<img alt="" src="https://secure.hims1nice.com/150891.png" style="display:none;">

Concrete Casting News from the Hill and Griffith Company

Formwork Rust: Reasons and Prevention

Posted by Hill and Griffith Company on Jan 23, 2020 8:00:00 AM

Excerpt from the April 2007 issue of Concrete Construction by Peter Boos and Reiner Haerdtl

Rust on steel formwork leads to stains on the concrete unit

Introduction

Steel formwork is used in prefabrication operations because of its robustness and reusability, as well as its ability to produce prefabricated units with smooth surfaces. On these steel molds, brownish-reddish rust spots sometimes form while the concrete hardens. This rust could lead to brown or red spotty discolorations on the concrete surface lower the concrete element's appearance. Removing these discolorations by sanding and resurfacing is costly and time-consuming.

Rusted Concrete Form

Reasons for corrosion

There are several reasons for metal corrosion, and thus different forms: contact corrosion, crack corrosion, inter-crystalline corrosion, pitting corrosion, etc. The corrosion of iron and/or steel is an electrochemical process in the presence of water and oxygen. Metal corrosion occurs at the spot with the higher electro-negative potential. Here, the metal ions dissolve from the surface into the solution and when they collide with hydroxide ions they precipitate as iron hydroxide.

The resulting iron minerals are formed, depending on temperature and air humidity. Due to constant recrystallization, no permanent protective rust layer is formed on the surface that would prevent further corrosion. Corrosion is prevented by protective coatings, such as greasy lubricants, a coat of varnish or other metals that prevent air and moisture from contacting the iron surface. Unfortunately, under the daily production load of a prefabrication plant, no protective layer will last long.

The appearance of rust on steel formworks can look quite different. While some steel molds rust over their whole surface, others show rust spots arranged linearly like pearls on a string. In other cases, rust spots occur only along the edges of the casting tables near the clamps. Frequently, rust appears periodically in certain seasons and disappears. Most causes for rust formation can be classified as process-related causes or environmental causes and causes related to concrete technology.

Process-related causes

Steel in direct contact with concrete forms a protective passivation layer in the alkaline milieu of concrete, which suppresses rusting. This hardened non-carbonated concrete is the best corrosion protection for reinforcement. Release agents are used to ensure reliable separation of the concrete from the formwork. This means that it acts like a contact barrier between steel formwork and concrete. Due to that, the formation of the protecting passivation is either slowed down or totally suppressed. Nevertheless, release agents prevent the direct contact of water to the steel surface. But a reliably effective form release agent is no rust protection agent for steel formwork, although a release agent may well contain small amounts of rust inhibitors. By taking the thinness of the release agent layers into account, no rust protection can be provided in this way.

In concrete's alkaline state, the metallic oxidation of the steel required for this effect to materialize does not take place. Rust can therefore develop only where water films or specific chemical elements and compounds enable oxidation, for example, in case of condensation water. It is always recommended to consult the supplier of the release agent when problems with rusting arise.

Magnets can promote rusting of steel casting tables, especially in contact with water. Clamps are placed over the magnets and positioned on the steel tables. When the magnets are placed on the casting tables before the surface has been sprayed and protected with release agent or when the steel surface underneath the clamps are not fully covered by the release agent, rust is more likely to occur. Typically, linear rust spot patterns are due to magnets.

Removing rust mechanically, such as by sanding, can lead to "activated" steel surfaces, which are especially prone to rust. Some manufacturers of casting tables sand the steel surfaces as a service. After sanding, the surface is treated with waxes and chemicals that penetrate deeply into the pores of the steel, which protect it from rusting for a period of time. Without such a treatment the formwork will definitely show rusting.

But this provides no long-term solution unless the real reason of the rust problem is eliminated. In the long-term, new rust will develop and the protective layer will wear off in the course of ordinary mechanical load. When the cause of rusting is analyzed and eliminated the rust spots will generally encapsulate themselves on their own (deeply embedded black rust).

Using chemicals to remove rust or attempts to form a protective coating on the casting tables, such as by phosphorizing, are usually no solution. The black coating that is produced in the process is not resistant to the mechanical load imposed on the surface during production and chips off, so steel surfaces can rust again. This chemical treatment may even lead to additional black discolorations on the concrete surfaces.

Environmental Causes

Read more

Technological Causes

Read more

Recommendations for Prevention

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 »

Tags: Concrete, Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Casting Products, Concrete Release Agents, Concrete Construction Magazine

Applying Concrete Form Release Agent

Posted by Hill and Griffith Company on Jan 16, 2020 8:00:00 AM

Excerpt from the August 2010 issue of Concrete Construction

Q: How often should concrete release agent be applied to plywood form panels?

A: Plywood forming panels usually are treated with a concrete form release agent at the mill, but it's still important to evaluate their condition carefully before using them for the first time. Unless the mill treatment is reasonably fresh, the panels may need another treatment of release agent before the first use. Even medium-density overlays should be treated with a chemical release agent before the first use and between each pour. 

Concrete_From_Release_1

Applying a thin film of concrete form release agent to both reused panels and new panels that are not freshly mill-treated will:

  • prolong the panel's life
  • enhance its release characteristics
  • minimize the potential for staining the concrete

Apply the release agent a few days before using the forms for best results.

You also should determine whether an edge sealer was applied at the mill, and if not, seal any cut edges with two coats of polyurethane paint or varnish before the first pour. Otherwise, the forming panels will absorb moisture and swell at the edges.

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 »

Tags: Concrete, Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Casting Products, Concrete Release Agents, Concrete Construction Magazine

Cutting-Edge Production Management System is a Game-Changer for Canadian Precast Manufacturer

Posted by Hill and Griffith Company on Jan 9, 2020 8:00:00 AM

Excerpt from issue 6 of Concrete Plant International by Claude Goguen

Traditional wetcast production plant setups make it nearly impossible to drive productivity because there are too many variables and there is no linear process flow that can be easily tracked, measured, analyzed and optimized. The Prima wetcast system offers a solution to this by organizing the different work processes in the plant and by tracking and measuring these processes for analysis and evaluation. Precast producers like M-Con Pipe & Products Inc have found that Prima helps them organize the wetcast production of many different kinds of products and is the solution they were seeking to drive efficiency while maintaining high quality.

1906_ro_afinitas

The Problem: Inefficiency and Floor Space

Doug Galloway had a problem and an idea. The president of Ontario-based M-Con Pipe & Products Inc., Galloway was out of space on his wetcast production floor and looking for ways to work more efficiently.

That was the problem. The idea? Some type of carousel system that would move forms to workstations set up on a production line - like an auto assembly plant. Instead of moving buckets of concrete and production teams around the plant to strip, prep and fill the forms, bring the forms to the workers. 

Galloway took the idea to HawkeyePedershaab in 2013, and, little more than a year later, the Precast Industrial Management System, or Prima, was born. The HawkeyePedershaab engineering and sales team took Galloway's concept and brought it to life, creating a wetcast production system that saves space, reduces labor, increases the throughput of products and provides comprehensive analytics to management.

Based in Ayr, Ontario, just west of Toronto, Canada, M-Con Pipe is known as an innovative leader in providing precast concrete infrastructure products throughout Central and Southwestern Ontario. Even though they have a 100,000 sq. ft. (approximately 9300 m2) manufacturing facility, things were tight on the production floor.

"We were doing a lot of wetcast products, and they were taking up a lot of floor space," Galloway said. "The floor space was crammed with products and forms, and we were having to move them with lift trucks to strip the product and to pour concrete. So, we were looking for a more efficient way to manage wetcast forms. That's when we started thinking of this system. Because of the work we had done in the past with Hawkeye, we approached them about putting together this carousel-type system that they eventually called Prima."

The Solution: Prima Automated Wetcast Production

To understand how Prima works, let's follow one form down the production line. At the beginning of the day, the form is located in its assigned spot on the floor, monitored by an RFID tag. As the production line starts, the previous day's product is stripped from the form and moved out to the yard by a chain conveyor.

The form sits on a cart that rides on a moving conveyor that sends it to the next station, where the form is cleaned, oiled and set up for pouring. From there, it moves to the reinforcement station, where the steel is placed. At this stage, there may be an option to pull the form offline if it needs any special preparation, reinserting it after the additional prep.

The next stop is the form filling station, where the operator confirms that all the preparation has been completed and the concrete is poured into the form. An automated overhead manipulator then moves the green product to predetermined curing location where the product cures in the form until it is ready to return to the production loop to start the process over. There is more to the system, of course, according to Randy Beelman, Eastern North America Sale Manager for HawkeyePedershaab.

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 »

Tags: Concrete, Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Casting Products, Concrete Release Agents, Concrete Plant International Magazine

5 Rules of Watertightness to Reduce Porosity and Permeability

Posted by Hill and Griffith Company on Jan 2, 2020 4:32:39 PM

Manufacturing specified watertightness in precast concrete products is straightforward if you play by the book.

Excerpt from the November 2012 issue of Pre-Cast Inc. by Claude Goguen

Dutch legend has it that there was once a small boy on his way to school who noticed a slight leak in a dike where the seawater trickled in through a small hole. Knowing that the dike held back the sea from flooding his village, the boy poked his finger into the hole, and so stemmed the flow of water. Sometime later, a passerby saw the boy and went to get help. Thus the villagers arrived, repaired the dike and sealed the leak.

If that dike had been made of quality precast concrete, this legend wouldn’t exist, and the boy would have gone to school without fanfare. A good precaster would have known the seawall’s intended use and would have followed industry guidelines to ensure a leak-proof and watertight dike.

Concrete_From_Release_2

Two “P’s” of watertightness

“Watertight” is a term we often hear in describing many precast products. Whether above-ground or underground products, in many instances, we want to prevent fluid from getting from one side of the concrete wall to the other. In making our structures watertight, there are two areas where we’re concerned: the concrete itself, and joints and penetrations.

Let’s start with the concrete. When discussing watertightness of concrete, we must consider the two P's: porosity and permeability.

Porosity is the ratio of the volume of openings (or voids) to the total volume of the material. It represents the storage capacity of the material. Concrete is inherently porous, although a sealer can be added to the concrete surface to prevent water penetration. It’s practically impossible to make an absolutely nonporous concrete where water won’t penetrate even a fraction of an inch. However, we can control the size and distribution of those pores and limit the penetration. The pores, which are tiny voids, reside in the cementitious paste (see Figure 1) and can be subdivided into two types: gel pores and capillary pores. The gel pores exist in every system and are part of the glue that forms around the aggregate to make concrete what it is. Gel pores are very small and not a real problem.

Permeability is the measure of the ease with which fluids can flow through a porous material. Permeability is expressed in terms of speed (in./s or mm/s) as opposed to porosity, which is expressed in volume per volume (cu in./cu in. or mm3/mm3).

Permeability depends on other factors, such as aggregate gradation and density. In high-quality concrete, infiltration is very slow, around the order of 3.94×10-11 in. / s (1.00076 x 10-12 m/s). To give you an idea of how slow that is, it would take about 4,800 years for water to breach a 6-in.-thick wall – well beyond the terms of your warranty for sure.

Watertightness Rule #1:
Use a low w/c ratio mix design
The w/c ratio is the most important factor in concrete design. The water content in a mix controls the moisture’s rate of entry (which may contain aggressive chemicals) and the movement of water during the freeze-thaw process. Compare the leading causes of low durability versus high-quality concrete listed in Figure 2. A mix design for durable, watertight concrete should have a maximum w/c ratio of 0.45 and require a well-graded mixture of fine and coarse aggregates.

The more excess water in a mix, the lower the strength, durability and watertightness. Excess mix water results in capillary pores – entrapped air pockets in hardened concrete that will reduce its resistance to leakage. On the other hand, too little water can cause placement difficulties and undesirable effects such as honeycombing. The effect w/c ratio has on the watertightness of a concrete mix is illustrated in Figure 3.

Durability and densification can also be improved with admixtures. Many admixtures can be used to improve concrete’s workability, durability and densification. In controlling our water content while trying to maintain workability, water-reducing agents can be used. Air entrainment agents produce near-microscopic independent bubbles that improve the watertight performance of hardened concrete. Air entrainment also improves concrete’s freeze-thaw performance and overall durability in addition to easing the placement process.

Watertightness Rule #2:
Meet minimums for cementitious material
Rich concrete mixes provide a denser, more impermeable and superior finished product. Consequently, specifying that cement content does not exceed a minimum amount is recommended. In the case of watertight structures, a minimum cement content of 564 lbs/cu yd is suggested (the effect of cement content on concrete permeability is illustrated in Figure 4).

Cement content or total cementitious content needs to be based on the guiding specifications, but generally, cements with a higher fineness (> 600 m²/kg Blaine fineness) will benefit workability and reduce bleeding, both of which are beneficial for watertight concretes.

The use of supplementary cementitious materials such as fly ash, slag and silica fume can also increase concrete’s density, thus reducing capillary porosity and permeability.

Watertightness Rule #3:
Use well-graded aggregates
Gradation of the aggregates is an important factor and should be of primary consideration. Shape and texture of the particles will also affect workability. Aggregate moisture needs to be accounted for when adjusting the mix design so that additional surface water from aggregates does not contribute to a more porous hardened product. Concrete mixtures that are not well-graded can permit water to pass through the finished structure, as illustrated in Figure 5.

Watertightness Rule #4:
Follow quality manufacturing processes
Quality concrete manufacturing processes are critical to the production of durable, watertight concrete products. Proper attention to important pre-pour activities such as maintaining prescribed mix proportions, form cleanliness, and specified reinforcement placement and minimum cover is very important. For concrete products permanently exposed to earth or moisture, increased concrete cover, as specified in ACI 318, is recommended to ensure the corrosion protection and proper bonding of concrete around the reinforcement. Adequate consolidation of freshly placed concrete is an extremely important factor to produce a high-quality, dense concrete. Added emphasis on consolidation is required for a desirable low w/c ratio concrete, as it requires a higher compactive effort (a summary of preferred practices is illustrated in Figure 6).

The degree of consolidation can have a marked effect on the watertightness of concrete. As illustrated in Figure 4, a 5% reduction in concrete consolidation can result in a 20% reduction in watertightness. This figure also shows that higher cement content improves watertightness. Defect-free surfaces produced by using smooth forms and appropriate release agents can considerably improve the impermeability of a precast concrete product. Concrete must be adequately cured if its optimum properties are to be developed. An adequate supply of moisture, either by covering or other means, is important to ensure full hydration and reduce the porosity level such that the desired durability is attained, as shown in Figure 7. Although a period of moist curing significantly reduces permeability, the effects of curing are less pronounced with lower w/c mixes.

Watertightness Rule #5:
Execute joints and penetrations carefully
A system is only as strong as its weakest link. Close attention to all jointed, connected and sealed areas is necessary to ensure watertightness. Potential differential settlements and thermal movements must be addressed in the design and manufacture of joints and penetrations.

Little Dutch boy or precaster: Rules matter
Whether you’re building a septic tank in Wisconsin or a dam in Holland, precast concrete products are well-suited for durable, watertight applications. The best strategy for manufacturing a durable, watertight concrete structure is to play by the book and pay close attention to all recommended concrete manufacturing and installation details. Like the legend of the little Dutch boy, the price of ignoring the rules can be enormous.

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 »

Tags: Concrete, Concrete Form Release Agents, Biodegradable Concrete Form Release, Concrete Casting Products, Concrete Release Agents, Precast Inc Magazine

Understanding Biodegradable Concrete Form Release Agents

Posted by Hill and Griffith Company on Dec 19, 2019 11:59:10 AM

Excerpt from the May 2018 issue of Concrete Products

As consumers become more eco-conscious and more informed about how the materials they buy affect the environment, the desire for environmentally friendly products is on the rise. This holds for concrete producers and contractors as well. Whether it’s to meet specific federal and state requirements on biodegradability, volatile organic compound (VOC) exposure limits, or because customers are requesting “green” materials, owners, contractors and architects want products on their job sites that are less harmful to the environment.

There are multiple ways to measure a product’s environmental impact. These include carbon offsets, whether or not the ingredients are compostable, non-toxic, ozone-safe, recyclable, refillable, and the percentage of recycled content in the product. When it comes to chemicals used in concrete production and construction, biodegradability is a primary measurement of eco-friendliness.

WHAT QUALIFIES AS BIODEGRADABLE?

A product is classified as biodegradable when it is capable of returning to its natural, raw material state quickly through biological means. A truly biodegradable material will break down into carbon dioxide, water, biomass and other natural minerals that don’t adversely affect the ecosystem.

The Federal Trade Commission’s (FTC) Green Guides, last updated in 2012, states that for marketers to make an unqualified claim on degradability, they must prove that the “entire product or package will completely break down and return to nature within one year after customary disposal.” This issue of “customary disposal” is key because the characteristics of the environment in which the material is disposed can greatly affect its ability to break down. 

READILY VS. INHERENTLY VS. ULTIMATELY BIODEGRADABLE

The U.S. Environmental Protection Agency and the FTC recognize biodegradability by two classes, readily and inherently. (A third class, ultimately biodegradable, covers both readily and inherently biodegradable and more.) Readily and Inherently biodegradable products have the natural ability to biodegrade to their natural state when subjected to sunlight, water and microbial activity. The difference lies in how quickly they achieve complete biodegradation. To measure the speed of biodegradability, EPA recognizes a 28-day half-life. Half-life is the time required for one-half of a given component to decay.

Readily biodegradable: Product is capable of biodegrading from 60-100 percent in 28 days or less. In other words, these materials achieve complete biodegradation at a quick rate.

Inherently biodegradable: The product is capable of biodegrading from as low as 20 percent to less than 60 percent in 28 days. Such products will achieve less biodegradation than readily biodegradable products in the same time span, but eventually, they all get to the same place.

Concrete Form Release Agents Help Form Removal

BIODEGRADABLE RELEASE AGENTS

As with any industry, concrete interests have set federal guidelines for classifying products as eco-friendly. Just as federal VOC regulations are put in place to protect the ozone, biodegradability standards are in place to protect land and water from contamination. Keep in mind, states can apply more stringent requirements.

Water-based release agents are suitable for most concrete form surfaces to include steel, plastic, fiberglass and bare or overlaid plywood. They can be used on many rubber and closed-cell foam forms and are safe for use in enclosed building sites. Water-based formulations are free of conventional form oil, diesel oil and kerosene. Because they are water-based, these release agents are susceptible to freezing, usually require mixing before use, and can have a shorter shelf life due to emulsion. While water-based release agents are typically inherently biodegradable, they are not always readily biodegradable. Even a water-based formulation must meet the EPA requirements of the 28-day half-life of 60 percent or more to be considered readily biodegradable.

When temperatures allow, an environmentally responsible, water-based release agent can produce smooth, uniform concrete surfaces without staining and with minimal surface voids while providing a crisp, positive release. With proper research and due diligence, concrete producers and contractors can find an environmentally responsible option that yields quality results in a readily or inherently biodegradable formulation.

Read more


Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend products that suit your needs.

Hill and Griffith Samples

Product Samples

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

 

Hill and Griffith Customer Service

Technical Services & Support

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

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

Properly Applying Concrete Release Agents

Posted by Hill and Griffith Company on Dec 13, 2019 8:31:59 AM

Reprinted from the National Precast Concrete Association Tech Notes

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).

Concrete_From_Release_1.pngApplying Release Agents

Release agents should be applied 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.

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.

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.

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.

Concrete_From_Release_2.pngSeasoning

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.

• 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 publication is designed to provide accurate and authoritative information, however the National Precast Concrete Association does not guarantee the validity or accuracy of any data, claim or opinion appearing in this publication. If engineering, legal or other professional services are required, the services of a competent professional should be obtained. The National Precast Concrete Association does not assume and hereby disclaims liability to any person for any loss or damage caused by errors or omissions in this publication, regardless of whether such errors result from negligence, accident or any other cause whatsoever.

Read the NPCA whitepaper in its entirety.


Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend products that suit your needs.

Hill and Griffith Samples

Product Samples

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

 

Hill and Griffith Customer Service

Technical Services & Support

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

Tags: Concrete, Concrete Casting Products, Concrete Release Agents, National Precast Concrete Association, NPCA

Coating Tilt Up Concrete Walls

Posted by Hill and Griffith Company on Oct 24, 2019 3:55:17 PM

Originally published in the March 2011 issue of Concrete Construction

Q: The painted surfaces of some of the tilt-up concrete walls on our projects seem to develop blisters, peeling, or flaking shortly after application. Sometimes this occurs after it rains. Is there anything different about tilt-up walls that makes this happen?

A: As with any paint or coating project, the key to good results is paying attention to the three Ps: Prep, Prime, and Paint. Procedures for painting and coating concrete surfaces are different from other surfaces, and tilt-up concrete surfaces do require special preparation.

Causes of Defects on Tilt Up Concrete Walls

Surface Preparation: The most likely reason for blistering and peeling in a tilt-up wall, especially if it occurs shortly after it rains, is failure to remove the mold release agents and bond breakers used for casting the concrete component.

This is the big difference between tilt-up concrete and other forms: It is cast on the jobsite in concrete forms. After the concrete wall or column has cured, a mobile crane tilts the piece up and moves it into place, where it is braced into position and secured. Painting contractors may not always be fully aware of this because they arrive on the jobsite after the walls are in place.

To prevent the concrete from adhering to the molds, contractors apply release agents, or bond breakers, to the mold before the concrete is poured. These release agents can be solvent-based, water-based, oil-based, silicone-based, silicone-free, silicone water-based and many other proprietary combinations. But they all perform the same function—they create lower surface energy between the concrete form and the concrete to mitigate adhesion. The objective is to be able to lift the cured concrete from the casting mold smoothly and cleanly.

Unfortunately, release agent residue also can inhibit adhesion of coatings and paint to the concrete surface. Most painting contractors are aware of this, and paint companies do a good job of educating painters about the need to remove release agent residue before painting or coating tilt-up concrete surfaces. Power washing at the specified pressure using the specified cleaning solvent should do the trick, but there are two cautions.

One, be methodical and thorough when power washing. Two, there is a trend toward making release agents and paints/coatings more compatible, but it is always prudent to power wash the surface first. Even with “compatible” release agents, if too much was applied to one area, it could swamp the system and adversely affect coating adhesion.

All concrete surfaces must be washed before coating to remove dirt, dust, and excess sand anyway, so always take the extra step of power washing tilt-up concrete to remove any release agent residue, whether they are compatible or not.

Read More


Additional news from Concrete Construction

Repairing Bugholes

Concrete Form Maintenance


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 Form Release Agents, Concrete Casting Products, Concrete Casting Supplies, Concrete Pipe, Concrete Safety, Precast Concrete, Grifcote FR 50 Concrete Form Release, Bio Gold Concrete Form Release, Grifcote, Concrete Construction Magazine

5 Options for Dry-Cast Concrete Pipe Dip Tank Maintenance

Posted by Hill and Griffith Company on Oct 10, 2019 2:24:06 PM

Originally published in the May-June issue of 2015 PRECAST INC, by Bob Waterloo

Maintaining the optimum reactive level of form release agents in pipe production dip tanks ensures performance and quality. 

Dip tanks play a critical role in the dry-cast pipe production process for many manufacturers. The reactive properties of the fatty acids in the form release agent enable the pipe to release from the pallet/header smoothly. Here’s the problem. The cement/concrete residue left behind when headers are dipped starts to negate the reactive properties of the fatty acids.

Left unchecked, the form release agent eventually begins to lose its effectiveness, pipes will not pull easily from the headers and quality could suffer. The solution: implement a regular program of monitoring and maintenance that keeps the form release at the optimum reactive release level and reduces replacement and disposal costs.

Precast Pipe Dip Tank Maintenance

Benefits of a dip tank
Reactive form release agents are the accepted standard in today’s precast and pipe-forming operations. Fatty acids, which are found in an infinite number of blends, are the most commonly used reactive material. Fatty acids have the unique ability to react with the free lime on the surface of the concrete, which results in a nonviolent chemical reaction. This neutralization (or saponification) forms a metallic soap, allowing the product to release easily.

There are several benefits to using a dip tank to apply form release during pipe-forming operations, including complete coverage, proper release and reduced chance of operator error. However, a common occurrence when using this method of manufacturing is increasing difficulty with “pulls” or “tip-outs” during stripping over a period of production time. This is generally the result of decreased reactive material in the dip tank as contaminants enter the system and negate some of the reactive material.

Maintaining the dip tank
Two areas must be addressed in the preventive maintenance program for this type of equipment:

  1. Regular maintenance to remove sludge that accumulates in the bottom of the dip tank
  2. Regular maintenance of the release agent’s reactive levels for effective release

The sludge generated in the dip tank includes contaminants from previously dipped headers/joint rings. These contaminants negate the reactive portion of the form release. As the reactive portion of the release agent gradually decreases, the possibility of concrete sticking to the headers increases, causing a more difficult release. The rate of decrease is gradual and depends on many factors, including rate of production and amount of contaminants allowed to enter the dip tank.

Ring-Oiling

Removing contaminants
Rather than disposing of the entire tank of form release, transfer it to a holding tank and shovel out the sludge. Because the sludge typically contains petroleum hydrocarbons, disposal should be in compliance with local regulations. Then, transfer the recovered form release agent back into the dip tank and top it off with fresh release agent.

Remember that by adding fresh release agent to the recovered material, rather than using all new release agent, reactive levels will be reduced and release problems will occur sooner unless the reactive portion is tested and brought back to a normal level. The discoloration of the recovered material from the dip tank is not relevant to the release characteristics, or levels of reactive material.

Maintaining reactive release levels
Maintaining the correct level of reactive agent in the form release is quite simple. Test the recovered material and bring the reactive portion back to optimum levels.

Test a sample from the dip tank (less than one ounce is sufficient) for the reactive level through either titration or infrared analysis. Your release agent supplier should be able to tell you the optimum level of reactive material required and may be able to run the analysis for you. Once you determine the level of fatty acids, a number of simple calculations determine the amount of pure reactive agent to be added to the dip tank to bring it back to the optimum reactive level.

After adding the recommended amount of reactive material to the dip tank, use an air lance for mixing for a minimum of two minutes, making sure to cover the entire area of the dip tank. Then top off the dip tank with fresh release agent and air lance again for good distribution.

Depending on the amount of contaminants and reduced reactive material, the timeframe between tests will vary. One way to determine the frequency between tests is to establish a baseline. Begin with tests every 30 days, which should be recorded, until a history can be compiled to determine the needed frequency. The normal frequency of adding more reactive ingredients is typically five gallons for every six weeks of regular production.

In many cases, production workers can see the reduced effectiveness of release agents. It’s important to train them to notify management to add additional reactive material to the dip tank. As usual, science is best, but practical application and analysis are also important.

Total replacement of form release
While removing sludge and maintaining dip tanks by adding new release as needed make sense from an environmental and cost perspective, on occasion, you may feel it necessary to clean the entire dip tank to remove all residual sludge and refill the cleaned dip tank with fresh release agent.

Cost-effectiveness
Dip tank maintenance comes down to five options. Option 1 is the least cost-effective, while Option 5 is the most cost-effective.

Option 1: Drain the dip tank, dispose of the sludge and old release material, then refill only with fresh form release agent.
Option 2: Remove the form release from the dip tank, dispose of the sludge, refill the dip tank with fresh form release, then use the recovered form release to replenish the dip tank as necessary.
Option 3: Remove the form release from the dip tank, dispose of the sludge, refill the tank with recovered form release, then top off with fresh form release.
Option 4: Remove the form release from dip tank, dispose of the sludge, test the recovered form release, add reactive ingredient to bring it back to an optimum level, then top off with fresh form release.
Option 5: If there is not enough sludge to remove but the release is not as good as it should be, test for the reactive level of the release agent in the tank, then add reactive material to return it to an optimum level.

In the long run, a little care and attention to the reactive content level in the dip tank will help to reduce labor costs and maintain or improve casting appearance.


Additional news from PRECAST INC

Evaluating and Diagnosing Unformed Surface Imperfections

One Thing: Concrete Consolidation


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 Form Release Agents, Concrete Casting Products, Concrete Casting Supplies, Concrete Pipe, Concrete Safety, Precast Concrete, Grifcote FR 50 Concrete Form Release, Bio Gold Concrete Form Release, Grifcote, Precast Inc Magazine

Preventing Bug Holes in Precast Concrete

Posted by Hill and Griffith Company on Sep 26, 2019 4:40:25 PM

From the June 2, 2014 PRECAST Magazine post Causes and Fixes for SCC Bug Holes, by John Pelicone

bugholes_th.jpgLike a persistent mosquito, one question has plagued precast concrete producers for years: “How can I eliminate bug holes?” In the past, this question was much harder to answer, because concrete was placed at a stiffer consistency that required excessive vibration. And excessive vibration sometimes caused more bug holes. After the introduction of self-consolidating concrete (SCC), bug holes(ii) became a less common occurrence. Yet, as a recent online industry discussion revealed, this perturbing problem is still with us.

"Two types of release agents

  1. Chemically reactive agents: 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.
  2. Barrier release agents: 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."

SCC-Bug-Holes-1

Read More

In summary,

"Bug Hole voids are formed during placement. Small pockets of air or water are trapped against the form. The problem increases with the height of the lift. Vibration may not be adequate or well spaced. The mix may be sticky.

  • Primarily caused by the way concrete is placed and compacted
  • Entrapped air not removed by vibration, air bubbles move to the form
  • Improper application of Form Release agent or wrong type 

SOLUTION I PREVENTION: Avoiding Bug Holes

  • Work the voids at the form face up and out of each lift
  • Let the vibrator drop through the lift, then vibrate upward
  • Don't overvibrate at the center of the wall
  • Move the vibrator as close to the form as possible
  • Add upward external vibration if necessary
  • Reduce the height of each lift to make void removal easier
  • Aggregate - consult ready mix producer and review aggregate size and shape
  • Reduce sand content
  • Use low slump concrete"

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 Form Release Agents, Concrete Casting Products, Concrete Casting Supplies, Concrete Safety, Precast Concrete, Grifcote FR 50 Concrete Form Release, Concrete Form Release for Wood, Bio Gold Concrete Form Release, Grifcote, Precast Inc Magazine

The Influence of Form Release Agent Application to the Quality of Concrete Surfaces

Posted by Hill and Griffith Company on Sep 19, 2019 11:00:54 AM

ACI 318-19 was published in response to new engineering practices and industry changes.

Excerpt from a technical paper by A. Klovas and M. Daukšys 2013 IOP Conf. Ser.: Mater. Sci. Eng. 47 012061.

Introduction

High quality surface finishes are a feature of self-compacting concrete (SCC), but by careful attention to mix design and job site workmanship, nice surfaces with the conventional concrete mixture could be achieved. The appearance of an element mainly depends on: the type of cement and addition used; the mix composition; the quality of the concrete mold and release agent; and the placing procedure. If compared self-compacting concrete with the conventional–the color is generally more uniform. Also, it is easier to avoid defects due to leakage spots at the location of mold joints. Blowholes, honeycombing and other blemishes can be found in all types of concrete but with more fluid concrete mixture it is possible to improve the surface finish. International Council for Building Research has provided guidelines how the concrete may be defined referring the surface quality:

  • ROUGH class – no special requirements for finishing
  • ORDINARY – surface finishing has a minor factor
  • ELABORATE – definite requirements for visual appearance
  • SPECIAL – highest standards for appearance
Concrete Form Release Agents Help Form Removal
photo credit: Bob Sawyer

Formworks are also very important factors for concrete surface quality. Scientist, J. Sousa Coutinho, has researched using two different formworks: controlled permeability (CP) and five-layer wood-based formworks. The results have shown that by using CP formworks, the pore diameter (nm) of concrete surface has decreased up to 50%, porosity – up to 45%, surface hardness (MPa) increased up to 70%, and blow-hole ratio has decreased up to 90 % compared with those concrete surfaces using five-layer wood-based formworks.
 
A number of studies determine how to achieve better consolidation resulting in fewer surface blemishes [7-15]. To minimize the size and number of bug holes and all other effects, the following practices should be followed:
  • Vibration period should be of sufficient duration
  • Vibrator insertions should be properly spaced and overlapped and the vibrator removed slowly
  • Each concrete layer should be consolidated from the bottom upward
  • Vibration periods should be increased on withdrawal when using impermeable forms that permit air trapped at the form surface to escape through joints as between
  • Inward sloping forms and other complex design details should be avoided
  • Vibrator should penetrate into the previous layer;

The main outcome of this research is to evaluate the usage of different form release agent applications on the formwork. In addition, this paper presents a technique which provides:

  1. A method how to evaluate the concrete surface quality using image analysis process;
  2. An evaluation of concrete surfaces quality by the following documents: CIB report no. 24 [4] and GOST 13015.0-83.
  3. A combined method how to evaluate and divide concrete surfaces into special categories provided by CIB report no. 24 GOST 13015.0-83 and “ImageJ” in respect to the area of blemishes.

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 Products, Concrete Casting Supplies, Concrete Safety, Precast Concrete, Grifcote FR 50 Concrete Form Release, Concrete Form Release for Wood, Bio Gold Concrete Form Release, Gricote, Concrete Form Release Agent

Subscribe to Concrete News

Concrete Posts

Concrete Casting News Categories

see all