Bridge constructoin -IRAQ
BAJI BRIDGE -5
1989Monday, 12 January 2009
General Informations
1. In checking the quality of weld, what are the pros and cons of various
non-destructive weld inspection methods i.e. ultrasonic test, radiographic inspection
and magnetic particle flaw detection test?
Currently, there are three common non-destructive testing of weld, namely radiographic
inspection, ultrasonic testing and magnetic flaw detection test.
The method of radiographic approach was used commonly in the past until the arrival of
ultrasonic inspection technique. The major difference between the two is that ultrasonic
testing detects very narrow flaws which can hardly be detected by radiographic method.
Moreover, it is very sensitive to gross discontinuities. Tiny defects, which characterize
welding problems, are normally not revealed by radiographic inspection.
Moreover, ultrasonic inspection possesses the advantages that it can accurately and
precisely locate a defect as well as figure out its depth, location and angle of inclination.
In the past, it was expensive to adopt ultrasonic means for inspection. Nowadays, the rates
for both inspection methods are comparable. Most importantly, the x-ray and gamma ray
used in radiographs are radioactive and pose potential safety hazard to testing technicians
on site. Reference is made to Paul G. Jonas and Dennis L. Scharosch.
Magnetic flaw detection test can only be used for checking flaws in any metallic objects.
This method is commonly used for inspecting surface cracks and slightly sub-surface
cracks. However, surface and sub-surface cracks can be readily detected by radiographs
and ultrasonic inspection.
2. Is the procurement of third party insurance necessary to be incorporated in
contract for construction works?
The purpose of third party insurance is to protect contractors from bankruptcy in case there
are severe accidents happened to the third party due to the construction work. Therefore, in
government contracts, contractors are requested contractually to procure third party
insurance from the commencement of contract until the end of Maintenance Period. If
contractors have the financial capability to handle the claims due to accidents to third party,
the client is not bound to include this requirement in the contract.
3. What is the difference between sureties and security?
In construction contracts, if a contractor fails to perform the works, the employer would
suffer from severe financial loss and therefore some forms of protection has to be
established in the contract.
For surety bond, the contractor obtains a guarantee from a third party i.e. a bank or an
insurance company, which in return for a fee, agrees to undertake the financial
responsibility for the performance of contractor’s obligations. This third party will pay to
the employer in case there is a contractor’s default.
For security, a sum of money is deposited in the employer’s account and upon satisfactory
fulfillment of contractor’s obligations, the sum will be repaid to the contractor
non-destructive weld inspection methods i.e. ultrasonic test, radiographic inspection
and magnetic particle flaw detection test?
Currently, there are three common non-destructive testing of weld, namely radiographic
inspection, ultrasonic testing and magnetic flaw detection test.
The method of radiographic approach was used commonly in the past until the arrival of
ultrasonic inspection technique. The major difference between the two is that ultrasonic
testing detects very narrow flaws which can hardly be detected by radiographic method.
Moreover, it is very sensitive to gross discontinuities. Tiny defects, which characterize
welding problems, are normally not revealed by radiographic inspection.
Moreover, ultrasonic inspection possesses the advantages that it can accurately and
precisely locate a defect as well as figure out its depth, location and angle of inclination.
In the past, it was expensive to adopt ultrasonic means for inspection. Nowadays, the rates
for both inspection methods are comparable. Most importantly, the x-ray and gamma ray
used in radiographs are radioactive and pose potential safety hazard to testing technicians
on site. Reference is made to Paul G. Jonas and Dennis L. Scharosch.
Magnetic flaw detection test can only be used for checking flaws in any metallic objects.
This method is commonly used for inspecting surface cracks and slightly sub-surface
cracks. However, surface and sub-surface cracks can be readily detected by radiographs
and ultrasonic inspection.
2. Is the procurement of third party insurance necessary to be incorporated in
contract for construction works?
The purpose of third party insurance is to protect contractors from bankruptcy in case there
are severe accidents happened to the third party due to the construction work. Therefore, in
government contracts, contractors are requested contractually to procure third party
insurance from the commencement of contract until the end of Maintenance Period. If
contractors have the financial capability to handle the claims due to accidents to third party,
the client is not bound to include this requirement in the contract.
3. What is the difference between sureties and security?
In construction contracts, if a contractor fails to perform the works, the employer would
suffer from severe financial loss and therefore some forms of protection has to be
established in the contract.
For surety bond, the contractor obtains a guarantee from a third party i.e. a bank or an
insurance company, which in return for a fee, agrees to undertake the financial
responsibility for the performance of contractor’s obligations. This third party will pay to
the employer in case there is a contractor’s default.
For security, a sum of money is deposited in the employer’s account and upon satisfactory
fulfillment of contractor’s obligations, the sum will be repaid to the contractor
Questions and Answers on practical civil engineering
1. What is the difference between epoxy grout, cement grout and cement mortar?
Epoxy grout consists of epoxy resin, epoxy hardener and sand/aggregates. In fact, there are
various types of resin used in construction industry like epoxy, polyester, polyurethane etc.
Though epoxy grout appears to imply the presence of cement material by its name, it does
not contain any cement at all. On the other hand, epoxy hardener serves to initiate the
hardening process of epoxy grout. It is commonly used for repairing hairline cracks and
cavities in concrete structures and can be adopted as primer or bonding agent.
Cement grout is formed by mixing cement powder with water in which the ratio of cement
of water is more or less similar to that of concrete. Setting and hardening are the important
processes which affect the performance of cement grout. Moreover, the presence of
excessive voids would also affect the strength, stiffness and permeability of grout. It is
versatile in application of filling voids and gaps in structures.
Cement mortar is normally a mixture of cement, water and sand. They are used as bedding
for concrete kerbs in roadwork.
2. In soil compaction test, if a test result exceeds 100%, should engineers accept the
result?
Soil compaction is the process of increasing the soil density by reducing the volume of air
within the soil mass.
Soil compaction depends mainly on the degree of compaction and the amount of water
present for lubrication. Normally 2.5kg rammers and 4.5kg rammers are available for
compaction in laboratories and the maximum dry densities produced by these rammers
cover the range of dry density obtained by in-situ compaction plant.
Regarding the second factor of water content, it affects the compaction in the following
ways. In low water content, the soils are difficult to be compacted. When water content is
increased gradually, water will lubricate the soils and this facilitates the compaction
operation. However, at high water content, as an increasing proportion of soils is occupied
by water, the dry density decreases with an increase in water content.
For soil compaction tests, the dry density obtained from compaction carried out in-situ by
vibrating roller/vibrating plate is compared with the maximum dry density conducted in
laboratories using 2.5kg rammer of compaction with similar soils. In essence, the in-situ
compaction is compared with the compacting effort of using 2.5kg (or 4.5kg) rammer in
laboratories. In case the compaction test results indicate values exceeding 100%, it only
means that the in-situ compaction is more than that being carried out in laboratories which
is treated as the basic criterion for satisfactory degree of soil compaction. Therefore, the
soil results are acceptable in case compaction test results are over 100%. However,
excessive compaction poses a risk of fracturing granular soils resulting in the reduction of
soil strength parameters.
Epoxy grout consists of epoxy resin, epoxy hardener and sand/aggregates. In fact, there are
various types of resin used in construction industry like epoxy, polyester, polyurethane etc.
Though epoxy grout appears to imply the presence of cement material by its name, it does
not contain any cement at all. On the other hand, epoxy hardener serves to initiate the
hardening process of epoxy grout. It is commonly used for repairing hairline cracks and
cavities in concrete structures and can be adopted as primer or bonding agent.
Cement grout is formed by mixing cement powder with water in which the ratio of cement
of water is more or less similar to that of concrete. Setting and hardening are the important
processes which affect the performance of cement grout. Moreover, the presence of
excessive voids would also affect the strength, stiffness and permeability of grout. It is
versatile in application of filling voids and gaps in structures.
Cement mortar is normally a mixture of cement, water and sand. They are used as bedding
for concrete kerbs in roadwork.
2. In soil compaction test, if a test result exceeds 100%, should engineers accept the
result?
Soil compaction is the process of increasing the soil density by reducing the volume of air
within the soil mass.
Soil compaction depends mainly on the degree of compaction and the amount of water
present for lubrication. Normally 2.5kg rammers and 4.5kg rammers are available for
compaction in laboratories and the maximum dry densities produced by these rammers
cover the range of dry density obtained by in-situ compaction plant.
Regarding the second factor of water content, it affects the compaction in the following
ways. In low water content, the soils are difficult to be compacted. When water content is
increased gradually, water will lubricate the soils and this facilitates the compaction
operation. However, at high water content, as an increasing proportion of soils is occupied
by water, the dry density decreases with an increase in water content.
For soil compaction tests, the dry density obtained from compaction carried out in-situ by
vibrating roller/vibrating plate is compared with the maximum dry density conducted in
laboratories using 2.5kg rammer of compaction with similar soils. In essence, the in-situ
compaction is compared with the compacting effort of using 2.5kg (or 4.5kg) rammer in
laboratories. In case the compaction test results indicate values exceeding 100%, it only
means that the in-situ compaction is more than that being carried out in laboratories which
is treated as the basic criterion for satisfactory degree of soil compaction. Therefore, the
soil results are acceptable in case compaction test results are over 100%. However,
excessive compaction poses a risk of fracturing granular soils resulting in the reduction of
soil strength parameters.
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