3. Quality assurance for concrete - strength,
durability, thermal properties – cracks, different
types,causes – Effects due to climate,
temperature, chemicals, corrosion – design and
construction errors – Effects of cover thickness.
4. Quality assurance for concrete
construction:
Quality management ensures that every
component of the structure keeps performing
throughout its life span.
5. Need for Quality Assurance :
• To give good performance and appearance throughout
its intended life.
• The client requires it in promoting his next engineering
scheme.
• The designer depends on it for his reputation and
professional satisfaction.
• The material producer is influenced by the quality of
work in his future sales.
• The building contractor also relies on it to promote his
organization in procuring future contracts, but his task is
often considerably complicated by the problems of time
scheduling and costs.
6. •Finally the user is rewarded by a functionally
efficient structure of good appearance. It would
seem to follow therefore that since all responsible
parties gain by quality it should be automatically
achieved.
The quality management system in a true sense
should have the following three components
(1) Quality assurance plan (QAP)
(2) Quality control process (QC)
(3) Quality audit (QA)
7. Quality assurance plan :
The following aspects should be addressed by any QAP:
•Organizational Set-up
•Responsibilities of personnel
•Coordinating personnel
•Quality control measure
•Control norms and limit
•Acceptance/rejection criteria
•Inspection program
•Sampling, testing and documentation
Material specification and qualification. Corrective measure for
noncompliance
Resolution of disputed/difficulties
Preparation of maintenance record
8. Quality Control Process :
•It is a system of procedures and standards by which
the contractor, the product manufacture, and the
engineer monitor the properties of the product.
•Generally the contracting agency is responsible for
the QC process.
•A contractor responsible for quality control incurs a
cost for it, which is less than the uncontrolled cost for
correcting the defective workmanship or replacing the
defective material.
•Hence it is prudent to introduce effective quality
control.
9. Quality Audit :
This is the system of tracing and documentation
of quality assurance and quality control program.
It is the responsibility of the process owner.
Both design and construction processes come
under this process.
The concept of QA encompasses the project as
a whole.
Each element of the project comes under the
preview of quality audit.
10. Concrete Properties
Strength :
Strength of concrete is defined as the
resistance that concrete provides against load so
as so to avoid failure. It depends on the water-
cement ratio, quality of aggregates, compaction,
curing etc.
11. Factors Influencing Strength of Concrete
Size of specimen
Moisture Content
Rate of loading
Type of testing machine used
Type of materials used
etc
12. Thermal Properties
Concrete is a material used in all climatic regions for all
kinds of structures.
Knowledge of thermal expansion is required in
i) long span bridge girders
ii) high rise buildings subjected to variation of
temperatures
iii) For calculating thermal strains in chimneys
iv) blast furnace and pressure vessels
v) pavements and construction joints
vi) dams other structures.
13. Three types of tests
(a) Unstressed Tests: Where specimens are heated under no
initial stress and then loaded until the point of failure.
(b) Stressed Tests: Where a fraction of the compressive strength
capacity at room temperature is applied and sustained during heating.
When the target temperature is reached, the load is increased until
the point of failure.
(c) Residual Unstressed Tests: Where the specimens are
heated without any load, cooled to room temperature, and then
loaded until the point of failure.
To study about the thermal properties of concrete the following
properties needs to be known,
•Thermal conductivity
•Thermal diffusivity
•Specific heat
•Coefficient of thermal expansion
14. Thermal Conductivity:
This measures the ability of material to conduct heat.
Thermal Diffusivity:
Diffusivity represents the rate at which temperature changes
within the concrete mass.
Specific Heat:
It is defined as the quantity of heat required to raise the
temperature of a unit mass of a material by one degree centigrade.
Coefficient of thermal expansion:
Coefficient of thermal expansion is defined as the change in length
per degree change of temperature.
15. ■ Development of a network of fine random cracks
on the surface of concrete
■ Excessive floating and traveling
■ Spreading dry cement on a surface and sprinkling
water on concrete
■ Use of highly absorptive aggregates batched in the
dry state
■ Use of over-wet concrete
■ Improper curing
■ Use of unvented heater (Salamanders) during the
curing period
16. ■ Honeycomb consists of exposed pockets of coarse
aggregates not covered by a surface layer of
mortar. This may be caused by inadequate
consolidation, presence of excess water in con-
crete or by leaky forms, which allow the mortar to
escape.
■ Preventive measures
(a) To follow good concrete construction practice
(b) To use workable concrete
(c) To provide good forms (tight)
(d) To give proper vibration (compaction)
(e) To be planned sequence of placing.
17. ■ Continuously in water from the time of
casting exhibits a net increase in volume
■ Due to continued hydration of cement is
known as swelling.
■ Due to the absorption of water by the
cement gel.
18. ■ Concrete, brickwork and timber when
subjected to sustained loads not only
undergoes instaneous elastic deformation
but also exhibit a time-dependent
deformation known as creep.
19. ■ Abrasion refers to wearing away of the
surface by friction.
■ Erosion refers to wearing away of the
surface by fluids.
■ The cavitations refer to the damage due to
non-linear flow of water at velocities more
than 12 m/sec.
20. ■ Settlement occurs after finishing of the
concrete surface, cracks will ensure
■ Prevented by proper attention to compacting and
draining
SUB-GRADE MOVEMENT
■ A crack open to the surface will allow access of water
to the interior of the concrete
■ An internal void may give rise to freezing or corrosion
problems
■ Prevented by a proper design of the forms with respect
to the details and deflections
21. ■ There is two types of mechanism in settlement and
movement in concrete structural members: differential
movement and subsidence.
FOUNDATION SETTLEMENT
■ Shear cracks occur when there is differential settlement of
foundation. Shear failure is predominant in made-up ground.
Some of the preventive measures:
■ Providing an impermeable apron all around the building,
■ Prevention of water stagnation around the building,
■ Providing adequate drainage system,
■ Avoiding the plantation of fast growing trees in the
immediate vicinity of the building
22. ■ Adding water to concrete
■ Improper alignment of formwork
■ Improper consolidation
■ Improper curing
■ Improper location of reinforcing steel
■ Premature removal of shores or reshores
■ Settling of the concrete
■ Settling of the subgrade
■ Vibration of freshly placed concrete
■ Improper finishing of flat work
■ Adding water to the surface
■ Timing of finishing
■ Adding cement to the surface
■ Use of tamper
■ Jointing
23. ■ Inadequate structural design
■ Poor design details
■ Abrupt changes in section
■ Insufficient reinforcement at reentrant corners and openings
■ Inadequate provision for deflection
■ Inadequate provision for drainage
■ Insufficient travel in expansion joints
■ Incompatibility of materials
■ Neglect of creep effect
■ Rigid joints between precast units
■ Unanticipated shear stresses in piers, columns, or abutments
■ Inadequate joint spacing in slabs
