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Epoxy Resin Strengths Explained

Compressive, Tensile, Flexural, and Bond Strengths of Epoxy Resin


What do the Strength Numbers for Epoxy Mean?

There are 4 primary strengths that are very important for most civil and mechanical engineering applications of epoxy: compressive strength, tensile strength, flexural strength, and bond strength. The test methods used to get the specific strength of the epoxy is done by the ASTM testing method listed on the epoxies technical data sheet. The master test standard for epoxy is ASTM C881. Norm Lambert the author of this page is a voting member of ASTM Technical Subcommittee C09.25 that sets the ASTM C881 standard.

Compressive Strength of Epoxy

This strength is the ability of the material to handle weight. Compressive strength tests are ran by pushing both sides of a cylinder of the epoxy (or concrete etc.) on the top and bottom of the cylinder. Typical numbers most non-flexible epoxies start at slightly under 10,000 psi (pounds per square inch) and work their way up from that. To put this into perspective typically quality concrete has a compressive strength of about 3,000 psi. Very high end concrete can have compressive strength of about 5,000 psi but concrete at that high a strength is not typical. Most concrete is 3,000 psi plus or minus.

Some people think that the higher the tensile strength the "better" the material. That is not necessarily true. As some epoxies get to very high compressive strength the may become brittle. If a product is brittle it can still break easily. That is because flexural strength has been compromised for the sake of getting a higher compressive strength number. More on this under tensile Strength below.

Epoxy.com Products are formulated to balance all the various strengths needed for a specific application. For example if you are installing an Epoxy.com Product over concrete, there is no need for the epoxy to have a compressive strength of more than a couple times more than the concrete. That gives you a high safety margin so that if there is a high compressive load the concrete will fail before the epoxy. Once the concrete has failed the epoxy is just along for the ride.

Interestingly enough in the real world materials don't really fail in compressive, they typically break on the side opposite the side of the load first, which means it actually fails in tension.

Tensile Strength of Epoxy

The Tensile of epoxy is basically the load in just the opposite direction of compressive strength. As you remember compressive strength tests are ran by pushing both sides of a cylinder of the epoxy or other material. Tensile strength is tested by pulling on the top and the bottom of the cylinders.

Materials do not break in compression, they break in tension. Prove this to yourself. Take a tooth pick or some material that you can bend in your hands until it breaks. It does not break on the side you are pushing on (the compressive side) first. It brakes on the side you are pushing towards first.  The side that is in tension is the side you are pushing to. That makes the tensile strength the most important one to consider when comparing materials.

In the case of concrete the compressive strength normally tests out at about 10% of the compressive strength. So concrete with 3,000 lb. compressive strength typically only has about 300 lbs. of tensile strength. By comparison Epoxy.com epoxy has a much higher tensile strength verses compressive strength.  By comparison Epoxy.com Product #10 Epoxy Mortar has a compressive strength of 10,000 PSI (about 3 times that of standard concrete) but Product #10  Epoxy Mortar has a tensile strength of 3,500 psi (at least 10 time stronger than concrete). So since materials break in tension first Epoxy.com Product #10 Epoxy mortar and most Epoxy.com Products are 10 times higher than standard concrete.

Flexural Strength

Flexural Strength is measured by supporting a bar of the epoxy or other material on both ends and then applying a load in the middle. Compressive strength and tensile strengths are measured differently, but in epoxy they really are talking about the same thing. These two tests measure the ability of the epoxy to resist being pulled apart. This test is much like what you are doing when you bend the toothpick in your hands, like we discussed earlier

Bond Strength

Bond strength is the measurement of how well an epoxy bonds to the substrate. Epoxy.com resins are designed to have a bond strength on concrete that is greater than the tensile strength of the concrete.  If the bond strength of the epoxy or epoxy like material is greater than the tensile strength of concrete than if there is a failure it will be a failure of the limits of the strength of the concrete not the epoxy. Epoxy bond strength is typically measured under ASTM D-882. Bond strength to concrete is measured under an American Concrete Institute test method "Adhesion to Concrete ACI Committee 403".

Cite: References Used on this Page

ACI Guide for Use of Epoxy Compounds with Concrete: "Adhesion to Concrete ACI Committee 403"
ASTM C109 / C109M - Standard Test Method for Compressive Strength Concrete
ASTM C881 / C881M - Standard Specification for Epoxy Resin Base Bonding Systems for Concrete
C882 Test Method for Bond Strength of Epoxy-Resin Systems By Slant Shear
D638 Test Method for Tensile Properties
D695 Test Method for Compressive Properties

Proper mixing and installation is critical to the optimal success of all product.  See Installation Tips, Techdata, & MSDS for more details on our products.  Be sure to contact us with any questions and/or concerns that you have.

For more information please contact:

Epoxy.com
A Division of Epoxy Systems, Inc
20774 W. Pennsylvania Ave.
Dunnellon, Florida 34431
Hundreds of Systems,
Since 1980 - Over 33 years
Florida & Vermont
USA


Customer and Technical Support Hours: 9AM-4PM Eastern Time (6AM-1PM Pacific Time).
Closed 12 Noon-1PM Eastern Time for Lunch

321-206-1833  Customer Service - Ordering and Order Status
                         Katey Fontaine, VP - Customer Service Director
                         sales@epoxy.com

                        Technical Support
352-533-2167  Norm Lambert, President - Technical Support Director 
                         info@epoxy.com

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                         Debby Lambert, CEO, and CFO
                         office@epoxy.com

352-489-1625   Fax line to all Departments

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Copyright © 1994-2014 (providing online information about the right product for the right job for 20 years) EPOXY.COM a division of Epoxy Systems, Inc. - Florida and Vermont.  All rights reserved.

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This information is presented in good faith to assist in determining whether this product is suitable for application. No warranty or representation, however, is intended or made, nor is protection from any law or patent to be inferred, and all patent rights reserved.

Epoxy.com a division of Epoxy Systems, Inc.  (hereinafter known as "Supplier" warrants its products (when properly stored) for the period of time as follows: Epoxy one (1) year; Polyesters, Methyl Methacrylates  and Polyurethanes Six (6) months.  Supplier warrants that its products will be free of manufacturing defects and will be in conformity with published specifications when handled, stored, mixed and applied in accordance with recommendations of Supplier. If any product fails to meet this warranty, the liability of Supplier will be limited to replacement of any non-conforming material if notice of such non-conformity is given to Supplier within the warranty period for the material (as indicated above), or within 1 year of the delivery of materials (whichever is sooner). Supplier may in its discretion refund the price received by Supplier in lieu of replacing the material. No customer, distributor, or representative of Supplier is authorized to change or modify the published specifications of this warranty in any way. No one is authorized to make oral warranties on behalf of Supplier. In order to obtain replacement or refund the customer must provide written notice containing full details of the non-conformity. Supplier reserves the right to inspect the non-conforming material prior to replacement. EXCEPT FOR THE EXPRESSED WARRANTY STATED ABOVE, THERE ARE NO OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING WITHOUT LIMITATION, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR PURPOSE. SUPPLIER'S OBLIGATION SHALL NOT EXTEND BEYOND THE OBLIGATIONS EXPRESSLY UNDERTAKEN ABOVE AND SUPPLIER SHALL HAVE NO LIABILITY OR RESPONSIBILITY TO THE PURCHASER OR ANY THIRD PARTY FOR ANY LOSS, COST, EXPENSE, DAMAGE OR LIABILITY, WHETHER DIRECT OR INDIRECT, OR FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES. All quotes and sales subject to availability.

Many of our products are batched on an individual order basis. Unless authorized by us in writing before the material is made, there are no returns on items purchased from us, once the order has been processed. In the event of authorized returns a restocking charge will be charged in the amount of 30% of the value of the material returned or $150 whichever is greater.  No returns on non-list priced items.  All Returns are for merchandise (store) credit only, no cash or credit card credits.  In the event of a return, buyer is responsible for the cost of shipping and handling in both directions.

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