1. PRECAST SEWER MANHOLES
CONSTRUCTION QUALITY CONTROL
Imtiaz Ur Rehman (B.Sc. Civil Engineer)

2. MANHOLE
CONSTRUCTION
PRELIMINARY WORKS
 APPROVALS
Shop Drawing Approval
Equipment Approval
Precast Yard Approval
Materials Approval
 PRE-POUR INSPECTIONS
Rebar
Formwork
Openings
Water stop
HDPE Lining
Lifting Hook

3. APPROVALS
 SHOP DRAWINGS APPROVALS
• The shop drawings are got approved & issued for construction
(IFC). Precast elements are casted as per these approved
drawings.
 Equipment / Tools & Plants Approval
• Form Work
• Vibratory Equipment
 Precast Yard
• Approved Site location of Precast Yard
• Leveled, Impervious and Equipped with lifting facility
• Concrete Curing Facility
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4. APPROVALS
• Transportation Facility
• Sun shade & other welfare facilities
 Materials Approvals
• Concrete
• Steel Reinforcement
• Water Stop, Rebar Cover Spacers
• HDPE Lining Material
• Curing Agent
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5. PRE-POUR INSPECTIONS
 Rebar inspection (lap length,
spacing, bar dia, cover etc)
 Formwork Inspection (water
tight, strong enough to hold
concrete, easy to remove
 Openings Inspection
(opening dia, opening
location etc)
 Water Stop Inspection (size,
location, joint etc.)
 HDPE Lining (size, location,
joint etc)
 Lifting Hook (capable of
lifting weight of manhole
including factor of safety)
 SAFETY PRECAUTIONS ARE
TAKEN INTO
CONSIDERATION FOR ALL
STAGES OF CONSTRUCTION
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MANHOLE
CONSTRUCTION
 IN PROCESS INSPECTION
 POST-PROCESS INSPECTION
 IN PROCESS INSPECTION
 Grade of concrete
 Cleaning
 Temperature of concrete
 Slump & Time of Batch
 Vibration/ compaction
 Crushing Strength
 POST-PROCESS INSPECTIONS
 Removal of Formwork
 Repair Works
 Iron Steps
 Curing
 Bitumen Coating
 Final Inspection through
MIR

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IN-PROCESS INSPECTION
 GRADE OF CONCRETE
(25 MPa Class Concrete-SRC/Type V cement. Concrete Specimen previously tested
for water tightness as per ACI 350.1)
 CLEANING
The surface receiving concrete must be clean and free from dust, rubbish etc.
 TEMPERATURE OF CONCRETE
Not above 32 Degree Centigrade. Batching Plants have chillers to produce chilled
water used for concrete production. More over, high temperature can be
controlled by provide shade to aggregate or sprinkle water on aggregate.
 SLUMP & TIME OF BATCH OF CONCRETE
• Site Slump =7.5 with tolerance of 2.5 cm
• Concrete to be delivered at site in 30 minute and to be poured within next 30
minutes. Number of drum revolutions of concrete truck not to exceed 300 during
travel time.

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IN-PROCESS INSPECTION
 VIBRATION & COMPACTION OF CONCRETE
Optimum vibration and compaction of concrete is
assured in order to get smooth compacted surface and to
avoid segregation of the ingredients of the concrete.
 CRUSHING STRENGTH OF CONCRETE
Specimen cylinders of concrete are casted and tested for
7 days and 28 days age strength of concrete. For precast
manholes, 25 MPa is required 28 days strength. On 7
days age 70-75% of strength is usually obtained and on
28 days age, 95-120% strength is achieved.

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POST-PROCESS INSPECTION
 REMOVAL OF FORMWORK
Usually after 24 hours of concrete pouring, formwork
removal is carried out.
 REPAIR WORKS
If minor holes in concrete are observed, they can be
repaired using 1:1 Cement Sand rich mortar. But if the
pores are larger or reinforcement is exposed, the job
done is straightaway rejected.

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POST-PROCESS INSPECTION
 FIXING OF IRON STEPS
Iron steps coated with 2 layers of PE are driven into the
freshly exposed concrete as per drawing locations using
hammer.
 CURING OF CONCRETE
7 days curing of concrete is done either by curing
compound or by sprinkling water after wrapping it in
hessian cloth. However, there are several other
methods of satisfactory curing of concrete e.g. ponding,
steam curing, using moist sand etc.

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POST-PROCESS INSPECTION
 BITUMEN COATING
After curing is complete, the manholes are applied with
two coats of bitumen epoxy paint. The second coat is
applied after complete drying of first coat.
 FINAL INSPECTION THROUGH MIR
The prepared manholes are finally inspected through
submission of MIR. After the manholes are approved,
they are fit for use at site.

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