ABSTRACT
This study investigates the electrical heating (also known as Joule heating) characteristics of cementitious composites containing multi-walled carbon nanotubes (CNT) and carbon fibers (CF) as electrically conductive media in an attempt to develop an eco-friendly and sustainable solution to snow and ice removal on roadway pavements during the winter season. Various dosages of CNT and CF between 0 and 1.0% (by weight of cement) were tested to find the optimum mixture proportions that yield high-energy and efficient electrical-heating performance with superior mechanical properties. The electrical properties were characterized by measuring the electrical resistivity and temperature rise when attached to a power source. Furthermore, this study examined how the crack width affects the electrical resistivity of cementitious composites containing CNT and/or CF. Compressive and flexural strengths were also measured at different ages of 1, 3, 7, and 28 days to identify how the additions of CNT and CF affect the mechanical properties. Results have shown that adding CF in combination with CNT substantially reduces the electrical resistivity and, in turn, improves the heating performance, as CFs further densify the electrically conductive network in the hydrated matrix; adding either CNT or CF alone was not an effective option to enhance the electrical characteristics. The findings of this study are expected to provide essential information for the design and construction of an electrically heated concrete pavement system with promoted energy efficiency, which will offer a promising solution to enhance winter road maintenance, improve public safety, and provide substantial social cost savings.
ABSTRACT
A new constitutive model for Q235B structural steel is proposed, incorporating the effect of dynamic strain aging. Dynamic strain aging hugely affects the microstructural behavior of metallic compounds, in turn leading to significant alterations in their macroscopic mechanical response. Therefore, a constitutive model must incorporate the effect of dynamic strain aging to accurately predict thermo-mechanical deformation processes. The proposed model assumes the overall response of the material as a combination of three contributions: athermal, thermally activated, and dynamic strain aging stress components. The dynamic strain aging is approached by two alternative mathematical expressions: (i) model I: rate-independent model; (ii) model II: rate-dependent model. The proposed model is finally used to study the mechanical response of Q235B steel for a wide range of loading conditions, from quasi-static loading ( ε Ë = 0.001 s - 1 and ε Ë = 0.02 s - 1 ) to dynamic loading ( ε Ë = 800 s - 1 and ε Ë = 7000 s - 1 ), and across a broad range of temperatures ( 93 K - 1173 K ). The results from this work highlight the importance of considering strain-rate dependences (model II) to provide reliable predictions under dynamic loading scenarios. In this regard, rate-independent approaches (model I) are rather limited to quasi-static loading.
ABSTRACT
In the construction field, adhesives are frequently used to improve adhesion between two objects. Epoxy adhesives are applied as long-term solutions, improving the bond between repair materials and existing concrete structures. Experimental investigations of the relationship between the thickness of an adhesive layer and its shear strength have been conducted by a number of industries outside of the construction sector. However, that research used metal plates as adherends when determining the shear strengths of epoxy adhesives. Therefore, this study examines epoxy adhesives' shear strength development when applied to concrete adherends. The test results show that the thickness of the bond layer did affect shear strength development in the epoxy adhesives examined.
