Aimin Sha

Greenhouse Gas Emissions from Asphalt Pavement Construction: A Case Study in China

In China, the construction of asphalt pavement has a significant impact on the environment, and energy use and greenhouse gas (GHG) emissions from asphalt pavement construction have been receiving increasing attention in recent years. At present, there is no universal criterion for the evaluation of GHG emissions in asphalt pavement construction. This paper proposes to define the system boundaries for GHG emissions from asphalt pavement by using a process-based life cycle assessment method. A method for evaluating GHG emissions from asphalt pavement construction is suggested. The paper reports a case study of GHG emissions from a typical asphalt pavement construction project in China. The results show that the greenhouse gas emissions from the mixture mixing phase are the highest, and account for about 54% of the total amount. The second highest GHG emission phase is the production of raw materials. For GHG emissions of cement stabilized base/subbase, the production of raw materials emits the most, about 98%. The GHG emission for cement production alone is about 92%. The results indicate that any measures to reduce GHG emissions from asphalt pavement construction should be focused on the raw materials manufacturing stage. If the raw materials production phase is excluded, the measures to reduce GHG emissions should be aimed at the mixture mixing phase.

The Greenhouse Gas Emission from Portland Cement Concrete Pavement Construction in China

This study proposes an inventory analysis method to evaluate the greenhouse gas (GHG) emissions from Portland cement concrete pavement construction, based on a case project in the west of China. The concrete pavement construction process was divided into three phases, namely raw material production, concrete manufacture and pavement onsite construction. The GHG emissions of the three phases are analyzed by a life cycle inventory method. The CO2e is used to indicate the GHG emissions. The results show that for 1 km Portland cement concrete pavement construction, the total CO2e is 8215.31 tons. Based on the evaluation results, the CO2e of the raw material production phase is 7617.27 tons, accounting for 92.7% of the total GHG emissions; the CO2e of the concrete manufacture phase is 598,033.10 kg, accounting for 7.2% of the total GHG emissions. Lastly, the CO2e of the pavement onsite construction phase is 8396.59 kg, accounting for only 0.1% of the total GHG emissions. The main greenhouse gas is CO2 in each phase, which accounts for more than 98% of total emissions. N2O and CH4 emissions are relatively insignificant.

Effect of styrene–butadiene rubber latex on the properties of modified porous cement-stabilised aggregate

As road base materials, porous cement-stabilised aggregates (PCSA) can reduce the erosion damage caused by the water inside pavement structure. However, due to the reduced deformation resistance and anti-cracking ability associated with the high porosity, the application of PCSA has been held back. A laboratory experiment was conducted in this study to improve the cracking properties of PCSA through the incorporation of the styrene–butadiene rubber (SBR) latex. The effects of the SBR latex usage on permeability, compressive strength, flexural strength and anti-freezing ability (AFA) of PCSA were investigated. In addition, the modification mechanisms of the SBR latex on the PCSA properties were analysed. Test results indicated that the air voids and permeability coefficient decreased with the increase in the SBR latex dosages. The flexural strength and AFA were improved when the SBR latex dosages are between 10% and 15%. 7 d compressive strength has a slight decrease, while the 28 d compressive strength is increased. The significant increase in flexural strength and AFA can be attributed to the interpenetrating matrices formation, stretching effect as well as flexibility enhancement after adding the SBR latex.

Portland Cement Hydration Behavior at Low Temperatures: Views from Calculation and Experimental Study

Environmental condition affects the property of construction materials. This study gives an initial understanding of Portland cement hydration under low temperatures from the views of laboratory experiments (including electrical resistivity, degree of hydration (DoH), and maturity) as well as thermodynamic calculation. The hydrates of Portland cement at the given period were detected with X-ray diffraction (XRD), and their microstructure was observed by scanning electron microscope (SEM). Experiment result (i.e., DoH and electrical resistivity) indicated that the hydration of Portland cement was delayed by low temperature without hydration stopping at −5°C. Based on a basic kinetics model, the thermodynamic calculation predicted that the final hydrate differs in dependence on environmental temperatures. The mechanical behavior trend of Portland cement paste affected by low temperatures potentially is linked to the appearing of aluminate compounds and reduction of portlandite.

Analysis of Dynamic Response of Asphalt Pavement in Heavy Vehicle Simulator Tests

In order to analyze the dynamic response of asphalt pavement, heavy vehicle simulator (HVS) was used to test with variables of axle load, speed, and temperature on five full-scale test sections with different structures. Pre-embedded strain sensors and pressure cells were used to measure the strain response at the bottom of the surface layer and the vertical stress at the top of the subgrade under wheel load. The results of tests show that the tensile strain at the bottom of surface layer of semi-rigid base asphalt pavement and rigid base asphalt pavement is small. The vertical stress at the top of the subgrade has a good positive exponential relationship with axle load. The maximum tensile strain at the bottom of surface layer gradually decreases with speed and increases with temperature. The tensile strain at the bottom of surface layer of flexible base asphalt pavement is affected by the speed most significantly. The increase rate of strain increases with temperature, which demonstrates the temperature has significant effects on the mechanical properties of the asphalt pavement. Based on the results of HVS tests, a prediction model of tensile strain at the bottom of the surface layer was established. Therefore, this paper could contribute to deepening the understanding of the dynamic response characteristics of asphalt pavement and improving the design of pavement structure.