MATERIALS

Technical visit to Building Diagnostics Technology Laboratory of the Building and Real Estate Department at the Hong Kong Polytechnic University By Ir LAM Chi Sing A technical visit to the Building Diagnostics Technology Laboratory at the Hong Kong Polytechnic University was held on 31 January 2009. Dr Steven Tsang introduced the theory and application of a host of building condition-monitoring techniques ie infrared thermography, forced structural vibration and electromagnetic microwave. Infrared thermography (IRT) is a heat sensing imagery technique which measures infrared radiation emitted from an object surface and displays them as colour coded visual image. It is used to assess external wall conditions. Traditionally, hammer tapping or sounding method was used to detect air-filled voids behind wall tiles IR was discovered by William Herschel and was currently used as a preliminary screening tool of possible defects of wall tiling. Several specimens of mosaic tiling system (with artificially introduced embedded defects) were tested to demonstrate the power as well as deficiency of IR. A pane of window glass, cementitious panel, PVC polythene sheet were also used for further testing and demonstrating various performance characteristics of infrared thermal cameras. In the second session, Mr Louis Chu, a PhD candidate under the supervision by Dr Tsang, introduced forced vibration of building structures. He cited the Tacoma Bridge as an example of structural failure under the resonant vibration (causing the bridge to oscillate violently in torsional mode under strong wind). A long thin steel ruler/beam was used for demonstration of exciting a beam's various vibratory modes through gradually stepping up frequencies. Vibration data could be observed, logged and read in the computer for subsequent detail modal analysis. In the final session, experimental demonstration was made to a full-scale balcony structure. Structural health condition monitoring was demonstrated by determining/tracking changes, if any, of the resonant frequency of one or more vibration modes using both instrumented impact hammer method and/or electro-magnetic shaker. Changes in the resonant frequencies of this balcony as a result of a number of predetermined structural deteriorations to the rebar areas were studied and quantified. Performance of RC balconies was obtained which can shed more light on the real structural behaviour of this type of structures. After the demonstrations, interactive discussions were made. Finally, on behalf of the BD, CV, MT Divisions and the participants, we would like to thank Dr Tsang, Mr Chu and his technical team for their hospitality and warm reception to our members. The visit has broadened their horizons and understanding of the latest advanced techniques in building diagnostics and monitoring.

Dr Steven Tsang (middle), the speaker and his teammates with the HKIE representatives Ir Sam Chan (left 2nd), Ir C S Lam (right 3rd) and Ir Adam Choy (right 2nd) The MI Division members and Dr Steven Tsang at PolyU

Technical seminar on materials contributions to Beijing 2008 Olympic Games and innovative solutions based on dry mortar technology By Ir LAM Chi Sing A technical seminar on materials contribution to Beijing 2008 Olympic Games and innovative solutions based on dry mortar technology was held on 3 February 2009. The speaker, Ir Raymond Wan, delivered the application of innovative pre-mixed dry mortar on floor usage and green solutions to building construction. Dry mortar is a pre-blended dry powdery material comprising of binders, fillers, additives and pigments. It can be immediately used after being mixed with water. They are usually termed as polymer modified cementitious mortars. For example, self-levelling floor compound can be applied onto floor substrates at a thickness from 3 mm to 10 mm. The products can be either colour or non-colour finish, it can be applied on defective and damaged floors with weak dusty, uneven, joints, cracks, damaged epoxy and wear-out surface. The products have high abrasive resistance, they are also durable, elastic and flexible. Its hardness can be tested by impact test method (a European test) with hard and sharp steel impactor. The innovative dry mortar (self levelling floor compound) had been applied as finished floors with a total of 87,000 sq m in the National Stadium, Olympic basketball Gymnasium and Olympic Green Car Park. Before application, minor crack was repaired and then applied primer to the cleaned floor, the raw dry mortar was mixed with water to produce consistent slurry, and a simple flow test was performed complying with the BSEN 12706. The mixed mortar was then pumped onto the floor and spread to level with a straight edge, allowed to finish resulting the self smoothing and hardened floor. The materials can be suitably used for repairing, maintenance, renovation and decoration. A number of examples on floor applications were demonstrated. Apart from applications on flooring, the innovative dry mortars can also be applied for waterproofing restoration and wall reinstatement, other applications include thermal insulation, fire resistance, noise absorbent, anti-radon and low VOC finishes. It is a green and environmental-friendly product. The polymer modified cementitious-based flexible waterproofing materials can achieve a seamless layer with good bonding, flexible and easy maintenance. It can also be applied on external tiled wall renovation work to replace tradition patch repair, re-render and re-tiling work. It can provide innovative enhanced alternative solutions for speedy and cost-effective external tile façade refurbishment. The seminar ended with the interactive question-and-answer session. On behalf of the MT, BD, EV Divisions and the participants, we would like to thank Ir Wan for giving us a meaningful and innovative talk and widen our knowledge on the development of innovative green products in construction.

Audience asking questions on the floor Ir P K Lee of the EV Division, Ir Raymond Wan, the speaker, Ir George Cheng of the BD Division and Ir Prof Lawrence Wu of the MT Division