How To Keep Your Concrete Mixer Driver Happy

Mort

You don't need a hose to add water. There is a valve on the back of the truck that adds the water directly into the drum from the onboard water tank. If you ever saw the drum rotating at full speed, that means the driver was adding water (because the contractor told him to).

As far as slump, to test it they use a slump cone.



It is precisely 12 inches tall, and is filled with concrete. When you pull it up, the concrete falls, and the slump is the measure of how far it falls. For example, if you pile it in the slump cone, pull up the cone, and the pile of concrete is now 8 inches tall, it has fallen 4 inches, so its a 4 inch slump.

I have never seen a contractor use a slump cone. I only see them on State jobs or huge commercial projects. Contractors can pretty much tell by looking at it (and mixer drivers too), and depending on the quality of their work, they will often pour it wetter so its easier to work with.

yesitsconcrete

morty, you do know your stuff ! ! !

concretemasonry

Many ready-mix companies require the driver to write down if water was added and the approximate amount. Some trucks also meter the amount added and used before "wash-out, if a site wash - out is permitted locally. The notation is usually on the copy/receipt the driver keeps and must be returned.

The reason for the notation on the water addition is that the mix placed was not the same as the mix that was batched for guarantee purposes.

Batch weights and water addition at the plant are usually kept for each batch automatically for accounting purposes also.

Tipping the driver for extra maneuvering and moving to minimize labor savings by the customer is frowned on by the concrete companies and the customers waiting for the truck to get back and reload for them.

Dick

rjordan392

Thanks Mort,
So in the future, what can a homeowner say or demand from the contractor to avoid overwatering? Is it too much to ask for a warranty for one year after installation? In my area, I have seen more cracks in concrete then spalling. I suspect they did not dig out the full 4 inches of dirt.

concretemasonry

In most areas, a ready-mix supplier will guarantee the concrete if used as batched. Here if it is for a driveway. it must be 4000 psi, 5% air entrained. Some people will sell anything, but others will not deliver if it is not that spec and they know it is for a driveway. - We have some tough winter conditions (ice melting daily at below zero up to 32F) and the absorbed water freezing nightly, so the producers have to establish tight requirements for a guarantee.

The suppliers guarantee does not extend to the placement. A contractor or concrete placer is the make-or-break item in the responsibility chain.

Any good contractor can give a guarantee (one year is a little short for durability issues). Shrinkage cracks should be taken care of by the control joints done by the contractor. Spalling is normally due to poor placement/finishing or curing. Spalling due to aggregates is rare since most producers use aggregates and mixes that are approved by the state/county/city. Cracks due to setting (structural) are the responsibility of whoever compacted and prapred the base.

Dick

Mort

As a homeowner, I would say to the contractor that he must not go over the allowable water.

What is allowable water? Glad you asked.

When concrete is batched (mixed together at the plant), the batchman usually batches it drier than spec allows. They do this because the driver needs to wash off the top of his truck, the top fins of the drum, etc. They also allow for the contractor to add a bit of water, so that if it is drier than they ordered (happens all the time), the can add some to adjust the slump. The allowable water is printed on our tickets, along with the computer-controlled batch weights.

Our company will guarantee the concrete if the water allowed is followed.

If they must have it wetter, due to the nature of the pour or whatever, they can use a super plasticizer (aka High Range Water Reducer). I know basically nothing about chemistry, but suffice it to say that it is a chemical that makes the concrete wetter without compromising the strength. It costs a bit to add it, but it will make everybody happy.

And we are required to write down the water added (you get written up at my company if you don't), and every other company that I've heard of is required to also.

And concretemasonry is right, a lot of the responsibility also lies with the contractor. We will guarantee it if it is placed properly (which includes watering).

rjordan392

Good Responces.
Thank you both.

BillyCement

Happens all the time, Mort. Sometimes the inspector takes his readings and leaves. That's when the contractor says "Soup it up.". I say "No problem".

BillyCement

Cracking is usually the result of water getting underneath the concrete. When the water freezes it pushes up against the slab and cracks it. Everything I've poured at my own house is deeper around the edges. The only crack I have is from an earth tremor we experienced years ago. And much of my concrete is well over 20 years old.

yesitsconcrete

while there're many reasons conc crks, wtr isn't the leading cause of any i've ever seen,,, while a ' thicken'd edge ' is an accept'd method of placing slabs/aprons/etc, it doesn't add any strength to tension rqmts,,, look to an incorrect jnt pattern OR jnts placed at the wrong time, instead.

wtr can exacerbate other causes, of course, but alone isn't the cause,,, many think placing's conc's not difficult but, altho it doesn't look like it to many, it is a specialty trade,,, just my $.03 ! ! !

cocobolo

Hi Mort: excellent thread.
Glad you mentioned the air entrainment. We used to have to use 6% up in the Yukon.
In case folks don't know, this air is to allow the concrete to expand and contract a little without breaking. And of course, it is the cold weather in which most of the problems arise.
As to the discussion regarding the contractor adding more water, I have always found that when you get to the final finish, too much water plays havoc with the concrete. The surface appears to get far too weak. A stiffer concrete always seems to finish better. Maybe not easier, but better.
And cost versus pre-mix bags!!! Here one bag of premix is $8+ with taxes. It takes 54 bags to make a yard. That's $432+ for one yard! Gimme the truck anytime!

Mort

I heard a great saying the other day at work, when the contractor said they weren't going to get a pump to do their slab, "We never have enough time to do it right, but we always have enough time to do it over."

yesitsconcrete

finishers ' LOVE ' to bless their work - that's why they carry the mason's ( blessing ) brush - especially when its HOT & they're a guy short on the crew,,, trouble is the finish'd product winds up craz'd & of lower strength than the rest of the slab - even on my own after i specifically told the guy ' NO EXCESS FINISHING WATER ' & ' SAW JNTS THE SAME DAY ! ! ! ',,, he did bless too much & he saw'd the next afternoon in HOT sun so now i've got crazing to shotblast & repair PLUS a couple random crks,,, they only measure .002 after 1 year but they will be a pita to repair as they become working joints.

sick part's i was placing driveways in augusta at the time for 2 1/2 X's the $$$ so i guess i can't really complain as its my fault ' those got pd & they're gone ! '

shumakerscott

I still try and mix my own. Haul in my sand gravel mix. Cement in a bag and mix in a mixer. Larger projects need a truck for sure in certain situations. I will be pouring my slab in my house by hand. I will be asking for advice as things go along. It will be a radiant slab. Dorf Dude...

__________________
Today is only yesterdays tomorrow, Now get to work!

Knucklez

wow, great post. in 2 years time i will be needing a basement pour and it is good to be educated DIY before i call the pro in to assess the job.

Knucklez