الفهرس 
INTRODUCTION,LITERATURE REVIEW AND OBJECTIVESOnly 14 pages are availabe for public view
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Abstract
Concrete is the most popular, versatile and widely used building material worldwide. Over the last two or three decades the construction industry has taken considerable strides forward with regard to higher performing concrete materials. Scientists and engineers are continuously working for better concrete characteristics from the physical, mechanical and durability aspects with the help of innovative chemical admixtures and supplementary cementing materials (SCM’s). The development in these materials is progressing rapidly.
The most significant and indispensable ingredient of concrete is cement. The cement manufacturing process release a significant amount of CO2 emissions, a major contributor to the greenhouse effect and the global warming of the earth planet. The most effective way to decrease the CO2 emissions of the cement industry is the substitution of a portion of the cement by supplementary cementing materials (SCM’s). The usage of these materials in cement has dramatically increased along with the development of concrete industry due to considerations of reducing the cement content of concrete (hence energy and cost saving), in addition to , alleviating atmospheric pollution, improving workability, increasing strength and enhancing durability through SCM’s pozzolanic activity.
The use of silica fume and various mineral admixtures (Pozzolanas), Particularly, coal fly ash and ground granulated blastfurnace steel slag have become staple ingredients that judiciously utilized in the production of concretes having particular strengths or where service environments, exposure conditions or life-cycle considerations dictate the usage of specific concretes (e.g. high performance concrete – HPC).
Metakaolin (dehydroxylated aluminium silicate – Al2O3. 2SiO2) is one of the innovative clay products developed in recent years. It is produced by thermal activation (calcination) (in the range of 500-800oC) of previously refined kaolin clay (i.e. phyllosilicates or layer silicates) under carefully controlled conditions to create a disordered, amorphous, reactive (highly pozzolanic) product.
Egypt could be considered devoid of the suitable local industrial wastes that could be used as SCM’s (Particularly fly ash and ground granulated blast furnace steel slag). On the other hand, silica fume that has been initially considered as an industrial waste (of silicon mineral or ferrosilicon alloys production) has now become world class product for which there is a constant demand as a SCM in the construction industry. However, this product is rather expensive. In Egypt most of the collected silica fume (from the ferrosilicon industry) is exported abroad as its cost is about 4 times the cost of ordinary Portland cement.
Fortunately, Matakaolin (MK) is produced in Egypt, particularly, by the calcination of raw kaolin during the manufacture of aluminium sulfate (alum). Raw kaolin is found in Egypt in two main locations near Abu Zinema, South Sinai and at South Aswan, Upper Egypt.
At “Aluminium Sulfate Company of Egypt – ASCE”, Abu Zaabal, Kaliobeya Governorate, natural kaolin (obtained from Abu Zinema area, Southern Sinai) is refined, crushed and collected in a silo, then, such kaolin is transferred to a vertical kiln where it is transformed to metakaolin through heating (calcining) at 750oC for 2 hrs. Part of the formed MK is stored as fresh metakaolin to be sold for usage in some industries. The other part of MK is conveyed to some sort of reactors where aluminium is leached out of MK by subjection to dilute H2SO4 acid, thus, forming aluminium sulfate (alum). The de- aluminated metakaolin is considered as a by-product used for land – filling in areas outside the company site.
Accordingly, the objective of the current study is to investigate the suitability of using such local MK as a pozzolanic material in concrete. This has been carried out through:
- Studying the performance of MK upon its usage as an admixture in cement and concrete, particularly, the development of strength and durability characteristics.
- The effect of MK incorporation in concrete upon maintaining the steel reinforcement passivity towards corrosion.
- Determination of the optimum cement replacement ratio by MK in hardened cement pastes, plain concrete and reinforced concrete.
Consequently, the current study started by a comprehensive literature review about:
- Pozzolanic materials, their types and their mechanism of action.
- Metakaolin as a supplementary cementing material and its impact on concrete characteristics.
- Metakaolin in Egypt, locations and industrial production.
- Bearing in mind the target of the current study, a detailed investigation program has been determined.
Evaluation of the pozzolanic activity of the local industrially produced metakaolin has been performed through determining:
- The characteristics of the produced MK.
- The role of MK, as a partial cement replacement material, on the physico – mechanical properties of the hardened MK/OPC mix.
- Determination of the superior MK dosage (S) in MK/OPC mix.
- This part of the study indicated that the superior MK percentages, as far as the compressive strength is concerned, are 10% and 15% MK. These percentages cause strength enhancement reaching 17% and 22%, respectively.
The characteristics of these superior MK dosages have been determined, it has been found that:
- They cause insignificant expansion for the cement paste and do not alter the cement alkalinity.
- Upon preparing the cement mixes (for different utilizations – other than concrete) incorporating MK as cement replacement, 15% MK is the optimum dosage. The characteristics of the 15% MK/OPC mix are almost comparable to those pertaining to the 10% SF /OPC mix
Studying the effects of MK on the properties of plain concrete (No steel reinforcement) have shown that:
- The dosage 10% MK, as cement replacement ratio in plain (Non-reinforced) concrete is considered (the optimum dosage) as far as the compressive strength enhancement of concrete is concerned.
- The plain concrete containing 10% MK, as cement replacement, manifests higher penetration resistance to aggressive agents (chlorides, sulfates, sea water). In addition, it maintains higher resistance to elevated temperature relative to concrete incorporating 15% MK or Mk-free concrete. The effects of 10% MK dosage is comparable to the effects of 10% SF, as cement replacement in concrete.
On the other hand, the current study elucidated that, 15% MK is the most reasonable dosage, as cement replacement in reinforced concrete for maintaining steel passivity against corrosion that can ensue due to the penetration of aggressive ions from the surrounding medium through the concrete. This behavior has been attributed to: Higher concrete alkalinity, lower Fe2O3 content and higher Al-2O3 content.
Based on the results of the current study for the characteristics and performance of the locally produced MK, the study recommended several additional applications for such MK including:
- Concrete constructions in marine areas.
- Geoplolymers.
- Concrete exposed to high temperature.
- Ceramic industry.
- Refractories and heat-resistant bricks and pipes.
- Heat – resistant paints.
At the quest of the “Suez Canal Economic Zone Organization” from the “Housing and Building National Research center – HBNRC” to present recommendations for new activities related to the field of construction to be considered in the plan of developing the industrial sector at Abu-Zinema area, Southern Sinai, Our research team recommended the establishment of a factory for MK production at Abu-Zinema industrial area. The research team presented our justifications for that. Also, the team presented a proposed (directive) lay-out for a new MK production plant.