Crystalline Admixture Research Articles

Effect of different exposure conditions on the self‐healing capacity of engineered cementitious composites with crystalline admixture

AbstractIn this study, the effect of different exposure conditions of ambient air, tap water, and seawater on two levels of crack widths in engineered cementitious composites (ECC) were investigated. Crystalline admixture (CA) was implemented in the ECC mix to promote self‐healing capacity. Flexural testing on prism specimens (100 × 100 × 350 mm) was conducted to evaluate self‐healing by recovering the stiffness in the specimens with crack widths below 200 μm. Water permeability test was also carried out to assess the crack‐filling capability of ECC disk specimens (100‐mm diameter × 50‐mm thickness) with single crack widths over 1 mm. Digital image correlation technique was used to monitor crack propagation patterns and crack widths. To analyze the microstructure of the healing products, X‐ray diffraction test was conducted on groups of tap water and seawater exposures. Concluding results proved seawater to be a promising environmental condition for the self‐healing process in ECC specimens incorporating CA, in terms of recovery of mechanical and transport properties. Brucite was found to be formed as the additional healing agent that promoted self‐healing in this condition. These results can be applied for coastal concrete structures.

Appropriate Selection of Materials for Making Durable Self Compacting Concrete for Using in Underground Structures

Abstract: Selecting appropriate and suitable of materials plays an important role in concrete mix design to meet the general requirements of European guidelines for self-compacting concrete and to ensure a balance between deformability and stability. The type of selected materials and the ratios of concrete ingredients can be affected by the fresh and hardened properties of the concrete. In the contract agreement of the Mumbai Metro underground project, the technical specifications clearly state the values of limits set for achieving the durability parameters for the life of 120 years of the structure. According to the requirement of the site conditions Self-compacting concrete was designed with available material, special material like Ultra GGBS- Alccofine 1203 and crystalline waterproofing admixture. Self-compacting concrete is superior concrete than the traditional concrete with high workability, no segregation, no bleeding, and it is also suitable for use in structures with long-distance pumping in the instant case i.e., more than 120-meter length in Underground NATM tunnels, cross-passages, and the concrete structure of the underground metro station box. The paper presents a comparison between concrete mix designs and their achieved test parameters suitable for the contract specification of Mumbai metro underground project

Improvising the Self-Healing Capabilities of Concrete Using Different Pozzolanic Materials and Crystalline Admixtures

Improvising the Self-Healing Capabilities of Concrete Using Different Pozzolanic Materials and Crystalline Admixtures

Corrosion resistance of RC/UHTCC beams with various healing promoters in marine environment

Four types of reinforced concrete/ultrahigh toughness cementitious composite (RC/UHTCC) composite beams with various healing promoters were prepared to study the effect of self-healing behavior on corrosion resistance in marine environment from the structural component level. Healing promoters included superabsorbent polymers (SAP), SAP treated with calcium solution, crystalline admixture (CA). The specimens with SAP were cured by dry-wet cycles, and other specimens were immersed curing. Self-healing behavior of crack was observed by the microscope before and after healing. Accelerated corrosion test was performed on pre-cracked specimens to test chloride permeability and corrosion resistance. The healing degree of crack was proposed based on the healing area of crack, increased by adding healing promoters, especially for CA. The corrosion resistance of four types of cracked members was improved after healing in marine environment, due to self-healing behavior of crack reducing chloride permeability. The increasing trend of corrosion resistance of four types of members was consistent with the healing degree of crack. The healing degrees of crack for specimens without healing promoters, with SAP, treated SAP and CA were 40.75%, 62.11%, 84.05% and 100%, the corresponding decrease range of corrosion ratios were 15.40%, 24.07%, 32.61% and 47.14%, respectively. This indicated that the corrosion resistance of cracked reinforced members was improved by healing promoters with excellent healing degree of crack in marine environment. The closure of crack and improvement of corrosion resistance verified that the reinforced members achieved good self-healing properties to improve the recovery of durability in marine environment from the structural component level.

Comprehensive evaluation of self-healing of concrete with different admixtures under laboratory and long-term outdoor expositions

This project presents the evaluation of the self-healing of fibre reinforced concretes containing various admixtures (crystalline admixture CA, expansive agent CSA, superabsorbent polymer SAP) and combinations. They were exposed to several laboratory conditions (water immersion, wet/dry cycles ambient air for 3 months, water flow for 1 week) and to a long-term outdoor exposure for 1 year. Self-healing capacity was assessed by water permeability measurements, mechanical recovery, visual observations and microscopic analyses on the same specimen. This paper presents the mechanical behaviour and microstructure of the healing products, and the correlations with the water permeability measures presented in previous research. The results showed that a high healing of cracks based on water permeability did not necessarily lead to a high mechanical recovery. The highest Strength Regains (109% in average) were obtained for specimens exposed outdoor that presented the lowest Healing Ratios (71% in average). The local density of the healing products may govern the Healing Ratio, while the type of healing products and their extent in the crack depth may control the Strength Regain. Finally, the SAP mix showed overall the best self-healing performance, regarding both durability and mechanical properties.

Evaluation of self-healing in concrete using linear and nonlinear resonance spectroscopy

In this study, self-healing in concrete incorporating two types of healing agents, i.e., 1) a self-healing capsule and 2) supplementary cementitious materials with crystalline admixtures, is monitored using linear and nonlinear resonance acoustic spectroscopy techniques. Beam-shaped concrete specimens are prepared using the healing agents, and after 28 days, a single vertical crack with a width ranging from 0.25 to 0.35 mm is generated at the center of the specimens. To monitor the self-healing process in concrete, the samples are vibrated via impact-based excitation methods in the flexural and longitudinal directions, whereas the linear resonance frequency and acoustic nonlinearity parameter α are measured for two months. Additionally, the acoustic nonlinearity parameter is analyzed using two different methods: 1) multiple impacts with manually controlled amplitude, and 2) single impact with artificially controlled amplitude by changing the windowing region in a signal. Test results show that the linear resonance frequency increases up to 86%–97% that of the uncracked condition after 63 days of self-healing. The linear trend of the resonance frequency is correlated significantly with the decrease in the external crack area, but the change in α is affected by the presence of partially filled cracks than by the overall crack area.

Textile-reinforced mortar: Durability in salty environment

Reinforcing a fine-grained cement-based matrix with a textile fabric is an emerging approach in civil engineering, termed Textile Reinforced Mortar (TRM). We propose to load the ultra-high-performance matrix with nano-additives, i.e., a crystalline admixture (CA) or CA plus alumina nanofibers. The mix was designed to yield flow values - in the fresh state - suitable for retrofitting, and to provide high compressive strength. Examination of the durability of the TRM elements exposed to salty environments unexpectedly showed enhanced tensile strength (<81%). This is owing to the growth of salt crystals at the matrix–textile interface resulting in stronger bond strength, as imaged by scanning electron microscopy, identified by acoustic emission measurements, and validated by pull-off tests.

Capacity of Self-Sealing Concrete Embedding Crystalline Admixture

Concrete is one of the most intelligent and widely utilized man-made materials in the construction industry. Despite this, even high-quality concrete is susceptible to porosity, which reduces its serviceability period. Furthermore, there is an increasing need to increase longevity due to environmental exposure such as soil moisture, corrosive outside elements, or structural defects forming in the surface of concrete. The use of crystalline admixtures in concrete is one of the many approaches to reducing these risks. When crystalline admixtures come into contact with water, they form thin crystals that fill pores, capillaries, and micro fractures, as a result making concrete a self-sealing material. When the concrete has dried, the crystalline particles remain dormant until they come into contact with additional water, which causes them to crystallize once more. This research aims to analyze and compare the material properties between commonly used concrete and concrete where crystalline waterproofing is present. Furthermore, experiments are conducted to evaluate each of the concrete samples: compressive strength, water permeability and flexure strength. As a result, demonstrating benefits or negative aspects in the use of crystalline admixture in the early stages of concrete is important. It is not yet defined, weather this is the future of cutting-edge concrete and the impact that it will have in the Albanian building market.

Performance and mechanisms of stimulated self-healing in cement-based composites exposed to saline environments

Performance and mechanisms of stimulated autogenous self-healing in cement-based composites with addition of crystalline admixtures (CAs) exposed to water, seawater and NaCl solutions were investigated. Crack closure, chloride penetration, water absorption and healing products were characterized for cracked mortars exposed to wet/dry cycles. Moreover, leaching and hydration of cement affected by CAs were studied to reveal mechanisms of stimulating self-healing. The slight difference in self-healing products formed in the three saline solutions between mortars with and without CAs indicated that the capacity of stimulated self-healing strongly depends on exposure environments. Correlation between crack closure and durability recovery for cracked specimens suggests a need for performance-recovery-based method for assessing the self-healing ability. Comparison of two commercial CAs having different alkalis and effects on cement hydration revealed that mechanisms of stimulated self-healing vary significantly with the type of CAs.

Self-healing of concrete containing different admixtures under laboratory and long-term real outdoor expositions based on water permeability test

This work assessed the self-healing capacity of fibre reinforced concretes containing different admixtures (crystalline admixture CA, expansive agent CSA and superabsorbent polymer SAP) and submitted to different exposure conditions in laboratory (water immersion, wet/dry cycles and ambient air for 3 months, water flow for 1 week) as well as a long-term real outdoor exposition (1 year in Montreal climate). Self-healing was assessed by water permeability measurements performed on prisms presenting a realistic flexural macrocrack. The results, presented in Healing Ratio and equivalent crack width, showed different self-healing kinetics and efficiency according to the mix composition, but especially to the exposition. The average final Healing Ratios reached 84% in water, 93% in wet/dry cycles and 71% in water flow and in real outdoor exposure. The SAP and CA mixes presented the best healing performance in real outdoor condition. No synergetic effect was found when combining CA+CSA and CA+SAP. Additional microscopic analyses showed different healing products according to the exposition.

A discrete numerical model for the effects of crack healing on the behaviour of ordinary plain concrete: Implementation, calibration, and validation

In the last decade the self-healing of cracks in cementitious materials has been gaining an increasing interest by both the concrete industry and the scientific community. Framed into the Horizon 2020 project ReSHEALience, the present research work aims to formulate a proposal for the numerical modelling of autogenous and stimulated autogenous healing in ordinary plain cement-based materials, whose composition is enriched, in the latter case, with crystalline admixtures. In this paper a meso-scale discrete model that also considers the healing process is presented, relying on the coupling and the enhancement of two models: the Hygro-Thermo-Chemical model, for the simulation of chemical, moisture and heat transport phenomena, and the Lattice Discrete Particle Model, for the mechanical part. The evolution of the healing phenomenon is implemented into the HTC discrete formulation, in order to simulate the degree of crack closure over time. The latter is then employed to capture how the self-repairing affects both moisture permeability and mechanical performances. Finally, the results of a laboratory campaign, carried out at the Politecnico di Milano, are used for calibrating and validating the model presented.

Influence of Crystalline Admixtures and Their Synergetic Combinations with Other Constituents on Autonomous Healing in Cracked Concrete-A Review.

Crystalline admixtures (CAs) are new materials for promoting self-healing in concrete materials to repair concrete cracks. They have been applied to tunnel, reservoir dam, road, and bridge projects. The fundamental research and development of CAs are needed concerning their practical engineering applications. This paper reviews the current research progress of commercial CAs, including self-made CA healing cracks; the composition of CA; healing reaction mechanism; the composition of healing products; distribution characteristics of healing products; the influence of service environment and crack characteristics on the healing performance of CA; and coupling healing performance of CA with fiber, expansive agent, and superabsorbent polymers. The current research findings are summarized, and future research recommendations are provided to promote the development of high-performance cement matrix composites.

The investigations on properties of self-healing concrete with crystalline admixture and recycled concrete waste

The concept of self-healing concrete is becoming more necessary as sustainability in construction is more desirable. Amongst the current solutions in this technology are autogenous, chemical, and bacterial self-healing. It is paramount that secondary raw materials be used in the production of selfhealing concrete as a form of a sustainable solution. Therefore, in this paper, the admixture “Betocrete-CP-360-WP”, which is a crystallizing waterproofing admixture with hydrophobic effect and is 100% recyclable, has been used and its effect on the physical, chemical, and mechanical properties of concrete, as well as selfhealing capabilities of concrete, have been determined. According to the obtained results, the crystalline additive “Betocrete-CP-360-WP” has no effect on density and slightly increases the amount of entrained air in the concrete mix. However, it does decrease the workability of the concrete mixture which could prove problematic in transportation to the construction site or in concreting in general. Also, with the crystalline admixture in the concrete mix, a 60% reduction in concrete compressive strength after one day of hardening has been estimated, but after 7 and 28 days, the strength attained is within the ranges of the control samples. In addition, concrete containing Betocrete-CP360-WP was 30% less water permeable as compared to control samples. The self-healing efficiency of the concrete was determined by a water flow test through a formed crack (approximately 0.35 mm wide). This was done by gluing a plastic pipe to the top of the cracked concrete specimens and maintaining a constant pressure of the water in the pipe. The experiment was continued for 28 days, and the crack self-healing efficiency of the concrete was calculated from the differences in the amount of water passed through the crack before healing and after 7, 14, 21 and 28 days of the healing process. After 28 days of the water flow test, the cracks in the concrete with the crystalline admixture and recycled concrete dust were completely healed, while the control specimens were not.

Effect of healing agents on the rheological properties of cement paste and compatibility with superplasticizer

Self-healing concrete is considered as a new generation of concrete with the ability to heal cracks without human intervention. The healing agents are incorporated into the concrete to activate the healing mechanism and to improve the healing efficiency. While both lab- and large-scale projects have shown that the addition of healing agents can have a possible positive effect on the hardened concrete properties (e.g. compressive strength), unfortunately, the evaluation of fresh properties of self-healing concrete mixes is often neglected. In the current study, the effect of healing agents is clearly identified starting from the paste level. Different techniques were used to study the effect of healing agents on the consistency, viscosity and adsorption behaviour of PCE-based superplasticizer in cement paste. A crystalline admixture and bacteria were used as healing agents, and CEM III/A was used as the binder component of the paste. The results showed that the inclusion of bacteria did not influence the rheological properties of the cement paste and no incompatibility issues were found with the superplasticizer. On the other hand, the presence of the crystalline admixture in the paste interfered with the rheological properties of the cement paste as a reduction of workability, an increase of paste viscosity, and an increased adsorption of superplasticizer.

Research upon self-sealing of fibre reinforced mortar with integral crystalline waterproofing admixtures

The paper presents results of an experimental research made upon the self-sealing of a fibre reinforced mortar with an integral crystalline waterproofing admixture in a dosage rate of 1-3 % of the cement mass. Samples were pre-loaded in three point bending up to 90 % of the ultimate capacity and conditioned in wet-dry cycles. Micro-cracks width was measured with a microscope after pre-loading, and up to 20 days. The results show that the 3 % admixture content presents the superior self-sealing performance both in the terms of the self-sealing degree and self-sealing rate. According to the results, lower contents of crystal-line admixture cannot predict a desirable self-sealing target, despite the fact that the self-sealing potential/ability is indisputable and may take longer periods.

Effect of Chelating Crystalline Admixture on Hydration, Microstructure and Self-Healing Ability of Cement-Based Binder Containing High-Volume Fly Ash and Blast-Furnace Slag

Effect of Chelating Crystalline Admixture on Hydration, Microstructure and Self-Healing Ability of Cement-Based Binder Containing High-Volume Fly Ash and Blast-Furnace Slag

Effect of Chelating Crystalline Admixture on Hydration, Microstructure and Self-Healing Ability of Cement-Based Binder Containing High-Volume Fly Ash and Blast-Furnace Slag

Effect of Chelating Crystalline Admixture on Hydration, Microstructure and Self-Healing Ability of Cement-Based Binder Containing High-Volume Fly Ash and Blast-Furnace Slag

Experimental Study on the Influence of a Cementitious Permeable Crystallization Admixture (CPCA) in Improving Concrete Durability

The corrosion of steel reinforcement in reinforced concrete is a serious problem affecting the durability of concrete structures. And the steel corrosion caused by chloride ion erosion is the most serious damage to reinforced concrete structures, which affects the safety and service life of the structure. In order to prevent steel corrosion caused by chloride, it is necessary to pay more attention to chloride ion penetration damage. At present, the most commonly used method is to use additives in concrete structures, so as to improve the durability of concrete by reducing its permeability coefficient. Cement‐based permeable crystalline admixtures can effectively improve the impermeability and mechanical properties of concrete by complex crystallization reactions between reactive chemicals and cement gels. In the paper, the Penetron admix 803 was selected as a typical CPCA in the experimental study, and the rapid chloride migration (RCM) experiments and mechanics experiments were carried out for four concrete structures with different dosages of Penetron admix 803 (PA8). Compared with plain concrete, the concrete structure containing PA8 makes it difficult for water and other liquids to enter by filling micropores and shrinkage cracks by scanning electron microscope test, so its impermeability is greatly improved. And concrete structure containing permeable crystalline admixture can reduce chloride ion permeability effectively. The experimental results showed that with the increase of PA8 content, the diffusion coefficient of the concrete structure decreased rapidly from 45.8 × 10−12 m2/s to 17.7 × 10−12 m2/s, while the service life of concrete structures increased continuously. And the mechanism of the chemical reaction between PA8 and the internal components of concrete structure was revealed, which was mainly due to the catalytic reaction between the reactive chemicals of PA8 and the cement hydrates of concrete structure forming insoluble crystals filled with concrete micropores. Experimental and theoretical results indicate that the permeable crystalline admixture can greatly improve the chloride‐related durability and mechanical properties of the concrete structure.

Piezoresistive performance of hydrophobic cement-based sensors under moisture and chloride-rich environments

Silicone hydrophobic powder (SHP) and crystalline waterproofing admixture (CWA) were used to improve the impermeability of carbon black (CB)/cement-based sensors. The mechanical, electrical and piezoresistive properties, waterproofing and chloride resistance of CB/cementitious composites were investigated in this study. The piezoresistivity before or after different durations of immersion in freshwater and 3% sodium chloride solution and the stability in freshwater and marine environment were studied and compared. The results show that compressive strength increased with the additions of CWA and SHP, while the tensile strength slightly decreased with CWA, due to the formation of crystalline. Moreover, cementitious composites with SHP exhibited the best water impermeability, while the counterpart containing CWA presented the optimal chloride resistance. Although cementitious composites with SHP exhibited the highest electrical resistivity, the most stable piezoresistivity occurred after 90 days of immersion in freshwater. On the other hand, cementitious composites incorporating CWA presented the lowest electrical resistivity, but the piezoresistivity continually decreased with the immersion duration. Because of the free ions, piezoresistivity increased as a result of the immersion in sodium chloride solution. The related results will provide an insight into the piezoresistivity of hydrophobic cement-based sensors under moisture and chloride environments for future structural health monitoring.

Understanding the Impacts of Healing Agents on the Properties of Fresh and Hardened Self-Healing Concrete: A Review

Self-healing concrete has emerged as one of the prospective materials to be used in future constructions, substituting conventional concrete with the view of extending the service life of the structures. As a proof of concept, over the last several years, many studies have been executed on the effectiveness of the addition of self-healing agents on crack sealing and healing in mortar, while studies on the concrete level are still rather limited. In most cases, mix designs were not optimized regarding the properties of the fresh concrete mixture, properties of the hardened concrete and self-healing efficiency, meaning that the healing agent was just added on top of the normal mix (no adaptations of the concrete mix design for the introduction of healing agents). A comprehensive review has been conducted on the concrete mix design and the impact of healing agents (e.g., crystalline admixtures, bacteria, polymers and minerals, of which some are encapsulated in microcapsules or macrocapsules) on the properties of fresh and hardened concrete. Eventually, the remaining research gaps in knowledge are identified.