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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 init...

In this study, incinerated sewage sludge ash (ISSA) was applied to replace ordinary portland cement (OPC) and quick (unhydrated) lime at different ratios of 0%, 20%, and 50% for improving t...

A considerable amount of solid wastes is generated every year from construction and demolition (C&D) activities in Hong Kong. The C&D waste can be classified into inert and noninert wastes, in which the inert waste is normally disposed of in public fills as reclamation materials and the noninert waste is dumped at landfills. Under the current waste generation trend, all landfills and public fills in Hong Kong will be used up within a few years. To tackle this problem, in December of 2005, the Hong Kong Government implemented the Construction Waste Disposal Charging Scheme (CWDCS) to provide financial incentives to C&D waste generators to reduce waste and encourage reuse and recycling. This paper presents the results of a study to explore the perceptions of the Hong Kong construction participants toward the CWDCS after three years of implementation. The study was conducted by a survey with follow-up interviews to experienced professionals in the building industry. The results revealed no consensus ...

The use of green specifications as a contractual tool to promote sustainable development should be adopted in the construction industry. The definition and characteristics of green specifications are presented in conjunction with the results of a cross-sectional survey on the possible barriers to their implementation. Generally, construction stakeholders agree that environmental considerations should be included in construction specifications but their underlying motive may be simply for satisfying mandatory requirements. Among the potential barriers identified, the additional cost associated with green requirements is perceived to be the most dominant barrier, followed by possible delay and a limited pool of competent suppliers. Although the crucial barriers based on overall responses were identified, different groups of stakeholders have shown their concerns on particular barriers. Hence, their concerns should be addressed with due regard to these differences during implementation of green specification...

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 f...

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...

The cement paste attached to natural aggregates has a significant effect on the quality of recycled concrete aggregates (RCAs) because it usually has higher porosity and lower strength than natural aggregates. This work attempted to improve the quality of RCAs through carbonation of the attached cement paste. During carbonation reactions, CO2 reacted with Ca(OH)2 and calcium silicate hydrate (C─S─H) to form CaCO3 and silica gel, which filled the pores in the attached cement paste. Thus, carbonation increased the density, and decreased the water absorption and crushing values of the RCAs. It, thus, increased the flowability and compressive strength and decreased drying shrinkage of the recycled aggregate mortars.

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.

The lack of the expertise and resources, the unavailability of sufficient and complete operations data, and the absence of relevant site information present obstacles to applying combined simulation modeling in practice. Construction modelers are required to make critical decisions in a short turnaround time for planning operations and improving productivity. Thus, a more convenient discrete event simulation-based approach in simulating the production capacity of the continuous plant given limited data availability is desirable and formalized, which essentially discretizes the modeling of continuous elements in a predominantly discrete system without loss of significance or accuracy. As such, a direct application of a discrete simulation method intended for construction applications will offer a straightforward, sufficient solution to model the whole system. A concrete pumping case is used to illustrate the proposed approach. The effectiveness of the proposed approach is further demonstrated to ta...

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 ...

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.