In construction industry every project involves nearly some form of cutting concrete or core boring. Hand-held saws are used in the construction project to cut or shape paving slabs, stones or other concrete products.
Cutting concrete may seem to be simple but on practical ground there are several safety measures to keep in mind to have a safe and successful concrete cutting or boring project.
Safety and concern becomes an issue with concrete cutting because the concrete dust generated by the cutting action contains high respirable crystalline silica content. Breathing in this dust can lead to the development of respiratory ill health affecting your lung tissue resulting in serious breathing difficulties depending on the extent of exposure
Therefore, dust control becomes an important consideration when cutting concrete either with a saw or a drill or core boring bit.
The two most dust Control methods are:
- 1. Wet Cutting System:
In wet cutting the dust is collected in the cooling water and pneumatic devices that pulls the dust away in an air stream. Wet systems are preferably used on saws powered by combustion engines or compressed air. Wet dust suppression should not be used on saws that are electrically operated.
Wet cutting systems spray water onto the rotating cutting disk to reduce dust emissions. There are two sources by which water may be supplied.
(a) Portable Pressurised Tank System
This pressurized tank system consists of a polypropylene bottle containing approximately eight litres of water. The bottle is connected by narrow plastic tubing to two spray heads or jets normally attached to opposite sides of the guard. An on-off valve is fitted to control the water supply. An in-line filter is often fitted to prevent the heads becoming blocked. The spray heads/jets can be made from polypropylene but brass is considered a more resilient material. Water flow is produced by pressurizing the tank by hand.
(b) Mains Water System
This system is essentially the same as the tank, except the water source is from mains supply through a hose to the two water jets. Studies have shown that a minimum flow rate of about 0.5 litres per minute is required to optimise dust suppression. Low flow rates will reduce performance. Very much higher flow rates do not improve dust suppression, they only increase the need to refill the portable tank more often.
Difference between Portable and Main Water System
The portable tank needs to be regularly pressurised to maintain the flow rate.
The mains water system does not have this limitation but portability is restricted by the need to cut near a mains supply. The portable tank is more flexible as it can be easily transported around the site but it still requires a water source for refill.
For cutting a paving slab with a diamond tip blade normally requires a single pressurization stroke with portable system whereas tank sytem require re-pressurising during the cut if adequate control is to be maintained.
Diamond cutting blade or other abrasive disk cutting device such as concrete saw, uses water to lubricate and cool the cutting tools. The spillage of cooling water on to the surface during cutting should be managed by providing a drainage or a vacuum system like a wet vacuum which can be used to control the spillage of cooling water.
When using electric powered tools, adequate grounding, insulation and appropriate ground fault protection must be provided. If proper safety measures are not taken by the operator while operating electric toll and standing in a puddle of water can be fatal .
Core drilling machine requires an additional precaution as most of the machines depend on suction to keep the base in place during the drilling operation. The friction of the base suctioned against the floor provides the resistance to rotation while drilling depending on wether the floor is slicker or rough. The rough floor may provide more friction and will not allow a strong vacuum seal against the floor. In either case the vacuum seal is not completely reliable and may fail during the drilling operation. The operator must be aware about this and should keep his body out of the possible rotation path of the machine base during core drilling operation.
A reliable and secure method to work with core drilling machine is to have a concrete anchor through the base in addition to the vacuum seal. Most machines have a provision for such an anchor and the small hole required for the anchor is easily repaired in the concrete floor.
What lies beneath the concrete should be an important consideration even for a straight line cut with a concrete saw or making a round hole with a core drill. Concrete imaging and scanning is the technique used for relocating the presence of rebar,pipes, conduits, steel wire mesh,sinkholes, plumbing holes or even electrical conduits often buried in or under the concrete.
Concrete cutting equipments require sharp tools, a good supply of cooling water and a skilled operator to handle these machines. Operating concrete cutting equipment can be simple and safe, but the operator must be familiar with the potential hazards and should be well skilled in his concrete cutting profession.
- 2. Local Exhaust Ventilation:
The method of local exhaust ventilation used on hand held concrete cutting saws uses the saw’s guard as a type of high velocity hood. The guard is connected to an industrial vacuum cleaner which provides sufficient exhaust ventilation to capture the majority of dust emitted during the cutting operation. Guards with adjustable inner sleeves are preferable. These maximize enclosure and can be adjusted to accommodate different depths of cut. This system does not produce the wet slurry associated with wet dust suppression.
Common Problems and Solutions with Control Systems:
• Chalk is used to mark the line of cut which can easily wash off by water supply generated in wet system. Wax crayons or a carbon brush (from old electric motors) are better options to be used instead of chalk.
• Operators require waterproof PPE as both pressurized portable system and mains water system make use of water.
(b)Local Exhaust Ventilation
• Abrasive wheels wear during cutting activities. A system with an adjustable inner sleeve does not automatically compensate for abrasive wheel wear. Diamond wheels wear less quickly and are recommended for this system.
• A generator is required for both vacuum cleaner and saw. Small portable generators can be moved around the site on a wheel barrow.
• Operators should be aware of correct posture as local exhaust uses 9 inch diameter wheels which require operators to bend a little lower during cutting operation.
Personal Protective Equipment
• Concrete cutting operator should be provided with suitable RPE as concrete cutting products contain high silica.
• Dust mask is required while emptying the vacuum cleaner.