Application of various microscopy techniques to study early-age and longer-term behaviour of super sulphated cement microstructure.

Super sulphated cement (SSC) is a very promising substitute for traditional construction materials (i.e. Portland cement), due to its enhanced durability and particularly low environmental impact. This paper explores the microstructure and certain properties of SSC, focusing on the particular complexities of its microstructure and the difficulties of microanalysis of its hydrates. To do so, SSC paste samples were first cast to identify hydration products using X-ray diffraction, then observed at early age using confocal laser scanning microscopy (CLSM) and at early and late age using scanning electron microscopy. In addition, concrete cores impregnated with fluorescein in order to highlight porosity, cracking and aggregates debonding were observed under UV light using optical microscopy (OM), showing a complete absence of cracking and aggregate debonding. Both microscopy techniques (CLSM and UV light OM) have been applied to this type of binder for the first time. The results show that SSC microstructure is characterised by a sophisticated intergrowth of various phases, including ettringite and amorphous calcium-(alumina)-silicate hydrate gels. Finally, Monte-Carlo simulation of electron-matter has been provided for a better understanding of EDS analysis.

Impact of a biorepair treatment on the diversity of calcifying bacterial communities at the surface of cracked concrete walls.

Changes in the diversity of indigenous calcifying bacterial communities were determined before and after 1 year of biorepair treatment applied on indoor micro-cracked concrete walls. The biotreatment was based on the formation of an organo-mineral coating generated by Alkalihalobacillus pseudofirmus cultured in the presence of calcium lactate. Before and after the biotreatment, the calcifying bacterial strains belonging to either Firmicutes or Actinobacteria phylum were dominant depending on the sampling area. Nevertheless, the proportion of the calcifying Bacillus, Brachybacterium, Microbacterium, and Rhodococcus genera changed. These bacterial strains were likely to participate in the effectiveness of the biotreatment. Isolated bacteria of Microbacterium and Rhodococcus genera reported interesting calcifying capacity associated to microbial growth rates greater than the one observed for Alkalihalobacillus pseudofirmus. A bacterial consortium containing Alkalihalobacillus pseudofirmus, Rhodococcus cercidiphylli, and Microbacterium schleiferi demonstrated an improved calcifying capacity. Consequently, using a bacterial consortium instead of a single strain is an efficient way to improve the robustness of the biorepair treatment. KEY POINTS: • Indigenous calcifying bacteria mainly belonged to Firmicutes and Actinobacteria • Microbacterium and Rhodococcus reported the quickest growth rate with calcium lactate • A bacterial consortium with improved calcifying capacity is proposed.

Quantification of the Hardened Cement Paste Content in Fine Recycled Concrete Aggregates by Means of Salicylic Acid Dissolution.

Adherent hardened cement paste attached to recycled concrete aggregates (RCA) generally presents a higher porosity than natural aggregates, which induces a lower porosity in the properties of RCA. The characterization of the adherent hardened cement paste content (HCPC) in the fine RCA would promote better applications of RCA in concrete, but the determination of HCPC in fine RCA is not well established. A simple method based on salicylic acid dissolution was specifically developed to quantify the HCPC in RCA, especially for RCA containing limestone aggregates. The results demonstrated that the soluble fraction in salicylic acid (SFSA) was equal to the HCPC for white cement and slightly lower for grey Portland cement, which was also confirmed by a theoretical approach using modelling the hydration of cement paste with the chemical equations and the stoichiometric ratios. The physical and mechanical properties of RCA (e.g., water absorption) were strongly correlated to the SFSA. For industrial RCA, SFSA did not give the exact value of HCPC, but it was sufficient to correlate HCPC with the other properties of RCA. The water absorption could be estimated with good accuracy for very fine RCA (laboratory-manufactured RCA or industrial RCA) by extrapolating the relationship between water absorption and HCPC, which is very important for concrete formulation.

Colour and chemical stability of bismuth oxide in dental materials with solutions used in routine clinical practice.

Bismuth(III) oxide is included as a radio-opacifier in dental materials, including hydraulic silicate cements, the material of choice for several endodontic procedures. It has been implicated in tooth discoloration after contact with endodontic irrigants, in particular NaOCl solution, To date, there has been no work on the chemistry: all reports have been of clinical findings only. The purpose now was to report the reactions leading to colour change from Bi2O3 in contact with solutions used in routine endodontic practice. Ten-gram portions of Bi2O3 were immersed in either water, NaOH, NaCl, NaOCl or HCl solution, either in the dark or exposed to visible light, and samples retrieved at 1, 4, 12 and 24 weeks. After washing, these were exposed to either added CO2 or not, for 1 week while drying, and under the same dark or light conditions. Changes in appearance were monitored by photography and colour measurement, and chemically by X-ray diffraction and Fourier-transform infrared spectroscopy. 24-week material was studied using electron paramagnetic resonance and Raman spectroscopy; NaOCl-treated material was also examined by scanning electron microscopy. With water, NaCl and NaOH, bismuth subcarbonate was formed. With or without added carbon dioxide, discoloration occurred from pale yellow to light brown when exposed to light, and to a lesser extent in the dark, intensifying with time. In contrast, exposure to NaOCl rapidly formed a dark brown-black sodium bismuthate. With HCl, white BiOCl was formed. Bi2O3 is not at all inert in this context as is commonly believed, denying its principle of use. Previously unreported solution-mediated reaction occurs readily even in water and NaCl solution, forming new compounds that discolour. In contact with NaOCl sodium bismuthate is formed; severe darkening occurs rapidly. The reactivity is such that Bi2O3 is not indicated for dental materials and should be withdrawn from use.

Optimization of the formulation of an original hydrogel-based bone cement using a mixture design.

Highly swelling polymers, i.e. superabsorbent hydrogels, are hydrophilic, three dimensional networks that can easily absorb a significant amount water, fluid or drug. They are widely used in various applications such as foods, cosmetics, and medical devices. Bone cements are used in orthopaedics as a filling biomaterial or as a grout enhancing the embedding of a prosthesis into bone and fixation is achieved by mechanical interlock with metal or bone surfaces. Recently, hydrophilic bone cements have attracted the attention for bone tissue-engineering applications. Here a bone cement containing an acrylic hydrogel (HEMA) as a liquid phase and a blend of corn starch, cellulose acetate and bioceramic filler as a solid phase is investigated by means of a mixture design which is a special topic within statistical Design of Experiments (DoE). Output variables of interest, complex shear modulus, compressive modulus and swelling rate related to rheological, mechanical and swelling properties respectively, are measured for each cement formulation. Applying the mixture design strategy enables to assess the impact of the three powder components on each variable of interest and to determine the optimal formulation in order to achieve the required properties of this HEMA-based bone cement, especially the rheology adapted to the desired clinical application, but also appropriate mechanical and swelling properties.

Environmental hazard assessment by the Ecoscore system to discriminate PAH-polluted soils.

A bioassay battery-integrated index was applied to different soils sampled from a former coke factory, with the aim to evaluate the discriminating capacity of the Ecoscore system (ES) to assess the environmental hazard of PAH-polluted soils. Two soils from a former coke factory, polluted with polycyclic aromatic hydrocarbons (PAHs), were evaluated for their ecotoxicity to terrestrial and aquatic organisms and their genotoxicity. These soils have been already presented in a previous paper but data have been reanalyzed for the present article in an endeavor to standardize the ES. One soil was sampled in the untreated site and the second underwent a windrow treatment. While these soils had a similar total concentrations of US-EPA 16PAHs (around 3000 mg kg-1), different ecoscores were obtained when subjected to a set of solid- and liquid-phase bioassays measuring acute, chronic, and genotoxic effects. The total PAH content of the soil is not a pertinent parameter to assess soil pollution hazards contrary to the ES. ES is a robust method to classify soils according to their toxicity level. Four levels of toxicity have been defined: no (ecoscore = 0), weak (0 < ecoscore ≤33), moderate (33 < ecoscore ≤67), and strong toxicity (67 < ecoscore ≤ 100). The combination of chemical and toxicological data highlights the relationship between three-ring PAHs and acute ecotoxicity. Conversely, chronic effects of water extracts on algal growth could be explained by high molecular weight PAHs, such as five- and six-ring PAHs.

Microscopy in addition to chemical analyses and ecotoxicological assays for the environmental hazard assessment of coal tar-polluted soils.

Chemical analysis of soils contaminated with coal tar indicated that most organic compounds, and particularly PAHs, were contained in coarser particles (> 200 µm). Microscopic observations of this fraction, carried out on polished sections, reported the presence of organic particles in addition to mineral particles. Some organic particles had a very low porosity, and their microstructure did not evolve during biotreatment. Alternatively, other organic particles had a large porosity composed of an interconnected pore network that was open to coal tar surface and thus in contact with soil water. Interconnected porosity seemed to increase during biotreatment in relation to a decrease in the amount of organic compounds. The amount of open porosity in contact with soil water was expected to increase the desorption rate of PAHs. Consequently, the environmental hazard could depend on the amount of open porosity in addition to chemical properties of organic particles, such as their concentration in PAHs. Thus, microscopy can be complementary to chemical analysis and ecotoxicological assays to assess the best strategy for remediation but also to follow the advancement of a biotreatment.

In situ assessment of the setting of tricalcium silicate-based sealers using a dentin pressure model.

INTRODUCTION: EndoSequence BC Sealer (Brasseler, Savannah, GA) is a premixed tricalcium silicate-based root canal sealer that requires moisture from the root dentin to hydrate. The aim of this study was to investigate the setting of EndoSequence BC Sealer and other sealers in contact with human dentin in a simulated clinical environment. METHODS: EndoSequence BC Sealer, MTA Fillapex (Angelus, Londrina, Brazil), Septodont Sealer (Septodont, Saint Maur-des-Fosses, France), and Apexit Plus (Ivoclar, Schaan, Lichtenstein) were assessed. Caries-free lower premolars extracted for orthodontic purposes in patients aged 13-16 years were standardized to a 10-mm root length and were filled with test sealers and set up in a dentin pressure model for 14 days. In addition, set sealers immersed in physiologic solution for 14 days were also assessed. The set materials in solution and materials retrieved from the dentin pressure setup were characterized by scanning electron microscopy and X-ray diffraction analysis. The setting time and radiopacity were assessed using ISO 6876:2002 specifications. Furthermore, mineral ion leaching was evaluated by inductively coupled plasma mass spectrometry. RESULTS: All the sealers tested exhibited formation of a calcium phosphate phase when in contact with physiologic solution. Septodont Sealer and Apexit Plus did not exhibit the formation of a calcium phosphate phase in the dentin pressure setup. The fluid in the system was enough to allow the setting of EndoSequence BC Sealer, which did not set in a dry environment. All materials leached calcium with the Septodont Sealer, exhibiting double the calcium ion leaching compared with EndoSequence BC Sealer. CONCLUSIONS: Using the dentinal fluid pressure system resulted in an adequate flow of dentinal fluid that allowed EndoSequence BC Sealer to set inside the root canal. Although the sealers tested were tricalcium silicate based, the hydration reaction and bioactivity in the presence of dentinal fluid were different to hydration in vitro. Thus, clinically, material bioactivity cannot be assumed.

Investigation of the hydration and bioactivity of radiopacified tricalcium silicate cement, Biodentine and MTA Angelus.

OBJECTIVE: Novel root-end filling materials are composed of tricalcium silicate (TCS) and radiopacifier as opposed to the traditional mineral trioxide aggregate (MTA) which is made up of clinker derived from Portland cement and bismuth oxide. The aim of this research was to characterize and investigate the hydration of a tricalcium silicate-based proprietary brand cement (Biodentine™) and a laboratory manufactured cement made with a mixture of tricalcium silicate and zirconium oxide (TCS-20-Z) and compare their properties to MTA Angelus™. METHODS: The materials investigated included a cement containing 80% of TCS and 20% zirconium oxide (TCS-20-Z), Biodentine™ and MTA Angelus™. The specific surface area and the particle size distribution of the un-hydrated cements and zirconium oxide were investigated using a gas adsorption method and scanning electron microscopy. Un-hydrated cements and set materials were tested for mineralogy and microstructure, assessment of bioactivity and hydration. Scanning electron microscopy, X-ray energy dispersive analysis, X-ray fluorescence spectroscopy, X-ray diffraction, Rietveld refined X-ray diffraction and calorimetry were employed. The radiopacity of the materials was investigated using ISO 6876 methods. RESULTS: The un-hydrated cements were composed of tricalcium silicate and a radiopacifier phase; zirconium oxide for both Biodentine™ and TCS-20-Z whereas bismuth oxide for MTA Angelus™. In addition Biodentine™ contained calcium carbonate particles and MTA Angelus™ exhibited the presence of dicalcium silicate, tricalcium aluminate, calcium, aluminum and silicon oxides. TCS and MTA Angelus™ exhibited similar specific surface area while Biodentine™ had a greater specific surface area. The cements hydrated and produced some hydrates located either as reaction rim around the tricalcium silicate grain or in between the grains at the expense of volume containing the water initially present in the mixture. The rate of reaction of tricalcium calcium silicate was higher for Biodentine™ than for TCS-20-Z owing to its optimized particle size distribution, the presence of CaCO3 and the use of CaCl2. Tricalcium calcium silicate in MTA hydrated even more slowly than TCS-20-Z as evident from the size of reaction rim representative of calcium silicate hydrate (C-S-H) around tricalcium silicate grains and the calorimetry measurements. On the other hand, calcium oxide contained in MTA Angelus™ hydrated very fast inducing an intense exothermic reaction. Calcium hydroxide was produced as a by-product of reaction in all hydrated cements but in greater quantities in MTA due to the hydration of calcium oxide. This lead to less dense microstructure than the one observed for both Biodentine™ and TCS-20-Z. All the materials were bioactive and allowed the deposition of hydroxyapatite on the cement surface in the presence of simulated body fluid and the radiopacity was greater than 3mm aluminum thickness. SIGNIFICANCE: All the cement pastes tested were composed mainly of tricalcium silicate and a radiopacifier. The laboratory manufactured cement contained no other additives. Biodentine™ included calcium carbonate which together with the additives in the mixing liquid resulted in a material with enhanced chemical properties relative to TCS-20-Z prototype cement. On the other hand MTA Angelus™ displayed the presence of calcium, aluminum and silicon oxides in the un-hydrated powder. These phases are normally associated with the raw materials indicating that the clinker of MTA Angelus™ is incompletely sintered leading to a potential important variability in its mineralogy depending on the sintering conditions. As a consequence, the amount of tricalcium silicate is less than in the two other cements leading to a slower reaction rate and more porous microstructure.

Comparison of a bioremediation process of PAHs in a PAH-contaminated soil at field and laboratory scales.

A laboratory experiment was carried on the same initial soil and at the same time than a windrow treatment in order to compare results at field and laboratory scales for a soil mainly contaminated with PAHs. After 6 months, laboratory experiments gave similar but less scattered results than those obtained in the field indicating that the field biotreatment was well optimised. The total amount of PAHs degraded after 6 months was ca. 90% and degradation rates followed a negative exponential trend. Relative degradation rates of 3- and 4-ring PAHs were about 32 and 7.2 times greater than those of 5- and 6-ring PAHs, respectively. With respect to the bacterial community, bacteria belonging to Gamma-proteobacteria persisted whereas Beta-proteobacteria appeared after three months of biotreatment when PAH concentration was low enough to render the soil non-ecotoxic.

Stabilization of ZnCl2-containing wastes using calcium sulfoaluminate cement: cement hydration, strength development and volume stability.

The potential of calcium sulfoaluminate (CSA) cement was investigated to solidify and stabilize wastes containing large amounts of soluble zinc chloride (a strong inhibitor of Portland cement hydration). Hydration of pastes and mortars prepared with a 0.5 mol/L ZnCl(2) mixing solution was characterized over one year as a function of the gypsum content of the binder and the thermal history of the material. Blending the CSA clinker with 20% gypsum enabled its rapid hydration, with only very small delay compared with a reference prepared with pure water. It also improved the compressive strength of the hardened material and significantly reduced its expansion under wet curing. Moreover, the hydrates assemblage was less affected by a thermal treatment at early age simulating the temperature rise and fall occurring in a large-volume drum of cemented waste. Fully hydrated materials contained ettringite, amorphous aluminum hydroxide, strätlingite, together with AFm phases (Kuzel's salt associated with monosulfoaluminate or Friedel's salt depending on the gypsum content of the binder), and possibly C-(A)-S-H. Zinc was readily insolubilized and could not be detected in the pore solution extracted from cement pastes.

Stabilization of ZnCl2-containing wastes using calcium sulfoaluminate cement: leaching behaviour of the solidified waste form, mechanisms of zinc retention.

To assess the potential of calcium sulfoaluminate cement to solidify and stabilize wastes containing high amounts of soluble zinc chloride (a strong inhibitor of Portland cement hydration), a simulated cemented waste form was submitted to leaching by pure water at a fixed pH of 7 for three months, according to a test designed to understand the degradation processes of cement pastes. Leaching was controlled by diffusion. The zinc concentration in the leachates always remained below the detection limit (2 µmol/L), showing the excellent confining properties of the cement matrix. At the end of the experiment, the solid sample exhibited three zones which were accurately characterized: (i) a highly porous and friable surface layer, (ii) a less porous intermediate zone in which several precipitation and dissolution fronts occurred, and (iii) the sound core. Ettringite was a good tracer for degradation. The good retention of zinc by the cement matrix was mainly attributed to the precipitation of a hydrated and well crystallized phase with platelet morphology (which may belong to the layered double hydroxide family) at early age (≤ 1 day), and to chemisorption onto aluminum hydroxide at later age.

Comparison of solid and liquid-phase bioassays using ecoscores to assess contaminated soils.

Bioassays on aqueous and solid phases of contaminated soils were compared, belonging to a wide array of trophic and response levels and using ecoscores for evaluating ecotoxicological and genotoxicological endpoints. The method was applied to four coke factory soils contaminated mainly with PAHs, but also to a lesser extent by heavy metals and cyanides. Aquatic bioassays do not differ from terrestrial bioassays when scaling soils according to toxicity but they are complementary from the viewpoint of ecological relevance. Both aquatic and terrestrial endpoints are strongly correlated with concentrations of 3-ring PAHs. This evaluation procedure allows us to propose a cost-effective battery which embraces a wide array of test organisms and response levels: it includes two rapid bioassays (Microtox(®) and springtail avoidance), a micronucleus test and three bioassays of a longer duration (algal growth, lettuce germination and springtail reproduction). This battery can be recommended for a cost-effective assessment of polluted/remediated soils.

Evolution of bacterial community during bioremediation of PAHs in a coal tar contaminated soil.

The monitoring of a windrow treatment applied to soil contaminated by mostly 2-, 3- and 4-ring PAHs produced by coal tar distillation was performed by following the evolution of both PAH concentration and the bacterial community. Total and PAH-degrading bacterial community structures were followed by 16S rRNA PCR-DGGE in parallel with quantification by bacterial counts and 16 PAH measurements. Six months of biological treatment led to a strong decrease in 2-, 3- and 4-ring PAH concentrations (98, 97 and 82% respectively). This result was associated with the activity of bacterial PAH-degraders belonging mainly to the Gamma-proteobacteria, in particular, the Enterobacteria and Pseudomonas genera, which were detected over the course of the treatment. This group was considered to be a good bioindicator to determine the potential PAH biodegradation of contaminated soil. Conversely, other species, like the Beta-proteobacteria, were detected after 3months, when 2-, 3- and 4-ring PAHs were almost completely degraded. Thus, presence of the Beta-proteobacteria group could be considered a good candidate indicator to estimate the endpoint of biotreatment of this type of PAH-contaminated soil.

Comparison of solid-phase bioassays and ecoscores to evaluate the toxicity of contaminated soils.

Five bioassays (inhibition of lettuce germination and growth, earthworm mortality, inhibition of springtail population growth, avoidance by springtails) were compared, using four coke factory soils contaminated by PAHs and trace elements, before and after biotreatment. For each bioassay, several endpoints were combined in an 'ecoscore', a measure of test sensitivity. Ecoscores pooled over all tested bioassays revealed that most organisms were highly sensitive to the concentration of 3-ring PAHs. When four soils were combined, behavioural tests using the springtail Folsomia candida showed higher ecoscores, i.e. they were most sensitive to soil contamination. However, despite overall higher sensitivity of behavioural tests, which could be used for cheap and rapid assessment of soil toxicity, especially at low levels of contamination, some test endpoints were more sensitive than others, and this may differ from a soil to another, pointing to the need for a battery of bioassays when more itemized results are expected.