Research

Development of Sound-absorbable High Performance Concrete (SHPC) to mitigate traffic noise

In order to effectively control ambient noise from transportation, this experimental and theoretical study aims to develop sound-absorbable high performance concrete (SHPC). Effective continuous voids are needed to be promoted for the noise control and enough mechanical strength should be secured at the same time in order for structural purpose. Various types of raw materials including natural fibers and high strength material design should be incorporated for this purpose. Vegetation concrete design will also be considered in the following stage of the research.

vegetation concrete track

 

Development of Low-cost & Eco-friendly Ultra High Performance Concrete (UHPC) and its applications

UHPC is generally known as the most advanced cement-based construction materials and possess superior mechanical properties, including a compressive strength greater than 150 MPa, high ductility, impact resistance and durability. In order to achieve such impressive mechanical properties, most UHPC mixtures intentionally exclude coarse aggregates, which leads to high strength by minimizing the interfacial transition zone. The UHPC developed by us adopted an innovative design concept that incorporates proper coarser fine aggregates without sacrifice of mechanical properties, an innovation that has never been achieved before for UHPC. This way, our UHPC can lower material cost by up to 22% compared to standard UHPC.

The world’s first railway sleepers using UHPC were recently developed and designed to fully utilize the superior mechanical benefits of composites. The new design minimizes steel reinforcements in railway sleepers since all the reinforcing steel bars can be removed and the diameter of prestressed bars can be reduced from 11.0 mm to 9.2 mm, reducing steel usage by more than 25% compared to conventional concrete sleepers. Furthermore, the high durability, ductility and impact resistance of the UHPC makes it possible to extend their lifespan remarkably compared to conventional concrete sleepers. New innovative applications of the developed UHPC is wide open!

UHPCsleeper

Innovative laser fabrication technology on construction materials

Even though laser fabrication technology have been widely used in many industrial applications, there are relatively few applications in the field of construction industry. We strongly believed that this technology could apply not only to the concrete fabrication and vibration free tunneling but also to deconstruction of old nuclear power plants.

laser

Characterization of Ultra High Performance Concrete (UHPC) under impact loading

The experimental effort of this work focuses on investigating the strain rate sensitivity of UHPC as a function of fiber type (straight or twisted), characteristics and volume fraction. Low strain rate tests are conducted using a hydraulic actuator, whereas high strain rate tests are conducted using a new device that employs suddenly released elastic strain energy to apply an impact pulse. Developed and optimized through computational modeling, the new device permits accurate and practical testing of UHPC specimens in direct tension, under high strain rate, and can capture both hardening and post peak responses. It is compact compared to existing test methods and permits the use of specimens that are similar in size and geometry to the specimens tested with the hydraulic actuator.

A key experimental observation is that UHPC becomes significantly more energy dissipative in tension under increasing strain rates, which highlights the material’s potential for use in impact- and blast-resistant applications. Although specimens with twisted steel fibers show somewhat better mechanical properties than specimens with straight fibers due to the untwisting mechanism, comparable benefits could be obtained by using straight fibers with higher aspect ratios. Crack propagation studies show that crack speed increases asymptotically as notch tip strain rate increases.

The analytical portion of the study focuses on the source of strength enhancement for concrete materials under high rate tensile loadings, a topic of current controversy in the literature. Dynamic fracture models considering crack velocity dependency prove that strain rate sensitivity is strongly associated with the characteristics of dynamic crack growth, especially the asymptotic nature of crack speed versus strain rate and inertial effects at the crack boundaries. The theoretical observations are corroborated with experimental data in the literature and new data produced by this work.

impact

Elastic and elastoplastic multi-level damage models for composites with imperfect interface

Micromechanics-based multi-level damage models are developed to predict elastic and elastoplastic overall behavior and damage evolution in composite materials. First of all, Eshelby’s tensor for an ellipsoidal inclusion with slightly weakened interface is adopted to model particles with imperfect interface in particle reinforced composites and fibers with imperfect interface in fiber reinforced composites, respectively. Imperfect interfaces between inclusion and matrix in composites occur as deformations or loadings continue to increase. As an effort to realistically reflect the effect of loading history on the progression of imperfect interface, a multi-level damage model in accordance with the Weibull’s probabilistic function is developed. It is assumed that the progression of imperfect interface is governed by the average stress of inclusion. To the estimate overall elastoplastic behavior of ductile matrix composites, an effective yield criterion is derived based on the ensemble-volume averaging process and the first-order effects of eigenstrains due to the existence of spherical inclusions.

As applications, the overall elastic and elastoplastic stress-strain curves of particle reinforced brittle matrix composites, particle reinforced ductile matrix composites, and unidirectional fiber reinforced brittle matrix composites under uniaxial, biaxial, and triaxial loading are investigated in detail. A series of parametric analysis are carried out to investigate the influence of model parameters. Furthermore, the proposed multi-level damage models are compared with available experimental data in the literature to verify the accuracy of the models. Finally, proposed micromechanics-based evolutionary multi-level damage model for unidirectional fiber reinforced composites is implemented into a finite element program ABAQUS to predict behavior of laminated composites under various loading conditions.

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PROJECTS

NRF (한국연구재단) | A study on the reduction of railway noise through the development of structural vegetation concrete | Jun 2019-Feb 2021.

KAIA (국토교통과학기술진흥원) | Development of sustainable railway sleepers for upcycling of waste plastics | Apr 2019-Dec 2021.

KRRI (한국철도기술연구원) | A study on the analysis of the sound absorption characteristics and the durability of sound absorbable concrete for structural application | Feb 2019-Nov 2019.

UNIST | Material characterization research on cement mortar after high power laser interaction | Jan 2019-Jan 2022.