Old School Concrete Terms

Actually it is the # sacks of cement per cubic yard used in a mix design. This is not old school this is a common current term used for typical standard mix designs, such as 5 sk, 5.5 sk and 6 sk. 3/4" washed gravel unit weight depends on the angularity, void ratio, minerology, moisture content, and gradation of the gravel. This is weighed out at the mix plant. Each rock manufacturer will be knowledgeable about the unit weight of their 3/4" rock. Typically you would be looking at a unit weight of between 125 pcf and 145 pcf. Different sources will have slightly different unit weights. If you use approved sources, you should indicate the units weights for each source as provided by the manufacturer or a laboratory.

I ran a small concrete flatwork company from 94 -2000. My old world italian ex father in law had started the company in 1952. He taught me to order concrete according to the bag mix rather than the psi number. For example I would call the ready mix company and order say, 10 yards of 6 bag mix with air to be installed as garage floor and sidewalks for a new build home. He also knew the approximate weight of 4" of 3/4" washed gravel (also referred to as #57 gravel). 4" is the standard amount of gravel installed under residential walks, drives and garage slabs. It wasn't an exact figure, but, it was close enough to order the gravel for a job like we did with very little if any waste. Everything was figured on the square foot. So I could take the total square feet of an area multiply it by that gravel weight figure and then divide by 2000 to get the approximate tons of gravel to order. Concrete was sq ft divided by 80 for 4" and 54 for 6". Also approximations that got me close enough to not run out and not have more than 1/4 yard left in the truck. I was good at making sure the grade was right.

I am now working for a property management company. We manage condominium communities. Obtaining bids for Concrete repair and replacement in the communitites we manage is part of our service. I have been asked to put together a manual that the other property managers can refer to when comparing bids and overseeing the work. Most of the contractors that would do this kind of work are smaller more old fashioned type companies. When I sat down to put together this manual, I realized,,, I am senile. I can't remember the psi/bag mix and the gravel weight my father in law taught me. Father in law died a few years ago, I divorced his son, so I am out on the internet looking for someone who knows what I am talking about. I just want to give the other managers enough information to be able to determine if bid amounts are accurate and familiarize them with some of the terms used in that type of bid. Installing residential concrete is crazy fun and full of so many variables it has been hard to put together a few simple rules of thumb. All I am looking for is what is the psi of a yard of concrete that has 6 bags or sacks(whatever!) of concrete, the psi of 5 bag mix and the psi of 4 bag and the psi of 6 1/2 bag,,, aaaaaannnnd the approximate weight of 4" of gravel 1 foot square. So that I can show a bunch of women with no experience in concrete how to know if the bids they get are reasonable. If I trusted my ex husband I would ask him, but he would lie just to make me look bad and as I mentioned,, his Dad died.

I could make a form out of 2x4s one foot square, fill it with #57s and weigh it myself. I figured someone out there would know what I was talking about. I know a lot of old concrete guys still use those terms and have taught their sons the same way. These are the guys we will be dealing with for our concrete repairs. So,, long story short,,, does anyone know the answer to my questions?

Your approximation for the weight of aggregate per cubic foot seems low to me. Given 6" weighs about 32.4 lbs, this would result in a unit weight of approximately 64.8 lb/ft³, about half of what I would expect from experience. I would use on the order of 10lb/in/ft². This would be a matter of some importance if we were creating a mix design using it, or if we were ordering stone for below a slab.

Hello yoderengineering:

I found an article on the subject that mentions the weight that a cubic foot would be and your figure is about what it was. It all depend on what type of aggregate you use. If is is irregular there is going to be an awful lot of spaces. If it is crushed rock it will be even lighter.

I am not saying your not right, but I was builder for several years. And I could fill a cubic foot with about five shovels. I am not sure I could lift a shovel which weighed the best part of 20Lbs, over and over throughout the day. Get my drift. Five times 20 = 100, just over your suggested weight.

Hello yoderengineering:

It sounds like you really enjoyed and absolutely fully understood your job? Respect to you!. Let me know when you can find the details floating in the either somewhere, about the weight of the gravel. I mean I never weighed it. I would just order it by the yard³ (then, and later by a metre³. I would often do my own mixing, but on a big job would order a 6 bag mix 'dry'. Hell I want to find out how heavy a ft³ is!

And you cannot be senile lady, you look great......And, I am sorry, I should not have said that!. If you are in England ever, I will get you a drink. I did it again!

I am going before they chuck me out!

Take care...........

Hello yoderengineering: I found a site where I can double check the math and or volume to litre weight and worked out the weight of a litre, x 28.33 and the figures are below. So, it look like you remembered just fine! I have read on quite a few sights that 'in general' aggregates wiegh 105Lbs per foot³. This sight http://www.fishertopsoil.ca/faq.php#aggregates Has an equation which I reworked to get the weight per litre.

The volume in a 40 lb bag will vary somewhat, but will generally be around 11 to 12 Litres per bag (28.33 Litres = 1 Cubic Foot)...........It says there's 28.33 Litres per ft³.

To find the weight and not volume, I did this:*40Lbs 12 = 3.3333, (the litre weight) x 28.33 = 94.433.
*40Lbs 11 = 3.6363, (the litre weight) x 28.33 = 103.018.

http://www.tpub.com/content/engineering/14070/css/14070_406.htm

Check this site as it gives almost the same totals as above

This site had loads of info' but may be unneccessarily complicated? Very interesting though.

http://www.cement.org/tech/cct_port_cem_prod_tech.asp http://www.cement.org/tech/index.asp http://www.cement.org/tech/faq_cement.asp

This is from the same site as above and has some from PDF files and lots of other info, some is books, some is free and some if paid for PDF.

But have a look at the rest of the site, I bet this brings back some memories of a job well done? http://www.cement.org/bookstore/results_advsearch.asp

Q: How much cement is needed for a small concrete mixture?

I am considering mixing my own concrete for a small project. How much cement, coarse aggregate and sand are needed to produce a cubic yard of concrete; how do I calculate the volume of concrete material required for the project; and when does hand mixing become impractical compared to ready mixed concrete delivery?

A: The actual cement required for concrete is affected by the choice of the maximum coarse aggregate size. As the maximum coarse aggregate size is decreased the cement content must increase to provide the required quantity of cement paste to coat all of the aggregate particles. The table gives some guidance for the proper quantities by volume of the separate components of a concrete mixture.

Table: Proportions by Volume of Concrete for Small Jobs

These proportions are only a guide and may need adjustments to obtain a workable mix with locally available aggregates (PCA 1988). Packaged, combined, dry concrete ingredients (ASTM C 387) are also available.

More information is available in Concrete for Small Jobs (IS174).

Example: Assume that the proportions will be made based on one part being a cubic foot (this is convenient since a 94 lb. bag of cement is 1 cubic foot of bulk material). For a 3/4" maximum coarse aggregate, the mixture would be 1 part portland cement, 2 1/2 parts sand, 2 1/2 parts coarse aggregate, and 1/2 part water. The sum of the parts is 6 ½. In general the final volume of concrete produced will be approximately 2/3 of the sum of all the volumes included in the mixture. Therefore the approximate volume of this concrete mixture is 4.3 cubic feet. There are 27 cubic feet in a cubic yard so we divide 27 by 4.3 giving 6.2 batches for a cubic yard. Plan on making 7 batches to assure that you will have more than enough material at the start of the job.

In short, use the mixture indicated for the 3/4" aggregate and use 7 bags of cement, 17.5 cubic feet of sand, and 17.5 cubic feet of ¾ in. coarse aggregate unless you feel comfortable recalculating for a different size coarse aggregate.

The volume calculation for concrete is based on length x width x height to determine the cubic feet of concrete required for the project. EX: 20' * 12' * 0.5' = 120 cubic feet (be sure you always convert all of you measurements into feet units). This quantity is divided by 27 (there are 27 cubic feet in a cubic yard). 120 / 27 = 4.44 cubic yards. A word of caution, an increase in thickness of 1/2" would increase the required concrete by .37 cubic yards. Be sure that you order a little more material than you need.

Typically it is impractical to use bagged materials or hand mix concrete if the quantity exceeds one to two cubic yards because bagged materials and hand mixing require you to handle the materials several times. A cubic yard of concrete will weigh almost two tons and handling the material three to four times to transport and mix the material requires considerable labor. Hand mixing two cubic yards of concrete is the equivalent of handling 12 to 16 tons of material. As an alternative ready mixed concrete can be delivered and simply be unloaded from the truck to its final position using the chute on the truck or in some instances the concrete is discharged into wheel barrows simplifying the concrete placement. Most ready mixed concrete producers have minimum requirements for yardage, and short loads may include additional charges to offset delivery costs. Concrete is sold in increments of 1/4 yard so your concrete order for the preceding example would be 4.5 cubic yards. Again, be sure to order a little more than you need since charges for short loads to correct this kind of mistake can be very expensive.

Take care and good luck..............

Thank you for the clarification!

Hi ConcreteRestoration,

Not sure how I helped, but glad if I did!

Are you doing some concrete work, or are you an expert, and are just qualifying my post/s? Sorry, just being nosey.

I would suggest a visit to, "American Concrete Institute", "Aggregate Research Industries", or "Portland Cement Association", web sites to obtain this type of information. Forums such as ARI are very active, with worldwide participation [even Italians], from a bunch of " Old School " people.

More important than a Manager knowing of a mix design [called for in a specification by an engineer] is that managers be able to educate members of an association on Why a Repair is Needed, Different Repair Scenarios, Longevity of a Repair and in choosing a Competent Company.

Thousands of concrete repair companies can discuss, mixes, demolition, and patching but can't explain Anodic Ring Effect. What good is a repair that causes more aggressive corrosion to occur in three years necessitating another much more expensive repair. Chasing the Steel is a game that unfortunately, too many people play.. The mix may be appropriate for a repair -- just not compatible with the host material ! No Substitute for Hiring an Engineer and Contractor that understand corrosion of concretes.

Who the hell cares about 'Anodic Ring Effect' for concrete repairs in condominium complexes? Presumably, the repairs are to sidewalks and driveway areas. In that case they are exterior and would require air-entraining admixtures if they are in a climate that will experience freezing temperatures. Typically, in today's world, ready-mix concrete is ordered by its desired 28-day compressive strength, not by the amount of cement in the mix. There are plenty of mix designs submitted to batch plants by customers whose engineers have specified the ratios of ingredients and, the most important, water-to-cement ratio. If one simply orders mix to a desired strength value, say 3,000 psi, he/she will be provided with a suitable product. A very important issue, particularly with 'old school' cement contractors, is the management of the amount or water that they add during placement to make their work easier. The addition of too much water will weaken the concrete and could cause surface crazing or cracking as well as a poor resistance to premature surface wear.

If the project is in a climate that experiences feezing during the winter months, the time of placement is also important, as the latent moisture in the finished product takes a couple of months to dissipate to the extent that surface spalling does not occur during feeze cycles. This aspect is further exaccerbated by the inordinate use of additional water during placement. Further, in cold climates, only aggregates that are not susceptible to moisture absorption should be used for the mix, as soft, absorbent aggregates can retain moisture, then freeze and burst near the surface, causing spalling. Additionally, there are a number of more sophisicated issues with premature deterioration of concrete that are peculiar to certain regions of the country and the combination of variables that are associated with those regions. Simply put, it is anything but simple.

If you are truly interested in obtaining the best bang for your buck, you should consider seeking the consultation of a reputable materials testing lab in your area, as they are very familiar with the vagaries of concrete materials in their marketplace.

I am going to ask the next concrete contractor that bids one of my sidewalk repair jobs if his work will cause the "Anodic Ring Effect". (HaHaHa) Extra water in the concrete? That's hilarious. I have seen guys run the concrete truck out of water wetting up the concrete. Call a ready mix company and feel confident about getting a suitable product? Funny. I had 2 trucks on reserve for the mornings with a finish load from each truck. I wanted to get all my concrete poured before 2:00 because after 2 the drivers got too tired to wash out and I would get a hot load, or I got what I called the 10" slump load from the batcher not paying attention. I wouldn't be able to get a wheel barrel load from a ready mix company if I had the concrete tested. The Ohio Ready Mix Associations "handbook" says concrete shouldn't be on the truck more than 90 minutes or it should be sent back. Right,,,I sent a hot load back once. I had to switch companies, the one I sent it back to wouldn't take my calls. Small residential concrete work has no resemblence to commercial or public jobs,, at all. I loved it in spite of or because of all the challenges, but I am too old to be a woman out there beating myself up. I am happy now to be the person getting the bids.

Hello all,

Just a note to say the GA's are very welcome. Many thanks to those who voted!

Take care...............

I order it by the yard and with a PSI rating .

What I thought would be a simple question,,, "Does anyone out there know the psi of the different bag(sack) mixes". Example 3000psi is what bag mix? 4000psi and so orn. Or to put it the other way,,, what is the psi of 3bag, 4bag, 5bag, 6bag and so on? Apparently engineers don't know what it is or can't figure the question out.

We always ordered however many yards of concrete we needed for the day in terms of the bag mix,,, I just can't remember the psi. Example---if I was pouring a typical residential driveway and sidewalk I would order "X" number of yards of 6bag mix with air.

Now does anyone know the answer?

Hello JMCpropmgr,

Not sure if this answers your question fully?

Ready Mix Concrete Mixes are often referred to in terms of how many 94lb bags of cement are in each cubic yard of concrete. The most common residential mixes are as follows.

3000 psi or 5 3/4 bag mix
3500 psi or 6 1/2 bag mix
4000 psi or 7 bag mix

Concrete Strength

a. based upon bag mix

5 bag mix or 470 lb per cubic yard = 2500 psi

5 1/5 bag mix or 517 lb per cubic yard= 3000 psi

6 bag mix or 564 lb per cubic yard = 3500 psi

6 1/2 bag mix or 611 lb per cubic yard= 4000 psi

for concrete that cures hard faster specify 51/2 bag mix at 4000 psi

b. based upon water-cement ratio theory (pound of water per pound of cement)

0.75 - 2000 psi
0.68 - 2500 psi
0.62 - 3000 psi
0.56 - 3500 psi
0.50 - 4000 psi
0.45 - 4500 psi
0.41 - 5000 psi
0.38 - 5500 psi
0.34 - 6000 psi

Hello JMCpropmgr:

I found this as I was searching for psi linked to bag/mix.

(Before you start to get into the extra strenght concrete for high-rise building).

It would seem from this, that maybe up to a 7 Bag mix at least the rise in 'bags per mix' equals this equation.

1/2 bag = 500 psi. What do think think?

Basic standard concrete.

Bag Mix/psi Chart

4 Bag 1500 psi

4.5 Bag 2000 psi

5 Bag 2500 psi

5.5 Bag 3000 psi

6 Bag 3500 psi

6.5 Bag 4000 psi

7 Bag ...

Hope this helps.

Take care

YEA!! finally!!!! now I remember!!!!! All I wanted to do was make a general reference guide for those unfamiliar with the terms a small residential concrete contractor might use in a bid.

Thank YOU!!!!

Hello JMCpropmgr,

No problems! Just put my thinking hat on............Mind, is will cost you!

You no I did not think to look but CR4 has hundreds of formulea and it may wekk be in there?

Are you watching (Chris Leonard) Can you put this Chart for concrete mixes against strength in psi, in the CR4 Archives?

Take care........................