الفهرس 
Introduction and Object of InvestigationOnly 14 pages are availabe for public view
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Abstract
Portland cement production greatly contributes to the emission of greenhouse gases, which are responsible for climate change. Additionally, the adverse consequences of waste materials produced by various industries can be seen in various forms, such as air, water, and soil contamination. So, sustainable production is a fundamental aspect of the sustainable development goals (SDGs) as it contributes significantly to economic development as well as treating the issue of environmental pollution. To achieve the principles of the SDGs, it is necessary to reduce the presence of some industries and concurrently adopt waste recycling practices, thereby working towards a greener future.
Geopolymers and/or green cement are a category of inorganic polymers that result from the interaction between alumino-silicate materials and an alkaline activator solution (such as NaOH). These materials include fly ash, slag, and other industrial byproducts. The synthesis of geopolymers offers a replacement for conventional cement-based materials, as it requires lower energy consumption and emits fewer greenhouse gases. Furthermore, geopolymers have shown promising results in terms of durability, fire resistance, and chemical stability, making them a viable option for various engineering applications. So, using industrial byproducts as raw materials for green cement or geopolymers production can help reduce waste and promote sustainable practices.
The solid wastes used in this study are ground granulated blast furnace slag (GGBFS), which is the base material collected from the smelting of hematite ore in the blast furnace, cement kiln dust (CKD) which is generated from the combustion of raw materials used to produce clinker for cement manufacturing, lead bearing sludge (LBS) is a secondary substance derived from the manufacturing process of crystals or glass, fly ash (FA) which was accumulated from burning pulverized coal. Additionally, meta kaolin (MK), which was obtained from the calcination of kaolin is utilized in composites preparation.
Two groups of ternary-blended geopolymer (TBGs) pastes were prepared. The first group is composed of 90% GGBFS + 5% CKD or LBS + 5% FA or MK, while the second group is composed of 80% GGBFS + 10% CKD or LBS + 10% FA or MK, besides, the control specimen (100% GGBFS, S0). The fresh characteristics of the prepared pastes were evaluated by determining the setting time and workability. The compressive strength values of the prepared pastes were evaluated after 1, 3, 7, and 28 days of curing at normal conditions, as well as for the hardened specimens (cured for 28 days) after being fired at 200, 400, 600, and 900℃ and cooled by two ways (slow and rapid).
Additionally, some selected hardened specimens (cured for 28 days) were exposed to different doses of gamma-rays radiation (1000, 2000 and 3000 kGy) with a dosing rate of 0.717 kGy/hr at room temperature using a gamma-ray radiation source (60Co-γ-cell-220). The antimicrobial activity for selected hardened composites (after 28 days of curing) was investigated against two types of fungi (Aspergillus-oryzae “ATCC-10124” and Aspergillus-fumigatus “ATCC-96918”) and two types of bacteria (Bacillus-Cereus “Gram-positive, ATCC-14579” and Salmonella-typhi “Gram-negative, ATCC-6539”).
Also, the formed phases and morphological features of some selected composites were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG), and scanning electron microscope with energy dispersive X-ray (SEM/EDX). Finally, the lead leaching test for some selected specimens exposed to different conditions was carried out following the toxicity characteristics leaching procedure (TCLP).
The main outcomes of this investigation are summarized as follows:
1. All TBGs fresh pastes that containing CKD showed flowability (workability) and setting time lower than the control specimen (100% GGBFS, S0). This result is assigned to the high alkali/fineness and irregular morphology of CKD, which reduce the workability and setting time, while the FA/MK increase them due to their spherical/platy morphology and low reactivity, but the impact of CKD is dominant.
2. All TBGs fresh pastes containing LBS showed lower workability and higher setting time than S0. LBS reduces workability due to its high amount of organic matter that adsorbs the free water. Besides, it elongates the setting time due to the presence of PbO2 and some organic matter that act as barriers for geopolymerization reactions.
3. The compressive strength results of all TBGs composites that containing CKD are lower than that of the control (S0). This was attributed to the excessive amounts of lime (CaO) present in CKD since hydration of CaO produces Ca(OH)2, which has twice the volume of CaO, causing internal stress, leading to micro-cracks forming that weaken the hardened structure. However, the developed TBGs composites containing CKD can be employed as an alternative to Portland cement with grade 42.5 N/mm2.
4. Specimens made from GGBFS replaced with 10% (LBS + FA) SLF10 composite and 10% (LBS + MK) SLM10 composite showed compressive strength values higher than that of control (S0). This result is assigned to that SLF10 and SLM10 contain less organic matter, which negatively affects compressive strength. The developed TBGs composites containing LBS can be employed as alternatives to Portland cement with grade 53 N/mm2.
5. XRD, TGA/DTG and SEM techniques demonstrate the formation of C-S-H and C-A-S-H as main strength-giving-phases in the S0 specimen, while the incorporation of FA/MK promoted N-A-S-H formation.
6. The fabricated TBGs specimens showed greater strength retention and tolerance to different elevated temperatures than control (S0 specimens) due to the high-stability of N-A-S-H formed after involving FA and MK. The specimen made from GGBFS was replaced with 20% (LBS + MK) SLM20 specimens, which presented the best thermal stability.
7. Specimens made from GGBFS replaced with 20% (CKD + FA) SCF20 composite, 20% (CKD + MK) SCM20 composite, 20% (LBS + FA) SLF20 composite, and 20% (LBS + MK) SLM20 composite showed higher strength retention and tolerance to higher doses of gamma radiation than control (S0). SCF20 and SLM20 specimens showed better strength retention than their corresponding specimens after irradiation.
8. SCF20, SCM20, SLF20 and SLM20 specimens showed a great ability to inhibit the growth of micro-organisms compared to the S0 specimen due to Fe2O3 and TiO2 present in the chemical composition of FA and MK as well as PbO2 from LBS in SLF20 and SLM20 specimens. SCM20 and SLM20 specimens showed the best antimicrobial activity.
9. TBGs containing LBS can be used as safe binding materials, although they contain high percentages of LBS. This was proved by XRD-analysis and leaching test that indicated the Pb stabilization/solidification due to the transformation of PbO2 to insoluble Pb3SiO5.
10. The expected CO2 emissions from the OPC is 944 kg CO2/ton while the expected CO2 emissions for the used materials are 26.5, 0, 0, 11, 177, and 1232 kg CO2/ton for GGBFS, CKD, LBS, FA, MK, and NaOH. Besides regarding the cost calculation, according to Egyptian market prices, the average price of OPC is 65 $/ton, while the cost of GGBFS, CKD, LBS, FA, MK, NaOH, and superplasticizer are 28, 0, 0, 780, 80, 208.32, and 2000 $/ton. Indicating the high cost of OPC manufacturing as well as revealing the negative impact of OPC industry on the environment.
11. Comparing TBGs containing 5% MK (SCM10 and SLM10) and TBGs containing 10% MK (SCM20 and SLM20) with OPC, it was detected that the cost was reduced by 32.89 and 31.05 %, while the CO2 emission was reduced by 90.01 and 89.35 %, respectively. reflecting the role of these TBGs composites as a sustainable and eco-friendly alternative to OPC in the building sector.
12. from the economic, environmental impact, and mechanical properties points of view, the SLM20 composite is considered a suitable building material for several and specific applications.