Concrete foundations are fundamentally built using a specific mix of materials: cement, sand, water, and aggregates.
Concrete itself is a durable construction material created by combining these basic ingredients. The provided reference highlights that the type of concrete used for foundations is determined by the different ratios of these components and the types of aggregates employed.
Key Ingredients of Foundation Concrete
The essential elements that make up the concrete used in foundations are:
- Cement: This acts as the binder. When mixed with water, it undergoes a chemical reaction (hydration) that hardens and binds the other materials together.
- Sand: Also known as fine aggregate, sand fills the spaces between the larger aggregates and cement paste, contributing to the mixture's workability and strength.
- Water: Crucial for activating the cement and facilitating the hydration process. The amount of water influences the concrete's workability and final strength.
- Aggregates: These are typically coarse materials like gravel or crushed stone. Aggregates provide bulk, strength, and stability to the concrete mix. Different types of aggregates can be used depending on the required properties.
Concrete Mix Ratios and Strength
The specific proportions (ratios) of cement, sand, and water, and different types of aggregates, are varied to create different types of concrete suitable for various applications, including foundations. A critical factor for foundation concrete is its compressive strength, which is its ability to withstand weight pressing down on it.
As stated in the reference, often a mix of C25 is sufficient for smaller build foundations. This refers to a concrete mix designed to achieve a minimum characteristic compressive strength of 25 Newtons per square millimeter (N/mm²) after 28 days. However, the larger the project the higher the compressive strength required for the foundation to support the greater loads. Therefore, concrete mixes with higher strength ratings (like C30, C35, etc.) might be specified for larger or heavier structures.
The choice of aggregate type and the precise ratio of ingredients are tailored to meet the specific strength and durability requirements of the foundation based on the project's size and structural demands.