HOW TO EFFECTIVELY ESTIMATE CONCRETE PROJECTS.
When estimating the construction cost for placing concrete for footings, columns, slabs on grade, walls, beams, post tensioned slabs and other items, in addition to material and equipment, you need to considerer in to you construction bid, the next five categories of labor:
- Formwork preparation.
- Embedded items placements.
- Placement of concrete.
- Finish and cure.
- Formwork removal.
1. Formwork Preparation.
Concrete is placed in fluid consistency and must be contained in formed, normally build with wood or metal, or a combination of both, either you choose wood or metal, the cost will be listed in your concrete estimate, make sure you get the right price from your vendors.
The formwork labor cost include earth excavation for foundations, the next step is set up the forms to the proper elevation, this task is performed by your survey team, in columns, slabs, beams, walls and others, aligning the wood or metal forms become critical, to get the best result, bracing process is always require. Make sure your survey team check every form before pouring concrete, a wrong formwork set up will produce an extra cost, that maybe you are not include in your construction estimate.
2. Embedded Items Placements.
Labor will be require for the adequate placement of the embeds in to the concrete, normally these are metals embeds, steel plate columns, anchor bolds, beam connections, rebars, corner plates, angles, metal drainage, and more, when you are set up formwork, the survey team need to complete the layout of all elements mentioned before, some project will require more work and time, for example in tilt wall projects, you will found embed plates in every concrete panel, in the other hand, a conventional two story building will require a couple of hours for your team.
The type of jobs will affect directly the labor cost related to the placement of embeds.
3. Placement Concrete.
Once the concrete is delivered to the job site, you need to move the concrete from the truck to the final location, so, you need to consider in to you construction concrete estimate all cost equipment and labor, you can use chute, wheelbarrow, placing boom, pump truck, concrete hose and crane. Also the labor required will depend of the equipment you decide to use and the nature of the work that you are doing, different cost for different works, columns, beams, slabs or foundation.
The next step when the concrete is placed is the vibration and screed to the desire level. When a small amount of concrete is necessary, the labor cost associate to complete the work will be the necessary to mix the concrete, on this days, the ready mix-concrete bags just require the addition of water.
4. Finish, Protection and Cure.
The next cost to include in our concrete construction estimate is the finish and cure, after you vibrated and screed the concrete to the require elevation, the next step is finishing the surface, we need to make the surface free of void and unevenness.
As we know the concrete require chemical action to change it from fluid to solid condition, this reaction produce internal heat in the concrete, we recommended check the weather when you are pouring concrete, a fast concrete hardening process can generate cracks. To reduce the risk of cracks, we need to cover the surface concrete with polyethylene or curing compound, do not forget to add this cost in to your construction bid.
Concrete need to be protected from any form of precipitation before the setting process, drops of water causes small craters in the finish surface, ruining the quality of the finish and reducing the cement ratio of the concrete mix, making weakness at the top surface.
5. Form Removal.
The final step is the removal of the formwork once the concrete get hard, this operation include separate the form from the concrete, the removal of nails from the forms, cleaning the form removing the small concrete particles, prepare the form for the next use, apply the form release agent, and moving the forms using equipment and hands.
Make sure to complete the process of cleaning forms in the proper way, this allows us to reuse the forms as many time possible, reducing the cost for materials and labors in your concrete price.
Concrete formwork is estimated using the surface area of the form that is in contact whit the concrete. This is normally called as "contact surface". Then you need to categorized the quantities in groups like; beams, columns, walls, etc.
Conclusion.
These are the basic operation to be included in to you concrete estimate, the cost of labor may vary according to the experience of your team, this could affect your production rates and material cost, inexpert carpenter can make you spend more in materials, because they always want to use new sheet of plywood or lumbers. Have always a trained supervisor, to take care of the material use.