OK I have the answer now... The wrapping is there to prevent what is known as concrete cancer. This explains why only the pillars that do not have the flyover on top to protect them are wrapped in plastic. Apparently concrete cancer occurs when water enters the concrete and rusts the steel reinforcements. At this point the concrete degrades and that degradation can spread throughout the concrete hence the name concrete cancer. Big up my buddy @hydropunk for this information - he is a fount of knowledge. 😉