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Concrete Casting News from the Hill and Griffith Company

Get More from Your Mix - For Less

Posted by Hill and Griffith Company on Feb 6, 2020 8:00:00 AM

Excerpt from the July/August 2012 issue of Precast Inc. Magazine by Chris Von Handorf, P.E.

New material technologies and intelligent mix designs can significantly decrease production and labor costs.

Reducing material and labor costs makes sense for any manufacturing company, and increasing profits is even more imperative during a slumped economy. Companies in every industry have been forced to look at ways to lower production costs to remain competitive in our rapidly evolving marketplace. The precast concrete industry is no exception. Concrete constituents are only a portion of the costs incurred by a precast concrete manufacturing facility. This article shows how a smart mix design can help you cut costs. The important point to remember is that a lower-cost concrete does not always result in an inferior product. In fact, in some cases, lowering the cost of your mix design may actually yield a higher-quality concrete product.

Admixtures offer many cost-saving options
The cost of the materials that make up concrete is but one of the many expenses incurred by a precast concrete manufacturing facility. Another major expense is the labor cost to place and finish the product. This cost varies widely depending on a plethora of factors including: the type of product; the climate; the experience level of workers; and reinforcement required.

Here are just a few of the admixtures available that, in the right application, have the potential to significantly lower production costs:

1. Supplemental Cementitious Materials: The use of supplemental cementitious materials, such as silica fume and blast furnace slag, has the potential to enhance the performance of concrete while reducing any bleeding that may occur. When used properly, silica fume can improve concrete’s resistance to chemical attack. It can also increase concrete strength while reducing the permeability of the concrete.

2. Accelerators: The use of accelerators in precast applications has some obvious advantages. The faster concrete reaches the required stripping strength, the quicker the forms can be cleaned, prepped and used again. For a precaster, a quicker strength gain is huge if you are looking to go from pouring once per day in a given form to twice per day.

3. High-range water reducers: High-range water reducers (HRWRs) are excellent for nearly every precast concrete application. A good high-range water-reducing admixture will allow you to produce concrete batches with more consistent air entrainment and more consistent ultimate strengths. 

4. Release agents: While release agents are not a constituent of the mix, the use of a high-quality release agent is essential for a better-looking, lower-cost, finished product. As with HRWRs, release agent technology has improved significantly in recent history. Although many new release agents are more expensive per unit, most of them do allow for a lighter application than traditional release agents. As a result, the cost per square foot of coverage is often significantly lower using the newer form release agents.

Emerging technology and processes surrounding the concrete industry are rapidly advancing. Admixtures that cost only $1 to $2 per cubic yard may have the potential to save you hundreds of dollars or more in labor and rework. Many of these admixtures were not available a few years ago. Some material testing techniques that were not available years ago, or were very expensive, are now relatively inexpensive. Therefore, it is no longer economical or wise to continue precast production methods with a familiar, long-standing mix design simply because it has been the traditional way of doing things for the last 20 or 30 years.

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

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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 and non-petroleum concrete form release, biodegradable releases, rust inhibitors and concrete dissolver products that suit your needs.

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


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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

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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.

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 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

Article Review: Concrete Formed Surface Classifications & Specifications

Posted by Hill and Griffith Company on Jul 18, 2019 1:06:30 PM

Details on classifications & specifications for surface finishes

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

Evaluating_and_Diagnosing_Concrete_Formed_Surface_Imperfections

Less is better when spraying concrete form release agents on concrete forms.

In 1975, the International Council for Building Research established a general classification of formed surfaces which is referenced in the most recent edition of ACI 301.2R, "Identification and Control of Visible Effects of Consolidation on Formed Concrete Surfaces."

Those classifications are:

  1. Rough - No special requirements for finishing
  2. Ordinary - surface finishing has a minor factor
  3. Elaborate - definite requirements for visual appearance
  4. Special - highest standards for appearance [considered architectural]

Within ACI 347R-14, "Guide to Formwork for Concrete," there is a similar class system to differentiate concrete surface evaluation based on application:

  1. Class D - minimum quality requirement for surfaces where roughness is not objectionable, usually applied where surfaces will be permanently concealed.
  2. Class C - general standard for permanently exposed surfaces where other finishes are not specified
  3. Class B - intended for coarse-textured, concrete form surfaces intended to receive plaster, stucco or wainscoting
  4. Class A - suggested for surfaces prominently exposed to public view where appearance is of special importance

ACI 301-16, "Specifications for Structural Concrete," provides more detailed information.

5.3.3.3(a) Surface finish-1.0 (SF-1.0):

  • No formwork facing material is specified
  • Patch voids larger than 1-1/2-inch wide or 1/2-inch deep
  • Remove projections larger than 1 inch
  • Tie holes need not be patched
  • Surface tolerance Class D as specified in ACI 117-10, "Specification for Tolerances for Concrete Construction and Materials and Commentary."
  • Mockup not required

5.3.3.3(b) Surface finish-2.0 (SF-2.0):

  • Patch voids larger than 3/4-inch wide or 1/2-inch deep
  • Remove projections larger than 1/4 inch
  • Patch Tie holes
  • Surface tolerance Class B as specified in ACI 117
  • Unless otherwise specified, provide mockup of concrete surface appearance and texture

5.3.3.3(c) Surface finish-3.0 (SF-3.0):

  • Patch voids larger than 3/4-inch wide or 1/2-inch deep
  • Remove projections larger than 1/8 inch
  • Patch Tie holes
  • Surface tolerance Class A as specified in ACI 117
  • Provide mockup of concrete surface appearance and texture

5.3.3.5 Unspecified as - cast-finishes - if a surface finish is not specified, provide the following finishes:

  • SF-1.0 on concrete surfaces not exposed to view
  • SF-2.0 on concrete surfaces exposed to view

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.

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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, Precast Inc Magazine

Article Review: Evaluating and Diagnosing Formed Surface Imperfections

Posted by Hill and Griffith Company on Jul 11, 2019 4:18:57 PM

Precast formed concrete surface problems and how to identify and correct them

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

Evaluating_and_Diagnosing_Concrete_Formed_Surface_Imperfections

Less is better when spraying concrete form release agents on concrete forms.

Green Bay Packers Coach Vince Lombardi said, “Perfection is not attainable, but if we chase perfection, we can catch excellence.” Precast manufacturers try to make perfect products, but like most things, attaining complete perfection is elusive if not impossible. While the goal is to attain perfection, precasters recognize the economic and production realities that some product irregularities will occur. The goal is to mitigate imperfections while still maintaining tolerances and meeting owners’ expectations.

For (precast) formed concrete surfaces, many problems can be narrowed down to three practices: consolidation or vibration, form set up and maintenance, and form oil/release agent application.

Common issues:

  1. Bugholes
    1. Poor or improper concrete consolidation
    2. Excessive application of form release oil or agent
  2. Honeycombing
  3. Cracking
  4. Fins
  5. Form Bleed
  6. Poor Form Fit
  7. Sand Streaking
  8. Layering Marks
  9. Cold Joint
  10. Staining
  11. Color Continuity

Regardless of the end use, a well-cast product, free of formed surface irregularities, provides an excellent representation of a quality operation.

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

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