When the whole world is locked down, including us, we have only three words to react to the negative effects of the global coronavirus pandemic: Wait and see. The coronavirus (COVID-19) is affecting both indoor and outdoor work in construction industries. But we cannot stop our construction works. Even we must have to work more during and in post corona …
The quality of concrete satisfying the above requirements is termed as workable concrete. The word “workability” or workable concrete signifies much wider and deeper meaning than the other terminology “consistency” often used loosely for workability. Consistency is a general term to indicate the degree of fluidity or the degree of mobility. A block of concrete which has high consistency and which is more mobile, need not be of right workability for a particular job. Every job requires particular workability.
The slump test is the most commonly used method of measuring the consistency of concrete which can be employed either in a laboratory or at the site of work. It is not a suitable method for very wet or very dry concrete. It does not measure all factors contributing to workability, nor is it always representative of the placability of the concrete.
However, it is used conveniently as a control test and gives an indication of the uniformity of concrete from batch to batch. Repeated batches of the same mix, brought to the same slump, will have the same water content and water-cement ratio, provided the weights of aggregate, cement and admixtures are uniforms and aggregate grading is within acceptable limits.
The workability of fresh concrete is a composite property, which includes the diverse requirements of stability, mobility, compactability, placeability and finishability. There are different methods for measuring the workability. Each of them measures only a particular aspect of it and there is really no unique test, which measures workability of concrete in its totality. The Vee Bee Consistometer Test indicates the workability of fresh concrete.
This test gives an indication of the mobility and to some extent of the compactibility of freshly mixed concrete. The test measures the relative effort required to change a mass of concrete from one definite shape to another (i.e., from conical to cylindrical) by means of vibration. The amount of effort (called remoulding effort) is taken as the time in seconds, required to complete the change.