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This research resorted to the use of construction operations simulation modeling to investigate the cost efficiency of waste-handling practices on the Kai Tak Airport demolition project in Hong Kong. By modeling the site operation of sieving and stockpiling broken concrete, the well-established construction simulation methodology of CYCLONE was contrasted with the newly developed simplified discrete event simulation approach (SDESA). Further, the SDESA model was readily extended to include (1) raw demolition waste collecting and sorting; (2) broken concrete sieving and stockpiling; (3) steel bar recycling; and (4) debris disposal at the landfill. The production rate derived from simulation was indicative of a close match between the simulation model and the actual site system. The resulting simulation model provided a basis for evaluating the cost efficiency of actual site operations and alternative resource provision scenarios being postulated. Through computer simulation, the actual site operation was found smooth and efficient with utilization rates for resources of different types ranging from 79 to 99%. In addition, the cost--time reduction ratios were calculated for four alternatives of resource provisions in comparison with the original base case. The research findings suggested that provided the project budget had satisfied the higher cash flow requirement, doubling the resource provision on site would potentially cut the project duration by half and not increase the total direct cost. CE Database subject headings: Waste management; Computer aided simulation; Simulation models; Demolition; Case reports; Hong Kong; Airports and airfields.

The use of high percentages of recycled aggregates in concrete would usually worsen the concrete properties. This paper tries to address the deficiency of the use of recycled aggregates by systematically presenting results on the influence of incorporating Class F fly ash on concrete properties. In this study, two series of concrete mixtures were prepared with water-to-binder (W/B) ratios of 0.45 and 0.55. The recycled aggregate was used as 0, 20, 50, and 100% by weight replacements of natural aggregate. In addition, fly ash was used as 0, 25, and 35% by weight replacements of cement. The results showed that the compressive strengths, tensile strengths, and static modulus of elasticity values of the concrete at all ages decreased as the recycled aggregate and the fly ash contents increased. Further, an increase in the recycled aggregate content decreased the resistance to chloride ion penetration and increased the drying shrinkage and creep of concrete. Nevertheless, the use of fly ash as a substitute for cement improved the resistance to chloride ion penetration and decreased the drying shrinkage and creep of the recycled aggregate concrete. The results showed that one of the practical ways to utilize a high percentage of recycled aggregate in structural concrete is by incorporating 25-35% of fly ash as some of the drawbacks induced by the use of recycled aggregates in concrete could be minimized. DOI: 10.1061/(ASCE)0899-1561(2007)19:9(709) CE Database subject headings: Fly ash; Strength; Shrinkage; Creep; Aggregates; Recycling.

This research is focused on modeling waste-handling processes in construction, with particular emphasis on how to map out and simulate on-site waste sorting processes. The research proposes an application framework for (1) guiding the development of process mapping models and simulation models; and (2) further assessing the cost effectiveness of on-site waste sorting efforts under practical site constraints (such as labor resource availability, time control on refuse chute usage, and limited working area space in a building site). The connection has been established between the mapping and simulation techniques in the context of modeling waste handling processes in construction sites, such that the process flowchart resulting from the mapping technique can serve as convenient model input to facilitate the creation of a 'dynamic' operations simulation model. A case study of the on-site waste sorting method with one refuse chute for waste classification is presented to demonstrate the complete application framework spanning (1) process mapping; (2) mapping-to-simulation model conversion; and (3) method optimization based on valid simulations. CE Database subject headings: Waste management: Computer aided simulation; Simulation modems; Mapping; Construction management.

This paper presents experimental results on porosity and pore size distribution of fly ash and silica fume modified cement pastes and mortars using mercury intrusion porosimetry. It is found that replacement of cement by fly ash increases the porosity but decreases the average pore size of the pastes at the ages of 28 and 56 days. The additional replacement of cement by up 5% silica fume did not significantly change the pore size distribution and porosity of either the plain cement pastes or the fly ash cement pastes. Interfacial porosity, however, was significantly influenced by incorporating fly ash and silica fume in the mortars. The interfacial porosity was much reduced when fly ash and silica fume were incorporated. Compared with the porosity and average pore size of the pastes and mortars, the interfacial porosity better explains the results of a chloride diffusion test of the fly ash and silica fume concrete in most cases. However, for the concrete with 55% fly ash replacement at 28 days, the drop of ionic concentration of the pore solution seems to be more responsible for the low result of coulomb passed in the test.

The solid waste management plan of 1989 stipulates that landfilling is the chief waste disposal method in Hong Kong. Although currently no charge is involved in solid waste disposal, a landfill charge, covering the capital, operation, and maintenance costs but not the external environmental costs, will soon be introduced. This paper aims to identify the minimum size of the external costs involved with landfilling and incineration in Hong Kong with respect to global and local air pollution, water pollution, noise, and pollution from waste transport. It is found that landfilling results in a slightly lower external cost than incineration. However, factors not included in this paper, such as road casualties that arise from hauling waste and disamenities (a term coined to embrace negative impacts such as eyesores and loss of amenity values) may affect the preference of landfilling over incineration. The present study also shows that the external costs of landfilling are much greater than its capital, operation, and maintenance costs. The considerable size of the estimated external costs of traditional waste management methods demonstrates the need for in-depth and comprehensive research to develop local data.

In this work, the influence of a naphthalene sulfonate–based superplasticizer on the initial corrosion of galvanized steel bars in the simulated concrete pore solution was studied. The initial corrosion process of the galvanized steel in solution with superplasticizer was first monitored. The inhibition effect of the protective layer formed by the superplasticizer and the protective property of the calcium hydroxyzincate (CHZ) passive layer were defined. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) was used to observe the surface morphology of the CHZ passive layer. The results showed that the addition of superplasticizer delayed the initiation of the corrosion process of galvanized steel bar and inhibited the hydrogen evolution. The protective property of the CHZ layer on galvanized steel varied with the concentration of superplasticizer. The inhibition effects of the superplasticizer on the initial corrosion will be beneficial to the quality of the steel–concrete interface. [ABSTRACT FROM AUTHOR]