The compressive strength of concrete typically increases over time. For 3000 psi concrete, here are approximate values at different ages:

1 day: around 16% of the specified strength, so approximately 480 psi.

3 days: around 40% of the specified strength, so approximately 1200 psi.

7 days: around 65% of the specified strength, so roughly 1950 psi.

14 days: around 90% of the specified strength, so roughly 2700 psi.

21 days: around 96% of the specified strength, so approximately 2880 psi.

28 days: around 99%, achieving or slightly exceeding the specified strength, so around 3000 psi.

According to ACI code standard, concrete grade is categorised according to their compressive strength represented as concrete mix 2000 Psi, 3000 Psi, 4000 Psi, 5000 Psi, 6000 Psi, 8000 Psi and 10000 Psi. For example, in concrete mix 2000, numerical figure is compressive strength of concrete is 2000psi (13.8MPa or 13.8N/mm2) after 28 days of mixing on axial compression test on cylinder shape with 15cm dia and 30cm length cylinder.

Characteristic strength of concrete is their compressive strength which can be determined by axial compression test on cubic concrete block or cylinder shape. If Compression test is carried on cubic concrete block, when tested with cube size 15cm × 15cm × 15cm, that’s known as Cubic test and their strength is called cubic strength. And compression test is carried on cylinder shaped concrete block, when tested with 15cm dia and 30cm length of cylinder, that is known as cylinder test and their strength is called cylinder strength.

Value of cube strength and cylinder strength are different for same mix. Value of cube strength is higher than cylinder strength. Using Thumb Rule, value of cube strength is is 1.25 times higher than cylinder strength.

**Cube strength = 1.25 × cylinder strength**

Concrete mix 3000:- this is normal grade of concrete used for flooring, pcc slab formation of garage, parking, etc. As per American standard ACI codes, strength of concrete and mix of Portland stone cement, fine aggregate and coarse aggregate, design according to cylinder test.

In 3000 concrete mix, numerical figure 3000 represent it’s characteristics of compressive strength (fck) on cylinder test that is 3000psi (20.7MPa or 20.7N/mm2) at 28 days after mixing, when tested with 15cm dia and 30cm length of cylinder. So compressive strength (fck) value of Concrete mix is 3000psi based on cylinder test.

According to American standard (ACI), fck (characteristics of compressive strength) value for concrete mix 3000 is 3000psi (20.7N/mm2 or 20.7MPa) on cylinder test at 28days after mixing, when tested with 15cm dia and 30cm length of cylinder.

**3000 Psi concrete compressive strength at 3, 7, 21 and 28 days**

As per ACI standard, compressive strength of concrete measured in Psi (Pounds per square inch). A higher psi means a given concrete mixture is stronger, so it is usually more expensive and lower Psi means a given concrete mixture is on average strength.

Compressive Strength of concrete can be estimated by strength of cement attained in 1,3, 7, 14, 21 and 28 days. However it would certainly depends upon no of factors such as- type of cement and their grade, cement & sand Mix Ratio, water ratio, gravel ratio, Concrete compactness (Vibrator) etc.

Concrete gain its strength with time after casting. The rate of gain of concrete compressive strength is higher during the first 28 days of casting and curing and then it slows down.

The compressive strength gained by 3000 Psi concrete after 1, 3, 7, 14, 21 and 28 days of curing are 480 Psi (16% of total strength), 1200 Psi (40%), 1950 Psi (65%), 2700 Psi (90%), 2880 Psi (96%) and 3000 Psi (99%) respectively when tested with 15cm dia and 30cm length of cylinder of cylinder test.

**3000 Psi concrete strength at 1 day**

The compressive strength of 3000 Psi concrete at 1 day or after 24 hours of curing is typically about 480 Psi which is approximately equal as 16% of total strength gain in 28 days of curing after casting when tested with 15cm dia and 30cm length of cylinder of cylinder test.

**3000 Psi concrete strength at 3 days**

The compressive strength of 3000 Psi concrete at 3 days of curing is normally about 1200 Psi which is approximately equal as 40% of total strength gain in 28 days of curing after casting when tested with 15cm dia and 30cm length of cylinder of cylinder test.

**3000 Psi concrete strength at 7 days**

The compressive strength of 3000 Psi concrete at 7 days of curing is usually about 1950 Psi which is approximately equal as 65% of total strength gain in 28 days of curing after casting when tested with 15cm dia and 30cm length of cylinder of cylinder test.

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**3000 Psi concrete strength at 14 days**

The compressive strength of 3000 Psi concrete at 14 days of curing is typically about 2700 Psi which is approximately equal as 90% of total strength gain in 28 days of curing after casting when tested with 15cm dia and 30cm length of cylinder of cylinder test.

**3000 Psi concrete strength at 21 days**

The compressive strength of 3000 Psi concrete at 21 days of curing is usually about 2880 Psi which is approximately equal as 96% of total strength gain in 28 days of curing after casting when tested with 15cm dia and 30cm length of cylinder of cylinder test.

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**3000 Psi concrete strength at 28 days**

The compressive strength of 3000 psi concrete at 28 days of curing is typically about 3000 Psi which is approximately equal as 99% of total strength gain in 28 days of curing after casting when tested with 15cm dia and 30cm length of cylinder of cylinder test.

Finally, when its strength have reached 99% in 28 days, still concrete continues to gain strength after that period, but that rate of gain in compressive strength is very less compared to that in 28 days.