Tommy Y. Lo

Building defects diagnosis by infrared thermography

The application of infrared thermography has provided a reliable and accurate assessment method for the inspection of buildings and structures. The principle of the infrared thermography technique is the detection of energy by an infrared scanner and mapping the temperature contours over the surface of a target object to provide an appropriate measure of the damaged building or structure. This paper reviews the background of infrared thermography and the factors influencing the IR imaging. The applicability of infrared thermography in two particular situations is considered – the delamination of external wall finishes and a roofing system condition survey.

Comparison of workability and mechanical properties of self-compacting lightweight concrete and normal self-compacting concrete

Abstract The workability and mechanical properties of self-compacting lightweight concrete and normal self-compacting concrete have been studied. Self-compacting lightweight concrete with a binder content of 500–650 kg m−3 and a density of 1650 kg m−3 was made using less superplasticizer and viscosity modifying agent and a lower water/binder ratio than normal self-compacting concrete. The bulk density was only 75% of normal self-compacting concrete but with a similar compressive strength. The elastic modulus was about 80% of that of normal self-compacting concrete. These results indicate that self-compacting lightweight concrete is excellent in workability and has a lower density, a higher compressive strength and a relatively high elastic modulus than normal self-compacting concrete using the same design principles.

Quality culture: a product of motivation within organization

Quality management system provides the top management a self‐regulating tool to enhance the company’s operation. Hong Kong is coming to age with quality management. A trend has been developing in Hong Kong whereas construction contractors have to adopt and be certified under the ISO 9000 Quality Management Scheme (QMS) in order to become government contractors. It is found that even though the companies have adopted the QMS for over three years, however, their qualities of service do not improve as expected. Quality culture has not been firmly established in the construction sector in Hong Kong. Summarizes attitude, experience and the underlining factors that drive the construction contractors to the QMS system. Findings indicated that companies are forced to adopt the QMS rather than motivated from within the top management. The two distinctive incentives for adoption of QMS by the companies are to improve quality image and to satisfy client requirements, particularly the government. Concludes that motivation from within an organization is the only key to improving quality realistically.

The variation of radon exhalation rates from concrete surfaces of different ages

Abstract The radon exhalation rates from four concrete blocks cast with ordinary Portland cement (OPC) and four with substitution of pulverized fuel ash (PFA) were monitored for 34 months starting from November 1992. At the end of the 28th month, two OPC blocks and two PFA blocks were immersed in water, one from each group for 5 days the other one from each group for 10 days. These were then taken out of water and the radon exhalation rates monitored as usual. It was observed that the radon exhalation rate in general decreased with the age of the concrete blocks and the rate increased after the blocks were immersed in water. An explanation for the first result is that the gradual dehydration of concrete as it ages will reduce the water content in the pores of the concrete, thus reducing the probability of retaining radon within the pores and the probability of radon emanation from these pores. The second result gives strong support to this assertion.

Pozzolanic Reactivity of Silica Fume and Ground Rice Husk Ash as Reactive Silica in a Cementitious System: A Comparative Study

This study comparably assessed the pozzolanic effect of silica fume (SF) and ground rice husk ash (RHA) as supplementary cementing materials on the properties of blended cement pastes and concretes. A commonly commercial silica fume (SF) and locally-produced rice husk ash (RHA) samples with two finenesses (one with larger size than cement and the other with smaller size than cement) were used in this study. Material properties of SF and RHA were experimentally characterized. Hydration and mechanical properties of cement pastes incorporating SF and RHA were determined by thermogravimetric analysis (TGA) and compressive strength tests, respectively. Properties of concretes regarding workability, mechanical property, durability, and microstructure were evaluated. Results showed that, although the finely ground RHA used in this study possessed lower SiO2 content and higher particle size compared to SF, it exhibited comparable pozzolanic reactivity with SF due to the nano-scale pores on its each single particle, leading to a higher specific surface area. The optimal replacement levels of SF and RHA were 10% by weight of cement in pastes and concretes. Although addition of SF and RHA led to a significant reduction in slump for the fresh mixtures, inclusion of up to 30% of SF or 15% of ground RHA did not adversely affect the strength of concretes. At the same mix, incorporation of finely-ground RHA in cement composites provided comparable mechanical properties, hydration degree, and durability with SF blended cement composites, owing to the porous structure and high specific surface area of RHA particles. Microstructure morphology analysis of concretes explored by scanning electron microscopy (SEM) further validated the strength and the durability test results.

Properties of self-compacting lightweight concrete

Abstract This paper compares the fresh and hardened properties of self-compacting lightweight concretes (SCLCs). The effects of different dosages of binder materials, sand ratios and types of fine aggregate (i.e.river sand and crushed stone fine) on the performance of fresh SCLC and the properties of hardened SCLC were examined. Results indicated that air dry bulk density of SCLC ranged from 1760 to 1800 kg m–3, oven dry density ranged from 1630 to 1660 kg m–3 and elastic moduli ranged from 22 to 28 GPa. For fresh SCLC, the T 50 values decrease irrespective of the types of fine aggregate used and there is an optimal binder content >550 kg m–3. The bulk density of the concretes decreases slightly with increasing binder content.

Shear strengthening of polystyrene aggregate concrete beams with near surface mounted GFRP bars

Abstract The application of near surface mounted (NSM) fibre reinforced polymer (FRP) bars is emerging as an innovative and promising technology for increasing flexural and shear strength of deficient reinforced concrete members. In order for this technique to perform effectively, a series of experimental works have been carried out to characterise the flexural and shear behaviour of reinforced concrete members strengthened with NSM FRP bars. The latter is the focus of this paper, and some of the preliminary results are included. A total of eight beams were loaded under a two-point symmetrical bending test. The parameters examined were the type and inclination of NSM bars and the type of adhesives employed. Characterisation of the tested beams, including mode of failure and load–deflection response, is presented and discussed in this paper. The results of this investigation showed that the NSM bonded glass FRP bars can be used to significantly increase both shear and flexural stiffness and the ultimate moment capacity of the beams, with an efficiency that varies depending on the tested variables.

Study of short term shrinkage and creep of lightweight concrete

Abstract In the present paper, short term shrinkage and creep of lightweight concrete up to 100 days of designed strengths 25 and 35 MPa were investigated. Results indicated that the autogenous and total shrinkage of lower strength lightweight concrete were higher. The total shrinkage of the G35 mix was 320 × 10–6 comparable to 415 × 10–6 of the G25 mix after 3 months. Though the total creeps were the same at 590 × 10–6, the basic creeps per MPa of the G35 concrete mix are 16˙4% lower than the G25 mix after 3 months. The specific creeps of G35 and G25 mixes were 42˙8 × 10–6 and 60˙9 × 10–6 respectively after 3 months. The larger shrinkage and creep values of the lower grade lightweight concrete mixes were caused by the higher porosity ratio of the lightweight aggregates used and the dissipation of moisture kept inside the aggregate due to prewetting of aggregate during concrete mixing.

Bronchial Rn dose survey for residences

The bronchial dosimeter for Rn progeny proposed by Yu and Guan in 1998 was employed to survey the bronchial dose from Rn progeny in 30 residences in Hong Kong. An average bronchial deposition fraction of Rn progeny was obtained as 0.0334, which gave an average dose conversion factor (DCF) of 8.5 mSv WLM-1. The mean values of potential alpha energy concentration (PAEC) deposited in the tracheobronchial region (PAECT-B), total PAEC in air (PAECT), annual effective dose (E), concentration of Rn gas (RC) and annual dose conversion factor (ADCF) for all the residential sites combined were 0.11 +/- 0.05, 3.1 +/- 1.4 mWL, 1.2 +/- 0.5 mSv yr-1, 23 +/- 10 Bq m-3 and 0.055 +/- 0.020 (mSv yr-1 per Bqm-3), respectively, with air-conditioned sites (AC sites) and non-AC sites having significantly different mean ADCF values. The indoor relative humidity affected PAECT and RC with high confidence levels (> 95%).

Training programme for supervisors: An element in quality assurance of the construction industry

The purpose of this article is briefly to describe the developing and structuring of a concrete technology course for the construction companies in Hong Kong. Statistics on student profile and course enrolment are presented to demonstrate the characteristic of the local industry and course development. Over the year, more than 269 candidates coming from 33 companies have successfully completed the course which has established its status in the industry. Over 48.7 per cent of the enrolment comes from concrete suppliers, indicating the concern for the standard of their staff and showing their commitment towards quality production of concrete.