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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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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


More News from APCA

4 Ideas for Thinking Outside the Box (Culvert)

Is Concrete Pipe Innovative? Here are 4 Areas to Explore.


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 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 »

Precast Concrete in Google News and NPCA, National Precast Concrete Association

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PCI Certification Expands Smith-Columbia's Market Reach

Precast Concrete Infrastructure Construction Product Demand to Increase 4.4% Annually Through 2022


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."
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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 Institute, NSF/ANSI 61 Potable Water, Potable Water Tanks

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.

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.
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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, Water & Wastes Digest

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."

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.
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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, Water & Wastes Digest

Repairing Bug Holes

Posted by Hill and Griffith Company on Dec 24, 2020 8:00:00 AM

Excerpt from Concrete Construction's August 2012 Q&A Article by Kim Basham

QUESTION: About 2 months ago, we finished placing a concrete foundation for a large commercial building and now the owner is complaining about surface bug holes. The bug holes are fairly small (less than ½ inch wide) but occur fairly frequently in some places. Until the painters started painting the walls, everyone was pleased with our work.

Now, the owner claims the bug holes are unacceptable because they distract from the overall appearance of the painted walls. The owner claims the bug holes are defects and we are responsible for fixing them.

Are bug holes defects? Are we responsible for repairs?

Concrete Bug Hole Repair

 

ANSWER: ACI 347-04, "Guide to Formwork for Concrete," defines bug holes, or surface voids, as small regular or irregular cavities, usually not exceeding about 5/8 inch (or 15 mm) in diameter, resulting from entrapment of air bubbles in the surface of formed concrete during placement and consolidation.

Bug holes commonly occur in vertical cast-in-place concrete such as walls, columns, beams, etc. Both the number and size of bug holes vary and depend on many factors. These include form facing material and condition, release agent type and application thickness, concrete mix characteristics, and placing and consolidation practices.

The permissible number and size of bug holes in a concrete surface is not defined in either ACI 301-05 or ACI 301-10, "Specifications for Structural Concrete." In fact, ACI 301-05 does not limit either the number or size of surface voids in as-cast surface finishes.

ACI 301-05 specifies two as-cast surface finishes: rough-form and smooth-form. While it does list other requirements for rough- and smooth-form finishes, it does not limit the permissible number or size of bug holes.

Rough- and smooth-form finishes have been dropped in the more recent 2010 version of ACI 301. Now, as-cast surface finishes are SF-1.0, SF-2.0, and SF-3.0. Like ACI 301-05, ACI 301-10 does not limit either the number or size of bug holes in as-cast surface finishes.

However, ACI 301-10 does limit the maximum size of surface voids to 1½ inches wide or ½ inch deep for SF-1.0, and 3/4 inch wide or ½ inch deep for SF-2.0 and SF-3.0. According to ACI 301-10, bug holes or other surface voids exceeding these dimensions for the specified surface finish are defects and must be repaired. Otherwise, bug holes are allowed and considered surface imperfections, commonly referred to by ACI as surface effects.

The specifications for the project may limit the size of bug holes by specifying maximum widths and/or depths of surface voids. Review Section 03300 Cast-in-Place Concrete of the specifications for the project, especially the sections on Form-Facing Materials, Formwork, Finishing Formed Surfaces, and Concrete Surface Repairs.

Whether your bug holes are defects or not depends on:

  • The version of ACI 301 specified;
  • The size of the bug holes (the width and depth); and
  • The void size limitations, if specified by the contract.

If ACI 301-05 was specified and the contract documents did not limit the size of surface voids, bug holes are not defects but surface effects. If ACI 301-10 applies and SF-1.0, SF-2.0 or SF-3.0 was specified, or the specifications established a maximum void size, then only the bug holes that exceed the maximum allowable void size are defects. Otherwise, bug holes are surface effects. Only agree to repair those classified as surface defects.

If the owner wants a bug hole-free surface, then a smooth-rubbed or grout-cleaned rubbed finish as defined in ACI 301 should be specified. Create a smooth-rubbed finish by rubbing the wetted concrete surface with a carborundum brick within a day of formwork removal. This generates paste to create a uniform surface color and texture.

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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, Concrete Construction Magazine

Precast Concrete Overview

Posted by Hill and Griffith Company on Dec 17, 2020 4:55:46 PM

An overview for understanding precast concrete types and techniques

Article excerpt from the ConcreteNetwork.com by Bill Palmer

Precast concrete is simply concrete that is cast somewhere other than where it will be used. Most precast products are cast in a factory using a wet-cast method, but others are cast on site—such as tilt-up panels. There are lots of reasons—mostly advantages—why one would precast, and we'll get into those, but the biggest negative of precasting is that the resultant concrete item must be moved. Concrete is heavy—typically about 150 pounds per cubic foot—so concrete elements don't have to be very big before moving them becomes unrealistic.

Some decorative contractors, such as those that precast concrete countertops, stretch the boundaries on what's too big or heavy to move, developing special rigs to transport massive pieces of their concrete work. Other times, it's just simpler to cast the concrete in place as the precast advantages are outweighed by convenience, such as with concrete slabs and floors.

concretenetwork-com_12980 

Advantages of Precast Concrete

As long as there has been concrete, it has been precast—going clear back to the Romans. And there are lots of good reasons for that. The National Precast Concrete Association has information on its website outlining the value of precast concrete. Most of the advantages they cite are really advantages of concrete in general rather than specific to precast, but when compared to site-cast concrete, precast does have lots of advantages:

  • Since precast is manufactured in a controlled casting environment, it is easier to control the mix, placement, and curing
  • Quality can be controlled and monitored much more easily
  • Since a precaster can buy materials for multiple projects, quantity discounts can lower costs
  • Weather is eliminated as a factor—you can cast in any weather and get the same results, which allows you to perfect mixes and methods
  • Less labor is required, and that labor can be less skilled
  • On site, precast can be installed immediately, there is no waiting for it to gain strength and the modularity of precast products makes installation go quickly
  • Repeatability—it's easy to make many copies of the same precast product; by maximizing repetition, you can get plenty of value from a mold and a set-up
  • Accelerated curing, by heating the precast parts, greatly increases strength gain, reducing the time between casting the part and putting it into service
  • With the ability to so tightly control the process, from materials to consolidation to curing, you can get extremely durable concrete

Types of Precast Concrete

There are lots of applications for precast concrete across the industry, including:

    • Bridge beams
    • Double Ts
    • Hollow-core slabs
    • Septic tanks/manholes
    • Pipes/culverts
    • Foundation walls
    • Architectural panels
    • Traffic barriers and retaining/sound walls
    • Steps
    • Fences
    • Pool coping

Precast Structures

Another popular use for precast concrete is large-scale commercial buildings such as apartments, hotels, warehouses or office buildings. However, it is also possible to build smaller-scale structures, such as single-family residences using precast concrete.

Some of these buildings are built using a tilt-up construction method where concrete panels are cast flat, cured and then raised into position. Others are built with a prefab or modular approach where more complete units are created, delivered to the site and set in place.

Tips on Starting a Precasting Operation

Precasting offers contractors an opportunity to make more money—to increase the scope of the types of concrete work they can offer their customers. To begin precasting, you will need a shop large enough to accommodate the size of the pieces you intend to precast (or a yard if you intend to precast outside), material storage areas or bins, molds, a mixer sized for the precast products you are making, a way to consolidate the concrete in the molds, and a material handling system.

Quality Control for Precast

If you are going to manufacture precast products in your shop, you should consider doing your own quality control. Large precast operations have big labs and develop intricate quality procedures, testing all aspects of the concrete both before and after casting and developing extensive QC tools like fishbone charts and scatter diagrams and Pareto charts. You may not need to get to that level, but some basic testing and analysis can save you money both in production costs and higher quality precast products.

Starting with good materials is the first step. All aggregate is not acceptable for use in concrete. If there are organic materials, shale, chert, or other soft materials in your aggregate, you can't produce good concrete. Reactive aggregates can lead to alkali-silica reaction that can destroy your concrete. The best defense may be simply to require that the aggregate meets ASTM C 33, "Standard Specification for Concrete Aggregates." It's your aggregate supplier's responsibility to assure that you are getting good aggregate.

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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, Concrete Safety, Precast Concrete, Bio Gold Concrete Form Release, Gricote, Concrete Form Release Agent

ASCC's Guide for Surface Finish of Formed Concrete

Posted by Hill and Griffith Company on Dec 3, 2020 5:19:59 PM

(This week's post is a review of Guide for Surface Finish of Formed Concrete by ASCC Education and Training Committee. You can read it at Google Books here.)

Amazon Book's summary (April 1, 1999), "Exactly what is a smooth-form finish? What is a rough-form finish? To what extent are bugholes, voids and fins acceptable in each type? This easy-to-use guide explains and illustrates the answers to these questions and, even more importantly, serves as the standard for the differences between as-cast structural concrete finishes. The succinct, yet thorough, text includes a glossary and a handy table on as-cast finishes. But the guide's Presentation Photos are what make it truly unique. Three sets of 6 different, full-scale photographs depict various as-cast finishes, with bugholes and voids ranging from 1/16" or less to 2" across. Attach a Presentation Photo to a bid or specification to show what surface finish is to be expected."

Surface Finish of Formed Concrete.jpg 

Form Release Agents

Release agents are differentiated from form coatings or sealers that are usually applied in liquid form to contact surfaces either during manufacture or in the field. Coatings and sealers serve one or more of the following purposes:

  • Alter the texture of the contact surface 
  • Improve the durability of the contact surface
  • protect the contact surface from moisture

Release agents, on the other hand, are applied to the contact surface of the forms to prevent bond to the concrete and thus facilitate stripping. They can be applied to form materials during manufacture or applied to the form before each use. Manufacturers' recommendations should be followed in the use of coatings, sealers, and release agents (Reference 10-11), but ACI 347 recommends independent investigation of performance before using a new product.

There is no ACI standard to define these products, but the term form oil is frequently applied to petroleum compounds originally intended for other applications such as diesel fuel or heating oil, while release agent more often refers to products containing proprietary reactive ingredients specifically formulated for use on concrete forms. Release agents are commonly classified on the basis of how they act instead of what is in them. The two basic categories are barrier agents and chemically active agents, sometimes called reactive agents. Some release agents are a combination of the two types.

Barrier type releases agents create a physical barrier between the form surface and the fresh concrete, preventing the concrete from sticking to the form. Familiar examples are home heating oil, diesel oil, and used motor oil. U.S. environmental regulations prohibit the sale of these commodities as release agents, but they have been widely used because they are inexpensive and readily available. They are applied in relatively thick films, covering 200 to 600 sq ft per gallon, and such heavy applications can increase surface staining and bugholes on the concrete surface. If coated forms are left for several days before concrete is placed, barrier oils may evaporate, possibly leading to some sticking of the concrete to the form.

Chemically active or reactive agents contain an active ingredient that may be dissolver in an oil-based carrier or emulsified in a water-based carrier. The active ingredient is typically some type of fatty acid derived from plant or animal sources, and it combines chemically with calcium ions in the fresh concrete. The reaction product is a thin layer of what chemists refer to as a grease or metallic soap or salt; non-water-soluble, it permits the form to release readily from the hardened concrete.

The reactive fatty acid components are generally considered biodegradable and have found favor in the past decade because of increasingly stringent environmental regulations. For similar reasons, manufacturers have also been turning to water-based carriers, which will probably be subject to freezing.

(Jan 1, 2005 edition from Google Books)


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 Bulletins and Technical Papers for Concrete Casting Products

Tags: Concrete, Casting Solutions, Concrete Casting Products, Concrete Casting Supplies, Concrete Casting, Concrete Safety, Precast Concrete, Bio Gold Concrete Form Release, Gricote, Concrete Form Release Agent

Save Your Concrete Forms With Proper Use of Concrete Form Release

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

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

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

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

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

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

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

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

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

Concrete-Form-Rust-Preventative.jpg

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

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

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

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


Hill and Griffith Customer Service

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 Bulletins and Technical Papers for Concrete Casting Products

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

Concrete Form Removal Time, Specifications and Calculations

Posted by Hill and Griffith Company on Nov 12, 2020 5:07:24 PM

Excerpt from The Constructor

The removal of concrete forms also called as strike-off or form stripping should be carried out only after the time when concrete has gained sufficient strength, at least twice the stress to which the concrete may be subjected to when the forms are removed. It is also necessary to ensure the stability of the remaining forms during form removal.

Concrete Form Removal Time

The rate of hardening of concrete or the concrete strength depends on temperature and affects the form removal time. For example, time required for removal of concrete in winter will be more than time required during summer.

Special attention is required for form removal of flexural members such as beams and slabs. As these members are subjected to self-load as well as live load even during construction, they may deflect if the strength gained is not sufficient to handle to loads.

To estimate the strength of concrete before form removal, the tests on concrete cubes or cylinders should be carried out. The concrete cubes or cylinders should be prepared from the same mix as that of the structural members and cured under same circumstances of temperature and moisture as that of structural member.

When it is ensured that the concrete in the structural members has gained sufficient strength to withstand the design load, only then forms should be removed. The forms should be left for longer time if possible as it helps in curing.

Concrete Form Released After Curing

Removal of forms from the concrete section should not make the structural element:

  • Collapse under self load or under design load
  • deflect the structural member excessively in short or the long term
  • physically damage the structural member when the form is removed.

The following points must be kept in mind during form removal whether the structure will be prone to:

  • freeze thaw damage
  • cracks formation due to thermal contraction of concrete after form striking.

If there is a significant risk of any of the above damages, it is better to delay the removal time of forms. If forms have to be removed for optimizing the concrete construction activities, then these structures must be well-insulated to prevent such damages.

Calculation of Safe Form Striking Times:

Structural members are constructed based on designed load. But before a structure is complete and subjected to all loads assumed during structural design, the structural members are subjected to its self weight and construction loads during construction process.

So, to proceed with construction activities at a quicker rate, it is essential to calculate the behavior of structure under is self load and construction load. If this can be done and structural member is found to be safe, forms can be stripped-off.

If these calculations are not possible, then following formula can be used for calculation of safe form striking times:

Characteristic strength of cube of equal of maturity to the structure required at time of form removal

Form Removal Formula

This formula was given by Harrison (1995) which describes in detail the background of determination of form removal times. Another method to determine the strength of concrete structure is to conduct the non-destructive tests on structural member.

Factors Affecting Concrete Form Striking Times

The striking time of concrete forms depends on the strength of structural member. The strength development of concrete member depends on:

  • Grade of concrete – higher the grade of concrete, the rate of development of strength is higher and thus concrete achieves the strength in shorter time.
  • Grade of cement – Higher cement grade makes the concrete achieve higher strength in shorter time.
  • Type of Cement – Type of cement affects the strength development of concrete. For example, rapid hardening cement have higher strength gain in a shorter period than the Ordinary Portland Cement. Low-heat cement takes more time to gain sufficient strength than OPC.
  • Temperature – The higher temperature of concrete during placement makes it achieve higher strength in shorter times. During winter, the concrete strength gain time gets prolonged.
  • A higher ambient temperature makes the concrete gain strength faster.
  • Forms help insulate concrete from surroundings, so longer the forms remain with the concrete, the less loss of heat of hydration and rate of strength gain is high.
  • Size of the concrete member also affects the gain of concrete strength. Larger concrete section members gain strength in shorter time than smaller sections.
  • Accelerated curing is also a method to increase the strength gain rate with the application of heat.

Read More


Hill and Griffith Customer Service

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

Hill and Griffith Samples

Product Samples

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

 

Hill and Griffith Customer Service

Technical Services & Support

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

 

 Bulletins and Technical Papers for Concrete Casting Products

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

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