Martin Palou

Hydration of high alumina cement–silica fume composite with addition of Portland cement or sodium polyphosphate under hydrothermal treatment

Various hydrothermal curing regimes were used to investigate the hydration and physical characteristics of two kinds of inorganic binder composites: high alumina cement–silica fume–Portland cement and high alumina cement–silica fume–sodium polyphosphate. Simultaneous thermal analysis (DTA and TG) was used to identify temperature ranges of thermal decomposition of cured samples and to characterize the nature of hydrate products. Two kinds of products are formed. The first ones consist of C3AH6, AH3, calcium carbonate (C–C) as a product of carbonation, and C3AH1.5 resulted from the partial decomposition of C3AH6 under higher hydrothermal pressure. The second ones are the products formed by acid–base reaction between monocalcium aluminate and sodium polyphosphate to form NaCaPO4·xH2O and Al2O3·xH2O that could convert to chemically bonded ceramic binders like hydroxyapatite (Ca5(PO4)3OH) and gibbsite (Al(OH)3). These two hydroceramic products formed under these conditions act also as binder and could be useful as cement binders for the protection of petroleum, gas, or geothermal wells. Mercury intrusion porosimeter was used for the estimation of the pore structure parameters of the composites. It turned up that longer curing time coupled with higher hydrothermal pressure has improved the pore structure of the first composite, while that of the second has remained unchanged.

Preparation and properties of cementitious composites for geothermal applications

Three fiber-reinforced cement composites were prepared and cured in an autoclave for up to 168 h at 2 MPa of steam pressure in order to investigate the effect of hydrothermal curing on the alteration of pore structure, density, and formation and stability of hydrated products with time. Compressive strength was reviewed in connection with sample porosity. It was found that the time of autoclaving plays a crucial role in objective assessment of the durability of composites as potential candidates for geothermal applications. A mercury intrusion porosimeter Quantachrome Poremaster 60GT was used for the estimation of the pore structure parameters of composites. The thermal analysis method was used to identify different temperature ranges of cured samples’ thermal decomposition and to characterize the nature of hydrated products. Two kinds of products were formed. The first group consisted of calcium-silicate-hydrate (C-S-H), calcium-silicate-aluminate-hydrate (C-S-A-H), calcium-aluminate-hydrate (C-A-H), and calcium-carbonate (C-C) as a product of carbonation. The second group are chemically bond products, e.g. hydroxyapatite (Ca5(PO4)3(OH)) and gibbsite (Al(OH)3). These two hydroceramic products formed under hydrothermal conditions act also as binders and they can be useful as geothermal cement binders.

Mechanism and kinetics of glass-ceramics formation in the LiO2-SiO2-CaO-P2O5-CaF2 system

Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesised in the Li2O-SiO2-CaO-P2O5-CaF2 system with P2O5: CaO: CaF2 ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle sizes. Inclusion of FA in the LS2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (299 ± 1 kJ mol-1 for pure LS2 glass and 288 ± 7 kJ mol−1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS2 glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like phases after soaking in SBF.

Potential applications of fluorhydroxyapatite as biomaterials in medicine

The present work was undertaken to investigate the bioactivity and cytotoxicity of fluorhydroxyapatite ceramics. The bioactivity was evaluated by in vitro testing in simulated body fluid (SBF), in which ion concentrations are almost identical with inorganic ion concentrations of human blood plasma. Pellets of FA, HA and FHA were immersed in SBF for 48 hours, 1 week and 4 weeks at 36.5°C. Changes of the surface microstructure of the samples were observed by scanning electron microscopy (SEM). 48 hours and one week immersion in SBF did not result in any substantial progress in bioactivity. After 4 weeks in SBF a new biologically active layer was created on the surface of the biomaterials. In addition, the embryonal mouse fibroblast cell line NIH-3T3 was used for a comparative study of basal cytotoxicity of FHA, HA and FA discs. The sensitivity of these cells for tested biomaterials was evaluated on the basis of two cytotoxic end points: cell proliferation and cell morphology. The basal cytotoxicity of FHA, FA and HA discs was measured by a direct contact method. After 24, 48 and 72 hours, the cell growth was evaluated by direct counting of non-affected cells and cells treated by biomaterials. After 72 hours of biomaterials treatment, about 25% inhibition of cell number and unchanged morphology was found.

Geopolymer Cements and Their Properties: A Review

Abstract Concrete is the worlds most versatile, durable and reliable construction material. Next to water, concrete is the second most used substance on earth and it requires large quantities of Portland cement. The industrial sector is the third largest source of man-made carbon dioxide emissions after the transportation sector as the major generator of carbon dioxide, which pollutes the atmosphere. Ordinary Portland cement (OPC) production produces the largest amount of carbon dioxide amongst all industrial processes. In addition to that a large amount of energy is also consumed for the cement production. The production of OPC not only consumes a huge amount of the natural resources i.e. limestone and fossil fuels but also produces almost 0.9 t of CO2 for 1t of cement clinker production. Thus, the world cement production generates 2.8 billion tons of manmade greenhouse gas annually. Hence, it is inevitable to find an alternative material to the existing most expensive, most resource and energy consuming Portland cement. Geopolymer cements are innovative binders which can be produced by the chemical action of aluminosilicate materials plenty available worldwide. They are rich in silica and alumina reacting with alkaline solution and producing aluminosilicate gel that acts as the binding material for the concrete. Geopolymers are synthesized by polycondensation reaction of geopolymeric precursor and alkali polysilicates. The paper presents data on the important engineering properties of geopolymer cements showing that these cements offer an alternative to, and potential replacement for, OPC. Geopolymer technology also has the potential to reduce global greenhouse emissions caused by OPC production. Due to the high level of mechanical properties of geopolymer cements and their environmentally beneficial technology they appear as a prospective construction material for the future.

Synthesis of poly(vinyl alcohol) — hydroxyapatite composites and characterization of their bioactivity

A series of poly(vinyl alcohol) membranes reinforced with hydroxyapatite in various weight percent — 0%, 10%, 20%, 30%, 40% and 50% were prepared. Hydroxyapatite was prepared by a sol-gel procedure using diammonium hydrogen phosphate and calcium nitrate tetrahydrate as starting materials in an alkaline aqueous environment and then mixed with a solution of poly(vinyl alcohol), which was prepared by dissolving it in water at 85°C.The different mixtures were cast in a mould and evaporated for 7 days at a temperature of 30°C to obtain 1 mm thin membranes. FTIR spectroscopy was used to identify the different functional groups in the composites. The surface morphology was examined using a scanning electron microscope. In vitro bioactivity tests in Simulated Blood Fluid were performed for up to 28 days, especially for the membrane containing 50 wt.% HA. SEM was used to characterise the surface microstructure of biocomposite membranes before and after soaking in SBF. It was observed that the formation of clusters in membranes increases with increasing amount of HA. The clusters are formed due to agglomeration and crystal growth of HA particles during drying of the membranes. The in vitro bioactivity was found to increase with soaking time of biocomposite materials in simulated blood fluid.Graphical abstract

Characterization of cordierite-mullite ceramics prepared from natural raw materials

Abstract Series of six cordierite-mullite ceramics were synthesized via solid state reaction at various temperatures from 1250 °C for pure cordierite to 1500 °C for pure mullite. Then the samples were submitted to the test of thermal shock resistance based on cycling heating-quenching procedure. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Mercury intrusion porosimeter (MIP) have been used to characterize the samples before and after cycling heating-quenching method. Sample 6 was broken after 35 heating-quenching cycles, while the five other reminded stable. The refractoriness of samples is found to be higher than that of commercial ones. XRD shows that heating-quenching procedure has led to crystallization of cordierite and mullite phases. Apart from sample 6, the pore structure is stable with slight consolidation. The microstructure images confirm the results of XRD and MIP showing crack in sample 6 only, but compact and larger particles resulting from crystal growth in other samples due to the repeated action of heating.

Preparation, characterization and in vitro bioactivity of polyvinyl alcohol-hydroxyapatite biphasique membranes

Abstract Six membranes of polyvinyl alcohol (PVA) with various weight percent - 0 %, 10 %, 20 %, 30 %, 40 % and 50 % of hydroxyapatite (HA) were prepared. Fourier Transform Infrared (FTIR) spectroscopy was used to identify the different functional groups in membrane composites. The surface morphology was examined through scanning electron microscope. The in vitro bioactivity tests in Simulated Blood Fluid (SBF) have been performed up to 28 days, especially for membrane containing 50 wt. % HA. SEM was used to characterize surface microstructure of biocomposite membranes before and after immersion in SBF. It was observed the formation of clusters within membranes with increasing amount of HA particles due to hydrogen bond and also the agglomeration and crystal growth of HA particles during drying of membranes. The bioactivity was found increasing with time immersion of biocomposite materials in SBF solution.

The Role of Temperature on Hydration of Binary System of Metakaolin/Portland Cement

The role of temperature of metakaolin/Portland cement binary system was studied by isothermal calorimetry. Sample with 50 % of metakaolin replacement were monitored at 30 °C, 40 °C, 50 °C and 60 °C. Structural and chemical characterization of hardened pastes was obtained by scanning electron and Raman microscopy. Paper deals with kinetics of main exothermal reactions during early hydration of the system. Activation energies were calculated for processes related to each exothermic peak. The nature of hydration products at different temperatures was revealed by microstructural studies.

Application of Sol-Gel Method to Investigate the Influence of P2O5 on the Course of Reactions in CaO-SiO2 System

The effect of P2O5 addition on the calcium silicate phase equilibrium during the sol-gel synthesis of dicalcium silicate was investigated using Scanning electron microscope and X-ray diffraction. It is established that phosphorous oxide can form solid solution with dicalcium silicate, but its causes the formation of phosphatic calcium silicate phases such as Ca14.92 (PO4)2.35(SiO4)5.65 and 5CaO.SiO2.P2O5 also. Local analysis has demonstrated the presence of calcium phosphate epicenters containing silicon oxide and calcium silicate zones with minimum content of phosphorous oxide and intermediary areas of various phosphatic calcium silicates. The formation of two distinct islets of calcium silicate and calcium phosphate is due to the affinity between acid oxides (SiO2, P2O5) and basic one (CaO) during sol-gel process. Then, the formation of various phosphatic calcium silicates result from the diffusion of P2O5 towards calcium silicate and that of SiO2 towards calcium phosphate.