Concrete mix 2

[WHH47]

I am doing estimating for projects in rural foreign countries where, read-mixed concrete is not available, and they have to either hand mix or use portal concrete mixer.
Can anyone tell me how to mix cement, sand, gravel, water, etc. by weight, to make 3,000 psi, 22.5 MPa?
Thank you for your assistance

 

[concretemasonry]

One of your biggest challenges will be the aggregate. Very often in lesser developed areas, the aggregates are not washed and can contain a large amount of fines. The excessive fines can force a higher cement content since it may be cheaper to use more cement than modify the aggregate mining/processing process unless it is a very large project.

Dick

 

[WHH47]

Dick, thank you for your response. It is ten fold challenges than you can imange. Aggregate is just one, where to get cements and cent is another one, mixer, molds, quality, transportation, security, lodging, and many others have to be tackled too.
I am helping an organization building schools and churches in rural area of many undeveloped countries, from four classrooms to 2,000 m2 building, etc.
Your assistance will be appreciated.
Thank you

William

 

[miecz]

Typical 3000 psi mix around here is air entrained:


Cement: 517 lbs
Water: 285 lbs
Fine Agg: 1230 [±]70 lbs
Coarse Agg: 1700 [±]70 lbs
Air Entraining Admixture

For non Air Entrained mix, my notes say you need to add 92 lbs cement and 46 lbs water or a water reducing admixture.

 

[WHH47]

Hi, Miecz,
Thank you for your help. You won't believe how much a cubic yard of concrete would cost in a certain place in Africa - it is about $400/cy concrete material only, not including mixer (if we have to use it) and labor cost)
I were told by a friend of mine to use 1:2:4:0.5 for 3000psi (cement:sand:gravel:water & other admixtures). Your weight info is close to 1:2:3:0.5, am I correct?
Thank you again,

William

 

[miecz]

yes, you're correct.

 

[cvg]

from a mix design I reviewed today:

specified 3,000 psi mix design

442 lbs cement - Type II
95 lbs flyash - class F
1536 lbs sand
1536 lbs gravel (#57)
283 lbs water
includes air entraining and water reducing admixtures

28 day tests range from 3630 - 6430 psi
average 28 day strength is 4,900 psi

 

[concretemasonry]

If you are in Africa, you probably will have excess fines in the aggregate (unwashed) and your cement content will have to increase greatly to get the strengths required for a truly engineered design.

Most of the structures you have mentioned are usually relatively low structures with little seismic loading. The schools, especially, are usually a basic "cellular" layout (one story unless it is politically significant) with short roof spans and masonry walls to distribute the loads and reduce the need for higher strength concrete.

Take a hard look at the requirements for the concrete foundations/columns. Most structures have masonry walls and units are available nearby and can be stockpiled until needed. In some areas, the local "rammed cemented earth" units may be adequate for the walls.

If you are in or near South Africa, Botswana or Namibia, I have seen wall units that work well. Obviously, areas near Ghana and other areas have wall units available. Because of the European (German and Dutch)influence, there are many long established product plants that use cement in quantity and require quality aggregates for the automated equipment. They could be sources. When you are in Africa, you must rid yourself of the concept that everything has to be the highest quality and made to a specification that may be overly restrictive for the needs of the project. - Some of these areas also use footings and foundations made from concrete block because of the availability and economics for the structures. I assume these are not the high, impressive structured found in the major cities.

The areas I mentioned routinely use 6000-8000 psi concrete pavers made in similar plants.

It would help to know better where the projects are located.

Dick

 

[WHH47]

Thank you all for assistance,
Sorry I am not allowed to reveal the exact locations of construction, except a place four hours of driving from Juba, Sudan, where the road is only open four months a year.
As I were told, 42.5N cement were used in several places and has to be imported. Transportation adds up a lot of cost too. A 50kg bag of cement would cost up to $35 a bag by the time arriving at the jobsite, not mentioning the cost of sand and gravel.
Thank you again

William

 

[dicksewerrat]

Can you get any type of clay locally? Adobe bricks comes to mind.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[concretemasonry]

Clay suitable for adobe blocks" is not always found locally. In some areas of Africa they make "rammed earth" (dirt, cement and water) for blocks. The strengths are low, but the people can produce it and know how to use it. Since masonry is possibly the most common form of residential housing in the world, it would be a logical choice for bearing walls along with some concrete for selected columns and foundations. A portable mixer (1 or 2 bag) can do a lot of mixing if the products can be made with a lower cement content and local aggregates than ready-mix concrete on a low building.

I think that despite the travel time and distance, the price for the cement is inflated somewhat. There could be some added fees/tips that raise it so high. You cannot always design to the US or EU standards everywhere.

Designing and building to ACI (or other) standards may not be practical in the area described. It might be good to take a survey of the local materials and construction practices.

I know these development projects can get unrealistically mired down in standards and specifications, especially if the governments, bureaucrats and agencies (USAID, UN and others) get involved and try to build to a different standard with non-local materials and methods. I have seem brick and 30' long reinforcement delivered by bicycles in India.

Dick

 

[Zambo]

One way to achieve this would be to have a construction yard at the nearest town. The cement, sand and aggregates could then be delivered to one location. An area could be set up for washing the aggregates and then everything bagged in 50kg sacks. Then load everything into a container with sufficient materials for the job in hand.

If portable mixers are available it should be possible to get a good quality concrete. Many portable drum mixers have weigh mixing equipment which is better than volume mixing.

A block making machine for either concrete or soilcrete (as described by concretemasonary) would be a good investment.

 

[WHH47]

Concrete structure we plan to build in that part of world is basically constructed on foundation and columns - concrete, blocks or both; roof - concrete or tiles over roof framing. We have to follow EU standards.
Wall is to be either adobe bricks or cement blocks, and we were told to purchase molds from EU countries, for either hand making or machine making type of molds of various sizes.
Structures are mostly single story, and only one building I have seen so far is two stories with bell tower.

 

[19320]

You can check this paper for how to design efficient and economic concrete mixes with locally available materials.

http://cigmat.cive.uh.edu/CIGMAT Conference/CIGMAT-08/Poster 08/Emrah cigmat.pdf

 

[concretemasonry]

The previous reference/link is not applicable to any of the developing countries I have been in involving design and construction in remote areas.

The cement is not a big problem because it is probably not local and will be imported and made to both ASTM and EU. standards.

The aggregate is a totally different thing since it local. You can write all the ASTM and EU standards you want, let alone getting representative samples tested and certified. The familiar terms mentioned (sand. #57 gravel are not the same locally), so you have to deal with the locally available aggregates. Having the pre-weighed and bagged is good if it is economical, but often the cost of the bags is more than the cost of the aggregate in them. In many areas the bags have a refund value, but there is guarantee you will be able to salvage all of the good bags.

If you are in a relatively remote area and the cost of shipping is very high and not always reliable during certain times, I would suggest finding the biggest truck and trailer and buy as much as possible to minimize the cement delivery cost and store it on site and protect them from theft, since they have many uses.

You have accepted the obligation to build to EU standards, so the only reasonable solution is to make a series of mixes of the proposed locally available aggregates and corresponding samples. Ship them to a testing lab to determining the f'c (compressive strength)and then make a determination of what mix/aggregate proportions to use.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[RonRoberts]

How big are your structures? Might want to read this paper about domes.

http://static.monolithic.com/thedom... of Dome Housing in Sri Lanka reduced bpr.pdf

 

[concretemasonry]

Different technology, designs and construction methods are not compatible with developing countries since the materials and hands-on supervision is not available, no matter what the design documents, except that is horribly slows the progress and there is an unknown reliability.

The locally available materials at a reasonable cost and conventional techniques are very difficult to beat without a lot of money and time.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.