Friday morning 10 AM.
We were scheduled to pour 10 yards of cement..(40,000 pounds worth) for a new garage. When the cement truck driver stepped out of the cab, there was a nervous look in his eyes….
“It is already down to a 2 inch slump…I started out with 4 inch when I left the plant, and that was only 10 minutes ago.”
Come with me for a moment into the world of concrete….
Ever noticed how every vocation has its own lingo? You either know it or you don’t. Same goes for concrete. I’d like to give you a very basic working knowledge of the trade. You never know when this might come in handy 😉
Concrete (or cement) is measured in cubic yards…ie. a three ft by three-foot by three ft mass is one cubic yard of cement. A fully loaded cement truck can haul ten yards.
You purchase it in 1/4 yard increments.
Concrete is sold in various mixes…the higher the number (#3000, #3500, #4000, etc) the richer the mix. The stronger the mix, the easier it is to smooth out if it is going to be a floor.
Concrete becomes hard due to a chemical reaction. Heat and cold affect the speed of the chemical reaction. This time of year (late Fall) we begin to add various things to the mix to help speed up the process, because otherwise, the cement will just lay there…and if the temperatures are hovering close to freezing, you run the risk looking loosing it completely.
One of the most common additives is Calcium.
1% calcium will cut the curing time by 50%…2% will make it set up 4 times faster. (Are you still with me? ) Another variable is the temperature of the water…This time of year, you can also order concrete with hot water, which will also speed up the set time.
I need to tell you about slump.
Slump is how we measure the consistency of concrete… (wet or dry)
You take a one foot tall cone and fill it with concrete…stir it up then dump it. Measure how much it settles (slumps) (ie. If you have a 4 inch slump, then the pile has settled 4 inches) If you have a 6 inch slump, it is quite a bit wetter and has settled…. how much?
When I ordered the concrete Friday, I requested a 4 inch slump. That is the perfect consistency for placing without compromising the strength.
Side note…The higher the slump, the weaker the finished product. If someone is pouring your driveway, and they are the lazy type, they may pour a 7 or 8 inch slump. Very easy to work with, and you will be none the wiser. Not until a year or two later, when the new concrete starts to break up. SO, if you EVER, hire someone to pour any concrete for you…walk up to the foreman and ask him what slump he intends to pour? You will do two things. Probably stop him dead in his tracks, because no one ever asks that question, and two, he will realize he is working with an informed consumer. 🙂
If it is anything more than a 5, you tell him that is not acceptable. Basically he is selling you an inferior product. Unless you are on some type of state inspected commercial job…no one EVER inspects the slump. I see this sort of stuff happen all the time.
Anyway, the driver was nervous because in the ten minutes it took for him to drive from the concrete plant to me, it had gone from a 4 inch slump to a 2 inch slump. We potentially had what is called a “hot load” on our hands, where the concrete sets up so quickly, within minutes, you have a large blob of grey molten rock that has turned to stone.
I got nervous because, while a 24 ft by 24 ft garage slab is a slam dunk for a regular concrete crew we were not a seasoned crew. The four of us had never all worked together , and 2 of the 4 had done very little concrete work.
So, there I was with 40,000 pounds of concrete with 1% and hot water with a 2 inch slump, that needed to be placed and troweled, and I only had minutes to act.
Here we were, Friday morning before the truck arrived…
Little did we know.
Like I just did here for you, I would LOVE to learn a few snippets from some area of your life, that may be helpful to me and the average person probably doesn’t know unless they run in those circles… (ie. work related, hobby related, investment related, relationship related, etc, etc.DM
In case you were wondering…
Just finished power troweled garage floor
It turned out stellar!
Stellar: informal definition – exceptionally good; outstanding.