Concrete Monitoring: Calculating Concrete Compressive Strength

by | Nov 9, 2023 | Commercial

Concrete is one of the most widely used construction materials due to its high compressive strength, durability, and versatility. Compressive strength specifically refers to concrete’s ability to withstand loads that tend to crush it. This is a key engineering property that must be properly evaluated to ensure concrete structural integrity and performance. Compressive strength is affected by the concrete mixture design, curing conditions, age of the concrete, and other factors. Therefore, compressive strength testing and temperature monitoring are critical ways that concrete quality is evaluated during construction.

Knowing the compressive strength via standardized tests provides concrete producers, contractors, engineers, and inspectors with data to assess whether a batch of concrete is suitable for placement and meets project specifications. Concrete temperature monitoring provides additional insights into curing conditions and strength gain. This data can explain unexpected test results and confirm if potentially damaging thermal cracking may have occurred. Monitoring compressive strength development and temperature are thus essential tools for effective concrete quality control and performance prediction. 

Compressive strength is affected by many factors including the water-cement ratio, cement content, aggregate type and size, concrete age, curing conditions, and admixtures. Concrete gains strength over time through the process of hydration, so testing compressive strength requires breaking concrete samples and testing them at various ages.

Compressive strength testing is commonly conducted on concrete cylinder specimens. Cylinders are cast from fresh concrete and cured under standard conditions. They are then tested by applying compressive force along their vertical axis until failure. The peak load at failure divided by the cross-sectional area of the cylinder gives the compressive strength.

Test standards like ASTM C39 specify the cylinder size, testing ages, rate of loading, and other parameters for consistent and comparable results. Common cylinder sizes are 4 x 8 inches and 6 x 12 inches. Tests are often run at 7, 14, and 28 days to evaluate early and longer-term strength gain.


Knowing the compressive strength is essential for evaluating concrete quality and ensuring it meets the requirements of the job specification. Strength results are used to determine if a batch of concrete is acceptable and can be placed. Results are also used to confirm if formwork and shoring can be removed at the appropriate time.

For some applications like pavements and structures, continued strength gain after 28 days is also important. Later-age testing may be conducted to verify design strengths are achieved.

Monitoring concrete temperatures is also critical as it cures. The rate of hydration and strength gain are highly dependent on temperature. High temperatures speed up hydration while low temperatures slow it down.

Sudden drops in temperature can cause early-age cracking that reduces long-term strength. Large temperature differentials within a concrete element can also lead to cracking from internal stresses.


To track curing conditions, you will need a concrete temperature sensor to insert in the fresh concrete. Common sensor types include thermocouples, thermistors, and RTDs. Temperature data loggers record the readings at set intervals.

The temperature history provides a record of curing conditions. If strength results are lower than expected, the temperature data can help explain why. The temperature data also verifies if any potentially damaging thermal cracks may have occurred.

For large pours like dams, temperature control is vital. Concrete temperature monitoring enables the use of insulation, heating, or cooling to regulate temperatures and prevent cracking.

In summary, measuring compressive strength and temperature are crucial ways to monitor concrete quality. Strength testing evaluates if the concrete meets specifications. Temperature monitoring provides insight into curing conditions affecting strength. Together they enable better control over concrete construction.

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