•RCA can be fully used in pavement lower layers and concrete pavement surfacing.•There is disparity in reported replacement levels of RCA for asphalt mixtures.•RCA mixes can be improved by chemical, ...thermal, and biological treatments.•RCA is a sustainable alternative to natural aggregates for highway pavements.
Highway pavements are very expensive infrastructures that consume very high amounts of natural resources. Utilisation of recycled concrete aggregates (RCA) for highway pavement construction can bring a number of benefits towards environmental, economic and societal sustainability. This would reduce the carbon footprint of the construction industry, result in natural resource conservation, reduction in harmful emissions, and minimisation of cost of pavement construction. This paper reviews available literatures on the use of RCA for highway pavements. Both flexible and rigid pavements were covered. The studies revealed that RCA can be applied in all pavement layers; subgrade, capping, subbase, roadbase, and surfacing. The physical and mechanical properties of the RCA and how they affect its performance were studied and compared with those of natural aggregates (NA). Available techniques for improving the performance of RCA in concrete and asphalt mixes were also discussed. The benefits and sustainability gains of RCA utilisation were summarised from available life cycle assessments conducted in the literatures. RCA has been considered as a feasible sustainable alternative to NA in highway pavement applications, but there still exists a large disparity in the recommendations of the replacement levels for asphalt mixes. To ensure that the pavements are sustainable without compromising their quality and functionality, the utilisation of RCA should be encouraged after further indebt studies that would lead to a more consensus standard specifications and guidelines.
In 2010, Klang Valley has only 17% trips each day were completed using public transport, with the rest of the 83% trips were made through private transport. The inclination towards private car usage ...will only get worse if the transport policy continues to be inefficient and ineffective. Under the National Key Economic Area, the priority aimed to stimulate the increase of modal share of public transport in the Klang Valley to 50% by 2020. In the 10th Malaysia Plan, the Klang Valley Mass Rapid Transit was proposed, equipped with 141 km of MRT system, and will integrate with the existing rail networks. Nevertheless, adding kilometers into the rail system will not help, if people do not make the shift from private into public transport. This research would like to assess the possible mode shift of travellers in the Klang Valley towards using public transport, based on the utility function of available transport modes. It intends to identify the criteria that will trigger their willingness to make changes in favour of public transport as targeted by the NKEA.
This study aims to analyse the life-cycle assessment of biohydrogen production from palm oil mill effluent (POME) in a pilot-scale up-flow anaerobic sludge blanket fixed-film reactor. The SimaPro LCA ...software and ReCiPe 2016 impact assessment method were used. Electricity usage was found to be a significant source of environmental impacts, with 50–98% of the total impacts. Furthermore, an improvement analysis was conducted, resulted in a reduction in all impacts, especially global warming impact with 77% reduction from 818 to 189 kg CO2-eq per kg biohydrogen. While shifting the pilot reactor to Sarawak may further lessen the impact to 142 kg CO2-eq due to cleaner grid in that region. Besides, if the environmental burden avoided due to usage of POME is considered, the global warming impact can be further reduced to 54.9 kg CO2-eq. Thus, the pilot reactor has huge potential, especially in utilizing waste to produce bioenergy.
•The LCA of bio-H2 production from POME in the pilot-scale reactor was conducted.•Electricity usage contributed highest impact especially in global warming potential.•Improvement analysis was conducted to reduce impact to 54.9 kg CO2 eq per kg H2.
Paving block is a widely used pavement material due to its long service life, fast and easy production and easily replaced for maintenance purpose. The huge production volume of paving blocks ...consumes large amount of natural aggregates such as sand and granite. Therefore, there is a necessity to review the utilization of alternative materials as the aggregate replacement to cut down both the consumption of natural resources and disposal of various waste. This paper thus analyses published works and provides a summary of knowledge on the effect of utilizing selected waste materials such as soda-lime glass, cathode ray tube (CRT) glass, recycled concrete waste, marble waste, crumb rubber (CR) waste and waste foundry sand (WFS) as aggregate replacement in concrete paving blocks fabrication. The influence of each waste material on the properties of paving block is discussed and highlighted in this paper. The adherence of the waste material paving block to the standard requirements is also presented to provide a clear direction on the utilization of these materials for practical application. Soda-lime glass, CRT glass, pre-treated RCA and calcined WFS have the potential to be utilized in high quantities (30–100%), normal RCA and marble waste can be incorporated in moderate amount (30%) while CR waste and WFS is limited to low amount (6–10%). In overall, the usage of waste materials as aggregate replacement has good potential for producing eco-friendly concrete paving block towards the sustainable development of construction material.
As concrete is one of the most commonly used construction materials, there is a massive production of cement, which causes cement manufacturing to be an energy-intensive industry. A significant ...amount of the cost of cement production, ranging from 20% to 25%, is attributed to thermal energy. In addition, the action of mining and burning fossil fuels results in the unfavorable emission of hazardous compounds into the environment. Therefore, the switch from conventional fossil fuels to alternative fuels (AFs) in the cement manufacturing business has attracted attention due to environmental and financial concerns. In this paper, four commonly used AFs are discussed, which are waste tires, municipal solid waste, meat and bone meal, and sewage sludge. It is found that each AF has a unique calorific value and properties, attributed to its source, treatment, and technology. Furthermore, the availability of AF is important as the amount varies depending on the location. In addition, their effects on gaseous emissions from the cement plant and the quality of clinker are found to be inconsistent. Thus, there will not be a single best type of AF option to be used in the cement industry. A good AF should be able to provide sufficient thermal energy while reducing the environmental impacts and costs. A careful analysis and multicriteria decision-making approach are always vital when employing AFs in order to prevent environmental problems, cost increases, as well as clinker quality degradation.
Coal fly ash and granulated ground blast furnace slag (GGBS) are more widely used as supplementary cementitious materials in cement production. This study investigates the influence of high-volume ...ordinary Portland cement (OPC) replacement with fly ash and/or GGBS on the flow, compressive strength and environmental impacts of the resulting binary and ternary blends. Experimental results showed that the use of ternary blends enhanced the flow characteristics, specifically with the incorporation of 20% to 30% fly ash. Overall, partially replacing OPC in the ternary and binary blends reduced the early-age compressive strength, while an improvement to the later-age strength was observed. Nevertheless, beyond 28 days, the inclusion of 20% and 30% of fly ash in the ternary blends exhibited the highest compressive strength. The results from life cycle assessment (LCA) revealed that the OPC is the key contributor to the environmental impact where 50% and 70% OPC replacement reduced on average 44% and 61% of the total impacts, respectively, regardless of the blending system. As such, effectively the eco-mechanical performance of blends was improved. The 70% ternary blends gave superior eco-mechanical performance (lowest GWP/strength ratio) in the presence of 10% and 20% of fly ash. This study also showed that the artificial neural network model can be developed and adequately used to predict the properties of the OPC blends (i.e. eco-mechanical performance).
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Railway and metro transport systems (RS) are becoming one of the popular choices of transportation among people, especially those who live in urban cities. Urbanization and increasing population due ...to rapid development of economy in many cities are leading to a bigger demand for urban rail transit. Despite being a popular variant of Traveling Salesman Problem (TSP), it appears that the universal formula or techniques to solve the problem are yet to be found. This paper aims to develop an optimization algorithm for optimum route selection to multiple destinations in RS before returning to the starting point. Bee foraging behaviour is examined to generate a reliable algorithm in railway TSP. The algorithm is then verified by comparing the results with the exact solutions in 10 test cases, and a numerical case study is designed to demonstrate the application with large size sample. It is tested to be efficient and effective in railway route planning as the tour can be completed within a certain period of time by using minimal resources. The findings further support the reliability of the algorithm and capability to solve the problems with different complexity. This algorithm can be used as a method to assist business practitioners making better decision in route planning.
Mixed-use developments (MXDs) are a single development project that integrates and interacts with different land uses. Traffic is estimated to be reduced with such development. However, there is no ...standard procedure is available to estimate the MXD trip generation rates in Malaysia. The Malaysian Trip Generation Manual (MTGM) is the guidelines currently been used to forecast future trips for single land use. If the trip generation rates for multiple land uses are summed as MXD trips, the total trips will be overestimated without considering the internal trip capture. This study aimed to establish an improved method for estimating the MXD trip generation rates. Four MXD observation sites were selected in Klang Valley. Traffic survey counts were conducted considering person-trip, including passengers in vehicles and pedestrians. The results revealed that the MXD trip generation rates with MTGM were higher than actual traffic counts during peak hours. The MXD adjustment factor was established as 0.63, which can be applied by multiplying the MTGM trip generation rates to reduce the generated MXD trips in PCU per hour. This research has formulated a new data collection method by integrating person counts, alongside with new guidelines for pedestrian counts. The findings provide an option to adjust the MXD trips and prevent from overestimating future trips, which may result in overdevelopment and spending on mitigation measures in urban planning and road infrastructure.
•EVs running on Malaysian electricity mix produce larger environmental impacts vs HEVs.•EVs running on Malaysian electricity mix produce comparable environmental impacts vs ICEVs.•Environmental ...profile of EVs are linked to the national electricity mix.•Electricity must be made cleaner before the electrification of urban transport system.
The increase of public attention, scientific research and political interest in environmental problems associated with transportation has provided the motivation for re-invention of electric vehicles. However the usage of grid-dependent EVs with a high-carbon electricity grid might produce more damage to the environment. This study aims to provide an environmental impact comparison of ICEVs, HEVs and EVs during their usage cycle, by modeling their energy consumption (electricity or fuel) and the supply chains of the supplied energy, (well-to-wheel) based on a life cycle assessment. The results show that running EVs with the existing mixed sources of electrical energy produce larger impacts on the environment 60% of the time; when compared to HEVs. When compared to ICEVs, EVs produce a larger environmental impact on 7 out of 15 environmental impact categories. Overall the environmental impacts of EVs are substantial based on the well-to-wheel analysis. It will continue to be so if no change is made to the methods of electricity generation in the near future. Given that the environmental profile of EVs is linked with the existing national electricity generation mix, the national electricity supply must be made cleaner before the electrification of the urban transport system.
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