Name: how ready-mixed concrete is delivered
Uploaded: 2024-11-07T14:48:34.000Z
Duration: 1 min 26 s
Channel: JoVE

El concreto que se prepara en una instalación centralizada y luego se entrega en el sitio de trabajo en camiones, listo para su colocación, se conoce como concreto premezclado o premezclado. Viene en tres tipos: concreto mezclado central, concreto mezclado para camiones o tránsito y concreto mezclado con retractilado.
El hormigón mezclado centralmente se somete a la dosificación y a la mezcla completa de los ingredientes en la planta. A continuación, se transporta al lugar en un camión agitador que gira entre 2 y 6 rpm.
En el concreto mezclado con camiones o mezclado con tránsito, los ingredientes se dosifican en la planta y se mezclan en el camión, rotando entre 4 y 16 rpm, ya sea durante el tránsito o justo antes de descargar el concreto en el sitio.
El hormigón retractilado se mezcla parcialmente en la planta y se mezcla completamente en el camión, rotando entre 4 y 16 rpm en ruta hacia el sitio.
El concreto premezclado garantiza una calidad uniforme a través de la dosificación controlada, utiliza camiones agitadores para evitar la segregación y es adaptable para su uso en sitios congestionados o cuando se necesita concreto de manera intermitente.
De acuerdo con las pautas de ASTM, el mezclador del camión no debe exceder las 300 revoluciones para evitar la segregación, y el concreto debe colocarse dentro de los 90 minutos posteriores al inicio de la mezcla.

hormigón premezclado

Ready Mixed Concrete

El hormigón premezclado, también conocido como hormigón premezclado, se prepara en una planta central y luego se transporta en camiones a los sitios de construcción donde está listo para su colocación. Este tipo de hormigón se clasifica en hormigón de mezcla central, hormigón de mezcla en camión (o de mezcla en tránsito) y hormigón de mezcla por contracción. El hormigón de mezcla central se prepara íntegramente en una planta y se traslada al sitio en camiones agitadores que giran a una velocidad de 2 a 6 rpm. El hormigón de mezcla en camión, por otro lado, tiene los ingredientes dosificados en la planta, pero mezclados dentro del camión a una velocidad de 4 a 16 rpm, ya sea durante el tránsito o justo antes de descargar el hormigón. El hormigón de mezcla por contracción se prepara dosificando los ingredientes y mezclándolos parcialmente en la planta, luego mezclándolos completamente en el camión que gira a 4 a 16 rpm mientras se traslada al sitio.

El hormigón premezclado se utiliza mucho más que el mezclado en obra debido a sus ventajas, como una mayor uniformidad gracias a la dosificación controlada, la capacidad de evitar la segregación durante el transporte en camiones hormigonera, la idoneidad para sitios congestionados y proyectos que requieren vertidos de hormigón pequeños e intermitentes. Las directrices de la norma ASTM C 94-05 estipulan que el hormigón debe descargarse antes de que el camión hormigonera complete 300 revoluciones o dentro de los 90 minutos desde el inicio de la mezcla para garantizar la calidad del hormigón.

Hormigón premezclado

El hormigón que se prepara en una instalación centralizada y luego se entrega en el lugar de trabajo en camiones, listo para su colocación, se conoce como premezclado o ...

Education

Educación

JoVE Core

Civil Engineering

Ingeniería Civil

Unit 1

Unidad 1

Mixing, Placing and Curing Concrete 

Mezclado, colocación y curado del concreto

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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 concrete is batched at the plant but mixed inside the truck. The mixing can happen during transit or just before the concrete is discharged. In this type, the truck rotates at 4 to 16 rpm.

Shrink-mixed concrete is also batched at the plant, but it is only partly mixed there. The truck finishes the mixing while traveling to the site, and it also rotates at 4 to 16 rpm. Ready-mixed concrete is often chosen instead of on-site mixing because controlled batching improves uniformity, agitator trucks help prevent segregation during transport, and it works well for congested sites and for small, intermittent pours.

ASTM C 94-05 gives a time limit for handling this material. The concrete must be discharged before the truck mixer completes 300 revolutions or within 90 minutes from the start of mixing. These limits help protect concrete quality.

How Ready-Mixed Concrete Is Delivered

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

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 ready-mixed concrete is batched, mixed, and transported in trucks, plus the three types and the time limits used to protect quality.

How Ready-Mixed Concrete Is Delivered | 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 Ready-Mixed Concrete Is Delivered

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