastructure including the condition assessment and repair work is highly influenced by the allocated budget for that structure. This is why, an efficient methodology for the detection of defects in a structure can vastly reduce the rehabilitation cost.
The condition assessment of a structure usually starts with rapid investigation such as visual inspection. Based on the initial inspection, the structure may need to undergo a detailed investigation, which involves considerable cost and time. Visual inspection alone may not be able to provide necessary information regarding the hidden defects within the structure. In this regard, Impulse Response provides a proven method for rapid screening of the integrity of a structure. The Impulse Response test can be used to quickly screen a structure for defects and identify potential suspect locations within the structure. The suspect areas can then be investigated further using more detailed testing methods at a later stage.
The test is a low strain, elastic stress wave propagation method. The test measures the dynamic response of a structural element after an impact event. The impulse response test can be used for several applications such as:
- Location of voids under concrete slabs in slabs, pavements, bridge decks, walls, or other plate like concrete structures,
- Assessment of integrity of structural walls, and slabs,
- Assessment of quality of overlay structures such as asphalt or portland cement overlays on the bridge decks, slabs, or other elements.
- Location of delamination, honeycombing, poorly consolidated areas in concrete, and other defects,
- Assessment of variability in thickness of structural elements,
- Assessment of the structural support conditions.
ASTM C1740-10 “Standard Practice for Evaluating the Condition of Concrete Plates Using the Impulse-Response Method” provides the methodology for using the Impulse Response method to evaluate the condition of the concrete structures rapidly.
Infrastruct AMS Ltd uses the s’MASH system developed by Germann Instruments for carrying out Impulse Response test on site. Immediately after the completion of the test, s’MASH software analyses the data and provides colour contour plot of various parameters on site. The contour plot helps to locate the areas of concern to be investigated in follow-on investigations (if required). A few applications of the s’MASH Impulse Response test are presented in the photographs below.
Below are the contour plots of the average mobility parameter calculated from the s’MASH test performed on different sites.
Average Mobility Plot 1
The average mobility plot 1 shows the results of s’MASH testing on a slab in a floor area. The slabs in the floor area were evaluated using s’MASH testing as a part of a decision-making tool for further investigation. The s’MASH testing provided an indication on the poor performing slabs in the floor area and the suspected slabs were further evaluated by load testing for capacity evaluation. The s’MASH testing provided suspected areas of the slab which later confirmed by visual assessment.
Average Mobility Plot 2
The average mobility plot 2 shows the results of s’MASH testing on the wall of a concrete tank. The wall of the concrete tank was assessed using s’MASH to identify suspected areas within the concrete, if present. Specific areas on the wall can then be highlighted based on the s’MASH data for further non-destructive testing (NDT) and partially intrusive investigations.
For more information on the advantages of s’MASH testing on existing structures, please contact Dr. Thomas Callanan in Infrastruct AMS Ltd.