Cement and Concrete Composites(2022 - 2023)
Microcell and macrocell corrosion of steel bars in reinforced concrete slabs under different corrosive environments and cathode/anode configurations
Bui H.T.; Maekawa K.; Tan K.H.
Cement and Concrete Composites, Elsevier Ltd., Vol.138, 2023, .
(https://doi.org/10.1016/j.cemconcomp.2023.104989)
Abstract
This paper presents an experimental study and electrochemical mechanisms of microcell and macrocell corrosion kinetics of steel bars in reinforced concrete slabs subjected to three different corrosive environments and three configurations of uncorroded/corroded steel bars. Effects of combined chloride contamination and carbonation were investigated and compared to individual causes either from chloride contamination or carbonation. Under each corrosive environment, two cathode/anode area ratios, as well as steel bars-contact and -noncontact conditions, were tested. As a result, the combined chloride contamination and carbonation induced larger microcell and macrocell corrosion rates than those attacked by solely chloride or solely carbonation. Although a larger cathode/anode ratio increased macrocell current density, it actually decreased microcell rate compared to a smaller ratio. In addition, when corroded steel bars were in contact, microcell and macrocell current densities became larger than those in noncontact samples for all three corrosive environments. Based on the test results, electrochemical mechanisms of both microcell and macrocell corrosion were proposed using thermodynamic theory, anodic and cathodic polarisation kinetics to draw precious insights into the corrosion behaviour under different corrosive environments and cathode/anode ratios. c 2023
Multiscale chemo-mechanical modeling of concrete expansion with free lime-based expansive additives under restraint conditions
Gupta M.; Igarashi G.; Takahashi Y.; Ishida T.
Cement and Concrete Composites, Elsevier Ltd., Vol.141, 2023, .
(https://doi.org/10.1016/j.cemconcomp.2023.105126)
Abstract
Expansion of concrete due to expansive additives (EAs) is greatly affected by the degree of external restraints in the form of reinforcements and supports. Furthermore, the presence of anisotropic restraints influences concrete expansion in different directions. In this study, a chemo-mechanical model was developed to estimate concrete expansion under the framework of poromechanics. The volume of expansive hydrates was obtained from the hydration model, which was used for estimating the stress on the cement paste using poromechanical formulations. An external non-isotropic state of stress affects the orientation of crystal precipitating inside the pores of the cement paste. Thus, anisotropy in concrete expansion due to external stress was considered by maintaining the chemo-mechanical equilibrium of crystals of expansive hydrates, which was reflected in the poro-elastic constants utilized to estimate the stress at the cement paste scale. Poroelastic coefficients were estimated using a micromechanical scheme reflecting the effect of crystal orientation. Dedicated experiments were performed to comprehend the anisotropic expansion of concrete under anisotropic external restraint conditions. Finally, the applicability of the model was verified by comparing the expansion in different directions estimated from the model and experiments performed in this study with available literature data. Thus, the developed chemo-mechanical model could benefit practitioners and engineers in evaluating the expansion behavior of restrained concrete for a given application. c 2023 Elsevier Ltd
Analytical and experimental studies on alkali-silica reaction mechanism: Aggregate cracking and chemical composition change of gel
Joo H.E.; Takahashi Y.
Cement and Concrete Composites, Elsevier Ltd., Vol.139, 2023, .
(https://doi.org/10.1016/j.cemconcomp.2023.105003)
Abstract
This study aims at developing an analytical model to predict alkali-silica reaction (ASR) induced expansion in concrete considering the aggregate cracking and changes in the chemical composition of ASR gel. To this end, an aggregate cracking experiment was conducted to examine the conditions that cause the cracking of aggregates suffered by ASR, and the chemical compositions of the gels filling cracks were observed using scanning electron microscopy and energy dispersive X-ray spectroscopy. To reflect the effect of aggregate cracking and chemical composition change of gel on reaction kinetics in the analytical model, it was modeled that aggregate cracking leads to more diffuse alkalis into the aggregate, and the gel volume decreased while the gel reacted with calcium in the cement paste. The proposed model was verified by comparison with existing ASR test results, and the rate of change in the chemical composition of the gel was quantitatively investigated. c 2023 Elsevier Ltd
Effect of curing temperatures and additional activators on chloride ingress and its induced mineralogical alteration of ground granulated blast furnace slag activated by Ca(OH)2
Qi Z.; Zuo Y.; Kurumisawa K.; Lang A.
Cement and Concrete Composites, Elsevier Ltd., Vol.141, 2023, .
(https://doi.org/10.1016/j.cemconcomp.2023.105153)
Abstract
The impact of additional activators (sodium sulfate, sodium nitrite, and calcium nitrite) and curing temperature (20 and 35 C) on chloride binding and ingress resistance of ground granulated blast furnace slag activated by Ca(OH)2 was studied using X-ray diffraction, scanning electron microscopy, thermogravimetric and thermodynamic modeling. The outcomes of the study indicated that the difference in the chloride binding capacity at low chloride concentrations was primarily affected by the types of the AFm phase. The solid solution formed between Friedel's salt and various types of AFm phases resulted in a decrease in the chloride binding capacity. At a curing temperature of 35 C, the chloride binding capacity reduced due to the leaching of calcium ions and carbonation induced by the coarse pore structure. It was found that the chloride ingress resistance was significantly related to the leaching of calcium and carbonation, and the denser calcite layer formed at the exposure layer had a positive impact on the chloride ingress resistance. c 2023 Elsevier Ltd
Mesoscale modelling of SFRC based on 3D RBSM considering the effects of fiber shape and orientation
Sarraz A.; Nakamura H.; Miura T.
Cement and Concrete Composites, Elsevier Ltd., Vol.139, 2023, .
(https://doi.org/10.1016/j.cemconcomp.2023.105039)
Abstract
In this study, a mesoscale model of steel fiber reinforced concrete (SFRC) based on 3D RBSM (rigid body spring model), was proposed to take the fiber shapes (straight and hook end) and orientation into account in concrete. The steel fibers were distributed into the Voronoi mesh system of RBSM, and a zero-size spring was assigned at the interface of Voronoi mesh crossed by discrete fiber, to transfer the fiber pullout load to the nearest nodes of RBSM. The straight steel fiber was modeled based on proposed local bond-slip relationship and the mechanical hook action was proposed additionally to model the hook end fiber. The model can predict the macroscopic response and cracking of SFRC made with straight and hook end fibers under direct tensile and bending loads. The analysis results found the mechanical hook action as the governing parameter for hook end fiber then the bond-slip properties for straight fiber. The fiber orientation and matrix spalling due to friction induced pullout load component, were found prominent for steel fiber. The anisotropy induced by fiber shapes and orientations was headed by hook end fiber with superior macroscopic load capacity by delaying the crack propagation and transformation. c 2023 Elsevier Ltd
Electromagnetic pulse-induced acoustic testing enables reliable evaluation of debonding between rebar and concret
Zhou X.; Takeda S.; Uchimoto T.; Hashimoto M.; Takagi T.
Cement and Concrete Composites, Elsevier Ltd., Vol.142, 2023, .
(https://doi.org/10.1016/j.cemconcomp.2023.105170)
Abstract
An electromagnetic Pulse-Induced Acoustic Testing (EPAT) method was investigated for evaluating debonding between rebar and concrete. Debonding specimens were prepared by wrapping polystyrene foam around a rebar to induce debonding between the concrete and rebar. An acoustic emission sensor was placed on the concrete specimen surface to collect elastic wave signals. A powerful pulsed electromagnetic force was applied to the specimens and the elastic waves of the rebar were analyzed. By comparing the differences in signal reach time of the elastic waves between specimens with and without a debonding, it was demonstrated that EPAT is useful for non-destructive evaluation of debonding. Finite element simulations were also conducted, validating the reliability of EPAT for examining debonding in reinforced concrete. c 2023 Elsevier Ltd
Modeling of carbonation, de-carbonation and re-carbonation processes of structural concrete subjected to high temperature heating
Iwama K.; Maekawa K.
Cement and Concrete Composites, Elsevier Ltd., Vol.129, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104493)
Abstract
When structural concrete is exposed to a fire, various changes in chemical and mechanical properties proceed. The concentration of carbon dioxide CO2 rises to about 15% depending on the situation of fire accidents accompanying combustion of carbide. The self-healing of damaged concrete is expected by absorbing CO2 after fire. Thus, consideration of high temperature heating for carbonation is indispensable for performance assessment of structural concrete. This paper proposes a multi-scale thermo-chemo-physics model for carbonation, de-carbonation and re-carbonation processes during and after high-temperature heating. The proposed integrated model is experimentally validated by using the thermo-gravimetry experiments of cement paste and the strength of mortar composites immediately after high-temperature heating and after post-fire-curing. The CO2 concentration and the humidity are experimentally changed as the thermodynamic boundary conditions for wide-range verification and validation. The compressive strength is treated not as the material property but the computed structural capacity of a cylindrical solid in which the temperature, hydration degree and carbonation develop non-uniformly. The proposed model can capture the tendency of experimental results and allows practically reasonable assessment of fire-damaged and moist-cured concrete as a multi-scale composite. c 2022 The Authors
Twenty-two-year investigation of strength development and surface deterioration of cement-treated clay in an in-situ field test
Izuo H.; Nakarai K.; Kulik D.A.
Cement and Concrete Composites, Elsevier Ltd., Vol.134, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104783)
Abstract
The long-term strength development and durability of in-situ cement-treated soil were investigated by physicochemical analysis and geochemical thermodynamic modeling. The measured strength of the volcanic cohesive clay treated with high-sulfate cement continuously increased for five years and then persisted until 22 years. X-ray analysis revealed that the ettringite formation through cement hydration contributed to the early strength, while the stratlingite formation through pozzolanic reaction contributed to the long-term strength. Thermodynamic modeling pointed at the alumina dissolution from the treated clay in an alkaline environment as the main driving force for the pozzolanic reaction. Further, calcium leaching and carbonation caused surface deterioration of the cement-treated soil, thereby decomposing the hydration products and lowering the strength of the treated clay. c 2022 Elsevier Ltd
Investigation of the mechanical behaviour of concrete with severe delayed ettringite formation expansion focusing on internal damage propagation under various compressive loading patterns
Joshi N.R.; Matsumoto A.; Asamoto S.; Miura T.; Kawabata Y.
Cement and Concrete Composites, Elsevier Ltd., Vol.128, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104433)
Abstract
Expansion due to delayed ettringite formation (DEF) can cause severe concrete strength deterioration; the failure process related to internal damage remains unclear. In this study, the influence of pre-existing DEF cracks on the compressive failure process was demonstrated. Concrete specimens with DEF expansions greater than 2% were tested under monotonic, step, cyclic, and sustained loading patterns, providing stress?strain relationships. Internal crack propagation due to loading was quantified using X-ray CT images. Large plastic strains occurred, even at low stress levels. Peak stress and strain at failure were almost independent of the loading history. Gaps formed around the aggregate with increased loading were closed and opened in the loading and perpendicular directions, respectively, contributing to plastic strain accumulation. Gradual interconnection of cracks along the aggregate interfaces at high stress levels led to specimen failure. Gradual gap closing under cyclic or sustained loading reduced additional plastic deformation under the same stress. c 2022 Elsevier Ltd
An overview on the effect of pumping on concrete properties
Li F.; Shen W.; Yuan Q.; Hu X.; Li Z.; Shi C.
Cement and Concrete Composites, Elsevier Ltd., Vol.129, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104501)
Abstract
Pumping is a widely used placement means for concrete construction, but both fresh and hardened property changes in concrete due to pumping. In this review, the effects of pumping on both the fresh and hardened properties of various concrete mixtures are presented in terms of each specific characteristic. Analyses of data from the published literature showed that the air content of fresh concrete is altered after pumping. The general trend in the change in rheological properties of fresh concrete due to pumping was also determined, and the mechanisms of this trend were discussed. Moreover, the improvement in the compressive strength of hardened concrete was investigated, which is considered to result from the pumping-induced hydration acceleration and the air content variation. Finally, changes in the durability of hardened concrete were discussed, and future research topics were suggested. c 2022 Elsevier Ltd
Mesoscopic simulation of crack propagation and bond behavior in ASR damaged concrete with internal/external restraint by 3D RBSM
Luo J.; Wang Y.; Asamoto S.; Nagai K.
Cement and Concrete Composites, Elsevier Ltd., Vol.129, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104488)
Abstract
One of the most serious serviceability concerns for reinforced concrete (RC) structures is expansion and cracking resulting from the alkali-silica reaction (ASR), which has a negative effect on material properties as well as the bond between reinforcement and surrounding concrete. In a typical RC member, ASR induced concrete expansion and cracking are restrained by internal reinforcement as well as the boundary conditions. The mechanism is complex and difficult to understand through experimental study, so predicting the residual capacity of a damaged RC structure is not easy. In this study, the authors use a 3D Rigid Body Spring Model (RBSM) comprising mortar, aggregate and steel elements and which is able to simulate ASR expansion in reinforced concrete. To study the complex interactions among multiple parameters and quantify the effect of ASR damage on structural behavior, previously reported experiments on ASR induced expansion under internal and external restraint are simulated, along with experiments on pullout behavior after ASR expansion. The effect of restraints on macroscopic ASR expansion is well modeled in each case, and how the development of internal stresses and concrete cracking influenced by the restraint can be explained from the simulations. The simulations enable discussion of the number of ASR-induced cracks and the internal stress condition in various cases. The peak bond strength of concrete with different ASR damage levels, as reported in pullout experiments, is predicted accurately and the load-displacement curves of ASR damaged concrete are discussed. c 2022 Elsevier Ltd
Mechanism for reduction in compressive properties of cementitious materials in relation to internal crack patterns due to ASR and DEF expansion
Miura T.; Sato K.; Fujishima M.; Nakamura H.; Kawabata Y.
Cement and Concrete Composites, Elsevier Ltd., Vol.128, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104441)
Abstract
This study discusses the mechanism for the changes in the compressive properties of internally cracked concrete due to expansion phenomena. The internal crack patterns due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) are reproduced using the model concrete with artificial cementitious aggregate. The compressive behaviors are clarified using a uniaxial compressive test with digital image correlation. As a result, in terms of ASR, the trends for reduced mechanical properties in model concrete differ from the expansion phenomena under stress-free condition and the anisotropy of change in mechanical properties due to the aggregate crack orientation changes is observed. For DEF, the reduction in mechanical properties is independent of thickness of a debonding crack. Consequently, the mechanism for reduction in compressive strength and elastic modulus by the aggregate cracking and gap formation due to ASR and DEF based on the compressive stress transfer path at the cross-sectional area was proposed. c 2022 Elsevier Ltd
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, Elsevier Ltd., 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
Comparison of fire spalling behaviours between ring-restraint and pre-stressed concrete specimens during fire
Ozawa M.; Fujimoto K.; Ikeya H.
Cement and Concrete Composites, Elsevier Ltd., Vol.126, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2021.104341)
Abstract
Pre-stressed concrete (PC) structures have higher explosive spalling risk during fires than reinforced-concrete structures, because of the initial compressive stress due to the pre-stressing force. The Japanese Concrete Institute (JCI) has standardised a ring-restraint heating test. Herein, we investigated the explosive spalling of uniaxial PC beam specimens and ring specimens made of concrete with the same mix proportions. A fire test was performed by exposing the specimens at the bottom ends to one-sided heating. RABT 30 and ISO 834 heating curves were used. The spalling was evaluated using spalling indexes specified by the JCI in terms of the maximum spalling depth, spalling area ratio, spalling volume ratio, and maximum spalling depth ratio. The spalling behaviour depended on the shape, degree of restraint, and difference in the pre-stress levels of the specimens. We demonstrated the need to consider the spalling area, depth, and volume in spalling evaluations. c 2021
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, Elsevier Ltd., 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
Microstructural properties and water penetration resistance of cementitious binder combined with water-dispersible polyurethane
Takahashi K.; Asamoto S.; Babazono M.; Matsuda Y.
Cement and Concrete Composites, Elsevier Ltd., Vol.125, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2021.104326)
Abstract
To avoid the re-degradation of repaired regions and ensure the service lives of infrastructures, cementitious materials used for repair applications should possess excellent water penetration resistance. Organic polymers are widely used to enhance water resistance. In this study, the microstructural properties and water uptake of a cementitious material containing a newly developed water-dispersible polyurethane (PU) polymer were investigated. The results showed that the water uptake decreased significantly in the presence of PU. Microscopic observations and gas sorption isotherms indicated that submillimeter and capillary pores and the surfaces of calcium silicate hydrate were partially hydrophobized and/or blocked upon PU addition, which could contribute to the prevention of liquid water uptake. Nevertheless, based on a drying procedure performed prior to the water penetration tests, the specimens with and without PU exhibited similar water vapor uptakes owing to the eliminated difference in the volumes of their micro- and mesopores. c 2021 Elsevier Ltd
Mitigation effect of lithium nitrate on the alkali-silica reaction in alkali-activated slag mortars
Wang W.; Noguchi T.; Maruyama I.
Cement and Concrete Composites, Elsevier Ltd., Vol.130, 2022, .
(https://doi.org/10.1016/j.cemconcomp.2022.104532)
Abstract
Although lithium nitrate is a commonly used method to mitigate the alkali-silica reaction (ASR) in conventional Portland cement systems, such kind of research has not been conducted on alkali-activated material (AAM) systems. In this study, the mitigation effect of lithium nitrate on the ASR in an AAM system was investigated for the first time. The results indicate that lithium nitrate is not effective in mitigating the ASR in alkali-activated slag (AAS) mortars because of its inherently high alkalinity and dense microstructure. Although the lithium nitrate reduced the expansion of AAS mortars, the reduction was limited, and when the concentration of lithium nitrate further increased from 1.11 mol/L to 1.48 mol/L, the expansion did not reduce any more. No Li?Si crystals were found in the AAS pastes/mortars exposed to lithium nitrate-containing solutions. The SEM/EDS analysis revealed that there were still many ASR products that could be observed in AAS mortars exposed to the solution containing 1.48 mol/L lithium nitrate for 56 days, and the Na/Si ratio of the ASR products remained almost unchanged, while the Ca/Si ratio decreased. 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, Elsevier Ltd., 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, Elsevier Ltd., 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