What is Hydraulic Cement and How is it Used?

What is Hydraulic Cement and How is it Used?
Hydraulic cement is a modern invention, that reacts to water chemically to gain strength and form. Due to its unique properties, it is widely used across all forms of construction. In this Buzzle article, we shall understand what hydraulic cement is, its properties, and how it differs from the non-hydraulic variants.
Quick Tip
It is highly important that you prepare the area completely and ready all your tools before you mix water in this cement. This is because, hydraulic cement starts to harden in less than two minutes time.
Hydraulic cement is a construction/masonry product which is primarily used to close cracks and leaks in concrete structures, especially those that have weakened with age, or structures which are likely to be affected by water. The specialty of this cement is that is sets and hardens very quickly after it comes in contact with water. Most construction projects in the modern world use hydraulic cement, because it is durable, sets fast, is quite cheap, easy to use, will stay strong even when placed in water, besides many other benefits.
Hydraulic and Non-Hydraulic Cement
  • Hydraulic cement hardens due to hydration, i.e., exposure to water, while non-hydraulic cement hardens due to carbonation, i.e., exposure to carbon dioxide in the air. Therefore, hydraulic cements can be used underwater, while non-hydraulic versions cannot.
  • Hydraulic cement is made with limestone, gypsum, and clay, which is burned at high temperatures. Non-hydraulic cement is made with lime, gypsum, and oxychloride.
  • Hydraulic cement dries and hardens in a few minutes, while non-hydraulic versions can even take a month or more to reach usable conditions.
Lime and gypsum cements are some examples of non-hydraulic cements.

Types and Uses of Hydraulic Cement

Various types of hydraulic cements have been created for specific purposes. They are as follows:
  • General-use Hydraulic Cement: This cement is created as a general purpose variant, which is primarily used in fixing floors, pavements, buildings, bridges, pipes, etc., where it works well as a leakage stopper.
  • White Hydraulic Cement: The only difference between this and the general-use hydraulic cement is the color. It is manufactured using minimal amounts of iron and magnesium, which gives it a white color. It is mainly used in architecture, where white concrete will look good for decorative purposes.
  • Moderate Sulfate Resistant Hydraulic Cement: When water or moist soil come in contact with concrete, sulfates can react chemically and result in scaling cracking and expansion, which ruins the structure. This cement is used in such structures, due to its partial resistance to sulfates, which it gets due to the chlorides that are mixed with the raw materials. For this reason, it is mainly used in structures that are exposed to sea water.
  • High Sulfate Resistant Hydraulic Cement: This cement is used in concrete structures that face a high amount of sulfates on a regular basis. It uses a low water-to-cement ratio, and hence, gains strength much slower than general-use hydraulic cement. It is also highly resistant to corrosive materials, such as acids.
  • Moderate Heat of Hydration Hydraulic Cement: While general-use hydraulic cement generates a lot of heat while reacting with water, the moderate heat variant is specially designed to give out lesser heat. Such cement is commonly used in structures with huge mass, such as piers, foundations of buildings, and large retaining walls. This cement will reduce temperature-related cracking, making the structure more durable.
  • Low Heat of Hydration Hydraulic Cement: This cement gains strength much slower than the other types, because it gives out very little heat after mixing with water. It is only used in the largest of structures, such as dams, where heat minimization is necessary. This type is only available in large quantities on demand.
  • High Early Strength Hydraulic Cement: This cement gains full strength very quickly (in around a weeks time). It is highly similar to general purpose cement, where the main difference is that, early strength cement is very finely ground. It is used in places where the structure has to be used immediately.
How to Apply Hydraulic Cement
  • Hydraulic cement has to be applied on a surface that has been cleaned thoroughly. There should be no sign of grease, oil, dirt, or other contaminants.
  • It is highly recommended that one should use hydraulic cement based underlayments in the areas which the cement will be used.
  • It is important that the area is saturated for at least 24 hours, and the hydraulic cement application temperature should be maintained between 45 - 90 degrees Fahrenheit.
  • Hydraulic cement has to be mixed in a machine with rotational blades to get a uniform mix.
  • Mix only small amounts at one time, and follow the manufacturer's instructions to the letter, to get the best results.
  • Use the cement quickly, as it remains in a workable state only for 10 - 15 minutes.
Testing Hydraulic Cement Density

The density of hydraulic cement can be defined as the ratio between the weight of a given volume of cement and the weight of an equal volume of water. This density is responsible for its quality and its durability. To test the density, you will need a Lechatelier flask, a water bath, a tray, and a balance.

Procedure:
  1. Check that the Lechatlier flask is completely dry, and then fill it with kerosene to a level between 0 and 1 ml on the stem.
  2. Now, again dry the flask carefully till above the kerosene level.
  3. Place the flask in the water bath in room temperature for 10 to 15 minutes.
  4. Record the first reading as the level of the kerosene in the flask, and remove the flask from the bath.
  5. Very carefully pour some hydraulic cement into the flask till the kerosene reaches a 22 ml mark. Take care that there are no splashes in the kerosene. Also, be careful that the cement does not stick to the flask above the kerosene level.
  6. Gently roll the flask in a slanting position till no air bubbles are emitted.
  7. Place the flask once again in the water bath, wait for a while, and note the new level as the final reading.
  8. The difference between the 2 readings shows the volume of kerosene displaced by the cement. The formula for calculating the density is - mass of cement in grams ÷ volume of displacement in cm3. The reading should be taken till the second place after the decimal.
  9. Repeat the test again from scratch, and take an average of the 2 readings of density. The difference should not be more than 0.03. If you do not get this result, the cement cannot be considered as having normal consistency.
Testing for Compressive Strength

Checking hydraulic cement for its compressive strength is important to see how the cement increases in durability over a period of time after it sets. The equipment you would require for this test are a cube mold (70.6 mm3), vibration machine, balance, trowel, one poking rod, enamel tray, and a 200ml measuring cylinder.

Procedure:
  1. Mix 200 g of hydraulic cement with 600 g of standard grade sand.
  2. Add water to the mixture to create a paste, and stir it for 3 - 4 minutes. See that you get the correct color of wet concrete, and if you do not, discard the mixture and start over.
  3. Fix the mold on the vibrating machine with clamps.
  4. Oil the mold and fill it with the cement mixture, and vibrate it at a speed of around 12,000 for 2 minutes.
  5. Take the mold off the machine and let it rest for 24 hours in a place with 90% humidity and temperature of around 80 degrees Fahrenheit.
  6. Once the cement cube has completely rested, take it out of the mold and put it in clean water.
  7. Similarly create 5 more cement cubes.
  8. Place one cube in the compressive testing machine, and apply a load 35/N/mm2/minute.
  9. Calculate the strength by the formula - Maximum load applied on the cube in Newtons ÷ Cross-sectional area of cube in mm.
  10. It is important that you test the cubes immediately after taking them out of the water, without allowing them to dry during testing.
Also, it is important that one wears full protective clothing, along with gloves and a face mask while using hydraulic cement, to prevent any health hazard. Has to be said though, that usage of this product is fairly easy, and is proving to be boon to construction professionals and home owners across the world.