This study reports the investigation of the influence of adding waste glass on the properties of fired clay specimen. Four different particle sizes (smaller than 100 μm, 300μm, 500μm , and 800 μm) of waste glass were mixed with a clay material at contents of 0 % , 2 % , 6 % and 10% per weight. Specimen samples were fired at 750 ℃ in an electrical furnace for 6 hours, at a heating rate of 5℃/min. The physical and mechanical properties of terracotta are studied. The chemical analysis revealed that the clays were dominated by kaolinite and montmorillonite with small proportion of mixed layers clay. The fine grained texture (0.002 mm > 25%) and high plasticity ( WP > 30%) of the clays were responsible for the moderate and high values of shrinkage upon oven drying and firing. The firing color variation from reddish brown shade was due to the amounts of iron and titanium oxides present in the obtained material. The water absorption was varied between 17.40 % and 13.70%, while the linear shrinkage was estimated to be between 0.70 % and 1.20% and the flexural strength from 5.30 to 8.10 MPa. These results showed that mixing clay with waste glass at 750 ℃ is an interesting approach to obtain reddish brown ceramics destined for bricks or roofing tiles.
The term clay is generally referred to the fine grained earth materials with particles less than two microns (2 µm), of hydrous aluminum silicate minerals groups which are characterized by sheet silicate structure of composite layers stacked along the c-axis [
However, the most promising developments in the ceramic industry are related to processes that consume less energy. In fact, good quality terracotta requires high fired temperature (over 1100˚C) and thus more expensive. It is therefore essential to find methods that can lower the fired temperature.
Significant energy savings are expected in the crushing/grinding, drying and fired stages if a careful choice of raw materials is made. Everything is then implemented to optimize the thermal cycle by reducing the fired time either by a high rate of rising in temperature or by reducing the sintering temperature. The ceramic paste formulation can be adjusted accordingly to the fast firing by reducing the sintering temperature. This requires the use of fluxes (feldspar, talc) or the alkaline ions which will induce the formation of eutectic which could allow lowering the melting temperature. Thus, the firing temperature of the clay pastes is substantially reduced by the use of these fluxes. It is possible that these fondants have a high price.
The present work aims at the use of a colorless waste glass of recovery as an adjunct in the formulation of clay pastes. It is about getting products at relatively low firing temperatures (750˚C) with respect to energy costs in our developing countries. To achieve this goal, clay material were mixed at specific percentage and fired at 750˚C. The obtained material wax characterized in term of chemical composition using X-ray fluorescence spectrometry, structure using X-ray diffraction (XRD) and Infra-red spectroscopy (IR). The microstructure or morphology were analyzed using scanning electron microscopy (SEM). In addition, some technological properties such as the linear shrinkage, flexural strength and water absorption were performed.
The studied clay raw material were collected in the northern part of Ngaoundéré, located in the Adamawa region (Cameroon), and which is characterized by a Sudano Sahelian climate (precipitation between 1200 and 1500 mm/year). The Adamawa region is a vast plateau with gentle slope to the South and steep side at the North. From the South to North, altitude increase slowly and in a regular manner until around Meiganga locality where it begins at the Adamawa plateau with elevations between 1000 and 2000 m [
The most important mountains are: Guenfalabo, Tchabal Mbabo (2460 m) and Hossere Djinga Nganha (1923 m). On the tectonics plan, the region belongs to the Panafrican belt [
The detailed geological formations situated on the Ngaoundéré West uplift were been reported elsewhere [
Pedological formations of the Adamawa region are clays, alluvium sands and rarely of plain, arena (clayey sand and sandy soils), lateritic soils (laterites and graves). Clays are the weathered materials from rocks. The clays observed in the Adamawa region are estimated about 141,000,000 m3 available in various sites [
which are 1.5 - 3 m thick are not laterally continuous and they are usually interbedded with thin sandy facies. The natural moist color of the clay vary from light/dark grey to black with the latter turning brown or brownish grey when exposed to the sun. This is due to the oxidation of ferrous iron oxide to ferric state.
The clay material in this investigation was collected from the area of Wack in the Vina Division (Adamawa Region of Cameroun). Two representative clay materials were sample there. Light grey (W1) and dark grey (W2) colored clay were first cured at room temperature for 2 weeks then dried at 105˚C for 48 h. The dried blocks were crushed and then ground in a ball mill and the resulted powder was sifted by using a 200 µm mesh sieve.
The colorless waste glass bottles collected from garbage cans, were broken into pieces, washed and dried at 105˚C. The resulted particles were crushed then sieved at different grain size (100 µm, 300 µm, 500 µm and 800 µm).
Clays samples collected during field trips were subjected to standard laboratory analysis like particle size analyses (sieving and sedimentation) according to ASTM norm D422, Atterberg limits according to ASTM norm D4318. One type of addition was done (clay with waste glass powder) in order to improve the physical and chemical characteristics, thus giving the blocks great resistance after firing at 750˚C [
The mineralogical analysis of each sample collected was made by X-ray diffraction (XRD) using a Philip PW 3050/60 diffractometer which operated by reflection of Kα1 radiation of Copper. Semi-quantitative estimation of the amounts of the different minerals present in the sample was given measuring the diffraction peak height. Fourier transform infrared spectroscopy (FTIR) was performed with the aid of a Bruker Alpha-P, operating in absorbance mode. The microstructure of the samples was observed and analyzed using a HITACHI S-3600N scanning electron microscope (SEM). The Scanning Electron Microscope made it possible to observe the surface topography of a sample by scanning its surface by an electron beam and collecting the image formed. Since the samples are not conductive, metallization of the surfaces is necessary by covering them with a thin layer of gold. There are two methods to achieve this result. For this study, sputtering was used. It involves depositing on the sample atoms torn from a piece of metal (gold) by argon ionization in a partial vacuum chamber.
Linear shrinkage was determined on parallelepiped fired test specimens thanks to a caliper (ROCH France, Patented S.G.D.G.) and water absorption was carried out on cylindrical fired test specimens using NF-P-18-554 standard [
An electron microprobe wax employed to examine detailed mineral identification.
The clays are fine grained and characterized by a high proportion (>30%) of clay sized fractions. The proportion of sand is always less than 10%. Close examination of sand particles revealed that they are made up of a mixture of quartz grains and iron concretions. The latter is the product of tropical weathering of the clays (
The clays are all high plastic (20% > IP < 40%) which can be attributed to the low percentage of sand particles and the presence of significant amounts of expandable mixed layer clays, montmorillonite and/or organic matter. In Wack, the potter that use some of these clay deposits for pottery wares, blend the clays with cohesionless granular sand to reduce the high plasticity and the expected excessive drying shrinkage and severe internal cracking on firing.
The chemical compositions of the clays (W1 and W2) are presented in
Samples | Grading (%) | Plasticity (%) | ||||
---|---|---|---|---|---|---|
Sand | Silt | Clay | ωL | ωP | IP | |
W1 | 5.4 | 32.1 | 57.5 | 58.0 | 28.6 | 29.3 |
W2 | 2.0 | 19.5 | 50.5 | 60.1 | 33.5 | 26.6 |
SiO2 | Al2O3 | Fe2O3 | TiO2 | CaO | MgO | K2O | Na2O | MnO | LOI | |
---|---|---|---|---|---|---|---|---|---|---|
W1 | 50.20 | 23.30 | 9.40 | 1.37 | 0.98 | 1.27 | 3.63 | 0.88 | 0.17 | 8.08 |
W2 | 53.14 | 21.14 | 8.30 | 1.26 | 1.03 | 1.04 | 4.20 | 2.28 | <0.10 | 7.15 |
WG | 68.70 | 1.90 | 0.56 | <0.10 | 14.30 | 2.33 | 0.75 | 12.60 | <0.10 | 0.55 |
LOI = loss on ignition.
for ceramic industries with high mechanical value [
Silica and alumina vary from 50.20% - 55.71% to 21.14% - 24.34% respectively. It is suggested that the clays are low to medium quality refractory varieties. Generally, the clays contain high amounts of alkali and magnesia (>1%). The slightly higher amounts of lime (CaO) in samples are attributed to the presence of carbonates. The clays from Wack contain also restively higher amounts (0.47 - 2.70) of sodium oxide which is most probably due to the significant proportions of montmorillonite in these samples. The low content of potassium oxide in the clays indicates the presence low amount of illite. Generally, the amounts of sodium and calcium oxides in most of the clays are much higher than the amounts required for ceramic production. The appreciable amounts of these two oxides will lower the vitrification of the clays, thereby making them unsuitable for manufacturing of refractory bricks.
The clays mineral assemblage comprises of kaolinite, montmorillonite, illite, goethite and halloysite. Kaolinite is the dominant clay mineral in most deposits. Quartz, anatase, albite and not/and or those are the main subsidiary non clay mineral detected from the XRD patterns and they are estimated to 15% - 35% of most samples. The most significant amounts of montmorillonite in some of clays will result in high plasticity and shrinkage as well as low vitrification. These three properties are undesirable in the ceramic industries. That is why stabilization method was done to ameliorate the properties and quality of terracotta by adding waste glass powder [
The Fourier transform infrared spectroscopy (FTIR) spectrum of clays is shown in
The chemical compositions of waste glass (WG) are presented in
Five specimen tests were made from each formulation by adding the mixture of clay and waste glass powder by varying the amount and the grains size of the
additive. These specimen after the determination of their physical properties, were fired in an electric furnace at predetermined temperatures.
Some of the physical properties of the fired clays are presented in
Linear shrinkage, water absorption and flexural strength of samples initially fired at 750˚C are shown in
Samples | Waste Glass Grain Size (μm) | Amounts of Waste Glass (%) | Moist Color | Firing Color | Water Absorpt. (%) | Linear Shr. (%) | Flexural Strength (Mpa) |
---|---|---|---|---|---|---|---|
W1 | - | 0 | LG | RB | 15.20 | 0.492 | 3.35 |
100 | 2 | LG | RB | 21.28 | 0.491 | 1.50 | |
6 | LG | RB | 13.94 | 0.662 | 1.70 | ||
10 | LG | RB | 13.86 | 0.447 | 8.34 | ||
300 | 2 | LG | RB | 19.53 | 0.307 | 1.87 | |
6 | LG | RB | 15.29 | 0.723 | 3.65 | ||
10 | LG | RB | 14.37 | 0.546 | 6.86 | ||
500 | 2 | LG | RB | 16.15 | 0.307 | 3.42 | |
6 | LG | RB | 15.86 | 0.747 | 4.00 | ||
10 | LG | RB | 14.71 | 0.668 | 6.20 | ||
800 | 2 | LG | RB | 15.32 | 0.122 | 5.05 | |
6 | LG | RB | 16.19 | 0.970 | 6.35 | ||
10 | LG | RB | 14.76 | 0.670 | 5.94 | ||
W2 | - | 0 | DG | RB | 13.13 | 0.925 | 6.54 |
100 | 2 | DG | RB | 17.52 | 0.941 | 3.42 | |
6 | DG | RB | 11.33 | 0.747 | 3.68 | ||
10 | DG | RB | 10.86 | 0.769 | 8.72 | ||
300 | 2 | DG | RB | 16.39 | 0.490 | 4.00 | |
6 | DG | RB | 13.42 | 0.723 | 4.55 | ||
10 | DG | RB | 11.19 | 0.952 | 7.67 | ||
500 | 2 | DG | RB | 14.84 | 0.369 | 5.64 | |
6 | DG | RB | 14.17 | 0.743 | 5.60 | ||
10 | DG | RB | 12.51 | 1.243 | 6.83 | ||
800 | 2 | DG | RB | 14.68 | 0.246 | 5.92 | |
6 | DG | RB | 14.28 | 0.800 | 6.95 | ||
10 | DG | RB | 13.04 | 1.700 | 6.03 |
DG = dark grey; LG = light grey; RB = reddish brown.
phase (hematite), dissolution of quartz via the vitreous phase generated by the fusion of waste glass (
The water absorption percentage decreases when the percentage of waste glass increases up to 10% (
Flexural strength is a characteristic which is strongly dependent on voids: The lower there are voids, the higher are the values of flexural strength of fired products. As the mass percentage of waste glass increases up to 10%, there is a noticeable tendency of increase of flexural strength of fired samples [
As already mentioned above, these results are in accordance with the variation of water absorption as a consequence of viscous flow mechanism, inducing densification through consolidation of particles of fired samples. Therefore, the vitrification causes the reduction of porosity and samples experience increase of mechanical strength [
The observation of the specimen which without additive shows that the pore radius is between 0.5 microns and 2 microns (
W2 without additive, 2): W1 and W2 with additive (100 µm, 10%). X-ray diffraction patterns show the presence of different phases that are identified as: quartz α, metakaolinite, rutile and hematite. In
The influence of colorless waste glass on the mineralogical, microstructural and mechanical properties of terracotta made from local Wack clay was explored. With the addition of glass with a siliceous amorphous phase, it is possible to increase the content of the liquid phases during sintering. The amount of mullite is thus improved and hence the microstructure of the parts is more condensed with low porosities. The mechanical properties closely related to the mineralogy and the microstructures of the parts were significantly improved. The best performing products are obtained at 100 μm with 10% glass as fluxes. The contribution of glass in the melting temperature which is around 700˚C can allow significant energy savings, especially in developing countries such as Cameroon.
The authors declare no conflicts of interest regarding the publication of this paper.
Souaibou, Antoine, E. and Raidandi, D. (2019) Influence of the Colorless Waste Glass on the Mineralogical, Microstructural and Mechanical Properties of Clay Material from Wack (Adamawa, Cameroon). Advances in Materials Physics and Chemistry, 9, 89-102. https://doi.org/10.4236/ampc.2019.95008