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Concrete Casting News from the Hill and Griffith Company

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

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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

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 Bulletins and Technical Papers for Concrete Casting Products

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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

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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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 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)


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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 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

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, 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.
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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, The Constructor Magazine

Form Coatings and Mold Linings

Posted by Hill and Griffith Company on Nov 5, 2020 1:02:16 PM

Excerpt from the book, Formwork for Concrete Structures by Kumar Neeraj Jha

Mold surfaces of wood and steel in due course, after repeated use, warp and rust, respectively, making the molds unserviceable if unprotected. It is common to treat the sheathing materials with some coating or release agent for easy removal. Only a few special form face materials, such as expanded polystyrene, do not need release agents.

The coating or release agents are temporary coatings and composed of fatty acids that react with the alkali in cement. The reaction produces a soap-like substance on the contact surface, which helps remove forms easily. Coating agents can also help enhance the mold life. The form surface remains smooth, provides good abrasive resistance, makes the wooden surface moisture resistant and retards the rusting of steel.

Concrete Release Agents

 

There are many release agent chemical compounds that have been developed for use as the coatings for wood and steel. It is, therefore, important to select the right one.

The three most common types of release agents are:

1. Neat oils with surfactants: mainly used on steel faces, but can also be used on timber and plywood.
2. Mold cream emulsions: for use on timber and plywood – a good general-purpose release agent.
3. Chemical release agents: can be used on all types of form face recommended for all high quality work.

These release agents could be oils, emulsified wax, oil-phased emulsions with water globules, petroleum-based products, catalyzed polyurethane foam, etc. Waste oil is also used as a release agent.

The type of composition of the coating or release agent depends on the following:

1. type of sheathing materials
2. conditions under which it is applied
3. type of concrete
4. finish quality
5. form area
6. ease of application

Concrete_form_release_application_1

The primary objective of the coating and release agents is to ensure easy removal of the form material without damaging the form and concrete. The concrete surface should also not get any stain from the application of release agents. It should be possible to apply the form release agent in an even manner on the form surface. The form release agent should not react with the concrete and produce some undesirable substance in the process.

Coatings on all type of forms are employed with the following objectives:

1. Protection of the form for durability
2. On timber, it reacts with organic constituents and provides a uniform surface on each use. Penetration of the chemicals helps control grain or edge effect as well as fill pores in the wood.
3. Chemically active coating reacts with free lime from the fresh concrete and produces water-insoluble soaps. When dried, these soaps act as positive concrete release agents. When wet, they help move air voids along the form.

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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, Concrete Form Release for Wood, Gricote, Mold Releases and Release Agents, Concrete Form Release

Using Concrete Form Release Properly Can Save Your Forms

Posted by Hill and Griffith Company on Oct 28, 2020 4:39:24 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.

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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.

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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

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

Precast Concrete Architectural Repair

Posted by M.K. Hurd on Sep 24, 2020 5:45:39 PM

10 Aesthetic Defects; 10 Structural Defects; and Repair Techniques & Procedures

Excerpt from NPCA's 2013 downloadable guide.

This guide is not meant to be all-inclusive, but rather is a collection of best practices commonly used to repair precast concrete. The guide explains procedures and time-proven techniques used to make a multitude of precast concrete repairs. Precast concrete product repairs can be related to engineering and design, production, handling, shipping, erection, other trades (typically on the job site), job site conditions and environment. While it would be impossible to address every possibility where a repair may be needed, this guide will address some of the most common situations. It covers the basics and common methodologies of repairs. Unique situations will require you to develop repair techniques based on the appropriate methodology.

This guide is not a replacement for good quality concreting practices, which will reduce the amount of production-related repairs. For more information, see the NPCA Quality Control Manual for Precast and Prestressed Concrete Plants.

NPCA Precast Architectural Repair Guide

 

AESTHETIC DEFECTS

Aesthetic defects are considered minor defects. They are usually production-related and can be fixed quickly at the plant. Some examples include bugholes, small chips, crazing cracks or others described in this guide. Aesthetic defects do NOT impact the structural integrity or intended service life of the product.

Bugholes
Surface voids can be a common surface blemish on precast concrete. These are usually small voids found in clusters and commonly referred to as bugholes. While these do not compromise the structural integrity of the product, they can be considered unsightly, especially with architectural finishes. The common causes of bugholes include entrapped air, water pockets or the improper application of form release agent.

Release Agents
When a release agent is applied too heavily to the surface of a form, it can pool at the base of the mold or form droplets. When the concrete is placed into the form, the pools or droplets prevent the concrete from occupying that space so that when the form is removed a bughole is left behind where the droplet or pooling occurred.

Fine Cracks
Fine cracks occur at the surface and are very small, with a width typically less than 0.01 inches.

Shrinkage Cracks
Shrinkage cracks occur when water is removed too quickly from fresh concrete. The loss of water causes a volume change in the concrete, and since the concrete is still fresh, the tensile strength is not adequate to resist the volume-changing force. Shrinkage cracks can be avoided by placing concrete in a controlled environment where relative humidity, concrete temperature and wind velocity are favorable for concrete curing. When necessary, shrinkage cracks can be repaired using epoxy injection methods.

Crazing Cracks
Crazing cracks usually occur very soon after the concrete has been placed. The cracks are shallow and typically do not cause wear resistance or durability issues. Crazing cracks are often attributed to a lack of hydration on the surface of the concrete during the curing process. Crazing can be avoided by using curing compounds, covering the product during curing, refraining from "over-finishing" the surface of the concrete, and not finishing the product while bleed water is still present on the surface. Crazing cracks are typically not repaired because they are not structural and they are so small that it would be nearly impossible to fill them with any material.

Chips
Chips are relatively small sections of products that have been removed, typically as a result of impact. Chips may be as large as 8 in. in diameter by 1 in. deep and are usually of irregular shape. As chips become larger, they require a different approach to repair. This may include adding reinforcement (also known as pinning) and using a build-up application technique. This will be discussed under the section on spalls. Most chips can be repaired in one application with the appropriate patching material.

Efflorescence
Efflorescence occurs when soluble salts come to the surface of concrete. All concrete and mortars will experience some level of efflorescence. This natural phenomenon is most prevalent in moist environments and low- temperature conditions. Efflorescence will typically appear as a white substance, so it will be more noticeable on dark-colored concrete. Efflorescence can be removed by pressure washing before it reacts chemically to form calcium carbonate. Once the calcium carbonate reaction occurs, the use of a mild acid solution is often required to remove efflorescence. After application of the mild acid, it is important to rinse all acid and remaining calcium carbonate from the concrete to prevent discoloration of concrete or a relapse of the efflorescence cycle.

Missing Architectural Details
Missing architectural details such as false joints, quirks and miters occasionally can occur in the manufacturing of architectural precast concrete. The use of a thorough quality control program and a highly skilled design and detailing firm should greatly limit those occurrences, however.

Finish Problems
It's obvious, but should be stated: architectural precast must look good and meet the intended aesthetic purpose. Aesthetics can be subjective in nature, however, so this is always a potential area for dispute.

Blending
Precast products are cast over many days using several batches of concrete. The best way to minimize batch-to-batch variations is to follow good concreting procedures: Purchase all materials needed for a project from the same lot or run. Blend materials when more than one lot is used. Do not change from approved sources midstream in project. Maintain the specified water/cement ratio and mix design, control variations. Maintain proper placement and consolidation techniques. Follow consistent and proper curing procedures.

Discoloration
Discoloration can be caused by a multitude of factors. These factors include changing cement lots, varying aggregate properties, inconsistent mixing, inconsistent finishing or a change in curing conditions. Virtually any change in the concreting process can lead to a change in coloration.

Download the Complete Guide


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, NPCA

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