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This does vary because no two cements are the same, sands are of different grades, some additives are stronger than others but the general recipe is as follows;
A Equal parts Cementitious Material and Sand (Cementitious Material = Cement and up to 25% of Pozzolan)
B Acylic Polymer – 5-6% cement weight
C Superplasticiser – this requires slump testing but typically 0.25-1.0% cement weight
D Water – 29-30% of cement weight
E Alkali Resistant Glass Fibres – 3-5% cement weight
The recipe will also change depending on how the concrete is applied. For example if the concrete is to be sprayed, the superplasticizer will need to be dialled back. If a vertical hand-applied mix is required the sand to cement ratio as well as the superplasticizer will need changing. For a self-compacting mix just the right amount of water vs superplasticizer will need to be achieved.
Pozzolans are an element which should not be ignored because they provide a secondary element to the curing process. 10 to 25% of the cement weight should be swapped out for the pozzolanic material
Two types of pozzolans are generally available – silica fume (not to be confused with fumed silica) and METAKAOLIN.
Silica fume is much darker in colour and metakaolin is white. Our preference is metakaolin because it has less of an effect on the final colour of your concrete.
If you do choose to go down the “separates” route then we do recommend that you batch test your concrete mix to ensure its fit for purpose both on workability and also strength. For strength test should be carried out 24 to 48 hours after casting so you know you can move your concrete safely without it snapping and then after 30 days so you know it will be strong enough once in service.
Of course, with our Premix Kits we’ve done all the hard work for you from start to finish!