10 Feb What Is the Compressive Strength Of Concrete?
Compressive strength is the load-bearing ability of concrete. It is the point before it starts to break at the molecular level. In this article, we will explain everything about the compressive strength of concrete.
Compressive strength is a load concrete can withstand without cracking or breaking. We measure and express concrete strength in (psi) or (MPa). Compressive strength is important for defining the quality and strength of concrete.
Continue reading this to learn about the calculation and importance of compressive strength. We will also share tips on achieving good concrete compressive strength!
What Is Compressive Strength?
Compressive strength is concrete’s ability to withstand load and pressure without breaking.
Definition
Have you ever looked at a concrete building and wondered what is holding it together? Well, that’s concrete strength! Engineers carefully proportion the concrete mix to create concrete with high compressive strength.
Compressive strength can range from M10 to M50. Strength increases with higher grade numbers. M10 has the lowest, and M50 has the highest compressive strength.
Measurement Unit
We measure compressive strength in two units:
- Pounds per square inch (psi) is the number of pounds of load one square inch of concrete can withstand. It is used mainly in the U.S.
- Megapascals (MPa): This is a metric unit. 1 MPa equals 1 million pascals and 145 psi. It is more popular worldwide.
Significance
Compressive strength defines the strength and durability of concrete. Compressive strength is also an indicator for using concrete for a particular project. Higher compressive strength means concrete can withstand the load, weather changes, and damage. Higher compressive strength also means the concrete is durable for many years.
How Is Compressive Strength Measured?
The measuring process of compressive strength is simple. Let’s explain it in steps.
- Sample Preparation:
- The first step is the preparation of samples. Concrete cubes of size 15 cm x 15 cm x 15 cm or 10 cm x 10 cm x 10 cm are prepared. These cubes are then cured for:
- 7 days (early strength)
- 28 days ( standard curing time)
- Testing Process:
- Concrete cubes are tested using a compression-measuring machine
- Cube is placed on the machine and pressure is applied
- The load that breaks or cracks the cube is noted down, known as a fail load
- Calculation:
Compressive strength is calculated using the formula:
Compressive strength = Load at failure / Cross-sectional area of the sample.
For example :
- The size of the cube is 15 cm x 15 cm x 15cm.
- So crosse sectional area equals: side x side = 15 x 15 = 225 cm2.
- The Load fail is calculated to be 2000 N.
- So compressive strength equals= 2000 N / 225 cm2=0.889N/mm2=0.889MPa.
Factors Affecting the Compressive Strength of Concrete
Compressive strength depends on the mix ratio, curing time, content quality, and period. Let us explain each factor in detail.
Mix Ratio:
The proportion of each ingredient in concrete affects compressive strength. A higher cement-to-water ratio results in high compressive strength. A high sand or aggregate ratio to cement results in low compressive strength. It is important to balance the concrete ingredients to achieve high strength.
Curing Conditions:
Curing is crucial to the compressive strength of concrete. It is important to moisten concrete during curing. This avoids incomplete curing. The curing period ranges from 7 to 28 days, so allow your concrete to cure completely before adding a load.
Aggregate Quality
Aggregate quality impacts compressive strength. Aggregates made with steel slag are stronger than those made with calcareous limestone. The size of the aggregate also impacts compressive strength. For example, aggregate with a size of 4/8 mm has a high compressive strength.
Admixtures
We add admixtures to concrete to improve its quality and properties. They often include superplasticizers, accelerators, and waterproofers. The admixtures can greatly increase concrete’s compressive strength.
Age of Concrete
The compressive strength of concrete increases with time. Standardly, it takes 28 days for concrete to reach its full strength.
Standard Compressive Strengths for Concrete Grades
Concrete has different grades of compressive strength. A higher number means higher compressive strength. Concrete grades range from M5 and go up to M70.
M10 to M20
M10 to M20 are ordinary grades of compressive strength. M10 has 10 megapascals of strength. M20 has 20 megapascals. The ingredient ratio of M10 is 1:3:6 (1 part of cement, 3 parts of sand, and 6 parts of coarse aggregate). The ingredient ratio of M20 is 1:1.5:3. Concrete with this strength is ideal for non-structural use.
M25 to M30
M25 and M30 are ordinary concrete grades. They are used for residential and commercial structures. The mix ratio of M25 concrete is 1:1:2. M30 is a design mix, made in labs.
M35 to M50
M35 to M50 are standard and high-strength concrete. All these grades come under the category of design mix and do not have a fixed ratio. They are used for structural constructions such as bridges and buildings.
Above M50
Above M50 are high strength and ultra-high strength grades. They have a design mix ratio. Concrete with these grades of strength is used in projects such as nuclear power plants.
Importance of Compressive Strength in Construction
The compressive strength of concrete tells a lot about concrete quality and applications.
Safety
Testing and measuring compressive strength improves the safety of constructions. Compressive strength allows engineers to carefully construct materials. It also allows to use of the correct concrete grade for specific constructions. For example, bridges are constructed with M50-grade concrete for safety and strength.
Durability
High compressive strength allows concrete to bear load, stress, and weather effects. High compressive strength increases the durability of concrete.
Quality Control
Compressive strength tests allow engineers to analyze and cross-check concrete materials. Engineers can regularly verify mixed design and construction methods to achieve high-quality concrete constructions.
Structural Design
Measuring compressive strength helps decide the dimensions of concrete structures. For example, concrete has high compressive strength, which means smaller columns can support heavy loads.
Tips to Achieve Desired Compressive Strength
Here are some tips to achieve high compressive strength of concrete.
- Follow Mix Proportions:
Follow the concrete mix proportions. Do not modify them without professional help or opinion. Mix proportions play a crucial role in compressive strength. Any modification in mix proportions can affect the grade of compressive strength.
- Proper Curing:
Concrete has a curing period of 28 days to achieve its full compressive strength. Cure concrete properly. Do not put a load or start a construction on uncured concrete. During curing, provide adequate moisture to concrete to avoid improper curing.
- Use Quality Materials
Use high-quality material for high compressive strength. Use good quality cement. Add finely grained sand and clean coarse aggregate. High-quality materials allow for proper curing, hence increasing compressive strength.
- Avoid Overwatering
Maintaining a low water-to-cement ratio is important for high compressive strength. High water content can decrease the workability of concrete. High water content also weakens the cement resulting in cracks.
Conclusion
Compressive strength is the load-bearing ability of concrete without breaking. There are different grades of compressive strength. Compressive strength is vital for concrete strength, durability and workability. Prepare your concrete mix carefully and utilise admixtures for good compressive strength.