6. Sometimes the side of concrete bridges is observed to turn black in colour. What is the reason for this phenomenon?
I believe It might be due to dust and grime buildup in some situations. The bulk of such phenomena, however, are caused by fungus or algae development on concrete bridges. After the rain, the bridge surface absorbs and holds water for a length of time. As a result, this creates an ideal environment for the growth of fungus or algae. Furthermore, pollutants in the atmosphere and the vicinity of plants offer nutrients for their growth. Improvements in drainage details, as well as the application of painting and coating to bridges, aid in the resolution of this issue.