Preparation and polymeric encapsulation of powder mineral pellets for self-healing cement based materials

Using mineral additives and admixtures as self-healing agents in cement-based composites has been extensively researched. However, if the minerals are added directly to the cementitious matrix without any protection, they could immediately react, leading to a decrease in self-healing efficiency with further associated side-effects on the mechanical properties of cementitious composites. Thus, this paper describes the development of coated pellets as a self-healing system in cement based materials. Pan pelletisation was utilised for producing pellets from three different powder minerals as potential healing agents: reactive magnesium oxide (MgO), silica fume and bentonite. Of these materials, two types of developed prototype pellets in addition to another two commercial types of MgO pellets with different pellet sizes were then encapsulated in a polyvinyl alcohol (PVA) based film coating. The PVA coating was evaluated for the apparent solubility in water and in alkaline solution, swelling property, water permeability, dynamic mechanical properties, and shell thickness on pellets. Although PVA coating exhibited a decrease in its mechanical properties in water or in the simulated concrete environment, it retained integrity and stability in both environments. The PVA shell thickness varied from 10 to 50 µm. As the coated pellets partially replaced the natural sand in mortar mixtures, they were characterised in comparison with sand for the particle size distribution, density, porosity, crushing strength and particle shape. Experimental results indicated that the different types of pellets showed higher porosity and lower crushing strength compared to sand. In mortar mixtures, the pellets showed excellent compatibility with minimal influence on the fresh mixture properties and the compressive strength of the hardened specimens. This was accompanied by good distribution inside the concrete matrix. Further investigations on the self-healing performance of these pellets are under way

First UK field application and performance of microcapsule-based self-healing concrete

Maintaining the health and reliability of our infrastructure is of strategic importance. The current state of the UK infrastructure, and the associated huge costs of inspection, maintenance, repair and eventual replacement, is not sustainable and is no longer environmentally viable. The design of infrastructure, mainly concrete, remains traditional and poor material performance continues to be the main cause of deterioration and failure in our infrastructure systems. Biomimetic materials, that emulate natural biological systems in their ability to self-healing, provide an exciting and plausible solution. Embedding cementitious materials with in-built capabilities to sense and respond to their environmental triggers could potentially eliminate all external interventions and deliver a resilience infrastructure. The work presented in this paper forms part of a national initiative that has been developing biomimetic cementitious infrastructure materials which culminated in the first large-scale field trials of self-healing concrete in the UK testing four different but complementary technologies that were developed. This paper focuses on one self-healing technology, namely microcapsules, which contain a healing agent that is released on their rupture as a result of crack propagation. The paper will present details of the microcapsules used, their implementation in concrete and in the field trials and time-related, field and laboratory, assessment of the self-healing process. It also highlights challenges faced and improvements that are now on-going to produce the next generation of the microcapsule self-healing cementitious system

A novel membrane emulsification technique for microencapsulation in self-healing concrete: Development and proof of concept

Abstract Membrane emulsification is a promising new technique that can be deployed as a scalable modular conduit for the consistent and continuous production of single and complex emulsions. This work reports on the development of a manufacturing platform based on membrane emulsification for the first time for microcapsule-based self-healing cementitious materials. The feasibility of single and double emulsion production with wall formation as a secondary step through UV radical polymerisation was explored using a discrete membrane emulsification dispersion cell. The operational parameters (pressure, dispersed phase flux, temperature, shear rate) were established for the specific phase characteristics (viscosity, density, interfacial tension) to achieve control of emulsion droplets and maintain a high encapsulation of core content (high payload). Microcapsules with sodium silicate core and an average diameter of ∼130 μm were produced. Microcapsules were shown to achieve high payload (∼89%). Moreover their thermal stability was characterised and their release performance in the cementitious matrix established. The results demonstrated the capability of membrane emulsification to produce microcapsules with an aqueous core for use in self-healing of cementitious materials.</jats:p

Addressing the need for standardization of test methods for self-healing concrete: an inter-laboratory study on concrete with macrocapsules.

Development and commercialization of self-healing concrete is hampered due to a lack of standardized test methods. Six inter-laboratory testing programs are being executed by the EU COST action SARCOS, each focusing on test methods for a specific self-healing technique. This paper reports on the comparison of tests for mortar and concrete specimens with polyurethane encapsulated in glass macrocapsules. First, the pre-cracking method was analysed: mortar specimens were cracked in a three-point bending test followed by an active crack width control technique to restrain the crack width up to a predefined value, while the concrete specimens were cracked in a three-point bending setup with a displacement-controlled loading system. Microscopic measurements showed that with the application of the active control technique almost all crack widths were within a narrow predefined range. Conversely, for the concrete specimens the variation on the crack width was higher. After pre-cracking, the self-healing effect was characterized via durability tests: the mortar specimens were tested in a water permeability test and the spread of the healing agent on the crack surfaces was determined, while the concrete specimens were subjected to two capillary water absorption tests, executed with a different type of waterproofing applied on the zone around the crack. The quality of the waterproofing was found to be important, as different results were obtained in each absorption test. For the permeability test, 4 out of 6 labs obtained a comparable flow rate for the reference specimens, yet all 6 labs obtained comparable sealing efficiencies, highlighting the potential for further standardization

Breakthroughs in medicinal chemistry: New targets and mechanisms, new drugs, new hopes-6

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes is a series of Editorials that is published on a biannual basis by the Editorial Board of the Medicinal Chemistry section of the journal Molecules [...]

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes–4

Breakthroughs in Medicinal Chemistry: New Targets and Mechanisms, New Drugs, New Hopes is a series of Editorials, which is published on a biannual basis by the Editorial Board of the Medicinal Chemistry section of the journal Molecules. In these Editorials, we highlight in brief reports (of about one hundred words) a number of recently published articles that describe crucial findings, such as the discovery of novel drug targets and mechanisms of action, or novel classes of drugs, which may inspire future medicinal chemistry endeavours devoted to addressing prime unmet medical needs

Evaluation of Methodologies for Assessing Self-Healing Performance of Concrete with Mineral Expansive Agents: An Interlaboratory Study

Self-healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different self-healing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self-healing concrete with expansive mineral additions. Concrete prisms and discs with MgO-based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing-addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self-healing concepts in practical applications

Exploiting members of the BAHD acyltransferase family to synthesize multiple hydroxycinnamate and benzoate conjugates in yeast

BACKGROUND: BAHD acyltransferases, named after the first four biochemically characterized enzymes of the group, are plant-specific enzymes that catalyze the transfer of coenzyme A-activated donors onto various acceptor molecules. They are responsible for the synthesis in plants of a myriad of secondary metabolites, some of which are beneficial for humans either as therapeutics or as specialty chemicals such as flavors and fragrances. The production of pharmaceutical, nutraceutical and commodity chemicals using engineered microbes is an alternative, green route to energy-intensive chemical syntheses that consume petroleum-based precursors. However, identification of appropriate enzymes and validation of their functional expression in heterologous hosts is a prerequisite for the design and implementation of metabolic pathways in microbes for the synthesis of such target chemicals. RESULTS: For the synthesis of valuable metabolites in the yeast Saccharomyces cerevisiae, we selected BAHD acyltransferases based on their preferred donor and acceptor substrates. In particular, BAHDs that use hydroxycinnamoyl-CoAs and/or benzoyl-CoA as donors were targeted because a large number of molecules beneficial to humans belong to this family of hydroxycinnamate and benzoate conjugates. The selected BAHD coding sequences were synthesized and cloned individually on a vector containing the Arabidopsis gene At4CL5, which encodes a promiscuous 4-coumarate:CoA ligase active on hydroxycinnamates and benzoates. The various S. cerevisiae strains obtained for co-expression of At4CL5 with the different BAHDs effectively produced a wide array of valuable hydroxycinnamate and benzoate conjugates upon addition of adequate combinations of donors and acceptor molecules. In particular, we report here for the first time the production in yeast of rosmarinic acid and its derivatives, quinate hydroxycinnamate esters such as chlorogenic acid, and glycerol hydroxycinnamate esters. Similarly, we achieved for the first time the microbial production of polyamine hydroxycinnamate amides; monolignol, malate and fatty alcohol hydroxycinnamate esters; tropane alkaloids; and benzoate/caffeate alcohol esters. In some instances, the additional expression of Flavobacterium johnsoniae tyrosine ammonia-lyase (FjTAL) allowed the synthesis of p-coumarate conjugates and eliminated the need to supplement the culture media with 4-hydroxycinnamate. CONCLUSION: We demonstrate in this study the effectiveness of expressing members of the plant BAHD acyltransferase family in yeast for the synthesis of numerous valuable hydroxycinnamate and benzoate conjugates