الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
 |  | from | 125 |  |  |
| | | from | 125 | | |
Abstract
Introduction
The introduction of the research showed the light on the subject importance and the aim of the study. Waste management is one of the essential aspects of the environmental science. The ordinary portland cement is traditionally applied binder for fabrication of the concrete. CO2 gas emits during the production process of cement as a result of the firing of limestone and combustion of fossil fuel is about one ton CO2 for every ton of PC produced. In addition, the extent of energy required to produce PC is coming after steel and aluminum industry.
The presence of solid waste such as Partial de-aluminated metakaolinite (PDK) or the amorphous silica resulted as a by-product to aluminum sulphate manufacturing, gives the opportunity to utilize this by-product, as a source of silicate to synthesize geopolymer concrete. When PDK can be used as a partial replacement of PC, in the presence of water and in ambient temperature, PDK reacts with the lime water to form the calcium silicate hydrate binder.
Geopolymer concrete is an effective replacement of ordinary cement. Geo-polymer is a type of non-crystalline alumino-silicate binding material which can be synthesized by alkaline activation of siliceous and aluminous materials. Geopolymeric mortar/concrete can be manufactured by using of industrial solid waste material which have pozzolanic characteristics.
The various properties of geopolymeric products can be determined for using in construction applications are: mechanical characteristics (compressive strength), durability such as resistance to acidic and salt solutions, and fire-resistant properties of the composites.
Literature review
This literature review submits a brief text about an alternative binder used for manufacturing of geopolymeric mortar. Some of the published studies on the geopolymer techniques are shortly reviewed.
Geo-polymer formation is normally prepared by alkali activation of an alumino-silicate materials at the ambient conditions forming polymeric bonds [-Si–O–Al–O-]. The geo-polymer blends formed may be non-crystalline or semi-crystalline depending on the condition of geopolymerisation specifically temperature of processing.
Meta-kaolinite is the extensively used as a starting material for synthesis of geopolymer mortar or concrete. Metakaolinite is fabricated by thermal dewatering of kaolinite clay mineral. The thermal activation of clays is performed in a temperature range of 500- 800°C. The aluminates octahedral sheets lose the molecular water and the crystal lattice destructs and the mineral becomes amorphous material called ”Metakaolinite”. This Meta state of the clay is known to be pozzolana i.e. reacts with alkaline solution such as lime water forming cementitious products. Heating of the clay to very high temperatures results in the formation of inert mineral for chemical reactions named mullite and spinel.
Many research works have confirmed the utilization of some industrial solid wastes as a secondary resources for synthesis of geopolymer mortar/concretes. Such as: silica fumes fly ash, volcanic lava and granulated blast furnace slag.
Partial de-aluminated meta-kaolin (PDK) is a solid residue of aluminum sulphate manufacturing, whereas it is resulted from acid leaching of alumina from metakaolinite (MK) (e.g. calcinated kaolinite, Al2O3•2SiO2). The de-alumination process causes increase of ratio of both SiO2/Al2O3 and B.E.T. values. The increasing of surface area takes places as a result the thermal treatment of kaolinite at 700 °C and the chemical treatment and the extraction of aluminum in the form of aluminum sulphate by the action of sulphuric acid.
from this presentation, it was scientifically demonstrated the possibility of using PDK as an active silicate waste with MK with different ratios for making geopolymer mortar. These materials were collected from one location. The technique of investigation, the tools and instrumentations that commonly applied for fabrication of the portland cement mortar, were used for geopolymer mortar preparation.
The mortar properties studied included the mechanical characteristics such as compressive, tensile strengths, and the durability testes such as chemicals attacks. Material and methods
This chapter deals with utilization of metakaolinite and partial de-aluminated metakaolinite samples were obtained from the Aluminum Sulphate Company of Egypt, (ASCE) in Egypt. Both samples have undergone conditions for the polymerization process, starting with fine grinding and then drying at 105 °C for 24 hours to remove the humidity. The grain size distribution of the studied MK and PDK samples was identified by laser diffraction particle size analyzer. Different ratios of MK and PDK are mixed with sand, added as aggregates, for 5 minutes in a mixer to ensure its homogeneity. Then the mixer was stopped and the mixture was activated by adding NaOH (11.6 M) and mixed for an additional 5 minutes. The final mixture then molded into 5 cm3 cubes, the curing was done at room temperature.
Compressive strengths of the MK/PDK geopolymer cubes were measured after 28 days of curing according to the ASTM C 109 Method.
Scanning Electron Microscopy (SEM) was applied on selected samples in order to study the microstructural components of the MK/PDK geopolymer. Whereas, Energy Dispersive Analysis X-Ray (EDAX) technique was used to identify the chemical elements of the selected sample.
The chemical characteristics of meta-kaolinite will be determined using XRF and XRD. The meta-kaolin used is produced by thermal de-hydroxylation of kaolinite at 740 ̊C for 1.5 hours.
Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were performed, between 20 °C and 1000 °C and heating rate of 10 °C/min, according to DIN 51006 and DIN 51007 standards.
FTIR was performed to examine and to confirm the formation of metakaolinite and geopolymer mortar.
The durability of geopolymer mortar samples against sulphate medium, were done in 5 % solution of sodium Sulphate and 5 % sulphuric acid solution for 28 day.
The activity of the formed metakaolinite as a pozzolana was proved by Chappelle test
Results
The thermal behavior of the starting kaolin was tested. At temperatures lower than 200°C the moisture water go out of the surface pores. For the range 200 - 450 °C, the mass reduction is caused by the dehydration of strongly bound water, as a result of the rearrangement of the internal structure. While in the range 450–650 °C, the hydroxyl groups are rejected out of the crystal lattice of kaolinite and metakaolinite is developed. At about 1000 °C, new crystalline form is formed named mullite mineral, as indicated by an exothermic peak. The observed endothermic peak with a maximum at 559.5 ̊C attributes to starting of deformation of the ordered internal molecular structure to amorphous and releasing up of bound water.
FTIR spectra of the prepared geopolymer which having different ratios of DK. The broad band [O-H] stretching and bending localized at the range [3430-3460 cm-1] and at 1650 cm-1 characterize crystallization water of calcium silicate hydrate and calcium aluminate hydrate. The band intensities of the sample represents molar ratios of 2.96 SiO2 /Al2O3, 0.88 Na2O/Al2O3, at 13.1 H2O/Na2O for the samples and compressive strength 65 MPa is relatively bigger than the other blends.
Upon immersion in sulphuric acid (5 %) Concentration, the mortar, displayed losing of 10.3 %, of its mass after the 30 days.
The density of the geopolymers goes up with addition of PDK to MK (30 % PDK to 70% MK), whereas the density increases from 1.91 to 2.05 (4.59 %) after 28 days of curing.
The total porosity, bulk density and water absorption are dependent on to the hydration and formation of hydration-products that pack up the intermolecular cavities. In the optimal geopolymer blend the total porosity and water absorption are reduced with an increase of the bulk density. As expected, the trend of the water absorption is directly proportion with the total-porosity. The presence of 30% PDK reduces the percentage of water-absorption at the 28th day.
The weight loss of mortar subjected to continuous immersion in NaCl (5 %). The geopolymer mortar performed a steady weight loss, although it started with a considerable high value of 1.50% after two days. There was a steady trend of weight loss for the geopolymer mortar indicating no sign of chloride accumulation in the specimens. The mortar showed a constant change in weight loss with time, revealing that the microstructure changing occurred. There was a substantial initial weight loss of 5 % for the geopolymer after 30 days
The geopolymer recorded increase in mass over the duration of exposure to sodium sulphate (5 %) solution. The mass gained across the specimens was in the range ([0.09 - 0.12 %) which is too small. The increasing of mass may be caused by the white flaky or needle precipitate formed on the surface or within the surface pores.
Conclusion
For geopolymer mortar fabrication, partially dealuminated metakaolinite (solid waste of Aluminum Sulphate industry) can be used as an alternative for amorphous silicate .the produced geopolymer can be used for fixing of the bricks in chemical reactors.
RECOMMENDATION
Utilization of partially dealuminated metakaolinite (solid waste of alum, sulphate industry) as a source of amorphous silicate in geopolymer mortar fabrication. Further investigations should be done to test the durability of the geopolymer mortar regarding time of exposure for acids and heat.