Defects-Construction

Leakage 

Leaking terraces, tanks and bath-rooms  in several newly-built buildings, including multistoried ones are proof of a poorly made concrete mix. 

"Honeycombed"

"Honeycombed" concrete because of segregation of stones from cement in the concrete, and air voids due to excess water in the mix, is a familiar sight in buildings under construction. If a column or beam of concrete has honeycombs or voids in it, moisture, chemicals and salt (in a coastal area like Bombay) penetrate the structure and corrode the steel rods. 

Since rust occupies several times the original steel volume, the concrete gradually splits and weakens the whole structure. Five per cement voids in concrete could reduce the strength of a structure by 30 per cent and ten per cent of voids by 60 per cent. 

Since honeycombed concrete is generally superficially plastered over. it is not noticed till the reinforcement has corroded and the concrete has split, causing cracks. 

If minor cracks by honeycombing and voids not repaired properly, the disintegration would continue like cancer and result in a collapse. 

Voids in Concrete 

Voids in concrete are caused mainly due to wrong blending of stone and sand which has less fine particles. This causes lack of cohesion in the freshly made concrete and therefore it segregates during mixing, transporting  and placing and results in honeycombed concrete. 

Another cause of honeycombed concrete is the tendency for the workers not to use vibrators to fully compact the concrete, besides causing loss of strength in concrete and leakage in roofs, bathrooms and tanks. 

Excessive Fine Sand 

Excessive fine sands lead to general weakness in a concrete on account of the high water cement ratio which their use entails. A coarse sand gives a stronger concrete than fine sand for the former pennies cement to fill in the interstices between the sand particles  and thus bind them together. In order that the cement may exercise the maximum binding action, the sand should be coarse enough for cement and water to get through its pores and surround each particles of sand.  On the other hand, absence of sufficient fine sand below 300 micron mesh sieve tends to give harsh-working mixes prone to segregation and to local defects.