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Concrete Casting News from the Hill and Griffith Company

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


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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

Applying Concrete Release Agent Four Different Ways

Posted by Hill and Griffith Company on Sep 10, 2020 4:29:49 PM

Release agents, when properly used, aid in the stripping process, assist in producing sound defect-free concrete surfaces, simplify form cleaning and increase the working life of quality form surfaces.

There are two main categories of form release agents

  • Barrier – those that provide a physical barrier between the form and the concrete (such as petroleum-based products, soaps, synthetic resins, waxes)
  • Reactive – those containing fatty acids or other ingredients that react with the free lime in fresh concrete to produce a metallic soap interface between the form and the concrete. Such as proprietary products and vegetable oils that are typically found in petroleum-based carrying agent products.

Applying

Apply concrete release agent to a clean form before the reinforcement has been placed to reduce the likelihood of inadvertently applying it to the reinforcement. If the release agent does come in contact with reinforcement it should be wiped clean before placing the concrete. 

When applying a release agent it is best to follow the manufacturer’s instructions. When too much form release is used, it is not only wasteful and inefficient, but it leads to a number of other associated problems with the finished product. He who holds the wand determines the amount of material being applied, so proper training is crucial. As a rule of thumb, remember: Less is better. The amount needed to affectively coat a form is only about 0.005 inches thick. The actual cover thickness will depend on the application method and viscosity of the product, which is related to the ambient temperature. Typically, the colder it is in the plant, the thicker, or more viscous, the release agent will be. The warmer it is the plant, the thinner, or less viscous, it will be. Different measures can be taken during the application process to account for changes in material temperature (viscosity) throughout the year.

Biodegradable Concrete Form Release Agents 2 copy.jpg

Spraying

Spraying is probably the most efficient and common method for applying release agents. Keep the wand moving when applying form release. Broad nozzle/flat spray tips have been found to give the thinnest and most uniform cover. It should be noted that as the temperature drops and viscosity increases, the spraying pressure should be increased and the nozzle orifice size reduced. As temperatures rise, reduce pressure and increase nozzle size. It is a good practice to soak or mop up any puddles that may have formed at the bottom of the form Remember: Less is better. Only through experience and training will you learn what works best for your plant’s production line.

Caution: Fatty acids will react with brass, bronze, aluminum, grey ductile and malleable iron and mild steel, as well as some petroleum-based products used for making blockouts and other embedded items. It is best to use stainless steel, nickel or plastic for your spraying systems and to test for possible reaction of embedded materials prior to full implementation.

Application of Precast Concrete Form Oil - 2.jpg

Swabbing and Painting

Swabbing and painting by hand is an acceptable application method, with the benefit of eliminating the majority of airborne particulate. On the negative side, applications tend to be thicker than necessary, leading to wasted material and the potential for additional problems. 

Application of Precast Concrete Form Oil - 3.jpg

Wiping

Wiping is often the method of choice for architectural precasters concerned with a blemish-free surface. Wiping on release agents with a sponge or rag will normally result in the thinnest coating, but it is very labor intensive.

Dipping

Automated dipping systems are fast, labor efficient and ensure complete coverage. Excess material will usually drip back into a holding tank, reducing material waste. The application coat is often thicker than necessary, however, again creating the potential for future problems.

Biodegradable Concrete Form Release Agents 9 copy.jpg

Seasoning

Reactive form release agents, the most commonly used release agents in precast and pipe production, typically contain fatty acids. Fatty acids are mild acids composed of animal fats and vegetable oils. These fatty acids have a natural affinity for metal. They react with metal to form a protective barrier, which is a coating of metallic oleate. 

This process is known as seasoning. This protective layer prevents further application of fatty acids from migrating to the metal of the form and allows the fatty acid to remain on the surface of the form to react with the free lime on the surface of the casting. Seasoning serves two purposes. First, it enhances the easy separation of the form from the castings. Second, it enables free air to rise more easily on the vertical surfaces of the castings, resulting in fewer surface defects. Seasoning of forms is a very basic requirement to help minimize the amount of labor involved when forms are stripped or pipes are tipped out. If forms, pallets and headers are properly maintained, labor cost and better looking castings are the end result

New forms, pallets and headers will frequently arrive with a protective coating on them to help prevent rusting in transit or until the forms are sold and delivered. In order to season these forms, the protective coating can be removed with solvents or grinding and the form release applied liberally, allowing it to set for a minimum of four hours. A 24-hour period is better, as it allows more seasoning to take place. Also, forms that are exposed to the sun will season more quickly, as higher temperatures increase the reactivity with the metal forms and rings.

Care of Forms and Rings

At times, you may be storing forms inside or outside for short or long periods of time. Release agents can be used to protect this vital equipment from damage. For short-term or long-term storage, a good quality VOC-compliant petroleum solvent-based form release can be used by applying a liberal coating on the form. If the forms are stored outside, even for a short period of time, a quick walk-by is often necessary to ensure that the form release has not washed off from rain. If any evidence of rust is present, apply another coat of the form release on the forms and rings as quickly as possible. A biodegradable form release is preferred, as over-application is desired and some of the material will end up on the ground.

Identifying Potential Problems

Concrete is a highly variable material because it is comprised of raw materials that potentially have a lot of variability. It is often difficult to pinpoint exactly what causes a problem because it may be a combination of a number of factors. The following are two examples of common problems often associated with excessive form release agent coverage.

Staining has been linked to the use of excessive release agents and the use of dirty forms. Dirt, dust, rust or grease can easily be transferred from a dirty form to the finished surface of the concrete product. Once a form has been properly cleaned and coated with release agent, proper measures should be taken to minimize the potential for dust and debris to collect on the form before casting.

Biodegradable Concrete Form Release Agents 3 copy.jpg

Excessive bugholes occur when barrier-type release agents are applied to heavily. Barrier-type release agents tend to encapsulate free air along the vertical sidewalls, which leads to surface defects. In contrast, the metallic soap formed when using a reactive release agent allows the free air on the vertical walls to rise more easily to the surface. Proper vibration practices also reduces bugholes. The potential for bugholes and staining can be reduced by selecting an application method that produces the thinnest coat of release agent in accordance with the manufacturer’s recommendations.

Release agent should not be allowed to collect and pool in the forms. Applying a thin coat, wiping up puddles and avoiding contact with reinforcing steel greatly improves the odds of producing a defect-free concrete product.

This article was written by Bob Waterloo, Distributor Manager with the Hill and Griffith Company, for the National Precast Concrete Association's publication Precast Inc.


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.

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Tags: Concrete Casting Supplies, Form Seasoning Concrete Release Agent, Concrete Form Release Application, Concrete Form Release

Tips for Pre- and Post-Pouring of Precast Pipe

Posted by Hill and Griffith Company on Sep 3, 2020 8:31:17 PM

Presentation slides from the American Concrete Pipe Association February 12, 2015 presentation

The ACPA offers practical advice on how to inspect precast concrete before and after the pour. Not only does pre- and post-pour inspection prevent waste, but it ensures quality and long-term functionality and customer satisfaction. The best practices captured in the presentation give guidance on documentation, measuring equipment, proper storage and maintenance, pre-pour inspections, proper application of reinforcement, and different types of release agents and their uses. The post-pour advice describes common problems and how to inspect for different issues.

Precast Concrete Pipe Inspection Post Pour

1. Documentation

Documentation is not just recording for posterity. Performing this duty provides a legal record of what steps were taken throughout the pouring process. Should a claim come up downstream, the documentation can show exactly what happened and when. Without documentation, quality control is meaningless. This part of the process allows you to duplicate success, analyze failures, and prove compliance. This is a major benefit to any company and to the industry in general.

Some examples of documentation forms:

  • Joint forming equipment
  • Pipe, manhole and pre-cast reinforcing
  • Pipe, manhole and pre-cast post-pour
  • Box culvert equipment set-up
  • Box culvert reinforcing
  • Box culvert post-pour

Precast Concrete Documentation Forms

2. Pre-pour Inspection

The first step in the pre-pour inspection is to measure the incoming equipment. This is important for accuracy of the pipe or culvert. On the off-chance you were given the wrong size, a quick measurement check could prevent a costly error. Form equipment and joint forming equipment are key to measure prior to pouring.

Proper storage and maintenance will assure the pre-pour inspection goes smoothly. That means storing headers and pallets flat, covering or coating these parts, either priming, sand blasting or re-painting, and cleaning after each use. Performing these maintenance procedures will extend the life of the forms, headers and pallets. 

Measuring the Concrete Pipe Headers

Inspect equipment prior to each use for:

  • Cleanliness
    • Excess build-up
    • rust
    • other impurities
  • Check the condition of equipment for:
    • Chips
    • cracks
    • damage
  • Dimensions
    • Roundness
  • Also check vibrator mounts, seams, gates, lifting lugs, latching devices, bolts and welds

3. Form Release

The purpose of the form release agent is to prevent hardened concrete from adhering to the form. Not only does it protect the form, but it improves the appearance of the concrete. There are a few options in terms of concrete release forms. There are barrier (non-reactive) releases, chemically reactive releases, or some combination of the prior options. While barrier release agents create a physical barrier between the form and the concrete, there are some disadvantages. 

1. You need a thick application of the barrier agent to get an easy release (200-400 ft2/gal)
2. Can cause staining or bugholes
3. May not meet VOC requirements
4. Can cause buildup on forms

Chemically reactive agents are fatty acids (vegetable and mineral oils) that combine with calcium in fresh cement paste to produce a soap-like film between the concrete and the form. Some of the advantages include:

1.Prevents bonding of concrete to form
2. Ultra-thin Layer (approximately 0.005")
3. Reduce bugholes, stains, dusting
4. Typically meets VOC requirements (verify)

Download the full presentation for the full report.


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.

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 Bulletins and Technical Papers for Concrete Casting Products

Tags: Concrete Casting Products, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete, Gricote, Application of Precast Concrete Form Oil, Seasoning of Precast Concrete Metal Forms, Precast Pipe

Tips for Prolonging Form Life

Posted by Hill and Griffith Company on Aug 27, 2020 3:24:14 PM

An article excerpt from the March 1995 issue of Concrete Construction by John A. Koski

For most precasters, forms are one of their most valuable pieces of equipment. Unfortunately, despite the fact that they are a capital asset sometimes worth tens of thousands of dollars, they often are treated with little or no respect. With proper maintenance and handling, however, forms can have a working life of 25 years or more. Extending form life allows you to get maximum value from your forms investment and—perhaps more importantly—to produce products more cost-effectively and competitively. Here are some tips to help ensure that the forms you purchase will still be around well into the next century.

Proper Maintenance of Concrete Forms

1. Keep hammers away from forms.

Using hammers to knock buildup from a form can produce dents and other damage. This damage makes it more difficult to use the form the next time around. Dents in forms also can produce unwanted surface blemishes and other defects in the finished product. Instead of hammers, use scrapers to clean buildup off of forms. It may take longer, but the payback will come in longer form life and less frequent form replacement.

2. Handle forms carefully.

When forms are set into place and removed, make sure they are handled with care. Don’t allow crane operators to apply excessive force to break forms loose. Doing so can permanently twist or warp a form or cause welds to crack or break. Forms should not be thrown down when removed or haphazardly stacked. The reward for proper handling goes beyond extended form life; it also is seen in decreased setup time when the forms are reused and assemble easily without workers having to fight to get the form sections to line up properly.

3. Clean forms without delay.

Forms should be cleaned as quickly as possible after they are removed, while the concrete is still green. Waiting to clean forms allows the concrete to harden, making it more difficult to remove. In addition, removing hardened concrete from forms places them at greater risk of being damaged due to the extra cleaning effort required.

Accropode_Gomera_P8080013

4. Clean forms thoroughly.

Don’t just go over forms quickly to remove concrete from easily accessible places. Make sure that joints, seams, screed rails, corners, and other areas have been completely cleaned.

5. Don’t neglect the outside of forms.

Some producers sandblast and paint the outside of their forms every few years. The sandblasting helps to reveal any defects and makes it easier to obtain a competent repair. The painted surface, on the other hand, makes it easier to remove concrete on the form's exterior. In addition, some precasters oil the outside of their forms weekly to protect against rust and to make it easier to remove concrete.

6. Lubricate fittings and hinge points.

Neglecting to grease these areas can cause forms to wear out faster by permitting the wear caused by the metal-to-metal contact of moving or sliding parts. Lack of lubrication also allows concrete to get into these areas, further increasing abrasion and wear. In addition, built-up concrete in hinges and other areas requiring lubrication can cause the forms to misalign, resulting in twisted and warped forms.

For the full article, please visit the Concrete Construction site.


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Tags: Concrete Casting Products, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete, Gricote, Concrete Construction Magazine

Evaluating and Diagnosing Unformed Surface Imperfections

Posted by Hill and Griffith Company on Aug 20, 2020 4:39:16 PM

This article discusses uniformed surface imperfections and how to prevent them.

An article excerpt from the September 2019 issue of Precast Inc., by Eric Carleton, P.E., NPCA's director of codes and standards.

We always aim for perfection when producing precast concrete products, but sometimes it is just out of reach. This story continues our pursuit of eliminating the causes of imperfections on the surfaces of precast concrete.

New product lines equal more unformed surfaces

Many precast products cast vertically have a limited amount of unformed surfaces. As the precast concrete industry expands to include more plant-cast flatwork – such as precast bridge deck panels, paving slabs and traditional markets such as precast steps and docks – increased knowledge of best practices to eliminate unformed surface imperfections becomes increasingly important.

For the precast producer, unformed surface issues can manifest themselves as shrinkage cracks, crazing, blistering, scaling and delamination, dusting, discoloration or low spots. Technical literature and recommended industry practices contain a common thread of recommendations to reduce the likelihood of these imperfections occurring.

unformedsurfacesSO2019

Those recommendations include starting with a proper mix for both the application and environment, proper curing and careful timing when finishing. Though each item is critically important to produce the best precast product, the emphasis for this article will be placed on curing and timing.

For precasters familiar with only pouring and consolidating concrete within closed formwork, the proper finishing techniques needed for unformed surfaces to provide the strongest, most durable concrete with the desired surface texture is not necessarily intuitive.

Less is more

After casting the concrete, screeding the concrete to level, and possibly an initial float to eliminate low and high spots, it is time to wait. The concrete will begin its bleeding time – the mix will have the heavier constituents settle and consolidate on their own, squeezing excess mix water up and eventually out to the surface. It is most important to discontinue finishing operations until the concrete mix has begun its initial set and bleed water has stopped appearing. In good conditions, this can be identified when the initial sheen of the water has dissipated on the concrete. However, the atmospheric conditions around the concrete surface will dictate how quickly the surface bleed water will dissipate (or evaporate), if at all.

A high ambient temperature, direct sunlight, arid or low humidity and/or windy conditions can lead to surface water evaporating faster than new bleed water can be brought to the surface. That leads to drying of the surface concrete and creates a host of potential surface issues later for the hardened concrete. This premature drying of the concrete can also give the false impression that the bleeding has stopped.

Manufacturing products within a controlled environment is a big benefit for this critical time for the concrete mix. It is important to base the wait time on more than simply bleed water appearance. A true "rule of thumb" is if a gloved thumb pressing onto the concrete surface leaves a 1/4-inch indent or less, then the concrete is ready for final finishing. Similar indent rules have been used in the ready-mix industry for a foot or boot print with a 1/4-inch indent.

This wait time is perfect for setting up and pouring the next form, cleaning the concrete tools, having a safety conversation, etc. However, each precaster will need to determine the optimum wait time based on their mix and production processes and revise as needed when things change. It is a tricky optimization requiring careful thought, record keeping and training, as starting final finishing too early can create serious surface issues and starting too late will mean working with a stiffened concrete, which may be difficult to finish.

More is more

Curing is another important process within the early life cycle of concrete and cannot be overemphasized. It should begin immediately after the final finishing is completed. Proper curing of precast products with unformed concrete surfaces is like that of formed surfaces with respect to temperature conditions. However, large exposed surface areas need special considerations to ensure those areas remain in a moist condition by maintaining a high-humidity environment. At this point, following the initial set and finishing, any added water to the surface is beneficial. Therefore, direct gentle water spray, water-soaked coverings, or liquid membrane curing compounds in accordance with ASTM C309, "Standard Specification for Liquid Membrane-Forming Compounds for Curing Concrete," applied topically on all the exposed surfaces are all good methods to maintain moist conditions. Additional best practices and information on concrete curing can be found within ACI 308R-16 "Guide to External Curing of Concrete."

Common surface imperfections: Causes and solutions

Concrete Crazing

Shrinkage cracks

Crazing

Blistering

Delamination and scaling

Dusting

Discoloration

Low spots

For the full article, please visit the Precast.org site.


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 Products, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete, Gricote, Precast Inc Magazine, National Precast Concrete Association, NPCA

Cincinnati's State-of-the-Art West End Stadium Progresses

Posted by Hill and Griffith Company on Aug 13, 2020 12:21:28 PM

Exerpt from the June 2020 issue of Construction Equipment Guide by Cindy Riley

Construction crews in Ohio are working to complete a $250 million project created to bring an unprecedented fan experience to Cincinnati. Designed by the renowned architecture firm Populous, West End Stadium will serve as the home field of FC Cincinnati of Major League Soccer (MLS).

"West End Stadium will be Cincinnati's newest sports stadium, and the anchor for neighborhood revitalization in the West End, as the city continues its remarkable renaissance," said Lizz Summers, FC Cincinnati vice president of communications. "A world-class venue with a design unlike anything in North America, West End Stadium will have clear and close views from every single seat in the building.

900x0_s3-48856-M-OH-116_20-CR-1

"The fan experience is central to the design of the building, creating an intimate atmosphere that will create a true home field advantage for FC Cincinnati. With considerations also made to accommodate other events, both sporting and cultural, West End Stadium is set to become a key destination for patrons from all over the Midwest."

According to Summers, West End Stadium is envisioned to be the jewel in the Queen City's crown.

"With a fan-forward strategy, the stadium will draw eyes and attention to Cincinnati. Soccer is a global game, and West End Stadium will provide a platform to bring Cincinnati to people around the world. MLS is already broadcast in more than 170 countries, but when you then layer in national team games, international friendlies and other cultural events, Cincinnati will gain global attention. With the growth of corporate business and acclaimed cultural enterprises here in the city, we believe that West End Stadium will become another attraction that sets Cincinnati apart from other similar cities."

Jeff Berding, FCC president, had a vision for what FC Cincinnati could mean to the area.

"First, launching the club as a minor-league franchise and realizing that it would not only succeed, but flourish and set new business and on-field standards was rewarding and eye-opening for the entire region," said Summers. "It was a source of immense pride for an area that truly embraces hard work and community success. The resounding success of Jeff's vision helped launch FC Cincinnati into Major League Soccer in record time. Now, after the long hours, hard work and collaboration to get the stadium project approved and under way, seeing West End Stadium rise so quickly out of the ground and take shape is really inspiring.

"The club is very excited about the lighted fin structure that will make up the external skeleton of the facility. Each fin will have an LED light system built into it that, when programmed, will allow animation and motion graphics to appear on the east side of the building. It will be unique to any sports facility in North America, and is being prepared by SACO, the same company that installed the system on Burj Khalifa in Dubai."

 

The entire east side of the stadium is designed to serve as an entryway to the community. A grand staircase will lead to the main gates through a large open plaza. Both the northeast and southeast corners of the stadium also will serve the community, both with open, programmable areas and the largest team store in the city and Major League Soccer.

 

"The project team also is being considerate and thoughtful in the smaller touches throughout the stadium, including seating choices in every section and design themes in the four premium clubs and suites, as well as concourse layout and design to accommodate the 26,000 fans who'll be on site for each event," said Summers.

 

The owner's representative is Machete Group, while Turner Construction serves as the general contractor.

"To this stage, we've had two main challenges, but both have really boosted the project to make it better," said Turner Construction project manager David Bareswilt. "The first was collaborating with the city, county, state and the two immediate neighborhoods to gain project buy-in and approval so quickly. We worked hard to put a great community benefits agreement in place with the West End, unlike any other sports project in the city, to help ensure our actions and intentions of being a supportive citizen in our new neighborhood. We've received a lot of tremendously positive feedback from the overall West End neighborhood about our commitment and actions to support the revival of the West End.

"The other major challenge was that we changed architects midway through the design work and after site work began, but as Populous came on board with Jonathan Mallie as the lead architect, we worked hard to make a lot of really amazing adjustments and changes to reach the point we're at today. When it opens, through so much hard work from a tremendously dedicated stadium staff, the stadium is going to be world-class and garner worldwide attention. We're really excited about that, and it will make not only the city exceptionally proud, but make all the hard work worth the end product."

Site work began in the summer of 2018. After the completion of the high school football season, workers were able to deconstruct the existing high school stadium and stage the formal groundbreaking on Dec.18, 2018. MLS Commissioner Don Garber was among the attendees.

Now that all steel work for the lower bowl is complete, Turner is working on construction of the upper bowl and structure, including work on the canopy roof. Steel work for the 360-degree roofing system is expected to be complete in early July.

 

Simultaneously, concrete work is being performed on flooring levels. Fireproofing and other internal work is being carried out throughout the stadium non-public and team campus areas, and the precast is being installed in the lower bowl, with the upper bowl set to start installation.

 

Weather has not been a major factor, to date.

Read More


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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 »

 

Tags: Hill and Griffith, Concrete Form Release Agents, Concrete Release Agents, Concrete Casting Supplies, Precast Concrete Form Release, Concrete Form Release Application, Concrete Form Release, Concrete Form Release Agent, Construction Equipment Guide

Release Agents - Principles and Utilization in Precast Production Facilities

Posted by Hill and Griffith Company on Aug 6, 2020 4:21:10 PM

Exerpt from the December 2008 issue of Concrete Plant International by Volker Gretschel

For some years now, the trend in precast construction has been towards satisfying the desire for concrete without air voids and other cavities. There are many factors having a major influence on the appearance and quality of formed concrete surfaces. Once the concrete's recipe has been perfected, the key to high-class concrete surfaces is to be found in employing the right release agent.

Release agent types

A great variety of different concrete release agents are to be found on the market. The first release agents were made from mineral oils, which were then increasingly replaced by mineral oil additives. A further step brought about an advance in processing by adding solvents. Solvents improved penetration onto the formwork, and quantity dosage was simplified by the solvent's evaporation. Beginning with the nineties onwards, more concentrated work was carried out, together with colleges, on the development of emulsion products. These have been represented in many manufacturing operations for over 10 years now. 

SCC-Bug-Holes-2

Make-up and mode of operation
All release agents, which are used in larger quantities, have both a physical and chemical separating effect. The physical separation is assured by the oil proportion and the chemical by the additive part. The parts active in the separation process are generally fatty acids or ester. In the case of vegetable oils, there exist no strict dividing lines (physical/chemical) in the fatty acids they possess, i.e., just the oil phase alone can generate a chemical separation. Utilizing paraffin, naphthenic or aromatic oil bases makes little difference from a technical viewpoint but, nonetheless, have considerably more potential drawbacks concerning health and olfactory issues.

Chemical separation generally occurs between the COOH groups in the fatty acids and the calcium hydroxide in the concrete. The product thus created which causes separation is so-called calcium soap.

Compaction methods
Further influences come into play through the degree of compaction, the method of compaction, temperature and time. The greatest challenge for release agents is currently the vibratory compaction plants, which have been introduced in the last few years. Although these plants are very quiet, the contact surface is very abrasive and demands a release agent with a very strong adhesive force and excellent chemical separation. The formwork release agents designed for vibratory compaction are very frequently too reactive for agitation compaction or for self and easy compacting concretes. The result is extreme "powdering".

Application method and amount

The quantity of release agent is a very important factor in achieving a presentable concrete surface. It is affected by the application method, the type of release agent, the processor and the nozzle used. The objective is to have a thin and even film of release agent. Systems without solvent agents require very carful processing as the applied with layer is also the residual separating layer. The case is quite different with emulsion-based release agents or those with solvents, as only about one-third of the wet layer is left as a separating film. This means that a consistent reproduction can be obtained even with different layer thicknesses. 

A high-pressure sprayer continues to be the most common means of application. Its main benefit lies in its ability to be used precisely and everywhere but this advantage can also be a disadvantage as the result depends very much on the processor and his experience. This can be contrasted with gantry sprayers, which are ideal for large surface formwork, but only of limited use in spraying partial areas. Plant engineering developments are varied here. Plants with heated reservoirs are especially commendable even as they permit consistent viscosity, and thus, enable the release agent to be sprayed constantly even at varying atmospheric temperatures. When solvent-free release agents are employed and heated to 35° C, a very fine spray jet can be generated which, in turn, favors fine application. No further remarks will be made at this point on the utilization of rags, mops, etc., as these methods can only be taken into consideration for special cases.

Spraying with rotation sprayers poses problems in manual processing as the equipment is relatively heavy and fatigue symptoms quickly crop up. However, in combination with stationary spraying equipment, rotation sprayers are a good alternative to high pressure plants. Provision must nonetheless be made for spraying vertical formwork parts separately.

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Best Practices for Precast Concrete On-Site Wastewater Tanks

Posted by Hill and Griffith Company on Jul 30, 2020 5:09:20 PM

Exerpt from NPCA's Precast Concrete On-Site Wastewater Tank Best Practices Manual

Best_Practices_Concrete_Form_Release_Agents.jpgTable of Contents highlights
Structural Design ................................................4
Materials.............................................................4
Concrete Mix Proportioning..............................10
Lifting Inserts.................................................... 11
Coatings............................................................12
Production Practices.........................................12
Pre-Pour Checklist.............................................16
Casting Concrete..............................................17
Curing ...............................................................18
Post-Pour Operations........................................19
Post-Pour Checklist...........................................20
Finishing and Repairing Concrete.....................21
Seals, Fittings and Joints ..................................22
Tank Installation................................................24
Testing ..............................................................26 

Introduction
This manual provides guidance on material selection, manufacturing techniques, testing and installation to attain structurally sound, watertight precast concrete septic tanks and related components for on-site wastewater treatment systems. It is not intended for use as a regulatory code or minimum design standard, but rather as an aid to manufacturers, engineers, contractors and owners.

Chemical Admixtures
Although not mentioned specifically, this is good advice for concrete form releases as well, "Store admixtures as recommended by manufacturer and in a manner that avoids contamination, evaporation and damage. Protect liquid admixtures from freezing and extreme temperature changes, which could adversely affect their performance."

Concrete_Pre-Pour_Checklist_copy.jpgConcrete Mixture Proportioning
We liked this description of the "shock absorber" effect of air-entraining, "Air-entraining admixtures are designed to disperse microscopic air bubbles throughout the concrete’s matrix to function as small “shock absorbers” during freeze-thaw cycles. The required air content for frost resistant concrete is determined by the maximum aggregate size and severity of in-service exposure conditions (ACI 318, “Building Code Requirements for Structural Concrete and Commentary”) In addition, air entrainment improves workability and reduces bleeding and segregation of fresh concrete while greatly improving the durability and permeability of hardened concrete."

Production Practices
Excerpt from the part about form releases, "Apply form release agents in a thin, uniform layer on clean forms. Do not apply form release agents to reinforcing steel or other embedded items, as it can compromise the bond between the steel and the concrete. Do not allow the form release agent to puddle in the bottom of forms. Remove excess form release agent prior to casting."

Stripping and Handling Products
For the best release it's important not to remove the forms too quickly, "Concrete must gain sufficient strength before stripping it from the forms. Due to the nature of the precast business, the American Concrete Institute recognizes that forms will usually be stripped the next workday. Under normal conditions (concrete temperature greater than 50° F [10˚C]), a properly designed concrete can reach the minimum compressive strength for stripping within this time period. Periodic compressive strength testing of one-day strength or stripping strength cylinders is recommended to confirm that proper concrete strength is attained."

The manual concludes with a comprehensive glossary. Thanks to the NPCA for a great reference guide.

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Pre-Concrete Checks for Formwork and Release Agents

Posted by Hill and Griffith Company on Jul 23, 2020 4:02:25 PM

Excerpt from TheConstructor.org

Promising apparatus successfully tested in the laboratory

Before the concrete is poured into the formwork, it must be checked by someone who has been trained to inspect formwork. Depending on how big or complicated the pour is, the inspection may just take few minutes or it could take hours. Only when the formwork has been approved, may the pour take place.

Formwork pressures are function of height (including the height from which concrete is dropped into the forms) and are affected by concrete workability, rate of stiffening and rate of placing. One task of the temporary works co-ordinator is to consider such factors as ambient temperatures and concrete composition, when calculating maximum permissible rate of concrete placing.

 josue-isai-ramos-figueroa-qvBYnMuNJ9A-unsplash
 

Exceeding this limit may lead to unacceptable formwork deflections, loss of grout / concrete at joints, or even collapse. The cost of remedial work due to formwork deflection will usually exceed the original cost of doing the job properly.

Below are the checks that should be verified before pouring begins:

  • Is the formwork erected in accordance with the approved drawings?
  • Is the formwork restrained against movement in all directions?
  • Is it correctly aligned and leveled?
  • Are all the props plum, and at the right spacing?
  • Are bolts and wedges secure against any possible looseing?
  • Has the correct number of ties been used? Are they in the right places and properly tightened?
  • Are all inserts and cast-in fixings in the right position and secure?
  • Have all stop ends been properly secured?
  • Have all the joints been sealed to stop grout loss (especially where the formwork is against the kicker)?
  • Can the formwork be struck without damaging the concrete?
  • Are the forms clean and free from rubbish such as tie wire cuttings, and odd bits of timber or metal?
  • Has the release agents been applied, and is it the correct one?
  • Are all projecting bars straight and correctly positioned?
  • Is there proper access for placing the concrete and compacting?
  • Have all the toe-boards and guard rails been provided?

Release Agents for Formwork

Formwork needs to be treated with a release agent so that it can be removed easily after the concrete has set. Failure to use a release agent can result in the formwork sticking to the concrete, which may lead to damage of the concrete surface when it is pried off.

A single application of release agent is all that is required when forms are then used. Care must be taken to cover all the surface that will come in contact with the surface of concrete. However, if there is an excess of release agent, it may cause staining or retardation of the concrete.

There are different release agents depending on what material is used for the formwork. The three most common release agents for formwork are:

  1. Neat oils with surfactants: used mainly on steel surfaces, but also suitable for timber and plywood.
  2. Mold cream emulsions: good general purpose release agents for use on timber and plywood.
  3. Chemical release agents: recommended for high quality work, applied by spray to all types of form face.

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Coatings that Affect Bond to Reinforcement

Posted by Hill and Griffith Company on Jul 16, 2020 1:53:30 PM

ASCC Position Statement #3

Excerpt from March 2003 publication from the American Society of Concrete Contractors

ACI 318-02, "Building Code Requirements for Structural Concrete," Section 7.4.1 states, "At the time concrete is placed, reinforcement shall be free from mud, oil, or other nonmetallic coatings that decrease bond." The Commentary does not indicate which nonmetallic coatings decrease bond. It does, however, indicate that research has shown that a normal amount of rust increases bond, and further states that: "Specific limits on rust are based on tests, plus a review of earlier tests and recommendations."

Preparing Rebar for Concrete Pouring

ACI 301-99, "Specifications for Structural Concrete," Section 3.3.1.1 states, "When concrete is placed, reinforcement shall be free of materials deleterious to bond." No guidance is provided on which materials affect bond, but section 2.3.1.13 on Formwork states, "Do not allow formwork release agent to contact reinforcing steel…" This provision was introduced in ACI 301-1996.

Engineers or inspectors typically direct concrete contractors to clean bars that are coated with materials believed to decrease bond. Form release agents, bond breakers and cement splatter sometimes come in contact with reinforcing steel before concrete is placed. In the absence of data concerning the types of materials that decrease bond, cautious engineers and inspectors usually require all such materials to be cleaned from the reinforcing. However, two recent studies have provided test data showing that some of these materials don't decrease bond.

Preparing Rebar for Concrete Pouring

Two articles—"How Clean Must Rebar Be?" (Concrete Construction, June 1998) and "Effect of Reinforcing Bar Contamination on Steel Concrete Bond During Concrete Construction" (ACI SP-209, Proceedings, ACI Fifth International Conference, December 2002) — contain results of bond tests on reinforcing bars that had the entire surface covered with nonmetallic coatings. In the first study, bond was measured on bars embedded in cylinders (similar to tests used to establish the effect of rust on bond). In the second study, bars were embedded in beams to simulate flexural conditions in members. Both studies used three specimens for each coating to compare against three control specimens.

The test results of both studies indicate that form release agents (three different types including water and petroleum-based products), bond breakers (three different types including water- and solvent-based products), and cement splatter (same mix proportions as the concrete) did not affect the bond for concrete strengths of 4000 and 5000 psi. Based on these test results, and the statements in ACI 318 and ACI 301, removing these materials from reinforcing bars isn't required because the materials don't decrease bond.

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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.

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 Bulletins and Technical Papers for Concrete Casting Products

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