Influence of Humidity State on Dynamic Resilient Modulus of Subgrade Soils: Considering Repeated Wetting-Drying Cycles

The service performance of subgrade depends on the dynamic resilient modulus (MR) of subgrade soils. Meanwhile, due to complicated conditions such as rainfall infiltration, high temperature evaporation, and groundwater level fluctuations, it can be safely said that the humidity state and repeated wetting-drying (WD) cycles affect the MR of subgrade soils. The object of this study is to conduct a series of dynamic triaxial tests after WD cycles to investigate the characteristics of the MR under various factors. The main results are as follows: (i) the MR decreased with the increase of deviator stress and rose with the growth of confining pressure; (ii) the humidification effect caused by the increase in moisture content attenuated the MR; (iii) the accumulation of WD cycles damaged the MR; however the decline rate was gradually retarded until it was stable with WD cycles 5 times; (iv) the satisfactory prediction model for the MR of subgrade soils considering WD cycles was proposed and verified. It is expected that the findings can provide valuable contributions for road engineering.

Study on Crack Development and Micro-Pore Mechanism of Expansive Soil Improved by Coal Gangue under Drying–Wetting Cycles

Expansive soil is prone to cracks under a drying–wetting cycle environment, which brings many disasters to road engineering. The main purpose of this study is use coal gangue powder to improve expansive soil, in order to reduce its cracks and further explore its micro-pore mechanism. The drying–wetting cycles test is carried out on the soil sample, and the crack parameters of the soil sample are obtained by Matlab and Image J software. The roughness and micro-pore characteristics of the soil samples are revealed by means of the Laser confocal 3D microscope and Mercury intrusion meter. The results show that coal gangue powder reduces the crack area ratio of expansive soil by 48.9%, and the crack initiation time is delayed by at least 60 min. Coal gangue powder can increase the internal roughness of expansive soil. The greater the roughness of the soil, the less cracks in the soil. After six drying–wetting cycles, the porosity and average pore diameter of the improved and expanded soil are reduced by 37% and 30%, respectively, as compared to the plain expansive soil. By analyzing the cumulative pore volume and cumulative pore density parameters of soil samples, it is found that the macro-cracks are caused by the continuous connection and fusion of micro-voids in soil. Coal gangue powder can significantly reduce the proportion of micro-voids, cumulative pore volume, and cumulative pore density in expansive soil, so as to reduce the macro-cracks.

The Volumetric Analysis of Porous Mixture Containing Modified Plastic Waste

Porous Asphalt mixture is an asphalt mixture that uses open graded which has a functions as a drainage so that rainwater will not generate aqua planning on the road surface. The purpose of this study was to analyse the volumetric of modified asbuton with plastic waste and with no plastic waste of a mixture of porous asphalt. In this study we used asphalt porous specimens with dimensions of 10 cm in diameter and 8 cm in height. The specimens were made in 3 variations: 0% plastic, 0.5% 1.0% plastic with 9 specimens. This study uses PET (Polyethylene Terephlate) and laboratory experimental-based, where the gradation of porous asphalt mixture refers to the specifications of the Road Engineering Association of Malaysia (2008). The results of this study describe that there was an increase in VIM value due to the addition of PET plastic waste which is plastic is a replacement of aggregate total weight.

The implementation of public-private partnership models in road engineering

Investment in road infrastructure, i.e. its construction and maintenance, requires significant financial resources. When it comes to undeveloped and developing countries with limited funds, the available resources must be exploited in the most rational manner while obtaining the maximum benefits. One of the possible solutions is a public-private partnership (PPP) model. This paper analyzes different examples of applying PPP models in road engineering and their different rates of success. The analysis highlighted several key factors for the success of road infrastructure designs financed according to a PPP model. The key factors involve the appropriate traffic flow prediction, high-quality design process and construction cost prediction, the public partner’s decisive and strong attitude in negotiation with the private partner, as well as the contract based on positive regulations and containing thoroughly defined obligations of all parties. The conducted analysis should help decision-makers when making decisions regarding the selection of the appropriate PPP model in road design.