Fungi: A Neglected Candidate for the Application of Self-Healing Concrete

Self-healing mechanism in concrete has been so far achieved mainly by three approaches: autogenous healing, encapsulation of polymeric material, and biologically induced mineralization of calcium carbonate. The microbial approach prevails over the other two approaches due to the high compatibility between the filler material and the concrete compositions. Although the term “microbe” refers to many different types of organisms, research work on self-healing concrete has been so far restricted to bacteria. In this perspective article, we review the current status of bacteria-mediated self-healing concrete and summarize the prospects for future advances. In particular, we point out that fungi may have distinctive advantages over other microbes to be used as self-healing agents

Effect of Pre-dispersing Metakaolin in Water on the Properties, Hydration, and Metakaolin Distribution in Mortar

The effects of pre-dispersing metakaolin (MK) in water on the properties and hydration of mortar and distribution of MK particles in mortar were characterized by analytical techniques. Zeta-potential of MK-water dispersion significantly decreased with the increase of pH of solution, resulting in a stable dispersion at pH of 8 with zeta-potential of −40 mV. The bulk density of MK-water slurry rapidly increased with water/MK ratio due to the surface tension force of water and filling of spaces by water, resulting in a maximum bulk density of 665.2 kg/m3 at water/MK ratio of 1.0. Comparing to that of powder MK, pre-dispersing MK in water did not alter hydration products, slightly improved compressive strength, and pore structure, but further reduced shrinkage and significantly improved the uniformed distribution of MK particles in mortar

Water–Binder Ratio Monitoring as a Quality Control Tool for the High-Performance Concrete Used in the Construction of the Submerged Tunnel

The designed service life of Hong Kong-Zhuhai-Macao Bridge is 120 years. Concrete quality control for the submerged tunnel of the project is an important work to assure the designed service life. This article is to present an advanced concrete performance prediction method based on water–binder ratio (w/b) monitoring, which is used to serve for concrete quality control. During experiments in the lab, the w/b of submerged tunnel concrete mix proportion was designed to fluctuate up and down, while the other compositions were kept constant. Concretes with different w/b were prepared. The w/b of fresh concrete was tested, followed by preparation of specimens for compressive strength and chloride diffusion coefficient tests. The compressive strength and chloride diffusion coefficient of the hardened concrete were tested. Relationships between the tested w/b and the compressive strength and chloride diffusion coefficient were established. The fitting curves were taken as the prediction models. During construction of submerged tunnel in field, w/b of fresh concrete was tested. The compressive strength and chloride diffusion coefficient of the concrete were calculated using the established models. In addition, specimens of the tested concrete were prepared and cured for compressive strength and chloride diffusion coefficient tests. Finally, the predicted results and the tested results were analyzed, and the predicted deviation was calculated. Results of the calculations show that the prediction deviations of compressive strength and chloride diffusion coefficient ar

Fungi: A Neglected Candidate for the Application of Self-Healing Concrete

Self-healing mechanism in concrete has been so far achieved mainly by three approaches: autogenous healing, encapsulation of polymeric material, and biologically induced mineralization of calcium carbonate. The microbial approach prevails over the other two approaches due to the high compatibility between the filler material and the concrete compositions. Although the term “microbe” refers to many different types of organisms, research work on self-healing concrete has been so far restricted to bacteria. In this perspective article, we review the current status of bacteria-mediated self-healing concrete and summarize the prospects for future advances. In particular, we point out that fungi may have distinctive advantages over other microbes to be used as self-healing agents

Effects of Expansive Additives on the Shrinkage Behavior of Coal Gangue Based Alkali Activated Materials

The suitability of applying shrinkage reducing additives in alkali activated coal gangue-slag composites is discussed in this study. The effect of sulphoaluminate cement (SAC), high performance concrete expansion agent (HCSA) and U-type expansion agent (UEA) on the reaction process, shrinkage behavior, phase composition, microstructure and mechanical properties are evaluated. The results show that the addition of SAC slightly mitigates the early stage reaction process, while HCSA and UEA can either accelerate or inhibit the reaction depending on their dosage. The addition of SAC presents an ideal balance between drying shrinkage reduction and strength increment. As for HCSA and UEA, the shrinkage and mechanical properties are sensitive to their replacement level; excessive dosage would result in remarkable strength reduction and expansion. The specific surface area and average pore size of the hardened matrix are found to be closely related with shrinkage behavior. SAC addition introduces additional hydrotalcite phases within the reaction products, while HCSA and UEA mainly result in the formation of CaCO3 and Ca(OH)2. It is concluded that applying expansive additives can be an effective approach in reducing the drying shrinkage of alkali activated coal gangue-slag mixtures, while their type and dosage must be carefully handled

Water–Binder Ratio Monitoring as a Quality Control Tool for the High-Performance Concrete Used in the Construction of the Submerged Tunnel

The designed service life of Hong Kong-Zhuhai-Macao Bridge is 120 years. Concrete quality control for the submerged tunnel of the project is an important work to assure the designed service life. This article is to present an advanced concrete performance prediction method based on water–binder ratio (w/b) monitoring, which is used to serve for concrete quality control. During experiments in the lab, the w/b of submerged tunnel concrete mix proportion was designed to fluctuate up and down, while the other compositions were kept constant. Concretes with different w/b were prepared. The w/b of fresh concrete was tested, followed by preparation of specimens for compressive strength and chloride diffusion coefficient tests. The compressive strength and chloride diffusion coefficient of the hardened concrete were tested. Relationships between the tested w/b and the compressive strength and chloride diffusion coefficient were established. The fitting curves were taken as the prediction models. During construction of submerged tunnel in field, w/b of fresh concrete was tested. The compressive strength and chloride diffusion coefficient of the concrete were calculated using the established models. In addition, specimens of the tested concrete were prepared and cured for compressive strength and chloride diffusion coefficient tests. Finally, the predicted results and the tested results were analyzed, and the predicted deviation was calculated. Results of the calculations show that the prediction deviations of compressive strength and chloride diffusion coefficient ar

Recycling utilization of phosphogypsum in eco excess-sulphate cement: Synergistic effects of metakaolin and slag additives on hydration, strength and microstructure

Landfilled phosphogypsum would cause severe environmental issues, but the waste can be recycled for preparing excess-sulphate cement, an eco-friendly alternative to conventional cement. This paper investigates the effect of metakaolin (0–50%) on early hydration, phase assemblages and mechanical properties of the excess-sulphate phosphogypsum cementitious materials (ESPCMs). Results indicate that metakaolin is related to a new exothermic peak and significantly shortens the induction period. Setting time of ESPCM pastes is reduced by 13%–38% with 10%–50% dosage of metakaolin. More ettringite and highly disordered C-(A)-S-H gel are characterised when metakaolin dosage is below 20%, leading to 70% increase in 28-d compressive strength. With above 20% metakaolin dosage, portlandite consumption at early stage is promoted and hydration degree at late state is reduced. It turns out that within 20% metakaolin dosage is efficient to optimise setting time and strength development of ESPCMs, where slag and metakaolin synergistically promote the formation of ettringite and C-(A)-S-H gel to bind the unhydrated cement particles effectively

Effect of Vibration Procedure on Particle Distribution of Cement Paste

Vibration procedures significantly affect the performances of cement-based materials. However, studies on the distribution of certain particles within cement-based materials are limited due to the complexity and difficulty of identifying each specific particle. This paper presents a new method for simulating and quantifying the movements of particles within cement paste through the use of “tagged materials”. By separating the tagged particles from the cement paste after vibration, the distribution of the particles in the cement paste can be calculated statistically. The effect of the vibration time and frequency, fresh behavior, and powder characteristics of cement paste on particle motions are investigated. The results demonstrate that when the vibration exceeds 1800 s, it induces a significant uneven dispersion of microparticles. This effect is more pronounced at low viscosities (200 Hz). Larger and denser particles exhibit greater dispersion. This method provides a valuable tool for investigating the theory of particle motion in cement paste, which is crucial for understanding the influence of vibration on the properties of cement-based materials

Utilizing Iron Ore Tailing as Cementitious Material for Eco-Friendly Design of Ultra-High Performance Concrete (UHPC)

In this research, iron ore tailing (IOT) is utilized as the cementitious material to develop an eco-friendly ultra-high performance concrete (UHPC). The UHPC mix is obtained according to the modified Andreasen and Andersen (MAA) packing model, and the applied dosage of IOT is 10%, 20%, and 30% (by weight), respectively. The calculated packing density of different mixtures is consistent with each other. Afterwards, the fresh and hardened performance of UHPC mixtures with IOT are evaluated. The results demonstrate that the workability of designed UHPC mixtures is increased with the incorporation of IOT. The heat flow at an early age of designed UHPC with IOT is attenuated, the compressive strength and auto shrinkage at an early age are consequently reduced. The addition of IOT promotes the development of long-term compressive strength and optimization of the pore structure, thus the durability of designed UHPC is still guaranteed. In addition, the ecological estimate results show that the utilization of IOT for the UHPC design can reduce the carbon emission significantly