What Are The Advantages and Disadvantages Of Shotcrete:
Advantages Of Shotcrete:
- The high cost of shotcrete limits its application to certain special circumstances where considerable savings are accrued and where its peculiar adaptability and technical advantages ender it more suitable than conventional placing methods.Shuttering and formwork need be erected only on one side of the work and it does not have to be so strong as the shuttering for poured concrete. The saving in shuttering costs makes it particularly applicable for thin sections and although there is no technical reason why unlimited thicknesses cannot be deposited in horizontal and vertical work.
The cost generally limits it to a thickness of 200 mm. The possible rate of application is low particularly with the dry process. Normally not more than 80 mm thickness can be deposited in overhead work in one day and the possibility of this will depend on the use of a suitable accelerator.
- The fact that it can be conveyed over a considerable distance in a small diameter pipe makes this process suitable for sites where access is difficult. The other method that can be adopted in such a situation is pumping techniques. It cannot, however, be used in confined spaces as the expansion of the compressed air will cause air turbulences which make accurate placing difficult. A sufficient room is required to hold the nozzle, say 1 m from the work.
To accommodate a large radius bend of the delivery hose also requires considerable space. It will bond extremely well to the existing concrete, masonry, and exposed rock. Suitably prepared steel surface also can be covered with gunite concrete.
- The quality of the finished product is liable to be variable and particularly in the dry process, the quality is very much dependent on the skill of the nozzleman. Quality control is very difficult and it is not possible to cast reliable test cubes or cylinders.The only way of testing the strength of the work deposited is by taking drill cores or by making a parallel slab by uniting with the identical mix. It is difficult to remove rebound material as this tends to collect inside corners and behind reinforcing bars or other obstructions.
Pockets of rebound formed as above and due to lack of skill of the nozzleman form weak and porous patches in the finished work. The proportions of the concrete deposited are affected by variation of the water supply and variations in the amount of rebound caused by this and other reasons.
- Too low an air pressure and surges in the air and water supply also can cause patches of relatively dry material. Defects of this type can result in porous concrete and also contribute to high permeability. The amount of rebound greatly affects the economics of the shotcrete process as it has all to be discarded and involves labor in collection and disposal.
The area surrounding the work will be heavily coated with mortar particularly in windy weather. It is difficult to obtain a satisfactory surface finish with Shotcrete, particularly with the dry process, because it is almost impossible to trowel due to the low water content. Often it becomes necessary to apply a screed of about 2 cm over the gunite surface.
- The application of the shotcrete process is limited to exceptional areas and that too when good nozzleman having the required skill are available. The nozzleman’s job is a very strenuous one. It is, therefore, necessary to have relief nozzelmen and for high rates of application, some mechanical means of holding the nozzle are required. The maximum rate of deposition is about 15 m3/hr for the dry process but this can be exceeded with the wet process.
- The low water/cement ratio, the thinness of the section deposited, and the fact that normally only one side of the concrete is covered, necessitates careful attention to curing more than with normal concrete. The normal specifications concerning cement, aggregate, and water, also apply for shotcrete but the aggregate should be rather harder than normal to allow for attrition due to the action of the process. Any cement provided does not set too quickly, can be used.Admixtures can be used in shotcrete to produce the same effects as in ordinary concrete. They should be added to the water in the dry process, but some difficulty may be experienced in obtaining correct proportioning due to variations in the rate of feed of the dry materials.
- On account of the difficulty of precise control, admixtures whose effects are very sensitive to the proportion added should not be used. Great caution should be exercised in using accelerators in the wet process but accelerators causing an initial set within 30 seconds are used in the dry process.
The high cost of shotcrete limits its application in some special cases, where substantial savings are accumulated and its unique compatibility and technical advantages make it more suitable than traditional placing methods.
Shuttering and formwork should only be installed on one side of the work and not strong enough to shutter the poured concrete. The savings in valve cost are especially applicable to thin sections and there is no technical reason why irregular thicknesses cannot be deposited in horizontal and vertical work.
- Costs are usually limited to 200mm thickness. Especially with the dry process, the probability of application is low. Usually, a thickness greater than 80 mm is not deposited in overhead work in a day and is likely It depends on the use of the appropriate catalyst.
The fact that it can be addressed over a considerable distance in a small diameter pipe makes this process ideal for sites that are difficult to access. Another method that can be adopted in such a situation is pumping techniques. However, it cannot be used in confined spaces as the expansion of compressed air causes air turbulence, which makes accurate placing difficult. Need enough room to hold the nozzle, say 1m from work.
The distribution hose also needs a lot of space to accommodate a large radius bend. It binds well to existing concrete, masonry, and open rock. Properly prepared steel surfaces can be covered with Gunite concrete.
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- The quality of the finished product is variable, and in the dry process, in particular, the quality is highly dependent on the nozzle technique. Quality control is very difficult and reliable test cubes or cylinders cannot be cast.
The only way to test the strength of the deposited work is by taking drill cores or by combining them with a similar mixing. Rebound objects are difficult to remove because they accumulate inside corners and behind reinforcing bars or other obstacles.
Lack of recurring pockets and lack of nozzle skills, such as those formed above, make for weak and porous patches in the finished work. The amount of concrete deposited is influenced by variations in water supply and the rate of recirculation and other factors.
- Too little air pressure and surge in air and water supplies can lead to patches of relatively dry material. These types of defects can lead to porous concrete and contribute to greater permeability. The rate of recycling greatly affects the economics of the shotcrete process because it has to be discarded and involves workers in storage and disposal.
The area around the workplace is highly coated with mortar, especially in a windy environment. It is difficult to obtain a satisfactory surface finish with shotcrete, especially with the drying process, because of the low water content it is impossible to the trove. It is often necessary to apply a screed of about 2 cm above the gneit surface.
- Implementation of the shotcrete process is limited to exceptional areas, even when a good nozzle with the required skill is available. The nozzle work is very strenuous. Therefore, it is necessary to have relief nozzles, and for high rate application, some mechanism is required to hold the nozzle. The maximum rate of storage is about 15 m3. Hr to dry process but this can be exceeded with wet process.
The low water/cement ratio, the thinness of the deposited section, and usually only one side of the concrete are covered, requiring careful attention to curing more than ordinary concrete. The general specifications for cement, aggregate, and water also apply to shotcrete, but the aggregate must be stiffer than usual to allow deterioration due to process action. Any cement provided will not be set up very quickly, Can be used.
- Mixtures can be used in shot concrete to produce effects similar to those in ordinary concrete. They should be added to water during the drying process, but due to variations in the feed rate of the dry material, there may be some difficulty in obtaining the correct ratio.
Due to the difficulty of precise control, blends that are very sensitive to the added ratio should not be used. Great caution should be exercised in the use of catalysts in the wet process but catalysts are used in the dry process to cause the initial set in 30 seconds.
This allows the process to be used in very wet conditions and to seal the leaks. But there are sometimes difficulties in attaching concrete to very set surfaces and these fast catalysts can be very expensive.
- There is not much information on drying shrinkage and creeping of shotcrete. The drying shrinkage depends on the water content and, therefore, can be expected to be sufficiently low for the drying process. The creep of dry shotcrete is similar to that of high quality commonly placed concrete.
But the shrinkage and creeping of the wet shotcrete are likely to increase. Durability or resistance is better for Frost Action and other agencies of dry shotcrete. This is not good for wet shotcrete but can be satisfactorily improved with the use of air-entering agents. Half of the air entering the spray can be lost.
Disadvantages Of Shotcrete:
- The primary disadvantage of shotcrete compared to poured concrete is that the quantity of your time it takes to use giant structures, structural piers, and alternative cross-sections compared to traditional forms for these giant structures.
- Two common issues once applying shotcrete area unit that the concrete mixture is just too giant, which may interfere with concrete spraying; And mix concrete is just too wet (too slow), in order that it doesn’t stick well to vertical and overhead surfaces.
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The concrete applied by shotcrete usually incorporates steel reinforcing bars. ikon one shows all-time low and sides of the deep finish of an outsized municipal pool. Shotcrete crews area unit standing on steel reinforcement to an all-time low of the lake, supported by concrete masonry units resting on compact soil. This steel reinforcement is absolutely embedded within the concrete once it’s processed as within the back of the ikon close to the highest of the wall.
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