Building Materials and Aggregates

Building Materials

• Building materials are categorized as natural or synthetic.
• Natural materials include aggregates, sand, stones, and wood.
• Synthetic materials include cement, bricks, steel, concrete, and plastics.

Aggregates

• Aggregates are a significant component of concrete, comprising 70-80% of its volume.
• They provide form and reduce shrinkage in concrete.
• Aggregate shape is influenced by parent rock type and crushing process.
• Aggregates can be rounded, irregular, or partly rounded, angular, flaky, elongated, and flaky.
• Aggregates are classified as fine (sand) or coarse (gravel) based on size.

Bricks

• Bricks are building materials used for walls and roads.
• They can be connected using mortar, adhesives, or interlocking methods.
• Bricks are categorized based on quality (first, second, third class) and manufacturing processes (unburnt, burnt, overburnt).
• First-class bricks have standard sizes, regular shapes, consistent colors (yellow or red).
• Second-class bricks are similar to first-class but have slightly lower burning temperatures.
• Third-class bricks have irregular shapes, sizes, soft colors (light red), and are under-burnt.

Lime

• Lime is used in construction works, primarily as lime mortar.
• Lime can be categorized as hydraulic or non-hydraulic.
• Hydraulic lime sets in water, while non-hydraulic lime does not.
• Quicklime is a non-hydraulic lime produced by burning calcium carbonate.
• High-quality lime exhibits good plasticity, flexibility, and quick hardening.

Cement

• Cement is a fine powder that hardens into a strong material when mixed with water.
• Cement is primarily used to bind sand and aggregates in concrete.
• Portland cement is a common type, comprising limestone, clay, and iron oxides.
• Cement is categorized as hydraulic or non-hydraulic based on its ability to set in the presence of water.
• Non-hydraulic cement sets when dry.

Portland Cement Production

• Portland cement production involves two main steps: clinker formation and cement formulation.
• Clinker is created by heating cement raw materials in a rotary kiln to high temperatures (up to 2000°C).
• The presence of ferric oxide in the raw materials aids in lower temperature (around 1300°C) clinker formation.
• Formed clinker is crushed and ground to a fine powder in a cement grinding mill.
• Additives like limestone may be added to the cement grinding mill.

Cement Properties

• Clinker consists of four major phases:
• Tri Calcium Silicate (Alite)
• Di Calcium Silicate (Belite)
• Tri Calcium Aluminate
• Tetra Calcium Alumino Ferrite (Brownmillerite)
• Silicates provide mechanical properties, while others help liquid phase formation.
• Limestone is burned to create lime (calcium oxide) through a calcination reaction.
• Lime reacts with silicon dioxide (SiO2) to form dicalcium silicate and tricalcium silicate.
• Lime also combines with aluminium oxide to form tricalcium aluminate.
• Lime combines with aluminium oxide and ferric oxide to make cement.

Concrete

• Concrete is a heterogeneous mixture of cement, coarse and fine aggregates, and water.
• Chemical action between cement and water hardens the mixture.
• Aggregates (gravel) act as fillers, and fine aggregates (sand) fill spaces.
• Cement and water act as a binder.

Fresh Concrete Properties

• Concrete should maintain its form from mixing until compaction.
• Fresh concrete properties (consistency, workability, settlement, bleeding) are critical to the quality of hardened concrete.
• Consistency reflects the stiffness or fluidity of concrete.
• Workability is a measure of how easy concrete is to place, compact, and finish.
• Workability is influenced by aggregate size. Smaller aggregates result in more workable mixes.
• Settlement and bleeding are inherent issues due to differences in density between cement/aggregates and water. Water may rise to the surface as bleed water.

Cement Quality Tests

• Magnesium oxide percentage should not exceed 5%. Higher percentages indicate poor limestone quality.
• Powder size should have at least 98% passing through a 200 mesh sieve.
• Setting time, the time it takes for concrete to solidify after mixing, is an important measurement.