Concrete mix ratio

jimbobo

Member
Feb 9, 2014
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Hi everybody,

I was taught to mix concrete at a 1:2:3 ratio; that is 1 part cement to 2 parts sand to 3 parts of gravel. I noticed that here locals mix concrete 1 bag of cement to 2 wheelbarrows of "arena processada" (crushed stone sand) and 1 wheelbarrow of gravel.

I noticed the sand they use contains lots of gravel of the 3 - 5 mm range.

Does anybody know what is the right mix ratio for concrete with the "arena processada" (crushed stone sand)?
 

RDKNIGHT

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Mar 13, 2017
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Google it or u tube it ... its easy that way in here you are going to get a thousand opinons.
 

jimbobo

Member
Feb 9, 2014
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Google it or u tube it ... its easy that way in here you are going to get a thousand opinons.

I have googled it... it's just that I don't know the specs of the "arena processada" (crushed stone sand) that is commonly used here....
 

ju10prd

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Nov 19, 2014
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Stand back a minute and think what good concrete is.

It is a graded mix of aggregate with cement and the correct amount of water to create a material which is cohesive, more creamy than coarse and workable in it's plastic state and solid and with little air (less than 5%) in it's solid state.

The sand, cement and water provides a cream/matrix which coats the coarser aggregate and binds it all together as hydration takes place.

The actual sieve grading of the combined aggregates is thus important as is the cement to aggregate ratio and fundamentally important the water to cement ratio for strength.

One cement to six a combined graded aggregate mix from fine to coarse by weight is probably a better guide for DR....maybe more cement is a good idea too.

I faced a similar challenge some twenty years ago in Kenya and we designed, mixed, placed and tested a good concrete mix using similar equipment to that used here in the campo based upon a design developed using British Standard Road Note 4 with sieve analysed aggregates. Still have my concrete design and quality control document if any one is interested.

I can't emphasize enough the importance of water to cement ratio for strength and the need to compact concrete.

Neither is done in the campo here and the maestros here like concrete pea soup for ease of workability and compaction, so the day the earth rumbles a lot, the buildings will tumble down irrespective of reinforcement or not.
 

beeza

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Nov 2, 2006
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What happens if you use beach sand in the mix? What effect does the salt have?
 

ju10prd

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What happens if you use beach sand in the mix? What effect does the salt have?

There is a particularly good example of that just outside Porto Antonio in Jamaica where a celebrity built a rather large property and the contractor used unwashed beach sand.......deserted and unusable some years back. The salt reacts with the reinforcing bar which expands and bursts the concrete to simplify the reaction.

Fortunately in DR the normal source of the finer aggregate is rivers, so feel blessed even if it goes into incredibly weak concrete in campo domestic construction.

To expand, the small island of Barbuda a few hundred miles south east of here, is a major exporter of sand to other islands and they dig it from behind the beach but don't wash it! Saw that, tested the sand and it shocked me. So enjoy your investment in St Barts and BVI!!!! Even in TCI, Provo, as at least one other member probably knows, sand used to be excavated and used for construction from behind the beach north of Whelands.

DR is lucky in this respect, but if you use a maestro in the campo, temper your good feelings because you are going to get most likely very weak concrete with not dissimilar similar lifespan when all things considered here.
 

JD Jones

Moderator - Covid 19 in DR & North Coast
Jan 7, 2016
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Stand back a minute and think what good concrete is.

It is a graded mix of aggregate with cement and the correct amount of water to create a material which is cohesive, more creamy than coarse and workable in it's plastic state and solid and with little air (less than 5%) in it's solid state.

The sand, cement and water provides a cream/matrix which coats the coarser aggregate and binds it all together as hydration takes place.

The actual sieve grading of the combined aggregates is thus important as is the cement to aggregate ratio and fundamentally important the water to cement ratio for strength.

One cement to six a combined graded aggregate mix from fine to coarse by weight is probably a better guide for DR....maybe more cement is a good idea too.

I faced a similar challenge some twenty years ago in Kenya and we designed, mixed, placed and tested a good concrete mix using similar equipment to that used here in the campo based upon a design developed using British Standard Road Note 4 with sieve analysed aggregates. Still have my concrete design and quality control document if any one is interested.

I can't emphasize enough the importance of water to cement ratio for strength and the need to compact concrete.

Neither is done in the campo here and the maestros here like concrete pea soup for ease of workability and compaction, so the day the earth rumbles a lot, the buildings will tumble down irrespective of reinforcement or not.

IIRC, the correct amount is 5 gal of water for each back of cement and aggregate. Also, it's very difficult if not impossible to get a good mix using shovels to mix on the ground.

A powered mixing machine is imperative.
 

Kipling333

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Jan 12, 2010
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In some countries they use a little hydrated lime into the equation ...it is used when you want concrete to be load bearing and also it is water resisting . I have not seen it used in the DR but in my youth and for centuries before it was the norm .
 

jimbobo

Member
Feb 9, 2014
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In some countries they use a little hydrated lime into the equation ...it is used when you want concrete to be load bearing and also it is water resisting . I have not seen it used in the DR but in my youth and for centuries before it was the norm .

Is that what thet sell here in ferreterias under the name " cal viva " ? How much would you ad to, let's say, 1 bag of cement?
 

mobrouser

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Jan 1, 2002
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There is a particularly good example of that just outside Porto Antonio in Jamaica where a celebrity built a rather large property and the contractor used unwashed beach sand.......deserted and unusable some years back. The salt reacts with the reinforcing bar which expands and bursts the concrete to simplify the reaction.





The story of Folly Ruins
 

Kipling333

Bronze
Jan 12, 2010
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Is that what thet sell here in ferreterias under the name " cal viva " ? How much would you ad to, let's say, 1 bag of cement?

I have not seen that product so cannot say if it is hydrated lime but many years ago we would only use in the mixer less than one part to fifteen or even one part to twenty .