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Concrete Casting News from the Hill and Griffith Company

Precast Concrete Bugholes: Questions from the Field

Posted by Hill and Griffith Company on Mar 4, 2021 5:38:49 PM

Excerpt from NPCA's Precast Inc. Questions & Answers section from the March/April 2019 issue

Paul writes:

What factors could cause bugholes? How does aggregate gradation affect bugholes?

NPCA Technical Services engineers answered:

There are many different variables that could affect the surface finish of hardened concrete and cause bugholes. For conventional wet-cast concrete, the consensus is that the primary culprit is improper vibration, but that’s true even with self-consolidating concrete. The rapid placement of SCC could lead to entrapped air and, if procedures to remove the air aren’t in place, bugholes could form. 

Pouring Concrete to Reduce Bug Holes

Try to slow down the placement of fresh SCC into the form to see if this provides beneficial results. Also, you may need to reevaluate where the concrete is being placed in the form. The concrete may be getting pushed too far and trapping air on tricky corner sections or in areas with heavy reinforcement congestion. Other factors, including not properly applying form release agent, could also promote bughole development.

Your suggestion of aggregate gradations certainly can contribute to surface defects, including bugholes. The Portland Cement Association states, "Mix design can also be considered a significant contributor to bughole formation. Mix designs vary widely in their use of aggregate type, size, and grading and their use of admixtures and air-entrainment."

PCA also states, "Workable, flowing mixtures are easier to place and consolidate and therefore reduce the risk of bughole formation. Concrete with an optimally graded aggregate that avoids excessive quantities of fine aggregate, properly proportioned cement content, and any admixture that provides increased flow, workability, or ease of consolidation contributes to bughole reduction."

Another item to look into is the gradation of the fines. Very fine sands tend to hold more water, increase bleed water and add to the potential for trapped water, all of which could lead to bugholes. Also, sands that are very coarse without uniform gradation have been known to trap more air and, consequently, form bugholes. The best solution is to set up trial mixes to optimize the best results.

If you have a technical question, contact us by calling (800) 366-7731 or visit precast.org/technical-services.

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.

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

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

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

Top 5 Mistakes When Designing a Buried Pipe

Posted by Hill and Griffith Company on Feb 25, 2021 4:38:38 PM

Designing a buried pipe? Be sure to avoid these common—and potentially costly—mistakes.

Excerpt from the American Concrete Pipe Association (ACPA) website June 2020 article by Josh Beakley, P.E.

The design of buried pipe encompasses many of the basic civil engineering concepts we learned in college: hydraulics, soils engineering, and structural engineering. Yet, I’m willing to bet most of us didn't take a class specifically dealing with the design of buried pipe. Thus, it's easy to miss some of the finer nuances when designing buried pipe. Here are some areas where we have seen issues throughout our years in the industry. 

Top 5 Mistakes in Designing Buried Concrete Pipe 

 

 
 

1.  Relying on the installation more than the pipe

Pipe gets built in the manufacturing plant in a controlled environment, whereas the installation surrounding the pipe gets built in whatever Mother Nature provides. So, when the going gets tough, why ask the contractor to produce miracles? (Remember the saying, "it is not nice to fool with Mother Nature.") The pipe producer can typically build a product to accommodate the environment.

#ProTip – Just because you can't find a standard class of pipe, doesn't mean our manufacturers cannot make what you need. Contact a manufacturer near your location to discuss your options.

2.  Blindly using fill height tables

It sure is easy to look up what you need in a reference/fill height table, isn't it? No calculations involved! But somewhere along the way, calculations were performed to develop those fill height tables. Do you know what assumptions were made in those calculations? Do they match your site conditions?

#ProTip – Take a moment to review what assumptions were made and see if they match your site conditions. If the assumptions and your reality don't align, it's worth your time to calculate the correct value.

3.  Using direct vs. indirect design

Of course, you can calculate the stress and/or strain in the pipe based upon a particular soil-structure model for the pipe and its installed condition, and then specify the required properties of the pipe based on your direct design. Or, you could determine the load on the pipe, utilize a simplified relationship between the installed condition and a test condition in the plant, and employ an indirect design method to establish proof of performance of the pipe. Both methods have their uses.

#ProTip – Generally speaking, if you can find reinforcement requirements for the pipe in the tables of ASTM C76/AASHTO M170, Standard Specification for Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe, then the indirect design method is your best bet. If you can't find reinforcement values in C76/M170, then you'll be performing a direct design.

4. Overlooking Pipe Joint Requirements

5. Cut-and-Pasting Specifications

Read about the next 2 tips


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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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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.
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 Bulletins and Technical Papers for Concrete Casting Products

Tags: Concrete, Casting Solutions, Concrete Casting Products, Concrete Casting Supplies, Concrete Casting, Precast Concrete, Concrete Form Release Agent, American Concrete Pipe Association, Precast Pipe

Evaluating NSF Concrete Form Release Agents

Posted by Hill and Griffith Company on Feb 18, 2021 6:13:38 PM

Concrete additives or release agents that contain contaminants, can cause compliance problems for the municipal drinking water utility and present potential health risks to the consumer.

Overview

 

Drinking water contaminants can come from many sources, including the equipment used for water storage and transportation. Concrete used in large storage tanks, reservoirs and pipelines is usually a combination of cement, admixtures, curing compound, sand and gravel. It can also contain fly ash and other additives to strengthen the concrete and increase its durability. However, any of these additives can have contaminants that can cause compliance problems for the utility and present potential health risks to the consumer. If any of these additives can have contaminants that can cause compliance problems for the utility and present potential health risks to the consumer.
 
NSF Certified Form Release
 
 

The following are excerpts pertaining to release agents.
 
5 Barrier materials
 
5.1 Scope 
 
The requirements of this section apply to products and materials intended to form a barrier providing containment of drinking water or to prevent drinking water contact with another surface. The products and materials that are covered include, but are not limited to: coatings and paints applied to fittings, pipes, mechanical devices and non residential storage tanks, linings, liners, bladders and diaphragms, and constituents of concrete and cement-mortar (e.g., Portland and blended hydraulic cements, admixtures, sealers, and mold release agents. These products and materials can be field-applied, factory applied, precast, or cast in place.
 
5.2 Definitions
 
5.2.10 form/mold release agent: A material applied to the inside of a form or mold used to cast concrete or cement-mortar, which prevents adhesion of the concrete or cement-mortar to its surface. 
 
5.5 Extraction Procedures
 
5.5.2.4 Products requiring cement mortar cubes
 
Test sample mortar cubes shall be prepared in accordance to the applicable sections of ASTM C 109. Mix water shall meet reagent water requirements (see Annex B, section B.9.2.1 ). Sand shall be washed in accordance with the procedures in ASTM C 778. Mixing tools and other items coming into contact with the mortar shall be washed with soap and water, rinsed with tap water, rinsed with reagent water, and rinsed with isopropyl alcohol. The mortar shall be placed in polyethylene or polypropylene lined molds; no form release agents shall be used. Specimens shall be removed from the molds after 24 h and placed in glass or polyethylene beakers and covered with an inverted watch glass supported on glass Rebel hooks (or other devices to prevent air seal of the vessel) and placed for 28 d ± 12 h, or fewer as specified by the manufacturer, in a moist cabinet meeting the requirements of ASTM C 511. The specimens shall be removed from the moist cabinet and air dried at 23 ± 2 °C (73 ± 4 °F) and 50 ± 5% relative humidity for 7 d. 
 
5.5.2.4.4 Form and mold release agents
 
These products shall be applied per manufacturer specifications to the mold used during the preparation of the test cubes (see 5.5.2.4 ). 
 
5.5.4 Conditioning (optional)
 
Test samples shall be conditioned immediately after curing. This conditioning procedure simulates the disinfection of water mains and storage tanks prior to placing into service, and is based on AWWA Standards C651-05 and C652-02. Coatings intended for pipes and fittings can be conditioned as follows:
1) prepare 50 mg/L free available chlorine solution using sodium hypochlorite (NaOCI - reagent grade or equivalent);
2) using a spray bottle, spray the previously rinsed test samples, wetting all surfaces to be exposed;
3) let the test samples stand for at least 3 hours; and
4) place the test samples in racks, rinse with cold tap water, and rinse with reagent water, meeting the requirements of Annex B, section B.9.2.1.
 
5.5.5 Exposure protocols
 
For all test samples, exposure shall commence immediately following the conditioning step. If immediate exposure is not possible, the test samples shall be dried in a laminar flow hood and exposed within 4 h. Successful evaluation at an elevated exposure temperature shall preclude testing at a lower exposure temperature. A separate sample shall be exposed for each type of exposure water selected in 5.5.3.
 
The exact surface area-to-volume ratio achieved during the exposure shall be recorded.
 
5.5.5.1 Cold application
 
Cold application product samples, as designated by the manufacturer, shall be placed in an exposure vessel and completely covered with exposure water of the applicable pH (see 5.5.3). The exposure vessel shall be placed in a 23 ± 2 °C (73 ± 4 °F) environment for the duration of the exposure period.

Benefits of NSF Certification

To help minimize the risk of contaminants, NSF certifies individual concrete ingredients to the requirements of NSF/ANSI Standard 61: Drinking Water System Components – Health Effects. Our Concrete Site Mix Design Evaluation Program provides a one-time evaluation that certifies concrete consisting of non-certified cement or other ingredients against this same standard.

NSF/ANSI 61 testing covers all products with drinking water contact from source to tap, and determines what contaminants may migrate or leach from your product into drinking water. It also confirms if they are below the maximum levels allowed to be considered safe.
 
NSF Certification Process

We require information on each ingredient in the site mix and details of its end use structure. Since we have worked with the cement admixture industry for over 20 years, we are able to obtain any additional information on ingredient composition relatively quickly. We perform testing on concrete cylinders manufactured from the mix, including analysis for the potential release of regulated metals, radionuclides, volatile organics and other contaminants that may leach directly into drinking water. Results are typically available in 30 days or less.
 

For additional information, read these articles published in Precast Inc. by the Hill and Griffith Company:
  • "Biodegradability Redefined and Volatile Organic Compounds Update" by Bob Waterloo, Precast Inc.,
    January/February 2010
    Download Article »

  • Biodegradable, NSF Concrete Form Release Agents Offer a Range of Options for Concrete Applications
    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 »

 

 Bulletins and Technical Papers for Concrete Casting Products

Tags: Concrete, Casting Solutions, Concrete Casting Products, Concrete Casting Supplies, Concrete Casting, Precast Concrete, Concrete Form Release Agent, American Concrete Institute, NSF/ANSI 61 Potable Water, Potable Water Tanks

Innovative Solutions for Formlining, Lifting, and Reinforcing Precast Concrete

Posted by Hill and Griffith Company on Feb 11, 2021 8:39:55 PM

Excerpt from the December 2019 issue of Concrete Plant International by Michael Khrapko

The precast technique is practical and economical. This is proven by the very existence of the precast concrete industry and the numerous successful building projects achieved using precast concrete. A number of aspects make concrete precast different from in-situ concrete. Precast elements must be joined with each other to form a complete structure. A precast concrete structure is an assemblage of precast elements which, when suitably connected together, form a 3D framework capable of resisting gravitation and wind (or even earthquake) loads. Another unique concrete precast feature is vertical patterned texture, achieved by using formliners, which are essentially molds for giving texture and design.

New Zealand is a relatively young country. Europeans only started settling in New Zealand in any significant numbers of the past one hundred years. Being isolated geographically and having no cultural traditional building systems to change, New Zealand has been quick to adopt innovative precast building systems, which now enjoy a relatively high market share. Some of these innovative building systems, such as on-site precasting and moment-resisting precast building frames, have evolved their own style and character to meet New Zealand's unique needs. Over the years, innovative and unique systems to support precast concrete construction industry have been developed.

Precast Concrete Bridge Spaning Over 150 Feet

The precast concrete industry controls about 25 percent of the multi-story commercial and domestic building marketing, including frames, floors and cladding (facades). Precast concrete has many advantages over in-situ concrete and other materials. Precast concrete components are produced in controlled conditions that enable to manufacture units to tight tolerances, varying shapes and highly attractive architectural finishes. Controlled production processes allow for faster and most effective implementation of advanced material technologies, like self-compacting concrete and fiber composites. Compared with other materials, precast concrete can provide benefits in fire resistance, durability, thermal and acoustic properties, installation time and can perform its function immediately upon arrival at a construction site, therefore eliminating on-site curing time.

Precast concrete production and construction require efficient, effective and safe lifting and transporting methods. Growing concerns about safety on construction sites, together with escalating demands on cost efficiency, encouraged new developments in this area. Efficient and safe lining systems have been designed and successfully used.

Precast Concrete Made with 3D-Printed Forms

One of the characteristic features of precast elements is that they must be joined together to form a complete structure. The connections for precast concrete are important components of the building envelope and frame systems. The primary purposes of the connection are to transfer load to the supporting structure and provide stability. Connection of precast elements becomes an essential component for construction in seismic areas like New Zealand. Precast connections for seismic resistance is another area where innovative systems have been developed.

Architectural facades using formliners

One of the greatest advantages of working in concrete is its versatility. When viewed as an artistic medium rather than simply a construction component, the material offers infinite possibilities for creativity. Many tools for expressing this creativity have been around for a long time, but they are finding new uses. One proven system receiving renewed attention is formliners.

Formliners are essentially molds for giving texture and design to vertical concrete surfaces. Formliners can be described as "reverse stamp." Instead of pouring the concrete and applying a texturing tool, the tool (the formliner) is attached to the form and concrete is poured onto it. Formliners have been widely used for years to beautify buildings and otherwise ordinary structures such as highway walls, sound barriers, bridge supports and retaining walls. This market continues to grow as more and more communities demand beauty as well as functionality from their buildings and highway systems. In many cases, budgets for these projects include a required amount of art, a requirement that can be met with form liners. Decorative formliners have been further developed in recent years, and certain times can be reused 100 times or more. This is partially due to formliner quality and improvements in the technology of adhesives and concrete release agents. Significant advancements in concrete admixture technology have played an integral role in producing concrete mixes that minimize surface blemishes, enabling the production of the specified surface finish. The new generation of polymer-based admixtures have ensured that concrete placing is easier than in the past, enabling quicker, continuous pouring. It is possible to achieve a high-quality, dense surface finish using self-compacting concrete (SCC). This further increases the life of the formliner as vibrating apparatus is not used. 

Read More


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Hill and Griffith Customer Service

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

 

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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, Concrete Plant International Magazine

The Seven Precast Wastes: Waste #7 Defects

Posted by Hill and Griffith Company on Feb 4, 2021 2:27:41 PM

Article excerpt from the November/December 2020 issue of Precast Inc. magazine by Eric Carleton, P.E.

Editor’s Note: This is the final article in a year-long series about how seven common types of waste in manufacturing can create unprofitable activity and how to address them in your plant.

A precast concrete defect can be defined as a product not meeting a standard or a customer’s expectation. Like all wastes, defective products create additional problems and add costs throughout the production process. They also generate environmental wastes not identified in this series. For these reasons, many lean quality management experts consider defects to be the worst of the seven wastes.

However, defects are one of the easiest wastes to identify. Does the product meet all aspects of its respective ASTM, Department of Transportation or municipal standards? Does it display the aesthetics and company reputation as intended? If the answer is “no” to one of these questions, you have a defect that needs correction.

Precast Concrete Defects

While identifying a defect can be straightforward, understanding the cause and corresponding remedy can prove to be more difficult. When attempting to tackle defects, four guidance activities are often recommended1 by lean manufacturing experts2:

  • Determine one defect on which to place your primary emphasis. For example, a precast inlet was stripped from the form and has rough vertical wall edges that appear honeycombed or jagged. This defect not only creates issues with appearance and acceptance, but it can also affect long-term durability and possibly structural integrity. This type of defect often requires repair.
  • Determine when in the production process this defect occurs and identify the cause. If the product in question is wet-cast, is the issue related to stripping? Are you experiencing a paste leakage issue caused by forms not being connected or latched correctly, properly maintained or checked for dimensional tolerances? Are forms being damaged during production, crane operation or storage? Use root cause analysis procedures to identify where the problem originates and determine the appropriate solution. Ensure the solution totally corrects the identified problem at the source such that the problem does not proceed in some manner down the production line.
  • Revise the process and/or provide training to correct the defect. Investigate the form tolerances, ensure latch mechanisms are working properly and perform the necessary maintenance on the forms. Conduct form dimensional checks and maintenance at a greater frequency or add chamfers at the corner sections, which may prevent the loss of concrete paste at the form joints and improve appearance. Train your employees on proper production techniques and talk about why the issue has been occurring and why it’s imperative to make process changes. You can engage crews in helping to identify what other tools or resources may be needed to prevent the defect in the future.
  • Standardize the process to eliminate the defect. Leverage the data gathered during the process revision and training phase and include that information into the new process or method. For instance, incorporate the maximum allowable gap tolerances of form joints into the pre-pour dimensional inspection checklist. Develop simple gauges for your workers to verify tolerances are not exceeded. Ensure form dimensional compliance and latch connections are verified in good working order prior to production activities. When you’ve standardized your new process to eliminate the root cause of the defect, conduct ongoing and refresher training on the new process and correct techniques.

Precast Concrete Defects and Remedies

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Questions from the Field


Hill and Griffith Customer Service

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

Hill and Griffith Samples

Product Samples

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

 

Hill and Griffith Customer Service

Technical Services & Support

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

 

Bulletins and Technical Papers for Concrete Casting Products 

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

Form Oil on Concrete Rebar

Posted by Hill and Griffith Company on Jan 28, 2021 12:55:40 PM

Article excerpt from the August 2013 issue of Concrete Contractor magazine by James R. Baty II

The Concrete Foundations Association explains the code reference and common misconceptions regarding oil on rebar for residential concrete.

Question

On several of our most recent residential projects, the inspector in our area has been complicating our pour schedule when finding form oil over-sprayed on the rebar in our walls. Is it our misunderstanding that form oil on rebar shouldn’t pose a problem to the wall performance or the acceptance of our pre-pour inspection? – Concrete Contractor (Ohio)

Concrete Release Agent and Rebar

Answer

Your question addresses a common problem across the construction industry that is created as codes are modified over time. Regardless of the comparison of residential to commercial work, code edition after code edition presents challenges to professionals throughout the industry to remain current with the latest acceptable practices and minimum requirements. In the specific case of the acceptability of form oil sprayed on rebar for residential applications, this is both a question of appropriate code reference applying more properly to the residential concrete code — ACI 332 — rather than ACI 318, and of referencing the most recent version, ACI 332-10, instead of older versions -04 or -08.

Appropriately referencing ACI 332-10, your inspector and you can develop a common understanding of this issue based on the presented reference. Stated in section 4.2.4 of ACI 332-10, the code provides:

4.2.4 Surface conditions of reinforcement—At the time concrete is placed, deformed bar and welded wire reinforcement shall be free of materials deleterious to development of bond strength between the reinforcement and the concrete.

R4.2.4 Common surface contaminants such as concrete splatter, rust, form oil, or other release agents have been found not to be deleterious to bond.

This version of the residential concrete code presents two issues that are significant to this topic and to the successful resolution of the argument. The first is that during construction, nothing should be found on the reinforcement that would adversely affect the bond strength of the reinforcement in the concrete. The inspector on your project is rightly wanting to make sure the purpose for the steel present in the concrete is successfully achieved, or at the very least, not voided by preventing such a bond. However, the second issue is equally as important even though it occurs in the commentary. Referencing significant industry research, the explanation is given as to what common site conditions found on rebar are not to be considered deleterious to bond. As you might expect, form oil is one such surface contaminant that is not to be considered deleterious to bond.

The obvious next question in your discussion might be why such a surface contaminant is not deleterious to bond. This is the purpose of the reference to the type of reinforcement found in the code section. Deformed bar and welded wire are both designed to achieve a mechanical bond with the concrete rather than a chemical or adhesive bond. The mechanical bond relies on a keying action with the deformations along the length of the reinforcement bar. Therefore, as long as the surface contaminants do not effectively eliminate the presence of those deformations, they would not be considered deleterious to 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 and non-petroleum concrete form release, biodegradable releases, rust inhibitors and concrete dissolver products that suit your needs.

Hill and Griffith Samples

Product Samples

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

 

Hill and Griffith Customer Service

Technical Services & Support

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

 

Bulletins and Technical Papers for Concrete Casting Products 

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

Precast Shine in Treatment Plant Project

Posted by Hill and Griffith Company on Jan 22, 2021 3:41:16 PM

Article excerpt from the January 2018 issue of Precast Solutions magazine by Shari Held

Knox Borough, Pa., is a quaint community of approximately 1,000 residents tucked away in the northwestern quadrant of the state. Its original cast-in-place wastewater treatment plant was built in the 1930s and had only been upgraded twice – once in the ‘50s and again in the ‘70s.

The plant’s tanks showed evidence of spalling so severe that the reinforcement in the walls was exposed. The plant didn’t have the hydraulic or organic capacity to handle its customer base. It needed to be expanded or replaced quickly to keep Knox Borough in compliance with the Pennsylvania Department of Environmental Protection.

Wastewater-Plant-1

A winning solution

Replacing the wastewater treatment plant was the less expensive and more practical option. One of the first decisions to be made was what building material to use. The capacity of the new plant was 500,000 GPD, making it too large for steel, which poses issues with durability. Steel plants have a lifespan of 25-to-30 years, while concrete plants can last more than 50 years.

Martin English, P.E., an engineer with the EADS Group of Clarion, Pa., considered using cast-in-place concrete. Ultimately, though, he chose post-tensioned precast.

"Preventing leakage was our number one priority," English said. "The post-tensioning support available with precast concrete makes it a very advantageous product for both strength and durability in environmental structures."

The design for the new extended aeration plant called for two 45-foot (outside diameter) circular clarifier tanks and a 153-foot-by-76-foot rectangular tank subdivided into two aeration chambers, two digester chambers, a flow-splitter chamber and a return-activated sludge chamber. Precast caps on the wall tops create a walkway around the tanks.

Mack Industries' headquarters plant in Valley City, Ohio, produced the precast for the treatment plant, built it, and installed the tanks and equipment. The company, which had worked with English before, began consulting on the project more than two years prior to receiving official approval to begin.

"We are unique in that our salespeople are working with the engineer in the early stages of a project," said Betsy Mack Nespeca, president, Mack Industries. "The key to a customized solution is working hand-in-hand with the engineer."

Mount Braddock, Pa.-based Global Heavy Corporation served as the general contractor for the project.

Challenges along the way

Timing was a big challenge. English was concerned about meeting DEP-imposed deadlines. "We had an implementation schedule that had to be met from start to finish," English said. "It definitely helped knowing we could meet our schedule for installing the tanks."

Wastewater-Plant-2

On-site construction began in February 2016 under frigid conditions. Sub-freezing temperatures can impact the grouting and sealing process. Fortunately, precast panels can be set in the ground until there’s a deep frost, unlike cast-in-place concrete.

Because the original plant remained operational during construction, workers had to contend with space constraints. And making a safe conversion from the old system to the new one involved some tricky logistics.

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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.

Hill and Griffith Samples

Product Samples

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

 

Hill and Griffith Customer Service

Technical Services & Support

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

 

Bulletins and Technical Papers for Concrete Casting Products 

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

Tips to Minimize Concrete Consolidation Issues with Forming Projects

Posted by Hill and Griffith Company on Jan 14, 2021 5:38:43 PM

Avoid repair costs and aesthetic disputes in concrete forming projects by minimizing consolidation-related surface blemishes.

Article excerpt from the June 2012 issue of Concrete Contractor magazine

Honeycomb, subsidence cracks, cold joints and excessive surface air voids are common surface blemishes associated with ineffective concrete consolidation. In addition to being unsightly, formed surfaces with blemishes may not conform to the requirements of the contract documents. When this occurs, surface blemishes become defects and subsequently must be repaired. Along with the expense of repairing surface defects, it is difficult and sometimes impossible to make repairs match the color and texture of the surrounding concrete. By understanding the causes and using effective consolidation techniques, contractors can avoid repair costs and aesthetic disputes due to consolidation-related surface blemishes.

Concrete Bug Hole Porosity

Stages of consolidation

Consolidation using an internal vibrator occurs in two stages: 1) leveling and 2) de-aeration. During the first stage, concrete is temporarily liquefied due to the rapid oscillatory motion transmitted to the concrete by the vibrator. Due to the energy imparted to the concrete, coarse aggregate particles become suspended, large voids between aggregates fill with mortar and concrete settles due to gravity.

In the second, or de-aeration stage, the remaining entrapped air bubbles rise to the surface and escape, especially the large bubbles. It is not possible to remove all the entrapped air bubbles; however, vibration should continue until the cessation of large air bubbles occurs.

Use the largest and most powerful internal vibrator, systematically vibrate the concrete area through the full depth of the lift being sure to penetrate the previous lift, and limit the distance between insertions so the area visibly affected by the vibrator overlaps the adjacent just-vibrated area. Continue vibrating until the coarse aggregate particles become embedded, a thin film of mortar forms on the top surface and along the form faces, and large air bubbles stop escaping from the surface.

Also, listen to the pitch or tone of the vibrator. When the vibrator is first inserted into the concrete, vibrator frequency drops but then increases and finally becomes constant when the concrete is free of entrapped air bubbles.

Many times, untrained operators only level the concrete and fail to complete the de-aeration phase of consolidation resulting in unwanted surface blemishes. It is important for operators to understand the stages of vibration and indicators of well-consolidated concrete.

Surface air voids

Commonly called bug holes, surface air voids are small, regular or irregular cavities, usually less than 5/8 inch in diameter, caused by entrapment of air bubbles in the surface of formed concrete. Bug holes are normal for vertical cast-in-place concrete and not considered a defect unless voids exceed the maximum size specified by the contract documents.

Minimize bug holes by using: smooth, impermeable formwork; the thinnest coat possible of an appropriate release agent; limited lift thicknesses; high-frequency vibrators; and proper vibrating procedures with sufficient periods of vibration to de-aerate the concrete.

Honeycomb

Honeycomb occurs when mortar fails to completely fill the spaces between the coarse–aggregate particles leaving irregular voids or stony zones in the concrete. Typically, honeycombing occurs along the form face and in many cases is limited to the region between the form face and reinforcement. Causes include: congested reinforcement and narrow forms, insufficient paste due to segregation of the concrete, improper fine to coarse aggregate ratio, improper placement procedures (excessive concrete free fall and lift thicknesses), trying to place stiff and dry concrete, difficult construction conditions, and insufficient consolidation efforts.

Concrete Consolidation Honeycomb

Subsidence cracks

Sometimes called plastic settlement cracks, subsidence cracks occur when additional settlement or consolidation occurs after the freshly placed concrete has been vibrated and finished. Causes of delayed settlement include excessive bleeding and incomplete concrete consolidation. Cracks form in the plastic concrete because of some type of restraint that restricts concrete settlement. Subsidence cracking in columns and walls commonly occurs over fixed items such as tie bolts and reinforcement and in columns and walls where settlement is restrained by wedging or arching of the concrete. Deep concrete sections are more prone to subsidence cracking.

This form of plastic cracking can be minimized by using proper placing and consolidation procedures and essentially eliminated by re-vibration. Re-vibration is not harmful, can mend subsidence cracks and reconsolidate concrete after delayed settlement has occurred. If the vibrator can be inserted into the concrete and removed without leaving a hole, it is not too late to re-vibrate the concrete.

Cold joints

Cold joints are different than lift or layer lines. Lift lines occur when successive lifts of concrete are not completely knitted together. In many cases, lift lines occur because of color variations between loads of concrete and do not indicate there is a joint or discontinuity in the concrete.

In contrast, a cold joint is a discontinuity between two lifts of concrete. They occur when, due to a concrete placement delay, the earlier lift of concrete hardens sufficiently to preclude knitting and bonding of the two lifts. Except for the unsightly appearance, cold joints are typically not a concern unless the concrete is unreinforced or an environmental tank.

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PCI Announces 2020 Design Award Winners

Posted by Hill and Griffith Company on Jan 7, 2021 12:48:58 PM

Excerpt from Roads & Bridges February 2020 Article

Five transportation projects were among the design award recipients

The Precast/Prestressed Concrete Institute (PCI) recently announced its annual PCI Design Awards for 2020. 

Judges awarded 25 projects and five honorable mentions for design excellence in building and transportation categories. The awards program, now in its 57th year, was created to showcase the creative and innovative use of precast and prestressed concrete in a variety of applications.

"Once again, the precast, prestressed concrete industry has put its best foot forward and has delivered many inspiring and impressive projects," PCI President and CEO Bob Risser, P.E., said in a statement. "Each year, the PCI Design Awards program demonstrates that precast, prestressed concrete is not only a practical solution to many construction challenges, but also a head-turning aesthetic solution."

Precast Concrete Bridge Spaning Over 150 Feet

A panel of industry experts that includes precast concrete producers, engineers, and architects judges all nominees. PCI says the buildings and transportation categories are judged on aesthetic, structural, and use versatility; site, energy and operational efficiency, and risk reduction; and resiliency, such as structure durability, multi-hazard protection, and life safety and health.

PCI also selects several projects for special awards that are judged on similar criteria to the building and transportation projects, as well as additional requirements, including industry advancement, sustainable design, technology, and designs using all-precast concrete solutions. 

Some of the 2020 PCI Design Award winning projects in the transportation category included:

  • Main Span from 76-149 ft: Wekiva Parkway #204 Systems Interchange; Orange County, Florida; Dura-Stress Inc.
  • Main Span more than 150 ft: Marc Basnight Bridge/Replacement of Herbert C. Bonner Bridge; Dare County, North Carolina; Coastal Precast Systems
  • Non-Highway Bridge: Villanova University Pedestrian Bridge; Villanova, Pennsylvania; High Concrete Group LLC and Northeast Prestressed Products LLC
  • International Transportation Structure: Samuel De Champlain Bridge; Quebec, Canada; BPDL/SSLC
  • Special Solution: I-78 Bridge Underclearance Project; Berks County, Pennsylvania; PennStress, a division of MacInnis Group

The Marc Basnight Bridge also was named as a co-winner of the Sustainable Design award in the Specials category.

All winning projects were showcased and honored at the 2020 PCI Convention in Fort Worth, Texas, with an event on March 6, 2020.

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Saving Time & Money With Precast Concrete Buildings

Posted by Hill and Griffith Company on Dec 31, 2020 10:47:10 AM

Excerpt from Water & Wastes Digest's March 2017 Article

Texas utility selects precast option for buildings to house pumping equipment

When the timeframe for its project was too short for traditional construction methods to meet, the San Jacinto River Authority (SJRA) turned to a precast concrete building solution for its pump station installation in Baytown, Texas.

The new transfer pump station was needed because the Chevron-constructed facility in Baytown required more water for its operations. The new station has to pull 16.5 mgd from the Coastal Water Authority canal and pump it into the SJRA canal.  

Easi-Set CS Baytown TX 1

The Solution

The original specification was for a large concrete masonry unit (CMU) building. Houston contractor Boyer Inc. was the low bidder on the project, but its bid was still over budget. Through SJRA-initiated value engineering, Boyer offered a precast concrete building manufacturer as an alternative after determining a CMU could not be constructed in time or on budget.

Nathan Davis, a project manager for Boyer, says the building was an easy aspect to quantify.

"There were not only savings on the front end for cost of the structure, but there were savings on the back end with the reduced time from pouring the slab to setting the roof panels that allowed Boyer to reduce overall construction time, labor and equipment costs for the project," he said.

The buildings utilize clear-span precast concrete roof sections from 20 ft to 50 ft in width. Each 10-ft-deep roof section is post-tensioned to adjoining sections, allowing for buildings of virtually unlimited length to be manufactured.

Easi-Set CS Baytown TX 2

Two Easi-Span buildings – 40 ft by 40 ft by 16 ft and 30 ft by 60 ft by 20 ft – were needed to house all the pump station equipment. The buildings were manufactured and installed by Lonestar Prestress Manufacturing Inc. of Houston. Lonestar, a licensed producer for Easi-Set Buildings, works directly with customers to meet individual needs and ensure quality standards are met.

"Boyer was able to propose the use of the precast concrete buildings as a value engineering solution because it has worked with SJRA in the past and knew the building owner's project goals," said Leo Rowe, sales manager for Lonestar. "We were able to add our experience and expertise to Boyer's ingenuity to meet the project schedule and budget."

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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

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We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
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On-site casting defect investigations, product testing, machine start-ups and much more. Also, lab facilities are available to provide testing upon request.
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