ThinkCrete Series

Concrete: The Critical Chain thanks Mr S.M.Vaidya, for contributing this article for benefit of our readers.  Considered an authority on Concrete Theory & Practice, Mr Vaidya has written a Series of thought provoking articles on Concrete. Click Here to access complete list of articles under “ThinkCrete Series” 

Those who thought that this article is about the famous critical chain theory of E. Goldratt [Famous for the ‘Theory of constraints’ and thoroughly enjoyable and educative books “The Goal” and “The critical Chain” amongst others] are in for a disappointment. This article is not about project management, but delivery of high quality concrete. It is based on the well known maxim; “A chain is as strong as its weakest link”. I wish to deploy this one liner to emphasize why half measures won’t work if we want to produce high quality concrete [aka High Performance Concrete].

Let us critically examine the factors affecting any property of concrete and we will soon realize that the analogy of the chain is very apt. If the desired property is the chain, then each factor affecting it is the link in the chain. The end result, which is the attainment of the desired property, thus depends upon the weakest link.

Let us look at the compressive strength of the concrete. The chain would look something like that depicted in figure below:-.

Concrete - the Critical Chain

The steps in production of concrete are broken down into logically sequential activities and are proposed as the ‘links’. Thus any error or underperformance or not following the specifications results in the weakening of the link. And to take our analogy forward, the end result, the strength of the chain, will be determined by the weakest link. Thus the compressive strength of the concrete, which is the property depicted by this particular chain will be governed by the greatest weakness introduced in the chain!!

This analogy highlights the importance of the exacting quality control/ quality assurance requirements at every stage of the process, in every link. No step can be taken lightly else the end result would be failure. Unfortunately in a majority of sites, many of these processes, especially those handled manually are far below the desired level. I am sure few will argue if I single out curing, compaction and un-segregated placement as the main culprits.

Does the above analogy sound pretty convincing and attractive? If that is so, are you not surprised that the end result, that is concrete which doesn’t meet the requirements [compressive strength in this case] is not all pervasive as this model would lead us to think? Can one bury the weakest link in the so called ‘factor of safety’ in all cases?

Well, there is no doubt that we concrete engineers routinely produced multiple weak links in our concrete, but there ends the validity of the analogy. There is a flaw in the reasoning presented above. I’d urge all readers to re-read the above paragraphs and then think about the argument and identify the flaw in it. I may call this ‘critical thinking’, the ability not to get swayed / convinced by any arguments without application of mind! It is an important ability that will save us from accepting any written or spoken word just because it comes from an expert [or self proclaimed expert].

So, happy thinking !