Case 2

Cause of Defects

Defective concrete – honeycomb

A dense and good quality concrete can resist water penetration. However having honeycomb voids may 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.

Improper thermal joint dimension

These joints are required to accommodate thermal and moisture expansion and contraction as well as structural movement. On roofs, sealant serves as a joint filling material to seal expansion and thermal joints. Roofs are exposed to thermal shocks and the size of roof panels should be suitably sized to accommodate movements. Having a roof made up of numerous small panels allows accommodation of movement without cracking but also introduces more joints to be filled in. 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.