This study deals with application of sodium-paraben based anti-fungal agents in cement mortars and their effect on the physical, mechanical, and anti-fungal activity. The fungus Aspergillus Niger, typically found in damp buildings, grew on cement composites. Sodium propyl parahydroxybenzoate (SPP) and sodium methyl parahydroxybenzoate (SMP), two sodium paraben anti-fungal agents, were used in pastes and mortars at dosages of 1 and 2 wt.% relative to cement. The results of the study show that the use of anti-fungal agents containing sodium paraben reduces the compressive strength of cement mortar and the setting time of hardened cement paste. The results of the biodeterioration test demonstrated that mortars incorporating with anti-fungal agents containing sodium paraben are less susceptible to fungal attack. Analytical characterizations such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and energy dispersion X-ray spectroscopy (EDX) analysis showed that the use of sodium paraben based anti-fungal agents increased the resistance of mortars against the fungal attack.
This paper evaluates the efficiency of polypropylene fibers in improving the tensile and flexural characteristics of fiber-reinforced alkali-activated slag composites with strain-hardening behavior. Several different composites were produced and the mechanical properties of the composites were investigated during compressive and flexural tests. Furthermore, the mid-span curvature of the beams was measured by applying the digital image correlation technique to the flexural tests, and the curvature-deflection diagrams of the composites were analyzed and demarcated by structural mechanics. Finally, an analytical model considering strain-hardening behavior was proposed by fitting the calculated moment-curvature diagrams to the experimental results to recognize the tensile behavior of composites more precisely than the existing indirect methods. The results showed that an ultra-high tensile strain capacity was obtained for composites cured under laboratory conditions. Also, it was found that the fiber interfacial bond with the matrix was improved by using slag with lower Al2O3 content. Moreover, weakening the interfacial transition zone between the fine aggregate and the paste, the heat-treatment curing reduced the fracture energy of the composites which is favored to make strain-hardening cementitious composites.
The effects of graphene oxide (GO) with different contents on hydration process of tricalcium silicate (C3S) were investigated in this article. The scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, nitrogen desorption, nuclear magnetic resonance, Fourier transform infrared spectroscopy and Raman spectroscopy were used to analyze the micro-evolution of the GO/C3S hardened pastes, and the compressive strength of the GO/C3S was tested. The findings revealed that the addition of the GO increased the compressive strength of the GO/C3S because the GO can provide a large number of nucleation sites for hydration products, thereby accelerating the C3S hydration process. The GO also reduced the total pore volume of the C3S, leading to an increase in the proportion of gel pores and refinement in pore structure. Furthermore, the abundant oxygen-containing functional groups present on the GO surface can form hydrogen bonds with free water or interlayer water, thereby increasing the number of hydrogen bonds in the system.
This study examines the application of the maturity method to obtain the ultimate properties of ECC. Within the scope of the study, the maturity method according to the Arrhenius equation was applied to four different ECC mixtures encountered in the literature: the activation energies and the ages at which they achieve ultimate properties were determined. Subsequently, the mixtures were subjected to standard and accelerated curing to reach an equivalent age of 1 year. The properties of the specimens at 1-year equivalent age were determined after both standard curing at 23°C and accelerated curing at 60°C. Thus, both the validity of the maturity method and the effect of accelerated curing in ECC were evaluated. Mechanically, compressive and flexural tests were performed, while non-destructive tests such as ultrasonic pulse velocity, rapid chloride ion penetration, and resonant frequency were used to determine ECC properties. As a result, it was determined that all ECC mixtures achieved their ultimate properties in less than a year. Furthermore, it was revealed that ECC retains its distinctive properties even in the ultimate state. Additionally, while accelerated curing led to a slight decrease in all properties compared to normal curing, it contributed to a slight improvement in deformation capacity. Nevertheless, considering the proximity of the results between normal and accelerated curing, it can be concluded that accelerated curing has the potential to be applied in ECC, and based on the findings, the maturity method has the potential to predict the long-term properties of ECC mixtures.
This study aims to develop a simple yet accurate adaptive homogenization approach for modeling the effective elastic properties of concrete for the whole hydration range from early age to hardened state. Considering available data from a similar microstructure, the method accurately accounts for the impact of cement hydration degree on the effective elastic properties of the heterogeneous concrete mixture. The simulation results have been validated against experimental data and demonstrate exceptional agreement. Also, we have detailly discussed the role of water and the effect of the destructive and non-destructive measurement methods. The model’s simplicity and accuracy make it highly applicable in practical engineering scenarios.
The use of engineered cementitious composite with polyvinyl alcohol fiber has shown excellent potential in building facilities due to its strain-hardening and multiple-cracking features. However, when polyvinyl alcohol fiber melts at around 230°C, spalling behavior of engineered cementitious composite may occur, weakening the mechanical properties and reducing ductility of high strength engineered cementitious composite. Thus, investigating the fire resistance is of great significance. By adding steel fibers to cementitious composites, qualitative and quantitative comparisons were done through observing appearance changes, spalling extent, surface cracking, mass loss, and residual mechanical properties. Results indicate that steel fiber can increase the risk of spalling and surface cracking in high strength engineered cementitious composite, improve residual mechanical abilities also. The ductility varies with steel fiber content at different elevated temperatures. Scanning electron microscopy results show that more hydration products are produced on the surface of steel fiber at 400°C, which improves interface transition zones between fiber and cementitious materials. However, an oxidation film found on the surface of steel fiber at 800°C triggers negative effect on bridging.
Cement-based materials with self-sensing capabilities have the potential to be used as compression load cells in various applications. This study aims (i) to clarify the change in resistivity in self-sensing mortar (SSM) under nondestructive compressive stress and the underlying mechanism of this change, (ii) to examine the effects of different conditions such as electric circuit and specimen dimension on this relationship. The study involved SSM specimens containing 7% carbon black powder with various parameters, including excitation voltage, intermediate resistor for the electric circuit, and electrode distance, dimensions of the cube SSM specimen. Additionally, scanning electron microscopy (SEM) observations were performed to investigate the dispersion of carbon black in the cementitious matrix. SEM observations reveal the agglomeration and dispersion of carbon black within the cementitious matrix, creating a conductive network in SSM. The measurement results showed the resistivity change was nonlinear but displayed nearly linear behavior within a specific range of compressive stress. The slope of this change increased with larger specimen cross-section, shorter electrode distance, and a smaller value for the intermediate resistor in the electric circuit. A regression analysis was conducted to predict the change in resistivity of SSM under nondestructive compressive stress, while taking these effects into account.