Choosing a Standard Concrete Compression Testing Machine

Purpose of a concrete compression machine

The purpose of a Concrete Compression Machine is straightforward; it uses compressive force to load different types of concrete specimens to ensure the material meets design and structural strength requirements. These versatile machines are the centerpiece of any concrete testing lab. They can be configured in a variety of ways to adapt to different sample types, and the right one can shape the success of your testing program.

Advantages of having a compression machine

Technical advancements over time have enhanced the level of accuracy, repeatability, efficiency, and performance for testing concrete, grout, and mortar strengths in a wide range of sample types. These precision machines are often equipped for one specific sample type, for example, a 6x12in concrete cylinder specimen. However, they can be outfitted with adaptive accessories for testing multiple sample types and sizes. This blog post will guide you through the process of selecting the right machine and equipping it to be a versatile and efficient addition to your lab.

How to choose the right standard machine for your lab

In this blog, we created a 5-step buying guide to help you select the specific standard concrete compression machine and adaptive accessories that will best suit your laboratory concrete compressive testing needs.

Step 1: Understanding Frame Capacity and Stiffness

According to the National Ready Made Concrete Association, the compressive strength of concrete is “the most common performance measure used by the engineer in designing buildings and other structures.” It’s important to select a concrete compression machine that complies with ASTM C39 and other applicable ASTM and AASHTO standards. It should also adhere to rigidity recommendations in the ACI 363 Report on High-Strength Concrete. It states the load frame should have a total capacity of “at least 20% greater than the expected ultimate load of the cylinders.”

A load frame that is stiff, both longitudinally and laterally, assures uniform specimen loading, reduces explosive failures, and generally will have a longer service life. Explosive failures, especially with high-strength concrete samples, can produce shocks to the hydraulic and electronic systems, causing damage and loss of calibration.

Step 2: Know Your Sample Types and Strength Requirements

The size of specimens tested directly influences the maximum concrete strength the machine is capable of testing. For instance, following the guidelines indicated above, a compression machine with a total capacity of 250,000lbf can test 6x12in cylinders with expected strengths up to about 7,000psi. Using 4x8in cylinders in the same machine allows testing of concrete with strengths of 15,000psi or more, but precautions such as fragment guards should be in place.

Gilson's Standard Concrete Compression Machines are designed in a series of four different capacities: 250,000lbf, 300,000lbf, 400,000lbf, and 500,000lbf to meet such variances – and machines with greater capacities are available by special order.

There are other variables related to the machine’s functionality to keep in mind:

• Compatibility: Will you be testing only one sample type (for instance a cylinder), or do you want the capability to also test cubes, cores, prisms, and beams in a range of sizes? As stated earlier, there are accessories to adapt your compression machine for more than one testing application. Testing concrete beam specimens means you should make sure the machine retains its level of accuracy at lower loads. Flexural beam strengths are significantly lower than concrete cylinder compressive strengths.
• Strength: What range of strengths do you expect to test and are there specific precautions to consider? For instance, using 4x8in sample cylinders allows testing cylinders with higher design strengths, but some caution is advised since very high strength concrete samples can be prone to explosive failure. These failures can be hazardous due to flying fragments and may shock the electronic and hydraulic systems of the machines. It’s important to ensure that the compression machine is equipped with protective fragment guard doors and other safety features.
• Size: What are the specimen sizes you will be testing? The size of the compression machine’s frame openings, sometimes referred to as daylight openings, should be sufficient to accommodate the maximum size specimen and ensure ease of handling. Masonry prisms can require a surprising amount of space, especially if they are capped. Gilson Compression Machines have daylight openings up to 14x14.3in (356x363mm) WxH, with all platens in place. Machines with larger openings are also available. Spacers in a variety of sizes and thicknesses are available to adjust the opening size for each sample type.
• Type of Test: What do the test standards say? What are the requirements? In addition to ASTM C39, there are other industry standards that may apply to your specific testing applications. These include ASTM C109, ASTM C293, ASTM C78, ASTM E4, along with AASHTO T 22, BS 1610 and BS 1881.
• Features: What about the hydraulics system? Look for features like two-stage hydraulic systems and reliable hydraulic valve controls to regulate loading. A common and costly operation error is to allow the hydraulic ram to over-extend. Select a model with a pressure bleed hole to prevent this – and pay close attention to the maximum extension warning label marked on the frame.

Step 3: Operation and Data Collection

How do you handle your test data and results? Decide how you want your test data to be collected and distributed. If you only have a few cylinders to break now and then, perhaps a pencil and paper will do, but Gilson’s basic Pro Controller helps you organize and retain what you need for most testing. The memory capability of this controller saves the results of up to 600 tests with optional transfer to a PC or printer.

However, if you test on a regular basis, leverage available technology for data collection, log your test results, and generate reports in a way that streamlines lab efficiency and minimizes human error - the Pro-Plus Controller saves information for sample ID, size and type, operator while displaying live load, rate of load, and stress. For a more in-depth comparison between the two controllers view the comparison chart or video below.

Step 4: Increase Versatility with Adaptive Products

Once you have determined features, capacities, and capabilities for your testing machine, choose the model-specific accessories to optimize it for your applications. Adaptive accessories enhance the functionality of each compression testing machine by equipping it with products that expand the testing capability. These accessories allow testing of flexural beams, masonry prisms, different cylinder sizes, cubes – and there are even cylinder splitting fixtures.

Consider not only the accessories you’ll need but what it will take to change over the machine to accommodate them. Upper platens for accessories used to test 6in cubes and masonry block prisms are very heavy and difficult to install unless you use carrier bracket options. Locking stems make switching platens quick and easy, but threaded draw rods allow easy height adjustments with the right spacers.

Step 5: Pick the Compression Testing Machine that Best Meets Your Needs

Specific characteristics of Gilson’s Concrete Compression Machines in four standard capacities are shown below. Each can be supplied ready for testing 6x12in concrete cylinders with sulfur caps or unbonded pads, and each can be outfitted for testing other cylinder sizes, different-sized cubes, concrete masonry units, and flexural beams. Special-order Compression Testing Machines with load capacities up to 1,000,000lbf (4,448kN), special control consoles, and multiple loading frames are also available.

We hope the information contained within this guide will help you select the compression testing machine that gets the job done right the first time, adheres to industry standards and recommendations – and maintains quality control and quality assurance protocols. For additional information about compression testing machines, contact our technical support professionals by calling (800) 444-1508 or sending an email to techsupport@gilsonco.com.