Placing concrete is unique to almost every job and must be considered during the bidding stage and also long before the concrete trucks arrive. Finishing concrete can often be considered a ‘constant’ but placement and placement conditions can often vary widely. There are distinctive logistics to each project site and it’s conduciveness to productive concrete placement from the ready mix truck to the concretes final location.
There is an urgency to concrete placement that is like few other trades in that the material only has a small window of time to be placed easily and requires considerable manpower, tools, skill, and equipment to place due to its mass and weight. Because of this, meticulous planning is required with the concrete supplier, the placement tools and equipment required, and the manpower needed to get the concrete off the truck, placed, and in a ‘finishable’ condition.
Concrete is most commonly delivered in a ‘ready mix’ truck and lowered down a chute into the pump, buggy, or final placement location. The ideal situation for concrete placement is to get the concrete truck close to the final placement location and place the concrete direct with the chute on the ready mix truck.
Sometimes the concrete truck will not be able to reach directly with the chute and will require some other means to get it from point A to point B. Examples of such placement means from simplest to most complex are wheelbarrows, concrete ‘Georgia’ buggies, conveyors, and concrete pumps.
A wheelbarrow is often used for moving and placing small amounts of concrete, often a 3 cubic yard pour or less. Anything greater than 3 cubic yards can be time consuming, can risk the concrete setting up before placement/finishing has been completed, and thus will require additional manpower.
A Georgia buggy is a gas powered, stand-on, ride able buggy with a tub that will often carry a little over a half of a cubic yard. The Georgia buggy will typically travel 5-9mph and the tub is dumped by way of a motor.
A concrete conveyor is either mounted on the concrete truck or will be a standalone truck, often equipped with outriggers for stabilization. The concrete truck will place the ready mix concrete onto the hopper/conveyor which will convey large quantities of concrete into place.
A ready-mix truck mounted conveyor can typically reach from 25-40’ depending on the truck. A standalone telescopic belt conveyor truck can typically reach up to 120’ or more.
A concrete pump refers to a large pump truck equipped with outriggers and a long hose/boom assembly which pumps the concrete into place. Plasticizer is typically required in the concrete mix and the pump trucks boom and hose assembly can often reach up to 170’ for larger trucks and up to 120’ on smaller models. Concrete pumping is considered to be the most efficient way to place concrete and is the preferred placement approach for big concrete pours and hard to reach areas.
The most common hand tool used for placing concrete flatwork is a concrete rake or ‘mover’, also often called a ‘come along’. It is similar to a garden rake in appearance but has a flat solid head for pushing and moving concrete into place.
When placing concrete flatwork, the crew often must ‘eyeball’ the required amount of concrete that must be placed in certain areas to assure when the screed passes there will be no low spots which can later collect and pond water. When placing concrete it is important not to overwork the material as this can lead to segregation and a paste working its way to the top of the concrete which often has a higher water cement ratio than the rest of the concrete mix.
Once the concrete is rough placed, it is then ‘struck’ off with a screed which passes over the top of the concrete. The strike-off tool is often guided by the perimeter forms but in large areas must simply be ‘eyeballed’ in terms of elevation. This screed action pushes excessive concrete behind the screed leaving a rough semi-finished top of concrete elevation and grade.
At this point the placement operations are mostly complete (aside from adding concrete to low points and missed areas and spot rescreeding with a straight edge or darby) and the finishing operation will soon begin.