Environmentally Friendly Geopolymer Building Material: Production, Determination of 1 Physical-Mechanical-Radiation Absorption Properties and Mathematical Model Approach 2

Waste ashes and radiation cause important environmental and health problems. Therefore, reduction of their amount is vital. In this study, physical-mechanical and radiation absorption (RA) properties of eco-friendly alkali (NaOH and 17 Na 2 SiO 3 ) activated geopolymer building material (GPBM) produced by using the industrial solid waste class F fly ashes 18 (FFAs) are determined. The FFAs were supplied from thermal power plants operating in Zonguldak and Adana 19 (Turkey). The sieve analysis, loose/tight unit weight and loss on ignition analysis of the FFAs was conducted. Different 20 FFAs and alkali activator amounts were used for making GPBMs. After thermal curing in a laboratory oven at 70 °C and 21 100 °C, the produced GPBMs were kept to cool off to room temperature. Afterwards, compressive and flexural 22 strengths, water absorption, porosity tests and RA measurements were performed. Influence of several parameters (FFA 23 types, curing temperature and alkali ratios) on the RA properties of GPBM is discussed in this paper. According to the mathematical model developed in this study, the effect of FFAs supplied from different TPPs onto RA (%) is an 25 important issue. Because FFA quantity causes to increase RA (%) with respect to the composed mathematical model. The FFA-based GPBMs, which have a compressive strength of more than 30 MPa, have higher radiation absorption 27 (>12%) than ordinary Portland cement-based conventional building materials (9.52%). The highest compressive strength 28 and RA percentage were measured as 93.3 MPa and 12.54%, respectively, for the GPBMs that are (properly) suited for 29 the construction sector.


Introduction 37 38
The demand for building materials is increasing every day for sustaining the necessity of structure development. The 39 global consumption of concrete is ranked second after water. When demand for structural concrete increases, the 40 demand for Portland cement also increases. Ordinary Portland cement (OPC) production consumes both energy and 41 natural resources. Nevertheless, OPC emits huge amounts of CO 2 , a greenhouse gas causing global warming, to the 42 atmosphere. The process of calcination (which drives CO 2 from CaCO 3 in order to form CaO) is responsible for 43 approximately 50% of CO 2 emission, while the remaining CO 2 is released by energy production processes. As stated in 44 the International Energy Agency's Greenhouse Gas R&D Programme, production of cement releases an average CO 2 45 emission of 0.81 kg CO 2 per kg cement produced in the world (Okoye 2016). Additionally, the vulnerability of OPC 46 building material to acid attack (Irico et al. 2020) is a subject of concern for future durability of this binder.

47
Geopolymer as an alternative binder has been studied extensively in every part of the world to make the building 48 material environmentally friendly as part of the sustainable development (Dadsetan et al. 2019; Luhar and Luhar 2020).

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In fact, while comparing the OPC to geopolymer, the main advantage of the latter is its chemical resistance (Luhar and

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As an energy process, radiation can be divided into two groups: ionizing and nonionizing. The energy of ionizing 65 radiation (per photon or particle) to ionize atoms contains sufficient energy whereas nonionizing radiation (per photon or 66 particle) to ionize atoms is deficient. Radiation can be seen in different forms as particle alpha, beta and neutron or in 67 electromagnetic waves such as gamma and X rays (Evcin et al. 2018

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When OPC-based concrete and anti-radiation concrete are compared, we can see that anti-radiation concrete is 77 approximately 1.5 times heavier and denser than OPC-based concrete. As a result, it can be said that heavy concrete has 78 better absorbing substances than OPC-based concrete. Therefore, a number of studies have been performed in the last Isken Sugozu TPP (Adana, Turkey) as raw materials and NaOH and/or Na 2 SiO 3 as alkali activators were determined.

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The irradiation was performed with Cs-137 to the FFA-based GPBMs and radiation absortion (RA) percentage of these 99 materials was measured. A mathematical model is also developed in this study. The data was fitted to a suitable In this study, 4x4x16 cm cementless eco-friendly GPBMs were produced by using FFAs, alkali activators and Rilem 114 Cembureau standart sand as materials.

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The chemical composition analysis of FFAs

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The chemical composition of FFAs that have a maximum particle size of 500 µm is analysed ( Figure 1) and summarized 122 in Table 1     To make geopolymer paste by using only FFA, separate and normal mixing methods were used. For separate mixing, 176 FFA was mixed with NaOH for 10 minutes to enable leaching of ions; subsequently Na 2 SiO 3 solution was added to the 177 mixture. Since the mixtures were relatively viscous/fluid, only a short period of mixing time was needed to obtain a 6 FFA-chemical activator mixture rates (Table 4)  The measurements were performed by reading the value on the counter that detects gamma-rays emitted from the 236 radioactive source (Cs-137) that were placed behind the sample. In both measurements, data was taken for one hour and 237 a ratio was determined by averaging the two results obtained. Thus, the amount of radiation absorbed by the measured 238 sample was determined proportionally. This procedure was performed for all the GPBM samples, and the results are 239 listed in Table 4.

241
The 252 In order to obtain the most suitable fit curve for the data set, the square of the total error for points should be at 253 a minimum. This can be written as; 254 = ∑ ( ) 2 = ∑ ( − ( 0 + 1 + 2 2 + ⋯ + )) 2 (7)

255
In order to achieve a higher order degree curve fitting, should be at a minimum. Therefore, each partial

369
Compressive strength values of GPBMs produced in this study are presented in Table 4

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Considering mixtures, combination and design, GPBM production in this study is different from the studies in the 377 literature. Additionally, determination of RA by using a newly designed LRS cage has not been previously studied in the 378 literature.

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In this study, FAs are activated through grinding after by curing with a thermal processes and using alkali 380 activators. The water used in the mixing phase during the production of geopolymer is used for the workability of the 381 mixture. When the water leaves the geopolymer during the curing process, it creates discontinuous nano-voids. This 382 situation gives lightweight properties to GPBMs (bulk densities of them are below 2 g/cm 3 ).

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RA values of conventional building materials produced with OPC were determined as 9.52%. In this study, 384 cementless GPBM having higher RA capacity (12.54%) was produced. The highest RA values were measured in the 2 nd 385 and 11 th GPBMs produced by using FFAs of Catalagzi and Isken TPP. In these materials, alkali activator ratios 386 (Na 2 SiO 3 /NaOH) are higher than 2. GPBMs produced by using FFAs have higher RA percentage values than the 387 conventional building materials produced by using OPC without any waste.

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According to the mathematical model developed in this study, the effect of FFAs supplied from different TPPs onto 389 RA (%) is an important issue. Because FFA quantity causes an increase in RA (%) with respect to the this model.

391 392
Conclusions 393 394 NaOH and/or Na 2 SiO 3 -activated FFA geopolymers, cured at 70 and 100 ºC, were produced in this study. Based on the 395 research carried out, it can be concluded that GPBMs can have better engineering properties than the corresponding 396 properties of conventional OPC building material (C30). Also, there is an urgent need to produce an alternative to 397 building material with adequate strength in order to make construction industry more eco-friendly and sustainable.

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Materials of this type, however, are used in specific areas, as a kind of special materials, due to their unique properties 399 such as mechanical, chemical or fire resistance (Davidovits 2020;Pacheco-Torgal et al. 2008). Radiation damages the 400 cells making up the human body and causes serious diseases and health problems. Therefore, it is important to know if 401 such material is also beneficial for radiation protection. For this reason, RA rates of the materials produced in this study 402 were determined.