Cement And Concrete Are Not The Same Thing!
- Cement is a product made of finely ground limestone and clay and is used in the creation of concrete and mortar.
- Concrete is a mixture of aggregate (usually gravel), sand, cement and water.
Although mixing your concrete by hand will save a substantial amount of money, it is definitely back breaking work and for any slab that requires more than 1 cubic yards of concrete one should consider using a powered portable concrete mixer that operates using an electric motor or gas engine, as shown in Figure 1, 2 and 3. These mixers can be purchased, new and used, or rented.
Figure 1 - 3.5 cu. ft. Electric Cement Mixer |
Figure 2 - 5 cu ft Wheel Barrow Portable Electric Cement Mixer |
Figure 3 - 9 cu. ft., 13 HP Gas-Powered Cement Mixer |
If you require 3 cubic yards or more of concrete you should consider buying ready mix concrete.
For most applications the proper mixture of components for a good concrete mix is:
- 3 Parts Gravel
- 2 Parts Sand
- 1 Part Cement
- Water As Required
Blending the mixture of gravel, sand and cement is one of the keys to producing a good concrete.
Whether you are using a wheelbarrow, concrete mixing trough or a portable concrete mixer following these steps will help with the blending.
Note: Using a wheelbarrow to mix and or move wet concrete is common and so is having the wheelbarrow tip over as you are mixing or as you commence to move it. A wheelbarrow filled with wet concrete is very heavy!
- Always use the same size shovel to add the gravel, sand and cement. If you use a level shovel full of cement, use level shovels of the other 2 components - sand and gravel. Likewise, if you use a heaping shovel full of cement then use a heaping shovel for the other 2 components.
- Mix the sand and cement together thoroughly, add the gravel and mix together. If you are using a wheelbarrow or mixing trough use a rugged hoe to blend the dry products together. Once the dry components are thoroughly mixed, commence adding the water, a little at a time. You can always add more water, you cannot take it away.
The amount of water is key to a successful concrete mix.
- Too much water = weak concrete.
- Too little water = concrete that cannot be worked.
- Should you accidentally add to much water and end up with a thin sloppy mixture, thicken the mixture using small quantities of sand and cement in the ratio of 2 parts sand to 1 part cement.
By combining the four basic types you can define any room and create an appropriate message!
If you are concerned about the quality of a batch of concrete that you have just made you can perform a simple "slump test" to verify its suitability, as shown in Figure 4.
- Obtain a large paper or Styrofoam cup to act as a cone.
- Remove the bottom
- Invert it on a level piece of plywood.
- Fill the cup, while it is resting on the plywood with the concrete, pack it down a few times as you are filling it.
- Remove the cup from the concrete mixture.
- Place the inverted cup next to the concrete cone that remained after removing the cup.
- Without the support of the cup, the concrete should be 50% to 75% of the height of the cup.
Figure 4 - Concrete slump test