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Cement-aggregate ratio? Answered

Can you give some recipes, for when starting with plain cement, sand and water? Of course, I imagine it also depends on the cement used, but I also imagine that adding too much or too little cement to the mix has an influence on the strength of the cured product. Or at least describe what happens when there's too much cement - the obvious thing that's happening when there's too little is that the resulting concrete is too weak.

4 Replies

FlorinJ (author)mikeasaurus2017-12-01

I meant when starting without a sand/cement mix, having bought cement and sand separately. I re-read lessen 2 twice, but couldn't find anything about the sand/gravel/cement ratio.

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mikeasaurus (author)FlorinJ2017-12-01

I'd mix up a small batch of 1 cement : 2 sand and see how that works for you before committing to a larger batch for your application. Add more sand as needed for the look and strength you desire.

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FlorinJ (author)mikeasaurus2017-12-02

1:2 seemed odd to me, so I started googling. What I found is that when you exceed about 1:4 weight-wise, your concrete becomes crumbly.

As the cement starts to cure, it produces heat. Heat creates thermal stresses which cause micro-cracks. If these are too many, the strength of the concrete decreases.

Therefore, you need to create a mix that on one hand contains enough cement paste (i.e. cement plus water) to fill up all voids between your sand and aggregate particles, and on the other hand does not create so much heat, while curing, as to cause too many micro-cracks.

For a strong mix, used to pour basements, I found the following cement/sand + aggregates/water weight ratio listed on the web (on a non-English site): 2:10:1.

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