Unlocking the role of pores in chloride permeability of recycled concrete: A multiscale and a statistical investigation

Lian, Songsong; Ruan, Shaoqin; Zhan, Shulin; Unluer, Cise; Meng, Tao; Qian, Kun

doi:10.1016/j.cemconcomp.2021.104320

Cited by 29 publications

(5 citation statements)

References 45 publications

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“…Due to the presence of a layer of hardened cement mortar on the surface of RCA, discontinuous porous areas appear between the old aggregate and the cement paste, resulting in a low aggregate-crushing index, high water absorption, and low apparent density [5,6]. When RCA is directly used in concrete, harmful substances can easily erode the concrete through ion diffusion, capillary adsorption, and pressure penetration [7,8], thus weakening the bearing capacity of building structures and threatening the safety and durability of buildings [9,10].…”

Section: Introductionmentioning

confidence: 99%

Effect of Nano-TiO2 on Capillary Water Absorption of Recycled Aggregate Concrete

Zhong

Zhou

et al. 2022

Coatings

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To improve the durability performance of recycled aggregate concrete in actual use, this paper uses nano-TiO2-modified recycled coarse aggregate to study, through experiments, the effects of nano-TiO2 on the pore distribution of recycled coarse aggregate concrete after freeze–thaw. The capillary-water-absorption law was used as the evaluation index. The recycled coarse aggregate concrete was prepared with different contents of nano-TiO2, and changes in the 24 h capillary water absorption and porosity of the recycled aggregate concrete after freeze–thaw cycles were analysed. With the help of high-resolution image recognition and binary-image-processing technology, the pore distribution of the recycled aggregate concrete before and after freeze–thaw cycles was obtained. Through the analysis of the water-absorption data at different times, the initial capillary-water-absorption rate, S1, is obtained. The capillary water absorption of recycled aggregate concrete is reacted with S1, and the initial capillary-water-absorption prediction model of nano-TiO2 recycled aggregate concrete under freeze–thaw cycles is established. The results show that under the action of freeze–thaw cycles, the capillary water absorption of recycled coarse aggregate concrete increases with the increase in the RCA substitution rate and decreases with the increase in nano-TiO2 content. After 150 freeze–thaw cycles, the cumulative water absorption and porosity of RC25-NT1.2 decreased by 25.52% and 14.57%, respectively, compared with the test block without nanomaterials. It was found that nano-TiO2 has a prominent role in modifying recycled aggregate concrete. Nano-TiO2 can reduce the cumulative water absorption and porosity of recycled aggregate concrete and alleviate the negative impact of the recycled coarse aggregate on capillary water absorption of concrete after freeze–thaw cycles. It was observed by scanning electron microscopy that a large amount of C–S–H gel was produced inside the concrete mixed with nano-TiO2, which bonded the internal pores and cracks to form a dense structure.

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Section: Introductionmentioning

confidence: 99%

Effect of Nano-TiO2 on Capillary Water Absorption of Recycled Aggregate Concrete

Zhong

Zhou

et al. 2022

Coatings

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“…In addition, as the pore structures directly affect CO 2 diffusion, 26,52,53 pore distribution is of paramount significance for overall concrete performance. Therefore, to identify the pore distribution of RMC samples along with their depths, surface determination 54 of ROI (42 × 42 × 42 mm 3 ) was performed first after the background noise removal. Consequently, the porosity distribution of all groups along with the z‐axis was then analyzed.…”

Section: Resultsmentioning

confidence: 99%

“…51 In terms of porosity, the maximum pore volume, the mean diameter, and the mean surface area, the three kinds of samples in descending order of values are S2, S1, and C0, which is consistent with strength results. In addition, as the pore structures directly affect CO 2 diffusion, 26,52,53 pore distribution is of paramount significance for overall concrete performance. Therefore, to identify the pore distribution of RMC samples along with their depths, surface determination 54 of ROI (42 × 42 × 42 mm 3 ) was performed first after the background noise removal.…”

Section: Pore Structuresmentioning

confidence: 99%

Understanding the role of seeds in reactive magnesia cement (RMC) formulations

et al. 2023

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Nucleation effects of seeds in reactive magnesia cement (RMC) systems have been reported, but this process has never been directly observed. In this study, different types and contents of seeds were introduced in RMC formulations. Resultsshow that seeded RMC samples revealed accelerated hydration/carbonation that led to their more rapid strength development, and the use of magnesite outperformed other seeds given their overall performances, as explained by their more homogenous microstructures. Further, in the model solution, the amount of Mg2+ ions adsorbed onto seeds particles continuously increased with the increment of Mg2+ concentrations, confirming the nucleation effects of seeds in RMC formulations directly, and seeds surfaces revealed a much higher affinity for Mg2+ ions than other ions due to their acid-base interactions. Therefore, the use of seeds could act as accelerators that shorten the curing period of RMC-based concrete products on a large scale.

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“…The water–cement ratio ( W / C ) is an important parameter that determines the mechanical properties of concrete, such as strength, hardness and durability, and has a great influence on the permeability of concrete [ 44 ]. The degree of hydration ( α ) is another parameter closely related to porosity [ 45 ]. Therefore, it is very important to reveal the effects of water–cement ratio and degree of hydration on the chloride diffusion behavior, and on this basis, design concrete to reduce the permeability of chloride ions.…”

Section: Resultsmentioning

confidence: 99%

Exploring Exact Effects of Various Factors on Chloride Diffusion in Cracked Concrete: ABAQUS-Based Mesoscale Simulations

Zhao

Guan

2023

Materials

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Chloride ion attack is a major cause of concrete durability problems, and existing studies have rarely addressed the effects of damage zones. In this paper, an improved mesoscale model including five phases was constructed using the finite element software ABAQUS to study the diffusivity of chloride ions in cracked concrete. It was found that the damage zone is negligible when the crack width is less than 50 μm, while the width and depth of the damage zone are about 15 times the crack width and 15% of the crack depth when the crack is greater than 50 μm. The results show that the diffusion of chloride is greatly influenced by the crack width, while it is little-influenced by the crack shape. Low water–cement ratio and adequate hydration of the concrete are also key factors affecting chloride diffusion. In contrast, regular rounded aggregates have a positive effect on reducing chloride diffusion compared to irregularly shaped aggregates, and this effect becomes weaker with increasing service time. In addition, the protective layer can effectively prevent the diffusion of chloride in concrete. Therefore, when designing marine concrete, efforts should be made to ensure that the concrete has a low water–cement ratio, adequate hydration, less cracking and a protective layer.

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Unlocking the role of pores in chloride permeability of recycled concrete: A multiscale and a statistical investigation

Cited by 29 publications

References 45 publications

Effect of Nano-TiO2 on Capillary Water Absorption of Recycled Aggregate Concrete

Effect of Nano-TiO2 on Capillary Water Absorption of Recycled Aggregate Concrete

Understanding the role of seeds in reactive magnesia cement (RMC) formulations

Exploring Exact Effects of Various Factors on Chloride Diffusion in Cracked Concrete: ABAQUS-Based Mesoscale Simulations

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