Concreting Equipments in Construction

CONCRETING EQUIPMENTS

Concreting equipments are very much significant for the construction field. Using concrete in construction typically involves an extensive amount of labor. From mixing to pouring the concrete onto slabs, many workers have to work together to ensure the process goes well. With great quality concrete equipment machinery, quality construction can be attained in a lesser measure of time. Aside from potentially reducing labor costs, concrete equipment also lessens the risk of human error while allowing companies to finish projects much faster. Here are some of the most common concrete equipments used in construction:

(i) Concrete Batching Plant: Concrete batching plant, mixes various materials to form concrete. These materials include sand, aggregate, slag, cement, fly ash, and water among others. The batching plant comprises of adequate capacity gravel & sand hoppers, weighing conveyor suspended on electronic load cells, reversible drum type mixer unit, cement bin with screw conveyor, rubber belt type charging conveyor, cement batcher, PLC based control panel.

Concrete batching plants come in various types:

❖ Dry mix concrete plant

❖ Wet mix concrete plant

❖ Mobile concrete plant

❖ Stationery concrete plant

Mobile plants are used by temporary site projects and projects that don't require much concrete. But projects like large buildings, ports, bridges, tunnels and dams use stationary ones. Mobile batching plants can be used wet or dry and has a wide array of configurations and production types including Ready Mix, Precast & Prestressed, Central Mix, and RCC. Mobile Concrete Batching plant models are nowadays fully automatic. 20 cum/hr batching plant, 30 cum/hr concrete plant, 45 cum/hr, 60 cum/hr, 90 cum/hr, 120 cum/hr batching plant are a portion of the famous types of cement grouping plants utilized by the construction organizations.

Stationary concrete batching has seen an up surging rise in demand and manufacturers are modifying new models based on the customer need. These types are furnished with twin shaft mixers for maximized capacity and are also available with planetary mixers and batch sizes could be modified. The Stationary Plants are available in various capacities ranging from 30 m3 to 240 m3 per hour of compacted concrete. In stationary concrete plants, the aggregates are stored in horizontal bins. The gathering conveyor belt runs below the bins where the weighing of aggregates takes place and the aggregates are then discharged onto the charging conveyor. Pneumatically operated gates are provided for discharge of the aggregate on to the gathering conveyor. The material is all weighed accurately and transferred to the twin shaft mixer through a slinger conveyor. Nowadays batching plants also come with the skip hoist and belt arrangement option for mixer loading and a modular PLC-based control system with real-time control and data management. An admixture dosing unit and a standard cement screw conveyor are also a part of the stationery batching plant.

(ii) Concrete Pump: A concrete pump is one of the fastest concrete equipment which is significant in the construction industry because of its reliability and cost-effectiveness. A concrete pump is used to transport concrete from the production to the casting area. It works by having one piston drawing the concrete from the source and another one pushes it into the discharge pipe. Concrete pumps save the labor cost, time, and material with high power consumption are used for pumping the concrete from the mixer and send it directly to the construction site. There are two types of concrete pumps namely line pumps and boom concrete pumps. The line pump is mounted on a truck and placed on a trailer. Line pumps normally pump concrete at lower volumes than boom pumps and are used for smaller on to the volume volume concrete concrete placing applications such as sidewalks, small constructions and mostly ground slabs. Boom pumps are attached to a truck and use a remote-controlled articulating robotic arm. They are mostly used on big construction sites and pump at very high volumes, as it can pump in different heights and lengths. This makes it ideal for constructing multi-level buildings and bridges.

(iii) Concrete Mixer: A concrete mixer mixes cement, aggregates and water and produce concrete mechanically. It may have the same function as a batching plant but a concrete mixer is usually a single machine. Batching plants, on the other hand, belongs to a whole production line. There are various types of concrete mixers available which makes concrete production quick and economical. Depending on the type, a concrete mixer can produce concrete by batch or continuously. There are two broad types of concrete mixers which are as follows:

* Batch Concrete Mixers: Batch mixers are widely used machines for concrete mixing. Concrete mix obtained by this mixer is collected batch by batch and time by time. So, it is called as batch mixer. After pouring all the materials into pan or drum, it mixes all of those for some time and finally discharges. This process is repeated until required amount of concrete mix is obtained. In general Batch mixers are two types namely drum type and pan type.

* Drum Type Mixers: Drum type mixers concrete ingredients are mixed in a drum which is actually in double conical frustum shape. These are classified into the following types:

Tilting Drum Mixers means the drum will discharge concrete by tilting downwards. It is rapid discharge process and used for larger projects. Rapid means it delivers concrete by gravity that is tilting the drum downwards because of this the concrete mix obtained will be not subjected to segregation. Low workability concrete which contains larger size aggregates of size greater than 7.5cm are also mixed efficiently with this type of tilting mixers. But the mixing efficiency depends on the shape of the drum, angle of the drum, size of blades and angle of blades. The only disadvantage of this mixer is sticking of concrete to bottom of drum.

Non-Tilting Drum Mixers are not allowed to tilt and the drum rotates about its horizontal axis. For the discharge of concrete a chute is arranged in inclined position which will receives the concrete mix from drum and discharges out. In this case, the drum is opened at two ends and contains blades inside the drum for mixing. Here materials are poured through one end and mix is collected through another end. Rapid discharge of concrete is not possible in this case. Due to this delay, the concrete may be vulnerable to segregation. So, this type of mixers is generally used for small projects.

Reversing Drum Mixers are similar to non-tilting type mixers but in this case reversal of rotation takes place for different action. The drum has two openings, one end is for pouring materials and other end is for discharge of mix. The drum rotates about its horizontal axis. The rotation of drum takes place in one direction for mixing and in opposite direction for discharging. Two different set of blades are arranged for mixing and discharging. They are suitable for dry concrete mixes.

* Pan Type Concrete Mixers: It consists of a circular pan in which concrete is mixed. The mixing is done by blades which are arranged in star shape inside the pan. There are two types of pan mixers are available. In one case, the circular pan is constant and only star blades rotate about vertical axis of pan. In the other case, circular pan rotates while the blades are at static position. But in both cases, the mixing is efficient and concrete mixture is collected through central hole provided in the pan. The rotating star blades contain special blades called scrapper blades which will make concrete not to stick to the pan. The blades can also be adjusted in height, so there is no room for concrete to store in the pan. These are more efficient type of concrete mixers.

* Continuous Concrete Mixers: In this type of mixer, loading, mixing and discharging of mix is continuously done until the work is complete or work break occurs. The loading of materials is done continuously by screw feeders. Continuous mixtures are used for very large projects such as construction of high rise buildings, dams, bridges, etc.

(iv) Concrete Vibrator: Concrete vibrator is a mechanical device used to create vibration in wet concrete to compact the concrete. Concrete vibrator is fixed with motor and connected with a needle that creates the vibration inside the concrete mix and remove the all air in between the concrete mix. Vibration gives more strength and life to concrete. This concrete equipment is almost used by the entire civil industry from small civil work to large construction. Concrète vibrator can be of various types as given under: cont

❖ Internal Vibrator

❖ External Vibrator

❖ Table Vibrator

❖ Surface vibrator

* Internal or Needle Vibrators: Internal or Needle Vibrators are most commonly used vibrator for concrete. It consists of a steel tube with one end closed and rounded, having an eccentric vibrating element inside it. This steel tube called poker is connected to an electric motor or a diesel engine through a flexible tube. They are available in size varying from 40 to 100 mm diameter. The diameter of the poker is decided from the consideration of the spacing between the reinforcing bars in the form- work. The frequency of vibration varies up to 15000 rpm. The period of vibration required may be of the order of 30 seconds to 2 minute. The concrete should be placed in layers not more than 600mm high.

* External or Shutter Vibrators: These vibrators are clamped rigidly to the form work at the pre-determined points so that the form and concrete are vibrated. They consume more power for a given compaction effect than internal vibrators. These vibrators can compact upto 450mm from the face but have to be moved from one place to another as concrete progresses. These vibrators operate at a frequency of 3000 to 9000 rpm. The external vibrators are more often used for pre-casting of thin in-situ sections of such shape and thickness as they cannot be compacted by internal vibrators.

* Surface Vibrators: These are placed directly on the concrete mass. These best suited for compaction of shallow elements and should not be used when the depth of concrete to be vibrated is more than 250 mm. Very dry mixes can be most effectively compacted with surface vibrators. The surface vibrators commonly used are pan vibrators and vibrating screeds. The main application of this type of vibrator is in the compaction of small slabs, not exceeding 150 mm in thickness, and patching and repair work of pavement slabs.

* Table Vibrator: The vibrating table consists of a rigidly built steel platform mounted on flexible springs and is driven by an electric motor. The normal frequency of vibration is 4000 rpm. The vibrating tables are very efficient in compacting stiff and harsh concrete mixes required for manufacture of precast elements in the factories and test specimens in laboratories.

Most construction projects use internal vibrators as they are usually cheaper and offer more flexibility. But for vertical constructions like walls, an external vibrator is more suitable.

(v) Shotcrete Machine: Shotcrete machines are used for concrete spraying applications at the construction sites. It is a method of applying concrete proposed at high velocity primarily on a vertical or overhead surface. It is a mortar or high-performance concrete conveyed through a hosepipe and pneumatically shot at high force at the back surface. The force of this spraying action leads to compaction of the concrete which then forms layers of concrete to the necessary thickness. The impact created by the application consolidates the concrete. Even though the hardened properties of shotcrete are related to those of conservative cast-in-site concrete, the nature of the settlement process results in an excellent bond with most substrates, and rapid capabilities, particularly on composite forms or shapes. It has proved to be the greatest method for the construction of curved surfaces.

The shotcrete process needs less formwork and can be more cost-effective than traditionally placed concrete. It is applied by a wet- or dry-mix process. The wet-mix shotcrete method mixes all components with water before the introduction into the delivery hose. The dry-mix process adds water to the fusion at the nozzle. It is used in repairs and new construction also it is suitable for curved and thin elements. Because of their compact designs, these are useful at locations where space is at premium. Lining of water tanks, mines, swimming pools and backfilling of tunnel construction are some applications where these shotcrete machines are used.