CEMENT AND CONCRETE COMPOSITES(2022 - 2022)
Optimization of mix proportions and manufacturing conditions of fly ash-based geopolymer mortar by parameters design with dynamic characteristics
Onoue K., Sagawa Y., Atarashi D., Takayama Y.
CEMENT AND CONCRETE COMPOSITES, , Vol.133, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104645)
Abstract
This study attempted to optimize a manufacturing system for fly ash-based geopolymer (FAGP) using parameters design with dynamic characteristics. In the system, the volume ratio of powder to alkaline solution was used as the input value, while the flow value after fifteen drops, flexural strength, and compressive strength of the mortar were used as output values. Fly ash production area, lot number, and testing institute were set as noise conditions. The mixing protocol, mass ratio of water glass to sodium hydroxide in an alkaline solution (SS/SH), sodium hydroxide concentration, mixing time, curing holding temperature, and cumulative temperature during curing were considered as design parameters. The SN ratio was calculated from optimization testing performed a total of 432 times, and the optimum level for each design parameter was found. By investigating the effects of individual design parameters on the reaction product of FAGP mortar through design of experiments method, it was found that the alkaline solution preparation method affects both fly ash reaction rate and the amount of C-A-S-H generated, and, compared with a combination in which the alkaline concentration of the alkaline solution is higher, a combination in which the alkaline concentration is lower exhibited a higher fly ash reaction rate with a lower amount of C-A-S-H generated. It was also found that, under optimum conditions for other design parameters, the fly ash reaction rate was high and the amount of C-A-S-H generated was low, which suggests that these are related to improvement of the reproducibility of FAGP mortar. c 2022 Elsevier Ltd
Bond behavior simulation of deformed rebar in fiber-reinforced cementitious composites using three-dimensional meso-scale model
Sarraz A., Nakamura H., Kanakubo T., Miura T., Kobayashi H.
CEMENT AND CONCRETE COMPOSITES, , Vol.131, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104589)
Abstract
Fiber-reinforced cementitious composites (FRCC) can effectively develop the bond ductility of deformed rebar due to the high tensile resistance and strain capacity. This study presents a numerical method to evaluate the bond behavior of deformed rebar in FRCC based on 3D rigid body spring model (3D RBSM). Beam elements are used to model the rebar and the link elements are used to connect beam elements with RBSM elements as matrix. The same local bond-slip relationship for rebar is assigned at the link elements for both the simulation cases of plain mortar and FRCC. The model could properly simulate the single fiber to mechanical behavior of FRCC and the bond performance of rebar in FRCC. The results revealed that discrete fibers are the principal factors that preventing the splitting bond crack propagation and the stress propagation suggests the presence of high local bond stress around the rebar, improving bond ductility. c 2022 Elsevier Ltd
Multi-ion kinetics in pseudo-concrete electrolyte associated with macro-cell corrosion
Wang Z., Maekawa K., Takeda H., Gong F.
CEMENT AND CONCRETE COMPOSITES, , Vol.133, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104690)
Abstract
Steel corrosion is one of the damaging factors for structural concrete and has drawn engineering interest in the past decades. Macro-cell corrosion, a type of steel corrosion, is related to not only electric fields but also chemical substances of both polarized metals and electrolytes such as the concrete matrix. To investigate such multi-ion kinetics induced by macro-cell circuits, this study presents an experimental validation to build a numerical simulation platform using pseudo-concrete with which the speciesf chemo-electrical profiles are dynamically measured with elapsed time to obtain evidence for broad-band verification and validation. As a key species of cementing material, the authors focus on the profiles of Ca2+ concentrations as a major cation of concrete around the positive and negative electrodes, which are significantly affected by the initial saturation of calcium hydroxide and the supply of carbon dioxide. Experiments and numerical simulation applied to concrete show satisfactory correlation to reveal the governing mechanism based on polarization and the Nernst-Plank theory with multi-ion mass equation. c 2022 The Authors
Effects of cation in sulfate chloride and nitrite on Ca(OH)2 activated ground granulated blast-furnace slag
Zhai Q., Kurumisawa K.
CEMENT AND CONCRETE COMPOSITES, , Vol.133, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104648)
Abstract
This study explores the effects of the cations in sulfates, chlorides, and nitrites on calcium-hydroxide activated blast-furnace slag. Using several methods, it was demonstrated that the activators investigated could improve early strength development. Compared with chlorides and nitrites, the type of sulfate has a significant influence on slag hydration. Compared with K2SO4 and Na2SO4, the promotion of slag hydration in MgSO4, at an early age, is limited due to the precipitation of gypsum and brucite which retard the formation of hydrates and limits hydration kinetics during the initial stage. The high concentration of sulfate ions in the pore solution causes some ettringite to remain, promoting strength development. It was observed that the mechanism of pH increase in K2SO4 and Na2SO4 is due to the synergistic reactions between the sulfates and Ca(OH)2, while the low pH of MgSO4 due to the low solubility of brucite inhibits slag dissolution. The critical pH for promoting slag hydration was determined to be 13.1. c 2022 Elsevier Ltd