Lesson 6 Concrete Hollow Blocks (CHB) PDF

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Summary:

Concrete Hollow Blocks
Concrete Hollow Blocks are classified as bearing and non-bearing blocks. Load bearing blocks are those whose thickness ranges from 15 cm (6 in) to 20 cm (8 in) and are used to carry laod aside from its own weight. Non-bearing blocks on the other han...

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Concrete Hollow Blocks (CHB): CE 207 - Quantity Surveying

Lesson 6: Concrete Hollow Blocks (CHB) Concrete Hollow Blocks Concrete Hollow Blocks are classified as bearing and non-bearing blocks. Load bearing blocks are those whose thickness ranges from 15 cm (6 in) to 20 cm (8 in) and are used to carry load aside from its own weight. Non-bearing blocks, on the other hand, are blocks that are intended for walls, partitions, fences, or dividers carrying their own weight whose thickness ranges from 7.5 cm (3 in) to 10 cm (4 in).

Concrete Hollow Blocks has three whole cells and two one half cells at both ends having a total of four. These cells vary sizes as there are different manufacturers using different molds. The varying sizes of the cells will affect the estimated quantity of materials. For this reason, it it recommended that the bigger cell be adopted in the computations. Estimating the materials required for concrete hollow block works, comprises of the following major items: 1. Quantity of the blocks 2. Quantity of cement and sand mortar for block laying 3. Cement, sand and gravel filler of the hollow core or cell 4. Cement and fine sand for plastering 5. Cement, sand and gravel for CHB Footing anf Posts 6. Reinforcing steel bars From Figure 2-2, Determine the number of 10 X 20 X 40cm concrete hollow blocks and the materials required: 1/15

a) Mortar for block laying b) Mortar filller for the hollow core or cells. c) Plastering d) Concrete for CHB and Post footings e) Reinforcement

SOLUTION -1 (By Fundamental Unit Method)

A. Concrete Hollow Blocks 1. Divide the height of the fence by the height of one block. 3.00

m

= 15

pcs.

.20

2. Divide the total length of the fence by the length of one block 20.00

m

= 50

pcs.

.40

3. Multiply the result of 1 and 2

15 × 50 = 750

pcs.

TABLE 2-1 QUANTITY OF CEMNET AND SAND FOR MORTAR AND PLASTER MIXTURE PER CUBIC METER

CLASS MIXTURE

CEMENT IN BAG SAND 40 50 cu.m. KG KG

A

1:2

18.0 14.5

1.0

B

1:3

12.0 9.5

1.0

C

1:4

9.0 7.0

1.0

D

1:5

7.5 6.0

1.0

B. Mortar for Blocking Laying (.0125 average thickness) 1. Find the volume of the mortar (one layer)

V =t ×w ×l V = .0125 × .10 × 20m V = .025 cu . m.

2. Multiply the number of layers to get the total volume of the mortar:

Total V = .025 × 15 layers V = .375 cu. m. 3. Refer to Table 2-1 using class B mixture 40kg. cement Multiply: Cement: .375 × 12 = 4.50 bags Sand

: .375 × 1.0 = 0.375 cu .

m.

C. Mortar Filler for Hollow Cell 1. Find the volume of one cell

V = .05 × .075 × .20 V = .00075 cu. m. 2. Volume of 4 cells per block

V = .00075 × 4 V = .003 cu. m. 3. Total volume of cells for 750 CHB

V = .003 × 750 V = 2.25 cu. m. 4. Refer to Table 2-1 using class B mortar - 40kg. cement Multiply:

Cement : 2.25 × 12 = 27 bags

Sand

: 2.25 × 1.0 = 2.25 cu. m.

D. Plastering (at average of 16mm. thick) 1. Find the area of the fence (one side)

3.00 × 20 = 60

sq. m.

2. Find the area of the two sides

60 × 2 = 120

sq. m.

3. Solve the Volume

V = 120 × .016 V = 1.92 cu. m. 4. Refer to Table 2-1 using class B mixture - 40kg. cement Multiply: Cement : 1.92 × 12 = 23.04 bags Sand

: 1.92 × 1.0 = 1.92 cu. m.

E. Footing 1. Find the volume of the footing

V=t×w×L V = .15 × .40 × 20.00 V = 1.20 cu. m. 2. Refer to Table 2-1 using class "B" concrete 40kg. cement

Multiply: Cement : 1.20 × 7.50 = 9.00 bags Sand

: 1.20 × .50 = .60 cu. m.

Gravel : 1.20 × 1.00 = 1.20 cu. m. Summary of the Materials 1. CHB

----

750 pcs.

2. 40kg. Cement ----

63.54 say 64 bags

3. Sand

----

5.14 cu.m.

4. Gravel

----

1.20 cu.m.

TABLE 2-2 QUANTITY OF CEMENT AND SAND FOR CHB MORTAR PER SQUARE METER WALL Bags of Cement

Size of Number per CHB Sq.m. cm.

B

40 kg

50 kg

Sand

Mixture

Mixture

cu.m.

C

D

B

C

D

10 X 20 X 40

12.5

0.525 0.394 0.328 0.416 0.306 0.263 .0438

15 X 20 X 40

12.5

1.013 0.759 0.633 0.802 0.591 0.502 .0844

20 X 20 X 40

12.5

1.500 1.125 0.938 0.875 0.875 0.750 .1250

The problem above can be solved by the Area Methods with the aid of Table 2-2 and 2-3, thus, consider; SOLUTION - 2 A. Concrete Hollow Blocks 1. Find the area of the fence.

3.00 × 20.00

m.

= 60

sq. m.

2. Refer to Table 2-2, multiply:

60 × 12.5 = 750

pcs. CHB

B. Mortar For Blocking Laying and filler of the cell 1. Referring to Table 2-2 using class "B" mixture 40kg. cement Multiply: Cement : 60 × .525 = 31.5 bags Sand

: 60 × .0438 = 2.63 cu. m.

C. Plaster Mortar 1. Find the area to be plastered 60 × 2 = 120 sq. m. two faces 1. Referring to Table 2-4 using class "B" mixture 40kg cement Multiply:Cement : 120 × .192 = 23.04 bags Sand

: 120 × .016 = 1.92 cu. m.

2. Footing 3. Determine the total length of the footing = 20m 4. Referring to table 2-3 using class "B" concrete: For a 15 x 40cm. Footing, Multiply: Cement : 20 m. ×.450 = 9.0 bags Sand

: 20 m. ×.030 = .60 cu. m.

Gravel : 20 m. ×.60 = 1.20 cu. m. Summary of the Materials 1. Concrete Hollow Blocks --- 750 pcs. 2. 40 kg. Cement

--- 63.5 say 64 bags

3. Sand

--- 5.15 cu.m.

CONCRETE HOLLOW BLOCK REINFORCEMENT

Steel bar as reinforcement is a requirement for all types of concrete and masonry works. The National Building Code has promulgated guidelines on how and what kind of reinforcement is appropriate for a certain type or work depending upon the purpose for which it is to serve. The size and spacing requirements for concrete hollow block reinforcement must be indicated on the planor specifications. Concrete hollow block reinforcement could be determined in three different ways: 1. By the Direct Counting Method 2. By the Area Method

3. By the Unit Block Method

1. . The Direct Counting Method Under the direct counting method, the vertical and horizontal reinforcements are counted individually in the plan. The length is also determined from the elevation. The hook, bend and lapping splices are imaginably calculated and added to its length because it is very rare to see a plan in a large scale drawing showing this particular requirements of reinforcing steel bars. This, estimators must be familiar with the hook, the bend, and splicing requirements to be able to work effectively even if the plan is not accompanied with such details. 2. The Area Method The Area Method is the simplest approach in computing the steel bar reinforcement for CHB with the aid of Table 3-5. The values presented in the table include the allowances required for standard bend, hook, and lapping splices.

3. The Unit Block Method

S ummary: Concrete Hollow Blocks Concrete Hollow Blocks are classified as bearing and non-bearing blocks. Load bearing blocks are those whose thickness ranges from 15 cm (6 in) to 20 cm (8 in) and are used to carry laod aside from its own weight. Non-bearing blocks on the other hand, are blocks which are intended for wealls, partitions, fences or dividers carrying its own weight whose thickness ranges from 7.5 cm (3 in) to 10 cm (4 in).

Estimating the materials required for concrete hollow block works, comprises of the following major items: 1. Quantity of the blocks 2. Quantity of cement and sand mortar for block laying 3. Cement, sand and gravel filler of the hollow core or cell 4. Cement and fine sand for plastering 5. Cement, sand and gravel for CHB Footing anf Posts 6. Reinforcing steel bars

Solving CHB: S OLUTION -1 (By Fundamental Unit Method) A. Concrete Hollow Blocks B. Mortar for Blocking Laying C. Mortar Filler for Hollow Cell D. Plastering

E. Footing

S OLUTION - 2 (By Area Methods) A. Concrete Hollow Blocks B. Mortar For Blocking Laying and filler of the cell C. Plaster Mortar D. Footing

CONCRETE HOLLOW BLOCK REINFORCEMENT Steel bar as reinforcement is a requirement for all types of concrete and masonry works. The National Building Code has promulgated guidelines on how and what kind of reinforcement is appropriate for a certain type or work depending upon the purpose for which it is to serve. The size and spacing requirements for concrete hollow block reinforcement must be indicated on the planor specifications. Concrete hollow block reinforcement could be determined in three different ways: 1. By the Direct Counting Method 2. By the Area Method 3. By the Unit Block Method...