Dear reader we know water-cement ratio is the controlling factor for strength of concrete. Here, in no-fines concrete, water-cement ratio is not main controlling factor.
There have a narrow range of water-cement ration, which is optimum for a given batch of aggregate. We have already discussed about recommended aggregate for no-fines concrete. Aggregate grading and shape have influence on water-cement ratio.
An aggregate having more surface area will need more water than an aggregate of less surface area. Again a rough aggregate can held coating of cement paste more than smoother one.
We were discussing about optimum water/cement ratio, when provided water cement ratio is higher than optimum, the cement paste have tendency of draining out away from surface of aggregate particles.
Whereas, when provided water-cement ratio is lower than optimum, the paste becomes less adhesive which leads to deviation from desired composition of this concrete.
Again aggregate absorption plays an important role in defining water-cement ratio and in prediction of optimum water-cement ratio must included this factor.
However, in general, the water content for concrete mix can be applied as 180 kg/m3 of concrete mass. Thus cement content required to coat aggregate sufficiently is considered in defining water-cement ratio.
We can provide a typical value of W/C ratio 0.38-0.52. But the strength achieved with this W/C ration should examined by test. Dear reader in our next post we will discuss about strength of no-fine concrete in our next post.
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