4,038 publications found
Sort by
Comparison of thermal conductivity and electrical resistivity of carbon-based cementitious composites

In this study, it was aimed to produce the multifunctional cementitious composites with advanced thermal and electrical performance considering that these composites having high conductivity serve for the purpose of de-icing, electromagnetic shielding, anti-static, anti-corrosion, and so on. Carbon fiber (CF), and carbon powder (CP) were used singly or together to develop cementitious composites having high conductivity. The electrical resistance and thermal conductivity tests were performed to measure the conductivity of the cementitious composites. While mini-spreading test was applied to assess the consistency of the fresh-state cementitious composites containing conductive materials, in order to determine the distribution of the conductive material incorporated, SEM images were analyzed. In addition, compressive strength tests were carried out to determine the mechanical properties. According to the test results, the highest electrical conductivity result (197 Ω on the 1st day) were obtained from the binary mixtures, while the highest thermal conductivity result (1250 mW/m.K on the 7st day) were obtained from the mixtures containing only CP (by volume %0.6). 0.5% carbon fiber by volume mixture performed the worst in terms of mechanical and workability, with 20.5 MPa lower compressive strength and 16 cm lower mini-spread diameter values when compared to the control mixture.

Simplified numerical model for the collapse analysis of RC frame under the oblique impact

The objective of this study is to develop a simplified numerical model that can be used to accurately and quickly conduct the collapse analysis of reinforced concrete (RC) frames impacted by vehicle in 45-degree oblique direction. The simplified numerical model included introduce of a simplified RC frame and a simplified vehicle. For the simplified RC frame, a mixed modeling technique was used in which structural components that experienced serious damage were simulated using detailed elements, while the retained structural components were simulated by macro elements. A constraint algorithm of nodal rigid body in LS-DYNA was adopted to guarantee the displacement compatibility of two kinds of element. For the simplified vehicle model, the spring-mass system was improved on the basis of the energy conservation principle to represent the vehicle in a 45-degree oblique impact. Combining the simplified RC frame model and vehicle model, the impact response of RC frame subjected to vehicle impact was studied and compared with the results of detailed RC frame model impacted by detailed vehicle. The validation confirmed that these introduced simplifications could significantly improve the computational efficiency and ensure the computational accuracy for the collapse analysis of RC frame subjected to vehicle impact.

Characterisation and standardisation of different-origin end-of-life building materials for assessment of circularity

Construction and demolition waste (CDW) management and recycling practices are crucial for transitioning to a circular economy. The focus of this study was on the detailed characterisation of different CDWs (hollow brick (HB), red clay brick (RCB), roof tile (RT), concrete and glass) collected from seven different demolition sites in Turkey. The CDWs were characterised based on particle size distribution, chemical composition and crystalline nature. Pozzolanic activity was evaluated through compressive strength measurements of cement mortars made with 20% cement replacement by CDWs at 7, 28 and 90 days. The results showed that the clayey CDWs exhibited similar physical/chemical properties and crystalline structures. The compositions of the waste concretes varied significantly based on their original materials. All the CDWs satisfied the minimum strength activity index (SAI) for supplementary cementitious materials, with pozzolanic activity influenced by the fineness and silica + alumina contents. The average SAIs for the HB, RCB, RT, concrete and glass were, respectively, 84.5%, 86.3%, 83.4%, 80.7% and 75.8%. Clayey CDWs contributed to mechanical strength development, while the contribution of concretes was related to the hydration of unreacted cementitious particles. Glass exhibited the weakest pozzolanic activity due to its coarser particle size. Overall, the CDWs demonstrated suitable properties for use as supplementary cementitious materials in Portland cement based systems.