コンクリートの打設

Placing concrete close to its final position minimizes segregation, where heavier aggregate particles separate from the cement paste during transport. This ensures uniform material distribution and consistent strength throughout the structure. Avoiding excessive movement preserves the concrete's workability and quality.

Compacting concrete expels entrapped air pockets that weaken the material and reduce durability. Vibrating concrete removes these voids, creating a denser, stronger structure. Proper compaction must occur before the next layer is placed while the underlying layer remains in its plastic state.

Traditional concrete placement uses chutes, buggies, conveyor belts, and pumped concrete to transport material to forms. For vertical surfaces, concrete is filled at a minimum rate of 6 feet per hour to ensure consistent finish quality. These methods are suitable for most horizontal and sloping applications.

Tremie concreting places highly workable concrete in deep forms or underwater using a smooth vertical pipe with water-tight joints. As concrete flows down by gravity, the pipe is gradually lifted while its end remains submerged in concrete, preventing water intrusion and ensuring quality placement in challenging conditions.

Slip-forming continuously places and compacts low-workability concrete using forms that advance horizontally or vertically at a steady rate as concrete sets. This technique enables rapid construction of vertical structures by eliminating delays between placement cycles and maintaining consistent compaction throughout the process.

Cold joints form when considerable delays occur between filling concrete layers in vertical forms. To prevent them, maintain consistent placement and compaction rates, avoid hand shoveling, and use poker vibrators appropriately. Laying concrete in uniform horizontal layers while the previous layer remains plastic ensures monolithic structure formation.

When placing concrete in deep sections, avoid collisions with formwork and reinforcement that can disrupt placement and cause segregation. For inclined surfaces, place concrete in vertical planes against the preceding layer. Careful coordination between placement rate and compaction prevents air entrapment and ensures structural integrity.