Full Answer
What is striking in concrete casting process?
The process of removal of formwork or shuttering in the process of casting concrete is known as striking. Once the concrete has achieved the initial recommended strength, to support the self-weight and any imposed loads, the shuttering is removed for further curing.
What does strike off mean on concrete?
"Strikeoff" or "Screeding" the Concrete. Straightedges are used to "strikeoff" or "screed" the concrete. This process removes excess concrete and brings the top surface of the concrete to proper grade.
How to reduce the striking time of concrete?
The Striking time can be brought down to the required value by adding admixtures to the concrete. Common example for these admixtures are accelerators which reduces the setting time of concrete.
What is the striking time of concrete formwork?
The striking time of concrete formwork depends on the strength of structural member. The strength development of concrete member depends on: Grade of concrete – higher the grade of concrete, the rate of development of strength is higher and thus concrete achieves the strength in shorter time.
When should you strike concrete?
Concrete @ your Fingertips (a) Vertical surfaces can be struck when the concrete is strong enough to resist the adhesion on the concrete/form face surface. (b) Soffits cannot be struck until the concrete has gained sufficient strength for the element to support is self weight for all or part of the structural span.
What does striking mean with concrete?
The process of removal of formwork or shuttering in the process of casting concrete is known as striking. Once the concrete has achieved the initial recommended strength, to support the self-weight and any imposed loads, the shuttering is removed for further curing.
When should you strike shuttering?
FAQs. When should formwork be removed? The removal of concrete formwork also called as strike-off or stripping of formwork should be carried out only after the time when concrete has gained sufficient strength, at least twice the stress to which the concrete may be subjected to when the formworks are removed.
Can you leave concrete forms on too long?
In short, there is no such thing as leaving concrete forms on for too long, as they will simply continue the curing process as the forms remain in place. However, there is no real need to leave forms on for longer than necessary.
How long should concrete cure before putting weight on it?
Although concrete will harden soon after pouring, it's still susceptible to damage from weight during the first four weeks. Wait at least 24 hours before allowing foot traffic, including pets, on a newly poured sidewalk or slab, and don't drive a vehicle on a new driveway for at least 10 days.
How long should concrete cure before removing forms?
The forms or “molding” that holds the concrete in place until it dries should be left alone for at least two days to ensure that the concrete is completely dry. If the forms are removed too soon, the concrete can begin to sag, crack and collapse, especially if conditions like temperature affected its strength.
Do you have to water concrete after it is poured?
Properly curing your concrete improves strength, durability, water tightness, and resistance for many years. The first 7 days after installation you should spray the slab with water 5-10 times per day, or as often as possible. Once the concrete is poured the curing process begins immediately.
What are 2 types of formwork?
TypesTraditional timber formwork. The formwork is built on site out of timber and plywood or moisture-resistant particleboard. ... Engineered Formwork System. ... Re-usable plastic formwork. ... Permanent Insulated Formwork. ... Stay-In-Place structural formwork systems. ... Flexible formwork.
When can I walk on new concrete?
24 hoursPlease keep vehicles, children, pets, and yourself off of your newly poured concrete for the next 24 hours. After 24 hours, you can walk on your newly poured concrete, but avoid dragging your feet, 'doing the twist', or allowing your pets to walk on it as their claws can scuff the concrete.
How soon should I water concrete after pouring?
Concrete should be left to sit for 2-4 hours after pouring before watering. If it is supposed to rain in that window, the concrete should be covered. Additionally, if you cannot water the concrete as regularly as is recommended, covering concrete helps trap the moisture and slow the evaporation.
How long does 4 inches of concrete take to cure?
The general rule of thumb is that concrete takes about 28 days to dry for every inch of slab thickness.
What if it rains after pouring concrete?
Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish. Even worse, if too much extra water works its way into the concrete mix, this can result in weak concrete overall.
What is the purpose of a concrete strike?
Purpose: To strike off freshly placed concrete and make it as level as possible before finishing.
What is a straight edge in concrete?
Straightedges are used to "strikeoff" or "screed" the concrete. This process removes excess concrete and brings the top surface of the concrete to proper grade.
What is a vibrating screed?
Vibrating Screeds Vibrating screeds feature a metal screed blade attached to a handle that allows finishers to smooth and level fresh concrete from a standing position. A motor produces the vibrating action, reducing the effort required by the operator, who only needs to pull the screed across the surface. Screed blade lengths range from 4 to 16 feet, and the blades can be removed and replaced. Most vibrating screeds are gasoline powered, but some models are available in a battery-powered version. Applications include residential driveways, large patios and other slabs that don’t require extreme flatness. Features to look for include quick-change screed blades, variable speed control, ergonomic design and adjustable handles. Keep in mind that although a longer screed blade length will cover more surface area in one pass, it will be more cumbersome to maneuver, especially in tight spots. Top manufacturers of vibrating screeds include Trade Tool Innovations, Marshalltown, and Northern Industrial Tools.
How long is a screed?
Screed blade lengths range from 4 to 16 feet, and the blades can be removed and replaced. Most vibrating screeds are gasoline powered, but some models are available in a battery-powered version. Applications include residential driveways, large patios and other slabs that don’t require extreme flatness.
What is laser screeding?
A laser screed being used to flatten a concrete slab in preparation for polishing.
What to use to keep concrete out of concrete?
Buy metal straightedges with capped ends to keep out wet concrete. Some tools have wooden or plastic plugs in the ends, but these can fall out and allow the concrete to enter. Tools with welded metal end caps are a better bet.
What tools are needed to screed a surface?
It must be completed before excess bleedwater appears on the surface. There are a wide variety of screeding tools—both hand tools (wood and magnesium) and mechanical tools (vibratory, oscillating, and roller). The important thing for this discussion is what they achieve and when screeding must be done.
What is screeding concrete?
Screeding concrete is one of the first steps in placing and finishing concrete. Screeding is the art of skimming or striking off the surface of the concrete after rough raking it. Screeding when done properly will leave you with a good even flat surface free of humps, bumps holes and low spots.
What is the hardest way to screed concrete?
Picking the right tool for the job will of course depend on the job your performing. Hand Screeds – Hand screeding is physically the hardest way to screed the concrete, but in the right hands it is the most accurate way to screed. Hand screeds can be a straight wood 2X4.
How do laser screeds work?
A laser screed is operated usually by one guy, a couple of rakers and a laser set up for heights. This specialty screed is not usually something anyone can use, it requires special training to be able to operate it. Alot of times companies who own a laser will rent them out with the operator.
What is power screeding?
Power Screeds – Power screeding makes the smoothing out process alot easier by leveling out and/or vibrating the wet concrete mixture. They are usually used for larger pours. If quality is important I definitely would not recommend using one unless you have been trained. They do save time and effort but are not always the most accurate screed with experienced operators.
What is truss screed?
Truss screeds can have many sections bolted on for reaching across large spans. They are built to ride on forms or rails that are set out prior to pouring. Laser Screeds – Laser screeds are usually used on larger pours where accuracy is important. This is probably the easiest most accurate form of screeding.
How long is a roller screed?
The rollers are available up to 24 feet long with many different attachments available for perfect gutters, curbs and more. The roller screed is a must if you are using pervious concrete. The best thing is the roller screed is so simple to use, even a beginner can turn out decent quality.
How to determine the strength of concrete before formwork removal?
To estimate the strength of concrete before formwork removal, the tests on concrete cubes or cylinders should be carried out. The concrete cubes or cylinders should be prepared from the same mix as that of the structural members and cured under same circumstances of temperature and moisture as that of structural member.
What is the difference between grade of concrete and grade of cement?
Grade of concrete – higher the grade of concrete , the rate of development of strength is higher and thus concrete achieves the strength in shorter time. Grade of cement – Higher cement grade makes the concrete achieve higher strength in shorter time. Type of Cement – Type of cement affects the strength development of concrete.
Why is formwork important in concrete?
Formwork helps the concrete to insulate it from surrounding, so longer the formwork remain with concrete, the less is the loss of heat of hydration and rate of strength gain is high.
How does the rate of hardening of concrete affect the removal of formwork?
The rate of hardening of concrete or the concrete strength depends on temperature and affects the formwork removal time . For example, time required for removal of concrete in winter will be more than time required during summer.
What is accelerated curing?
Accelerated curing is also a method to increase the strength gain rate with the application of heat. Generally following values of concrete strength is considered for removal of formwork for various types of concrete structural members.
What cement is used to remove formwork?
In normal construction process Portland Pozzolana cement is used. So, the time shown in Table-2 should be modified.
Why do cracks form?
cracks formation due to thermal contraction of concreteafter formwork striking.
What is shrinkage in concrete?
Shrinkage of Concrete. Definition: decrease in either length or volume of a material resulting from changes in moisture content or chemical changes. -. ACI Concrete Terminology. Drying shrinkage is the contraction in the concrete caused by moisture loss from drying concrete.
Why is shrinkage compensating concrete used?
Shrinkage-compensating concrete is used to minimize cracking and structural movement caused by drying shrinkage in concrete. The amount of drying shrinkage that occurs in concrete structures depends on the constituent materials, mixture proportions, curing, drying environment, and restraint.
