With a world of emphasis stressed on the importance of water/binder ratios when mixing concrete, Sephaku Cement elaborates on the correct concrete mix and water/binder ratios. Blended with a variety of additives, aggregates, sand, gravel, course aggregates, waterproofing agents and even pigments, depending on its use, mixing concrete is a science and somewhat of an art when it comes to combining all the various materials and then the most important to have the correct ratios of water to binder. Characterised by definite properties and where the strength of the concrete is influenced by the additives properties, too much or too little water can have a grave and detrimental impact on the concretes strength and compatibility.

As a result of concrete’s adhesive and cohesive properties, Portland Cement is one of the most extensively unutilised materials in construction. Synonymous with strength and lasting durability, if accidentally mixed with the incorrect amount of water, the chemical reaction that takes place when cement become hydrated will be interrupted and have a negative impact on the bond that forms in the materials used as the concrete cures.

Understanding Water/Binder Ratio

Water/binder ratio refers to the ratio of the weight of water to the weight of the cement that is mixed together. Where water to cement ratios in adherence to IS 10262 (2009) for the concrete mix differs from 0.4 to 0.6. 0.7, the same water to cement ratios applies to pumped or industrial scale concrete mixing. A 0.5 w/c (water to cement) ratio indicates that for each 100 kg of cement, 50 litres of water must be added.

Deciphering water/binder ratio might be further understood by explaining in technical terms that for adequate curing, mixed concrete should contain the correct amount of water per mass of cement/binder. A performance curve graph for the correct water/ binder ratio can be obtained from the Sephaku Laboratory at Delmas, which can also assist you to make the correct cement choice as well as using the correct water/binder ratio for your particular required strength result for your project. There are limits to how low water/binder ratio should be used and generally it is professed to not go much lower than 0.30 but lowest 0.28 for full hydration of the binder.

For all home use and DIY concrete projects Sephaku Cement recommends following the manufacturer instructions catered for on the various product bags. While following these instructions, it’s also recommended to measure out water volumes before mixing (as opposed to adding water by measuring its volume by eye) as this will allow for greater control and easier mixing that requires far less elbow grease.

To see if your concrete mix is too wet or too dry by exercising a slump test

This can be done by observing the height of your concrete mix slump after mixing it with water.  Simply measure the height at which your concrete slump stands after making a “sand castle” with your mix. The ideal water/binder ratio will see your concrete slump to about half the height of the original mould used to make your “Sandcastle”.