Effect of Mechanical Properties of Cementitious Composites Having Optimized Particle Size Distribution of F-Class Fly Ash

*İlhami Demir and Ahmet Filazi* 

### **Abstract**

 Although gradation is considered in aggregates, it is ignored in powder materials such as cement and fly ash. Unless there is fine gradation, the void ratio will be high, and the products obtained as a result of hydration will not be able to fill all of the cavities. In this study, fly ash was sieved through vacuum sieves to determine gradation of the fly ash at 0–20-, 20–38-, 38–45-, 45–53-, and 53–63-μm intervals. Gradation of fly ash was optimized in these intervals. Using the Fuller-Thompson equation, depending on their particle size distribution and finding most ideal distribution module (n = 0.4), a more rigid structure was formed. The cement mortar was produced by substituting 0–60% of the optimized F-class fly ash with the particle size distribution. For the design of the most ideal "n" particle module of the cementitious composite created, mechanical strengths were investigated for 20% F-class fly ash (FA)-substituted cement mortar according to TS EN 196-1. After obtaining (n = 0.4) that compressive and flexural strengths of F-grade FA-substituted cementitious composite of 0–60% were tested, it has been observed that the same age of optimized fly ash-substitute cement mortar is better than unoptimized ones in compressive and flexural strengths.

**Keywords:** F-class fly ash, cement mortar, particle size optimization, mechanical strength

#### **1. Introduction**

 The damage to the environment during cement production is high; approximately 1-ton CO2 gas is released during production of 1 ton of cement [1]. In addition, too much energy is required to produce 1300 C to 1450 C in rotary kilns to produce cement. Cement is the most important material used in concrete production. By replacing the cement with various pozzolanic materials, a more economical and more environmentally sensitive concrete production will be achieved.

 The materials that do not have binding properties on their own but which have the property of binding with another binder such as cement are called pozzolans. In these materials, silica and alumina are present in the colloid, which binds to pozzolans [2]. The most widespread pozzolan is fly ash. This fly ash is a product that is produced by the combustion of ground coal in thermal power plants. The flue gases

 are obtained by collecting the fine particles in these gases before they are released into the atmosphere by the dust collection system. Particles are generally spherical and their diameters range from 1 to 150 μm [3]. The chemical composition and properties of the fly ash vary depending on the structure and composition of the used coal and ash formed by the combustion process [4]. The pozzolans are mineral additives which increase the physical, mechanical, and durability of cement of the concrete naturally and artificially with the development of concrete technologies and which contribute economically as a result of cement savings by replacing it with cement. Its use is increasing day by day. These materials play an important role in the formation of hydration products and play an important role in the desired properties of concrete by changing the structure of the bonding dough [5]. The world's fly ash production is approximately 450 million tons per year, but only 6% of it is used in the cement and concrete industry. The fly ash is about 15 million tons of annual production in Turkey, but its use in industry is low. There are two reasons for this: (i) inadequate information on fly ash properties; (ii) not always uniform fly ash properties [6, 7].

 To this day, various particle size distributions have been used for an economical concrete design. When selecting the particle size distribution, the gaps between large particles must be selected to be filled. Firstly, the distribution of particle was studied for an economical concrete design [8]. Fuller and Thompson methods have been used for determining the rate at which concrete aggregates are mixed during particle size distribution optimization [9]. Some researchers have suggested different values for the base in the equation to adjust the ideal curve (fuller curve) for special concrete [10]. For the design of particle size optimization, special concrete with a high content of filler was used. Furthermore, particle size optimization is an important concept for more environmental concrete production because the density of the highest particle size of aggregates is filled with cement mortar according to the lowest amount of cavities. With this method, it is stated that sufficient strength can be obtained with the mixture of aggregate and cement [11]. Some researchers working on aggregate gradation have proposed to design an ideal aggregate particle distribution curve. The granulometry curves obtained with the help of the formulas which were developed and presented to the literature yielded high compactness of the aggregate [9, 12]. These methods are made on the aggregate but not applied to provide high compactness in materials such as fly ash. The following are the purpose of this study: F-class fly ash particle size distributions are sieved by vacuum sieves to produce appropriate particle size distributions, to determine the optimum particle distribution by examining the effect of F-grade fly ash-substituted cementitious composite containing the formed particle size distributions on the strength, and to obtain the optimum design.

#### **2. Experimental program**

#### **2.1 Materials used during work**

#### *2.1.1 Portland cement*

 In the study, CEM I 42.5 R type Portland cement according to TS EN 197-1 was used [13]. The physical and chemical properties of the cement used are given in **Table 1**.

#### *2.1.2 CEN reference sand*

 Standard sand used in the study is CEN reference sand specified in TS EN 196-1 standards [14]. While preparing mortars and utilizing F-class fly ash with *Effect of Mechanical Properties of Cementitious Composites Having Optimized Particle Size… DOI: http://dx.doi.org/10.5772/intechopen.87836* 


#### **Table 1.**

*Chemical and physical properties of Portland cement and F-class fly ash.* 

 optimized PSDs, CEN standard sand which was in compliance with the TS 196-1 standard was also used.

#### *2.1.3 Fly ash*

In this study, F-class fly ash which is planned to be used in the cement mortar mixtures produced by Fuller-Thompson method is provided according to the standard specified in ASTM C618-15 "Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete." Physical and chemical properties of fly ash used according to particle size analysis are given in **Table 1**.

#### **2.2 Mixing ratio**

During the study, optimized particle distribution and untreated fly ash-substitute cementitious composite were prepared according to TS EN 196-1. The proportion of mortar components was prepared by mass: 1 part cement, 3 parts standard sand, and ½ part water (water/cement ratio: 0.5). Each mixture consisted of 450 ± 2 g fly ash-substitute cement, 1350 ± 5 g standard sand, and 225 ± 1 g of water. Materials at laboratory temperature are weighed with a scale of ±1 g [15]. Cementitious composite was produced by replacing 0% by weight of cement, 5, 10, 15, 20, and 60% by fly ash. Produced cementitious composite was kept in a moisture environment for 24 h and then matured in water cure until the desired age. The ratio of water-binding material (S/BM) in the fly ash-substitute cementitious composite produced during the study is (S/BM) 0.50. **Table 2** shows the material ratios of the mixtures.

#### **2.3 Method**

#### *2.3.1 Particle size distribution optimization of F-class fly ashes*

Class F fly ash 0–20-, 20–38-, 38–45-, 45–53-, and 53–63-μm intervals as shown in **Figure 1** by sieving the sieve size were determined by vacuum sieve. The sieving


**Table 2.** 

*Cement mortar mixing ratios.* 

*Effect of Mechanical Properties of Cementitious Composites Having Optimized Particle Size… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

**Figure 1.**  *Vacuum sieve system.* 

process is designed for each particle size with the help of vacuum sieve. In order to obtain particle size distribution, optimization by using Fuller-Thompson equation was used in normal concrete design (Eq. (1)).

$$\mathbf{P} = \mathbf{100.(d/D)}^{\mathbf{n}} \tag{1}$$

P(D), percentage of total material smaller than mesh size D; D, maximum particle diameter for fly ash; d, minimum particle diameter for fly ash; n, distribution module.

The proportions of the materials in the total mixture were determined according to the percentages obtained for the different values of the distribution module n. In this way, for different purposes using different distribution module, a specific purpose-appropriate cement mortar was designed. According to the equation for each of the fly ash, the distribution module n = 0.3 to n = 0.6 was increased with a precision of 0.05, and optimum particle distribution was determined according to the n distribution module n = 0.35–0.45. Optimum particle distribution was determined as n = 0.4 by minimizing the sensitivity 0.02 between the two most suitable values.

The proportions of the materials in the total mixture were determined according to the percentages obtained for the different values of the distribution module n. In this way, for different purposes using a different distribution module, a specific purpose-appropriate cement mortar design was prepared. As the numerical value of the distribution module increases, the mixture becomes larger, decreases, and turns into a thinner mixture. For particle distribution, particle diameter is 0–63 μm. According to these materials, the distribution curves were obtained based on the percentages for each distribution module.

 The particle size distribution to be designed is determined by 20% of the fly ash to the cement. A 20% replacement rate was chosen to further understand the efficacy of fly ash. After obtaining n distribution for optimum design, for 5, 10, 15, 20, 25, 30, 35, 40, 50, 50, and 60% substitution proportion, optimum design was obtained.

#### *2.3.2 Determining flexural and compressive strength of F-class fly ash optimized particle size distribution*

Flexural strengths of cementitious composite with fly ash dispersion optimized and not optimized have been prepared according to TS EN 196-1. The cementitious composite, which was kept in normal water for 7, 28, and 90 days for flexural strength, was removed from the curing pool and subjected to the flexural strength test at N/s loading speed of TS 196-1 (50 ± 10) with the flexural strength test given

in **Figure 1,** 40 × 40 × 160 mm size prismatic bars, three pieces for each value, and three results are evaluated by taking the arithmetic mean. The compressive strengths of cementitious composite with fly ash substitution optimized and unoptimized have been prepared according to TS EN 196-1. As a result of the flexural strength, six 40 × 40 × 40 mm cementitious composites were tested by pressure piston. The compressive strength device has been set at the appropriate capacity and N/s loading speed according to TS 196-1 (2400 ± 200). After the flexural strength test, the half prisms to be obtained were placed in the center of the device with no more than ±5 mm. The device (2400 ± 200) is loaded at N/s until the prism breaks [14].

#### **3. Experimental findings and discussion**

#### **3.1 F-size distribution of F fly ash by vacuum sieve**

 In the study optimization was made by using Fuller-Thompson formula P = 100 (d/D)<sup>n</sup> used in the design of the cement. The proportions of the materials in the total mixture were determined according to the percentages obtained for the different values of the distribution module n. In this way, a different distribution module was used for different purposes, and a specific concrete design was made. According to the equation for each of the fly ash, the distribution module n = 0.3–0.6 was increased with a precision of 0.05, and the optimum particle distribution was determined by n = 0.35–0.45. Optimum particle distribution was determined as n = 0.4 by minimizing the sensitivity 0.02 between the two most suitable values. The proportions of the materials in the total mixture were determined according to the percentages obtained for the different values of the distribution module n. In this way, for different purposes using a different distribution module, a specific purpose-appropriate cement mortar design was prepared. As the numerical value of the distribution module increases, the mixture becomes larger, decreases, and becomes a thinner mixture. For particle distribution, particle diameter is 0–63 μm. In **Figure 2**, the percentages of the total material passing through the sieve diameters specified for the 20, 38, 45, 53, and 63 sieves we use for the values taken by the "n" distribution module were determined, and according to these determined materials, distribution scales were obtained by taking the percentages for each distribution module.

 In this study, the effect of particle distributions on mechanical properties according to different n distribution modules was analyzed. In order to see the fly ash activity according to the different values of "n" distribution module, 20% fly ash-substituted cement mortar mechanical properties were analyzed. The results of 7- and 28-day strengths of cementitious composite with 20% F-class fly ash are given in **Figures 3** and **4**.

 According to **Figure 3**, F-class fly ash-aged cement has been determined to give the best flexural strength of 0.4 dispersion modules for different distribution modules. While the distribution module was increased from 0.3 to 0.4, the flexural strength was increased, and the flexural strengths of the distribution modules from 0.4 to 0.6 were reduced. n = 0.4 dissipation module provided the highest increase in the compactness of flexural strengths. Considering the flexural strength of 7 days, the highest flexural strength was 6.02 MPa for n = 0.4 dispersion module. Considering the flexural strength of 28 days, the highest flexural strength was obtained as 9.52 MPa for n = 0.4 dispersion module.

According to **Figure 4**, the best compressive strengths of F-class ash-aged cement for different distribution modules were determined as 0.4 dispersion modules. While *Effect of Mechanical Properties of Cementitious Composites Having Optimized Particle Size… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

**Figure 2.**  *Particle distribution curves for different distribution modules.* 

**Figure 3.**  *7- and 28-day flexural strengths of F-class fly ash-cementitious composite.* 

**Figure 4.** 

*7- and 28-day compressive strength of F-class fly ash-controlled cementitious composite.* 

the distribution module was increased from 0.3 to 0.4, the compressive strength was increased, and the compressive strengths of the distribution modules from 0.4 to 0.6 were gradually decreased. The distribution module gave the best compressive

 strength values for 0.3.5–0.45. This is why we can see the filler effects in cementitious composite very well. n = 0.4 dissipation module provided the highest increase in the compressive strength. When 7-day compressive strengths were taken into consideration, the highest compressive strength was 32.57 MPa for n = 0.4 dispersion module. When 28-day compressive strengths were taken into consideration, the highest compressive strength was obtained as 43.40 MPa for n = 0.4 dispersion module. In the particle dispersion optimization study for F-class fly ash, high values were obtained with the filler effect, and high values were obtained in the pressure and flexural strengths of 7 days and 28 days in the distribution modules q = 0.3, q = 0.4, and q = 0.5. In the n = 0.4 distribution module, the highest increase in the pressure and flexural strength was obtained by providing the maximum increase in the compactness. According to the obtained results, it is seen that particle distribution has a very important place in the effect of filler by looking at changes in pressure and flexural strength. The filler effect provides high occupancy by minimizing the gaps in fly ash distribution. This ensures a high dispersion of the compactness. As in the aggregates, it was observed that fly ash was also very good with high compaction. According to these results, the best filler effect was found to be effective on fly ash. For the n = 0.4 dispersion module, high compressive strengths were obtained according to the reference strengths by obtaining the best component and filler effect. With the filler effect, it was observed that the pressure strength of 28 days increased significantly compared to the reference compressive strength.

#### **3.2 Production of cement mortar by replacing the F-class fly ash with 0–60% cement in optimized particle size distribution**

 After "n" distribution, for 5, 10, 15, 20, 25, and 30% substitution proportions, designs were made according to n distribution module for best optimum design. In order to determine the optimum particle size ratio, cementitious composite was subjected to flexural and pressure tests according to TS EN 196-1.

 As shown in **Table 3**, in 7 days' flexural strengths, optimum flexural strengths increased by 7.40% at 5%, 7.84% at 10%, 7.95% at 15%, 8.07% at 20%, 9.16% at 25%, and 9.61% at 30% with the difference of unoptimization related to compressive strengths. The highest flexural strength among the results of 7 days was obtained as 6.68 MPa in 5% optimum F-class fly ash-substituted cementitious composite. The flexural strength in the 5% substitution ratio was 4.91% higher than the flexural strength of unreinforced cementitious composite. As seen in **Table 3**, the optimum bending strengths of all substitution ratios were higher than the unoptimized F-class fly ash-substituted cement mortar flexural strength. After determining the bending strength at 28 days, related to unoptimized compressive strength, optimum bending strengths of 20.27% at 5% substitution rate, 20.26% at 10%, 21.05% at 15%, 21.27% at 20%, 21.63% at 25%, and 21.91 at 30% increase were observed. Among the 28-day results, the highest bending strength was obtained as 10.68 MPa in 5% optimum F-class fly ash-substituted cement mortars. The bending strength of the 5% substitution ratio was 18.40% higher than the bending strength of additive-free cement mortars. The optimum cement mortars with 10, 15, 20, and 25% substitution were higher than the unsupported cement mortar. Among the 90-day results, the highest bending strength was obtained as 13.12 MPa in 5% optimum F-class fly ash-substitute cement mortars. The bending strength of the 5% substitution ratio was 14.88% higher than the bending strength of additive-free cement mortars. As shown in **Table 3**, the optimum bending strengths of all substitution ratios were higher than the unsupported F-class fly ash-substitute cement mortar bending strengths. Bending strengths of 5, 10, 15, 20, 25, and 30% of the optimum fly ash substitution ratio were higher than unsupported bending strength.

#### *Effect of Mechanical Properties of Cementitious Composites Having Optimized Particle Size… DOI: http://dx.doi.org/10.5772/intechopen.87836*

As can be seen in **Table 4**, in the 7-day compressive strengths, optimum compressive strengths 7.80% at 5%, 7.93% at 10%, 8.47% at 15%, 8.47% at 15%, 12.38% at 20%, 12.43% at 25%, and 12.52% at 30% increase were observed. Optimal substitution rate of 5% was found to be the best for 7-day compressive strength. The compressive strength of 5% substitution rate was 2.18% higher than the compressive strength of unreinforced cementitious composite. Optimal compressive


**Table 3.** 

*7, 28, and 90 daily average flexural strengths of F-class particle distribution and non-particle distribution.* 


**Table 4.** 

*7, 28, and 90 daily average compressive strengths of F-class particle distribution and non-particle distribution.* 

 strengths were higher than the non-optimization strengths at all replacement rates. The compressive strength of 5% optimized fly ash displacement rate is higher than the unsupported compressive strength. The compressive strength of 10, 15, 20, and 25% optimum F-class fly ash replacement ratio was very close to the value of the unsupported compressive strength. In the compressive strengths of 90 days, the optimum compressive strengths were determined as 6.24% at 5%, 6.43% at 10%, 6.60% at 15%, 6.85% at 20%, 6.95% at 25%, and 7.25% at 30% increase in compressive strength. The highest compressive strength of 90-day results was obtained as 54.46 MPa in 5% optimum F-class fly ash-cementitious composite. The optimum replacement rate was found to be 5%, which best improves the compressive strength of 90 days. The compressive strength of the 5% substitution ratio was 3.75% higher than the compressive strength of unadulterated cementitious composite. Optimal compressive strengths were higher than the non-optimization strengths at all replacement rates. The compressive strength of 5, 10 and 15% optimum F-class fly ash was higher than the unsupported compressive strength. The compressive strength of 20, 25 and 30% optimum F-class fly ash displacement was very close to the value of the unsupported compressive strength.

### **4. Conclusions**

Within the scope of the study, F- and C-class fly ash n distribution modules divided into 5 different groups as 0–20, 20–38, 38–45, 45–53, and 53–63 μm, by increasing its distribution module between n = 0.3 and n = 0.6 0.5 in sensivity, between n = 0.35 and n = 0.45 0.02 precision n distribution module for different values of mechanical properties, were investigated. The results are given below:


*Effect of Mechanical Properties of Cementitious Composites Having Optimized Particle Size… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

amount of cement required for the same target distribution will decrease, and the use of fly ash will increase.

As a result, the high capacity of the fly ash is optimized, and the mechanical properties have been improved in good proportions. By making the fly ash particle distribution optimization, the amount of cement required for the same target distribution will decrease, and the use of fly ash will increase. In this way, the cost of concrete obtained will decrease, the use of waste materials will increase, and the release of carbon dioxide (CO2) into the nature will be reduced by the less use of cement. The high occupancy effect, i.e., the finding of the best particle distribution providing the compaction, will reduce the amount of carbon dioxide (CO2) emissions that pollute the environment in the cement production and will contribute to the economy of the country by saving on the economy by saving a lot of cement.

#### **Acknowledgements**

The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council of Turkey (TUBITAK) provided under Project: 115 M325.

#### **Author details**

İlhami Demir and Ahmet Filazi\* Department of Civil Engineering, Kırıkkale University, Kırıkkale, Turkey

\*Address all correspondence to: ahmetfilazi@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 21**
