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What are the Proper Concrete Mix Proportions?

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Getting the right mix ratio for concrete is crucial for the best results.

Concrete is an important building material. It is one of the building blocks for our cities, our buildings, and infrastructure. So getting the right concrete mix ratio is crucial.

The concrete mixture consists of 4 ingredients: sand, cement, water, and aggregate, and understanding the correct quantities is the difference between getting the right concrete recipe and failure.

Concrete Ratios: What They Are and What They Mean

Understanding what concrete ratio mixes are is crucial if you want the correct consistency. The basic ingredients of concrete consist of aggregate, sand, cement powder, and water to start the chemical reaction with the quicklime in the cement. The most common ratio is 1-2-3 and 1-2-4, but for industrial projects, there are several other ratios. Concrete is measured in compressive and tensile strength. The higher the sand content, the weaker the concrete.


What Is a Concrete Mix Ratio?

Understanding the concrete mix ratio is vital if you want the correct consistency. Too dry and it will not bond and dry brittle, whereas too wet and it won’t set. You should also consider the type of job you are undertaking and the environment where you place the concrete.

For example, a concrete patio will not get the same punishment as a concrete driveway, so you can change the ratios to suit the task. Your driveway would need more aggregate to make it more robust.

And you really don’t want to be taking any chances when it comes to structures because their strength and building integrity depend on that concrete mix being right.

Basic Ingredients

To understand concrete mix ratios, we first need to know the ingredients and what they do.

Cement

Cement contains calcium oxide, which is produced when you superheat limestone. In essence, cement is a bonding agent, like an adhesive to bind the mixture together. It also contains aluminum, silicon, iron, and a variety of secondary ingredients.

As an ingredient, cement is quite weak on its own. It bonds and dries hard, but it is quite brittle, which is where the aggregate comes in.

Aggregate

Aggregate provides structural strength to the mix. Concrete has compressive strength, which means it can withstand huge amounts of weight, but without the aggregate, it would struggle.

Sand

Sand also has immense compressive strength. When added to the concrete mix, it fills all those small pockets and minimizes air bubbles that could later expose the concrete and weaken the structural integrity.

Water

Water is the ingredient that kick starts the chemical reaction with the quicklime to get it to bond with the aggregate and sand. It also makes the concrete workable, enabling you to mold it to any shape and size.

What Is the 1-2-3 Concrete Mix Ratio?

The 1-2-3 ratio is exactly what the name suggests; 1 part cement powder, 2 parts sand, and 3 parts washed aggregate. Water can be added in any volume depending on how you use the concrete.

If you are putting up fence posts, you want the mixture a little on the wet side so you can pour it into the hole. You also vary the water content to suit your environment because so many factors can affect the mixture.

Are you working in direct sunlight? What’s the moisture content in the atmosphere, and what is the air temperature?

What Is a Concrete Grade?

The concrete grade is the minimum strength the concrete should hold after 28 days of curing. To understand the acronyms used in the formula, we have broken each element down.

M

M stands for the mix of the concrete. So is it a 1-2-3 ratio or a 1-2-4 or a 1-5-10? Each mix varies in compressive strength because the ingredients are adjusted to be compatible with the project.

MPA

MPA stands for megapascal, which is the compressive strength of the concrete. Understanding how much pressure the concrete can withstand is crucial because if the MPA is deficient, it could lead to structural problems down the line.

Without measuring the MPA, cracking and crumbling would occur, and that leads to weaker structural integrity.

PSI

PSI stands for pounds per square inch, and all concrete comes in different strengths, applications, compositions, and types. Understanding the concrete’s compression in pounds per square inch enables us to know when and where to use the concrete.

Most concrete has a PSI of between 2,500 and 5,000.

Types of Concrete Grades

So, now we understand what a concrete grade is, let’s look at the different types.

Nominal

The nominal concrete grade is the most widely used, although it is not the strongest. When you go to the DIY store and pick up ready mixed concrete, this is the grade you would usually get. Nominal is another way of saying a prescribed mix, and it requires no skill to make.

It is great for general repairs and applications that don’t require too much compression. M5, M7.5, M10, M15, M20, and M25 are all nominal mixes of concrete.

Standard

Standard concrete grades are intended for medium to heavier applications. Again, standard grades are sufficient if you are performing general repairs or undertaking some small to medium projects.

The range of concrete mixes classed as standards are M25, which is a 1-1-2 and M30, M35, M40, and M45.

High Strength

As the name suggests, this is the most robust mix of concrete. It is intended for heavy-duty work, like construction and industrial applications.

Typical mix ranges are M50, M55, M60, M65, and M70, which have the strongest PSI rating of 10,150.

Mix Ratio Tables

Nominal Grade

Concrete Grade Mix Ratio MPa PSI
M5 1-5-10 5 725
M7.5 1-4-8 7.5 1087
M10 1-3-6 10 1450
M15 1-2-4 15 2175
M20 1-1-5-3 20 2900

Standard Grade

Concrete Grade Mix Ratio MPa PSI
M25 1-1-2 25 3625
M30 Design mix 30 4350
M35 Design mix 35 5075
M40 Design mix 40 5800
M45 Design mix 45 6525

High Strength Grade

Concrete Grade Mix Ratio MPa PSI
M50 Design mix 50 7250
M55 Design mix 33 7975
M60 Design mix 60 8700
M65 Design mix 65 9425
M70 Design mix 70 10150

What Is the Best Concrete Mix Ratio for the Job?

How the concrete pours and cures is all down to the mix, and the ratios vary according to the task at hand. High-strength concrete ratios include less sand and more aggregate to withstand industrial applications.

The general rule of thumb is the higher the sand content, the weaker the concrete mix. Adding more aggregate gives the mix more tensile strength, which increases the compressive power of the concrete.

Getting the right mix is crucial if you want to get the most from your concrete, and it needs to last the distance.

Below is a chart showing the ratios and the best applications.

Concrete grade Environment Applications
C10 Domestic and commercial Patios and pathways
C15 Domestic and commercial Floors, curbs, small commercial projects
C20 Domestic Floors, garages, workshops
C25 Domestic and commercial Flooring, building foundations
C30 Commercial Roads, driveways, heavy-duty flooring
C35 Commercial (large projects) Walls and pilings
C40 Commercial (large projects) Heavy traffic roads, farm buildings, and industrial buildings

Concrete Mixing Tips

What are the best tricks and hints to help you achieve your goals when mixing concrete? Let’s take a leaf out of the professional’s manual and reveal all.

Water Proportions

The single most unpredictable element to mixing concrete is the water. The amount of water you need depends on many factors, including the weather, sunlight, moisture in the air, and temperature.

The more water you add to the mix weakens the cement’s tensile and core adhesive strength. For the most robust concrete, try and use the least amount of water possible. This is challenging when fixing concrete posts for fencing, where the workability of the concrete trumps the extra tensile strength needed.

Add More Rocks

The more rocks you include in the formula, the greater the tensile strength of the concrete. Think of the stones as thousands of tiny hooks holding the concrete mix together.

Mix in Small Batches

If you are working at home and mix too much concrete, you risk it starting to cure before you are ready to use it. It works out to be an expensive mistake and a waste of energy. Working in smaller amounts keeps you in control, and you get lower wastage.

It also puts less strain on your back, arms and wrists.

Don’t Work in High Heat

Heat is your enemy when mixing concrete. It starts to dry the mixture immediately, causing it to start setting. You will then need more water to make the formula wet again, which could reduce the tensile strength of the cement.

Get the Right Tools for the Job

Nothing is as frustrating as trying to get a job done with the wrong tools. If you are mixing concrete,you will need:

  • Concrete mixer if you are taking on a significant project.
  • A face mask to protect against the quicklime entering your lungs.
  • Gloves to keep your hands from touching the corrosive concrete mix.
  • A wheelbarrow for smaller jobs.
  • Work boots in case you get splashed with the wet mixture.
  • Safety glasses to protect your eyes from splashes.
  • A shovel to help you mix the concrete by hand.
  • A screed to help you level the concrete if you are laying a floor.
  • A bucket to help you add the water and move smaller amounts of concrete to the worksite.
  • Water to add to the mix to get the right consistency.
  • A trowel or spreader to get the concrete into all the edges and corners.

Concrete Mix Calculation

Concrete is measured in cubic yards, so 1 cubic yard equals 27 cubic feet. The easiest way to calculate how much concrete you need is to divide your project area into smaller sections and then multiply them by the thickness of concrete required. Now convert it to cubic yards, and you will know how much concrete you will need.

So, for a standard square or rectangle, you would divide the length by the width by the depth, calculate the total feet and convert it into cubic yards.


It’s All in the Mix

Concrete is useful in so many ways. From minor repairs and maintenance to major infrastructure, buildings, and bridges, concrete is possibly the most important building material on earth. Imagine a world without concrete, and it would look very different.

The great thing about working with concrete is it is very satisfying. It is also forgiving, so you can always add more sand or aggregate to the mix if it’s too wet or more water if too dry. And when you master the mixing ratios, you will be able to make up a batch with your eyes closed.

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About the Author

Mark Weir

Mark spent 24 years working in real estate, so he knows his way around a home. He also worked with contractors and experts, advising them on issues of planning, investments, and renovations. Mark is no stranger to hands-on experience, having renovated his own home and many properties for resale. He likes nothing better than seeing a project through to completion.