Estimating Concrete Works for Slab, Footing, and Columns

Estimating Concrete Works

Basic Components of Plain Concrete

1 Cement

It serves as the binder, it holds everything together once mixed with water. Mostly made of lime and silica plus a few other minerals.

2. Fine Aggregates

Particles that pass through a 5mm sieve is considered as sand. It fills the gaps and made the mix workable.

3. Course Aggregates

Particles that are retained on a 5 mm siever are usually gravel or crushed stoned. It adds bulk and compressive strength to the mixture.

4. Water

It activates the cement, it must be clean and free from salt to avoid the steel from rusting. Also the water-cement ration controls the strength, too much water weakens the mix.

Estimating Concrete Slab

CONCRETE SLAB (VOLUME METHOD)

Step 1: Determine the Volume

$Vol=W \times L \times thk$

Step 2: Compute fot the quantity of cement, sand, gravel and water. Identi

$Cement: C=V_{conc.} \times multiplier$
$Sand: S=V_{conc.} \times multiplier$
$Gravel:G=V_{conc.} \times multiplier$

EXAMPLE

A Slab on Grade (S.O.G.) has a dimension of 10 x 4 x 0.15 m. Determine the number of cement in bags, sand (cu.m), and gravel required using Class B mixture and 40 kg./bag.

$G: 6 m^3 \times 1.0 = 6 m^3$

$V_{conc} = 10 m \times 4 m \times 0.15 m = 6 m^3$

$C: 6 m^3 \times 7.5 \frac{bags}{m^3} = 45 bags$
$S: 6 m^3 \time 0.5 = 3 m^3$
$G: 6 m^3 \times 1.0 =6 m^3$

Estimating Concrete Footings & Columns

CONCRETE FOOTING (VOLUME METHOD)

Step 1: Determine the Volume

There are various kinds of footing but in residential or commercial structure, shallow foundations are most common.

Step 2: Multiply to the number of footing

$V_{conc}=V_{vol} \times no. of posts}$

Step 3: Compute fot the quantity of cement, sand, gravel and water.

EXAMPLE

There are 10 isolated stepped footings with columns in the plan with the dimensions in the figure below. Determine the number of cement in bags, sand (cu.m), and gravel required using Class AA mixture and 40 kg./bag.