Concrete is very sensitive to crack formation. As wide cracks endanger the durability, repair may be required. However, these repair works raise the life-cycle cost of concrete as they are labor ...intensive and because the structure becomes in disuse during repair. In 1994, C. Dry was the first who proposed the intentional introduction of self-healing properties in concrete. In the following years, several researchers started to investigate this topic. The goal of this review is to provide an in-depth comparison of the different self-healing approaches which are available today. Among these approaches, some are aimed at improving the natural mechanism of autogenous crack healing, while others are aimed at modifying concrete by embedding capsules with suitable healing agents so that cracks heal in a completely autonomous way after they appear. In this review, special attention is paid to the types of healing agents and capsules used. In addition, the various methodologies have been evaluated based on the trigger mechanism used and attention has been paid to the properties regained due to self-healing.
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•We achieved CaCO3 precipitation yields up to 18.9gCaCO3/gNO3-N in 2 days.•Repetitive CaCO3 precipitation can be achieved from single inoculation.•Precipitation formed around the ...cells decreases nutrient uptake rate and activity.•Denitrifiers removed Ca2+ from paper mill wastewater through CaCO3 precipitation.
So far, researchers investigated microbially induced CaCO3 precipitation (MICP) for soil reinforcement, self-repairing concrete and Ca2+ removal from industrial waste streams. Reported MICP yields were mainly achieved under nutrient-rich conditions. However, creating the tested nutrient-rich conditions in intended applications is both an economical and a practical issue. Therefore, investigation of MICP in more realistic conditions is necessary. This study presents optimization of MICP through denitrification in minimal nutrient conditions. To optimize their MICP performances, we isolated two strains, Pseudomonas aeruginosa and Diaphorobacter nitroreducens, by following an application oriented selection procedure. Upon performance optimization, in 2 days, D. nitroreducens and P. aeruginosa precipitated 14.1 and 18.9gCaCO3/gNO3-N, respectively. Repetitive CaCO3 precipitation was also achieved from a single inoculum in both 2 days and 3 weeks intervals. Selected strains and the process were further evaluated for three MICP applications: (1) Ca2+ removal from paper mill wastewater (2) soil reinforcement, (3) crack repair in concrete. Overall, denitrification was found to be an effective process to remove Ca2+ from paper mill wastewater. P. aeruginosa and D. nitroreducens could be introduced as potential candidates for soil and concrete applications due to their enhanced precipitation yields, resilience and performance under minimal nutrient conditions.
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.
Surface treatments play an important role in the protection of construction materials from the ingress of water and other deleterious substances. Due to the negative side-effects of some of the ...conventional techniques, bacterial induced carbonate mineralization has been proposed as a novel and environmental friendly strategy for the protection of stone and mortar. This paper reports the effects of bacterial CaCO
3 precipitation on parameters affecting the durability of concrete and mortar. Pure and mixed cultures of ureolytic bacteria were compared for their effectiveness in relation to conventional surface treatments. Bacterial deposition of a layer of calcite on the surface of the specimens resulted in a decrease of capillary water uptake and permeability towards gas. This bacterial treatment resulted in a limited change of the chromatic aspect of mortar and concrete surfaces. The type of bacterial culture and medium composition had a profound impact on CaCO
3 crystal morphology. The use of pure cultures resulted in a more pronounced decrease in uptake of water, respectively less pronounced change in the chromatic aspect, compared to the use of mixed ureolytic cultures as a paste. The results obtained with cultures of the species
Bacillus sphaericus were comparable to the ones obtained with conventional water repellents.
For many microstructural studies it is necessary to “stop” cement hydration—to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on ...the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH)
2
content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round robin test three recommendations are made. (1) Oven drying at 105 °C is not recommended. This dehydrates, alters and decomposes calcium aluminate hydrates significantly more than other methods and often produced carbonation artefacts. (2) Isopropanol exchange is the most appropriate hydration stoppage method for the study of the complete hydrate assemblage of cements, including calcium aluminate hydrates such as ettringite and AFm phases. (3) For quantification of portlandite (Ca(OH)
2
) all tested hydration stoppage protocols are satisfactory, with the exception of oven drying.
This recommendation is an outcome of the work carried out by a working group within the RILEM Technical Committee 238-SCM “Supplementary Cementitious Materials”. The working group studied the effect ...of supplementary cementitious materials on the pore solution, the microstructure and the hydration product assemblage of hardened Portland cements blended with common supplementary cementitious materials. The recommendation reflects the results of a round robin test programme on common hydration stoppage methods in 10 participating laboratories. Among four different methods tested, solvent exchange by isopropyl alcohol (isopropanol) gave the best results in terms of preservation of the cement hydrate assemblage and overall reproducibility of the results
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. The current protocol is developed based on best laboratory practices of the participating laboratories and literature reports
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–
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. The presented hydration stoppage protocol is recommended for the study of Portland cement-based hydrate assemblages by common material characterization techniques such as thermogravimetry and X-ray powder diffraction.
This article presents the results of an interlaboratory experimental study performed by 13 international research groups within the framework of the activities of the RILEM Technical Committee ...225-SAP “Applications of Superabsorbent Polymers in Concrete Construction”. Two commercially available superabsorbent polymers (SAP) were tested in terms of their influence on the freeze–thaw resistance of ordinary concrete. To test the robustness of the method, all participating laboratories used locally produced materials. Furthermore, following this aim, various accelerated methods were used to estimate the resistance of the concrete to freeze–thaw cycles. The effect of adding SAP was from insignificant to considerably positive in terms of improvement in material performance as determined by reduced mass loss after freeze–thaw cycles; only one participant observed worsening of the material behaviour. At the same time, due to the addition of SAP, a much less pronounced decrease in the dynamic Young’s modulus was observed as a result of freeze–thaw testing without deicing salt.
Since the construction sector uses 50% of the Earth's raw materials and produces 50% of its waste, the development of more durable and sustainable building materials is crucial. Today, Construction ...and Demolition Waste (CDW) is mainly used in low level applications, namely as unbound material for foundations, e.g., in road construction. Mineral demolition waste can be recycled as crushed aggregates for concrete, but these reduce the compressive strength and affect the workability due to higher values of water absorption. To advance the use of concrete rubble, Completely Recyclable Concrete (CRC) is designed for reincarnation within the cement production, following the Cradle-to-Cradle (C2C) principle. By the design, CRC becomes a resource for cement production because the chemical composition of CRC will be similar to that of cement raw materials. If CRC is used on a regular basis, a closed concrete-cement-concrete material cycle will arise, which is completely different from the current life cycle of traditional concrete. Within the research towards this CRC it is important to quantify the benefit for the environment and Life Cycle Assessment (LCA) needs to be performed, of which the results are presented in a this paper. It was observed that CRC could significantly reduce the global warming potential of concrete.
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•Polysaccharide-based SAPs sustainable alternative for conventional, synthetic SAPs.•Semi-synthetic SAPs with fine-tuned properties for specialized applications.•Smart SAPs ...particularly interesting for specific applications such as drug delivery.
The current review provides an overview of different types of superabsorbent polymers (SAPs) together with appropriate strategies elaborated to enable their synthesis. The main focus will be on polysaccharide-based, semi-synthetic and ‘smart’ SAPs along with their derivatives. SAPs have already shown their use in a plethora of applications including diapers, the biomedical field, agriculture, etc. The different polymer classification possibilities are discussed, as well as the classification of the constituting building blocks. The main part of SAPs still has a synthetic origin. However, as they are often not biocompatible, biodegradable or renewable, natural SAPs based on polysaccharides have gained increasing interest. Due to the low solubility of synthetic polymers, purification problems or the need for organic solvents, a trend has emerged towards combining polysaccharides with synthetic monomers to create semi-synthetic, hybrid SAPs for specialized applications with fine-tuned properties including wound dressings, fertilizers or self-healing concrete. These specialized, semi-synthetic SAPs offer strong potential for a series of applications in the future. However, future research in this respect is still needed to optimize homogeneity and to increase gel fractions. A final part of this review includes ‘smart’ SAPs such as SAPs with a T-, electro- and pH-sensitivity. These ‘smart’ SAPs are especially becoming useful for certain biomedical applications such as drug release for which an in vivo location can be targeted. The use of ‘smart’, semi-synthetic SAPs with fine-tuned characteristics combining the best characteristics of both synthetic and natural SAPs, offer the greatest potential for the future.
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