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19 pages, 5097 KiB

Open AccessArticle

Use of ZnAl-Layered Double Hydroxide (LDH) to Extend the Service Life of Reinforced Concrete

by Celestino Gomes, Zahid Mir, Rui Sampaio, Alexandre Bastos, João Tedim, Frederico Maia, Cláudia Rocha and Mário Ferreira

Materials 2020, 13(7), 1769; https://doi.org/10.3390/ma13071769 - 9 Apr 2020

Cited by 38 | Viewed by 5264

Abstract

This work investigated the use of ZnAl-layered double hydroxide (LDH) intercalated with nitrate or nitrite ions for controlling the corrosion of steel in reinforced concrete. The work started by analyzing the stability of the powder in the 1–14 pH range and the capacity [...] Read more.

This work investigated the use of ZnAl-layered double hydroxide (LDH) intercalated with nitrate or nitrite ions for controlling the corrosion of steel in reinforced concrete. The work started by analyzing the stability of the powder in the 1–14 pH range and the capacity for capturing chloride ions in aqueous solutions of different pH. The effect of the ZnAl-LDH on the corrosion of steel was studied in aqueous 0.05 M NaCl solution and in mortars immersed in 3.5% NaCl. It was found that the LDH powders dissolved partially at pH > 12. The LDH was able to capture chloride ions from the external solution, but the process was pH-dependent and stopped at high pH due to the partial dissolution of LDH and the preferential exchange of OH^– ions. These results seemed to imply that ZnAl-LDH would not work in the alkaline environment inside the concrete. Nonetheless, preliminary results with mortars containing ZnAl-LDH showed lower penetration of chloride ions and higher corrosion resistance of the steel rebars. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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21 pages, 7505 KiB

Open AccessArticle

Severe Sulfuric Acid Attack on Self-Compacting Concrete with Granulometrically Optimized Blast-Furnace Slag-Comparison of Different Test Methods

by Sara Irico, Laurence De Meyst, Dirk Qvaeschning, Maria Cruz Alonso, Kristina Villar and Nele De Belie

Materials 2020, 13(6), 1431; https://doi.org/10.3390/ma13061431 - 21 Mar 2020

Cited by 25 | Viewed by 4183

Abstract

The corrosion by severe sulfuric acid attack at pH 2 of two self-compacting concrete (SCC) types that are based on ordinary Portland cement (OPC) and granulometrically optimized blast-furnace slag cement was evaluated by three complementary tests that were performed in different research institutes. [...] Read more.

The corrosion by severe sulfuric acid attack at pH 2 of two self-compacting concrete (SCC) types that are based on ordinary Portland cement (OPC) and granulometrically optimized blast-furnace slag cement was evaluated by three complementary tests that were performed in different research institutes. The use of SCC is a smart and promising solution to improve the performance of concrete in an aggressive environment, especially regarding ready-mixed concrete applications, since good compaction is less dependent on workmanship. The relevance and practical advantages of the different test protocols and the influence of the experimental parameters are discussed. It appears that the frequency of renewing the acid solution during the exposure period is the main parameter that influences the mass loss and the rate of degradation, while the sample geometry and the ratio between the volume of solution and concrete surface area had no clear influence. Nevertheless, there was reasonable agreement between the methods regarding the magnitude of the concrete degradation (resulting in a mass loss of about 2.5 kg/m² in six months time). The use of granulometrically optimized slag cement provided a moderate increase of the concrete resistance against acid attack, and this practice might be recommended in order to increase the durability of structures exposed to sulfuric acid media. The fact that the difference in comparison with SCC-OPC was rather limited shows that the influence of the cement type becomes less relevant in the case of concrete with low w/c ratio and optimized concrete technology. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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25 pages, 13655 KiB

Open AccessArticle

Development of 3D Printed Networks in Self-Healing Concrete

by Cristina De Nardi, Diane Gardner and Anthony Duncan Jefferson

Materials 2020, 13(6), 1328; https://doi.org/10.3390/ma13061328 - 14 Mar 2020

Cited by 34 | Viewed by 4573

Abstract

This paper presents a new form of biomimetic cementitious material, which employs 3D-printed tetrahedral mini-vascular networks (MVNs) to store and deliver healing agents to damage sites within cementitious matrices. The MVNs are required to not only protect the healing agent for a sufficient [...] Read more.

This paper presents a new form of biomimetic cementitious material, which employs 3D-printed tetrahedral mini-vascular networks (MVNs) to store and deliver healing agents to damage sites within cementitious matrices. The MVNs are required to not only protect the healing agent for a sufficient period of time but also survive the mixing process, release the healing agent when the cementitious matrix is damaged, and have minimal impact on the physical and mechanical properties of the host cementitious matrix. A systematic study is described which fulfilled these design requirements and determined the most appropriate form and material for the MVNs. A subsequent series of experiments showed that MVNs filled with sodium silicate, embedded in concrete specimens, are able to respond effectively to damage, behave as a perfusable vascular system and thus act as healing agent reservoirs that are available for multiple damage-healing events. It was also proved that healing agents encapsulated within these MVNs can be transported to cracked zones in concrete elements under capillary driving action, and produce a recovery of strength, stiffness and fracture energy. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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21 pages, 4357 KiB

Open AccessFeature PaperArticle

Behaviour of Pre-Cracked Self-Healing Cementitious Materials under Static and Cyclic Loading

by Giovanni Anglani, Jean-Marc Tulliani and Paola Antonaci

Materials 2020, 13(5), 1149; https://doi.org/10.3390/ma13051149 - 5 Mar 2020

Cited by 29 | Viewed by 3298

Abstract

Capsule-based self-healing is increasingly being targeted as an effective way to improve the durability and sustainability of concrete infrastructures through the extension of their service life. Assessing the mechanical and durability behaviour of self-healing materials after damage and subsequent autonomous repair is essential [...] Read more.

Capsule-based self-healing is increasingly being targeted as an effective way to improve the durability and sustainability of concrete infrastructures through the extension of their service life. Assessing the mechanical and durability behaviour of self-healing materials after damage and subsequent autonomous repair is essential to validate their possible use in real structures. In this study, self-healing mortars containing cementitious tubular capsules with a polyurethanic repairing agent were experimentally investigated. Their mechanical behaviour under both static and cyclic loading was analysed as a function of some factors related to the capsules themselves (production method, waterproof coating configuration, volume of repairing agent stored) or to the specimens (number, size and distribution of the capsules in the specimen). Their mechanical performances were quantified in terms of recovery of load-bearing capacity under static conditions and number of cycles to failure as a function of the peak force under cyclic conditions. Positive results were achieved, with a maximum load recovery index up to more than 40% and number of cycles to failure exceeding 10,000 in most cases, with peak force applied during cyclic loading at least corresponding to 70% of the estimated load-bearing capacity of the healed samples. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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19 pages, 10171 KiB

Open AccessArticle

Self-Compacted Concrete with Self-Protection and Self-Sensing Functionality for Energy Infrastructures

by Alonso Maria Cruz and Puentes Javier

Materials 2020, 13(5), 1106; https://doi.org/10.3390/ma13051106 - 2 Mar 2020

Cited by 13 | Viewed by 2848

Abstract

This paper aims to demonstrate the self-protection and self-sensing functionalities of self-compacted concrete (SCC) containing carbon nanotubes (CNT) and carbon microfibers (CMF) in a hybrid system. The ability for self-sensing at room temperature and that of self-protection after thermal fatigue cycles is evaluated. [...] Read more.

This paper aims to demonstrate the self-protection and self-sensing functionalities of self-compacted concrete (SCC) containing carbon nanotubes (CNT) and carbon microfibers (CMF) in a hybrid system. The ability for self-sensing at room temperature and that of self-protection after thermal fatigue cycles is evaluated. A binder containing a high volume of supplementary mineral additions (30%BFSand20%FA) and different type of aggregates (basalt, limestone, and clinker) are used. The self-diagnosis is assessed measuring electrical resistivity (ER) and piezoresistivity (PZR) in compression mode within the elastic region of the concrete. Thermal fatigue is evaluated with mechanical and crack measurements after heat cycles (290–550 °C). SCC withstands high temperature cycles. The protective effect of the hybrid additive (CNT+CMF) notably diminishes damage by keepinghigher residual strength and lessmicrocracking of the concrete. Significant reductions in ER are detected. The self-diagnosis ability of functionalized SCC isconfirmed with PZR. A content of the hybrid functional additive (CNT+CMF) in the percolation region is recommended to maximize the self-sensing sensitivity. Other parameters as sample geometry, sensor location, power supply, and load level have less influence. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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20 pages, 7862 KiB

Open AccessArticle

First Large Scale Application with Self-Healing Concrete in Belgium: Analysis of the Laboratory Control Tests

by Tim Van Mullem, Elke Gruyaert, Robby Caspeele and Nele De Belie

Materials 2020, 13(4), 997; https://doi.org/10.3390/ma13040997 - 23 Feb 2020

Cited by 63 | Viewed by 7121

Abstract

Due to the negative impact of construction processes on the environment and a decrease in investments, there is a need for concrete structures to operate longer while maintaining their high performance. Self-healing concrete has the ability to heal itself when it is cracked, [...] Read more.

Due to the negative impact of construction processes on the environment and a decrease in investments, there is a need for concrete structures to operate longer while maintaining their high performance. Self-healing concrete has the ability to heal itself when it is cracked, thereby protecting the interior matrix as well as the reinforcement steel, resulting in an increased service life. Most research has focused on mortar specimens at lab-scale. Yet, to demonstrate the feasibility of applying self-healing concrete in practice, demonstrators of large-scale applications are necessary. A roof slab of an inspection pit was cast with bacterial self-healing concrete and is now in normal operation. As a bacterial additive to the concrete, a mixture called MUC+, made out of a Mixed Ureolytic Culture together with anaerobic granular bacteria, was added to the concrete during mixing. This article reports on the tests carried out on laboratory control specimens made from the same concrete batch, as well as the findings of an inspection of the roof slab under operating conditions. Lab tests showed that cracks at the bottom of specimens and subjected to wet/dry cycles had the best visual crack closure. Additionally, the sealing efficiency of cracked specimens submersed for 27 weeks in water, measured by means of a water permeability setup, was at least equal to 90%, with an efficiency of at least 98.5% for the largest part of the specimens. An inspection of the roof slab showed no signs of cracking, yet favorable conditions for healing were observed. So, despite the high healing potential that was recorded during lab experiments, an assessment under real-life conditions was not yet possible. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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21 pages, 6567 KiB

Open AccessArticle

Preparation and Characterization of Self-Healing Mortar Based on “Build-In” Carbonation

by Xin Wang, Wenting Li and Zhengwu Jiang

Materials 2020, 13(3), 644; https://doi.org/10.3390/ma13030644 - 1 Feb 2020

Cited by 8 | Viewed by 2918

Abstract

In this study, a new type of cement-based healing pellets (CHPs) were proposed to accelerate the healing efficiency of concrete, which was mainly based on the introduced Na₂CO₃ on promoting the formation of calcium carbonate (CaCO₃) in cracks. [...] Read more.

In this study, a new type of cement-based healing pellets (CHPs) were proposed to accelerate the healing efficiency of concrete, which was mainly based on the introduced Na₂CO₃ on promoting the formation of calcium carbonate (CaCO₃) in cracks. The effects of Na₂CO₃ on the characteristics of CHPs were firstly investigated, and then the properties of cement mortar mixed with CHPs were studied quantitatively, including the workability, mechanical properties and healing ability. The results showed that higher dosages of Na₂CO₃ in CHPs decreased the size range of pellets and reduced the setting time, fluidity and heat of hydration of mortar. Still more, CHPs reduced the early strength of mortar but kept the intensity growth rate stable such that it had nearly no negative effect on the later strength. With the content of CHPs increasing, the strength of mortar showed a decreasing trend, while the pore-filling efficiency and strength healing rate of mortar were further improved. In addition, as a new type of self-healing pellets for concrete based on the “build-in” carbonation, CHPs improved the strength and healing effectiveness of cement mortar. When the dosage of Na₂CO₃ in CHPs and the content of CHPs in mortar were at 10% and 25%, respectively, mortar obtained highest strength in the later stage and the best healing effect. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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11 pages, 10525 KiB

Open AccessArticle

Preparation and Self-Healing Properties of Clinker/PVP Microsphere in Cement Paste

by Jun Li, Zhengwu Jiang and Wenting Li

Materials 2020, 13(3), 589; https://doi.org/10.3390/ma13030589 - 27 Jan 2020

Cited by 10 | Viewed by 2640

Abstract

This paper presents a new insight into the autolytic mineral self-healing method for cementitious materials. The clinker/PVP (polyvinyl pyrrolidone) autolytic microsphere was prepared via the film coating method with cement clinker as a healing agent and PVP as the autolytic coating film. The [...] Read more.

This paper presents a new insight into the autolytic mineral self-healing method for cementitious materials. The clinker/PVP (polyvinyl pyrrolidone) autolytic microsphere was prepared via the film coating method with cement clinker as a healing agent and PVP as the autolytic coating film. The morphology and chemical structure of the microsphere were characterized by environmental scanning electron microscopy (FESEM) equipped with energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR), respectively. The clinker retaining original mineral healing composition was successfully coated with a PVP film confirmed by FTIR. The maximum film thickness was 7.54 μm, which was determined by laser particle size measurement. The autolytic behavior was measured using isothermal calorimetry and successfully controlled by pretreatment degree (i.e., silane coupling agent amount). Experimental results showed that the compressive strength recovery of cement paste with a 30% microsphere was 54% higher than ordinary cement paste specimens. The damage degree of the specimen was also decreased by adding the autolytic microsphere. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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17 pages, 6337 KiB

Open AccessArticle

Development and Application of Novel Sodium Silicate Microcapsule-Based Self-Healing Oil Well Cement

by Wenting Mao, Chrysoula Litina and Abir Al-Tabbaa

Materials 2020, 13(2), 456; https://doi.org/10.3390/ma13020456 - 17 Jan 2020

Cited by 45 | Viewed by 4890

Abstract

A majority of well integrity problems originate from cracks of oil well cement. To address the crack issues, bespoke sodium silicate microcapsules were used in this study for introducing autonomous crack healing ability to oil well cement under high-temperature service conditions at 80 [...] Read more.

A majority of well integrity problems originate from cracks of oil well cement. To address the crack issues, bespoke sodium silicate microcapsules were used in this study for introducing autonomous crack healing ability to oil well cement under high-temperature service conditions at 80 °C. Two types of sodium silicate microcapsule, which differed in their polyurea shell properties, were first evaluated on their suitability for use under the high temperature of 80 °C in the wellbore. Both types of microcapsules showed good thermal stability and survivability during mixing. The microcapsules with a more rigid shell were chosen over microcapsule with a more rubbery shell for further tests on the self-healing efficiency since the former had much less negative effect on the oil well cement strength. It was found that oil well cement itself showed very little healing capability when cured at 80 °C, but the addition of the microcapsules significantly promoted its self-healing performance. After healing for 7 days at 80 °C, the microcapsule-containing cement pastes achieved crack depth reduction up to ~58%, sorptivity coefficient reduction up to ~76%, and flexural strength regain up to ~27%. The microstructure analysis further confirmed the stability of microcapsules and their self-healing reactions upon cracking in the high temperature oil well cement system. These results provide a promising perspective for the development of self-healing microcapsule-based oil well cements. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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14 pages, 4111 KiB

Open AccessArticle

Evaluation of the Self-Healing Ability of Mortar Mixtures Containing Superabsorbent Polymers and Nanosilica

by Gerlinde Lefever, Didier Snoeck, Dimitrios G. Aggelis, Nele De Belie, Sandra Van Vlierberghe and Danny Van Hemelrijck

Materials 2020, 13(2), 380; https://doi.org/10.3390/ma13020380 - 14 Jan 2020

Cited by 49 | Viewed by 3366

Abstract

Addition of superabsorbent polymers (SAPs) to cementitious mixtures promotes the self-healing ability of the material. When cracking occurs; SAPs present inside the crack will swell upon contact with water and subsequently release this water to stimulate the further hydration of unhydrated cement particles [...] Read more.

Addition of superabsorbent polymers (SAPs) to cementitious mixtures promotes the self-healing ability of the material. When cracking occurs; SAPs present inside the crack will swell upon contact with water and subsequently release this water to stimulate the further hydration of unhydrated cement particles and the calcium carbonate crystallization. However; the inclusion of SAPs affects the mechanical performance of the cementitious material by the creation of macro-pores as water is retracted from the swollen SAP. To counteract the reduction in strength, part of the cement is replaced by nanosilica. In this research, different mixtures containing either SAPs or nanosilica and a combination of both were made. The samples were subjected to wet–dry cycles simulating external conditions, and the self-healing efficiency was evaluated by means of the evolution in crack width, by optical measurements, and a water permeability test. In samples containing SAPs, an immediate sealing effect was observed and visual crack closure was noticed. The smaller influence on the mechanical properties and the good healing characteristics in mixtures containing both nanosilica and SAPs are promising as a future material for use in building applications. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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24 pages, 5417 KiB

Open AccessArticle

Chloride Resistance of Portland Cement-Based Mortar Incorporating High Aluminate Cement and Calcium Carbonate

by Yunsu Lee, Seungmin Lim and Hanseung Lee

Materials 2020, 13(2), 359; https://doi.org/10.3390/ma13020359 - 12 Jan 2020

Cited by 10 | Viewed by 3614

Abstract

Whether chloride resistance is highly influenced by chloride binding capacity remains unknown. In this study, the chloride resistance of Portland cement-based mortar incorporating aluminate cement and calcium carbonate was investigated considering the chloride binding capacity, pore structures and chloride diffusion coefficient from non-steady [...] Read more.

Whether chloride resistance is highly influenced by chloride binding capacity remains unknown. In this study, the chloride resistance of Portland cement-based mortar incorporating aluminate cement and calcium carbonate was investigated considering the chloride binding capacity, pore structures and chloride diffusion coefficient from non-steady state chloride migration and natural chloride diffusion. The cement hydrates were investigated using X-ray diffraction and thermogravimetric analysis. The chloride binding capacity was evaluated based on the chloride adsorption from the solutions using the adsorption isotherm. The aluminate cement, as an available alumina source, can stimulate the formulation of layered double hydroxides, which in turn can increase the chloride binding capacity. The results of mercury intrusion porosimetry show that non-substituted (control) and substituted (only aluminate cement) specimens have capillary pore volume 8.9 vol % and 8.2 vol %, respectively. However, the specimen substituted with aluminate cement and calcium carbonate shows a higher capillary volume (12.9 vol %), which correlates with the chloride diffusion coefficient. Although the specimen substituted with calcium carbonate has a higher chloride binding capacity than the control, it does not necessarily affect the decrease in the chloride diffusion coefficient. The capillary pore volume can affect not only the chloride diffusion but also the chloride adsorption. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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19 pages, 6933 KiB

Open AccessArticle

The Self-Sealing Capacity of Environmentally Friendly, Highly Damped, Fibre-Reinforced Concrete

by Xu Huang, Jun Ge, Sakdirat Kaewunruen and Qian Su

Materials 2020, 13(2), 298; https://doi.org/10.3390/ma13020298 - 9 Jan 2020

Cited by 17 | Viewed by 3419

Abstract

Cracks could attenuate the service life of concrete structures because of the intrusion of hazardous substances such as water. In this study, different proportions of Duras S500 fibre were employed to investigate the self-sealing capacity of environmentally friendly, highly damped, fibre-reinforced concrete (EFHDFRC) [...] Read more.

Cracks could attenuate the service life of concrete structures because of the intrusion of hazardous substances such as water. In this study, different proportions of Duras S500 fibre were employed to investigate the self-sealing capacity of environmentally friendly, highly damped, fibre-reinforced concrete (EFHDFRC) containing 5% crumb rubber. The workability of EFHDFRC with different proportions of the fibre was investigated by mechanical properties test. The self-sealing capacity was first measured by introducing the ultrasonic pulse velocity (UPV) test combined with the damage degree in a time-dependent manner. In addition, the regained compressive strength test and visual inspection were applied as additional measures of the self-sealing capacity. The experimental results show that EFHDFRC with different proportions of fibre showed the maximum sealing degree between the 42nd and 51st days after casting the concrete. EFHDFRC with 0.1% fibre had the best performance and the maximum self-sealing degree (2.82%). In summary, it has been proven that 0.1% fibre could stimulate the self-sealing capacity of EFHDFRC by bridging cracked concrete. Moreover, it is noted that sufficient space in cracks is essential for precipitation formation, which could seal the cracks. The new insights of this innovative self-healing, high-damping material are essential for industrial applications exposed to dynamic load conditions such as railway turnout bearers and sleepers, highspeed rail track slabs, blast-resistant walls and columns, and so on. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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16 pages, 4739 KiB

Open AccessArticle

Corrosion Features of the Reinforcing Bar in Concrete with Intelligent OH⁻ Regulation of Microcapsules

by Shuxian Hong, Shaofeng Qin, Biqin Dong and Feng Xing

Materials 2019, 12(23), 3966; https://doi.org/10.3390/ma12233966 - 29 Nov 2019

Cited by 9 | Viewed by 3098

Abstract

Corrosion is a challenging problem for marine concrete infrastructure projects. In this study, an intelligent OH⁻-regulated microcapsule is designed to prevent reinforcement corrosion, taking ethylcellulose (EC) as shell material and calcium oxide (CaO) as core material. X-ray computed tomography (XCT) is [...] Read more.

Corrosion is a challenging problem for marine concrete infrastructure projects. In this study, an intelligent OH⁻-regulated microcapsule is designed to prevent reinforcement corrosion, taking ethylcellulose (EC) as shell material and calcium oxide (CaO) as core material. X-ray computed tomography (XCT) is used to trace and contrast the corrosion profiles of the concrete reinforcement bar with and without the microcapsule. The results show that the OH⁻-regulated microcapsule exhibits effective corrosion protection by delaying corrosion initiation and cracking. An SEM study revealed that the microcapsule could be broken as Cl⁻ invades the concrete. However, intelligent OH⁻ regulation was realized by releasing CaO. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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21 pages, 5358 KiB

Open AccessArticle

Sensing of Damage and Repair of Cement Mortar Using Electromechanical Impedance

by Hussameldin Taha, Richard J. Ball and Kevin Paine

Materials 2019, 12(23), 3925; https://doi.org/10.3390/ma12233925 - 27 Nov 2019

Cited by 11 | Viewed by 2864

Abstract

Lead zirconium titanate (PZT) has recently emerged as a low-cost material for non-destructive monitoring for civil structures. Despite the numerous studies employing PZT transducers for structural health monitoring, no studies have assessed the effects of both damage and repair on the electromechanical impedance [...] Read more.

Lead zirconium titanate (PZT) has recently emerged as a low-cost material for non-destructive monitoring for civil structures. Despite the numerous studies employing PZT transducers for structural health monitoring, no studies have assessed the effects of both damage and repair on the electromechanical impedance response in cementitious materials. To this end, this study was conducted to assess the effects of the damage and repair of mortar samples on the electromechanical response of a surface-mounted PZT transducer. When damage was introduced to the specimen in stages, the resonance frequencies of the admittance signature were shifted to lower frequencies as the damage increased, and an increase in the peak amplitude was detected, indicating an increase in the damping and a reduction in the material stiffness properties. Also, increasing the damage in the material has been shown to decrease the sensitivity of the PZT to further damage. During the repair process, a noticeable difference between the after-damage and the after-repair admittance signatures was noted. The root-mean-square deviation (RMSD) showed a decreasing trend during the repair process, when compared to the before repair RMSD response which indicated a partial recovery for the material properties by decreasing the damping property in the material. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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14 pages, 1530 KiB

Open AccessArticle

Influence of Effective Water-to-Cement Ratios on Internal Damage and Salt Scaling of Concrete with Superabsorbent Polymer

by Minsoo Kim, Sung-Hoon Kang, Sung-Gul Hong and Juhyuk Moon

Materials 2019, 12(23), 3863; https://doi.org/10.3390/ma12233863 - 22 Nov 2019

Cited by 17 | Viewed by 3210

Abstract

Superabsorbent polymer (SAP) is attracting attention as a water-entraining admixture that reduces shrinkage or heals cracks in concrete. Cross-linked sodium polyacrylate SAPs, which are the most widely produced SAPs in the global market, are applicable as concrete admixtures. However, there have been contradictory [...] Read more.

Superabsorbent polymer (SAP) is attracting attention as a water-entraining admixture that reduces shrinkage or heals cracks in concrete. Cross-linked sodium polyacrylate SAPs, which are the most widely produced SAPs in the global market, are applicable as concrete admixtures. However, there have been contradictory results on the freeze–thaw resistance of concrete with SAPs. This study aims to clarify these results considering the water absorption behavior of SAPs in hardened concrete when effective water-to-cement ratios are different. Firstly, the absorbencies of one kind of cross-linked sodium polyacrylate SAP (SAP_SP) in pore solution and fresh mortar were measured by a tea bag test and flow test, respectively. Pore size distribution, capillary water absorption, and deformation during freeze–thaw cycles were analyzed for mortar samples with varying SAP_SP dosages. In the main tests, concrete samples with three different SAP_SPs/cement ratios (0.1%, 0.2%, and 0.3%) and a reference sample were prepared, and internal damage and salt scaling were measured under freeze–thaw cycles. Because SAP_SP absorbs water in fresh mixtures, additional water was added to the mixture considering the water absorbency of the SAP_SP. It was found that the used SAP_SPs prematurely release their stored water so the effective water-to-cement ratio was increased when a larger amount of SAP_SP was used. The higher effective water-to-cement ratio caused more internal damage and salt scaling due to the weaker cementitious matrix. In addition, mortar samples with a high SAP_SP content show a larger absorption of capillary water than the reference sample. The result can be interpreted by an observation that SAP_SP in air voids absorbs water and expands to relatively large capillary pores or neighbor air voids during the capillary water absorption process. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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15 pages, 3656 KiB

Open AccessArticle

Discussing Different Approaches for the Time-Zero as Start for Autogenous Shrinkage in Cement Pastes Containing Superabsorbent Polymers

by José Roberto Tenório Filho, Maria Adelaide Pereira Gomes de Araújo, Didier Snoeck and Nele De Belie

Materials 2019, 12(18), 2962; https://doi.org/10.3390/ma12182962 - 12 Sep 2019

Cited by 30 | Viewed by 3073

Abstract

Many studies have already been published concerning autogenous shrinkage in cementitious materials. Still, no consensus can be found in the literature regarding the determination of the time-zero to initiate the recording of autogenous shrinkage. With internal curing agents, a correct evaluation of their [...] Read more.

Many studies have already been published concerning autogenous shrinkage in cementitious materials. Still, no consensus can be found in the literature regarding the determination of the time-zero to initiate the recording of autogenous shrinkage. With internal curing agents, a correct evaluation of their efficiency depends on an appropriate choice of the time-zero. This study investigates different approaches to estimate the time-zero for cement paste mixtures with and without superabsorbent polymers as internal curing agents. The initial and final setting times were determined by an electronic Vicat and ultrasonic pulse velocity measurements (UPV); the transition point between the fluid and solid state was determined from the autogenous strain curve; the development of the capillary pressure was also studied. The choice of time-zero before the transition point led to higher values of shrinkage strain that should not be taken into account for autogenous shrinkage. A negligible difference was found between the strains when the final setting time and the transition point were taken as time-zero. Considering the artefacts and practical issues involving the different methods, the use of the transition point from the autogenous strain curve is the most suitable technique for determining the time-zero. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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14 pages, 4907 KiB

Open AccessArticle

Effect of Addition of Ca²⁺ and CO₃²⁻ Ions with Temperature Control on Self-Healing of Hardened Cement Paste

by Heesup Choi, Masumi Inoue, Dongmin Kim, Hyeonggil Choi and Risa Sengoku

Materials 2019, 12(15), 2456; https://doi.org/10.3390/ma12152456 - 1 Aug 2019

Cited by 8 | Viewed by 3289

Abstract

Concrete has a remarkably low ratio of tensile strength to compressive strength, and is widely used in construction. However, the occurrence of cracks in a concrete structure is inevitable. Nevertheless, in the presence of adequate moisture, small cracks in the concrete structure exhibit [...] Read more.

Concrete has a remarkably low ratio of tensile strength to compressive strength, and is widely used in construction. However, the occurrence of cracks in a concrete structure is inevitable. Nevertheless, in the presence of adequate moisture, small cracks in the concrete structure exhibit a propensity to self-heal by getting filled due to the rehydration of cement particles and the subsequent precipitation of calcium carbonate (CaCO₃). According to previous studies, the self-healing performance can be maximized by optimizing the temperature and pH to control the crystal formation of CaCO₃. This study focused on the crystal form of CaCO₃ generated in the self-healing of a cement-based composite material. To evaluate the self-healing performance depending on the type of aqueous solution and the temperature, the weight change, the weight change rate, and the porosity reduction in each case were evaluated. Moreover, to increase the generation of CaCO₃ (which is a self-healing precipitate), nanosized ultrafine CO₂ bubbles using CO₂ gas were used, along with an adequate supply of Ca²⁺ by adjusting the aqueous solution (Ca(OH)₂, CaO + ethanol). For greater pore-filling effects by controlling the CaCO₃ crystal forms in the cement matrix, the change in the crystal form of the precipitated CaCO₃ in the hardened cement paste with changing temperature was analyzed by scanning electron microscopy and X-ray diffraction. As a result, the possibility of the effective generation and control of vaterite with a dense pore structure together with calcite was confirmed by adjusting the temperature to approximately 40 °C at a pH of 12. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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21 pages, 3639 KiB

Open AccessArticle

Using the Steady-State Chloride Migration Test to Evaluate the Self-Healing Capacity of Cracked Mortars Containing Crystalline, Expansive, and Swelling Admixtures

by Fahad ul Rehman Abro, Abdul Salam Buller, Kwang-Myong Lee and Seung Yup Jang

Materials 2019, 12(11), 1865; https://doi.org/10.3390/ma12111865 - 9 Jun 2019

Cited by 25 | Viewed by 4010

Abstract

Interest in self-healing-crack technologies for cement-based materials has been growing, but research into such materials remains in the early stage of development and standardized methods for evaluating healing capacity have not yet been established. Therefore, this study proposes a test method to evaluate [...] Read more.

Interest in self-healing-crack technologies for cement-based materials has been growing, but research into such materials remains in the early stage of development and standardized methods for evaluating healing capacity have not yet been established. Therefore, this study proposes a test method to evaluate the self-healing capacity of cement-based materials in terms of their resistance to chloride penetration. For this purpose, the steady-state chloride migration test has been used to measure the diffusion coefficients of cracked mortar specimens containing crystalline, expansive, and swelling admixtures. The results of the present study show that the time to reach a quasi-steady-state decreased and the diffusion coefficients increased as the potential increased because of the potential drop inside the migration cell and self-healing that occurred during the test. Therefore, use of a high potential is recommended to minimize the test duration, as long as the temperature does not rise too much during the test. Using this test method, the self-healing capacity of the new self-healing technologies can be evaluated, and an index of self-healing capacity is proposed based on the rate of charged chloride ions passing through a crack. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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15 pages, 1764 KiB

Open AccessArticle

Parameter Study of Superabsorbent Polymers (SAPs) for Use in Durable Concrete Structures

by Laurence De Meyst, Els Mannekens, Maria Araújo, Didier Snoeck, Kim Van Tittelboom, Sandra Van Vlierberghe and Nele De Belie

Materials 2019, 12(9), 1541; https://doi.org/10.3390/ma12091541 - 10 May 2019

Cited by 39 | Viewed by 4231

Abstract

Superabsorbent polymers (SAPs) can be added to a concrete mixture to provide internal curing and reduce the risk for early-age shrinkage cracking. Hence, they can help to increase the overall durability of concrete structures. The type, swelling characteristics, kinetics of water release, amount [...] Read more.

Superabsorbent polymers (SAPs) can be added to a concrete mixture to provide internal curing and reduce the risk for early-age shrinkage cracking. Hence, they can help to increase the overall durability of concrete structures. The type, swelling characteristics, kinetics of water release, amount and particle size of the SAPs will dictate their effectiveness for this purpose. In this paper, SAPs with different cross-linking degrees, particle sizes and amount of solubles are investigated. By varying these parameters, insight can be gained on the influence of each of these parameters on SAP properties such as the swelling capacity. In a next step, the SAPs can be implemented in mortar to assess their influence on mortar properties like workability, compressive strength or hydration kinetics. Based on these results, the ‘ideal’ SAP with tunable properties for a specific concrete application can be selected. For this purpose, an anionic SAP was synthesized with varying amounts of cross-linker and ground to particle sizes with d₅₀ varying between 10 and 100 µm. The swelling capacity in demineralised water of 40 µm SAP particles increased with a decreasing degree of cross-linker from 66 g/g SAP with 1 mol% cross-linker to 270 g/g SAP in case of 0.15 mol% cross-linker, and was about three to four times larger than the swelling capacity in the prepared cement filtrate. The SAPs were tested for their effect on mortar workability, cement hydration kinetics and mechanical properties of the hardened mortar. With proper compensation for the absorbed water by the SAPs, the mortar workability was not negatively affected and the reduction in flow over the first two hours remained limited. The SAPs with the lowest swelling capacity, resulting in the smallest total amount of macro pores formed, showed the smallest negative effect on mortar compressive strength (a reduction of 23% compared to the reference after 28 days for an addition of 0.5 m% SAP) and a negligible effect on cement hydration. The difference in strength with the reference decreased as a function of mortar age. When using SAPs with particle sizes in the range of 10–100 µm, no significant differences between the studied particle sizes were found concerning the mortar properties. With the ease of upscaling in mind, the need to purify the SAPs and to remove the non-cross-linked soluble fraction was further investigated. It was shown that the solubles had no effect on the mortar properties, except for increasing the setting time with almost 100%. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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Review

Jump to: Research

23 pages, 1245 KiB

Open AccessReview

Recent Advances on the Application of Layered Double Hydroxides in Concrete—A Review

by Zahid M. Mir, Alexandre Bastos, Daniel Höche and Mikhail L. Zheludkevich

Materials 2020, 13(6), 1426; https://doi.org/10.3390/ma13061426 - 20 Mar 2020

Cited by 42 | Viewed by 4751

Abstract

The issue of chloride induced corrosion of reinforced concrete is a serious problem affecting infrastructure globally and causing huge economic losses. As such this issue has gained a considerable attention in the scientific community in the recent past. Layered Double Hydroxides (LDHs) have [...] Read more.

The issue of chloride induced corrosion of reinforced concrete is a serious problem affecting infrastructure globally and causing huge economic losses. As such this issue has gained a considerable attention in the scientific community in the recent past. Layered Double Hydroxides (LDHs) have recently emerged as a new class of concrete-additives with a potential to increase the chloride resistance of concrete and mitigate corrosion. LDHs are clay like structures consisting of positively charged layers of cations with associated hydroxides and exchangeable anions in between the layers. Due to this charge balanced structure, LDHs possess the property of encapsulating an anion from the environment and replacing it with an exchangeable anion present in its layers. Potential applications include chloride entrapment in concrete and delivery of corrosion inhibiting anions. However, many versatile compositions of LDHs can be easily synthesized and their application as cement additives reach far beyond corrosion mitigation in concrete. This review presents a summary of recent advances on the applications of LDH in concrete. An extensive set of recently published literature has been critically reviewed and trends have been identified. Full article

(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)

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