Dry Mix Concrete: What Is It and How To Use It

Dry mix concrete, as the name suggests, has no water or liquid added during the preparation and bagging stage. To make the dry concrete mortar, the cement, sand, and aggregate are thoroughly and evenly mixed until a consistent texture is attained. This concrete can be stored in bags or in bulks to be mixed with water at the construction site. Bags can be transported using vehicles or, in large quantities, by a concrete transit mixer.

Concrete is made up of different ratios of cement, sand, and aggregate. The most commonly used concrete mix is made up of one part Portland cement, two parts sand, and three parts aggregates. The ratios are adjusted to increase the strength according to the project.

Cement mixes with water through the hydration process and binds the aggregates. Without water, the mixture remains just as aggregates.

Concrete can be used for foundations, roads, paving purposes, and other masonry structures.

The sand for the dry mix concrete is dried first. Drying the sand gives an accurate ratio and, the final quality of the mortal after construction is better.

To use the dry concrete mix in construction, water or other specified liquid has to be added to the mixture and mixed evenly at the area of construction. The dry mix concrete has a shelf life of three to six months.

The dry mix of concrete contrasts with the wet concrete mixture is made by mixing cement, sand, aggregates, and water. Mix thoroughly until a regular and consistent mixture is made.

The wet concrete mix is fed onto the construction site directly or through a hose. The wet mixture has a 24 hours shell life, after which it condenses and cannot be used. This mix can only be transported by using a concrete mixer truck, to ensure that the wet mortar does not delaminate or segregate during transportation.

How to Use It

Dry mix concrete is mainly used in small and medium-sized projects such as pavement or driveway repairs. Work starts by gathering the materials and tools needed. Prep the work area by cleaning the area of dirt and debris. Use a stiff brush to clean cracks and holes in the working surface. Set any formwork and mesh as needed for the project to increase the strength of the area.

To start the project, you will need the dry mix concrete, a mixing surface, a shovel, and clean water. Gather personal protective gear to protect you against dust and debris from the cement. You require a mouth or nose mask, thick work gloves, and safety goggles.

Firstly, decide on the quantity of the dry mix concrete to use. The quantity used is determined using the volume and the packaging yield. The dry mix is packed in 20, 40, and 80 pounds units. In a work surface area or a barrow for small projects, pour the dry mix in the direction of the wind to avoid breathing in the dust.

It is a good idea to mix half the quantity first, then saving the rest for later to avoid it from going to waste. If the project is large, you can consider using a concrete mixer.

Next, make a small hole in it and pour some water. Don’t worry about water splashing around as you will have to evenly mix until a workable consistency is achieved.

Use volume and not weight to determine the water to be used. The 80 pounds dry concrete mix needs about a gallon of water.

Use the shovel to mix the water and the concrete. Move the shovel-like you are canoeing, moving the shovel up and down till all the concrete mixes with water.

To test if it’s the right consistency, take a handful of the prepared concrete mixture, and if it forms a solid round shape when pressed in the palm of your hand, then it’s too dry. If it runs through your fingers, then it has too much water.

Too much water and the concrete will bleed off the project area and lose its strength. Getting to the right consistency takes experience.

Mix for a minute or two until all the concrete mixes with water. Concrete mixing with water hardens through hydration to gain strength.

Finally, place the concrete into the working area form, using the shovel to smoothen. Use a screed board to smoothen and compact the work area to remove trapped air and voids while placing the concrete.

Finish off laying the concrete according to your project specifications and barricade the area to prevent people from stepping on it and ruining the work.

Lastly, clean off the area around, remove the concrete bags and clean your work tools ready for storage. Sprinkle water into the work area for a week until it cures and dries.

For commercial projects, shotcreting is done. Shotcreting is the process of applying layers of concrete through the use of compressed air from a mortar gun.

In shotcreting, the dry concrete mixture is pneumatically shot through a hose at the construction surface. Water is conveyed with a different hose and added to the nozzle as the dry concentrate is sprayed.

The dryness of the sand will determine the quantity of water to use. The drier it is, the more water it uses. A trained technician operates the shotcreting gun and regulates the water.

Wet mix concrete does not need additional water and is short directly onto the construction site.

The construction site is first prepped to receive the concrete mixture. If the surface is too smooth, the surface is sandblasted. You would also require formwork and wire mesh to hold the concrete mix and to add strength to the construction.

Shotcreting dry mix concrete is widely used in mining and narrow areas with difficult vehicle access. The dry mix can be shot 300m horizontally and 150m vertically from the nozzle.

The advantages of dry mix technology are: it is easy to start up as it does not need elaborate mixing with water. It is also easy to clean up and shut down. The dry concrete mix technology has minimal wastage and makes less mess.