Hydration and properties
- Hydraulic cement reacts with water to form a paste that hardens and binds aggregates. Fineness and composition affect hydration rate and strength development.
- Heat of hydration matters particularly in massive elements, where limited heat dissipation can create thermal gradients and stresses.
Physical tests
- Fineness can be estimated by measuring air flow through a compacted cement bed or by sieving, among other methods.
- Paste consistency is determined by penetration; initial and final setting times are defined by penetration under controlled conditions.
- Soundness testing looks for delayed expansion; methods such as Le Chatelier or autoclave accelerate detection of expansion tendencies.
Mortar strength
- Mix mortar using defined proportions and sequence, mould specimens, and compact them as required by the standard.
- Maintain controlled curing, temperature, and humidity; specimens may be tested in flexure and then compression as specified.
Comparability
- Take increments from several bags or points in a lot and prepare a representative composite sample.
- Dimensions, penetration thresholds, compaction, and curing differ between standards. Follow the contractual edition and method without mixing requirements.
Mix proportions and strength
- Water-cement ratio: w/c = mwater/mcement, by mass. For pastes or mortars, also record additions, sand moisture, and effective water.
- Compressive strength: fc = Fmax/A, with Fmax in N and loaded area A in mm²; the result is N/mm² = MPa. Use the area and specimen geometry specified by the test method.
- Flexure of a rectangular prism under centre-point loading: Rf = 3Fmax·L/(2b·h²), where L is span and b and h are section dimensions. Other loading arrangements require their own equation.
- Water-cement ratio affects porosity and strength, but it cannot predict them alone; cement type, compaction, curing, age, and test method also matter.
Educational reference guide. Check the current standard, calculation assumptions, and project specification before applying a procedure or acceptance criterion.