No, V30 and U3 are not the same. V30 and U3 refer to different parameters related to concrete strength testing. Specifically:
- V30 refers to the compressive strength of concrete cylinders tested at 30 days.
- U3 refers to the compressive strength of concrete cubes tested at 28 days.
While V30 and U3 are both measures of concrete strength, they differ in the shape of the test specimen (cylinder vs cube), the test age (30 days vs 28 days), and the typical strength values. So they should not be used interchangeably.
More Details on V30 and U3
Here are some more details on V30 and U3:
V30
- V30 stands for the compressive strength of concrete cylinders tested at 30 days.
- The test involves taking concrete samples during construction and pouring them into cylinder molds (usually 6 inch diameter and 12 inch height).
- The cylinders are then cured under standard conditions.
- After 30 days, the cylinders are tested for compressive strength as per ASTM C39.
- V30 aims to evaluate the rate of concrete strength gain and assess whether the concrete meets the desired strength at 30 days.
- V30 values typically range from 2500-5000 psi for normal strength concrete.
U3
- U3 stands for the compressive strength of concrete cubes tested at 28 days.
- The test involves taking concrete samples during construction and pouring them into cube molds (usually 6 inch x 6 inch x 6 inch).
- The cubes are cured under standard conditions.
- After 28 days, the cubes are tested for compressive strength.
- U3 aims to evaluate whether the concrete meets the target strength at 28 days.
- U3 values typically range from 2500-6000 psi for normal strength concrete.
As seen above, the major differences are:
- V30 uses cylindrical specimens while U3 uses cubic specimens.
- V30 is tested at 30 days while U3 is tested at 28 days.
- The typical strength range for V30 is 2500-5000 psi while for U3 it is 2500-6000 psi.
So V30 and U3 are not interchangeable and reference different parameters for concrete strength.
Reasons for Differences Between V30 and U3
There are a few key reasons why V30 and U3 are not the same:
Shape of Test Specimens
V30 uses cylindrical specimens while U3 uses cubic specimens. The shape affects the measured concrete strength.
For the same concrete mix:
- Cubes typically give higher strength results than cylinders.
- The cube strength is usually 1.25 times the cylinder strength.
This is because cubes have less surface area in relation to their volume. This reduces the defects at the specimen surface that can initiate failure.
Testing Age
V30 is tested at 30 days while U3 is tested at 28 days.
Concrete gains strength over time as the cement hydration process continues. So concrete will have higher strength at 30 days versus 28 days.
The 2 day difference in testing age accounts for some of the typical variance between V30 and U3 strength.
Historical Conventions
V30 and U3 evolved as standard tests in different regions:
- V30 is widely used in North America and many other countries.
- U3 originated in the UK and is more common in Europe.
So part of the reason they are different is due tolocalized standards and conventions.
Relation Between V30 and U3
While they are not the same, there is a relationship between V30 and U3 strength:
- As a general rule of thumb, V30 is around 0.8 times U3.
- So an equivalent V30 strength can be estimated from U3 using V30 ≈ 0.8 U3.
- For example, 3000 psi U3 strength would correspond to around 2400 psi V30 strength.
However, this relation can vary based on factors like concrete mix design, curing conditions, and testing procedures.
For a more accurate conversion:
- Test cylinders and cubes from the same concrete samples.
- Cure them under same conditions.
- Test them at both 28 and 30 days.
- Develop a correlation factor between U3 and V30 based on the test results.
This localized correlation factor will give the most precise conversion between the two.
Summary
In summary:
- V30 and U3 are not the same. V30 uses cylinders tested at 30 days, while U3 uses cubes tested at 28 days.
- The shape, test age, and conventions account for their differences.
- As a general rule of thumb, V30 is around 0.8 times U3 strength.
- For accurate conversion, localized test data should be used to develop a correlation factor.
- They cannot be used interchangeably and refer to different parameters of concrete strength.
So while related, V30 and U3 are distinct measures that must be interpreted appropriately. Care should be taken to avoid confusing them when specifying, testing or reporting concrete strengths.
Frequently Asked Questions
Why is there a difference between V30 and U3?
The main reasons for the difference between V30 and U3 are:
- V30 uses cylindrical specimens while U3 uses cubic specimens
- V30 is tested at 30 days while U3 is tested at 28 days
- They originated due to different standards and conventions in North America and Europe
The shape, test age, and conventions all contribute to V30 and U3 being different measures.
Can V30 and U3 be used interchangeably?
No, V30 and U3 should not be used interchangeably. Since they represent the compressive strength of different specimen shapes tested at different ages, the values cannot be considered equivalent. Interchanging them could lead to incorrect evaluation of concrete strength.
How are V30 and U3 related?
As a general rule of thumb, V30 is around 0.8 times U3. However, the exact relation can vary based on concrete mix, curing, and testing methods. To accurately convert between them, localized test data should be used to develop a correlation factor. But broadly, U3 results are expected to be 20-25% higher than equivalent V30 results.
What is a typical V30 strength range?
For normal strength concrete, the typical V30 strength range is:
- 2500 – 5000 psi (17 – 35 MPa)
High strength concrete can have V30 strengths above 5000 psi. Specialized concrete mixes can produce even higher strengths exceeding 10,000 psi.
What is a typical U3 strength range?
For normal strength concrete, the typical U3 strength range is:
- 2500 – 6000 psi (17 – 40 MPa)
High strength concrete can have U3 strengths above 6000 psi. Specialized concrete mixes can produce strengths exceeding 10,000 psi.
Example Strength Specification
Here is an example concrete strength specification using V30:
- Concrete must have a minimum V30 compressive strength of 4000 psi.
- Cylinders for testing shall be 6 inch diameter x 12 inch height.
- A set of 4 test cylinders shall be sampled for every 50 cubic yards of concrete placed.
- Cylinders shall be cured in accordance with ASTM C31.
- Compressive strength testing shall be done per ASTM C39 at 30 days after pouring the cylinders.
- The average compressive strength of the set shall meet the minimum 4000 psi requirement.
This provides clear instructions for concrete sampling, curing, testing and acceptance criteria based on the V30 parameter.
Example Conversion Between V30 and U3
Let’s look at an example converting between V30 and U3 using the 0.8 ratio:
- Specified U3 strength: 3000 psi
- Estimated equivalent V30 strength:
- V30 ≈ 0.8 x U3
- V30 ≈ 0.8 x 3000 psi
- V30 ≈ 2400 psi
So in this case, a mix designed for 3000 psi U3 strength would be expected to produce around 2400 psi V30 strength.
This demonstrates how to provide an approximate conversion between the two measures.
Conclusion
V30 and U3 are distinct measures of concrete compressive strength that should not be interchanged. While related, they differ in specimen shape, test age, typical values, and originating conventions. Approximate conversions can be made using a 0.8 factor, but localized test data should be used for more accuracy. When specifying, testing, and reporting concrete strength, care must be taken to interpret V30 and U3 appropriately based on their definitions and how they were determined. This helps ensure structural concrete performance is properly evaluated.