Concrete masonry units (CMUs) are precast rectangular blocks used in construction projects for their reliability and durability. ASTM C140 covers the standard method for ensuring CMUs and related concrete units check those boxes.
Masonry and reinforced concrete are the most common materials used in construction. Concrete masonry units are made out of concrete and aggregates, such as sand, gravel and crushed stone. Known for their strength and durability, CMUs can withstand significant forces, including fire and harsh weather conditions.
In this article, we cover the basics of sampling and testing concrete masonry and related units according to ASTM C140:
- What does ASTM C140 include?
- Recommended equipment for ASTM C140
- Test procedure and calculations
What Does ASTM C140 Include?
ASTM C140 provides general testing requirements for a broad range of concrete products, including:
- Concrete masonry units
- Concrete and calcium silicate brick
- Segmental retaining wall units
- Concrete interlocking paving units
- Concrete grid paving units
- Concrete roof pavers
- Dry-cast articulating concrete block
Related Reading | Simple Guide to ASTM C1884: Manufactured Concrete Ballast Units
To evaluate the characteristics of these materials, ASTM C140 provides methods for sampling, measuring dimensions, testing compressive strength and flexural load, and determining absorption, unit weight, moisture content, and ballast weight.
In the case of concrete masonry units, the relevant test methods outlined in ASTM C140 are:
- Sampling
- Measuring dimensions and unit weight
- Determining absorption and moisture content
- Testing compressive strength
Here’s what you will need to perform these methods.
Recommended Equipment for ASTM C140
To take measurements and test the strength of concrete masonry units, you will need:
- Caliper for dimension measurements
- Scale for weight
- Water container for absorption measurements
High quality results that truly prove the CMU’s reliability and durability rely on accurate absorption and compressive strength calculations. To achieve the highest level of accuracy and assurance, machine technicians can use a Connected Compression Machine.
A Connected machine has a native two-way integration with CMT software, providing pre-test “Smart Checks” to validate test parameters, automatic preload calculations, and automatic controls. After the test, calculations are automatically run and values transfer to your LIMS or other software. This allows technicians to get more done faster while ensuring the highest level of quality for testing concrete masonry units.
Read More | What Are Connected CMT Machines?
ASTM C140 Test Procedure & Calculations
#1. Sample Concrete Masonry Units
Sample six units with an identical size and configuration. Three of these will be used for measurements and absorption testing, and the other three will be used for compression testing.
To ensure the results don’t misrepresent the properties of the lot, here are some guidelines to keep in mind:
- Samples should be randomly taken, as opposed to hand selecting the most or least desirable units.
- Samples should have the same mix design and manufacturing and curing procedures.
- Samples can be taken from the job site or the manufacturer’s storage inventory.
- Samples should be marked with a unique identification and weighed.
#2. Measure Unit Dimensions & Weights
Measure the length, width and height of the same CMUs that you plan to use for absorption testing – prior to immersing the units in water. This will verify that the dimensions are within allowable tolerances before and after moisture content.
With these dimensions, you can calculate the normalized web area, which is an important measurement that ensures the units have sufficient web material (the solid portions in between the voids of the unit) connecting the face shells. To do this:
- Measure the thickness and height of each web
- Calculate the total web area of the unit
- Divide the web area by the unit face area
Weigh the units at least five times in this order:
- Received weight (dry) at least once
- Immersed weight (wet) at least once
- Saturated surface dry weight at least once
- Oven-dry weight at least twice
#3. Calculate Absorption & Density
Absorption describes a unit’s ability to soak up and hold water. When absorption varies across a sample, this might be an indication of deleterious materials in the mix, poor mixing quality, or compaction of the concrete mix, which can impact compressive strength and durability.
With the above measurements, you can calculate absorption for each unit:
- Calculate unit volume.
- Determine the difference between saturated surface dry weight and oven-dry weight.
- Divide the above difference by the volume.
- Calculate the average absorption of three units.
Then, you can calculate density by dividing the oven-dry weight by the volume. Calculate the average density of three units, too.
#4. Test Units for Compressive Strength
To test CMUs for compressive strength, use the three fresh units from your sample – not the three that were used for absorption testing – so the results aren’t influenced by residual moisture content.
- Prepare concrete masonry units and cap in accordance with ASTM C1552.
- Position unit in the testing machine so the center of mass aligns with the machine’s center of thrust.
- Apply preload followed by uniform load until failure (maximum load).
- Calculate compressive strength by dividing the maximum load by the cross-sectional area of the unit.
Conclusion
ASTM C140 helps ensure the reliability and durability of concrete masonry units and other related concrete materials. This simple guide gives you everything you need to get started, but please reference the current ASTM standard before you do.
Forney has the compression machines, related accessories and software for ASTM C140. Shop the Forney store today or find your machine. Shop the Forney store today or find your machine.