1. What is concrete and how is it made?
Concrete is the second most used commodity on the planet. it mainly includes cement, aggregates(fine aggregates and coarse aggregates), addictives (cellulose ether, fiber...), water and admixtures (Pigment, Plasticizers... ). Like the following picture. Today, it is an indispensable material in the construction industry. Concrete contractors are also on the rise across the country.
1.1 Cement is one of the ingredients in concrete.
It’s like flour to make bread. It is the most expensive ingredient.
These are the terminology for mixing commonly made with cement;
1) Paste is when you take cement and you add water. It’s like a glue that holds everything together.
2) Cement, water and sand make a Mortar or Grout. Sand is also known as fine aggregate.
3) To make Concrete, you need one more ingredient, you need water, sand, and stone or gravel or rocks. Rocks are also known as coarse aggregate.
1.2 Admixtures are anything else you throw on the mixture.
Concrete admixture could be a form of chemical or mineral that you add. Generally, it is powder or liquid material. The reasons for adding admixture to concrete is that can bring some properties that it does not have, such as durability, corrosion resistance, workability... the best admixtures are retarding admixtures and accelerating admixtures.
1.2.1 What are the types of concrete admixture?
2. Air-Entraining Admixture
3. Retarding Admixtures
4. Water-proofing Admixtures
5. Water Reducer
6. Gas Forming Admixtures.
7. Accelerating Admixtures
8. Segregation Reducing, Viscosity Modifying Amixtures
9. Shrinkage Reducing Admixtures
10. Polymer Dispersion Admixtures
11. Ready-to-use Mortar Admixtures
12. Sprayed Concrete Admixtures
13. Bonding Admixtures
14. Grouting Admixtures
15. Corrosion Inhibiting Admixtures
16. Coloring Admixtures
17. Pumping aids
To make a durable structure, you need to add aggregates. Aggregates do a lot of stuff. They restrain shrinkage (prevent changing shape over time), restrain cracks, and are way cheaper than cement.
70-80% of concretes are made of aggregates. Aggregates can be classified into two such as Fine aggregates and Coarse aggregates. Fine aggregate is an aggregate smaller than a number 4 sift. Sift is a screen with a certain size opening on it. Number 4 sift means 4 opening per inch. The size of each of these openings is about 0.2 inches. Coarse aggregate is an aggregate larger than the number 4 sift. Anything that will be caught in the number 4 sift will be considered as coarse aggregates. The typical max size is about 1 inch. It usually uses larger rocks depending on where it is being used for.
Water is another important thing because it reacts with cement. Water should be clean and free of chloride because chlorides attack your steel. They cause corrosion. Any potable water source can be used for beton.
1.4 Another Ingredient for Concrete is Fiber.
Fibers help hold the concrete together and are sometimes used as reinforcement. They are becoming more popular these days. There are types of fibers like polypropylene fibers are flexible plastic fibers. They help in the fresh state. Another one is, steel fibers this will help the hardened state. This helps stitch the cracks together.
2. Types of concrete
There are classes of concrete, some people call it weight or density which is the weight of the material per volume. In Light weight concrete, a typical density should be < 110 LB/ft3 or < 1760 kg/ m3. A normal weight is 145-150 LB/ft3 or 2300-2400 kg/ m3. Very rarely, you get heavy weight which is > 195 LB/ft3 or 3100 kg/ m3.
Strength in concrete is also called compressive strength which can be classified into low, moderate and high strength. Low strength has < 3000 PSI or <20 MPa. Moderate has 3000-6000 PSI or 20-40 MPa. High strength has > 6000 PSI or >40 MPa.
One of the main keys to the strength of the concrete is W/cm ratio means water over cementitious or binder. To get this range is somewhere from 0.4- 0.6 W/cm. Before, strength is one of the main measures of the quality of beton. but now, it should also be durable, constructable, and strong.
Aside from compressive strength, there are other ones that we do measure. Compression strength has 4000 PSI or 28 MPa. Tension strength is about ten percent of the compression strength (400 PSI) or 2.8 MPa. Flexural is equal to 7.5 to the square root of the compression strength which is equal to 475 PSI 3.3 MPa. Shear strength is equal to four times to the square root F prime c or 0.6 to the tension strength. As we can see from all of these, concrete is weak in tension and strong in compression.
3. Concrete as the Secret Weapon.
It is considered to be great because it is made out of local materials, it can be formed into any shape, it uses recycled materials, and it is very strong.
4. Concrete is Everywhere.
When you look around you, you can see buildings, houses, or even roads. Those things are made out of concrete. We need constructable, economical, durable, and sustainable and that is what we are looking for.