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

z kruszywem zastępowanym jest wytwarzany przez wstępne umieszczenie w szalunku gruboziarnistego kruszywa o gradacji szczelinowej, które jest wystarczająco mokre i zagęszczenie go.
Pozostałe puste przestrzenie, stanowiące około jednej trzeciej całkowitej objętości, są następnie wypełniane zaprawą składającą się z cementu portlandzkiego, pucolany, drobnych kruszyw, wody i środka upłynniającego.
Alternatywnie można zastosować zaprawę cementową i z drobnego piasku, zmieszaną w szybkoobrotowym mieszalniku koloidalnym.
Zaprawę wprowadza się pod ciśnieniem przez szczelinowe rury o średnicy około 1,5 cala rozmieszczone w regularnych odstępach. Rury są następnie stopniowo usuwane wraz ze wzrostem poziomu zaprawy.
Wibracje zewnętrzne na najwyższym poziomie zaprawy mogą poprawić wykończenie odsłoniętych powierzchni.
kruszywowy zastępowany wykazuje jednorodność przy zmniejszonej segregacji i jest stosowany do budowy tarcz jądrowych i projektów podwodnych.
W konstrukcjach zatrzymujących wodę, dużych bloczkach monolitycznych i pracach naprawczych stosuje się również z kruszywa zastępowanego ze względu na jego niski skurcz i zmniejszoną przepuszczalność.
W dużych projektach budowlanych przed nałożeniem zaprawy cyrkulująca schłodzona woda wokół kruszyw kontroluje ciepło hydratacji, a w niskich temperaturach krążąca para rozgrzewa kruszywa.

beton kruszywowy wstępnie ułożony

Beton kruszywowy wstępnie układany jest idealny do trudno dostępnych środowisk budowlanych. Proces rozpoczyna się od odpowiedniego zwilżenia gruboziarnistego kruszywa o szczelinowej strukturze w celu usunięcia brudu, a następnie umieszczenia go w formie i zagęszczenia. Pustki wypełnia się mieszanką zaprawy pompowaną pod ciśnieniem przez rury szczelinowe. Zaprawa ta zazwyczaj składa się z cementu portlandzkiego, pucolany, drobnych kruszyw, wody i środka wspomagającego upłynnianie. Pucolana pomaga zmniejszyć wyciek i segregację, jednocześnie poprawiając płynność zaprawy, podczas gdy środek wspomagający upłynnianie opóźnia wiązanie zaprawy. Stosowana jest również zaprawa cementowo-drobnoziarnista. Jest ona przygotowywana w szybkoobrotowym mieszalniku koloidalnym w celu utrzymania cementu w zawiesinie do momentu pompowania zaprawy. W miarę jak zaprawa unosi się do góry, rura jest stopniowo wyciągana. Zastosowanie zewnętrznych wibracji do górnej warstwy zaprawy może poprawić wykończenie odsłoniętych powierzchni.

Wstępnie ułożony beton jest preferowany ze względu na jego jednorodność i zmniejszone ryzyko segregacji, co jest niezbędne do budowy tarcz nuklearnych i projektów podwodnych. Ze względu na niski skurcz i przepuszczalność beton wstępnie ułożony jest stosowany w konstrukcjach zatrzymujących wodę, dużych blokach monolitycznych i pracach naprawczych. W budownictwie na dużą skalę schłodzona woda krąży wokół kruszyw przed dodaniem zaprawy, aby kontrolować ciepło z hydratacji cementu. Natomiast para krąży, aby zapobiec uszkodzeniom spowodowanym mrozem w zimnych warunkach.

Beton kruszywowy wstępnie ułożony

z kruszywem zastępowanym jest wytwarzany przez wstępne umieszczenie w szalunku gruboziarnistego kruszywa o gradacji szczelinowej, które jest wystarczająco mokre i zagęszczenie go.
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Education

JoVE Core

Civil Engineering

Inżynieria lądowa

Unit 1

Jednostka 1

Mixing, Placing and Curing Concrete 

Mieszanie, układanie i pielęgnacja betonu

KEY TERMS AND CONCEPTS

KLUCZOWE TERMINY I POJĘCIA

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 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 provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Concrete Placement for Tight Spaces

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