Pouring concrete foundation is a considerably important phase of foundation construction and plays a vital role in the success of a project. Proper planning, suitable equipment selection, and good placement practice shall be adopted for concrete pouring of foundation to make sure that it corroborates the drawings and specifications.
Although the details and consideration are not entirely the same for different foundations such as shallow and deep foundation, however, essential practical considerations and pouring procedures are similar. Greater details regarding pouring of concrete can be found in ACI 304R-00 (Guide for Measuring, Mixing, Transporting, and Placing Concrete).
Planning for Pouring Process
Adequate planning is crucial since it guarantees sufficient and consistent supply of concrete. The Adequate placement capacity shall be insured to prevent cold joint formation during concrete pouring. Here are some points one should be heedful of when planning to pour concrete :
1). Concrete pouring machinery shall be cleaned and kept in good condition. To avoid unnecessary delays, concrete placement equipment should be arranged in an organized way and the manpower should be enough to ensure the proper placement, consolidation, and finish of the concrete.
2). Concrete should be delivered to the site at a uniform rate compatible with the manpower and equipment being used in the placing and finishing processes.
3). Concrete placement should not begin when there is a chance of atmosphere reaching freezing temperatures, unless adequate facilities for cold-weather protection have been provided (ACI 306R). Curing measures should be ready for use at the proper time (ACI 308).
4). Finally, inspection of the foundation, construction joints, forms, reinforcement, and any other embedments in the placement should be made immediately before the concrete is placed.
Prior to the start of concreting, forms should be protected from deterioration, weather, and shrinkage by proper oiling or by effective wetting. Form surfaces should be cleaned and of uniform texture. When re-utilization is allowed, formworks shall be properly and oiled. Lastly, it is recommended to apply oils to the formwork before reinforcement and other embedments are placed.
Reinforcement and Embedded Items
At the time of pouring concrete, reinforced steel and embedded items should be clean and free from mud, oil, and other materials that can adversely affect the steel’s bonding capacity.
Correct size, length, splices, and position of reinforcements and sufficient concrete cover shall be checked. Bars and embedded items should be held securely and the supports shall be adequate to carry expected loads before and during concrete placement.
Selection of Concrete Pouring Equipment
When choosing concrete placement equipment, consider the ability of the equipment to place the concrete in the correct location economically without compromising its quality.
Equipment selection is influenced by the method of concrete production. Certain types of equipment, such as buckets, hoppers, and buggies suit batch production; whereas other equipment, such as belt conveyors and pumps, are more appropriate for continuous production.
Before concrete pouring begins, care shall be taken to prevent concrete stream separation due to free falling over rods, spacers, reinforcement, or other embedded materials. Concrete should be deposited at or near its final position because it tends to segregate when it has to flow laterally into the place.
Internal vibration is the most effective method of consolidating concrete for most applications. Vibration machine should be inserted and withdrawn vertically so that they quickly penetrate the layer and are withdrawn slowly to remove entrapped air.
Concrete re-vibration can be carried out till running vibration machine sink into the concrete under its self-weight. Re-vibration of concrete improves compressive and bond strengths.
Construction joints are observed wherever concreting is stopped or delayed and freshly poured concrete fails to integrat with the previously placed concrete.
Horizontal construction joints form at the levels between lifts, whereas vertical joints occur where the structure is of such length that it is not feasible to place the entire length in one continuous operation.
The surfaces of all construction joints should be cleaned and properly prepared to ensure adequate bond with concrete placed on or adjacent to them.
Finishing Concrete Surface
After concrete compaction, the operations of screeding, floating, and first troweling should be performed in such a manner that the concrete can be worked and manipulated to gain the desired result.