Difference between Strength & Durability

Short answer: Strength is 'how much load will it take?' & Durability is 'how long it will keep taking it's designed load?'

In our training programs, we often find that audience take little longer time for defining Durability than Strength. At times they cannot differentiate them properly & feel that - 'Strength is equal to Durability'.

 This is happening mainly due to two reasons,

1. In our college we study lot about strength and very less about durability

2. In our construction sites we worry lot of Strength than Durability

The compressive strength of concrete is measure by cube tests. This test is very direct & easy to conduct in our construction sites if we have Compression Testing Machine(CTM).

But measuring durability is little complicated. There are number of laboratory tests conducted to measure the durability of concrete against various aspects. (ex: Air or Water permeability tests, Chloride diffusion test, Electrical resistivity tests, etc.,). The main aim of all these tests is to find out the porosity of concrete.

Higher the pores higher the permeability. Higher the permeability lower the Durability.  When pores are higher in concrete, it is easy for elements to enter inside, create unwanted chemical reactions and start deteriorating the concrete matrix.

So one important factor playing higher role in 'durability' than 'strength' is Porosity.

There is one more aspect we need to clarify here, that is role of 'Porosity' in strength. Yes strength is affected due to high porosity. Yet required strength can be achieved by altering the mix design with certain porosity level, but durability will get affected with this porosity.