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Concrete Casting News from the Hill and Griffith Company

Concrete Form Removal Time, Specifications and Calculations

Posted by Hill and Griffith Company on Nov 12, 2020 5:07:24 PM

Excerpt from The Constructor

The removal of concrete forms also called as strike-off or form stripping 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 forms are removed. It is also necessary to ensure the stability of the remaining forms during form removal.

Concrete Form Removal Time

The rate of hardening of concrete or the concrete strength depends on temperature and affects the form removal time. For example, time required for removal of concrete in winter will be more than time required during summer.

Special attention is required for form removal of flexural members such as beams and slabs. As these members are subjected to self-load as well as live load even during construction, they may deflect if the strength gained is not sufficient to handle to loads.

To estimate the strength of concrete before form 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.

When it is ensured that the concrete in the structural members has gained sufficient strength to withstand the design load, only then forms should be removed. The forms should be left for longer time if possible as it helps in curing.

Concrete Form Released After Curing

Removal of forms from the concrete section should not make the structural element:

  • Collapse under self load or under design load
  • deflect the structural member excessively in short or the long term
  • physically damage the structural member when the form is removed.

The following points must be kept in mind during form removal whether the structure will be prone to:

  • freeze thaw damage
  • cracks formation due to thermal contraction of concrete after form striking.

If there is a significant risk of any of the above damages, it is better to delay the removal time of forms. If forms have to be removed for optimizing the concrete construction activities, then these structures must be well-insulated to prevent such damages.

Calculation of Safe Form Striking Times:

Structural members are constructed based on designed load. But before a structure is complete and subjected to all loads assumed during structural design, the structural members are subjected to its self weight and construction loads during construction process.

So, to proceed with construction activities at a quicker rate, it is essential to calculate the behavior of structure under is self load and construction load. If this can be done and structural member is found to be safe, forms can be stripped-off.

If these calculations are not possible, then following formula can be used for calculation of safe form striking times:

Characteristic strength of cube of equal of maturity to the structure required at time of form removal

Form Removal Formula

This formula was given by Harrison (1995) which describes in detail the background of determination of form removal times. Another method to determine the strength of concrete structure is to conduct the non-destructive tests on structural member.

Factors Affecting Concrete Form Striking Times

The striking time of concrete forms 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.
  • 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. For example, rapid hardening cement have higher strength gain in a shorter period than the Ordinary Portland Cement. Low-heat cement takes more time to gain sufficient strength than OPC.
  • Temperature – The higher temperature of concrete during placement makes it achieve higher strength in shorter times. During winter, the concrete strength gain time gets prolonged.
  • A higher ambient temperature makes the concrete gain strength faster.
  • Forms help insulate concrete from surroundings, so longer the forms remain with the concrete, the less loss of heat of hydration and rate of strength gain is high.
  • Size of the concrete member also affects the gain of concrete strength. Larger concrete section members gain strength in shorter time than smaller sections.
  • Accelerated curing is also a method to increase the strength gain rate with the application of heat.

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 Bulletins and Technical Papers for Concrete Casting Products

Tags: Concrete, Casting Solutions, Concrete Casting Products, Concrete Casting Supplies, Precast Concrete, Gricote, Concrete Form Release, The Constructor Magazine

Concrete Forms - Types and Selection of Concrete Forms

Posted by Hill and Griffith Company on May 1, 2020 4:24:36 PM

Excerpt from the instructional website, The Constructor.

Bond Breakers

Concrete forms can be defined as a solid barrier that helps to hold the fluid concrete in place until it hardens and acquire a particular shape. The concrete takes the shape of the form or the mold in which it is contained. Now new concrete form systems are developed that provides additional properties like insulation, surface patterns and effects to the concrete cast.

The different types of concrete forms used in concrete casting are:

  1. Wooden Forms
  2. Insulated Concrete Forms
  3. Foam Concrete Forms
  4. Concrete Wall forms
  5. Steel Forms
 
Wooden Concrete Forms

Wooden Concrete Forms

Wooden form is the basic and the most conventional type of concrete form. It is employed mainly for concrete casting that does not exceed 6 inches of height. The wooden form types consist of wooden boards. These are either nailed or screwed together to the desired mold or formwork shape. Special leveling devices are used to properly level or slope the form based on the requirement.

In order to cast concrete with curves or any sort of free-form designs, thinner cross-sections are employed to make the form. Before pouring concrete, the inner surfaces are applied with low-grade oil or any form releasing agent so that concrete does not stick to the surfaces.

If properly cleaned and maintained, these forms are suitable for multiple uses.

Insulated Concrete Forms

The insulated concrete forms (ICF) compromises of hollow blocks made of insulating material that is fit together like building blocks as shown in figure-2. These systems are constructed on the foundation slab. This forms a part of the foundation and the wall systems. Reinforcement is placed within these blocks and filled with concrete of required slump and cast. The form and concrete are placed like a sandwich. This system provides high energy efficiency. Removal of forms is not necessary by implementing ICFs. Once the concrete is filled it need not be removed.

Insulated Concrete Forms

Read More


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Pre-Cast Concrete Walls – Types, Connections, and Advantages


Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water concrete form release, non-petroleum concrete form release, biodegradable concrete form release, rust inhibitors and concrete dissolver products that suit your needs.

Hill and Griffith Samples

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We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
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Hill and Griffith Customer Service

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On-site casting defect investigations, product testing, machine start-ups and much more. Also, lab facilities are available to provide testing upon request.
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Bulletins and Technical Papers for Concrete Casting Products

 

Tags: Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Release Agents, Concrete Forms, Concrete Form Seasoning, Concrete Casting Supplies, Concrete Pipe, Concrete Form Release, The Constructor Magazine

Formwork Lubricants - Types and Uses of Release Agents for Formworks

Posted by Hill and Griffith Company on Feb 13, 2020 4:51:40 PM

Excerpt from The Constructor Magazine by Kavita Pai

Concrete formwork lubricants are high-quality form seasonings that are applied to the inner surface of a formwork before pouring concrete. Formwork lubricants are also known as form or mold release agents.

Uses of Formwork Lubricants

Release Agents are used for the following reasons:

  1. Application prevents sticking of formwork to the concrete surface thereby permitting easy stripping of formwork after the concrete has hardened.
  2. Protects the formwork and hence the formwork can be reused several times.
  3. Provides good finishing surface of the concrete with minimum defects.
  4. In the case of wooden formwork, prevents water absorption from concrete by the wooden formwork.
  5. Reduces leakage of water during the curing process.
  6. Prevents steel formwork corrosion.

Precast Concrete Form Seasoning 2

The performance of release agents are largely dependent on the type of formwork used. For wooden formwork, straight refined, pale, paraffin-based mineral oil and oil-phase emulsion have been successfully used. The oil that is chosen should be capable of penetrating the wood to some extent while leaving the surface slightly greasy to touch.

There should not be any free release agent on the wood surface. The form release agents that are good for wooden formwork are not always suitable for steel formwork. And hence the choose form release agents based on the type of formwork used for construction.

 

Types of Release Agents:

1. De-Shuttering Oil (DSO)

This is a water-based mold release agent, which produces clean and stain-free, high-quality concrete. It is available in a sprayable form and ready to use as a direct application on required places. It should be applied in light film either by brush or sprayer. If it is over applied, excess release agent should be drained before it dries. Pools of DSO cannot be allowed to dry as it causes surface retardation of concrete.

Advantages of De-Shuttering Oil are as follows:

  • DSO is economical to use.
  • It is non-toxic and non-hazardous.
  • It can be used for all types of concrete formworks.
  • It helps reduce the cleaning efforts before reusing of the formwork.
  • DSO provides a damp proof interface that protects the formwork and ensures even texture and color of concrete.

Read More


More News The Constructor Magazine

Concrete Sweating – Phenomenon, Causes and Prevention

Pre-Concrete Checks for Formwork and Release Agents


Hill and Griffith Customer Service

We're known for our hands-on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water and non-petroleum concrete form release, biodegradable releases, rust inhibitors and concrete dissolver products that suit your needs.

Hill and Griffith Samples

Product Samples

We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
Contact Us »

 

Hill and Griffith Customer Service

Technical Services & Support

On-site casting defect investigations, product testing, machine start-ups and much more. Also, lab facilities are available to provide testing upon request.
Contact Us »

Tags: Concrete, Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Casting Products, Concrete Release Agents, The Constructor Magazine

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