The main difference between hydraulic cement and what is often considered "regular" cement (typically referring to non-hydraulic cement) lies in how they harden. Hydraulic cement hardens through a chemical reaction with water, while non-hydraulic cement hardens through a reaction with carbon dioxide (CO2) from the air, which also takes a significantly longer time to achieve full hardness compared to hydraulic cement.
Understanding Cement Types
When people refer to "regular cement," they often mean Portland cement, which is the most common type used in construction today. Portland cement is a type of hydraulic cement. Therefore, the question is better understood as the difference between hydraulic cement and non-hydraulic cement.
Let's break down the key distinctions based on their properties and how they set and harden.
Hardening Mechanism
- Hydraulic Cement: As stated in the reference, hydraulic cement hardens when water reacts with the cement powder. This reaction, known as hydration, creates a strong, solid paste that binds materials together. This process can occur even underwater or in very wet conditions.
- Non-Hydraulic Cement: In contrast, non-hydraulic cement hardens through carbonation, a reaction with carbon dioxide (CO2) from the air. This reaction requires the presence of moisture initially but relies on dry conditions to complete the hardening process effectively over time.
Hardening Time
Another crucial difference highlighted by the reference is the time it takes to harden:
- Hydraulic Cement: Hydraulic cements, like Portland cement, typically set and develop strength relatively quickly, usually beginning within a few hours and reaching significant strength within days or weeks.
- Non-Hydraulic Cement: Non-hydraulic cements needs a long time to harden compared to hydraulic. This slow hardening process can take months or even years to reach full strength.
Key Differences at a Glance
| Feature | Hydraulic Cement | Non-Hydraulic Cement |
|---|---|---|
| Hardening | Reacts with water (hydration) | Reacts with CO2 from air (carbonation) |
| Environment | Can harden in wet conditions or underwater | Needs dry conditions to harden effectively |
| Hardening Time | Faster (hours/days to set, weeks for strength) | Needs a long time to harden compared to hydraulic (months/years) |
| Strength | Generally achieves high compressive strength | Lower compressive strength than hydraulic types |
| Common Example | Portland cement | Lime-based cements (e.g., lime mortar, lime plaster) |
Applications
Understanding these differences is vital for selecting the right material for a project:
- Hydraulic Cements are essential for modern construction where strength, durability, and the ability to set in various moisture conditions are required.
- Used in concrete for buildings, bridges, pavements.
- Used in mortar for laying bricks or blocks.
- Used in grout for filling gaps.
- Non-Hydraulic Cements, primarily lime-based, are often used in restoration work on historic buildings or in specific applications where flexibility and breathability are desired.
- Used in traditional plasters and mortars for historical structures.
- Suitable for environments where slow, gradual hardening is acceptable or beneficial.
In summary, while "regular cement" most often refers to the hydraulic Portland cement we see daily, the fundamental difference lies in the chemical process of hardening and the rate at which it occurs, contrasting hydraulic types with non-hydraulic types.
