Name: concrete mixer charging and timing
Uploaded: 2024-11-07T14:48:34.000Z
Duration: 1 min 19 s
Channel: JoVE

콘크리트 믹서는 처음에 전체 물의 10%를 충전한 다음 고체 물질과 전체 물의 80%를 지속적으로 추가합니다.
혼합 기간은 모든 구성 요소가 믹서에 들어가자마자 시작됩니다. 나머지 10%의 물은 총 혼합 기간의 초기 분기 내에 통합됩니다.
1분에서 1.5분 미만으로 혼합하면 강도가 낮은 균일하지 않은 콘크리트 혼합이 발생할 수 있습니다.
균일한 콘크리트를 생산하기 위한 최적의 혼합 시간은 믹서 용량에 따라 다릅니다. 최대 1입방 야드의 용량을 가진 믹서의 경우 최소 1분의 혼합이 필요하며, 이는 추가 입방 야드당 15초씩 증가합니다.
또한 믹서 유형, 회전 속도 및 재료 충전 중 혼합 품질은 최적의 혼합 시간을 결정하는 데 중요합니다.
장기간 혼합하면 혼합물에서 수분 증발, 연질 골재의 분쇄, 혼합물의 작업성 감소, 마찰 효과로 인한 혼합 온도 증가, 공기 동반 콘크리트의 공기 함량 감소로 이어질 수 있습니다.

혼합 시간

Mixing Time

혼합 시간의 개념은 필요한 강도의 균일한 콘크리트 혼합물을 생산하는 데 중요합니다. 혼합 기간은 모든 재료가 믹서에 들어가면 시작됩니다. 처음에 믹서에 10퍼센트의 물을 채우고, 고형물을 지속적으로 추가한 후에 물의 80퍼센트를 추가합니다. 나머지 물은 나중에 혼합 기간의 첫 1/4 이내에 추가합니다. 최소 혼합 시간은 믹서의 용량에 따라 다릅니다. 예를 들어, 용량이 최대 0.76입방미터인 믹서는 최소 1분이 필요하며, 추가 0.76 입방미터당 15초씩 증가합니다. 최적의 혼합 시간을 결정할 때 믹서 유형, 회전 속도 및 충전 중 블렌딩 품질을 고려하는 것도 중요합니다. 표준 믹서는 종종 최소 1~1.5분의 혼합 시간이 필요하지만 최신 믹서는 더 짧은 시간에도 효과적입니다. 경량 골재를 사용하는 경우 혼합 기간은 5분 미만으로 떨어지지 않아야 하며 공기가 포함된 콘크리트의 경우 최소 2~3분이어야 합니다. 장시간 혼합하면 수분 증발, 골재 등급 변화, 작업성 감소, 온도 상승, 그리고 공기가 섞인 콘크리트의 경우 공기 함량 감소 등의 현상이 나타날 수 있습니다.

콘크리트 믹서는 처음에 총 물의 10%를 충전한 다음 고체 물질과 전체의 80%를 지속적으로 추가합니다.

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 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 1 minute, and the time increases by 15 seconds for each extra cubic yard. Mixer type, rotation speed, and how well the materials blend during charging also affect the best mixing time. Standard mixers often need at least 1 to 1.5 minutes, while modern mixers can work well in less time.

Some concrete mixes need longer mixing periods. If lightweight aggregate is used, the mixing time should be at least 5 minutes. For air-entrained concrete, the time should be at least 2 or 3 minutes. Too much mixing can cause water to evaporate, change aggregate grading, lower workability, and raise the temperature. In air-entrained concrete, prolonged mixing can also reduce air content.

Concrete Mixer Charging and Timing

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 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

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...

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 concrete mixer charging order and mixing time affect mix quality, strength, workability, and air content in high school concrete science.

Concrete Mixer Charging and Timing | 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 Mixer Charging and Timing

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