Case 3
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
Defective concrete – honeycomb
A dense and good quality concrete can resist water penetration naturally. However having honeycomb voids will weaken the concrete structure substantially.
Honeycombs may have been formed due to poor workmanship during casting as well as insufficient vibration provided after being placed, allowing excessive segregation in the plastic concrete. As the heavier components settle, water will rise. Voids will be formed after the water dries up.
Poor workmanship during concrete casting
Poor workmanship during concrete casting may lead to concrete cracking. For example, if the curing of concrete is not done properly and there would be excessive rapid evaporation of water from the surface of the concrete that will lead to plastic shrinkage cracks on the surface.
In addition early thermal contractions may also induce in formation of micro-cracks. It may be formed when the concrete dissipates heat of hydration and adjacent structures posed external restraint on the concrete causing the formation of cracks upon contraction.
Poor maintenance
Air gaps in concrete slab that are less compact, could allow water seepage via capillary action. Water may run through the concrete to accumulate in between the concrete panels and the waterproofing membrane. When the defect is left unattended, the presence of water encourages the growth of fungi which will affect the performance of the waterproofing membrane.
Insufficient design of thermal joint
Combined effects of solar irradiance, temperature, oxygen and ozone, moisture, air pollutants, and microbiological factors can cause synergetic deterioration of sealants. Various modes of degradation include thermal, mechanical, photochemical/ radiation, biological, hydrolytic and chemical reactions.
Improper surface preparation of the substrate before the application of sealant would allow dirt, grease, and other foreign substances to be present on the surface. This will lead to loss of adhesion between the sealant and the substrate.