The paper industry burns or buries a significant amount of waste paper sludge. This issue is not suitable from environmental and economic aspects. In this study, the mechanical and durability properties of high-strength concrete containing waste paper sludge ash (WPSA) were evaluated. The variables were WPSA (0, 5, 10, and 15% by weight of cement), silica nanoparticles (0 and 2.5 by weight of cement), and aluminum oxide nanoparticles (0 and 2.5 by weight of cement). Compressive strength, splitting tensile strength, flexural strength, and ultrasonic pulse velocity tests were conducted to evaluate the mechanical properties. The durability properties were also investigated using water penetration depth, water absorption, and electrical resistivity tests. The microstructure of the specimens was analyzed by preparing electron microscopic images. The combined effect of WPSA and nanoparticles on improving the mechanical and durability properties of high-strength concrete are better than using each of them alone. WPSA and nanoparticles react with calcium hydroxide formed due to cement's hydration, and silica produces hydrated calcium, which is the hard material that makes concrete strength. Consumption of calcium hydroxide and production of more hydrated calcium silicate in the presence of nanoparticles and WPSA are among the reasons for water absorption reduction, increased electrical resistance, and water penetration depth reduction in concrete specimens. By replacing part of the cement with WPSA, silica nanoparticles, and aluminum oxide nanoparticles, the transition zone between the aggregates strengthens, and the tensile and flexural strengths increased.
Heavyweight concrete is used to prevent harmful radiation for the construction of hospital, military, and nuclear power plants and also to increase the durability for the construction of marine concrete structures. In this research, using a combination of serpentine aggregates and lead slag, the mechanical, durability, impact resistance, and shielding properties of heavyweight concrete were examined. The variables included fine and coarse serpentine aggregates, which were replaced with normal fine and coarse aggregates in amounts of 0, 25, 50, and 100 percent, respectively. The lead slag in all samples was considered constant. Slump, compressive strength, flexural strength, water penetration depth, impact resistance (drop hammer), and gamma ray attenuation coefficient tests were conducted. The chemical composition of serpentine aggregates and lead slag were evaluated by X-ray powder diffraction. The results showed that the density and linear attenuation coefficient (LAC) increased with the increase of fine and coarse serpentine aggregates in heavyweight concrete containing lead slag. The highest density and LAC were obtained in a sample in which 100% fine serpentine aggregates and 100% coarse serpentine aggregates were used. Using 25% of serpentine fine aggregates and 25% of serpentine coarse aggregates in heavyweight concrete samples containing lead slag has achieved the highest compressive strength and flexural strength. But with the increase of fine and coarse serpentine aggregates to more than 25%, the upward trend of increasing compressive strength decreased. Silica constitutes a large part of the chemical structure of serpentine aggregates (about 42%). Increasing the amount of serpentine aggregates in concrete mixes leads to excessive release of calcium hydroxide in concrete. This issue can lead to the formation of a weak zone in concrete and decrease the compressive and impact resistance.
Purpose
This paper aims to study the influence of the presence of steel and polyolefin (PO) fibers on the mechanical and durability properties of fiber and hybrid fiber-reinforced concrete (FRC and HFRC).
Design/methodology/approach
Hooked-end steel fibers having a length of 35 mm were applied at four different fiber content 1.0%, 1.5%, 2.0% and 2.5%, respectively. PO fibers having the length of 45 mm were also replaced with steel fibers at three different fiber content, 0.6%, 0.8% and 1.0%, to provide HFRC. The compressive, indirect tensile and flexural strengths; electrical resistivity; and water absorption were evaluated in this study.
Findings
The results showed that the addition of both steel and PO fibers led to improvements in the mechanical properties of FRC and HFRC. However, the replacement of steel fibers with PO fibers led to a slight loss in mechanical properties. Also, it was concluded that the addition of various types of fibers to concrete decreased both the electrical resistivity and water absorption compared with the control sample. Finally, distance-based approach analysis was used to select the most optimal mix designs.
Originality/value
According to this method, the HFRC specimen including 1.2% of steel and 0.8% of PO fibers was the most optimal mix design among all fiber-reinforced mix designs.
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