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Concrete Casting News from the Hill and Griffith Company

Save Your Concrete Forms With Proper Use of Concrete Form Release

Posted by Hill and Griffith Company on Nov 19, 2020 5:58:44 PM

Concrete formwork is a major investment for a precast or prestress plant. Taking care of the forms extends form life and protects a valuable investment and contributes to a healthy bottom line.

Concrete-Form-Release-Agent-Application-1.jpg

Care of concrete forms needs to be considered every time they are used. Steel form damage can occur with lack of cleaning or with too much use of wire brushes and sandblasting. Vibrators can damage form surfaces.

Proper selection and application of release agents is necessary for lower cost, producing the best product possible and for minimizing form clean up.

Grifcote-Concrete-Form-Release-Agent-Sizes.jpg

There are two types of release agents but they can also be combined for some applications.

The first is the barrier type. They provide a barrier between the concrete and the form. Originally form oils were barrier types of diesel fuel, greases, used motor oil, etc. These produced a good release but lowered product quality by causing bug holes, and staining, resulting in poor product appearance. They hard to apply due to their high viscosity.

The second type of release agent is chemically active and react with lime in the concrete to produce a soap-like film on the form. This type of release agent is the most widely used. Because they are easily applied in a very stable thin film by spraying, wiping, or brushing, you can produce stain-free, void-free concrete surfaces even after the form has been exposed for a day or two. Reactive type release agents applied in a thin film allow the form to strip cleaner which saves on labor costs related to form cleaning and extends the life of the form.

Concrete-Form-Rust-Preventative.jpg

In September of 1999 release agent manufactures and concrete producers were required by the EPA to make and use limited VOC products. Some companies, including Hill and Griffith, saw this coming years in advance and were already producing VOC compliant products. Some states, such as California have stricter rules than that passed nationally.

There are four main application methods-spraying, wiping, mopping or brushing and dipping. Spraying is the most common method of application. Avoid over application to reduce your cost. An extremely thin film of release agent is all that is needed, "The thinner the better." Pump unit sprayers or centralized systems with air pressure regulators give a good consistent pressure and work well. Spray pressures of 35 to 50 psi are best. Higher pressures put more airborne particles in the air throughout the plant and can be harmful to personnel in the plant. Lower pressures cause puddling in the form, and wasted release agent. A flat fan spray nozzle of .1 or .2 gpm will spray a good thin release agent. Many of these thin, chemically active release agents are more expensive per gallon. But with coverage rates at 2000-2500 sq. ft. per gallon the cost is much less than a cheaper barrier release agent. A second type of application is wiping on the release agent. Architectural precasters like wiping the release agent on the form because over application is eliminated. Burial vault manufactures use a sponge for application because they clean the form each time as well. A third type of application is with mop or brush with which over application can be a problem. The mop or brush must be wrung out in order to achieve the desired results. Wipe up puddles. Dipping systems are fast, labor efficient, and assure total coverage of the form. And they collect the excess release agent that drains off the form.

The investment in forms needs to be protected from rust and corrosion, use grease, diesel fuel, or release agent. A better choice is a good rust preventative that offers quality protection, long life, ease of application, and easy removal.

Taking care of forms each time they are used can save thousands of dollars and make a concrete business more profitable.


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

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 »

 

 Bulletins and Technical Papers for Concrete Casting Products

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

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.

Read More


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

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 »

 

 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

Form Coatings and Mold Linings

Posted by Hill and Griffith Company on Nov 5, 2020 1:02:16 PM

Excerpt from the book, Formwork for Concrete Structures by Kumar Neeraj Jha

Mold surfaces of wood and steel in due course, after repeated use, warp and rust, respectively, making the molds unserviceable if unprotected. It is common to treat the sheathing materials with some coating or release agent for easy removal. Only a few special form face materials, such as expanded polystyrene, do not need release agents.

The coating or release agents are temporary coatings and composed of fatty acids that react with the alkali in cement. The reaction produces a soap-like substance on the contact surface, which helps remove forms easily. Coating agents can also help enhance the mold life. The form surface remains smooth, provides good abrasive resistance, makes the wooden surface moisture resistant and retards the rusting of steel.

Concrete Release Agents

 

There are many release agent chemical compounds that have been developed for use as the coatings for wood and steel. It is, therefore, important to select the right one.

The three most common types of release agents are:

1. Neat oils with surfactants: mainly used on steel faces, but can also be used on timber and plywood.
2. Mold cream emulsions: for use on timber and plywood – a good general-purpose release agent.
3. Chemical release agents: can be used on all types of form face recommended for all high quality work.

These release agents could be oils, emulsified wax, oil-phased emulsions with water globules, petroleum-based products, catalyzed polyurethane foam, etc. Waste oil is also used as a release agent.

The type of composition of the coating or release agent depends on the following:

1. type of sheathing materials
2. conditions under which it is applied
3. type of concrete
4. finish quality
5. form area
6. ease of application

Concrete_form_release_application_1

The primary objective of the coating and release agents is to ensure easy removal of the form material without damaging the form and concrete. The concrete surface should also not get any stain from the application of release agents. It should be possible to apply the form release agent in an even manner on the form surface. The form release agent should not react with the concrete and produce some undesirable substance in the process.

Coatings on all type of forms are employed with the following objectives:

1. Protection of the form for durability
2. On timber, it reacts with organic constituents and provides a uniform surface on each use. Penetration of the chemicals helps control grain or edge effect as well as fill pores in the wood.
3. Chemically active coating reacts with free lime from the fresh concrete and produces water-insoluble soaps. When dried, these soaps act as positive concrete release agents. When wet, they help move air voids along the form.

Read More


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

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 »

 

 Bulletins and Technical Papers for Concrete Casting Products

Tags: Concrete, Casting Solutions, Concrete Casting Products, Concrete Casting Supplies, Precast Concrete, Concrete Form Release for Wood, Gricote, Mold Releases and Release Agents, Concrete Form Release

Using Concrete Form Release Properly Can Save Your Forms

Posted by Hill and Griffith Company on Oct 28, 2020 4:39:24 PM

Concrete formwork is a major investment for a precast or prestress plant. Taking care of the forms extends form life and protects a valuable investment and contributes to a healthy bottom line.

Concrete-Form-Release-Agent-Application-1.jpg

Care of concrete forms needs to be considered every time they are used. Steel form damage can occur with lack of cleaning or with too much use of wire brushes and sandblasting. Vibrators can damage form surfaces.

Proper selection and application of release agents is necessary for lower cost, producing the best product possible and for minimizing form clean up.

Grifcote-Concrete-Form-Release-Agent-Sizes.jpg

There are two types of release agents but they can also be combined for some applications.

The first is the barrier type. They provide a barrier between the concrete and the form. Originally form oils were barrier types of diesel fuel, greases, used motor oil, etc. These produced a good release but lowered product quality by causing bug holes, and staining, resulting in poor product appearance. They hard to apply due to their high viscosity.

The second type of release agent is chemically active and react with lime in the concrete to produce a soap-like film on the form. This type of release agent is the most widely used. Because they are easily applied in a very stable thin film by spraying, wiping, or brushing, you can produce stain-free, void-free concrete surfaces even after the form has been exposed for a day or two. Reactive type release agents applied in a thin film allow the form to strip cleaner which saves on labor costs related to form cleaning and extends the life of the form.

Concrete-Form-Rust-Preventative.jpg

In September of 1999 release agent manufactures and concrete producers were required by the EPA to make and use limited VOC products. Some companies, including Hill and Griffith, saw this coming years in advance and were already producing VOC compliant products. Some states, such as California have stricter rules than that passed nationally.

There are four main application methods-spraying, wiping, mopping or brushing and dipping. Spraying is the most common method of application. Avoid over application to reduce your cost. An extremely thin film of release agent is all that is needed, "The thinner the better." Pump unit sprayers or centralized systems with air pressure regulators give a good consistent pressure and work well. Spray pressures of 35 to 50 psi are best. Higher pressures put more airborne particles in the air throughout the plant and can be harmful to personnel in the plant. Lower pressures cause puddling in the form, and wasted release agent. A flat fan spray nozzle of .1 or .2 gpm will spray a good thin release agent. Many of these thin, chemically active release agents are more expensive per gallon. But with coverage rates at 2000-2500 sq. ft. per gallon the cost is much less than a cheaper barrier release agent. A second type of application is wiping on the release agent. Architectural precasters like wiping the release agent on the form because over application is eliminated. Burial vault manufactures use a sponge for application because they clean the form each time as well. A third type of application is with mop or brush with which over application can be a problem. The mop or brush must be wrung out in order to achieve the desired results. Wipe up puddles. Dipping systems are fast, labor efficient, and assure total coverage of the form. And they collect the excess release agent that drains off the form.

The investment in forms needs to be protected from rust and corrosion, use grease, diesel fuel, or release agent. A better choice is a good rust preventative that offers quality protection, long life, ease of application, and easy removal.

Taking care of forms each time they are used can save thousands of dollars and make a concrete business more profitable.


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

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 »

 

 Bulletins and Technical Papers for Concrete Casting Products

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

How Precast Concrete is Made

Posted by Hill and Griffith Company on Oct 22, 2020 3:23:17 PM

A case study in reinforced concrete

Excerpt from the November 2016 article on BuildingSolutions.com

Precast concrete structures are manufactured in a factory then delivered to a job site, ready to be installed. But, have you ever wondered how precast concrete products are made? In this video, you’ll get a behind-the-scenes look at one of our Oldcastle Infrastructure, a CRH Company, plants and gain first-hand experience on the manufacturing process.

Precast concrete structures are used in many types of construction and for many different purposes, including electrical and communication utilities, stormwater storage and conveyance, wastewater applications, bridges, building structures, and more.

There’s good reason for using precast concrete – it provides many benefits on a project, including quick and easy installation since there are no on-site forms to construct or waiting for the concrete to cure in the field, improving job site safety by decreasing the amount of time an excavation is open, and providing a high-quality, higher-strength product since it is produced in a controlled environment.

How Precast Concrete is Made

Engineering & Design

The process starts with engineering. On each project, a design engineer or owner (such as a Department of Transportation, DOT) sets requirements for their precast components. When we get the drawings and requirements, every product is engineered in-house according to the design engineer and owner’s specifications.

The engineers ensure each precast structure has the appropriate steel reinforcement (rebar) and meets the structural requirements for the area in which it will be installed. Some important considerations include the soil type, whether the precast structure will be adjacent to a building or other structure, and the water table of the area.

Once the calculations are complete, the drafting team creates detailed drawings. These drawings, called submittals, are then sent to the design engineer or owner for approval. When the submittal drawings are approved, the engineering and drafting teams create production drawings sent to the factory floor and used to manufacture the product. The production drawing set includes a bill of materials, or BOM, which includes all the components that go into the product, including sizes and lengths of each piece of rebar and how much concrete (measured in cubic yards) will be used.

Prepping the Rebar Cage

When the production team receives the drawings, the first step is to assemble the rebar cage. To do so, they must cut all rebar to the appropriate lengths according to the BOM and then bend and tie them together. Rebar wheelchairs, sometimes called wagon wheels, are round plastic components that hook onto the rebar and ensure it is properly positioned inside the walls of the precast product – not too close to either side of the wall – matching the engineer’s design and meeting the structural requirements.

Prepping the Form

While the rebar cage is made, another team preps the forms. This team reviews the drawings to see if the structure has any openings or knockouts and places foam inserts (removed after the concrete cures) into the form.

Openings are used where pipes connect or where other junctions are needed. Knockouts are thinner wall sections which allow openings to be “knocked out” in the field once the subcontractor knows where electrical conduit or communication lines would enter the vault. These inserts, along with the proper lifting hardware, are embedded and secured to the form so they don’t move when the concrete is being poured.

Next, the team applies a form oil used to ensure the concrete releases easily from the form after curing. Finally, the rebar cage is lifted using a crane and is lowered down into the form. Before concrete can be poured, each product undergoes a pre-pour inspection by a certified quality control technician to ensure it conforms to the production drawings. Once approved, the technician signs off and flags the form, indicating approval to pour the concrete.

Read More


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 »

 

Bulletins and Technical Papers for Concrete Casting Products 

Tags: Concrete Form Release Agents, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete, Precast Concrete Form Release, Concrete Form Release

Double Curved Concrete Surface

Posted by Hill and Griffith Company on Oct 15, 2020 5:02:06 PM

A case study in reinforced concrete

Excerpt from the May 2018 issue report by Luis Pedro Sarmento Esteves and Goncalo Castro Henriques

This paper deals with digital integration between design and fabrication in order to construct a complex double-curved concrete surface. This research focuses on the practical application of CNC technology to polyurethane (EPS), as an alternative to concrete formwork. The influence of specific EPS properties as deformability under compression, water tightness and finish on concrete pre-fabrication was analyzed. This enabled high flexibility of architectural forms and textures, integrated in structural elements. Limitations were found on the mold reuse for several elements.
 

1. Introduction

Since industrialization, construction of complex non-standard structures in concrete considerably diminish. These structures became less common due to the lack of construction and design processes capable of generating viable concrete elements and shapes, according to the mass production of elements in series. Specialization and a lack of collaboration between architecture, engineering and material science led to segregation of investigation on the field. Concrete structures are usually narrow and integrate production techniques that are optimized for linear elements. When facing more complex forms, concrete is seen as a non-flexible material, which is bonded to limitations of molding options and solutions.

Double Curved Concrete Surface

Buildings like the "Sagrada Família" designed by Gaudí in 1926, seem difficult to attain or complete due to the economic restraints and skill limitations of the workers. Recently with the digital revolution, CAD-CAM (computer aided design, computer aided manufacture) technologies offer us the possibility to regain a new integration of disciplines, Kieran (2004). The building "Zollhof Towers" (2000) in Dusseldorf, by Frank Gehry was overlooked as a practical example of the use of different pre-cast panels built off the site.

In this case study, we developed a complex double-curved surface in concrete, and the CAD-CAM process integrated design, engineering and fabrication. Data flow in a non-linear process accompanied all the stages from conception until the final product was made.
 
We used two molds to pre-cast the double-curved surface in self-compactable concrete. The molds were milled with the help of a CNC four axes machine that translated the data in 3D trajectories and made successive paths, subtracting material until obtaining the desired form. After that, they were filled with concrete and dried in the mold to gain resistance.
 
The digital integration can provide a shorter production process and the integration of disciplines engaged in collective intelligence. One could start to think about a building information model to be used by the collaborating disciplines, Kolarevic (2005). With the development of parametric design, fabrication and materials science integrated with digital collaboration, a wider range of solutions will be available. From this, a different logic of production is derived regarding the limitation of mass production, the mass-customization:
 
"Things used to be made to order and made to fit. But they were labor-intensive and expensive. Mass production came along and made things more affordable, but at a cost of the sameness, the cost of one-size-fits-all.
 
Technology is beginning to let us have it both ways. Increasingly we're getting more personalization at mass production prices. We’re moving towards mass customization," McTeer (1998). This new situation enables us to think of complex concrete structures, in a differentiated pre-fabrication process where choice is present.

Read More


 

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 »

 

Bulletins and Technical Papers for Concrete Casting Products 

Tags: Concrete Form Release Agents, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete, Precast Concrete Form Release, Concrete Form Release

3D-Printed Tooling Offers Durability for Precast Concrete

Posted by Hill and Griffith Company on Oct 8, 2020 4:24:36 PM

As an alternative to wooden tooling, 3D-printed forms for precast concrete are proving to be more durable and better able to support a large-scale renovation project.

Article excerpt from the May 2018 issue of Additive Manufacturing by Stephanie Hendrixson

There are certain applications today where 3D printing makes sense. An injection molder might choose to print a small batch of plastic parts that would be cost-prohibitive to mold. A machine shop might invest in a 3D printer to make jigs to aid in inspecting short runs of parts. A service bureau might rely on 3D printing for product development work, as a way to make prototypes quickly and easily.

What these scenarios have in common is that 3D printing makes it easier to produce a small, custom quantity: A few dozen parts, a couple of temporary fixtures, one prototype. There are exceptions, but manufacturers today don’t necessarily see 3D printing as the solution for repeatable, high-volume jobs.

Precast Concrete Made with 3D-Printed Forms


One of those exceptions is proving to be the precast concrete industry. Gate Precast, a supplier of precast structural and architectural concrete, is finding that 3D-printed tooling is exactly the right solution for a job requiring high repeatability over many concrete pours: manufacturing hundreds of punched windows for the façade of a 42-story building in New York City. For this large-scale project, 3D-printed forms have proved their worth in terms of faster lead times, increased durability and better quality in the end product.

Precast Concrete 3D Printed Form

Enter 3D Printing

Gate Precast manufactures precast concrete in nine locations nationwide. Some of these facilities focus on structural concrete—weight-bearing items like the beams and columns that make up parking garages—which is produced with metal forms, often in very large quantities. Others, like its Winchester, Kentucky, plant, specialize in architectural pieces that are typically made in smaller batches.

For most jobs, the Winchester plant builds its own concrete forms from plywood and fiberglass through an in-house carpentry department. These forms are not highly durable, but they don’t need to be. A wood form will start to break down, typically after 15 to 20 castings. But for a typical job where only 5 to 10 castings might be needed, this is no problem. It’s larger jobs that are the challenge when multiple forms must be built to support many concrete pours—which is where 3D printing comes in.

Pouring Concrete with a 3D-Printed Form

In practice, pouring concrete with a 3D-printed form is not much different from pouring with a wooden one. The windows are typically cast three together on top of a large platform in Gate Precast’s Winchester facility. The 3D-printed forms actually represent the front and inner sides of the window cavities, with the outer edges formed by removable plywood walls. Both the forms and sides are treated with a form release oil to help with the unmolding process.

Although they are not structural features, the punched windows still require reinforcement in the form of rebar, which helps to support the windows during stripping and shipping. The rebar is set into the empty form before the pour, along with lifting inserts and tiebacks that will serve to enable shipping, lifting and eventually hold the windows onto the building.

An overhead crane carries buckets of concrete to the platform; it takes about three buckets of concrete to fill one of the three-window forms, Schweitzer says, with each concrete cast weighing 20,000 to 30,000 lbs. depending on the profile. The pour stops periodically to allow the platform to vibrate and consolidate the concrete around the rebar, removing any air pockets from the face. Once the form is filled, workers manually smooth the top surface of the concrete (which will be the back of the windows) and clear the areas around the lifting and tieback inserts.

Inspecting Precast Concrete

Concrete pours take place each day in the afternoon, and then cure for 12 to 14 hours. The plywood walls are stripped from the cast first, and then the concrete pieces are lifted from the forms around 3 a.m. each morning. Each window frame is manually cleaned with an acid wash spray that exposes the sand in the mix. Then, some of the front faces are polished to expose the sand and aggregate. The resulting finish sparkles—quite intentionally—like sugar cubes.

Read More


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Getting Ready for Additive Manufacturing


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 »

 

Bulletins and Technical Papers for Concrete Casting Products 

Tags: Concrete Form Release Agents, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete, Precast Concrete Form Release, Concrete Form Release, Additive Manufacturing

Cleveland Rocks: Precast Concrete

Posted by Hill and Griffith Company on Oct 1, 2020 4:44:51 PM

Allega Cos. answers Corps contract commanding nearly 120,000 tons of wave-worthy precast

Article excerpt from the January 2017 issue of Concrete Products

A weather front emanating from Superstorm Sandy in October 2012 tested infrastructure well inland of metro New York and New Jersey, the area hardest hit by precipitation, wind and storm surge. Among federal and state agencies contending with long-term responses to Sandy-level exposure is the U.S. Army Corps of Engineers Buffalo District. It capped the 2015 and 2016 construction seasons closing repair and upgrade contracts—Oswego Harbor Detached Breakwater, New York; Cleveland Harbor East Breakwater, Ohio—using non-proprietary precast concrete structures known as dolosse, in tandem with limestone or granite armor block.

Site_i


District engineers outlined finished structure air content, flexural and compressive strength, plus surface quality specifications for respective Oswego and Cleveland project precasters, Lakelands Concrete Products of Lima, N.Y., and Allega Cos. of Valley View, Ohio. Both determined that highly fluid, self-consolidating mixes are the best solution for accelerated production of structures that will be submerged or subject to frequent Great Lakes wave exposure through a service life plausibly extending into the next century. Early indicators suggest the dolosse installations contribute to a Corps roster proving the efficacy of SCC for structures prone to extreme weather or temperature events, sharp freeze-thaw cycles, and rare, but catastrophic loads.

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Dolosse resist breakwater or shoreline erosion from waves and undercurrent through their mass and energy-dissipating geometry. Known as dolos individually, the monolithically cast structures comprise three members of octagonal cross section: Uniformly sized shanks connect fluke ends. The latter are flared, tapered members running in opposite directions, along X and Y axes. Dolosse are fabricated in four- to 16-ton sizes, sans lifting hardware, and placed by sling so each structure interlocks such that even the most forceful waves or undercurrents meet long plain or reinforced precast concrete chains of inordinate tonnage.

The Corps Buffalo District used a formula factoring statistical 20-year wave height and 10-year water level to determine 16-ton and 6.5-ton dolos sizes for the New York and Ohio installations. Located near the southeastern corner of Lake Ontario and serving the first U.S. port from the St. Lawrence Seaway, the upgraded Oswego Harbor structure marks the District’s first use of 16-ton dolosse. Lakelands Concrete fabricated 997 of the 11-ft. long structures with conventional reinforcement (Concrete Products, July 2015). The dolosse represented the bulk of a $19 million contract Michigan’s Durocher Marine completed in November 2015.

Slightly trailing the New York engineering and casting schedule were preliminaries for the much more ambitious Cleveland Harbor work, centered in Lake Erie about two miles east and one-half mile north of downtown Cleveland. Buffalo District engineers specified the 6.5-ton dolosse, plain and 8.3-ft. long, for 4,400 feet of breakwater structure, which sustained more than $31 million in damage attributable to the Superstorm Sandy-spurred weather system. The Corps found that the intensity of the winds over Lake Erie created extraordinarily rare waves, measured at nearly 18 feet offshore of Cleveland.

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Precast Concrete Architectural Repair

Posted by M.K. Hurd on Sep 24, 2020 5:45:39 PM

10 Aesthetic Defects; 10 Structural Defects; and Repair Techniques & Procedures

Excerpt from NPCA's 2013 downloadable guide.

This guide is not meant to be all-inclusive, but rather is a collection of best practices commonly used to repair precast concrete. The guide explains procedures and time-proven techniques used to make a multitude of precast concrete repairs. Precast concrete product repairs can be related to engineering and design, production, handling, shipping, erection, other trades (typically on the job site), job site conditions and environment. While it would be impossible to address every possibility where a repair may be needed, this guide will address some of the most common situations. It covers the basics and common methodologies of repairs. Unique situations will require you to develop repair techniques based on the appropriate methodology.

This guide is not a replacement for good quality concreting practices, which will reduce the amount of production-related repairs. For more information, see the NPCA Quality Control Manual for Precast and Prestressed Concrete Plants.

NPCA Precast Architectural Repair Guide

 

AESTHETIC DEFECTS

Aesthetic defects are considered minor defects. They are usually production-related and can be fixed quickly at the plant. Some examples include bugholes, small chips, crazing cracks or others described in this guide. Aesthetic defects do NOT impact the structural integrity or intended service life of the product.

Bugholes
Surface voids can be a common surface blemish on precast concrete. These are usually small voids found in clusters and commonly referred to as bugholes. While these do not compromise the structural integrity of the product, they can be considered unsightly, especially with architectural finishes. The common causes of bugholes include entrapped air, water pockets or the improper application of form release agent.

Release Agents
When a release agent is applied too heavily to the surface of a form, it can pool at the base of the mold or form droplets. When the concrete is placed into the form, the pools or droplets prevent the concrete from occupying that space so that when the form is removed a bughole is left behind where the droplet or pooling occurred.

Fine Cracks
Fine cracks occur at the surface and are very small, with a width typically less than 0.01 inches.

Shrinkage Cracks
Shrinkage cracks occur when water is removed too quickly from fresh concrete. The loss of water causes a volume change in the concrete, and since the concrete is still fresh, the tensile strength is not adequate to resist the volume-changing force. Shrinkage cracks can be avoided by placing concrete in a controlled environment where relative humidity, concrete temperature and wind velocity are favorable for concrete curing. When necessary, shrinkage cracks can be repaired using epoxy injection methods.

Crazing Cracks
Crazing cracks usually occur very soon after the concrete has been placed. The cracks are shallow and typically do not cause wear resistance or durability issues. Crazing cracks are often attributed to a lack of hydration on the surface of the concrete during the curing process. Crazing can be avoided by using curing compounds, covering the product during curing, refraining from "over-finishing" the surface of the concrete, and not finishing the product while bleed water is still present on the surface. Crazing cracks are typically not repaired because they are not structural and they are so small that it would be nearly impossible to fill them with any material.

Chips
Chips are relatively small sections of products that have been removed, typically as a result of impact. Chips may be as large as 8 in. in diameter by 1 in. deep and are usually of irregular shape. As chips become larger, they require a different approach to repair. This may include adding reinforcement (also known as pinning) and using a build-up application technique. This will be discussed under the section on spalls. Most chips can be repaired in one application with the appropriate patching material.

Efflorescence
Efflorescence occurs when soluble salts come to the surface of concrete. All concrete and mortars will experience some level of efflorescence. This natural phenomenon is most prevalent in moist environments and low- temperature conditions. Efflorescence will typically appear as a white substance, so it will be more noticeable on dark-colored concrete. Efflorescence can be removed by pressure washing before it reacts chemically to form calcium carbonate. Once the calcium carbonate reaction occurs, the use of a mild acid solution is often required to remove efflorescence. After application of the mild acid, it is important to rinse all acid and remaining calcium carbonate from the concrete to prevent discoloration of concrete or a relapse of the efflorescence cycle.

Missing Architectural Details
Missing architectural details such as false joints, quirks and miters occasionally can occur in the manufacturing of architectural precast concrete. The use of a thorough quality control program and a highly skilled design and detailing firm should greatly limit those occurrences, however.

Finish Problems
It's obvious, but should be stated: architectural precast must look good and meet the intended aesthetic purpose. Aesthetics can be subjective in nature, however, so this is always a potential area for dispute.

Blending
Precast products are cast over many days using several batches of concrete. The best way to minimize batch-to-batch variations is to follow good concreting procedures: Purchase all materials needed for a project from the same lot or run. Blend materials when more than one lot is used. Do not change from approved sources midstream in project. Maintain the specified water/cement ratio and mix design, control variations. Maintain proper placement and consolidation techniques. Follow consistent and proper curing procedures.

Discoloration
Discoloration can be caused by a multitude of factors. These factors include changing cement lots, varying aggregate properties, inconsistent mixing, inconsistent finishing or a change in curing conditions. Virtually any change in the concreting process can lead to a change in coloration.

Download the Complete Guide


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Tags: Concrete, Casting Solutions, Concrete Casting Products, Concrete Casting Supplies, Concrete Casting, Precast Concrete, Concrete Form Release Agent, NPCA

Prevent Formation of Concrete Bughole Surface Voids

Posted by Hill and Griffith Company on Sep 17, 2020 5:34:35 PM

Using concrete as an architectural material has brought the quality in surface appearance to an important consideration.

One of the problems affecting the surface aesthetics of concrete are bugholes. Bugholes are surface voids from the migration of mostly entrapped air to the fresh concrete form surface, mostly in the vertical plane.

preventing_bug_holes

Photo from Precast Inc. Magazine's May/June 2014 issue.


During setting, the shrinkage of the concrete forces entrapped air voids and excess water out of the mix. Water migrates upward due to density and becomes bleed water. The air bubbles seek pressure equilibrium and when in a vertical form, that's to the interior surface. These bubbles need to be directed vertically to the surface of the concrete form. Bugholes are found in the upper portion of the concrete structure or at angled form surfaces as a result of accumulation of escaping air along the height of the structure. They are primarily an aesthetic problem for exposed surfaces.

Causes

The biggest cause of bugholes is improper vibration. Consolidation through vibration, sets the bubbles into motion and sends both entrapped air and excess water to the surface.

Bughole formation can also be caused by the form material and the type of form release used.

When a chemically reactive form release agent is used, a nonviolent chemical reaction takes place when fatty acids react with free lime on the surface of fresh concrete. This reaction results in the formation of a metallic soap, a slippery material that allows air bubbles to rise along the vertical surface. This “soapy” film also prevents the hardened concrete from adhering to the forms during stripping.

Thicker coatings on forms are typical of the older barrier-type materials, like heavyweight used motor oil, vegetable oils, diesel fuel and kerosene. Barrier type release agents are less expensive than chemically reactive agents, but they are not generally recommended for reducing SCC bug holes."

Mix design can also contribute to bughole formation. A sticky or stiff mixture that is hard to consolidate can increase surface void formation.

Reduce Bugholes

Solutions

The vibrator should penetrate the previous lift and work the entrapped air towards the form and then up the sides. More vibration is necessary with impermeable forms, to move the air voids to the free surface of the concrete.

Flowing mixtures reduce bughole formation. Concrete that limits excessive fine aggregate, has the proper cement content, and uses admixture for increased flow contributes to bughole reduction. Self-consolidating concrete is becoming increasing popular for precast to improve surface quality.

Bugholes are not detrimental to structural concrete. But, with the increased use of concrete in finished construction, surface quality is important. Through careful selection of materials, quality workmanship, and dutiful supervision, surface voids can be minimized.

Learn more, "Concrete Bug Hole Prevention"

Causes & Fixes for SCC Bug Holes


Hill and Griffith Customer Service

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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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Bulletins and Technical Papers for Concrete Casting Products 

Tags: Concrete Form Release Agents, Concrete Release Agents, Concrete Casting Supplies, Concrete Form Release, American Concrete Institute, Concrete Bugholes, Bug Hole

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