Product
Pile Cap Formwork
The pile cap refers to the reinforced concrete platform set on the top of the foundation pile to connect the top of each pile in order to bear and distribute the load transmitted by the pier. The cap is the connecting part of the pile and the column or pier. The pile cap connects several or even a dozen piles together to form a pile foundation. The plane shape of the pile cap depends on the arrangement of the piles and is usually rectangular or strip-shaped. For the pile foundations of structures such as wharves and bridges, the pile tops are often higher than the ground or river bottom. This kind of pile is called a high pile, and its cap is called a high pile cap. For the pile foundations of industrial and other civil buildings, the top of the pile is often lower than the ground. Such piles are called low piles, and their caps are called low pile caps.
Pile caps are constructed by excavating an area around the group of piles to enable formwork to be inserted. The pile tops may be trimmed to ensure they are at the same height. A reinforcement cage is then built and positioned in the formwork cast box and fastened to the piles. The concrete is then poured and left to cure, after which the formwork is removed.
Pile cap used to transfer the loads from the superstructure to the piling. The pile cap is a thick concrete mat that rests on piles. It is part of the foundation and used to distribute the loads over the piles. Piles used when the soil bearing is not enough to carry loads of the structure.
Pile Cap Construction Procedure
Excavation Around Piles
After 7 days of the casting of the pile the concrete will gain approximately, 70% of it is compressive strength. The soil around piles will be removed to the required levels and dimension that allows the construction of the pile cap. A step shall be made if the excavation is more than 1.5 m to prevent soil collapse.
Pile Head Cutting
Concrete will be removed up to cut off level. If concrete under the cut off level is unsound. It shall be removed, and the pile will be repaired. The pile must be free from cracks and unsound concrete.
Blinding Concrete
After completion of concrete cutting for piles. Blinding concrete shall be cast. Following points illustrating the procedure for pile cap blinding concrete.
1.Soil shall be removed and leveled to the formation level. The formation for blinding concrete shall be compacted properly and tested for field density tests.
2.Two layers of polyethylene sheet will be laid above the formation layer.
3.Now you can cast the blinding concrete. The thickness and dimension should be matching to shop drawing.
4.Termination grooves (2x2 cm) shall be provided to blinding concrete to terminate the waterproofing for pile cap and blinding concrete.
5.The blinding concrete will be cured for a minimum of 24 hours.
Waterproofing for Blinding Concrete
To prevent groundwater ingress from the pile cap bottom. It is recommended to waterproof pile cap blinding, especially in areas of the high water table and harsh environment. The sequence of waterproofing is as follows.
1. To obtain strong adhesive, it is essential to clean the blinding concrete thoroughly from any dirt or debris.
2. A chamfer shall be cast around piles head to provide a smooth transition between piles head and pile cap.
3. The surface of blinding concrete shall be painted with primer. Primer shall cover the area evenly.
4.Before laying of the waterproofing membrane. The surface of the primer shall be cleaned thoroughly to enhance the adhesive of the waterproofing membrane. The membrane shall be overlapped sufficiently to prevent water flowing from weak joints.
Protection of Waterproofing
Waterproofing shall be protected to avoid damages during the construction process. The protection depends on the alignment of waterproofing.
1.Screed: screed will be provided for horizontal waterproofing such as blinding concrete waterproofing. To protect the waterproofing from any damage during fixing reinforcement and shutter for pile cap.
2..Protection board: This board will be used for vertical waterproofing such as waterproofing for pile cap.
Reinforcement Fixing for Pile Cap
Pile cap reinforcement shall be fixed as per approved drawing. In the field, the designer will provide you with the shop drawing for each structural element. These drawing shall consider as a guide. However, there are some important points. That should not be ignored.
1. Enough cover block should be provided to maintain the required cover. Maintaining the needed coverage is very important, and ignoring cover requirements can lead to reducing structure durability. The importance of cover can be briefed in the following points
2. The concrete cover will form a barrier between reinforcing steel and corrosive agents such as chloride.
3. Protect reinforcing steel from concrete carbonation. Concrete carbonation can cause steel corrosion.
4. Fire Protection: concrete cover will protect the steel from fires and prevent steel from melting.
5. Enough chairs shall be provided to maintain reinforcement rigid and avoid movement and deformation during concreting.
6. Dowel (starter) bars shall be provided for the pier column. Dowel bars shall be adequately braced to avoid movement during casting. Also, dowel bars shall be maintained vertical
Formwork Installation for Pile Cap
1. The engineer will provide a detailed drawing for the pile cap shutter and the required supports such as jacks, tie road. In the field, the fabricated shutter shall be identical to the provided drawing.
2. Corner chamfer shall be fixed on all sides and top of the shutter to provide a smooth edge.
3. The concrete cover should be maintained after fixing the shutter as shown on the drawing.
4. The alignment and verticality of the shutter shall be checked by the surveyor.
5. The kicker and shear key shutter for the pier shall be fixed and location checked by the surveyor. Thermocouples shall be fixed before the concreting of the pile cap to measure the temperature difference between the top, middle, and bottom of pile cap concrete. Thermocouples used to monitor the differential temperature between different concrete layers in case of mass concrete. The differential temperature should be less than 20 C. If the differential temperature increased more than 20 C, this could cause tensile stress more than concrete strength, which can lead to internal cracks.
6. Prior to the concreting the area should be clean and free from any dirt.
Concreting of the Pile Cap
Before the concrete pile cap area should be cleaned again. In the events of dust or sand accumulation. The blower should be used to assure removing all dirt. If the temperature during casting of the pile cap is high, then the shutter shall be sprinkled with water to prevent the plywood from absorbing concrete moisture. A sufficient number of vibrators and a competent person should be present during the casting process to produce a dense concrete surface free from honeycombs. Concrete shall be cured for a minimum period of two weeks. The concrete surface shall be covered with a hessian sheet, and it shall be kept wet all time during the curing period.
Waterproofing for Pile Cap
Waterproofing of the pile cap is similar to the waterproofing of blinding concrete. The a significant difference in the way of protection for the waterproofing membrane. The Protection board will be used for pile cap walls. But for pile cap top screed concrete will be used to protect the waterproofing membrane.
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