Study on Strengthening Mechanism of Epoxy Resin/Rubber Concrete Interface by Molecular Dynamics Simulation

Rubber concrete has high environmental and economic benefits. However, the difference in the physical and chemical properties of the interface causes a weak interface between rubber and concrete, which limits the use of rubber concrete to a certain extent. Based on the macroexperiment of epoxy resin (EP) modified rubber concrete, from the nanoscale level, three interface models of Rh (natural rubber)/C-S-H, EP/C-S-H, and Rh/EP/C-S-H were constructed by molecular dynamics simulation to explore the interaction between epoxy resin and rubber cement-based interface and reveal its microreinforcement mechanism. The results of interaction energy, radial distribution function, and mean square displacement show that the addition of EP not only improves the interface interaction energy between Rh and C-S-H but also provides a large number of hydrogen bond donors and receptors, promotes the diffusion of Ca, and increases the adhesion between Rh and cement matrix. The results of the analysis of mechanical properties show that the elastic modulus of the rubber concrete interface model is improved and the interface properties are improved after adding EP.

Experimental Study on Freeze-Thaw Effects on Creep Characteristics of Rubber Concrete

Crumb Rubber Concrete (CRC) can exhibit high freeze-thaw resistance, but its long-term creep behavior under various freeze-thaw conditions remains unclear, which is essential for the safety of pavement engineering in the severe cold zone. In this study, the freeze-thaw effects on the creep behavior of CRC under different stress levels were systematically analyzed by testing the compressive strength, the uniaxial creep under different stress levels, and the dynamic elastic modulus. To simulate real conditions of the road environment in the cold area, the lowest temperature of −20°C, six freeze-thaw cycles of 0, 30, 60, 90, 120, and 150, and seven different stress levels of 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 of the compressive strength were employed in this study. The test results showed that the mass loss rate was 6%–11.2% and the compressive strength decreased by 6.51%–47% after 30–150 freeze-thaw cycles. When the stress level reached its critical value, the relative dynamic elastic modulus decreased with the number of freeze-thaw cycles. After 150 freeze-thaw cycles, failure did not appear when the stress level was lower than 50%, above which the creep failure was determined by the stress level and the number of the freeze-thaw cycles. Meanwhile, it was found that the cracking and interfacial debonding between the matrix and the crumb rubber particle were the main reasons for the degradation of CRC creep performance. Finally, a Weibull distribution-based empirical creep damage model was established to predict the failure of CRC, which can enhance its application to related engineering.

30 years of rubberized concrete investigations (1990-2020). A bibliometric analysis

This work presents a bibliometric study of the literature on the use of caucho in the construction to promote the interest of using rubber as a prime material to reduce pollution at a global level. Published papers in the period 1999-2020 in both databases, Scopus and Web of Science (WoS), are taken into account using the Methodi Ordinatio and the VOSviewer software. A total of 967 documents on the use of rubber in structural and non-structural concrete have been published in this period and 1182 authors have contributed on the subject. Since 2010, the interest of researchers in introducing rubber in construction has increased. China, USA and Australia are the countries with the greatest interest in investigating about rubber-concrete.

Experimental Investigation of Internal Friction in Rubber Concrete and Fiber-Reinforced Rubber Concrete

Постановка задачи. Работа посвящена экспериментальному определению внутреннего трения в таких материалах, как каучуковые бетоны (каутоны) на основе низкомолекулярного полибутадиенового каучука смешанной микроструктуры марки ПБН и цис-полибутадиенового низкомолекулярного каучука марки СКДН-Н, с помощью метода импульсного воздействия. Результаты. Установлено, что каутон на основе каучука марки ПБН обладает более выраженными вязкоупругими свойствами по сравнению с аналогичным материалом на основе каучука марки СКДН-Н. Введение стальной фибры снижает внутреннее трение в материале, в то время как полимерная фибра дает обратный эффект. Это связано с тем, что волокнистая пропиленовая фибра служит дополнительным демпфирующим материалом, усиливающим диссипацию энергии при динамическом нагружении. Выводы. Впервые измерено внутреннее трение для каутона и фиброкаутона. Полученные данные являются дополнительными микроструктурными характеристиками материалов, описывающими их вязкость. Определены реальные значения исследуемых величин, которые позволяют применять модели с дробными производными при расчете строительных конструкций из каутона и фиброкаутона на динамические воздействия с учетом явления вязкоупругости. Statement of the problem. The paper is devoted to the experimental identification of damping for such materials as butadiene rubber (BR) and cis-butadiene low-molecular weight rubber (SKDN-N) based concrete and fiber-reinforced rubber concrete by means of the Impulse Excitation Technique (IET). Results. It was found that BR based concrete with or without fiber-reinforcement shows more obvious viscoelastic properties than the corresponding materials based on SKDN-N rubber. The addition of steel fiber reduces internal friction in the material, while propylene fiber has the opposite effect. This is due to the fact that the fibrous propylene acts as an additional damping material, which enhances energy dissipation under dynamic loading. Conclusion. The internal friction in the rubber concrete and fiber-reinforced rubber concrete has been measured for the first time. The obtained data are the additional microstructural characteristics of polymer concrete, which describes its viscosity. The actual values of the investigated quantities have been determined, which makes it possible to use the models with fractional derivatives in the calculations of building structures made of rubber concrete and fiber-reinforced rubber concrete for dynamic loads taking into account the phenomenon of viscoelasticity.

Optimal Design Approach for One-dimensional Rubber-Concrete Periodic Foundations based on Analytical Approximations of Band Gaps

This research investigates band gaps and frequency responses of one-dimensional periodic structures and further presents an optimal design approach for one-dimensional rubber-concrete periodic foundations based on the proposed analytical formulas for approximating the first few band gaps. The presented design approach is optimal for being able of globally searching the best solution which effectively cooperates the band gaps with the superstructure’s resonance frequencies. Firstly, frequency responses of one-dimensional periodic structures and the corresponding approximation method are studied. Furthermore, analytical approximation formulas for the first few band gaps, localization factor, attenuation coefficient, and frequency responses of one-dimensional rubber-concrete periodic foundations are proposed and verified. Lastly, inspired by the proposed analytical approximation for computing band gaps, an optimal design approach for one-dimensional rubber-concrete periodic foundations is presented and applied to a practical example, whose optimality is verified theoretically and numerically.