8.8 : 事前配置骨材コンクリート

Preplaced aggregate concrete is produced by initially placing gap-graded coarse aggregate that is sufficiently wet within the formwork and compacting it.

The remaining voids, constituting about one-third of the total volume, are then filled with mortar comprising Portland cement, pozzolan, fine aggregates, water, and a fluidizing aid.

Alternatively, a cement and fine sand mortar, blended in a high-speed colloid mixer, can be used.

The mortar is introduced under pressure through slotted pipes about 1.5 inches in diameter spaced at regular intervals. The pipes are then gradually removed as the mortar level rises.

External vibration at the top level of the mortar can improve the finish of exposed surfaces.

Preplaced aggregate concrete exhibits uniformity with reduced segregation and is used in constructing nuclear shields and underwater projects.

Water-retaining structures, large monolithic blocks, and repair works also use preplaced aggregate concrete due to its low shrinkage and reduced permeability.

In large construction projects, before applying mortar, circulating chilled water around the aggregates controls the heat of hydration, and in cold conditions, circulating steam warms up the aggregates.