In Australia, concrete grades are specified by the Australian Standard AS 3600-2018 “Concrete Structures.” Common concrete grades and their corresponding compressive strengths include:

1. N20: Nominal 20 MPa

2. N25: Nominal 25 MPa

3. N32: Nominal 32 MPa

4. N40: Nominal 40 MPa

5. N50: Nominal 50 MPa

These grades represent the characteristic compressive strength of cylindrical concrete specimens at 28 days.

According to Australian standard (AS), as per Australian standard, concrete grade represented as N20, N25, N32, N40, N50, N65, N80 and N100. For example, N20 concrete grade, It is indicated as N, which N is stand for nominal concrete strength followed by a numerical figure 20, which is compressive strength of concrete is 20MPa after 28 days of mixing on axial compression test on cylinder shape with 15cm dia and 30cm length cylinder.

**The** **grade** **of** N20 concrete is **denoted** **by** N, **where** N is **the** nominal strength **of** **the** **concrete,** followed by **the** **number** 20, which **represents** **the** **concrete** compressive strength of **20** **MPa** after 28 days of mixing **in** **the** axial compression test **over** **a** **15** **cm** **diameter** **and** **30** **cm** cylinder **length.**

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**

Australian Standard (AS) codes concrete grade generally refers cylinder test, compression test is carried on cylinder shaped concrete block, when tested with 15cm dia and 30cm length of cylinder for finding out compressive strength of different mix of concrete at 28 days after mixing. In this article we read about types of concrete grade and their compressive strength as per Australian Standard.

**Types of concrete grade and their compressive strength as per Australian Standard (AS)**

According to Australian standard (AS), there are three types of concrete grade, 1) normal concrete grade is indicated as N20, N25, 2) standard concrete grade, indicated as N32, N40 & N50 and 3) high strength concrete grade, indicated as N65, N80 and N100. For example N20, It is indicated as N, which N is stand for nominal concrete strength followed by a numerical figure 20, which is compressive strength of concrete is 20MPa after 28 days of mixing on axial compression test on cylinder shape with 15cm dia and 30cm length cylinder.

**What are the grades of concrete and their compressive strength as per Australian standard**

As we know that concrete are made of mixing of cement, sand and aggregate in required proportion. What are the grades of concrete?, according to Australian standard concrete grade is three types, 1) normal concrete grade, 2) standard concrete grade and 3) high strength concrete grade. the grades of concrete represented as N20, N25 is known as normal grade of concrete, N32, N40 & N50 is known as standard grade of concrete which are generally used and N65, N80 and N100 is known as high strength concrete grade used for special construction.

**N20 concrete grade**

● N20 concrete grade:- this is normal grade of concrete have secondary uses for flooring. According to Australian standard, strength of concrete and mix of Portland stone cement, fine aggregate and coarse aggregate, design according to cylinder test.

Meaning of N20 or 20 mpa concrete grade is N indicates nominal concrete strength, numerical figure 20 represent it’s characteristics of compressive strength (fck) on cylinder test that is 20MPa at 28 days after mixing, when tested with 15cm dia and 30cm length of cylinder. So compressive strength (fck) value of N20 concrete grade is 20MPa or 20 N/mm2 based on cylinder test.

According to Australian standard (AS), fck (characteristics of compressive strength) value for N20 concrete grade is 20N/mm2 or 20MPa on cylinder test at 28days after mixing and curing, when tested with 15cm dia and 30cm length of cylinder.

The typical strength of N20 concrete is at 1 days or after 24 hrs is about 3.2 mpa which is approximately equal as 16% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

20 MPa concrete strength at 3 days:- strength of 20 mpa concrete at 3 days of curing is about 8 mpa which is approximately equal as 40% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

20 MPa concrete strength at 7 days:- strength of 20 mpa concrete at 7 days of curing is about 13 mpa which is approximately equal as 65% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

20 MPa concrete strength at 14 days:- strength of 20 mpa concrete at 14 days of curing is about 18 mpa which is approximately equal as 90% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

20 MPa concrete strength at 28 days:- strength of 20 mpa concrete at 28 days of curing is about 20 mpa which is approximately equal as 99% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

The compressive strength of M20 concrete is approximately 8 MPa (1160 psi) at 3 days, approximately 13 MPa (1900 psi) at 7 days, approximately 18 MPa (2600 psi) at 14 days, and approximately 20 MPa (2900 psi) at 28 days.

N20 concrete mix ratio:- The typical ratio of cement, sand and aggregate in N20 concrete mix is 1:2:4. This means that for every 1 part of Portland cement there are 2 parts of sand and 4 parts of aggregate. The water-cement ratio for N20 concrete mix is usually between 0.4 and 0.6.

**N25 concrete grade**

● N25 concrete grade:- This is normal grade of concrete used for flooring, slab of garage, parking, pcc, etc, according to Australian standard, strength of concrete and mix of Portland stone cement, fine aggregate and coarse aggregate, design according to cylinder test.

The compressive strength of N25 concrete is approximately 10 MPa (1450 psi) at 3 days, approximately 16.25 MPa (2360 psi) at 7 days, approximately 23.5 MPa (3260 psi) at 14 days, and approximately 25 MPa (3625 psi) at 28 days.

**The** **grade** **of** N25 concrete is **denoted** **by** N, **where** N is **the** nominal strength **of** **the** **concrete,** followed by **the** **number** 25, which **represents** **the** **concrete** compressive strength of **25** **MPa** after 28 days of mixing **in** **the** axial compression test **over** **a** **15** **cm** **diameter** **and** **30** **cm** cylinder **length.**

Meaning of N25 or 25 mpa concrete grade is N indicates nominal concrete strength, numerical figure 25 represent it’s characteristics of compressive strength (fck) on cylinder test that is 25MPa at 28 days after mixing, when tested with 15cm dia and 30cm length of cylinder. So compressive strength (fck) value of N25 concrete grade is 25MPa based on cylinder test.

N25 concrete mix ratio:- The typical ratio of cement, sand and aggregate in N25 concrete mix is 1:1.5:3. This means that for every 1 part of Portland cement there are 1.5 parts of sand and 3 parts of aggregate. The water-cement ratio for N25 concrete mix is usually between 0.4 and 0.6.

According to Australian standard (AS), fck (characteristics of compressive strength) value for N25 concrete grade is 25N/mm2 or 25MPa on cylinder test at 28days after mixing, when tested with 15cm dia and 30cm length of cylinder.

25 MPa concrete strength at 1 days:- strength of 25 mpa concrete at 1 days or after 24 hrs is about 4 mpa which is approximately equal as 16% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

25 MPa concrete strength at 3 days:- strength of 25 mpa concrete at 3 days of curing is about 10 mpa which is approximately equal as 40% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

25 MPa concrete strength at 7 days:- strength of 25 mpa concrete at 7 days of curing is about 16 mpa which is approximately equal as 65% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

25 MPa concrete strength at 14 days:- strength of 25 mpa concrete at 14 days of curing is about 22.5 mpa which is approximately equal as 90% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

25 MPa concrete strength at 28 days:- strength of 25 mpa concrete at 28 days of curing is about 25 mpa which is approximately equal as 99% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

**N32 concrete grade**

● N32 concrete grade:- This is standard grade of concrete, used for rcc structure of low rise building, according to Australian standard, strength of concrete and mix of Portland stone cement, fine aggregate and coarse aggregate, design according to cylinder test.

N32 concrete mix ratio:- The typical ratio of cement, sand and aggregate in N32 concrete mix is 1:2:3. This means that for every 1 part of Portland cement there are 2 parts of sand and 3 parts of aggregate. The water-cement ratio for N32 concrete mix is usually between 0.4 and 0.6.

**The** **grade** **of** N32 concrete is **denoted** **by** N, **where** N is **the** nominal strength **of** **the** **concrete,** followed by **the** **number** 32, which **represents** **the** **concrete** compressive strength of **32** **MPa** after 28 days of mixing **in** **the** axial compression test **over** **a** **15** **cm** **diameter** **and** **30** **cm** cylinder **length.**

Meaning of N32 or 32 mpa concrete grade is N indicates nominal concrete strength, numerical figure 32 represent it’s characteristics of compressive strength (fck) on cylinder test that is 32MPa at 28 days after mixing, when tested with 15cm dia and 30cm length of cylinder. So compressive strength (fck) value of N32 concrete grade is 32MPa based on cylinder test.

According to Australian standard (AS), fck (characteristics of compressive strength) value for N32 concrete grade is 32N/mm2 or 32MPa on cylinder test at 28days after mixing, when tested with 15cm dia and 30cm length of cylinder.

32 MPa concrete mix ratio:- nominal mix ratio for 32 mega pascal standard concrete is 1:2:3 in which 1 part of Portland stone cement mix with 2 parts of find and well graded dry sand and 3 parts of gravel or coarse aggregate with required amount of water. If you buy premix bag of concrete then you add 1kg to 1.5kg of cement per 20 kg bag of concrete to achieve 32 MPa concrete.

32 Mpa concrete to Psi:- 32 MPa compressive strength of concrete is approximately equal to 5000 psi. To achieve 5000 Psi strength of concrete you should add 1kg to 1.5kg of cement per 20 kg bag of concrete which is best used for Foot paths, slab, footing, garden edges & etc.

32 MPa concrete strength at 1 days:- strength of 32 mpa concrete at 1 days or after 24 hrs is about 5 mpa which is approximately equal as 16% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

32 MPa concrete strength at 3 days:- strength of 32 mpa concrete at 3 days of curing is about 13 mpa which is approximately equal as 40% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

32 MPa concrete strength at 7 days:- strength of 32 mpa concrete at 7 days of curing is about 21 mpa which is approximately equal as 65% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

32 MPa concrete strength at 14 days:- strength of 32 mpa concrete at 14 days of curing is about 29 mpa which is approximately equal as 90% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

32 MPa concrete strength at 28 days:- strength of 32 mpa concrete at 28 days of curing is about 32 mpa which is approximately equal as 99% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

**N40 concrete grade**

● N40 concrete grade:- This is standard grade of concrete used for septic tank, water tank, sea side condition, according to Australian standard, strength of concrete and mix of Portland stone cement, fine aggregate and coarse aggregate, design according to cylinder test. In N40 concrete grade, N indicates nominal concrete strength, numerical figure 40 represent it’s characteristics of compressive strength (fck) on cylinder test that is 40MPa at 28 days after mixing, when tested with 15cm dia and 30cm length of cylinder. So compressive strength (fck) value of N40 concrete grade is 40MPa based on cylinder test.

According to Australian standard (AS), fck (characteristics of compressive strength) value for N40 concrete grade is 40N/mm2 or 40MPa on cylinder test at 28days after mixing, when tested with 15cm dia and 30cm length of cylinder.

40 MPa concrete strength at 1 days:- strength of 40 mpa concrete at 1 days or after 24 hrs is about 6.5 mpa which is approximately equal as 16% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

40 MPa concrete strength at 3 days:- strength of 40 mpa concrete at 3 days of curing is about 16 mpa which is approximately equal as 40% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

40 MPa concrete strength at 7 days:- strength of 40 mpa concrete at 7 days of curing is about 26 mpa which is approximately equal as 65% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

40 MPa concrete strength at 14 days:- strength of 25 mpa concrete at 14 days of curing is about 36 mpa which is approximately equal as 90% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

40 MPa concrete strength at 28 days:- strength of 40 mpa concrete at 28 days of curing is about 40 mpa which is approximately equal as 99% of total compressive strength when tested with 15cm dia and 30cm length of cylinder.

N50, N65, N80 and N100 are higher strength concrete are used in extreme environmental condition, sea side condition, formation of septic tank and water tank, and basement formation, bridge & dams formation and heavy loaded structural commercial and industrial building, mostly high rise building, it is used for special uses.