2018年1月26日星期五

HKCTC Seminar on the Latest Development in Construction Material Testing, Inspection and Certification

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)

The last speaker was Ir. Dr. Jeffery Lam (Technical Manager, Construction & Building Materials Sector, NAMI) and his topic entitled “Development and Characterisation of C-100 High Strength Concrete”.  In the beginning, Dr. Lam introduced Nano and Advanced Materials Institute (NAMI) history and its mission.  


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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