[Show abstract][Hide abstract] ABSTRACT: Superabsorbent polymers (SAPs) are a promising additive to be used in the building industry but may induce microstructural changes. Water vapour sorption may be used to characterize the change in pore structure of cementitious materials, but the technique is difficult to interpret. In the present paper, static and dynamic vapour sorption (DVS) measurements were performed and compared to nitrogen adsorption experiments. The models of Dubinin-Radushkevich and Barrett-Joyner-Halenda were hereby applied to study pores in the micro- and mesopore range. The results show that cement pastes with SAPs and without additional water show a slight decrease in porosity in the micro- and mesopore range. Cement pastes with SAPs and with additional water show no significant change of porosity in the micropore range and a slight increase in the larger mesopore range. These new findings give insight into the effects of SAPs on the microstructure and strength of cementitious materials.
Cement and Concrete Research 11/2015; 77:26-35. DOI:10.1016/j.cemconres.2015.06.013 · 3.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cracks in concrete are inevitable and for durability reasons, the cracks should be repaired. Concrete has the intrinsic property to heal itself. But, the passive form of autogenous healing plays only an inferior role for a complete repair of a cementitious material. The main cause is that only cracks of limited width may heal completely. For that reason, microfibers are added to the mixture, as they cause the formation of multiple small cracks. In this way, a ductile material is designed with the property to heal itself efficiently. This paper will overview the different fiber reinforced cementitious composites of the last decade, the link with autogenous healing, results from the literature and future prospects.
Construction and Building Materials 10/2015; 95:774-787. DOI:10.1016/j.conbuildmat.2015.07.018 · 2.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fiber cement panels were treated with urea and various calcium solutions with and without live or dead cells of Bacillus sphaericus LMG 222 57, to produce a surface layer of biocalcite; they were then exposed to the environment in São Paulo, Brazil, for 22 months. The calcifying treatment that produced the most colonisation-resistant surface was living bacteria + medium B4 + urea. The resistance of these biocalcified panels was related to their low water absorption, porosity and surface hydrophilicity, linked to the smaller size of the crystals compared to other treatments. Carbonation of the fiber cement before calcification visually increased biofilm formation, but the same calcifying treatment produced highest fouling resistance in this pre-carbonated group. Control samples, without calcification, allowed the development of considerable fouling, sometimes including the filamentous cyanobacterial genus, Scytonema, indicative of mature sub-aerial biofilms. There was no significant visual degradation of the calcite crystals associated with the colonising fungi and phototrophs after 22 months’ exposure. Biocalcification may safely be used to reduce the fouling-associated darkening of fiber cement and for protection and repair of cementitious building materials.
[Show abstract][Hide abstract] ABSTRACT: Fly ash and blast-furnace slag containing binders are frequently used in the construction industry and it is important to know the extent of autogenous shrinkage and its (ideal) mitigation by superabsorbent polymers in these systems as a function of their age. In this paper, the autogenous shrinkage was determined by manual and automated shrinkage measurements. Autogenous shrinkage was reduced in cement pastes with the supplementary cementitious materials versus Portland cement pastes. At later ages, the rate of autogenous shrinkage is higher due to the pozzolanic activity. Internal curing by means of superabsorbent polymers is successful, independent of this long term higher rate of shrinkage in mixtures with supplementary cementitious materials.
Cement and Concrete Research 08/2015; 74:59-67. DOI:10.1016/j.cemconres.2015.03.020 · 3.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bacteria that can induce calcium carbonate precipitation have been studied for self-healing concrete applications. Due to the harsh environment of concrete, i.e. very high pH, small pore size and dry conditions, protection methods/materials have been used to preserve the bacterial agents. A wide screening of commercially available materials is thus required to evaluate them as alternatives. This study describes the influence of six commercially available possible protection approaches (diatomaceous earth, metakaolin, expanded clay, granular activated carbon, zeolite and air entrainment) on mortar setting and compressive strength when combined with either Bacillus sphaericus spores or Diaphorobacter nitroreducens and their respective nutrients. The influence of two novel, self-protected, bacterial agents was also investigated within the same scope. The most severe effect on setting time was observed as an undesirable delay of 340 min in all samples containing nutrients for ureolytic bacteria. Samples containing B. sphaericus spores showed the most significant decreases in compressive strength up to 68%. Yet, the addition of either D. nitroreducens or its respective nutrients did not cause major impact on both the setting times and the compressive strengths of the mortar specimens. The latter thus appears to be a suitable bacterial agent for further research on self-healing concrete. Likewise, the use of the novel self-protected bacterial agents did not affect the setting and the compressive strength of mortar. These results pave the way to replace protection materials with self-protection techniques. The latter should be further investigated for development of microbial self-healing concrete.
Construction and Building Materials 07/2015; 88. DOI:10.1016/j.conbuildmat.2015.04.027 · 2.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Concrete's intrinsic ability to heal, called autogenic healing, has been reported for many years. This natural process is being improved and supplemented for some years by promising engineered additions such as mineral additions, capsules containing healing agents, minerals producing bacteria, or fibres limiting the crack width. However, a deeper understanding of the natural phenomenon could help to design innovative healing solutions based on cementitious materials themselves. In this study, self-healing potential of cementitous materials is studied both experimentally and numerically, modifying a hydration code (CEMHYD3D) and coupling it with a mechanical code (Cast3M). Experimental work, based on three-points-bending tests, has been conducted on specimens preferentially cracked at early age to investigate their healing potential according to various parameters (e.g. healing time, initial crack width, age at cracking and water-to-cement ratio). A focus is put on the minimum time to obtain mechanical regain for a given crack width in order to explain the development of the healing phenomenon and compare the results with the simulations. Experimentally, small cracks with a width of around 10 µm can quickly heal within several days by immersion into water. Mechanical regain up to 80% of an uncracked specimen is observed for several water-to-cement ratios and is proportional to the initial crack width. The major influencing parameter is the age at cracking: when the crack is created after 72 h, the mechanical regain is considerably decreased and the healing period needs to be several weeks. Numerical models can provide further information. The mechanical regain is due to the formation of bridges between the two cracks lips by ongoing hydration. According to the model, the major healing products in the crack are porlandite and calcium silicate hydrate.
Fifth International Conference on Self-Healing Materials (ICSHM 2015), Durham, NC, USA; 06/2015
[Show abstract][Hide abstract] ABSTRACT: Cracks are concrete's worst problem. External, passive treatments are expensive and time consuming. pH-responsive superabsorbent polymers (SAPs) offer an internal active solution. When cracks occur, the SAPs can swell, fill the crack (self-sealing) and assist in the formation of healing products (self-healing). In previous work, a range of (superabsorbent) polymers have been synthesized and characterized. Based on these results, the two best performing SAPs were chosen for further characterization. The results indicate that the SAPs developed do not show degradation in cement filtrate solutions. Upon addition of SAPs, a decrease in mortar strength occurred, yet a positive effect on self-sealing was observed since the water permeability decreased. Furthermore, the formation of products became apparent at the sealed cracks of the mortar samples containing 1 m% SAPs. Identification using scanning electron microscopy, infrared spectroscopy and thermogravimetric analysis indicated that the products mainly consisted of healing products (more specifically CaCO3) which is illustrative for self-healing.
Reactive and Functional Polymers 06/2015; DOI:10.1016/j.reactfunctpolym.2015.06.003 · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Concrete is an important building material, due to its ease to use and relatively low cost. However, the presence of cracks endangers the durability of concrete and can result in reinforcement corrosion, since a pathway for harmful particles dissolved in fluids and gases is generated. Manual repair costs can go up to half of the annual construction budget. Instead, introducing a superabsorbent polymer (SAP) during concrete mixing can create a self-sealing and -healing material.
Some SAPs undergo major characteristic changes by small environmental variations. These so-called ‘smart’ polymers have the ability to sense environmental stimuli. The use of pH-responsive SAPs can be extremely useful for the envisaged application (i.e. self-sealing and self-healing of cracks). When cracks in concrete are subjected to external wetting, ingress of moisture will cause the SAP to swell. When the external fluid possesses a low ionic strength, the SAP will swell to such an extent that it completely fills the crack and slow down or even prevent the further infiltration of water. In addition, these polymers may promote autogenous healing.
The proposed paper discusses the effect of a plethora of pH-responsive SAPs. First, the SAPs have been characterized by means of attenuated total reflectance-infrared (ATR-IR) spectroscopy and high resolution magic-angle spinning (HR-MAS) 1H-NMR spectroscopy. In addition, the sorption and desorption of moisture at different relative humidities have been measured through dynamic vapour sorption (DVS) experiments. Furthermore, their swelling capacity at varying pH-values in aqueous solutions and (acidified) cement filtrate have been compared. In a second part, the mechanical properties of mortar mixtures with(out) SAPs have been assessed by performing flexural and compressive strength tests. The sealing efficiency has been measured through a water permeability set-up. The results indicate that these newly developed polymers are promising for their crack-sealing and -healing potential in concrete.
Fifth international conference on self-healing materials, Durham; 06/2015
[Show abstract][Hide abstract] ABSTRACT: As an alternative to the usual strategy of manual repair of concrete cracks as they arise, concrete
elements can be designed with an incorporated self-healing mechanism. Crack initiation will trigger the
self-healing activity; the repair components are transported towards the location of damage and should
heal the crack efficiently. Depending on the type of structure and the loading situation, the healing
material should be able to heal a static or dynamic crack, and should provide mere crack filling, a regain
in liquid-tightness or recovery of (some of the) mechanical properties.
Therefore different self-healing strategies were developed, including stimulated autogenous healing by
introduction of superabsorbent polymers; autonomous healing by encapsulated calcium carbonate
precipitating bacteria; and autonomous healing by an encapsulated polyurethane-based healing agent.
These systems were first tested at laboratory scale for their effects on concrete properties and selfhealing
efficiency. Additionally, a large scale lab test was performed on self-healing concrete beams of
150 mm x 250 mm x 3000 mm, loaded in 4-point bending mode. Crack formation was monitored with
a linear variable differential transformer, acoustic emission, digital image correlation and ultrasonic
wave propagation technique based on embedded piezoelectric transducers. Crack healing was followed
with crack microscopy and water ingress measurements.
International Conference on the Regeneration and Conservation of Concrete Structures (RCCS); 06/2015
[Show abstract][Hide abstract] ABSTRACT: Autogenous healing is an already-present feature in strain-hardening cementitious materials, but it is an inferior mechanism because it can only heal small cracks in the presence of water. A cementitious material with synthetic microfibers and superabsorbent polymers (SAPs) could provide a solution. In this study, the ability of repeatable promoted autogenous healing in fiber-reinforced, strain-hardening cementitious materials with and without SAPs is investigated by comparing their mechanical properties after they are subjected to two cycles of loading under a four-point-bending test. The results indicate that SAP particles promote self-healing. The main mechanisms of the autogenous healing are the hydration of unhydrated cementitious materials in cracks and the precipitation of calcium carbonate on the crack faces. The healed specimens are able to regain some of their mechanical properties (up to 75%). Even second reloading of those healed samples leads to partial additional regain in mechanical properties (up to 66%).
Journal of Materials in Civil Engineering 06/2015; 04015086:1-11. DOI:10.1061/(ASCE)MT.1943-5533.0001360 · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Autogenous healing of cracks may offer a solution for brittle cementitious materials. Further cement hydration and calcium carbonate crystallization will hereby heal the cracks if sufficient building blocks and water are present. The building blocks are available through the well-designed mixture with a low water-to-binder ratio and water is available through the inclusion of superabsorbent polymers. These polymers are able to extract moisture and fluids from the environment and to provide it to the cementitious matrix for autogenous healing. This healing will lead to the regain in mechanical properties, as already found in previous research. As the crack seems to be completely visually closed at the surface, one may ask whether this healing is also present in the interior of the crack. X-ray computed microtomography was therefore used to study the extent of autogenous healing in cracked cylindrical specimens after autogenous healing. It was found that the autogenous healing in a cementitious material is dependent on the crack depth. Only the first part of the crack is closed by crystal formation in case of wet/dry cycles. In combination with superabsorbent polymers, the extent of healing was more substantial, even in the interior of the crack. There was even partial healing in the interior of the crack when stored at a relative humidity of 60% or more than 90%, but only in mixtures containing superabsorbent polymers. The smart cementitious material with superabsorbent polymers thus is an excellent material to use in future building applications as the healing extent is improved.
Fifth international conference on self-healing materials, Durham; 06/2015
[Show abstract][Hide abstract] ABSTRACT: 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 18.9 g CaCO3/g NO3-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.
[Show abstract][Hide abstract] ABSTRACT: The bio-based self-healing concrete market demands an inexpensive bio-agent. The use of axenic ureolytic spore cultures has been demonstrated to be efficient but too expensive, due to an operational expense (OPEX) cost of about 500 €/kg of bio-agent. A new selection process to obtain a powderous material containing an efficient ureolytic microbial community (Cyclic EnRiched Ureolytic Powder or CERUP) has been developed. Ureolytic activity, calcium carbonate precipitation capability and the effects in concrete were evaluated at production scales of 5 L and 50 L. The non-axenic culture obtained following this new selective process, at both 5 L and 50 L scales, proved to be as good as the benchmark Bacillus sphaericus both in urea hydrolysis (20 g urea/L in 24 h) and calcium carbonate precipitation (0.3 g CaCO3/g VS.h). Plain incorporation of CERUP in concrete was found to be efficient at levels of 0.5% and 1% of the cement weight. Furthermore, a brief economical evaluation was performed to verify the economic feasibility of this product. Only OPEX costs were considered since capital expense (CAPEX) costs are directly related to the dimensions of scale and thus not possible to estimate at this stage of the research. The OPEX cost per unit of CERUP is about 40 times lower than the OPEX cost of a B. sphaericus axenic culture. However, even with such decrease in cost, the production of bacterial spores to incorporate in concrete is too expensive.
Construction and Building Materials 05/2015; DOI:10.1016/j.conbuildmat.2015.05.049 · 2.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study focused on identification of denitrifiers that can be used to achieve microbial self-healing concrete. By using heat treatment and minimal medium, 9 denitrifying strains were isolated from soil. Upon identification of the strains, their capability of handling dehydration stress was investigated. Qualifying 7 strains were further investigated at N:P ratio of 70:1. Finally, 2 strains, Pseudomonas aeruginosa and Diaphorobacter nitroreducens, were selected and investigated at pH 7, pH 9.5 and pH 13 with and without protection. As a protective carrier diatomaceous earth and expanded clay were used. Significant activity observed at pH 9.5 and with protection both strains could survive pH 13 for 14 days and reduced 20-30 mg/L NO 3 -in 4 days after the pH adjustment to ~10. Overall, the results indicated that Pseudomonas aeruginosa and Diaphorobacter nitroreducens can resist mild heat, dehydration, starvation and relatively alkali environment, which are the main concerns in use of bacteria for concrete structures.
[Show abstract][Hide abstract] ABSTRACT: This paper is the work of working group 2 of the RILEM TC 238-SCM. Its purpose is to review methods to estimate the degree of reaction of supplementary cementitious materials in blended (or composite) cement pastes. We do not consider explicitly the wider issues of the influence of SCMs on hydration kinetics, nor the measurement of degree of reaction in alkali activated materials. The paper categorises the techniques into direct methods and indirect methods. Direct methods attempt to measure directly the amount of SCM remaining at a certain time, such as selective dissolution, microscopy combined with image analysis, and NMR. Indirect methods infer the amount of SCM reacted by back calculation from some other measured quantity, such as calcium hydroxide consumption. The paper first discusses the different techniques, how they operate and the advantages and limitations along with more details of case studies on different SCMs. In the second part we summarise the most suitable approaches for each SCM, and the paper finishes with conclusions and perspectives for future work.
Materials and Structures 04/2015; 48(4). DOI:10.1617/s11527-015-0527-4 · 1.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During the last years, more and more research has been devoted to self-healing in cementitious materials. While most research is still done on carefully prepared small-scale mortar samples with predefined cracks, the healing efficiency should be investigated after exposure of the capsules to the concrete mixing and casting process and for random appearing cracks. In the current study, the resistance of brittle encapsulation materials, containing polyurethane, against the mixing and manufacturing process of concrete was studied. Different methods to protect the capsules were proposed and evaluated. In addition, realistic crack patterns were created in beams with embedded capsules. Non-destructive testing techniques such as digital image correlation, acoustic emission analysis and X-ray radiography were used to evaluate the survivability of the capsules upon mixing and the breakability of the capsules upon crack formation. Evaluation of the crack repair efficiency by performing water permeability tests showed some improvement in water tightness due to self-healing, but the water ingress into the cracks was not completely prevented.
[Show abstract][Hide abstract] ABSTRACT: This paper aims to examine the use of fines generated out of recycled aggregates production as an alternative raw material for Portland clinker kilns with enumeration of possible limitations. Different technical set-ups were used to separate these fines from the recycled aggregates. The relationship between the particle size distribution of the generated fines fraction and their chemical composition as well as the relationship between the final filler (<63 μm) content [wt%] and the water demand of the treated sand fraction were investigated. Numerical simulations were carried out to maximise the fines fractions as raw materials in clinker kilns based on which experimental clinkers were produced. The final clinkers were fully analysed and evaluated on possible mineralogical influences.
[Show abstract][Hide abstract] ABSTRACT: Up to now, glass capsules, which cannot resist the mixing process of concrete, have been mostly used in lab-scale proof-of-concept to encapsulate polymeric agents in self-healing concrete. This study presents the design of polymeric capsules which are able to resist
the concrete mixing process and which can break when cracks appear. Three different polymers with a low glass transition temperature Tg have been extruded: Poly(lactic acid) (PLA) (Tg = 59 °C), Polystyrene (PS) (Tg = 102 °C) and Poly(methyl methacrylate/n-butyl methacrylate) (P(MMA/n-BMA)) (Tg = 59 °C). After heating the capsules prior to mixing with other components of the mix, to shift from a brittle state to a rubbery state, their survival ratio considerably increased. Moreover, a part of the capsules, which previously survived the concrete mixing process, broke with crack appearance. Although some optimization is still necessary concerning functional life of encapsulated adhesives, this seems to be a promising route.
Cement and Concrete Composites 01/2015; DOI:10.1016/j.cemconcomp.2014.09.022 · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Incorporation of living organisms, such as photosynthetic organisms, on the structures envelope has become a priority in the area of architecture and construction due to aesthetical, economic and ecological advantages. Important research efforts are made to achieve further improvements, such as for the development of cementitious materials with an enhanced bioreceptivity to stimulate biological growth. Previously, the study of the bioreceptivity of cementitious materials has been carried out mainly under laboratory conditions although field-scale experiments may present different results.
This work aims at analysing the colonisation of cementitious materials with different levels of bioreceptivity by placing them in three different environmental conditions. Specimens did not present visual colonisation, which indicates environmental conditions have a greater impact than intrinsic properties of the material at this stage. Therefore, it appears that in addition to an optimized bioreceptivity of the concrete (i.e. composition, porosity and roughness), extra measures are indispensable for a rapid development of biological growth on concrete surfaces. An analysis of the colonisation in terms of genus and quantity of the most representative microorganisms found on the specimens for each location was carried out and related to weather conditions, such as monthly average temperature and total precipitation, and air quality in terms of NOx, SO2, CO and O3.
OPC-based specimens presented the higher colonisation regarding both biodiversity and quantity. However, results obtained in a previous experimental program under laboratory conditions suggested a higher suitability of Magnesium Phosphate Cement-based (MPC-based) specimens for algal growth. Consequently, carefully considering the environment and the relationships between the different organisms present in an environment is vital for successfully using a cementitious material as a substrate for biological growth.
Science of The Total Environment 01/2015; 512-513:444-453. DOI:10.1016/j.scitotenv.2015.01.086 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Self-healing concrete has been scrutinized by several researchers and some industrial concrete producers in relation to the remediation of the occurrence of micro-cracks. Such cracks are a quite well known problem that can lead to corrosion of the steel reinforcement and thus to the possible failure of the entire concrete structure. The need to repair these cracks as soon as possible leads to maintenance costs which can be of the order of €130 (direct costs) per m3 of concrete. Recent scientific studies indicate that a Microbial Induced Carbonate Precipitation (MICP), using microbial spores as active agent, can be an alternative for the actual repair methods. However, the production of bacterial spores is yet imposing considerable costs. According to some concrete producers they would be willing to pay about €15 to €20 per m3 of concrete for a bio-based self-healing product. However, the actual cost of spores production and encapsulation represent a total cost which is orders of magnitude higher. This article analyzes the costs for the biological self-healing in concrete and evaluates the industrial challenges it faces. There is an urgent need to develop the production of a bio-additive at much lower costs to make the biological self-healing industrial applicable. Axenic production and a possible non-axenic process to obtain ureolytic spores were analyzed and the costs calculations are presented in this paper.
Journal of Commercial Biotechnology 01/2015; 21(1):31-38. DOI:10.5912/jcb662