This pipe is located almost underground. Due to the blockage the water from the terrace instead flowing to the underground main pipe flows out at the first floor opening in the balcony. The pipe is a direct pipe from the terrace to the ground with a break at the balcony, but due to the blockage at the end overflowed water fills the balcony. Hence it starts entering the rooms at the first floor. Our house is made of bricks and cement, it is situated in Pakistan. Problems of overflowing increase durng the rain( Monsoon) season.
Acid will 'eat' cement, but not PVC. it takes time though. You might need to power flush the sand that will be left behind.
Irv S is right, Anamarshad; I just wanted to add that there is an acid sold in India (and therefore your country too) called Muriatic acid. It is used specifically to wash (dissolve) cement from the surface of bricks or other ceramic products. It is quite corrosive and should be very carefully used taking precautions such as wearing gloves and eye protection. Depending upon the diameter of the pipe and the amount of cement it may take, as Irv S mentions, some time and, since the sand in the cement will not dissolve, some sort of probe to remove the remaining sand. In the U.S. we have a thing called a plumber's snake, which is a stiff long coiled wire which can be threaded through clogged pipes to remove debris.
Find something you can push along the inside of the pipe to break up the blockage - maybe stiff fence-wire, or something similar. Try to introduce this as close as possible, but upstream, of the blockage (which might mean opening the joint at the balcony, for instance). Work it backwards and forwards until the blockage is broken up and washed away.
