Zhen Leng

Bio: Zhen Leng is an academic researcher from Hong Kong Polytechnic University. The author has contributed to research in topics: Asphalt & Materials science. The author has an hindex of 31, co-authored 119 publications receiving 2485 citations. Previous affiliations of Zhen Leng include RWTH Aachen University & University of Illinois at Urbana–Champaign.

Portland Cement Paste Modified by TiO2 Nanoparticles: A Microstructure Perspective

Abstract: Nanomodified Portland cement paste with a water/cement ratio of 0.4 was prepared with the addition of TiO2 nanoparticles at 0.1, 0.5, 1.0, and 1.5% by mass of cement. The flexural strengths of the prepared cement-based composites were tested, and the fracture surfaces were observed by scanning electron microscopy (SEM). The flexural strength of the nanomodified TiO2 Portland cement paste reached the highest value with a dosage of 1.0 mass %. The SEM observation shows that admixing of the TiO2 nanoparticles largely decreased the quantity of internal microcracks in the cement paste. A new type of needle-shaped hydration product was observed, and its potential growth mechanism was proposed. Atomic force microscopy was introduced to observe the microstructure of nanomodified Portland cement paste, and the results show that the nanoroughness of the hardened cement pastes with admixed TiO2 nanoparticles was much lower than that without the TiO2 nanoparticle addition. Coupled with X-ray diffraction data, the mor...

In-Place Hot-Mix Asphalt Density Estimation Using Ground-Penetrating Radar

Abstract: This research proposes the innovative use of ground-penetrating radar (GPR) for effectively, continuously, and rapidly estimating in-place hotmix asphalt (HMA) density. On the basis of electromagnetic mixing theories, three candidate models were developed to determine HMA's dielectric constant, considering dielectric and volumetric properties of its three major components of HMA: air, binder, and aggregate. Laboratory tests were conducted on midsize HMA slabs (60 cm x 60 cm x 7.5 cm) to evaluate the models. After evaluating and comparing the three models, it was determined that the prediction model based on the Rayleigh mixing theory was the most accurate. The selected model was calibrated with a field core and then validated using field GPR measurements of a composite pavement with an HMA surface. The selected model provided accurate HMA density within a reasonable range.

Methods of Numerical Integration

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A review of Ground Penetrating Radar application in civil engineering: A 30-year journey from Locating and Testing to Imaging and Diagnosis

Abstract: The GPR (Ground Penetrating Radar) conference in Hong Kong year 2016 marked the 30th anniversary of the initial meeting in Tifton, Georgia, USA on 1986. The conference has been being a bi-annual event and has been hosted by sixteen cities from four continents. Throughout these 30 years, researchers and practitioners witnessed the analog paper printout to digital era that enables very efficient collection, processing and 3D imaging of large amount of data required in GPR imaging in infrastructure. GPR has systematically progressed forward from “Locating and Testing” to “Imaging and Diagnosis” with the Holy Grail of ’Seeing the unseen’ becoming a reality. This paper reviews the latest development of the GPR’s primary infrastructure applications, namely buildings, pavements, bridges, tunnel liners, geotechnical and buried utilities. We review both the ability to assess structure as built character and the ability to indicate the state of deterioration. Finally, we outline the path to a more rigorous development in terms of standardization, accreditation, and procurement policy.