In Nigeria, 9 inches hollow block (450mm x 225mm x 225mm) is normally employed for the construction of block work of buildings exceeding one storey. The length of the block is 450mm, the height is 225mm, and the width is 225mm. Contractors and builders are often faced with the challenge

of either buying blocks for construction or moulding it on their own. When the conditions are right, builders will prefer to mould their own blocks, especially for the purpose of controlling the quality of the blocks moulded, and to ease the cost of transportation.

Let us assume that you have decided to mould your own blocks, and you have been faced with the challenge of estimating the quantity of cement and sand to purchase that will satisfy the construction requirement. This post (which is merely informative and not normative) will give you a guide on how to make such estimate. I am going to work it through steps, so that you will be able to make calculations just in case you are using any other size of block.

**Initial data**

Number of blocks required = 3000 pieces

Recommended production = 1 bag of cement to produce 35 blocks

**Step 1: Calculate the volume of the block**

For the block size shown above;

Volume of block without holes = (0.45 × 0.225 × 0.225) = 0.02278125 m

^{3}

Volume of holes = 2(0.225 × 0.125 × 0.15) = 0.0084375 m

^{3}

Therefore volume of the block = 0.02278 - 0.0084375 = 0.0143 m

^{3}

**Step 2: Calculate the volume of the 35 blocks**

If the volume of 1 block is 0.0143, the volume of 35 blocks = (0.0143 × 35) = 0.502 m

^{3}

^{ }

**Step 3: Calculate the volume sand required for the 35 blocks**

The volume of 1 bag of cement is 34.72 litres = 0.03472m

^{3}.

This is obtained by knowing that the mass of 1 bag of cement = 50kg, and the density = 1440 kg/m

^{3}

The volume of a standard builder’s wheel barrow is 0.065 m

^{3}(unheaped). We assume that approximately 2 bags of cement will fill one builder's wheel barrow.

Now, we can estimate the number of wheel barrow trips of sand that the moulder should provide in order to make 35 blocks from one bag of cement.

Total volume of 35 blocks required = 0.502 m

^{3}

Let the number of wheel barrow trips of sand be

*x*

Hence, (volume of 1 bag of cement) + (Total volume of sand) = Volume of 35 blocks

Hence, 0.03472 +

*x*(0.065) = 0.502m

^{3}

On solving,

*x*= 7.1889 unheaped wheelbarrow trips of sand

The volume of sand required to make 35 blocks = 7.1889 × 0.065 = 0.46728 m

^{3}

**Step 4: Calculate the total volume of materials required**

We can therefore estimate the quantity of materials to be purchased;

If 1 bag of cement is needed for 35 blocks, therefore 86 bags of cement is needed to mould 3000 blocks (gotten by 3000/35)

If 0.46728 m

^{3}of sand is required to make 35 blocks, therefore, 41 m

^{3}of sand (about 67.60 tonnes assuming density of dry sand = 1600 kg/m

^{3}) is needed to make 3000 blocks.

For a 5 tonne tipper of 3.8 m

^{3}capacity, we have to order for 11 trips of sharp sand.

You have to be very sure of the size of the tipper that will be delivering the sand to you in order to make your estimates more reasonable. On the other hand, you can make the considerations for variations between the weight of materials when wet and when dry. However, this will never be critical for block moulding based on experience. But in concrete it can be very considerable.

**Therefore summarily, we need 86 bags of cement and 11 trips of sand to mould about 3000 pieces of 9 inches blocks with holes (for 1 bag = 35 blocks).**

Thank you for reading, and God bless.

*READ ALSO IN THIS BLOG*

How to calculate the number of blocks required for the construction of a 3 bedroom flat

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kindly help with the section for 150 mm block .. Nice analysis I commend your simplicity

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ReplyDeleteVery nice and simile accurate analysis. Thank you very much.

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ReplyDeletePlease whats the total cost for 3 bed, 2bed and 1 bed building?

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Deletesir how do you get 41m3 of sand and 7.1889 unheaped wheelbarrow

DeleteThe smalles Tipper is 3.8m3 by volumn weighing, it means to know the no of tips that make up 41m3, devide it by 3.8 = 11 Tips

Deleteso dont we need granite if you are trying to fence a 4 and half plot, because we need cement , sharp sand , water dont we need granite

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