The Hong Kong Council for Testing
and Certification (HKCTC) and Hong Kong Accreditation Service (HKAS) co-organized
a seminar named “Latest Development in Construction Material Testing,
Inspection and Certification” held on 26th Jan 2018. In recent years, infrastructure and construction projects in Hong Kong
are being carried out in full swing.
Product certificate schemes for a wide range of construction materials
have been developed to help safeguard the quality of construction materials. In the beginning, all guest speakers and
organizers took a group photo.
(Left: Ir. Dr. Jeffrey Lam, Ir.
Dr. Wallace Lai, Prof. Albert Yu (Chairman, HKCTC), Ir. Prof. Joseph Mak, Ir.
Prof. Philip Chung and Ms. Jane Lee (Secretary-General (Test &
Certification), HKCTC))
The first speaker was Ir. Prof.
Philip Chung (Deputy Head of Geotechnical Engineering Office (Planning and
Standards); Hon. Professor, Department of Earth Sciences, HKU) and his
presentation entitled “Testing of Cores taken from Cement Stabilised Soil”.
Firstly, he introduced what was
deep mixing that was a technique of mixing chemical binder (cement/lime) with
soil to improve the engineering properties of the soil. (In diagram – Improved ground area). There are three mechanism of Deep Cement Mixing
(DCM) to improve consistency and increase strength below.
-
Ion exchange at the surface of clay minerals
-
Bonding of soil particles
-
Filling of void spaces by chemical reaction products.
(Example by HK Airport Authority –
Deep Cement Mixing for
the three-runway system)
Prof. Chung estimated there would be more than 300,000 umbers of the quantity of cement stabilized soil cores tested / planned within a few years in Hong Kong. He focused on the testing of unconfined compressive strength (UCS) of soil-binder mixtures. For Third Runway project, UCS value was about 0.8 to 1.4 MPa; and UCS values in Tung Chung East reclamation project was about 1MPa. The following table showed approximate UCS values of different construction materials.
Different between lab strength
and field strength was discussed.
Advantage of lab specimen was better quality control and advantage of
field product was effects of confinement, potentially higher curing
temperature. Usually field product
result was lower than lab specimen. However, there was no standard for testing unconfined
compressive strength (UCS) of DCM. Many
countries employed soil testing standards (e.g. BS1377-7:1990; BS1924-2:1990;
ASTM D2166/D2166M-16; CS1:2010, etc.)
Therefore, HKIE issued an interim guideline which was issued in late
2017 entitled “Interim Guidelines on Testing of Unconfined Compressive Strength
(UCS) of Cement Stabilised Soil Cores in Hong Kong”. The scope of test method is applicable to
cement soil formed in field or in laboratories which diameter of cores is
preferably between 63mm and 100mm, with UCS values below 10MPa. Proficiency
Testing had been arranged with 11 participating laboratories.
The second speaker was Ir. Prof.
Joseph Mak (Head of Department of Civil Engineering, Chu Hai College of Higher
Education; Former Chief Structural Engineer, Hong Kong Housing Authority) and
his presentation topic was “Sharing Experience on Product Certification in Hong
Kong Housing Authority Development Projects”.
Firstly, Prof. Mak explained quality housing was assuring built quality
that included assuring quality of workmanship and materials on site, as well
as, off-site.
Then Prof. Mak briefed HA’s
surveillance check of building material on site before employing product
certification. And then he explained the
implementation of product certification through upstream quality control.
Product Conformity Certification
Scheme (PCCS) for ceramic tile and repair mortars were mentioned. The schedule of surveillance and
re-certification audit on different products was showed. Prof. Mak also explained product
certification should address more on the technical aspects of process
control. Techincal aspects of process
control on different products were discussed and including Timber Doorset, Tile
Adhesive, Mesh Reinforcement, Water Closet, etc.
Q&A session I
Prof. Philip Chung explained why
HKIE issued the guideline first because CDM in coming few years would be as
much as 30 year of Japan. For short
period of time, we need a guideline for HOKLAS accreditation. After consolidating PT results and project
review, government would be issued formal guideline for industry.
The third speaker was Ir. Dr. Wallace Lai (Assistant Professor, Department of Land Surveying and Geo-Informatics, PolyU) and his presentation named “Underground Utility Mapping, Imaging and Diagnosis”. He firstly briefed the diagnostic test on concrete based on HOKLAS supplementary criteria no. 19 and most of them were Non-Destructive Testing (NDT).
Dr. Wallace Lai said there were
highly similarity between concrete diagnosis and underground utility (UU)
diagnosis. Then he introduced Mandatory
Building Inspection Scheme (MBIS) under the Buildings (Amendment) Ordinance
2011 and then compared with Underground utilities requirement such as ETWB, Gas
Safety Ordinance Cap 51B and Electricity Supply Lines (Protection) Regulation
Cap 406H.
After that he compared different
technologies employed in Building and UU.
The four common technologies were Electromagnetic Induction, Infrared
Thermography, Electromagnetic Wave and Stress Wave.
Finally, he said the most
important for UU diagnostic was the people competence. They needed had knowledge and experience to
validate the result from different technologies. Lastly, he introduced the first underground
utility testing laboratory in Asia was established in PolyU. (See Underground
Utility Survey Laboratory)
Then Dr. Lam said Hong Kong had
the largest number (~315) of skyscrapers and high-rise buildings over the
world, 92% of high-rise buildings are made of concrete. He explained the requirement of concrete and
how to avoid spall after exposure to fire.
They then developed Grade 100 high strength concrete and enhanced
compressive strength, fire resistance and slump workability.
NAMI developed fire resistance
High Strength Concrete (HSC) through selection of suitable ingredient such as
steel fibers and polypropylene fibers.
After fire tests on full-scale
HSC columns, it was found that NAMI’s C80, C90 and C100 could maintain their
structural. But the normal C100 HSC was cover
spalled. This 100MPa+ concrete
formulation had fulfilled HK Concrete Code, and could withstand 4 hours fire
test.
Q&A session II
Ir. Dr. Wallace Lai said many
people were not available to identify the UU and pointed out as equipment
problem. However, the skill to validate
the image and result from equipment was more important.
Reference:
HKAS - http://www.itc.gov.hk/en/quality/hkas/about.htm
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