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Given the rising popularity of foam concrete (FC) for both structural and insulating purposes, evaluating the feasibility of recycling after its lifespan is crucial in the context of the growing emphasis on sustainable building practices. One approach to recycling FC incorporating microencapsulated phase change material (MPCM) involves utilizing recycled foam concrete powder (RFCP) as an additive in cement composites. This article aims to investigate the impact of RFCP without and with MPCM when employed as a partial replacement for cement in mortars. Furthermore, the study verifies various processing methods such as crushing, grinding, and heat treatment for RFCP. The results reveal that introducing RFCP, regardless of the MPCM presence and processing method, significantly affects the properties of both cement and mortar. The presence of MPCM in RFCP negatively influences the flowability of fresh mortars, delays the setting time, and reduces the hydration heat within the first 48 h. However, the presence of MPCM does not significantly affect mortars' strength and water absorption but simultaneously it increases shrinkage and decreases thermal conductivity. Grinding RFCP mitigates the adverse effects of MPCM, while thermal processing removes MPCM from RFCP, albeit with an associated increase in water demand. A noteworthy finding is that mortars having 20 % RFCP, with or without MPCM, exhibit compressive strengths exceeding 16 MPa and 42.5 MPa after 2 and 28 days, respectively. These results meet the requirements outlined in EN-196-1 for cement of class 42.5, highlighting the potential to produce CEM II/A-F 42.5 using RFCP with MPCM., Materials- Mechanics- Management & Design, Arts & Crafts, Materials and Environment

Implementing nature in cities has great potential to improve urban liveability by providing ecosystem services, which can help mitigate heat stress, improve air quality, attenuate noise, and reduce rainwater run-off. However, widespread adoption of urban nature and green building typologies is still limited due to their costs, environmental impact, and space constraints. Bioreceptive concrete can form the basis of a new green building typology, where the concrete mixture is adjusted to allow for biological growth, specifically mosses, to occur on its surface. This literature review aims to give an overview of the current state of the art on bioreceptive concrete as a material in general and specifically the (potential) ecosystem services provided by the mosses growing on this bioreceptive concrete. This review shows that bioreceptivity can be achieved in concrete in several ways, including minor adjustments to standard concrete recipes. While quantitative data on the ecosystem services provided by mosses in an urban context is still limited, potential gains appear significant. The main challenges lie in the durable long-term development of mosses on the bioreceptive concrete and the valuation through quantification of the ecosystem services they provide. However, moss-receptive concrete shows promise as a new green building typology if these challenges are bridged., Materials and Environment, Materials- Mechanics- Management & Design

This study presents an early-stage design exploration of NRG-Foam, an innovative insulation material composed of cementitious foam doped with microencapsulated phase change materials (MPCMs). The study comprises the static part that utilizes life cycle assessment and life cycle costing assessment for getting insight into the impacts of the NRG-Foam production process and the dynamic part that identifies the trade-offs between performance characteristics of NRG-Foam using multi-objective optimization. The production of MPCMs was found to be a major contributor to environmental impacts while the addition of small amounts of reduced graphene oxide amplifies the impacts even further. The hot spot analysis pinpointed high electricity consumption as the main driver of environmental impacts. A multi-objective optimization analysis revealed trade-offs between performance characteristics, emphasizing the necessity of compromises during material development. The selection of the MPCM type was shown to be determinative of the final properties of NRG-Foam., Materials and Environment

The current study investigates short-term and long-term crack-healing behaviour of mortars embedded with bacteria-based poly-lactic acid (PLA) capsules under both ideal and realistic environmental conditions. Two sets of specimens were prepared and subjected to different healing regimes, with the first set kept in a mist room for varying short durations (i.e., 1 week, 2 weeks, 3 weeks and 8 weeks) and the second set placed in an unsheltered outdoor environment for a long-term healing process (i.e., 1 year). Alteration of microstructure because of self-healing was characterized by backscattered electron (BSE) imaging and energy dispersive X-ray spectroscopy (EDS) via crack cross-sections. Results show that visible crack healing enabled by bacteria began after 2 weeks in a humid environment. The healing products initially precipitated at crack mouths and gradually moved deeper into cracks, with the precipitated calcium carbonate crystals growing larger over time. After 8 weeks, healing products can be found even a few millimetres deep inside cracks. Observations of crack healing in a realistic environment revealed significant differences compared to healing under controlled conditions. While no healing products can be found at crack mouths, a substantial healing process was observed throughout the entire crack depth. It is likely that the environmental actions such as rainfall and/or freeze and thaw cycles may have worn away the healing products at crack mouths and thus led to a deeper ingress of oxygen into cracks, which promoted the activation of healing agents and associated calcium carbonate precipitation deep inside a crack., Materials and Environment

In the current study, experiments were carried out to investigate the structural performance of reinforced concrete (RC) beams with a self-healing cover zone. The cover zone consists of a 1.5-cm-thick layer of bacteria-embedded strain hardening cementitious composite (SHCC) for a combination of crack width control and crack healing. The aim is to bring together two emerging technologies (i.e., self-healing and strain-hardening) that show great potential for realizing highly efficient concrete structures. RC beam without the self-healing cover was also prepared as the control specimen for comparison purposes. The experimental program includes loading the beams to failure in four-point bending configuration and sawing the beams to segments for crack pattern analysis and crack healing. Results show that the beams with self-healing cover exhibited a 45-60% improvement in structural capacity. The crack patterns of the hybrid beams were also largely modified. While the reference beam formed only a few major cracks, the hybrid beams formed around 40 fine cracks in the constant bending moment region with an average crack width smaller than 0.2 mm even at maximum load. By having an improved cracking behavior and an enhanced self-healing capacity, it is expected that the beams with a self-healing cover will possess an extended service life at the expense of minimal additional cost., Materials and Environment, Concrete Structures

The possible beneficial impact of self-healing on chloride transport through cracks has been assessed for two bacteria-based self-healing mortar mixtures in comparison with Ordinary Portland cement mortar. Intact self-healing specimens featured lower chloride transport coefficients thanks to a denser microstructure and to the formation of a layer of calcium carbonate on their surface. However, self-healing of cracks of cracked mortar specimens did not significantly reduce chloride penetration during 28 days of chloride exposure compared to cracked and non-healed specimens. On the other hand, this study demonstrated that self-healing of 150–200 µm wide cracks reduced chloride ingress during shorter term (14 days) chloride exposure in comparison to cracked but non-healed specimens. The results of this study suggest that self-healing of cracks through calcium carbonate formation results in water blockage (sealing) of cracks but that the limited amount of limestone formed creates an imperfect barrier against diffusion of chloride ions through the apparent porous limestone. The short-term positive effect of self-healing with respect to reduced chloride ingress could be beneficial in applications where chloride exposure is limited or non-permanent such as concrete structures irregularly exposed to deicing salts or located in the splash zone in marine environments., Materials and Environment

In this study, the applicability of two bacteria-based healing agents (e.g., poly-lactic acid and polyhydroxyalkanoate) in blast furnace slag cement (BFSC) mortar has been assessed. An experimental campaign on the functional properties, self-healing capacity, freezing–thawing and carbonation resistance has been conducted in comparison with plain mortar (Ctrl). Due to the relatively low alkalinity of the mixture, the addition of poly-lactic acid healing agents (PLA) caused coarsening of the micro-structure, decrease of strength and did not improve the self-healing capacity of the material. Among other consequences, the mass loss due to the freezing–thawing of PLA specimens was about 5% higher than that of the Ctrl specimens. On the contrary, no detrimental effect of the mortar functional properties was measured when polyhydroxyalkanoate healing agents (AKD) were added. The self-healing capacity of AKD specimens was higher than that of the Ctrl specimens, reaching a maximum healed crack width of 559 µm after 168 days of self-healing, while it was 439 µm for the Ctrl specimens and 385 µm for PLA specimens. The air void content of the AKD mixture was 0.9% higher than that of the Ctrl, increasing its resistance against freezing–thawing cycles. This study aims to confirm the potential applicability of AKD particles as self-healing agents in low-alkaline cementitious mixtures., Materials and Environment

The urban heat island, is a serious threat for the urban well-being, and can be determined by the local energy balance. The surface energy balance, with respect to incoming radiative energy and subsequent partitioning into reflected energy (albedo), absorbed energy and further partitioning of latter into convectional heat (QH), radiative heat (QR) and latent heat (QE) by using commonly applied urban materials and vegetation types, was therefore experimentally quantified in this study. In agreement with previous studies it was found that materials convert most of absorbed energy into convectional heat (>92%) while vegetation channels a substantial part of absorbed radiative energy into latent heat (27–50%). It is for the first time experimentally demonstrated that significant differences in thermal behaviour between different types of urban vegetation surfaces occur. Of the investigated vegetation types ivy and moss showed respectively the highest (0.10) and lowest (0.07) albedo, but sedum and moss channelled respectively lowest (27%) and highest (50%) percentage of the absorbed radiative energy into latent heat production. Of the four investigated plant types, moss appeared most effective in preventing UHI, converting only 50% of incoming radiative energy into convectional heat, while sedum was least effective converting 73% of incoming radiative energy into convectional heat. These quantitative measurements show that strategic use of specific types of urban vegetation surfaces, instead of commonly applied building materials, can be an effective measure for mitigation of UHI leading to improved climate resilient cities., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment, Atmospheric Remote Sensing

Asphalt pavement consists of aggregates resulting in a waste material at end of its life. The aggregates can be reused as basic material for asphalt or cementitious binding agents. In both scenarios, the recycled aggregates should provide a good bond with the binder to achieve strength. This study focuses on reusing recycled asphalt aggregates (RAA) in mortar. The major weakness of RAA is the thin oily film originating from the asphalt residue, weakening the bond with cement. The pyrolysis method is accessed in an attempt to overcome this weakness. Three scenarios were investigated; the use of virgin aggregates (VA), RAA, and pyrolysis recycled asphalt aggregate (PRAA) as constituent in mortar. All variables were set a constant except for the aggregate type, the VA mortar function as controlling element. This research is methodologically based on experimental data conducted in the laboratory, while aggregate samples were taken from the field. To analyze the influence of pyrolysis to the aggregate-to-cement bond behaviour, qualitative and quantitative data were collected. The quantitative data were the mechanical properties, the mortar tensile, and compression strength. The qualitative data were obtained from scanning electron microscope readings to visually observe the aggregate surface roughness and voids, including the aggregates cross-section and pre-existing micro-cracks in the aggregate-to-cement interface. Supporting data were the aggregates‘ abrasion rate and absorption. The RAA resulted in a significant mortar strength decrease. This conclusion was supported by the findings of pre-existing cracks in the interfacial transition zone. The pyrolysis method improved the compression strength but negligibly affected the tensile behavior. The compression and tensile strength increased as a function of time for both RAA and PRAA, and a strength convergence was reached at 28 days. The PRAA is considered an option for reuse in mortar, supporting nature conservation., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

Earthen construction is re-gaining popularity as an ecological and economical alternative to contemporary building materials. While building with earth offers several benefits, its performance due to water ingress is a concern for its widespread application. This limitation is often solved by adding chemical stabilisers such as Portland cement and hydraulic lime. Chemical stabilisers are a subject of widespread debate as they increase the cost and embodied energy of the structure, and reduce the desirable characteristics of raw or unstabilised earth. This along with perceived environmental performance, renewability, and proven effectiveness in traditional earthen construction has led to a growing interest in biological or organic stabilisers. Although the strengthening mechanism of biological stabilisers is widely covered in scientific studies, discussion regarding the water-resistance is limited. This review aggregates the research from the field of earthen construction and geotechnical engineering and extends it to explain the possible mechanism responsible for the water-resistance behaviour of biologically stabilised earthen materials. This study includes a wide range of traditional and industrial biological stabilisers derived from animals (cow-dung, casein, chitosan), plants (starch, guar gum, cactus mucilage, lignin, tannin) seaweeds (alginate, agar, carrageen) and microbes (xanthan gum, gellan gum). A conceptual model of water-ingress in unstabilised earthen blocks is proposed and the response of biological stabiliser to water ingress and related physico-chemical and physical factors is discussed using the model at microscale (stabiliser interaction with clay, sand) and macroscale (hydraulic conductivity of block). Properties of stabilisers such as hydrophobicity, stability under wet conditions or interaction with cations have a dominant effect on the overall response to water ingress. Key gaps have been identified in the existing knowledge that are necessary, Materials and Environment, Geo-engineering, BT/Environmental Biotechnology, Space & Type

In this study, the applicability of two bacteria-based healing agents (e.g., poly-lactic acid and polyhydroxyalkanoate) in blast furnace slag cement (BFSC) mortar has been assessed. An experimental campaign on the functional properties, self-healing capacity, freezing–thawing and carbonation resistance has been conducted in comparison with plain mortar (Ctrl). Due to the relatively low alkalinity of the mixture, the addition of poly-lactic acid healing agents (PLA) caused coarsening of the micro-structure, decrease of strength and did not improve the self-healing capacity of the material. Among other consequences, the mass loss due to the freezing–thawing of PLA specimens was about 5% higher than that of the Ctrl specimens. On the contrary, no detrimental effect of the mortar functional properties was measured when polyhydroxyalkanoate healing agents (AKD) were added. The self-healing capacity of AKD specimens was higher than that of the Ctrl specimens, reaching a maximum healed crack width of 559 µm after 168 days of self-healing, while it was 439 µm for the Ctrl specimens and 385 µm for PLA specimens. The air void content of the AKD mixture was 0.9% higher than that of the Ctrl, increasing its resistance against freezing–thawing cycles. This study aims to confirm the potential applicability of AKD particles as self-healing agents in low-alkaline cementitious mixtures., Materials and Environment

The possible beneficial impact of self-healing on chloride transport through cracks has been assessed for two bacteria-based self-healing mortar mixtures in comparison with Ordinary Portland cement mortar. Intact self-healing specimens featured lower chloride transport coefficients thanks to a denser microstructure and to the formation of a layer of calcium carbonate on their surface. However, self-healing of cracks of cracked mortar specimens did not significantly reduce chloride penetration during 28 days of chloride exposure compared to cracked and non-healed specimens. On the other hand, this study demonstrated that self-healing of 150–200 µm wide cracks reduced chloride ingress during shorter term (14 days) chloride exposure in comparison to cracked but non-healed specimens. The results of this study suggest that self-healing of cracks through calcium carbonate formation results in water blockage (sealing) of cracks but that the limited amount of limestone formed creates an imperfect barrier against diffusion of chloride ions through the apparent porous limestone. The short-term positive effect of self-healing with respect to reduced chloride ingress could be beneficial in applications where chloride exposure is limited or non-permanent such as concrete structures irregularly exposed to deicing salts or located in the splash zone in marine environments., Materials and Environment

The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel networks can mechanically "mold" calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically "molding" biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties., Accepted Author Manuscript, Materials and Environment, BT/Environmental Biotechnology

In this study, a novel non-toxic, biodegradable bacteria-based healing agent known as alkanoate derivatives (AKD) derived from wastewater was investigated for its self-healing efficiency of the mortar specimens in comparison to the already-developed healing agents made of lactic acid derivatives (PLA). Mortar with different percentages of healing agent inclusions (2.6% and 5% w/w cement) have been evaluated in this study. To assess the self-healing improvements of the mortar incorporated bacteria-based bio-plastic healing agent's self-healing capacity, quantification of self-healing efficiency was performed at two different healing intervals of 28 and 56 days through optical determination of crack closure by stereomicroscope, recovery of water tightness by rapid water permeability test and determination of mass percentage increase of calcium carbonate by thermogravimetric analysis (TGA). The healing products formed in the cracks were analyzed by TGA and X-ray diffraction (XRD). Furthermore, a statistical analysis was performed to understand the variability in the crack width, water flow and the correlation of self-healing ratios between the stereomicroscope and permeability measurements. The results revealed that series containing the healing agents displayed a higher crack closure ratio compared to plain mortar series for initial crack widths greater than 0.4 mm at 56 days of healing. Moreover, the recovery of water tightness for series containing bacteria were greater compared to plain mortar for initial crack widths greater than 0.6 mm at 56 days of healing. However, in healing agent incorporated mortar series, only alkanoate derivatives at 5% dosage reported an increase in mass % of calcium carbonate precipitation at 56 days of healing. From the statistical analysis, it was confirmed that the influence of internal crack geometry plays a significant role in the degree of healing and variation of the water flow for smaller crack widths as the healing period inc, Materials and Environment

Sustainability transitions require that sustainable innovations develop and scale-up. Two promising approaches contribute to this purpose. Design thinking (DT) focuses on the creative development of sustainable innovations to achieve desirable, feasible and viable products. Strategic niche management (SNM) addresses how sustainable innovations should be deployed to the market. At first sight, these concepts seem to pursue a complementary mission, yet, academic literature has not explicitly addressed their complementary nature. Therefore, this paper addresses this gap by reviewing, proposing and empirically exploring the merits of SNM and how these can be used in DT through a workshop to increase successful market implementation of sustainable innovations. The study finds that SNM potentially helps the DT design process to (1) change market preconditions for the design, (2) create a protected niche for development, (3) establish a (long term) commercial viability, and (4) create an innovation development plan through definition of a set of testable propositions. The paper concludes that the inclusion of SNM into DT substantially increases the preparedness of an innovation team for a successful market implementation of sustainable innovations and coins the term ‘Design to Market Thinking’ for the integrated use of SNM in DT., Integral Design and Management, Materials and Environment

Polyhydroxyalkanoate (PHA) production is a promising opportunity to recover organic carbon from waste streams. However, widespread application of waste-derived PHA as biodegradable plastic is restricted by expensive purification steps, high quality requirements, and a fierce competition with the conventional plastic market. To overcome these challenges, we propose a new application for waste-derived PHA, using it as bacterial substrate in self-healing concrete. Self-healing concrete is an established technology developed to overcome the inevitable problem of crack formation in concrete structures, by incorporating a so-called bacteria-based healing agent. Currently, this technology is hampered by the cost involved in the preparation of this healing agent. This study provides a proof-of-concept for the use of waste-derived PHA as bacterial substrate in healing agent. The results show that a PHA-based healing agent, produced from PHA unsuitable for thermoplastic applications, can induce crack healing in concrete specimens, thereby reducing the water permeability of the cracks significantly compared to specimens without a healing agent. For the first time these two emerging fields of engineering, waste-derived PHA and self-healing concrete, both driven by the need for environmental sustainability, are successfully linked. We foresee that this new application will facilitate the implementation of waste-derived PHA technology, while simultaneously supplying circular and potentially more affordable raw materials for self-healing concrete., BT/Environmental Biotechnology, Materials and Environment

The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel networks can mechanically "mold" calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically "molding" biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties., Accepted Author Manuscript, Materials and Environment, BT/Environmental Biotechnology

Sustainability transitions require that sustainable innovations develop and scale-up. Two promising approaches contribute to this purpose. Design thinking (DT) focuses on the creative development of sustainable innovations to achieve desirable, feasible and viable products. Strategic niche management (SNM) addresses how sustainable innovations should be deployed to the market. At first sight, these concepts seem to pursue a complementary mission, yet, academic literature has not explicitly addressed their complementary nature. Therefore, this paper addresses this gap by reviewing, proposing and empirically exploring the merits of SNM and how these can be used in DT through a workshop to increase successful market implementation of sustainable innovations. The study finds that SNM potentially helps the DT design process to (1) change market preconditions for the design, (2) create a protected niche for development, (3) establish a (long term) commercial viability, and (4) create an innovation development plan through definition of a set of testable propositions. The paper concludes that the inclusion of SNM into DT substantially increases the preparedness of an innovation team for a successful market implementation of sustainable innovations and coins the term ‘Design to Market Thinking’ for the integrated use of SNM in DT., Integral Design & Management, Materials and Environment

In this study, a novel non-toxic, biodegradable bacteria-based healing agent known as alkanoate derivatives (AKD) derived from wastewater was investigated for its self-healing efficiency of the mortar specimens in comparison to the already-developed healing agents made of lactic acid derivatives (PLA). Mortar with different percentages of healing agent inclusions (2.6% and 5% w/w cement) have been evaluated in this study. To assess the self-healing improvements of the mortar incorporated bacteria-based bio-plastic healing agent's self-healing capacity, quantification of self-healing efficiency was performed at two different healing intervals of 28 and 56 days through optical determination of crack closure by stereomicroscope, recovery of water tightness by rapid water permeability test and determination of mass percentage increase of calcium carbonate by thermogravimetric analysis (TGA). The healing products formed in the cracks were analyzed by TGA and X-ray diffraction (XRD). Furthermore, a statistical analysis was performed to understand the variability in the crack width, water flow and the correlation of self-healing ratios between the stereomicroscope and permeability measurements. The results revealed that series containing the healing agents displayed a higher crack closure ratio compared to plain mortar series for initial crack widths greater than 0.4 mm at 56 days of healing. Moreover, the recovery of water tightness for series containing bacteria were greater compared to plain mortar for initial crack widths greater than 0.6 mm at 56 days of healing. However, in healing agent incorporated mortar series, only alkanoate derivatives at 5% dosage reported an increase in mass % of calcium carbonate precipitation at 56 days of healing. From the statistical analysis, it was confirmed that the influence of internal crack geometry plays a significant role in the degree of healing and variation of the water flow for smaller crack widths as the healing period inc, Materials and Environment

Bacteria-based self-healing concrete has the ability to heal cracks due to the bacterial conversion of incorporated organic compounds into calcium carbonate. Precipitates seal the cracks, theoretically increasing the service life of constructions. The aim of this paper is to propose a precursor for bacteria-based self-healing concrete derived from organic waste streams, produced is in line with the circular economy principle and ideally more affordable than other substrates. To verify the applicability of the proposed healing agent, some fundamental requirements of the proposed system are studied, such as its influence on functional properties, crack sealing capacity and evidence of bacterial activity in concrete., Materials and Environment, BT/Environmental Biotechnology

Polyhydroxyalkanoate (PHA) production is a promising opportunity to recover organic carbon from waste streams. However, widespread application of waste-derived PHA as biodegradable plastic is restricted by expensive purification steps, high quality requirements, and a fierce competition with the conventional plastic market. To overcome these challenges, we propose a new application for waste-derived PHA, using it as bacterial substrate in self-healing concrete. Self-healing concrete is an established technology developed to overcome the inevitable problem of crack formation in concrete structures, by incorporating a so-called bacteria-based healing agent. Currently, this technology is hampered by the cost involved in the preparation of this healing agent. This study provides a proof-of-concept for the use of waste-derived PHA as bacterial substrate in healing agent. The results show that a PHA-based healing agent, produced from PHA unsuitable for thermoplastic applications, can induce crack healing in concrete specimens, thereby reducing the water permeability of the cracks significantly compared to specimens without a healing agent. For the first time these two emerging fields of engineering, waste-derived PHA and self-healing concrete, both driven by the need for environmental sustainability, are successfully linked. We foresee that this new application will facilitate the implementation of waste-derived PHA technology, while simultaneously supplying circular and potentially more affordable raw materials for self-healing concrete., BT/Environmental Biotechnology, Materials and Environment

Bacteria‐based self‐healing concrete is an innovative concrete that contains a self‐healing agent that provides the material with enhanced autonomous crack‐sealing performance. A specific type of this concrete, based on a healing agent composed of bacterial spores and lactate as carbon source, has been developed and applied by the Delft University of Technology for over ten years. Under laboratory conditions it was proven that, depending on the dosage of healing agent, self‐healing of cracks up to 0.8 mm widths occurs. As such the material potentially allows reduction of steel reinforcement used for crack width limitation in watertight constructions. Application of self‐healing concrete would therefore not only result in a reduction of costs but also in improvement of environmental performance (lower CO2 footprint) and ease of in situ casting due to reduction of use of steel in waterproof applications. However, according to the EN 1990 Eurocode (Basis of structural design), customary application of a novel type of concrete must be preceded by full scale demonstrators proving evidence for safe and functional performance. In this contribution we portray full scale application of bacteria‐based self‐healing agent as developed by the Delft research group in two repair mortar‐ and in two concrete construction demonstrator projects. These demonstrator projects show that addition of the bacteria‐based self‐healing agent to the concrete mix is safe as no negative side effects on construction performance was observed. However, it also proved difficult to find evidence for increased crack‐healing performance as cracking in the demonstrator constructions hardly occurred. In further full scale demonstrators we therefore plan to drastically reduce amount of crack width‐restraining reinforcement to show crack-healing capacity and potential to save on use of reinforcement steel in watertight concrete constructions., Materials and Environment

There is an enormous demand for rural housing in India that needs to be catered for within a short span of time. Building with earth (mud) is proposed as an economical and environmental friendly alternative due to the rising costs of conventional building materials. However, the construction of earthen houses has significantly declined in India and thus it is necessary to evaluate if they can make a valuable contribution to contemporary housing shortage. Therefore, an informal survey was conducted in India to understand factors favouring or limiting the construction and daily use of earthen houses. The outcome of the survey suggests that ‘Image’ is the key barrier against a wide acceptance of traditional earthen houses which are linked to poverty. While modern earthen construction is desired, it is expensive for low-income households. The role of earth in addressing the contemporary housing shortage is analysed and suggestions are given for the implementation of modern earthen technologies for low-cost affordable rural housing. Initiatives by middle-high income households, entrepreneurs and government can trigger a widespread interest in earthen construction. Successful demonstration of durable earthen structures at diverse locations and contexts can act as catalysts for change of the image of earth and make it a desirable material for low-cost housing in rural India., Materials and Environment, Form, Space & Type, Geo-engineering, BT/Environmental Biotechnology

Bacteria‐based self‐healing concrete is an innovative concrete that contains a self‐healing agent that provides the material with enhanced autonomous crack‐sealing performance. A specific type of this concrete, based on a healing agent composed of bacterial spores and lactate as carbon source, has been developed and applied by the Delft University of Technology for over ten years. Under laboratory conditions it was proven that, depending on the dosage of healing agent, self‐healing of cracks up to 0.8 mm widths occurs. As such the material potentially allows reduction of steel reinforcement used for crack width limitation in watertight constructions. Application of self‐healing concrete would therefore not only result in a reduction of costs but also in improvement of environmental performance (lower CO2 footprint) and ease of in situ casting due to reduction of use of steel in waterproof applications. However, according to the EN 1990 Eurocode (Basis of structural design), customary application of a novel type of concrete must be preceded by full scale demonstrators proving evidence for safe and functional performance. In this contribution we portray full scale application of bacteria‐based self‐healing agent as developed by the Delft research group in two repair mortar‐ and in two concrete construction demonstrator projects. These demonstrator projects show that addition of the bacteria‐based self‐healing agent to the concrete mix is safe as no negative side effects on construction performance was observed. However, it also proved difficult to find evidence for increased crack‐healing performance as cracking in the demonstrator constructions hardly occurred. In further full scale demonstrators we therefore plan to drastically reduce amount of crack width‐restraining reinforcement to show crack-healing capacity and potential to save on use of reinforcement steel in watertight concrete constructions., Materials and Environment

There is an enormous demand for rural housing in India that needs to be catered for within a short span of time. Building with earth (mud) is proposed as an economical and environmental friendly alternative due to the rising costs of conventional building materials. However, the construction of earthen houses has significantly declined in India and thus it is necessary to evaluate if they can make a valuable contribution to contemporary housing shortage. Therefore, an informal survey was conducted in India to understand factors favouring or limiting the construction and daily use of earthen houses. The outcome of the survey suggests that ‘Image’ is the key barrier against a wide acceptance of traditional earthen houses which are linked to poverty. While modern earthen construction is desired, it is expensive for low-income households. The role of earth in addressing the contemporary housing shortage is analysed and suggestions are given for the implementation of modern earthen technologies for low-cost affordable rural housing. Initiatives by middle-high income households, entrepreneurs and government can trigger a widespread interest in earthen construction. Successful demonstration of durable earthen structures at diverse locations and contexts can act as catalysts for change of the image of earth and make it a desirable material for low-cost housing in rural India., Materials and Environment, Space & Type, Geo-engineering, BT/Environmental Biotechnology

The choice of structural system has a big influence on the environmental impact of structural materials in tall building design. This paper provides a comparison of the environmental impact of several structural systems for high-rise buildings. The environmental performance for relatively slender buildings in the range of 150 to 250 meters in Western Europe is analyzed for five different types of structural systems in cast-in-situ concrete, precast concrete, and steel. The cradle-to-gate environmental impact was determined by using environmental cost, an assessment method including 10 impact categories. Compared to tube structures, diagrid structures reduced the impact by 17-33% for the concrete models and 28-41% for the steel models, due to reduction of material use. By using non-conventional structural systems such as diagrids, reductions in environmental impact can be achieved relatively easily., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Applied Mechanics, Materials and Environment

This paper investigates the effects of alkaliphilic spore-forming bacteria of the genus Bacillus on the compressive strength of the mortar cube and the healing capacity of the bacteria as healing agent on mortar containing crack. The experiments were carried out using cube test, stereomicroscopy and environmental scanning electron microscopy (ESEM). Cracked mortar specimen with and without the presence of the bacteria-healing agent were prepared. Results showed that the inclusion of these bio-healing agent in mortar mixtures cause more pore volume, which has no significant effect on compressive strength development at 28 days. In the series of healing capacity test, the cracks were significantly healed in bacteria-based than in control specimens after 28 days incubated in water bath and thus, increase permeability resistance of bacteria-based mortar specimens., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public. Part of the Special Issue: Civil Engineering, Materials and Environment

Bijna alle stedelijke klimatologische problemen zijn te herleiden naar het ontbreken van ecosysteemdiensten. Dat blijkt uit onderzoek van de TU Delft Faculteit Civiele Techniek, afdeling Materialen en Duurzaamheid. ‘Ook vonden we dit gebrek medeverantwoordelijk voor veel stedelijke sociale problemen,’ aldus de auteurs. Op basis van het onderzoek ontwikkelden zij een module die inzicht verschaft in de verbeteringen die ecosysteemdiensten ons bieden., Materials and Environment

Presented is a modified test for generating crack permeability data for cementitious materials. Single-parallel cracks were generated in mortar specimens. The width of the cracks was analysed through stereomicroscope and computer tomography, and the water permeability of the cracks was determined. Reduction factors and crack flow models were generated, and the reliability of those predictions was assessed. Cracks analysed through stereomicroscope produced reliable crack permeability predictions (r 2 = 0.97–0.98), highlighting the importance of testing multiple (≥ 7) replicates. The modified test produced accurate cracks (i.e., cracks that were within 20 µm of their desired crack width) and was easy to use allowing rapid permeability data (i.e., 10 h for 21 specimens) to be generated. The modified test will be of great use for those wanting to generate rapid, accurate, and reliable crack permeability data for cementitious materials., Materials and Environment

The choice of structural system has a big influence on the environmental impact of structural materials in tall building design. This paper provides a comparison of the environmental impact of several structural systems for high-rise buildings. The environmental performance for relatively slender buildings in the range of 150 to 250 meters in Western Europe is analyzed for five different types of structural systems in cast-in-situ concrete, precast concrete, and steel. The cradle-to-gate environmental impact was determined by using environmental cost, an assessment method including 10 impact categories. Compared to tube structures, diagrid structures reduced the impact by 17-33% for the concrete models and 28-41% for the steel models, due to reduction of material use. By using non-conventional structural systems such as diagrids, reductions in environmental impact can be achieved relatively easily., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Applied Mechanics, Materials and Environment

This paper investigates the effects of alkaliphilic spore-forming bacteria of the genus Bacillus on the compressive strength of the mortar cube and the healing capacity of the bacteria as healing agent on mortar containing crack. The experiments were carried out using cube test, stereomicroscopy and environmental scanning electron microscopy (ESEM). Cracked mortar specimen with and without the presence of the bacteria-healing agent were prepared. Results showed that the inclusion of these bio-healing agent in mortar mixtures cause more pore volume, which has no significant effect on compressive strength development at 28 days. In the series of healing capacity test, the cracks were significantly healed in bacteria-based than in control specimens after 28 days incubated in water bath and thus, increase permeability resistance of bacteria-based mortar specimens., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public. Part of the Special Issue: Civil Engineering, Materials and Environment

Bijna alle stedelijke klimatologische problemen zijn te herleiden naar het ontbreken van ecosysteemdiensten. Dat blijkt uit onderzoek van de TU Delft Faculteit Civiele Techniek, afdeling Materialen en Duurzaamheid. ‘Ook vonden we dit gebrek medeverantwoordelijk voor veel stedelijke sociale problemen,’ aldus de auteurs. Op basis van het onderzoek ontwikkelden zij een module die inzicht verschaft in de verbeteringen die ecosysteemdiensten ons bieden., Materials and Environment

Presented is a modified test for generating crack permeability data for cementitious materials. Single-parallel cracks were generated in mortar specimens. The width of the cracks was analysed through stereomicroscope and computer tomography, and the water permeability of the cracks was determined. Reduction factors and crack flow models were generated, and the reliability of those predictions was assessed. Cracks analysed through stereomicroscope produced reliable crack permeability predictions (r 2 = 0.97–0.98), highlighting the importance of testing multiple (≥ 7) replicates. The modified test produced accurate cracks (i.e., cracks that were within 20 µm of their desired crack width) and was easy to use allowing rapid permeability data (i.e., 10 h for 21 specimens) to be generated. The modified test will be of great use for those wanting to generate rapid, accurate, and reliable crack permeability data for cementitious materials., Materials and Environment

With rapid industrialisation and the increase in popularity of concrete and brick constructions, a decline in earth houses has been observed especially in the rural areas of India. A survey was carried out in five regions of India to understand the technical and social factors favouring/limiting the construction and everyday use of earth houses. As an outcome of the survey, a low societal image of earth houses and durability issues, such as termite infestation and poor resistance to rain water, were the main reasons behind the choice of low-income households in favour of modern building materials over earth construction., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Space & Type, Materials and Environment, BT/Environmental Biotechnology, Geo-engineering

Autonomous repair systems in construction materials have become a promising alternative to current unsustainable and labor-intensive maintenance methods. Biomineralization is a popular route that has been applied to enhance the self-healing capacity of concrete. Various axenic microbial cultures were coupled with protective carriers, and their combination appears to be useful for the development of healing agents for realizing self-healing concrete. The advantageous traits of non-axenic cultures, such as economic feasibility, self-protection, and high specific activity have been neglected so far, and thus the number of studies investigating their performance as healing agents is scarce. Here we present the self-healing performance of a mortar containing a healing agent consisting of non-axenic biogranules with a denitrifying core. Mortar specimens with a defined crack width of 400 μm were used in the experiments and treated with tap water for 28 days. Self-healing was quantified in terms of the crack volume reduction, the thickness of the sealing layer along the crack depth and water permeability under 0.1 bar pressure. Complete visual crack closure was achieved in the bio-based specimens in 28 days, the thickness of the calcite layer was recorded as 10 mm and the healed crack volume was detected as 6%. Upon self-sealing of the specimens, the water permeability decreased by 83%. Overall, non-axenic biogranules with a denitrifying core shows great potential for development of self-healing bioconcrete., Materials and Environment

Earth houses are considered sustainable and affordable as compared to houses built with concrete or fired clay bricks. Moreover, it preserves the vernacular social and spatial traditions (cultural identity) of the community. With rapid industrialization and the increase in popularity of concrete and brick constructions, a decline in earth houses has been observed especially in the rural areas of India. A survey was carried out in four regions of the country (Himachal, Orissa-Jharkhand, Gujarat, Tamil Nadu) to understand the technical and social factors favouring/limiting the construction and everyday use of earth houses. As an outcome of the survey, two specific but opposing motivations were identified: 1. Lowincome families living in traditional earth houses that aspire for a brick or concrete house and 2. Families that have adopted an alternative and sustainable life-style and prefer living in a “natural habitat”. Although the advantages of mud houses, such as better indoor climate, better affordability, and ease of construction and maintenance were widely acknowledged, limitations with regard to abrasion, poor water-resistance and termite infestation were the major technical drawbacks that motivates the aspiration (for concrete/brick house) of lowincome households. However, the social aspects such as a low societal image of earth houses as compared to modern building materials and comparison with fellow community households were the main reasons behind the choice in favour of modern building material over the earth. The identified negative social and technical aspects place new requirements and demands reinvention of earth house as a necessary step toward their acceptance., Applied Sciences, Geo-engineering, OLD Woningbouw, BT/Environmental Biotechnology, Materials and Environment

Earth houses are considered sustainable and affordable as compared to houses built with concrete or fired clay bricks. Moreover, it preserves the vernacular social and spatial traditions (cultural identity) of the community. With rapid industrialization and the increase in popularity of concrete and brick constructions, a decline in earth houses has been observed especially in the rural areas of India. A survey was carried out in four regions of the country (Himachal, Orissa-Jharkhand, Gujarat, Tamil Nadu) to understand the technical and social factors favouring/limiting the construction and everyday use of earth houses. As an outcome of the survey, two specific but opposing motivations were identified: 1. Lowincome families living in traditional earth houses that aspire for a brick or concrete house and 2. Families that have adopted an alternative and sustainable life-style and prefer living in a “natural habitat”. Although the advantages of mud houses, such as better indoor climate, better affordability, and ease of construction and maintenance were widely acknowledged, limitations with regard to abrasion, poor water-resistance and termite infestation were the major technical drawbacks that motivates the aspiration (for concrete/brick house) of lowincome households. However, the social aspects such as a low societal image of earth houses as compared to modern building materials and comparison with fellow community households were the main reasons behind the choice in favour of modern building material over the earth. The identified negative social and technical aspects place new requirements and demands reinvention of earth house as a necessary step toward their acceptance., Applied Sciences, Geo-engineering, OLD Woningbouw, BT/Environmental Biotechnology, Materials and Environment

The since 2010 running research program 'Bio-Based Geo & Civil Engineering for a Sustainable Society (BioGeoCivil)', funded by the Dutch technology foundation STW, aims to develop novel bio-based construction materials that can be used in Civil- and Geo-engineering constructions to enhance the sustainability performance of the sector. Rationale is that the sector produces still today excess amounts of waste in all life cycle phases of a construction, from building to use phase as well as end-of-life phase. Aim of the program is to mimic nature as 'building' processes in nature do not produce any waste as all elements, also residual material. is considered a high grade resource. In order to substantially improve the sustainability profile of the sector, upgrading of secondary- or byproducts must be achieved to allow functional performance similar to primary materials and resources. The challenge of the six currently running projects within the BioGeoCivil program is therefore not only to mimic nature but also to include bio-based materials or processes in civil- or geo-engineering applications which result, in comparison to traditional building products, in drastically improved performance both on sustainability and durability level. The six projects comprise: 1. Fungal biofilms (coating) for wood protection, 2. Bacteria-based repair and performance improvements of aged concrete structures, 3. Bacteria-based ground stabilization to mitigate liquefaction and piping of granular sediments, 4. Engineering of bacterial biofilms on buildings and infrastructure as a basis for natural protection, 5. Lift up Lowlands: upgrading of natural materials (bio-remediation of sludge) for sustainable lift up of low lying polder areas, and 6. Towards the development of carbon dioxide neutral renewable cement., Materials and Environment

Starch is a natural polymer which is commonly used as a cooking ingredient. The renewability and bio-degradability of starch has made it an interesting material for industrial applications, such as production of bioplastic. This paper introduces the application of corn starch in the production of a novel construction material, named CoRncrete. CoRncrete is formed by mixing corn starch with sand and water. The mixture appears to be self-compacting when wet. The mixture is poured in a mould and then heated in a microwave or an oven. This heating causes a gelatinisation process which results in a hardened material having compressive strength up to 26 MPa. The factors affecting the strength of hardened CoRncrete such as water content, sand aggregate size and heating procedure have been studied. The degradation and sustainability aspects of CoRncrete are elucidated and limitations in the potential application of this material are discussed., Materials and Environment, Geo-engineering

Bacteria induced calcium carbonate precipitation based on metabolic conversion of nutrients has been acknowledged for having potentials in self-healing cement-based materials. Recent studies have shown the development of bacteria-based repair solution (liquid) for concrete surface repair. This article demonstrates the feasible application of the solution as healing agent to be injected into porous network concrete (PNC). This type of concrete has a porous core which can be used as a media to transport healing agents into the fracture zone. The repair capacity of the solution have been assessed by monitoring the bio-mineral precipitation in the porous cylinder cores. The X-ray tomography and permeability tests at certain time interval were carried out before and after injection of the solution. Polished sections were prepared and examined under ESEM after healing period to investigate healing capacity. The healing potential was then tested by injecting the solution into PNC. The injection of tap water and bacteria based solution was performed through porous network until it reached and flew out through the crack which was formed by three-point bending loading. The healing efficiency was measured by water permeability test before and after injection at several time intervals. The specimens injected with bacteria based solution and cured in wet condition showed higher healing efficiency compared to dry cured specimens., Materials and Environment

Biogenic self-healing cementitious materials target on the closure of micro-cracks with precipitated inorganic minerals originating from bacterial metabolic activity. Dormant bacterial spores and organic mineral compounds often constitute a biogenic healing agent. The current paper focuses on the investigation of the most appropriate organic carbon source to be used as component of a biogenic healing agent. It is of great importance to use an appropriate organic source, since it will first ensure an optimal bacterial performance in terms of metabolic activity, while it should, second, affect the least the properties of the cementitious matrix. The selection is made among three different organic compounds, namely calcium lactate (CaL), calcium acetate (CaA), and sodium gluconate (NaG). The methodology that was used for the research was based on continuous and non-continuous oxygen consumption measurements of washed bacterial cultures and on compressive strength tests on mortar cubes. The oxygen consumption investigation revealed a preference for CaL and CaA, but an indifferent behavior for NaG. The compressive strength on mortar cubes with different amounts of either CaL or CaA (up to 2.24% per cement weight) was not or it was positively affected when the compounds were dissolved in the mixing water. In fact, for CaL, the increase in compressive strength reached 8%, while for CaA, the maximum strength increase was 13.4%., Materials and Environment

Water tightness of a concrete cover layer is important, as it is typically used as a protective coating of the steel reinforcement. Water tightness can be impaired by crack formation or by permeability. A bacteria-based lactate-derived healing agent (HA) can be added to concrete to enhance the potential for restoration of water tightness. Bacterial conversion of the included carbon source results in CO2 production and subsequent CaCO3 precipitation, similar to the mechanism of concrete carbonation. Carbonation is known to densify concrete, particularly when using ordinary Portland cement (OPC), but to a much lower extend in slag-based concrete (CEM III/B). To identify the effect of HA addition on concrete properties, this study focusses on the ingress of moisture in non-cracked concrete surfaces by assessing capillary water absorption. Surface properties were determined for sealed and unsealed surfaces of concrete—either based on OPC or CEM III/B—before and after curing under three different conditions: Dry, wet, or humid. HA addition to concrete containing slag cement generated a surface less prone to continued drying, but resulted in higher water absorption. In contrast, surface water absorption significantly decreased upon HA addition to OPC-based samples, independent of the curing regime. It is therefore concluded that HA in its current form is suitable for application in OPC, but less in CEM III/B-based mixtures, Materials and Environment

The since 2010 running research program 'Bio-Based Geo & Civil Engineering for a Sustainable Society (BioGeoCivil)', funded by the Dutch technology foundation STW, aims to develop novel bio-based construction materials that can be used in Civil- and Geo-engineering constructions to enhance the sustainability performance of the sector. Rationale is that the sector produces still today excess amounts of waste in all life cycle phases of a construction, from building to use phase as well as end-of-life phase. Aim of the program is to mimic nature as 'building' processes in nature do not produce any waste as all elements, also residual material. is considered a high grade resource. In order to substantially improve the sustainability profile of the sector, upgrading of secondary- or byproducts must be achieved to allow functional performance similar to primary materials and resources. The challenge of the six currently running projects within the BioGeoCivil program is therefore not only to mimic nature but also to include bio-based materials or processes in civil- or geo-engineering applications which result, in comparison to traditional building products, in drastically improved performance both on sustainability and durability level. The six projects comprise: 1. Fungal biofilms (coating) for wood protection, 2. Bacteria-based repair and performance improvements of aged concrete structures, 3. Bacteria-based ground stabilization to mitigate liquefaction and piping of granular sediments, 4. Engineering of bacterial biofilms on buildings and infrastructure as a basis for natural protection, 5. Lift up Lowlands: upgrading of natural materials (bio-remediation of sludge) for sustainable lift up of low lying polder areas, and 6. Towards the development of carbon dioxide neutral renewable cement., Materials and Environment

Bacteria induced calcium carbonate precipitation based on metabolic conversion of nutrients has been acknowledged for having potentials in self-healing cement-based materials. Recent studies have shown the development of bacteria-based repair solution (liquid) for concrete surface repair. This article demonstrates the feasible application of the solution as healing agent to be injected into porous network concrete (PNC). This type of concrete has a porous core which can be used as a media to transport healing agents into the fracture zone. The repair capacity of the solution have been assessed by monitoring the bio-mineral precipitation in the porous cylinder cores. The X-ray tomography and permeability tests at certain time interval were carried out before and after injection of the solution. Polished sections were prepared and examined under ESEM after healing period to investigate healing capacity. The healing potential was then tested by injecting the solution into PNC. The injection of tap water and bacteria based solution was performed through porous network until it reached and flew out through the crack which was formed by three-point bending loading. The healing efficiency was measured by water permeability test before and after injection at several time intervals. The specimens injected with bacteria based solution and cured in wet condition showed higher healing efficiency compared to dry cured specimens., Materials and Environment

Water tightness of a concrete cover layer is important, as it is typically used as a protective coating of the steel reinforcement. Water tightness can be impaired by crack formation or by permeability. A bacteria-based lactate-derived healing agent (HA) can be added to concrete to enhance the potential for restoration of water tightness. Bacterial conversion of the included carbon source results in CO2 production and subsequent CaCO3 precipitation, similar to the mechanism of concrete carbonation. Carbonation is known to densify concrete, particularly when using ordinary Portland cement (OPC), but to a much lower extend in slag-based concrete (CEM III/B). To identify the effect of HA addition on concrete properties, this study focusses on the ingress of moisture in non-cracked concrete surfaces by assessing capillary water absorption. Surface properties were determined for sealed and unsealed surfaces of concrete—either based on OPC or CEM III/B—before and after curing under three different conditions: Dry, wet, or humid. HA addition to concrete containing slag cement generated a surface less prone to continued drying, but resulted in higher water absorption. In contrast, surface water absorption significantly decreased upon HA addition to OPC-based samples, independent of the curing regime. It is therefore concluded that HA in its current form is suitable for application in OPC, but less in CEM III/B-based mixtures, Materials and Environment

Biogenic self-healing cementitious materials target on the closure of micro-cracks with precipitated inorganic minerals originating from bacterial metabolic activity. Dormant bacterial spores and organic mineral compounds often constitute a biogenic healing agent. The current paper focuses on the investigation of the most appropriate organic carbon source to be used as component of a biogenic healing agent. It is of great importance to use an appropriate organic source, since it will first ensure an optimal bacterial performance in terms of metabolic activity, while it should, second, affect the least the properties of the cementitious matrix. The selection is made among three different organic compounds, namely calcium lactate (CaL), calcium acetate (CaA), and sodium gluconate (NaG). The methodology that was used for the research was based on continuous and non-continuous oxygen consumption measurements of washed bacterial cultures and on compressive strength tests on mortar cubes. The oxygen consumption investigation revealed a preference for CaL and CaA, but an indifferent behavior for NaG. The compressive strength on mortar cubes with different amounts of either CaL or CaA (up to 2.24% per cement weight) was not or it was positively affected when the compounds were dissolved in the mixing water. In fact, for CaL, the increase in compressive strength reached 8%, while for CaA, the maximum strength increase was 13.4%., Materials and Environment

Starch is a natural polymer which is commonly used as a cooking ingredient. The renewability and bio-degradability of starch has made it an interesting material for industrial applications, such as production of bioplastic. This paper introduces the application of corn starch in the production of a novel construction material, named CoRncrete. CoRncrete is formed by mixing corn starch with sand and water. The mixture appears to be self-compacting when wet. The mixture is poured in a mould and then heated in a microwave or an oven. This heating causes a gelatinisation process which results in a hardened material having compressive strength up to 26 MPa. The factors affecting the strength of hardened CoRncrete such as water content, sand aggregate size and heating procedure have been studied. The degradation and sustainability aspects of CoRncrete are elucidated and limitations in the potential application of this material are discussed., Materials and Environment, Geo-engineering

The invention provides a process for the production of a cementitious material, comprising mixing cement starting materials, a healing agent and a fibrous reinforcing material, wherein the healing agent comprises bacterial material, and wherein the fibrous reinforcing material comprises a biodegradable polymer, having an average molecular weight selected from the range of 10 - 1500 kg/mol, and wherein the fibrous material comprises fibers having diameters selected from the range of 5 -750[mu]m, and having lengths selected from the range of 50 [mu]m -150mm., Structural Engineering, Civil Engineering and Geosciences

The invention provides a process for the production of a cementitious material, comprising mixing cement starting materials, a healing agent and a fibrous reinforcing material, wherein the healing agent comprises bacterial material, and wherein the fibrous reinforcing material comprises a biodegradable polymer, having an average molecular weight selected from the range of 10 - 1500 kg/mol, and wherein the fibrous material comprises fibers having diameters selected from the range of 5 -750[mu]m, and having lengths selected from the range of 50 [mu]m -150mm., Structural Engineering, Civil Engineering and Geosciences

Concrete structures are often reinforced with steel. In order for the reinforcement to take over tensile forces, concrete has to crack. Through such cracks, water and compounds that are harmful to concrete can enter. This can cause durability issues like leakage, concrete degradation and reinforcement corrosion. In situ repair of cracks is often labour-intensive and inefficient. Preferentially, cracks are autonomously healed from the inside out in an early stage, preventing the ingress of water. This can be achieved by incorporating healing agent particles composed of nutrients and bacterial spores into the concrete matrix. The bacteria will germinate when water is available, plugging cracks with calcium carbonate. However, a coating is needed to protect the water-soluble healing agent from water during mixing. In order to allow the bacteria access to water for activation after the concrete has hardened, such a coating should break whenever a crack occurs in the concrete. Therefore, it should adhere well to the concrete matrix. It is possible to achieve this by protecting the particles with a brittle geopolymer coating. For this study, healing agent particles are coated with geopolymers following different mixture recipes. Metakaolin is used as an aluminosilicate source and sodium silicate as well as sodium aluminate are used as activator liquids. The particles are coated by granulation in a low-shear granulator. In order to improve the coating process, the operating window and the granulation mechanism are determined for all activator liquids used. Leaching and strength tests are performed and coated particles are incorporated in cement paste in order to determine the feasibility of application of the particles in concrete. Results show that the prepared particles are better protected from leaching than untreated particles. Using a high pressure single-fluid nozzle to improve nebulisation when coating produces more particles of the desired size than coating with a, Structural Engineering, Civil Engineering and Geosciences