Name: concrete placement for tight spaces
Uploaded: 2024-11-07T14:48:35.000Z
Duration: 1 min 29 s
Channel: JoVE

Preplaceed 골재 콘크리트는 거푸집 내부에 충분히 젖은 갭 등급의 굵은 골재를 초기에 배치하고 압축하여 생산됩니다.
전체 부피의 약 1/3을 차지하는 나머지 공극은 포틀랜드 시멘트, 포졸란, 미세한 골재, 물 및 유동화 보조제로 구성된 모르타르로 채워집니다.
또는 고속 콜로이드 믹서에 혼합된 시멘트와 고운 모래 모르타르를 사용할 수 있습니다.
모르타르는 일정한 간격으로 직경이 약 1.5인치인 홈이 있는 파이프를 통해 압력을 받아 도입됩니다. 그런 다음 파이프는 모르타르 수준이 상승함에 따라 점차적으로 제거됩니다.
모르타르 최상부의 외부 진동은 노출된 표면의 마감을 개선할 수 있습니다.
Preplaced 골재 콘크리트는 분리가 감소하여 균일성을 나타내며 핵 차폐 및 수중 프로젝트를 건설하는 데 사용됩니다.
저수 구조물, 대형 모놀리식 블록 및 수리 작업도 수축률이 낮고 투과성이 감소하기 때문에 사전 교체된 골재 콘크리트를 사용합니다.
대규모 건설 프로젝트에서는 모르타르를 바르기 전에 골재 주위를 냉각수로 순환시켜 수화열을 조절하고, 추운 조건에서는 순환 증기로 골재를 가열합니다.

미리 배치된 골재 콘크리트

Preplaced Aggregate Concrete

미리 배치된 골재 콘크리트는 쉽게 접근할 수 없는 건설 환경에 이상적입니다. 이 과정은 틈새 등급의 거친 골재를 적절히 적셔서 먼지를 제거한 다음, 폼에 놓고 압축하는 것으로 시작합니다. 공극은 슬롯형 파이프를 통해 압력을 가해 펌핑한 모르타르 혼합물로 채웁니다. 이 모르타르는 일반적으로 포틀랜드 시멘트, 포졸란, 잔골재, 물 및 유동화 보조제로 구성됩니다. 포졸란은 모르타르의 유동성을 개선하는 동시에 유출 및 분리를 줄이는 데 도움이 되는 반면, 유동화 보조제는 모르타르의 응고를 지연시킵니다. 시멘트-잔모래 모르타르도 사용됩니다. 모르타르를 펌핑할 때까지 시멘트를 부유 상태로 유지하기 위해 고속 콜로이드 믹서에서 준비합니다. 모르타르가 위로 올라가면 파이프를 점차적으로 빼냅니다. 모르타르의 최상층에 외부 진동을 가하면 노출된 표면의 마감을 향상시킬 수 있습니다.


 미리 배치된 골재 콘크리트는 균일성과 분리 위험 감소로 선호되며, 이는 핵 보호막과 수중 프로젝트를 구축하는 데 필수적입니다. 미리 배치된 콘크리트는 수축률과 투과성이 낮아 물을 유지하는 구조물, 대형 모노리식 블록 및 수리 작업에 사용됩니다. 대규모 건설에서는 시멘트 수화로 인한 열을 제어하기 위해 모르타르를 추가하기 전에 냉장수를 골재 주위로 순환시킵니다. 반면에 증기는 추운 환경에서 동파를 방지하기 위해 순환시킵니다.

Preplaceed 골재 콘크리트는 거푸집 내부에 충분히 젖은 갭 등급의 굵은 골재를 초기에 배치하고 압축하여 생산됩니다.
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Education

교육

JoVE Core

Civil Engineering

토목공학

Unit 1

제1단원

Mixing, Placing and Curing Concrete 

콘크리트의 배합, 타설 및 양생

KEY TERMS AND CONCEPTS

주요 용어 및 개념

concrete placement for tight spaces

Preplaced aggregate concrete is used when a construction site is hard to reach. The process starts by wetting gap-graded coarse aggregates. This helps remove dirt from the stones. The aggregates are then placed in the form and compacted.

Next, a mortar mix is pumped under pressure through slotted pipes to fill the spaces between the aggregates. The mortar usually contains Portland cement, pozzolan, fine aggregates, water, and a fluidizing aid. The pozzolan reduces bleeding and segregation and also improves mortar flow. The fluidizing aid delays the setting of the mortar.

A cement and fine sand mortar can also be used. It is mixed in a high-speed colloid mixer so the cement stays suspended until pumping. As the mortar rises to the top, the pipe is slowly withdrawn. External vibration can be applied to the top layer to improve the finish of the exposed surface.

This method is valued for its uniformity and its lower risk of segregation. That makes it useful for nuclear shields and underwater projects. Its low shrinkage and low permeability also support water-retaining structures, large monolithic blocks, and repair work. In large-scale construction, refrigerated water may be circulated around the aggregates to limit heat from cement hydration. In cold conditions, steam may be circulated to help prevent frost damage.

Concrete Placement for Tight Spaces

mixing concrete

Concrete Mixer Types and Capacity

Concrete mixing creates a uniform blend of cement, aggregates, and paste. The goal is to coat the aggregates evenly with cement paste. Mixers used for this job are usually grouped into two main types: batch mixers and continuous mixers. Batch mixers handle one load at a time. They mix the materials thoroughly, discharge the batch, and then receive the next one. Continuous mixers work differently. They take in a steady flow of ingredients, mix them at a constant rate, and discharge the concrete...

mixing time

Concrete Mixer Charging and Timing

Concrete mixer charging and timing are key to making a uniform concrete mix with the needed strength. Mixing begins only after all ingredients are inside the mixer. The usual charging order starts with 10% of the water, then the solid materials are added steadily, followed by 80% of the water. The last portion of water is added later, within the first quarter of the total mixing period. The minimum mixing time depends on mixer capacity. Mixers with up to 1 cubic yard of capacity need at least...

ready mixed concrete

How Ready-Mixed Concrete Is Delivered

Ready-mixed concrete is prepared at a centralized plant and then delivered by truck to a construction site. It arrives ready for placement, which makes it different from concrete mixed entirely on site. Ready-mixed concrete includes three main forms: central-mixed, truck-mixed, and shrink-mixed. Central-mixed concrete is fully mixed at the plant and carried to the site in agitator trucks. These trucks rotate at 2 to 6 rpm, which helps keep the concrete in motion during transport. Truck-mixed...

pumped concrete

Concrete Pumping for Hard-to-Reach Sites

Concrete pumping moves large amounts of concrete through pipes to places that are hard to reach. It is used for sites such as deep foundation pits and other inaccessible locations. The system includes a hopper, a pump, and pipelines that carry the concrete to the placement point. Direct-acting pumps use a piston to move the concrete. Concrete enters the pump through the inlet valve by gravity and by suction created as the piston moves. The forward movement of the piston then pushes the...

placing concrete

Concrete Placement Methods and Compaction

Concrete placement methods focus on keeping the mix in a uniform shape and position. The concrete is placed as close as possible to its final location to reduce segregation, which is the separation of ingredients. It is then fully compacted to remove trapped air. The next layer is added while the layer below is still plastic, or soft enough to shape. The rate of placing and compacting concrete is kept equal. Concrete is laid in uniform layers, and hand shoveling is avoided. Moving concrete...

vibrating concrete

Concrete Compaction with Vibrators

Concrete compaction with vibrators helps newly poured concrete settle inside formwork and around reinforcement bars. The goal is to remove trapped air pockets and create a dense concrete mass. Mechanical vibration is a key part of that process. One common method uses an internal vibrator, also called a poker vibrator or immersion vibrator. It is quickly inserted through the full depth of the fresh concrete and slightly into the layer below, which is still in a plastic state. The vibrator is...

shotcrete

Shotcrete for Vertical and Overhead Surfaces

Shotcrete is a concrete spraying method used on vertical and overhead surfaces. It uses mortar or small aggregate concrete with a high cement content. The material is sprayed at high velocity, and the impact helps compact it so it can cling without sagging. Builders place shotcrete in layers until it reaches about 4 inches thick. The quality depends strongly on the operator’s skill in managing the nozzle. Careful nozzle control helps the material land evenly and build up properly. Shotcrete...

preplaced aggregate concrete

Preplaced aggregate concrete is used when a construction site is hard to reach. The process starts by wetting gap-graded coarse aggregates. This helps remove dirt from the stones. The aggregates are then placed in the form and compacted. Next, a mortar mix is pumped under pressure through slotted pipes to fill the spaces between the aggregates. The mortar usually contains Portland cement, pozzolan, fine aggregates, water, and a fluidizing aid. The pozzolan reduces bleeding and segregation and...

finishing concrete

Concrete Surface Finishing Steps

Concrete surface finishing begins right after the concrete has been placed and consolidated. The first step is screeding, which levels the surface by removing extra material until it is even with the top of the formwork. A screed is a straight edge used for this leveling step. After screeding, a bull float or darby is used to smooth the surface further. These tools help lower high spots, fill low areas, and push larger aggregate particles deeper into the concrete. This preparation should...

curing of concrete

How Curing Improves Concrete Strength

Curing helps concrete gain strength after it has set. It keeps the concrete moist and at the right temperature so cement hydration can continue. Hydration is the process where cement reacts with water in the water-filled capillary pores and forms the products that fill spaces in the paste. Dry air can interrupt this process by pulling water from the concrete surface. Concrete with a water-cement ratio below 0.5 can also lose water through self-desiccation, which means internal water is used up...

curing methods

Concrete Curing for Moisture Retention

Concrete curing for moisture retention helps fresh concrete keep the water it needs as it hardens. For members with a small surface-to-volume ratio, the forms are often oiled and moistened before the concrete is placed. These forms may stay in place for a long time to reduce moisture loss. If the form material can be wetted, it can also be kept damp. When forms are removed early, the concrete member is moistened and then covered with polythene sheets. Large horizontal concrete surfaces in dry...

accelerated curing of concrete

How Concrete Gains Strength Faster

Concrete can gain strength faster when heat and extra moisture speed up cement hydration. This faster hydration helps the concrete build early strength sooner than normal curing. The process is used when quicker hardening is needed after casting. One common method is steam curing. Concrete products may move through a chamber on a conveyor belt, or they may be encased in plastic so steam at atmospheric pressure can circulate around them. Steam curing starts with moist curing for about 3 to 5...

key terms and concepts

Learn how preplaced aggregate concrete fills hard-to-reach forms with pumped mortar, low segregation, and uses in underwater, repair, and water-retaining projects.

Concrete Placement for Tight Spaces | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Concrete Placement for Tight Spaces

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