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  1. #1
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    Default Concrete mix ratio

    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)?

  2. #2
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    Google it or u tube it ... its easy that way in here you are going to get a thousand opinons.

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  4. #3
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    Quote Originally Posted by RDKNIGHT View Post
    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....

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    What will it be used for?

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    Quote Originally Posted by Wishing you well View Post
    What will it be used for?
    It will be used to pour a concrete ceiling, above a bedroom...

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    Then you are looking at concrete mixed for a 4000 psi strength. 1:3:3 ratio between cement and aggregates.

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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.

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  10. #8
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    What happens if you use beach sand in the mix? What effect does the salt have?

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    Quote Originally Posted by beeza View Post
    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.

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  13. #10
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    Quote Originally Posted by ju10prd View Post
    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.

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