How Do You Use Cement in Concrete?

Cement is a crucial ingredient in concrete, acting as the binder that holds the aggregate (sand, gravel, or crushed stone) together. It undergoes a chemical process called hydration when mixed with water, forming a hard, stone-like material.

Here's how cement is used in concrete:

1. Proportioning the Mix: The first step is determining the appropriate mix design. A common concrete mix for slabs is 1 part cement : 2 parts sand : 4 parts coarse aggregate by volume. This ratio can vary depending on the desired strength, workability, and application of the concrete. Different concrete mixes exist to suit different needs.

2. Dry Mixing: Before adding water, thoroughly mix the cement with the sand and aggregate in a dry state. This ensures a more even distribution of cement throughout the mixture.

3. Adding Water: Gradually add water to the dry mix while continuing to mix. The amount of water is critical; too much will weaken the concrete, while too little will make it unworkable. The ideal consistency is a plastic, moldable mixture that isn't too watery.

4. Mixing Thoroughly: Mix the ingredients until a homogenous mixture is achieved. This can be done by hand (for small batches) or with a concrete mixer. Proper mixing is essential for uniform strength and durability.

5. Placement: Concrete must be placed within a reasonable timeframe, ideally within half an hour of mixing to prevent premature hardening.

6. Consolidation: After placing the concrete, consolidate it to remove air pockets. This can be done by rodding, vibrating, or tapping the formwork. Consolidation improves the density and strength of the concrete. You need to work the concrete into awkward places and corners using a shovel or trowel, as mentioned in the references.

7. Curing: Curing is the process of keeping the concrete moist to allow the cement to fully hydrate. This is crucial for achieving its full strength and durability. Curing can be done by spraying with water, covering with plastic sheeting, or using curing compounds.

Here's a summary in table form:

Step	Description	Importance
Proportioning	Determining the correct ratio of cement, sand, aggregate, and water.	Achieving the desired strength, workability, and durability of the concrete.
Dry Mixing	Mixing cement, sand, and aggregate before adding water.	Ensuring even distribution of cement.
Wet Mixing	Adding water and mixing until a homogenous mixture is achieved.	Creating a workable and consistent concrete mix.
Placement	Pouring the concrete into formwork.	Shaping the concrete to the desired form.
Consolidation	Removing air pockets from the concrete.	Increasing density and strength.
Curing	Maintaining moisture to allow cement hydration.	Achieving full strength and durability.