Preplaced aggregate concrete is ideal for construction environments that are not easily accessible. The process begins by properly wetting the gap-graded coarse aggregates to remove the dirt, then placing it in the form and compacting it. Voids are filled with a mortar mix pumped under pressure through slotted pipes. This mortar typically consists of Portland cement, pozzolan, fine aggregates, water, and a fluidizing aid. The pozzolan helps reduce bleeding and segregation while improving the fluidity of the mortar, whereas the fluidizing aid delays the setting of the mortar. A cement-fine sand mortar is also used. It is prepared in a high-speed colloid mixer to keep the cement suspended until the mortar is pumped. As the mortar rises to the top, the pipe is gradually withdrawn. Applying external vibration to the top layer of the mortar can enhance the finish of the exposed surfaces.
Preplaced aggregate concrete is favored for its uniformity and reduced risk of segregation, which is essential for constructing nuclear shields and underwater projects. Due to its low shrinkage and permeability, preplaced concrete is used in water-retaining structures, large monolithic blocks, and repair works. In large-scale construction, refrigerated water is circulated around the aggregates before adding the mortar to control the heat from cement hydration. In contrast, steam is circulated to prevent frost damage in cold conditions.
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.
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