Case 1
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Maintenance and Diagnostics
Inspection should be done annually to ensure the buildings are in good condition and to identify necessary repairs in accordance with BS 6150, SS 542 or equivalent. Walls that are lightly soiled should be washed with water and mild detergent. For severe soiling, wash with a strong alkali solution in warm water. The walls should be repainted regularly. Repair hairline cracks by repainting the wall with a flexible sealant/elastomeric paint to seal the cracks. For wider cracks, engage a contractor to carry out repair works. Conduct regular inspections with the aid of paint detectors to identify latent paint problems. When a paint is found to be unsound, remove it. Do not repaint over the blister as the unsound paint has suffered from poor adhesion with the substrate. When necessary, conduct paint adhesion test (pull-off).
Ensure unsound paint is stripped back to sound substrate before a new paint is applied.
Carry out a visual inspection of the integrity of the joints in accordance with BS 8102, SS 637 (formerly
CP 82) or equivalent. Use non-destructive field diagnostic techniques to identify seepage through joints
where visual inspection is not sufficient (e.g., infrared thermography for moisture detection, portable microwave tomography to identify the source of leakage).
Replace the old sealant with a suitable one in accordance with ASTM C1193-16. Inspect joints at intervals
equivalent to one-fifth of their expected life (additionally, all joints subject to movement to be inspected for signs of premature failure after their first year in service) in accordance with BS 6093. When the source of leakage could not be identified, repair using PU injection to ensure that capillaries and porous concrete
are filled.
A water-spraying test should be carried out at the precast joints to check for watertightness in accordance
with BS 8102, SS 637 (formerly CP 82) or equivalent. To repair, find the source of water ingress and block
seepage from the source. In the case when the source of leakage could not be identified, repair using PU injection to ensure that capillaries and porous concrete are filled to the source.
Routine visual inspections should be carried out for joints and look for telltale signs of water seepage in basement areas (e.g., deteriorated or damaged wall/floor/ceiling material, biological growth). If seepage through joints is suspected, non-destructive tests should be carried out to assist with the identification
of the sources of water.
Diagnostics of Defect (see also NDT)
Thermography can be used to identify the position of cracks. A range of crack widths, representing mechanical damage, has been induced under controlled laboratory conditions. The method is based on the characteristics of heat flow phenomenon, in a conductive medium of specific geometry, which is intended to model predetermined boundary conditions.
Ultrasonic Pulse Velocity (UPV)
UPV can identify non-homogeneous conditions such as voids, cracks and honeycombs using the optional hand-held terminal. This method can also be used to estimate the depth of cracks [18-19].
Microwave tomography is a technique to measure the moisture of various materials based on the relatively high dielectric constant of “water” in comparison to the dielectric properties of the material. An electrical field (microwave) is applied to the material, and the microwave induces oscillations of bipolar molecules (i.e., water). Water molecules will reflect and absorb an electrical field during oscillations. A higher electrical field reflected indicates higher water content.
The technique is non-destructive and applicable to wood, brickwork and concrete. The uniqueness of this technique is its ability to measure moisture content at various depths up to 110 mm, allowing the plotting of a 3-D contour of moisture content and facilitating the tracing of the water source.
