BTECH M3

Plain concrete
Reinforced concrete

Two Types of Concrete

Plain concrete

is a mixture of cement, sand, gravel, and water without any steel reinforcement. It performs well in compression but is weak in tension.

Reinforced concrete

combines plain concrete with steel bars (rebars) to resist both compression and tension. The steel reinforcement is embedded within the concrete to carry tensile loads

•Cement

•Sand

•Gravel

•Water

Concrete is a composite material made by mixing:

Cement

the binder

Sand

fine aggregate

Gravel

coarse aggregate

Water

activates cement and enables workability

40 kg bags

In the Philippines, cement is sold in _______

cubic meters (cu.m.)

Aggregates are measured in

1.Lime (CaO)

2.Silica (SiO₂)

3.Alumina (Al₂O₃)

4.Iron Oxide (Fe₂O₃) .

5.Gypsum (CaSO₄·2H₂O)

The main components of Cement are

Lime (CaO)

– the major component responsible for strength.

Silica (SiO₂)

– contributes to strength and durability.

Iron Oxide (Fe₂O₃)

– influences color and contributes to strength

Gypsum (CaSO₄·2H₂O)

– added during grinding to regulate setting time.

Alumina (Al₂O₃)

affects setting time and heat of hydration.

Fine Aggregates
Coarse Aggregate

Two Classifications of Aggregates

Fine Aggregates

Typically composed of natural sand or crushed stone that passes through a ¼ inch sieve. Used to fill voids between coarse aggregates and improve workability. Commonly sourced from riverbeds or processed sand

Coarse Aggregate

Made up of gravel, crushed stone, or crushed slag that is retained on a ¼ inch sieve. Provides bulk and strength to the concrete mix. Sizes typically range from ¾ inch to 1½ inches, depending on the structural requirement

Correct Proportioning of Materials
Clean and Quality Materials
Proper Mixing Method
Right Water-Cement Ratio
Timely Placement and Curing

Principles of Concrete Mixing

Correct Proportioning of Materials

• Use standard mix ratios (e.g., 1:2:4 for Class B) based on volume, not weight.

• Ensure consistency in measuring—use calibrated boxes or containers.

• Adjust for moisture content in aggregates to avoid excess water

Clean and Quality Materials

• Cement should be fresh and dry.

• Sand and gravel must be free from clay, silt, and organic matter.

• Water should be potable—free from salts and contaminants.

Proper Mixing Method

•Mix thoroughly to ensure uniform distribution of cement paste.

•Use manual mixing for small volumes; mechanical mixers for larger batches.

•Follow the correct sequence: mix dry materials first, then add water gradually. Incomplete mixing results in honeycombing and poor bonding.

Right Water-Cement Ratio

•Avoid excessive water—it weakens concrete and causes segregation.

•Maintain a workable slump (typically 75–100 mm for slabs).

•Use only enough water to achieve the desired workability.

Too much water is the enemy of concrete

Timely Placement and Curing

•Place concrete immediately after mixing to avoid setting delays.

•Compact properly to eliminate air pockets. \

•Cure for at least 7 days using water, burlap, or plastic sheets.

In tropical climates like the Philippines, curing is critical to prevent rapid drying and cracking.

Concrete Hollow Blocks

is popularly known as CHB. It is classified as load bearing and non bearing blocks.

Load bearing blocks

are those whose thickness ranges from 15 to 20 centimeters and are used to carry load aside from its own weight

Non bearing blocks

on the other hand, are blocks intended for walls, partitions, fences, dividers and the like carrying its own weight whose thickness ranges from 7-10 centimeters.