- Email: [email protected]
Effect of fly ash particle size on thermal and mechanical properties of fly ash-cement composites
Accepted Manuscript Effect of fly ash particle size on thermal and mechanical properties of fly ashcement composites Ayse Bicer PII: DOI: Reference:
S2451-9049(17)30521-8 https://doi.org/10.1016/j.tsep.2018.07.014 TSEP 208
To appear in:
Thermal Science and Engineering Progress
Received Date: Revised Date: Accepted Date:
28 December 2017 24 July 2018 25 July 2018
Please cite this article as: A. Bicer, Effect of fly ash particle size on thermal and mechanical properties of fly ashcement composites, Thermal Science and Engineering Progress (2018), doi: https://doi.org/10.1016/j.tsep. 2018.07.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
EFFECT OF FLY ASH PARTICLE SIZE ON THERMAL AND MECHANICAL PROPERTIES OF FLY ASH-CEMENT COMPOSITES
Ayse BICER1 Department of chemical Engineering, Firat University, Elazig Turkey
ABSTRACT In this study, fly ash was used in concrete and plaster in place of sand and the impact of fly ash grain size on thermal and mechanical performance of composite material was examined. Fly ash used in the experiments was received from Soma Thermal Power Station and separated into the various grain size groups namely unsieved, >75x10-6 m, (45-75)x10-6 m and <45x10-6 m. In all fly ash and cement mixtures, the weight percentages of fly ash were accepted as 10, 30, 50, 70 and 90%. Cement IV/B (P) 32.5 R was used as the binding material and 20 specimens were prepared according to the grain diameter and percentage of fly ash. Some tests were performed using the new products to find out their detailed properties including density, thermal conductivity, compressive tensile strength, and elasticity module and water absorption. It was found in the experiments that i) as the grain size diameter decreased, ash density increased 16.12%, and porous structure was replaced by full-grain ash and its color turned to light brown; ii) as the ash addition ratio increased 10-90% in fly ash cement mixtures, thermal conductivity coefficient and compressive strength values decreased in the rates of 14.47-24.52% and 1.25-9.4% respectively; iii) concrete or plaster turned into an insulator due to fly ash. Keywords: Fly ash, light concrete, insulation plaster, waste management
Ayse Bıcer, Phone: +90-424-2370000/5504, Fax: +90-424-2415526 E-mail: [email protected]
Nomenclature Porosity, (%) fly ash
: Density of fly ash, (g/cm3)
fly ash matrix : Density of fly ash with 0 % porosity ratio (after milling and so causing no porosity), (g/cm3) cement
: Density of cement, (g/cm3)
cement matrix : Density of cement with 0 % porosity ratio, (g/cm3) Wk
: Dry weight of sample, (g)
Wd
: Wet weight of sample, (g)
Z
: Fly ash ratio, (%)
(1-Z)
: Cement ratio, (%)
1. INTRODUCTION Nearly 15x106 tons of fly ash is generated annually in Turkey at thermal power plants. One of these factories is Soma Power Plant. Storage of fly ash or disposal from the facility is one of the significant problems concerned with power plants. Hence, waste fly ashes’ negative effects on the environment should be assessed. Fly ashes are classified as artificial pozzolanic. Puzzolanic character can be described as a non-bonding material to gain the capacity to be bonding only when mixed with water. The studies accelerated because fly ash of appropriate amounts was used within concrete in place of concrete. Numerous studies were conducted on fly ash up until today. Previous researches shown that fly ash is a potential source of construction material [1].
These studies were summarized in two groups. In the first group, fly ash was assessed as an additive material in cement. Karaşin and Doğruyol [2], reported that there was no change in strength values of concrete when 20% fly ash was added in concrete. The second group consist of studies conducted on partial or complete use of fly ash within the concrete instead of conventional aggregate. This study is included in the second group of studies. Some of the studies that were carried out for this group are summarized as follows: Silva and Andrade [3], researched the mechanical properties of concretes produced with recycled coarse aggregate within the rates of 25%, 50%, 75% and 100% instead of natural aggregate, and taking the water/cement rate as 0.40, 0.45, 0.50, 0.55 and 0.65 in their studies.
Golewski [4], Sunayana and Barai [5], in the studies that were carried out on an individual basis, produced samples using ash at the rates of 20% and 30% instead of natural aggregate, in order to minimize the negative impacts of coal fly ash on nature and to decrease the consumption of cement. The results of mechanical tests applied on the samples displayed comparable results with the natural aggregated concrete. In similar studies, Rafieizonooz et al [6 ], identified the mechanical characteristics of samples porduced with fly ash at the rates of 0, 20, 50 and 100% by Siddique [7], 10%, 20%, 30%, 40% and 50% by Dan [8] and 10%, 30% instead of natural sand. Aydın and Arel [9], as well as Yu et al [10] carried out researches on the physical and mechanical properties of fly ash additive cement in high ratios to reduce the material costs and for using them in low strength concrete practices, in their studies that were carried out on an individual basis. Babu at al [11], Thirumal and Harish [12], Rivera at al [13] and Duran [14], also carried out researches on the mechanical properties of samples produced by partly fly ash instead of sand as aggregate in the concrete within the scope of their individual studies. Li et al [15], proved that the selective dissolution method and thermal analysis method can be used to measure the fly ash content within fly ash additive solidified concrete. As differing from these studies, Yazıcı and Arel added fly ash to concrete in the ratios of 5%, 10%, and 15% and investigated the effect of fly ash fineness on the mechanical properties of concrete [16]. Saumya et al studied the effect of fly ash and vegetable oils on mechanical properties of concrete, which consisted of fly ash, vegetable oil and PVC plastic [17]. In this study, small pores were generated in the structure of ash as a result of coal burning a t high temperatures. By using this feature of thermal power station, it was thought that low density construction material could be produced. In order to determine the effect of fly ash grain diameter on the properties of new materials, ash was divided into four groups namely unsieved ash, and ashes of grain diameters of <45x10-6 m, (45-75)x10-6 m and >75x10-6 m. Thermal and mechanical properties of 20 different samples were determined. In this study, small pores were generated in the structure of ash as a result of coal burning a t high temperatures. By using this feature of thermal power station, it was thought that low density construction material could be produced. In order to determine the effect of fly ash grain diameter on the properties of new materials, ash was divided into four groups namely unsieved ash, and ashes of grain diameters of <45x10-6 m, (45-75)x10-6 m and >75x10-6 m. Thermal and mechanical properties of 20 different samples were determined.
2. EXPERIMENTAL 2.1. Materials Fly ash: Sulpho-calsic fly ash that was produced by burning lignite coal at Soma Power Plant in Kütahya City, Turkey was used in this study. Fly ash had an amorphous structure (glassy), had SiO2+Al2O3+Fe2O3=82.69 % ratio and fulfilled the conditions of ASTM C-350 and TS 639 standards stating that SiO2+Al2O3+Fe2O3 should be minimum 70%. Fly ash’s color is gray, darker than cement’s color, and it is very fine grained and is a soft material sensible when touched by hand. The fineness of ash is generally between 1x10 -6 m - 200x10-6 m. The density values of fly ash are shown in Fig. 1. Density values of fly ashes and cements are shown in Table 1. As seen in microscope, it has a structure with various forms and sizes. It is generally globe-like, transparent, sometimes light in color, partially black, and its grains are light brunette red colored (Fig.2). Its tone depends on the used coal and its burning characteristics. Depending on the burning properties, its principal components are silica, aluminum and iron oxide. Fly ash has a pozzolanic character. The particle distribution of fly ash is 36.4% (<45x10-6 m), 39.3% ((45-75)x10-6 m) and 24.3% (>75x10-6 m) by weight according to their grain diameters. Cement: CEM IV/B(P)32.5 R pozzolanic cement was used to produce concrete. The chemical component of fly ash and cement used in this study and the details of mix proportion are given respectively in Table 2. The water and cement + fly ash ratio (W/(C+F)) is set as 0.5
2.2. Testing methods
The prepared mortars were molded to 100x100x100 mm formworks for mechanical tests and they were molded to 20x60x150 mm formworks for thermal tests and they were left to dry for standard period of 28 days at room temperature. 20 specimens were prepared depending on the grain diameter and percentage of fly ash. At the end of the drying period, the samples were packed and stored until the measurement time.
Thermal conductivity was measured by using Isomet 2104 unit which applies hot wire method according to DIN 51046 standards. Its range and sensitivity were 0.02-10 W/mK and ± 5 % of the scale respectively [18, 19]. Measurements were taken for all samples at 3 different points at room temperature (22-25oC). Thermal conductivity values were determined by calculating arithmetic averages of that measurement. Compressive strength tests were performed on the samples according to ASTM C 109-80 standard [20]. Water absorption test is important to determine the suitability of a material to freezing hazard. The critical amount of moisture is 30% of the total dry-volume and below this volume, the material doesn't deform when frozen [18, 19]. The experiments were performed according to the BS 812 Part 2 standard. Dry and wet weights of the samples need to be known for water absorption ratio estimation. The samples were left at the drying room at 40oC of temperature for 12 hours and subsequently they were weighted by using a sensitive scale and their dry weights were measured. Then, water was added in the test cup and the samples were soaked there for 15 minutes as 1/3, 2/3 and the entire of their bodies to remain in water. Subsequently, they were removed from the water, wiped with a piece of rag, weighted and their wet weights were measured. The water absorption values were calculated by Eq. (1) and they are shown in Table 3. Water absorption ratio={[Wd-Wk]/Wk}.100
(1)
The purpose of drying ratio test was to determine respiration abilities of the samples. After the samples were soaked in water for 48 hours, they were removed, wiped with a piece of wet rag and dried naturally at 22oC room temperature. The drying ratio values were calculated by Eq. (2). Drying occurs by evaporation from the material surface; water moves from the deep of the material through capillary canals, in other words, moisture is expelled from the body through steam permeability resistance and then drying occurs. Drying ratio={[Wd-Wk]/Wd}.100
(2)
Porosity ( is defined by Eq (3), [18].
(3)
3. RESULTS AND DISCUSSIONS
Following coal burning, fly ashes with little beads of different sizes emerge. As grain size shrinks, full beads replace porous beads and the density increases (Table 1). The dry densities of samples cured for 28 days are given in Table 3. The results show that there was a decrease in dry density as the fly ash aggregate content increased. In non-sieved fly ash samples, dry density value of mixtures containing 10% fly ash aggregate decreased from 1.624 g/ cm3 to and dry density value of mixtures containing 90% fly ash aggregate decreased from 1.270 g/cm3. The reduction rate was 21.79% (Fig. 3). This is due to the porous structure of fly ash. As the grain diameter of fly ash was reduced density values increased. In fine grain sized samples, if most of the porous samples were placed with nonporous grains, fly ash samples’ densities got higher. Comparing the densities of fly ash samples with grain sizes >75x10-6 m and densities of the unsieved samples showed that while fly ash densities increased in rate of 10-90%, sample densities were reduced in rates of 6.344.96%. Thermal insulation properties of composite specimens were determined by thermal conductivity test. Thermal conductivity values decreased as fly ash ratio increased (Fig. 4-a). Because interior parts of micro structured pores were full of gases that were generated from burning and the average thermal conductivity coefficient of inert gases is almost 0.0214 W/mK. The minimum thermal conductivity coefficient measured in 90% fly ash samples of grain size >75x10-6 mm ( sa mp le 20) was 0. 2 4 0 W/ mK. I n uns ie ved fly as h sa mp les , t he r at io o f fly as h incr eased fr o m 10% to 90% and thermal conductivity coefficient values dropped to 31.32%. There’s a strong relationship between density and thermal conductivity Fig 4-b). As density dwindles, porous fly particles grow and thermal conductivity of samples dwindles even more. Because of the pozzolanic characteristics of fly ashes, when they are mixed with water without using any bonding material they gain bonding characteristics. Mortars prepared in this way can be used as sub-roof isolation plaster or they can be used as intermediate backfill materials inn sandwich walls. In such plaster forms, thermal conductivity coefficient is 0.2200.230 W/mK, and in dust forms and if they are used as an intermediate back fill material, it was detected empirically that the value was 0.140 W/mK. Figure 5 shows that compressive strengths of ash-free samples (sample with 0% fly ash) and samples with 10% fly ash additives are nearly equal. In other words, addit io n o f fl y
ash t o ceme nt in r at e o f 10% mea ns a saving fr o m t he ce me nt in r at e o f 10%. As lo ng as t he fly as h r at e in t he sa mp les incr ease d co mpr ess ive st r engt hs successive l y in t he uns ieved gr o up , t he gro up wit h a gr ain s ize o f <45x10-6 m, (45-75)x10-6 m and the group with a g r ain s ize o f >75x10-6 m are reduced in rate of 69. 03 %, 62. 08% , 74.17 % and 81. 35% . I n fly as h aggr egat ed mat er ia ls, it is no t int ended t o o bt ain lo wer st r engt h va lues, wher e t he fly a sh r at e incr eases. Ho wever, t he dens it y and t her ma l co nduct ivit y co effic ie nt ar e r educed despit e t his negat iv e char act er ist ic o f t he mat er ia l. T her e fo r e, t he place w her e t he produced samp les ar e go ing t o be used can be clearly identified. Based on these results, it can be recommended that concretes with fly ash (excluding 10% fly ash) must not be used in columns and beams of buildings. Nevertheless, these low density concretes are designated as panel walls, brick, concrete briquettes, inner and outer plaster, concrete partition elements, and insulation material. The results of water absorption of different mixtures are shown in Figure 6. The water absorption increased with the increased fly ash aggregate ratio. Whereas water absorption ratio of the samples, which have fly ash rates ranging between 10 and 30%, are lower than the critical value (30%), the other samples have a value higher than the critical value. Hence, (50-90) % fly ash concrete samples must not be used in places having direct contact with water. They must not also be used against inner wall elements where (briquette or brick) inner plaster, isolation plaster are used as low density construction materials. Table 3 shows that the drying ratios of the samples increased as fly ash ratio increased. The loss of water, which occurs towards the material surface through capillary canals, shows the ability to respire, albeit it is negligible. Considering the adherence experience of the prepared samples on the wall, when construction materials are used such as plaster mortars, brick, briquettes, it was detected that a flat and smooth surface was obtained. Within the processing experiments of fly ash samples, it was detected that it can be cut through by a saw in a proper way, it can be drilled with a drilling machine, a channel through it can be opened, and all sorts of dyes and wall papers shall be applied to such mortars without taking any precautions (Fig 7).
4. CONCLUSIONS
This manuscript was prepared to find out the influence of fly ash particle size on thermal and mechanical properties of fly ash cement composites. The following conclusions can be drawn from this experimental study: Removal of fly ashes from power plants is one of the significant problems of power plants. In this study, it is recommended that fly ash is used along with cement in concrete and plaster applications. Making use of fly ashes and storage and moving these waste materials from power plants can solve the undesired effects and problems. Moreover, significant energy savings can be achieved by using construction materials, which are obtained by using fly ash and which have a low thermal conductivity coefficient, in buildings. The usage area and purposes of fly ash cement composites can be determined by studying the effect of fly ash grain diameter on some properties of concrete. For example, the use of fly ashes with large grains for isolation purpose and the use of fly ashes with small grains in concretes that require strength quality, etc. It is possible to use less cement (10%) in comparison to ordinary concrete or plasters in concrete or plasters consisting of fly ash owing to their puzzolanic properties. Since concrete or plaster gains an insulation property owing to fly ash, heating costs would be lower in buildings. It is hoped that the results of this study will help the economy of the state. In samples with fly ash ratios up to 30%, water suction ratios remain below the critical value. Up to this ratio, fly ash concrete or plaster must be used at locations having direct contact with water without the risk of freezing. The inner surface plasters produced by using fly ash have identical properties as the ordinary plasters such as respiration capability, nailing, boring, cutting, sticking on the wall, giving a smooth surface and painting. The results of the present study have shown that fly ash can be used as sand-substitution in concrete and cement composites and simultaneously solve the environmental problem by recycling waste fly ash.
REFERENCES [1] Xiao H, Wang W. Goh SH. Effectiveness study for fly ash cement improved marine clay. Construction and Building Materials 2017; 157: 1053-1064. [2] Karaşin A, Doğruyol M. An experimental study on strength and durability for utilization of fly ash in concrete mix. Advances in Materials Science & Engineering 2014; 25: 1–6. [3] Silva RS, Andrade JJO. Investigation of mechanical properties and carbonation of concretes with construction and demolition waste and fly ash. Construction and Building Materials 2017; 153: 704-715.
[4] Golewski GL. Improvement of fracture toughness of green concrete as a result of addition of coal fly ash. Characterization of fly ash microstructure. Materials Characterization 2017; 134:335-346. [5] Sunayana S, Barai SV. Recycled aggregate concrete incorporating fly ash: Comparative study on particle packing and conventional method. Construction and Building Materials 2017; 156: 376-386. [6] Rafieizonooz M, Mirza J, Salim MR, Hussin M. Investigation of coal bottom ash and fly ash in concrete as replacement for sand and cement. Construction and Building Materials 2016; 116: 15–24. [7] Siddique R. Effect of fine aggregate replacement with class F fly ash on the mechanical properties of concrete, Cement and Concrete Research 2003; 33: 539–547. [8] Dan R. Properties of fresh concrete incorporating a high volume of fly ash as partial fine sand replacement, Materials and Structures 2004; 30: 473-479. [9] Aydın E. Arel HS. Characterization of high-volume fly-ash cement pastes for sustainable construction applications. Construction and Building Materials 2017; 157: 96-105. [10] Yu J, Lu C, Leung CKY, Li G. Mechanical properties of green structural concrete with ultrahigh-volume fly ash Construction and Building Materials 2017; 147: 510-518 [11] Babu DS, Babu KG, Wee TH. Properties of lightweight expanded polystyrene aggregate concretes containing fly ash. Cement and Concrete Research 2005; 35: 1218-1223. [12] Thirumal JR, Harish R. Performance study of self-compacting concrete by fly ash and silica fume for sustainability in building construction. Engineering Materials 2016; 692: 7481. [13] Rivera F, Martínez P, Castro J, López M. Massive volume fly-ash concrete: A more sustainable material with fly ash replacing cement and aggregates, Cement and Concrete Composites 2016; 63: 104–112. [14] Duran AC. Carbonation-porosity-strength model for fly ash concrete, Journal of Materials in Civil Engineering 2004; 16: 91-94. [15] Li Y, Lin H, Wang Z. Quantitative analysis of fly ash in hardened cement paste. Construction and Building Materials 2017; 153: 139-145. [16] Yazıcı S and Arel HS. Effects of fly ash fineness on the mechanical properties of concrete, Indian Academy of Sciences 2012; 37: 389–403. [17] Saumya KM, Alam M, Hussain A. Effect of fly ash particle and vegetable oil on the mechanical properties of fly ash-vegetable oil reinforced hard PVC plastic. International Research Journal of Engineering and Technology 2016; 3: 833-839 [18] Kaya A, Kar F. Properties of concrete containing waste expanded polystyrene and natural resin. Construction and Building Materials 2016; 105: 572-578. [19] Devecioglu AG, Bicer Y. The effects of tragacanth addition on the thermal and mechanical properties of light weight concretes mixed with expanded clay. Period. Polytech. Civil Eng. 2016; 60(1): 45-50. [20] ASTM. Standard specification for fly ash and raw or calcined natural pozzolan for use as mineral admixture in Portland cement concrete, ASTM, Philadelphia, ASTM C 1985; 618685
FIGURE CAPTIONS Figure 1. Density values distribution of fly ash Figure 2. View of samples under microscope Figure 3. Change of the density according to fly ash ratio Figure 4. Reduction in thermal conductivity according to a) fly ash ratio b) density Figure 5. Reduction in compressive strength according to fly ash ratio Figure 6. Water absorption ratio of samples versus fly ash percentages Figure 7. Samples can be different types of dyes can be applied a) drilling, b) silicone rubber coating and oil painting
FIGURES
Figure 1
Pore
Cement + ash
Figure 2
Figure 3
a)
b)
Figure 4
Figure 5
Figure 6
a)
b)
Figure 7
TABLE CAPTIONS Table 1 Density values of fly ashes and cement (g/cm3) Table 2 Chemical composition of the components (%) Table 3. Thermal and mechanical properties of samples
TABLES
Table 1 Fly ash Cement
unsieved 2.03
>75x10-6 m 1.94
(45-75)x10-6 m 2.29 3.10
<45x10-6 m 2.42
Table 2 Chemical characteristics SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O TiO2 LiO2 Sodium oxide (Na2O) Loss on ignition (L0I) Not available Total
Fly ash 51.25 26.15 5.29 7.85 1.66 0.23 1.3 0.83 0.13 0.67 3.32 -100.4
Cement 18.65 6.15 3.25 57.71 2.34 2.91 0.7 ---2.84 6.08 100.03
Table 3 Code 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Article Fly ash Density Porosity diameter ratio (g/cm3) (%) (x10-6 m) (%) Unsieved 10 1.624 4.18 “ 30 1.558 11.09 “ 50 1.461 17.07 “ 70 1.355 23.02 “ 90 1.270 26.13 <45 10 1.661 3.53 “ 30 1.583 7.24 “ 50 1.524 11.51 “ 70 1.396 15.41 “ 90 1.302 18.98 45-75 10 1.581 4.32 “ 30 1.528 9.34 “ 50 1.433 14.36 “ 70 1.342 19.38 “ 90 1.238 23.62 >75 10 1.521 5.41 “ 30 1.489 13.03 “ 50 1.375 19.12 “ 70 1.305 25.17 “ 90 1.207 29.03
Thermal conductivity (W/m K) 0.463 0.442 0.390 0.349 0.318 0.475 0.457 0.420 0.383 0.362 0.428 0.407 0.350 0.318 0.282 0.396 0.371 0.321 0.286 0.240
Compre. Water strength absorption (MPa) (%) 23.90 24.07 20.40 26.39 16.10 31.17 11.40 32.09 7.4 35.70 24.00 23.58 21.15 24.64 17.15 30.56 12.66 31.02 9.10 33.71 23.70 25.78 20.05 28,89 15.05 31.78 10.08 32.66 6.12 34.08 23.60 27.45 19.15 29,10 14.10 33.06 8.50 34,78 4.40 36.55
Drying ratio (%) 8.16 8.52 8.87 9.13 9.60 8.90 9.17 9.45 9.88 10.14 8.61 8.95 9.05 9.11 9.88 8.03 8.15 8.29 9.0. 9.28
HIGHLIGHTS New lightweight concrete was produced by using fly ash instead of natural sand Thermal and mechanical properties of these materials have been determined The lightweight materials can be used as partition walls, floorings, ceiling concretes, bricks and plaster in building.
S2451-9049(17)30521-8 https://doi.org/10.1016/j.tsep.2018.07.014 TSEP 208
To appear in:
Thermal Science and Engineering Progress
Received Date: Revised Date: Accepted Date:
28 December 2017 24 July 2018 25 July 2018
Please cite this article as: A. Bicer, Effect of fly ash particle size on thermal and mechanical properties of fly ashcement composites, Thermal Science and Engineering Progress (2018), doi: https://doi.org/10.1016/j.tsep. 2018.07.014
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
EFFECT OF FLY ASH PARTICLE SIZE ON THERMAL AND MECHANICAL PROPERTIES OF FLY ASH-CEMENT COMPOSITES
Ayse BICER1 Department of chemical Engineering, Firat University, Elazig Turkey
ABSTRACT In this study, fly ash was used in concrete and plaster in place of sand and the impact of fly ash grain size on thermal and mechanical performance of composite material was examined. Fly ash used in the experiments was received from Soma Thermal Power Station and separated into the various grain size groups namely unsieved, >75x10-6 m, (45-75)x10-6 m and <45x10-6 m. In all fly ash and cement mixtures, the weight percentages of fly ash were accepted as 10, 30, 50, 70 and 90%. Cement IV/B (P) 32.5 R was used as the binding material and 20 specimens were prepared according to the grain diameter and percentage of fly ash. Some tests were performed using the new products to find out their detailed properties including density, thermal conductivity, compressive tensile strength, and elasticity module and water absorption. It was found in the experiments that i) as the grain size diameter decreased, ash density increased 16.12%, and porous structure was replaced by full-grain ash and its color turned to light brown; ii) as the ash addition ratio increased 10-90% in fly ash cement mixtures, thermal conductivity coefficient and compressive strength values decreased in the rates of 14.47-24.52% and 1.25-9.4% respectively; iii) concrete or plaster turned into an insulator due to fly ash. Keywords: Fly ash, light concrete, insulation plaster, waste management
Ayse Bıcer, Phone: +90-424-2370000/5504, Fax: +90-424-2415526 E-mail: [email protected]
Nomenclature Porosity, (%) fly ash
: Density of fly ash, (g/cm3)
fly ash matrix : Density of fly ash with 0 % porosity ratio (after milling and so causing no porosity), (g/cm3) cement
: Density of cement, (g/cm3)
cement matrix : Density of cement with 0 % porosity ratio, (g/cm3) Wk
: Dry weight of sample, (g)
Wd
: Wet weight of sample, (g)
Z
: Fly ash ratio, (%)
(1-Z)
: Cement ratio, (%)
1. INTRODUCTION Nearly 15x106 tons of fly ash is generated annually in Turkey at thermal power plants. One of these factories is Soma Power Plant. Storage of fly ash or disposal from the facility is one of the significant problems concerned with power plants. Hence, waste fly ashes’ negative effects on the environment should be assessed. Fly ashes are classified as artificial pozzolanic. Puzzolanic character can be described as a non-bonding material to gain the capacity to be bonding only when mixed with water. The studies accelerated because fly ash of appropriate amounts was used within concrete in place of concrete. Numerous studies were conducted on fly ash up until today. Previous researches shown that fly ash is a potential source of construction material [1].
These studies were summarized in two groups. In the first group, fly ash was assessed as an additive material in cement. Karaşin and Doğruyol [2], reported that there was no change in strength values of concrete when 20% fly ash was added in concrete. The second group consist of studies conducted on partial or complete use of fly ash within the concrete instead of conventional aggregate. This study is included in the second group of studies. Some of the studies that were carried out for this group are summarized as follows: Silva and Andrade [3], researched the mechanical properties of concretes produced with recycled coarse aggregate within the rates of 25%, 50%, 75% and 100% instead of natural aggregate, and taking the water/cement rate as 0.40, 0.45, 0.50, 0.55 and 0.65 in their studies.
Golewski [4], Sunayana and Barai [5], in the studies that were carried out on an individual basis, produced samples using ash at the rates of 20% and 30% instead of natural aggregate, in order to minimize the negative impacts of coal fly ash on nature and to decrease the consumption of cement. The results of mechanical tests applied on the samples displayed comparable results with the natural aggregated concrete. In similar studies, Rafieizonooz et al [6 ], identified the mechanical characteristics of samples porduced with fly ash at the rates of 0, 20, 50 and 100% by Siddique [7], 10%, 20%, 30%, 40% and 50% by Dan [8] and 10%, 30% instead of natural sand. Aydın and Arel [9], as well as Yu et al [10] carried out researches on the physical and mechanical properties of fly ash additive cement in high ratios to reduce the material costs and for using them in low strength concrete practices, in their studies that were carried out on an individual basis. Babu at al [11], Thirumal and Harish [12], Rivera at al [13] and Duran [14], also carried out researches on the mechanical properties of samples produced by partly fly ash instead of sand as aggregate in the concrete within the scope of their individual studies. Li et al [15], proved that the selective dissolution method and thermal analysis method can be used to measure the fly ash content within fly ash additive solidified concrete. As differing from these studies, Yazıcı and Arel added fly ash to concrete in the ratios of 5%, 10%, and 15% and investigated the effect of fly ash fineness on the mechanical properties of concrete [16]. Saumya et al studied the effect of fly ash and vegetable oils on mechanical properties of concrete, which consisted of fly ash, vegetable oil and PVC plastic [17]. In this study, small pores were generated in the structure of ash as a result of coal burning a t high temperatures. By using this feature of thermal power station, it was thought that low density construction material could be produced. In order to determine the effect of fly ash grain diameter on the properties of new materials, ash was divided into four groups namely unsieved ash, and ashes of grain diameters of <45x10-6 m, (45-75)x10-6 m and >75x10-6 m. Thermal and mechanical properties of 20 different samples were determined. In this study, small pores were generated in the structure of ash as a result of coal burning a t high temperatures. By using this feature of thermal power station, it was thought that low density construction material could be produced. In order to determine the effect of fly ash grain diameter on the properties of new materials, ash was divided into four groups namely unsieved ash, and ashes of grain diameters of <45x10-6 m, (45-75)x10-6 m and >75x10-6 m. Thermal and mechanical properties of 20 different samples were determined.
2. EXPERIMENTAL 2.1. Materials Fly ash: Sulpho-calsic fly ash that was produced by burning lignite coal at Soma Power Plant in Kütahya City, Turkey was used in this study. Fly ash had an amorphous structure (glassy), had SiO2+Al2O3+Fe2O3=82.69 % ratio and fulfilled the conditions of ASTM C-350 and TS 639 standards stating that SiO2+Al2O3+Fe2O3 should be minimum 70%. Fly ash’s color is gray, darker than cement’s color, and it is very fine grained and is a soft material sensible when touched by hand. The fineness of ash is generally between 1x10 -6 m - 200x10-6 m. The density values of fly ash are shown in Fig. 1. Density values of fly ashes and cements are shown in Table 1. As seen in microscope, it has a structure with various forms and sizes. It is generally globe-like, transparent, sometimes light in color, partially black, and its grains are light brunette red colored (Fig.2). Its tone depends on the used coal and its burning characteristics. Depending on the burning properties, its principal components are silica, aluminum and iron oxide. Fly ash has a pozzolanic character. The particle distribution of fly ash is 36.4% (<45x10-6 m), 39.3% ((45-75)x10-6 m) and 24.3% (>75x10-6 m) by weight according to their grain diameters. Cement: CEM IV/B(P)32.5 R pozzolanic cement was used to produce concrete. The chemical component of fly ash and cement used in this study and the details of mix proportion are given respectively in Table 2. The water and cement + fly ash ratio (W/(C+F)) is set as 0.5
2.2. Testing methods
The prepared mortars were molded to 100x100x100 mm formworks for mechanical tests and they were molded to 20x60x150 mm formworks for thermal tests and they were left to dry for standard period of 28 days at room temperature. 20 specimens were prepared depending on the grain diameter and percentage of fly ash. At the end of the drying period, the samples were packed and stored until the measurement time.
Thermal conductivity was measured by using Isomet 2104 unit which applies hot wire method according to DIN 51046 standards. Its range and sensitivity were 0.02-10 W/mK and ± 5 % of the scale respectively [18, 19]. Measurements were taken for all samples at 3 different points at room temperature (22-25oC). Thermal conductivity values were determined by calculating arithmetic averages of that measurement. Compressive strength tests were performed on the samples according to ASTM C 109-80 standard [20]. Water absorption test is important to determine the suitability of a material to freezing hazard. The critical amount of moisture is 30% of the total dry-volume and below this volume, the material doesn't deform when frozen [18, 19]. The experiments were performed according to the BS 812 Part 2 standard. Dry and wet weights of the samples need to be known for water absorption ratio estimation. The samples were left at the drying room at 40oC of temperature for 12 hours and subsequently they were weighted by using a sensitive scale and their dry weights were measured. Then, water was added in the test cup and the samples were soaked there for 15 minutes as 1/3, 2/3 and the entire of their bodies to remain in water. Subsequently, they were removed from the water, wiped with a piece of rag, weighted and their wet weights were measured. The water absorption values were calculated by Eq. (1) and they are shown in Table 3. Water absorption ratio={[Wd-Wk]/Wk}.100
(1)
The purpose of drying ratio test was to determine respiration abilities of the samples. After the samples were soaked in water for 48 hours, they were removed, wiped with a piece of wet rag and dried naturally at 22oC room temperature. The drying ratio values were calculated by Eq. (2). Drying occurs by evaporation from the material surface; water moves from the deep of the material through capillary canals, in other words, moisture is expelled from the body through steam permeability resistance and then drying occurs. Drying ratio={[Wd-Wk]/Wd}.100
(2)
Porosity ( is defined by Eq (3), [18].
(3)
3. RESULTS AND DISCUSSIONS
Following coal burning, fly ashes with little beads of different sizes emerge. As grain size shrinks, full beads replace porous beads and the density increases (Table 1). The dry densities of samples cured for 28 days are given in Table 3. The results show that there was a decrease in dry density as the fly ash aggregate content increased. In non-sieved fly ash samples, dry density value of mixtures containing 10% fly ash aggregate decreased from 1.624 g/ cm3 to and dry density value of mixtures containing 90% fly ash aggregate decreased from 1.270 g/cm3. The reduction rate was 21.79% (Fig. 3). This is due to the porous structure of fly ash. As the grain diameter of fly ash was reduced density values increased. In fine grain sized samples, if most of the porous samples were placed with nonporous grains, fly ash samples’ densities got higher. Comparing the densities of fly ash samples with grain sizes >75x10-6 m and densities of the unsieved samples showed that while fly ash densities increased in rate of 10-90%, sample densities were reduced in rates of 6.344.96%. Thermal insulation properties of composite specimens were determined by thermal conductivity test. Thermal conductivity values decreased as fly ash ratio increased (Fig. 4-a). Because interior parts of micro structured pores were full of gases that were generated from burning and the average thermal conductivity coefficient of inert gases is almost 0.0214 W/mK. The minimum thermal conductivity coefficient measured in 90% fly ash samples of grain size >75x10-6 mm ( sa mp le 20) was 0. 2 4 0 W/ mK. I n uns ie ved fly as h sa mp les , t he r at io o f fly as h incr eased fr o m 10% to 90% and thermal conductivity coefficient values dropped to 31.32%. There’s a strong relationship between density and thermal conductivity Fig 4-b). As density dwindles, porous fly particles grow and thermal conductivity of samples dwindles even more. Because of the pozzolanic characteristics of fly ashes, when they are mixed with water without using any bonding material they gain bonding characteristics. Mortars prepared in this way can be used as sub-roof isolation plaster or they can be used as intermediate backfill materials inn sandwich walls. In such plaster forms, thermal conductivity coefficient is 0.2200.230 W/mK, and in dust forms and if they are used as an intermediate back fill material, it was detected empirically that the value was 0.140 W/mK. Figure 5 shows that compressive strengths of ash-free samples (sample with 0% fly ash) and samples with 10% fly ash additives are nearly equal. In other words, addit io n o f fl y
ash t o ceme nt in r at e o f 10% mea ns a saving fr o m t he ce me nt in r at e o f 10%. As lo ng as t he fly as h r at e in t he sa mp les incr ease d co mpr ess ive st r engt hs successive l y in t he uns ieved gr o up , t he gro up wit h a gr ain s ize o f <45x10-6 m, (45-75)x10-6 m and the group with a g r ain s ize o f >75x10-6 m are reduced in rate of 69. 03 %, 62. 08% , 74.17 % and 81. 35% . I n fly as h aggr egat ed mat er ia ls, it is no t int ended t o o bt ain lo wer st r engt h va lues, wher e t he fly a sh r at e incr eases. Ho wever, t he dens it y and t her ma l co nduct ivit y co effic ie nt ar e r educed despit e t his negat iv e char act er ist ic o f t he mat er ia l. T her e fo r e, t he place w her e t he produced samp les ar e go ing t o be used can be clearly identified. Based on these results, it can be recommended that concretes with fly ash (excluding 10% fly ash) must not be used in columns and beams of buildings. Nevertheless, these low density concretes are designated as panel walls, brick, concrete briquettes, inner and outer plaster, concrete partition elements, and insulation material. The results of water absorption of different mixtures are shown in Figure 6. The water absorption increased with the increased fly ash aggregate ratio. Whereas water absorption ratio of the samples, which have fly ash rates ranging between 10 and 30%, are lower than the critical value (30%), the other samples have a value higher than the critical value. Hence, (50-90) % fly ash concrete samples must not be used in places having direct contact with water. They must not also be used against inner wall elements where (briquette or brick) inner plaster, isolation plaster are used as low density construction materials. Table 3 shows that the drying ratios of the samples increased as fly ash ratio increased. The loss of water, which occurs towards the material surface through capillary canals, shows the ability to respire, albeit it is negligible. Considering the adherence experience of the prepared samples on the wall, when construction materials are used such as plaster mortars, brick, briquettes, it was detected that a flat and smooth surface was obtained. Within the processing experiments of fly ash samples, it was detected that it can be cut through by a saw in a proper way, it can be drilled with a drilling machine, a channel through it can be opened, and all sorts of dyes and wall papers shall be applied to such mortars without taking any precautions (Fig 7).
4. CONCLUSIONS
This manuscript was prepared to find out the influence of fly ash particle size on thermal and mechanical properties of fly ash cement composites. The following conclusions can be drawn from this experimental study: Removal of fly ashes from power plants is one of the significant problems of power plants. In this study, it is recommended that fly ash is used along with cement in concrete and plaster applications. Making use of fly ashes and storage and moving these waste materials from power plants can solve the undesired effects and problems. Moreover, significant energy savings can be achieved by using construction materials, which are obtained by using fly ash and which have a low thermal conductivity coefficient, in buildings. The usage area and purposes of fly ash cement composites can be determined by studying the effect of fly ash grain diameter on some properties of concrete. For example, the use of fly ashes with large grains for isolation purpose and the use of fly ashes with small grains in concretes that require strength quality, etc. It is possible to use less cement (10%) in comparison to ordinary concrete or plasters in concrete or plasters consisting of fly ash owing to their puzzolanic properties. Since concrete or plaster gains an insulation property owing to fly ash, heating costs would be lower in buildings. It is hoped that the results of this study will help the economy of the state. In samples with fly ash ratios up to 30%, water suction ratios remain below the critical value. Up to this ratio, fly ash concrete or plaster must be used at locations having direct contact with water without the risk of freezing. The inner surface plasters produced by using fly ash have identical properties as the ordinary plasters such as respiration capability, nailing, boring, cutting, sticking on the wall, giving a smooth surface and painting. The results of the present study have shown that fly ash can be used as sand-substitution in concrete and cement composites and simultaneously solve the environmental problem by recycling waste fly ash.
REFERENCES [1] Xiao H, Wang W. Goh SH. Effectiveness study for fly ash cement improved marine clay. Construction and Building Materials 2017; 157: 1053-1064. [2] Karaşin A, Doğruyol M. An experimental study on strength and durability for utilization of fly ash in concrete mix. Advances in Materials Science & Engineering 2014; 25: 1–6. [3] Silva RS, Andrade JJO. Investigation of mechanical properties and carbonation of concretes with construction and demolition waste and fly ash. Construction and Building Materials 2017; 153: 704-715.
[4] Golewski GL. Improvement of fracture toughness of green concrete as a result of addition of coal fly ash. Characterization of fly ash microstructure. Materials Characterization 2017; 134:335-346. [5] Sunayana S, Barai SV. Recycled aggregate concrete incorporating fly ash: Comparative study on particle packing and conventional method. Construction and Building Materials 2017; 156: 376-386. [6] Rafieizonooz M, Mirza J, Salim MR, Hussin M. Investigation of coal bottom ash and fly ash in concrete as replacement for sand and cement. Construction and Building Materials 2016; 116: 15–24. [7] Siddique R. Effect of fine aggregate replacement with class F fly ash on the mechanical properties of concrete, Cement and Concrete Research 2003; 33: 539–547. [8] Dan R. Properties of fresh concrete incorporating a high volume of fly ash as partial fine sand replacement, Materials and Structures 2004; 30: 473-479. [9] Aydın E. Arel HS. Characterization of high-volume fly-ash cement pastes for sustainable construction applications. Construction and Building Materials 2017; 157: 96-105. [10] Yu J, Lu C, Leung CKY, Li G. Mechanical properties of green structural concrete with ultrahigh-volume fly ash Construction and Building Materials 2017; 147: 510-518 [11] Babu DS, Babu KG, Wee TH. Properties of lightweight expanded polystyrene aggregate concretes containing fly ash. Cement and Concrete Research 2005; 35: 1218-1223. [12] Thirumal JR, Harish R. Performance study of self-compacting concrete by fly ash and silica fume for sustainability in building construction. Engineering Materials 2016; 692: 7481. [13] Rivera F, Martínez P, Castro J, López M. Massive volume fly-ash concrete: A more sustainable material with fly ash replacing cement and aggregates, Cement and Concrete Composites 2016; 63: 104–112. [14] Duran AC. Carbonation-porosity-strength model for fly ash concrete, Journal of Materials in Civil Engineering 2004; 16: 91-94. [15] Li Y, Lin H, Wang Z. Quantitative analysis of fly ash in hardened cement paste. Construction and Building Materials 2017; 153: 139-145. [16] Yazıcı S and Arel HS. Effects of fly ash fineness on the mechanical properties of concrete, Indian Academy of Sciences 2012; 37: 389–403. [17] Saumya KM, Alam M, Hussain A. Effect of fly ash particle and vegetable oil on the mechanical properties of fly ash-vegetable oil reinforced hard PVC plastic. International Research Journal of Engineering and Technology 2016; 3: 833-839 [18] Kaya A, Kar F. Properties of concrete containing waste expanded polystyrene and natural resin. Construction and Building Materials 2016; 105: 572-578. [19] Devecioglu AG, Bicer Y. The effects of tragacanth addition on the thermal and mechanical properties of light weight concretes mixed with expanded clay. Period. Polytech. Civil Eng. 2016; 60(1): 45-50. [20] ASTM. Standard specification for fly ash and raw or calcined natural pozzolan for use as mineral admixture in Portland cement concrete, ASTM, Philadelphia, ASTM C 1985; 618685
FIGURE CAPTIONS Figure 1. Density values distribution of fly ash Figure 2. View of samples under microscope Figure 3. Change of the density according to fly ash ratio Figure 4. Reduction in thermal conductivity according to a) fly ash ratio b) density Figure 5. Reduction in compressive strength according to fly ash ratio Figure 6. Water absorption ratio of samples versus fly ash percentages Figure 7. Samples can be different types of dyes can be applied a) drilling, b) silicone rubber coating and oil painting
FIGURES
Figure 1
Pore
Cement + ash
Figure 2
Figure 3
a)
b)
Figure 4
Figure 5
Figure 6
a)
b)
Figure 7
TABLE CAPTIONS Table 1 Density values of fly ashes and cement (g/cm3) Table 2 Chemical composition of the components (%) Table 3. Thermal and mechanical properties of samples
TABLES
Table 1 Fly ash Cement
unsieved 2.03
>75x10-6 m 1.94
(45-75)x10-6 m 2.29 3.10
<45x10-6 m 2.42
Table 2 Chemical characteristics SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O TiO2 LiO2 Sodium oxide (Na2O) Loss on ignition (L0I) Not available Total
Fly ash 51.25 26.15 5.29 7.85 1.66 0.23 1.3 0.83 0.13 0.67 3.32 -100.4
Cement 18.65 6.15 3.25 57.71 2.34 2.91 0.7 ---2.84 6.08 100.03
Table 3 Code 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Article Fly ash Density Porosity diameter ratio (g/cm3) (%) (x10-6 m) (%) Unsieved 10 1.624 4.18 “ 30 1.558 11.09 “ 50 1.461 17.07 “ 70 1.355 23.02 “ 90 1.270 26.13 <45 10 1.661 3.53 “ 30 1.583 7.24 “ 50 1.524 11.51 “ 70 1.396 15.41 “ 90 1.302 18.98 45-75 10 1.581 4.32 “ 30 1.528 9.34 “ 50 1.433 14.36 “ 70 1.342 19.38 “ 90 1.238 23.62 >75 10 1.521 5.41 “ 30 1.489 13.03 “ 50 1.375 19.12 “ 70 1.305 25.17 “ 90 1.207 29.03
Thermal conductivity (W/m K) 0.463 0.442 0.390 0.349 0.318 0.475 0.457 0.420 0.383 0.362 0.428 0.407 0.350 0.318 0.282 0.396 0.371 0.321 0.286 0.240
Compre. Water strength absorption (MPa) (%) 23.90 24.07 20.40 26.39 16.10 31.17 11.40 32.09 7.4 35.70 24.00 23.58 21.15 24.64 17.15 30.56 12.66 31.02 9.10 33.71 23.70 25.78 20.05 28,89 15.05 31.78 10.08 32.66 6.12 34.08 23.60 27.45 19.15 29,10 14.10 33.06 8.50 34,78 4.40 36.55
Drying ratio (%) 8.16 8.52 8.87 9.13 9.60 8.90 9.17 9.45 9.88 10.14 8.61 8.95 9.05 9.11 9.88 8.03 8.15 8.29 9.0. 9.28
HIGHLIGHTS New lightweight concrete was produced by using fly ash instead of natural sand Thermal and mechanical properties of these materials have been determined The lightweight materials can be used as partition walls, floorings, ceiling concretes, bricks and plaster in building.