Concrete Pump Truck Arriving
On Tuesday of this week we poured the first structural walls of our Big Project, our future on-farm slaughterhouse and butcher shop. We had been waiting for the right warm weather – With the cold snow the warm air caused a heavy mist to shroud the mountain. On Tuesday it got up above freezing so I called S D Ireland, the concrete company, and they sent out a pump truck at about 11:30 am. This pumping of concrete was sandwitched inbetween two farm tour groups from the New England Culinary Institute (NECI) so it was a particularly busy and exciting day.
The concrete mix was 14 cubic-yards of 3500 PSI air entrained concrete with a 3/8″ grit, hot water, fiber, 2% PolarSet non-chloride curing accelerant and Super P flow agent.
Grasshopper Legs & Boom Extending
The 3500 PSI refers to the compressive strength of the concrete. This is medium grade concrete suitable for walls – the basic used for most projects. For high traffic floors, roads, sidewalks or bridge surfaces one would want a higher PSI to resist wear going up to 4500 or even 5000 PSI.
Pump Truck Front View
Those grasshopper like stabilizing legs are steel booms with steel feet that make contact with the ground. If I held onto the hose with the concrete flowing and touched one of our pieces of rebar I got a good 1,000 volt shock – back flow from our livestock electric fencing. This suggests a problem with the grounding, possibly related to going into winter. I quickly learned to hold onto the wooden form work and avoid touching the rebar whenever possible…
Air entrainment means little bubbles in the concrete that give it flexibility in freeze thaw conditions like Vermont’s annual cycle. In the final building it will be very thermally stable but until we are closed in we must deal with the real world.
We used 3/8″ stone, what they call grit, instead of the normal inch and a half stone in order to make it flow better through the pump, forms and in the tight spaces under doorways and blinds. This cost a little extra but means we get a more solid pour even in small spots.
Long Arm of the Extended Pump Boom
The concrete company starts using hot water November 1st. The hot water is needed to bring the temperature of the concrete and cold stone up to 70°F when the fresh mix met our rough cold slab. This helps to make a better union and it helps with the initial setup of the cure. Our forms are insulated with 2″ to 6″ of pink foam closed-cell insulation. That helps to retain that large number of BTUs so the concrete will have time to cure before it chills.
Fiber might not seem necessary since we have steel in the walls in the form of 661010 Welded Wire Mesh (WWM) and #4 (1/2″) rebar rods but there are thin places in the walls where we have blinds for future potential doors and windows. The fiber reduces cracking in thin areas. The blinds are sort of like a waffle effect in the wall.
The reason for using an accelerant is we were pouring in cold weather. Keep in mind that the point with concrete is not to dry it but to cure it. This is a chemical process that hardens the material to a solid – very different than mud, which concrete is sometimes called. To cure the concrete needs to stay warm. It is an endothermic reaction, generating some heat, but not enough to keep active in our cold weather. Having insulated forms helps to keep the heat in the concrete so the mix does not freeze before curing. We also covered the tops of the walls when we were done to help keep the heat in the forms.
The reason for the accelerant being non-chloride based is to protect the steel work in the concrete, the iron of the rebar, welded wire mesh and threaded rods, from corrosion. I like the PolarSet and used it at 4% when we built our Tiny Cottage, which we also did in this weather. We put the concrete ferrocement roof of our cottage on during freezing weather and it is only 1.5″ thick. I found that I could pour far below freezing and still produce excellent concrete.
The super plasticizer make concrete wet more easily which means less water can be used to achieve a very fast flowing concrete that goes through the pump and thin wall spaces easily. This mean we could place the end of the pump hose at each corner of the forms and then it flowed each way about 15 to 20 feet with about 2′ of head in the forms. This cross flow speeds up the pouring process.
Contrary-wise, I didn’t want things going too fast as we needed to watch the forms. This was our first tall pour over 4′. I’m not ready to do higher forms, yet, which involve a lot more force. I feel confident that my design of the forms is good but I lack real world experience in the greater heigh so we’ll take it a few baby steps at a time. In line with this we had the first truck come and place about 18″ of concrete all the way around the forms, a short delay while that stiffened and then the second truck came to bring the forms up to the slightly higher than 4′ of this first structural ring.
View from Middle Whey Tank Camera
Previously we had used back dumping and then front dumping trucks with their higher chutes and an extension position up hill of the foundation. Now we were too high. The pump truck was a must have at this point because our outer wall ring was almost 9′ tall up on top of almost 4′ of foundation as seen from the road side. The pump truck has a six inch diameter hose that is about 10′ long of flexible black rubber like material at the end of the 30 meter booms.
Brad the Pump Truck Man – One Smooth Operator
The pump truck operator controlled the booms and turned the pump on and off. I held the end of the hose in the forms and got splashed with concrete. My heavy work suit got heavier and my hard hat with face mask made the process more pleasant! The process went amazingly smoothly. I had done this once before, about 20 years ago when putting a foundation under the old farm house. In the intervening decades I had forgotten most of the details but fortunately it was pretty easy to do with a good pump truck operator at the controls.
Pump Truck Sky View from Inside Form Work
I held the end of the hose in place Will, Holly and Ben stood on opposing sides of the forms watching for leaks and signs of danger. Everyone stood back, except myself who was standing up on the forms. The rule was if anything goes wrong, move away, not toward the form work. We are puny little people who can have no impact once something goes bad. We simply have to get it right when we’re building all the forms. Once the concrete’s flowing there is little you can do to change the situation other than going slowly and backing off if something looks alarming.
We built the forms up the full height in the administrative and smoker area as well as the abattoir but in the reefer section of the building we left the inner forms down at about 56″. The reason is the insulation is much more complex in there. Doing all 9′ at once would have been difficult plus I just wasn’t comfortable pouring 9′ walls in one shot – that’s a lot of force.
Concrete Delivery to Pump Truck
As the 28 tons of concrete poured into the forms the wood vibrated, creaked and groaned. The threaded rod tightened up, sometimes making alarming snapping sounds as form work found its resting place. Exciting. It all held though. Nothing gave and nobody got hurt. It was a well and boring pour as we like to say. There was one very tiny leak at the farm kitchen door of about a gallon of concrete. Will plugged that small hole up as I worked on filling another section and then I came back to that section to finish it.
Just as we got finished with our third pass around, gradually adding height to the walls, the second tour group arrived. I went out to guide them around the farm while Will and Ben finished off the concrete surfacing and gathered up tools to wash up.
Ben’s Nano-Snowman Observer Watched Everything
A boring pour. A great pour.
Outdoors: 17°F/-6°F Sunny
Tiny Cottage: 65°F/54°F