Name: how concrete gains strength faster
Uploaded: 2024-11-07T14:48:35.000Z
Duration: 1 min 25 s
Channel: JoVE

L'indurimento del calcestruzzo viene accelerato applicando calore e aggiungendo umidità, ottenendo un calcestruzzo con una maggiore resistenza iniziale.
La polimerizzazione a vapore, spesso utilizzata per i prodotti prefabbricati, li sposta su un nastro trasportatore attraverso una camera o li ricopre di plastica, consentendo la circolazione del vapore a pressione atmosferica.
Il tipico ciclo di indurimento a vapore per il calcestruzzo inizia con un periodo di ritardo iniziale di indurimento a umido, seguito da un periodo di riscaldamento, aumentando la temperatura del vapore a una velocità compresa tra 40 e 60 gradi Fahrenheit all'ora fino a raggiungere un massimo di 150-180 gradi Fahrenheit.
Questa temperatura di picco viene mantenuta senza l'applicazione di calore aggiuntivo e il calcestruzzo assorbe il calore residuo e l'umidità durante questo periodo.
Il ciclo di indurimento a vapore si conclude con un periodo di raffreddamento, durante il quale la temperatura diminuisce.
La tecnica di indurimento elettrico applica corrente alternata per riscaldare l'elemento in calcestruzzo attraverso elettrodi esterni, l'acciaio di rinforzo all'interno del calcestruzzo o coperte elettriche, accelerando il processo di indurimento.
In alternativa, il riscaldamento del calcestruzzo con riscaldatori a infrarossi, la circolazione di olio caldo intorno alle forme di acciaio o la copertura del calcestruzzo esposto a basse temperature con coperte isolanti facilitano l'indurimento accelerato.

stagionatura accelerata del calcestruzzo

Accelerated Curing of Concrete

L'accelerazione della stagionatura del calcestruzzo si ottiene applicando calore e umidità aggiuntiva. Questo processo accelera l'idratazione del cemento, con conseguente aumento anticipato della resistenza del calcestruzzo. La stagionatura a vapore è un metodo in cui i prodotti in calcestruzzo vengono trasportati attraverso una camera su un nastro trasportatore o racchiusi in plastica, consentendo al vapore a pressione atmosferica di circolare liberamente attorno a essi. Questo processo inizia con una fase di stagionatura umida che in genere dura tra le 3 e le 5 ore, dopodiché la temperatura viene gradualmente aumentata a una velocità di 4-15 gradi Celsius all'ora, fino a raggiungere un massimo di 65-82 gradi Celsius. Il calcestruzzo viene quindi lasciato assorbire il calore residuo e l'umidità senza aggiungere altro calore. Segue un periodo di raffreddamento, durante il quale la temperatura può diminuire. La stagionatura a vapore ad alta pressione viene utilizzata principalmente per la stagionatura di prodotti in calcestruzzo prefabbricato più piccoli, come blocchi di muratura in calcestruzzo cavi. In alternativa, il calcestruzzo viene riscaldato applicando corrente alternata tramite elettrodi esterni, acciaio di rinforzo o coperte elettriche avvolte attorno al calcestruzzo. Altre tecniche prevedono l'uso di riscaldatori a infrarossi o la circolazione di olio caldo attorno alle forme di acciaio. Per il calcestruzzo esposto a temperature gelide, vengono utilizzate coperte isolanti o strati di materiali porosi come fieno o paglia per prevenire la perdita di calore e facilitare la stagionatura.

Stagionatura accelerata del calcestruzzo

L'indurimento del calcestruzzo viene accelerato applicando calore e aggiungendo umidità, ottenendo un calcestruzzo con una maggiore resistenza iniziale.
Indurimento a vapore, spesso utilizzato per la prefabbricazione ...

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Mixing, Placing and Curing Concrete 

Miscelazione, posa e stagionatura del calcestruzzo

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 hours. The temperature is then raised slowly, usually by 40 to 60 degrees Fahrenheit per hour, until it reaches about 150 to 180 degrees Fahrenheit.

After the target temperature is reached, the concrete is held so it can absorb the remaining heat and moisture without more added heat. A cooling period follows, and the temperature is allowed to drop. High-pressure steam curing is mainly used for smaller precast products, such as hollow concrete masonry blocks.

Other heating methods can also speed curing. Concrete may be warmed by alternating current through external electrodes, reinforcing steel, or electric blankets wrapped around it. Infrared heaters and hot oil around steel forms are other options. When concrete is exposed to freezing temperatures, insulating blankets or porous materials like hay or straw help reduce heat loss and support curing.

How Concrete Gains Strength Faster

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

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

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 heat, steam, and insulation speed concrete curing, from moist curing and temperature control to precast blocks and winter protection.

How Concrete Gains Strength Faster | 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

How Concrete Gains Strength Faster

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