Abstract: Experimental results and theoretical models are used to assess the effective thermal conductivity of porous inorganic polymer cements, often
indicated as geopolymers, with porosity between 30 and 70 vol.%. It is shown that the bulk chemical composition affects the microstructure (grains
size, pores size, spatial arrangement of pores, homogeneity, micro cracks, bleeding channels) with consequently the heat flow behaviour through
the porous matrix. In particular, introduction of controlled fine pores in a homogeneous matrix of inorganic polymer cements results in an increase
of pore volume and improvement of the thermal insulation. The variation of the effective thermal conductivity with the total porosity was found
to be consistent with analytical models described by Maxwell–Eucken and Landauer.
Abstract: Geopolymer material based K2O–Al2O3–SiO2 systems were investigated for high temperature
applications. High viscous geopolymer paste was prepared using standard grade metakaolin
dissolved in potassium hydroxide/potassium silicate solution (volume ratio, 1 : 1). The alkalinity of
the solution was predetermined to optimise the dissolution of amorphous aluminosilicate. Quartz
sand and alumina (25, 50 and 75 wt-%) were successively introduced as filler to form refractory
concretes. RGPS4, RGPS2 and RGPS34 for sand and RGPA4, RGPA2 and RGPA34 for alumina
were produced. The samples obtained were cured in sealed plastic containers for 7 days at room
temperature before sintering at 200, 800, 1000, 1100 and 1200uC. The heating rate was
5uC min21, and the dwelling time at peak temperature completes the sintering time to 4 h.
Unvaried mechanical strength, up to 800uC, was observed: y25 MPa for biaxial and y20 MPa
for uniaxial four-point bending strengths. This behaviour was ascribed to the maintenance of the
structure of the geopolymer materials within the temperature interval considered. Above this
temperature, all the samples presented significant densification; the most important increase in
mechanical strength was y65 and y60 MPa respectively for biaxial and uniaxial four-point
bending strengths. This was accompanied by a decrease in porosity. The dense structures
observed at 1000–1100uC were affected by a further increase in temperature. Microcracks,
vitrification and deformation appeared at 1200uC, which can be considered as detrimental to the
mechanical properties. The mechanical properties and the microstructural evolution were found
to be influenced by the amount of fillers added. Si and Al rich geopolymer concretes were found
promising for the development of potential thermoresistant materials through the cold process.
Abstract: Lateritic soils are formed in the tropics through weathering processes that favor the formation of iron, aluminum, manganese and titanium oxides. These processes break down silicate minerals into clay minerals such as kaolinite and illite. Iron and aluminum oxides are prominent in lateritic soils, and with the seasonal fluctuation of the water table, these oxides result in the reddish-brown color that is seen in lateritic soils. These soils have served for a long time as major and sub-base materials for the construction of most highways and walls of residential houses in tropical and sub-tropical countries of the world. Civil engineering applications of these lateritic soils are continually being developed with the use of different types of stabilizers. The stabilized soil-based products are as such viewed as environmentally-friendly and low-cost energy materials for sustainable building applications. This work aims at presenting a global view of what has been done in the field of lateritic soil improvement for construction purposes in tropical countries such as Cameroon. This shall be discussed through the presentation of the structure, composition and properties of lateritic soils, the various ways of improving their properties for construction purposes, the properties of products obtained and other prospects.
Abstract: To improve long-term hydraulic properties of binders from RHA and lime, 25–75% MK was added to RHA.
Binders were formulated and properties were compared to that containing RHA or MK as only pozzolans.
The lime–pozzolan ratio was 1:3. The properties tested after 7, 28 and 56 days were: absolute density and
fineness of the binders, initial setting time, chemical and mineralogical composition of hydrated binders,
flexural and compressive strengths and water absorption of mortars. The micrographs of the hardened
binder pastes at 56 days permitted to evaluate the densification of different matrixes and the development
of pores. From the results obtained, it was concluded that, MK increased the density of mixtures
and decreased their grindability. The presence of MK decreased the SiO2 content of binders and increases
their Al2O3 and Fe2O3 contents. Calcium-silicate hydrates (CSH) gel and gehlenite (C2ASH8) were the main
phases formed during the pozzolanic reaction in the presence of MK. No reduction in flexural and compressive
strengths was observed after 28 days for binders containing MK. The mixture of 25% MK and 75%
RHA which is recommended gave flexural and compressive strengths higher than binder with RHA or MK
as the only pozzolan. Water absorption of mortars was less than 20%.
Abstract: Two metakaolins from Al-rich and Si-rich kaolinitic clays were used to design polysialate matrices with different Si/Al and NaK/Al ratios. The aim was to investigate the influence of oligomers formed during dissolution and hydrolysis on the polycondensation and transformation to hard and stable matrices. Products of geopolymerization of the different matrices were subjected to mechanical testing considering various loading configurations. The geopolymer matrices showed compressive strength from 51 + 5 MPa (Si/Al=1.23) to 61 + 2 MPa (Si/Al = 2.42) and bi axial four-point strength from 11 + 2 MPa to 16 + 1.1 MPa respectively. These results were consistent with density, leaching ability and microstructure. It is proposed that the mechanical properties and the stability of the products of reactions can be discussed as the important parameters for the evaluation of the quality of geopolymer matrices. Moreover, polycondensation and the final performance of the product are greatly influenced by the unreacted crystalline or semi-crystalline phases that act as fillers and contribute to increased stability and mechanical properties. A good geopolymer material resulting from our study will be defined as an amorphous matrix of polysialates in which various unreacted or partly reacted crystalline phases are embedded. It is suggested that Si-rich metakaolin will present the more hardening and stable matrix with shorter setting time leading to small pores and an enhanced interlocked microstructure.
Abstract: Because of concerns over the construction industry‘s heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of ―green‖ binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given their numerous advantages over the latter including lower carbon dioxide emissions, greater chemical and thermal resistance, combined with enhanced mechanical properties at both normal and extreme exposure conditions. The paper focuses on the use of geopolymer binders in building applications. It discusses the various options for starting materials and describes key engineering properties associated with geopolymer compositions that are ideal for structural applications. Specific properties, such as compressive strength, density, pore size distribution, cumulative water absorption, and acid resistance, are comparable to the specifications for structures incorporating conventional binders. This paper presents geopolymer binders, with their three dimensional microstructure, as material for structural elements that can be used to advance the realization of sustainable building systems.
Abstract: Kaolinite–corundum (derived from bauxite) associations are assessed as candidate matrices in the field of porous refractory composites. Particles of corundum are expected to behave as non reactive second phase, deflecting the matrix cracks and increasing the toughness. Porosity and densification are monitored by developing coarse grains (67 vol.% of grains < 1 mm and 33 vol.% of grains between 1 and 4 mm) of bauxite based chamotte with corundum as principal phase. The main features resulting from the use of bauxite-based chamotte are the increase of softening point, the absence of vitrification in the temperature range of refractory composites in service and the achievement of a good thermal stability. For temperatures ranging between 1200 and 1300 °C, flint kaolin matrix shows no reaction with the red corundum grains. Refractory composites elaborated with more than 30% of corundum exhibit typical final characteristics which satisfy ASTM C155 and ISO1109 standards for refractory materials. Namely: the chemical composition (Al2O3 > 56.%), the secondary expansion (<0.1%), the open or total porosity (45 vol.%) and the bulk density (1.9 g/cm3). Such materials are promising low costs solutions for the production of porous refractory composites
Abstract: Nowadays, the design of building and construction materials should be straightly linked to the environmental context of industrial development and the many regulations and constraints linked to energy, ecosystems, geography and communities. In one word, building materials today have to be sustainable. In this paper, the authors turn back to the history of structural clay products and described their evolution and the factors that have affected the evolution of their products.
Abstract: Municipal solid waste incinerators every year produce tons of fly ashes which, differently from coal fly
ashes, contain large amounts of toxic substances (heavy metals, dioxins, furans). The stabilization/solidification
(S/S) technology known as geopolymerization is proposed with the purpose to bond physically
and chemically incinerator fly ashes (IFA) in a solid matrix, in order to reduce pollutant mobility. The
chemical stability of geopolymers with Si/Al ratio of 1.8–1.9 and Na/Al ratio of 1.0, synthesized by alkali
activation of metakaolin and the addition of 20 wt% of two different kinds of IFA, is presented. The concentration
of the alkaline solution, water to solid ratio and curing process have been optimized. The room
temperature consolidation of IFA containing geopolymers has been tested for leachability in water for
1 day, accordingly to EN 12457 regulation and extended to 7 days to increase the water attack on solid
granules. Leachable metals in the test solution, determined by ICP_AES, fall within limit values set by regulation
for non-dangerous waste landfill disposal. Geopolymeric matrix evolution with leaching time has
been also evaluated in terms of pH and electrical conductivity increase in solution.
Abstract:
Three bauxite samples (BX3, BX5 and BX8) of high alumina content from the
region of Haleo-Danielle, Minim-Martap in Cameroon were characterized
thermally at temperatures between 1000 °C and 1600 °C with the objective
to study their suitability for dense refractory materials. The water absorption,
porosity, linear shrinkage, flexural strength and bulk density were assessed. At
1600 °C, BX3 and BX5 presented high densification (bulk density of 3.4 g/cm3)
with low porosity (7%) with a bi-axial bending strength of 75 and 41MPa
respectively. On the contrary at the same temperature, BX8 presented 31.5%
porosity, bulk density of 2.54 g/cm3 and bi-axial bending strength of 55MPa. The
low content in iron and titanium oxides give BX8 a clear grey color at 1600 °C.
BX3 and BX5 presented an average linear shrinkage of about 27% while that of
BX8 was only 13% at 1600 °C.
Abstract: In this study different geopolymers have been investigated and characterized as
potential biomaterials. The work presents exhaustive FT-IR, SEM/EDS and X-Ray studies of two
geopolymer formulations, where water content, water to solid content and curing conditions have
been varied during mixing stage, maintaining constant the ratios among Na-Al-Si. The amorphous
matrix is typical of sodium aluminosilicates, as shown by the FT-IR spectra. The presence of
zeolitic phases has been observed by XRD at the surface of the material while the main matrix was
characterized by amorphous aluminosilicate phases. The compressive strength of all the
compositions was higher than 50 MPa. In order to study their bioactivity, samples of the studied
materials were soaked in a simulated body fluid (SBF). The bioactivity of the synthesized
geopolymers was shown by the formation of a layer of hydroxyapatite on the surface of the
materials by using the SEM.
Abstract: Based on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K2O–Al2O3–SiO2 system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the range 0.1 μm to 1 mm) and fine powder alumina (grain size in the range 0.1–100 μm). The consolidated samples were characterized before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25–900 °C was less than 3%, reduced with respect to the most diffused potassium or sodium based geopolymer systems, which generally records a >5% shrinkage. The maximum shrinkage of the basic geopolymer composition was recorded at 1000 °C with a 17% shrinkage which is reduced to 12% by alumina addition. The temperature of maximum densification was shifted from 1000 °C to 1150 or 1200 °C by adding 75 wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to the importance of liquid phase. The geopolymer formulations developed in this study appeared as promising candidates for high-temperature applications: refractory, fire resistant or insulating materials.
Abstract: Geopolymer has been developed as an alternative material to Portland cement. Geopolymer
is based on the polymerization of alkaline activation and oxide of silicon and aluminium. These
oxides can be found in many pozzolanic materials such as metakaolin and the wastes from
industries and agricultures in Thailand, e.g., fly ash, bagasse ash and rice husk ash.
Pozzolanic materials were selected as source materials for making geopolymers into 4
different types. Sodium hydroxide concentration of 10 Molar (10MNaOH) and sodium silicate
(Na2SiO3) solutions were used as alkaline activators by the mass ratio of Na2SiO3/NaOH at 1.5. The
mixtures were cast in 25×25×25 mm. cubes. After casting, the geopolymers were cured at 80à¹C for
24 hrs. in an oven and then at room temperature for 7 days. The pozzolanic materials effects, the
Si/Al molar ratio and the Na/Al molar ratio were studied and characterized.
An X-ray fluorescence (XRF) was chosen to determine the percentages of silica and alumina
in order to verify the proper ratio of the fly ash, Rice husk ash, Bagasse ash and Metakaolin.The
study also included the impact on mechanical and physical properties such as compressive strength,
water absorption, density and porosity.
Abstract: The effect of alkali-silica glassy matrixes (AGM), as replacement for feldspar, on the microstructure, physical properties and mechanical strength of conventional porcelain has been studied. AGM with chemical composition similar to feldspars has been prepared to introduced alkali-ions (Na+ and K+) in porcelain compositions. It has been found that the replacement of feldspar by AGM ameliorates the mechanical properties of the material. The improvements are attributed to sharp changes in the microstructure as result of a reduction of glassy phase and increase in crystalline mullite amount. AGM were found to be promising candidates as substitutes for feldspar in conventional porcelain.
Abstract: Noncontact dilatometry, compared to differential
scanning calorimetry (DSC), was used together with
scanning electron microscopy and densification behavior
studies to investigate the parameters that govern the
kinetics of transformation of kaolin to mullite during sintering.
Three kaolinitc clays from Cameroon, with different
SiO2/Al2O3 molar ratio, were examined. The temperatures
of mullite nucleation were 973, 979, and 984 C at 5 C/
min heating rate, respectively, for values of SiO2/Al2O3
molar ratio equal to 4.22, 2.22, and 2.08. At 20 C/min
heating rate, the temperatures are shifted to higher values,
992, 997, and 1,001 C. The mullitization phenomenon,
which includes a first step of nucleation and a second one
of crystal growth, presented activation energy in the range
of 650–730 kJ/mol, depending on the nature of the sample
investigated. These values, obtained by noncontact dilatometer
measurements, were comparable to those obtained
by means of DSC and are in agreement with literature
values. The difference in sintering kinetics for the three
kaolinitic clays could explain the different morphologies
obtained for the mullite grains.
Abstract: The paper examines the influence of Al2O3/SiO2 ratio, bulk chemical composition and
temperature in mullite nucleation and growth from kaolinitic clays. Samples from NTAMUKA
(TAN), Mayouom (MAY) and Wabane (WAB), region of high hills of West-Cameroon, undergo
series of phase changes during sintering between 1000 and 1500uC. Phases transformation
included: amorphous SiO2 and Al2O3 as result of breakdown of kaolin above 700uC, nuclei of
mullite that growth with temperature development to fine and then large grains at high
temperature. The microstructure of the sintered products consisted on the elongated secondary
mullite (types II and III) interlocking with primary (type I) mullite in a compact matrix with relative
amount of liquid film for MAY and WAB. The morphology of mullite grains in TAN was more
different being larger cuboid grains aggregated to form together with cristobalite a compact
microstructure. The formation of TiO2 crystals and then Ti–Al (tialite: Al2TiO5) crystals influenced
the microstructure of MAY and WAB. The microstructure at high temperature of the three kaolinitic
clays indicated their suitability for dense refractory and fine ceramic applications.
Abstract: Crystals of the pyroxene group (diopside,
augite and enstatite, hedenbergite), series of crystals with
the general formula (MgxFe1–x)2SiO4 having various geometry,
identified as spinel (and olivine), and plagioclase
crystals from anorthite to anorthoclase that grow together
in mass having thin parallel groves embedded in a complex
matrix together with calcium alumina silicate grains were
found to be the descriptive microstructure of fired volcanic
ash. Quartz grains were rarely present as confirmed by
dilatometry analysis, XRD, SEM and DTA. The presence
of dendrites continuously growing to pyroxene crystals
indicated the precipitation/crystallization of these crystals
from matrix and regions of glass concentration enhance
by ions diffusion. Rings of Ti-rich iron micro-crystals
observed around spinel (and olivine) suggested the probable
nucleating role of these micro-crystals for the precipitation/
crystallization phenomenon. The various types of
crystals formed, the difference in their geometry and size
and their interlocking mechanism result in a contiguous
and dense structure with relevant characteristics at relative
low temperature (1125–1150 _C) confirming volcanic ash
as a promising alternative raw material for vitrified ceramic
products. It was concluded that controlled precipitation/
crystallization of raw volcanic ash results on microstructure
similar to that of glass-ceramic materials. The observation
of fracture surface allowed comparison of fracture
mechanics of volcanic ash ceramic to that of conventional
vitrified ceramics.
Abstract: A complete investigation on the sintering behaviour, involving ceramic transformation, of volcanic ash is reported. Sintering and softening points, vitrification and fusion of finely ground powders of volcanic ash were obtained by hot stage microscope observation. Then, a suitable thermal cycle, which matches the better microstructure and mechanical properties, has been performed. The low quartz content of the final product, the relative high density together with the particular structural complexity of the matrix consequence of the interlocking of various crystalline phases conferred to fired volcanic ash relevant ceramic characteristics. Nucleation and microcrystallisation of pyroxene together with oxidation and cation enrichment are indicated as the main sintering mechanism of fired volcanic ash. Differently from conventional vitrified ceramics, i.e. quartz and mullite in vitreous matrix, the microstructure of the fired products presents spinel, anorthite, diopside, enstatite, pyroferrite, fayalite and hedenbergite crystals embedded in the high viscous liquid phase resulting in dense and resistant materials.
Abstract: Ultrasonic pulse velocity testing and image analysis were used to predict the thermal stability of cordierite–mullite refractories. Two compositions used as substrates in fast firing of porcelain whiteware, characterized by different microstructure and crack propagation behavior, were investigated. Fracture strength and fracture toughness values were obtained from three point bending test and chevron notched specimen technique, respectively. The measurement of the ultrasonic velocity was used to assess the material degradation with increasing number of thermal-shock cycles and specimen damage was monitored using image analysis to obtain further evidence of material degradation. The correlation between thermo-mechanical properties, ultrasonic velocity, microstructure, crack-propagation behavior and thermal-shock resistance was discussed. A remarkable similarity was found between the variation of ultrasonic velocity (when measured through the length of the refractory plates) and fracture strength with number of thermal shock cycles. On the other hand, the development of surface microcracking, as monitored by image analysis, is in good agreement with the variation of K IC with the number of thermal-shock cycles. The variation of the ratio with number of thermal-shock cycles shows the highest gradient of the investigated trends and it is proposed as a promising parameter to differentiate refractory materials regarding their different thermal shock behavior. Service life prediction models for refractory plates, from measured values of ultrasonic velocity and surface damage analysis, were proposed and validated.
Abstract: Three kaolinitic clays from Cameroon were studied for their mullitization behavior. The three clayey materials were from Ntamuka (TAN), Mayouom (MAY) and Wabane (WAB) all localities of high hills of western Cameroon. X-ray diffraction and complete thermal and dilatometry as well as SEM-EDS analyses were used to follow up the phase evolution, sintering kinetic and microstructure of the three materials as function of temperature (1000-1500°C). Fine powders of each sample were pressed and treated in above range of temperatures with the goal to correlate the phase evolution with densification parameters (shrinkage, porosity, density and mechanical strength). The nucleation of mullite and the increase of peak intensities were directly correlated to continuous densification and reduction of open porosity as observed from SEM. The temperatures of the peak mullitization were 973°C and 979.1°C, 983.6°C respectively for TAN, MAY and WAB, at 5°C/min while in the same order 992.1°C, 997.4°C and 1001.2°C were the temperatures at 20°C/min. The mullitization phenomenon, which includes a first step of nucleation and a second of crystal growth, shows an activation energy with variation depending on the nature of sample investigated: the values ranged from 650 to 730 kJ.mol-1 . The microstructure of the sintered products consisted on the elongated secondary mullite (types II and III) interlocking with primary (type I) mullite in a compact matrix with relative amount of liquid film for MAY and WAB. The morphology of mullite grains in TAN was more different being larger cuboid grains aggregated to form together with cristobalite a compact microstructure. The formation of TiO2 crystals and then Ti-Al (tialite: Al2TiO5) crystals influenced the microstructure of MAY and WAB.
Abstract: Investigation on the use of volcanic ash as 100% raw materials for traditional vitrified ceramic products is reported. X-ray diffraction (XRD), thermogravimetric-thermal differential analyses (DTA-TGA) and chemical analysis were used to characterise raw samples. Fired specimens were used to evaluate their ceramic properties. Volcanic ash contains essentially classical traditional ceramic oxides, plagioclase, pyroxene and olivine as principal minerals. In the temperature range 1100-1150°C, they present dense structure, low open porosity, without isolated quartz grains. The fired materials properties were found to be in agreement with those of stoneware class BI referring to standard ISO 13006 (i.e.the water absorption values were <1·5%). The presence of a sufficiently extended glassy phase capable of embedding crystalline phases developed during sintering allows comparison of the microstructure of fired volcanic ash with that of traditional porcelain or stoneware.
Abstract: Abstract
Thermal shock resistance of refractory materials is one of the most important parameters in refractory material characterization since it determines their performance in many applications. Ultrasonic pulse velocity testing was used for non-destructive quantification of thermal shock damage in refractory plates used as support for the firing of porcelain articles. When refractory materials are subjected to the industrial thermal cycles crack nucleation and propagation occurs resulting in loss of strength and material degradation. The formation of cracks decreases the velocity of ultrasonic pulses travelling in the refractory because it depends on the density and elastic properties of the material. Therefore measuring either of these properties can directly monitor the development of thermal shock damage level. Young's modulus of representative samples was calculated using measured values of ultrasonic velocities obtained by ultrasonic pulse velocity technique. Results were compared with industrial statistical data of thermal shock behaviour of the investigated materials. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable non-destructive characterisation of thermal shock damage was demonstrated in this investigation.
Abstract: Abstract
Mayouom and Ntamuka china clays, from Cameroon were used to produce porcelain bodies. Two soft porcelain formulations: PSI (with Mayouom) and PSII (with Ntamuka) and one hard porcelain, PH (with both Mayouom and Ntamuka) were prepared.
The maximum density and flexural resistance for these formulations were obtained at 1200 °C for PSI, 1225 °C for PSII and 1350 °C for PH. Their properties and values were, respectively, density (2.42, 2.58 and 2.59 g/cm3), water absorption (0.15, 0.15 and 0.02%), porosity (4.3, 5.3 and 4.2%) and flexural strength (148, 148 and 160 MPa). In addition to varying amounts of liquid phase, the soft porcelain formulations contained mullite and quartz crystals while the hard porcelains contained quartz and more intense mullite peaks. At 1250 °C PSI and PSII presented a self-glazing phenomenon which gave significant brightness and high aesthetic quality. PH with lower alkali (especially Na+) did not self-glaze even at 1400 °C. Considering the soft porcelain formulations, the higher amounts of TiO2 (0.83%) and Fe2O3 (0.31%) in PSI (with Mayoum clay) resulted in a higher sintering effect at lower temperatures, giving lower water absorption and higher resistance. Both Mayouom and Ntamuka china clays were found to be suitable raw materials for the production of porcelain stoneware tiles. Ntamuka could also be used for the manufacture of optimal quality whitewares.
Abstract: Parallelepiped and disc specimens of soft and hard porcelain compositions with feldspar and, for comparison, alkali-silicate glassy matrices as source of alkali were subjected to uniaxial (three and four-point) and biaxial (four-point) flexural strength tests with the aim to evaluate the strength of the materials under different loading configurations. The bending strength values were in the range of 40–75 MPa, 57–99 MPa and 130–180 MPa for three-point, four-point uniaxial and four-point biaxial respectively. The elastic moduli were in the range of 60–110 GPa. The variation in bending strength was ascribed to the nature of the stress or strain as well as to the chemical composition and firing cycle. The elastic modulus of porcelain was found to be influenced by the intrinsic characteristic of the porcelain material such as phase content, porosity and homogeneity.
Abstract: Two different porcelain compositions were studied: a soft and a hard one. DTA, optical non-contact dilatometry and DSC were used to evaluate the thermal behaviour of the porcelain compositions with the aim to master the suitable thermal cycle for each. Results were interpreted on the basis of mineralogy and microstructure: the amorphous phase, abundant in soft porcelain, plays an important role on thermal expansion (8·10–6 K–1 for soft and 6·10–6 K–1 for hard at 1000°C). Thermal expansion behaviour as function of firing time was also studied. Non-contact dilatometry characterisation of porcelain bodies enable to master the suitable thermal cycle for the sintering.
Abstract: The aim of this study was to synthesize different hydroxide-activated geopolymer materials and to assess their potential application as biomaterials. Two geopolymers with empirical formula Si31O79H24K7Al through two different KOH addition methods (separately or jointly with potassium silicate solution) were also thermally activated: 60°C for 150 min and at 500°C for 180 min. The XRD diffractograms showed only low quartz already present in metakaol while FT-IR spectra showed amorphous matrix of aluminosilicates. Compressive strength tests were carried out on both activated sample series and demonstrated that when added separately the activator leads to more fragile specimens (0.9 MPa vs 1.95MPa). The bioactivity was successfully tested with the soaking of the samples in a simulated body fluid (SBF). The formation of a layer of hydroxyapatite on the surface of the materials was shown both by SEM micrograph and EDS analysis.
Abstract: Elie. Kamseu, Cristina Leonelli
Department of Materials and Environmental Engineering, University of Modena and Reggio Emilia, Via Vignolese 905, 41100 Modena, Italy.
Email: elie.kamseu@unimore.it
Abstract: Bi-axial four points bending and compressive strength tests were used for the assessment of mechanical properties of geopolymer materials based calcined kaolin and kaolinitic clays. Various activating solutions which consist in the mixture of potassium and sodium hydroxide, water and sodium silicate were designed and optimised. Six specimens named GPM1 to GPM6 were considered among larger number of investigated compositions with SiO2/Al2O3 varying from 1:1 to 3:1. The compositions 1:1 and 2:1 were achieved by using two different grade of kaolin as raw material (standard and sand-rich), while the 3:1 was obtained by adding required amount of silica to either kaolin or kaolinitic clay. All the samples were prepared by slip casting using density (>1,5) as indicator of the better viscosity of geopolymer pastes.
The bi-axial four points flexural strength values vary from 13 to 21 MPa while the compressive strength vary from 45 to 67 MPa being essentially influenced by setting time, SiO2/Al2O3 and K2O/Na2O ratios. Increasing the SiO2/Al2O3 ratio in the range of 1:1 to 3:1, the mechanical properties increase but with elongated setting and curing times. Low SiO2/Al2O3 results to appearance of micro cracks and deformations during curing. The flexural and compressive behaviour of the specimens studied were directly correlated to the porosity, density and the microstructure of the obtained products. The chemical behaviour of the six compositions is discussed with the respect to basic dissolution-hydrolysis-polycondensation processes that occur in Na2O-K2O-Al2O3-SiO2 systems.
Abstract: Ultrasonic pulse velocity testing was used to perform non-destructive quality control of refractory plates used as substrates in fast firing of porcelain whitewares. The measurement of the ultrasonic velocity was used to asses the presence of internal voids or cracks originated from the manufacturing procedure. Image analysis was used to predict thermal stability of the refractory materials. Two cordierite-mullite compositions were investigated that are characterized by different microstructure morphologies and crack propagation behaviour. A brief discussion about the correlation between microstructure, crack propagation behaviour and thermal shock resistance is presented. Moreover, empirical models were developed to predict the service life of refractory plates from measured values of ultrasonic velocities in plates in the as-received state.
