ASTM Standard Test Method C39: Compressive Strength of Concrete Cylinders

Updated on January 16, 2019
Lissa Clason profile image

Melissa has a bachelor's degree in geology, and is an ACI-certified field and lab technician at Froehling and Robertson.

Significance and Use of ASTM C39

Concrete's compressive strength determines whether the concrete placed in a structure can bear the weight of what's on top of it, or if it will splinter into a million pieces and cause the structure to collapse. It is highly important for engineers to know how strong concrete is, and so construction materials testing companies send their field technicians to various construction sites to make cylindrical samples out of the same concrete that is being poured (read ASTM C31 to learn how cylinders are made).

Back at the lab, these samples are cured in a temperature-controlled moisture room with a constant fog spray, and on certain days a couple of samples from that set are loaded to their breaking point with a hydraulic press machine. There is usually a 7 day break and a 28 day break, and if something fails to meet strength a spare sample is set aside for a 56 day break. This way, you have a record of how the concrete gained strength over that period of time, and you may be able to pinpoint problems in the making or curing of the concrete or in the mix itself.

Concrete strength is highly variable and can change with many factors, including the size and shape and condition of the cylinder, the way it was batched and mixed and transported from the concrete plant to the job site, the way it was molded in the field, and the temperature and moisture conditions during the curing process. Lightweight concrete will differ in mix design and strength compared to regular concrete, and smaller samples may be able to handle less load than larger ones.

Engineers can use strength test results to see if the concrete being poured fits with what it is being used for and meets their specification's requirements. These results are their quality control for the whole process of pouring concrete from batching to placement. Strength test information can also help them figure out if admixtures put into the concrete mix at the job site are effective.

Technicians who test these cylinders must be appropriately trained and certified. ASTM C1077 requires that an examiner not related to your company must see you demonstrate this test in order to be qualified to do it. The ACI Lab Technician Certification Course will serve this purpose for lab techs in America.

Equipment for Concrete Strength Testing

To break cylinders, you will need several pieces of equipment.

  • Testing Machine - The testing machine is powered by hydraulic fluid, and uses a piston to lift the lower bearing block and push the cylinder into the upper bearing block, loading the cylinder with increasing weight until it ruptures. It is typically operated by a lever or several buttons to retract, hold, or advance the lower bearing block, and its results may be reported by a dial gauge or a digital readout. This is a sensitive piece of equipment and it must regularly be calibrated and maintained. ASTM C39 section 6 goes more into depth about the specifications of the machine's individual parts.
  • Calipers or Ruler - Measuring the diameter of each cylinder is vital to the test results, as you will need to calculate the area of the cylinder to find the strength. Keeping a daily record of your cylinder diameters is recommended. No individual diameters on the same cylinder can vary by more than 2%, or the sample is invalid.
  • Carpenter's Square - These are useful to check the perpendicularity of the cylinder's axis, making sure that the cylinder does not depart from perpendicularity by more than 0.5 degrees. It helps to get one that comes with a bubble level.
  • Straight Edge, 1/8 inch nail and 1/5 inch nail - This is used to check the planeness of the ends of the cylinder. You put the straightedge across the end of the cylinder, and poke the nail at it to see if it goes underneath. The 1/8 inch nail is used if capping with ASTM C617, and the 1/5 inch nail is used for unbonded caps (ASTM C1231).
  • Cylinder Wraps - This is safety equipment, and also helps to keep the testing machine and its surrounding area clean. They are rectangular pieces of canvas with velcro on the ends that wrap around the cylinder and keep concrete fragments contained, protecting the machine operator from sudden ruptures shooting concrete everywhere.
  • Retaining Rings - If you are using unbonded caps, these contain neoprene pads that help absorb the shock on the cylinder as it breaks, and go over the ends of the cylinder. Make sure they are level when you place them on. If you work in a lab where these are exposed to the elements and you don't want them to rust, regularly clean them with a wire brush and some WD-40. You can learn more about unbonded caps in ASTM C1231.
  • Sulfur capping equipment - This equipment consists of sulfur mortar, a sulfur pot apparatus to melt the mortar in, capping plates, spoons, and various other items. Refer to ASTM C617 to learn more about the capping procedure.
  • Spacers - Break machines are typically built to break 6x12 cylinders, so if you have smaller samples you will need to put something in there for them to sit on, kind of like a booster seat for a small child. Typically these are made of steel or some other strong material, and are cylindrical in shape, but a little wider than the diameter of the cylinders that sit on them.
  • Brush and dustpan - Keeping the bearing surface of the testing machine clean and clear of debris is very important, because it needs to be plane and level for each cylinder to break properly. It is recommended that you sweep it clean after each break.
  • Wheelbarrow - A wheelbarrow can be used to hold broken samples to throw them away after you are done testing. Don't let it get too full or you might spill it and leave concrete fragments all over the lab that will take forever to clean up.
  • Safety goggles - Wear eye protection, as this can get messy!

ASTM C39 Procedure

1. Bring the cylinders out of the moisture room, keeping them covered with wet burlap to keep them moist. Check the cylinders over for defects (holes, cracks, crumbliness) as you set them on the table, use your straight edge and nail to check for planeness, and set the ones with ends that are not plane aside to be saw cut. You will want to look at the perpendicularity of the cylinder as well, to make sure it does not depart from a vertical axis by more than half a degree. If you want to break cylinders uncapped, they must be plane within 0.002 inches. Most cylinders don't meet this requirement, so you'll want to either cap them with sulfur or gypsum paste (ASTM C17), or unbonded neoprene caps (ASTM C1231).

2. Measure the diameter of each cylinder twice, in the center of each cylinder at 90 degree angles. Make sure that your two diameters are not off from each other by more than two percent, or a test on that cylinder would be considered invalid. With the average diameter, calculate the surface area of each cylinder:

Diameter / 2 = Radius

Area of the cylinder face = Pi * Radius * Radius

3. Make sure that the bearing surfaces of the machine are clean and free of debris, and if you are using unbonded caps, check the cleanliness of your neoprene caps. You should have a record at your break station of the number of cylinders that have been broken on those particular caps. Discard the caps and put new one in the retaining rings if there are large cracks or gouges in them, or if you have broken over 100 cylinders on those caps. It is also recommended that you flip the caps at 50 cylinders.

4. Put the neoprene caps on the ends of your cylinder, and check to make sure they fit right and are plane and level. Place the specimen on the lower bearing block (or on a centered spacer, if breaking a 4x8 cylinder) and align it with the upper bearing block, using the rings on the bottom block to center it.

5. Zero out the machine, and then apply a load at full advance until you get to about 10% of the estimated load. A good spot is around 11000 lbs for a 6x12 cylinder breaking at 4000 psi. Remember that psi is load divided by the area, so you could calculate this for any size cylinder and any specified strength. Put the machine on hold and check the cylinder's alignment with your carpenter's square, making sure it doesn't depart from vertical by more than 0.5 degrees. If everything is good, proceed to the next step, but if the cylinder is off center, remove the load and readjust the position of the cylinder.

6. You can now apply load to the cylinder. It is permissible to go faster than the recommended rate of about 28-42 psi/second for the first half of loading. Switch to a metered advance around 50% of the estimated strength of the cylinder. This will look like an increase of 1000 lbs/second for a 6x12 cylinder, and 500 lbs/second for a 4x8 cylinder.

7. Don't mess with the loading rate after the halfway point, as the cylinder approaches its peak load. The cylinder will hit a peak, then drop. If it drops slightly, the load may begin to increase again, so let it go until the load is decreasing steadily and you can see clear evidence of a forming fracture pattern, and then turn the lever back to the off position.

8. Pull the cylinder out of the machine, and then remove the caps. Carry it over to your wheelbarrow and remove the wrap, letting the pieces fall into the wheelbarrow. Determine the type of fracture and then write down the load and the type of fracture. Calculate the strength of the cylinder, reporting it to the nearest 10 psi:

Strength in psi = load in pounds / area in square inches

Cylinder Fracture Types

A Video of the ASTM C39 Procedure

ASTM C39 Quiz

view quiz statistics

Questions & Answers

© 2018 Melissa Clason

Comments

    0 of 8192 characters used
    Post Comment

    • Eurofile profile image

      Liz Westwood 

      4 months ago from UK

      This is a very topical and interesting article especially in view of the collapse of the bridge in Genoa. We use concrete so much in construction.

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, owlcation.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://owlcation.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)