Abstract--Carbon Capture and Storage (CCS) has appeared as an efficient approach to alleviate the intimidating effect of the growing concentration of CO2. Recently, Fly-ash (FA), which is an industrial alkali residue and rich in metal oxides, has been proven as one of the potential agents for CCS through mineral carbonation. In this research, an attempt has been made to sequester CO2 by using FA via chemical activation technique and subsequently use this Carbonated Fly Ash (CFA) as filler materials to fabricate a new class of E-glass fiber reinforced polymer (GFRP) composite. Further, the dry sliding wear properties (Pin-on disc) of these CFA composites are investigated at room temperature according to Taguchi design of experiment and the effect of diverse control factors are deliberated. The ANOVA revealed that the applied normal load and weight% of CFA significantly affect the wear rate of the presently developed CFA composites and the optimal SWR is attained corresponding to 10 wt.% CFA, 50N Load and 339rpm.
Keywords--Mineral Carbonation, Carbonated fly ash, GFRP Composite, Pin-on disc wear test, Taguchi experimental method, Optimization.
I. INTRODUCTION
A composite is a man-made material made up of dissimilar materials with significantly different chemical and physical properties, when merged together produce a material with quite different characteristics. They are popular in fields such as sports equipment, aeronautical industries, aerospace and civil construction and marine structures. Fiber-reinforced composites have found a vital importance as structural components in high performance engineering industry due to their specific properties. Synthetic fibers like glass, carbon, aramid (Kevlar) etc. are being widely used in polymer matrix composites (PMCs) because of their high stiffness, strength light weight properties. Glass fibres are a type of thermal insulator that is made from molten glass. In the reinforcing glass layers, they usually have a laminate structure with varied fibre orientations. They have desired fibre qualities including strength, stiffness, and flexibility, as well as beneficial bulk properties like hardness, stability, and inertness.
Fillers are added to a polymer matrix for one or more of reasons like to reduce weight and cost, increase stiffness, thermal resistance, stability, strength, etc. Addition of ceramic filler materials improves the surface quality, strength and performance of PMCs in industrial and structural applications (Vigneshwaran et al., 2018). Fly ash (FA, the burnt end result of pulverized coal from thermal power plants) is widely regarded as the most significant industrial waste. It consists 54% of SiO2, 15% of Al2O3 and 12% of CaO and potentially used as functional filler in synthetic/natural fiber PMCs (Gangwar and Pathak, 2021). We also note that numerous methods have been adopted in past by the researchers related to CCS through FA as medium. In this regard, a simple and flexible CO2 capture technology with reduced energy consumption is the chemical adsorption process. It is the surface phenomenon, essentially the attraction between the adsorbate molecules and an adsorbent surface. The fly ash with CO2 sequestration and storage in ex-situ mineral carbonation is regarded as Carbonated Fly Ash (CFA). CFA has been successfully used as the partial replacement of cement in concrete (Dhal et al., 2014) but, the use of CFA as filler material for the fabrication of PMCs and exploring its potential use is yet to be investigated.
Among other properties, wear behaviour is vital for PMCs that makes them suitable for tribological applications over conventional metallic materials (Edoziuno et al., 2021; Chetia and Samanta, 2020; Upadhyay and Kumar, 2018; Difallah et al., 2012). Improvement of wear characteristics of the PMCs is a major challenge for the researchers for mitigating their applicability under sliding environment. Therefore, the wear analysis of GFRP composites filled with Bio waste (Pradhan et al., 2021; Ranganathan et al., 2019) as well as industrial wastes namely blast furnace slag (Padhi et al., 2015), SiC particles (Patnaik et al., 2008), red mud (Satapathy and Patnaik, 2010), rice husk ash (Rout and Satapathy, 2012), walnut shell powder (Doddamani et al., 2017), Cenosphere (Singh and Siddhartha, 2015), marble dust (Lendvai et al. 2021) and FA (Sharma, et al. 2021; Gohatre et al., 2020; Pattanaik et al., 2016) have been performed every now and then. Taguchi’s experimental design method have been effectively implemented to identify the significant control factors affecting the wear rate and subsequent optimization. It has also been revealed that the reinforcement of FA particles significantly enhances the mechanical as well as tribological properties of PMCs (Kasar, et al., 2020; Barpanda et al., 2009). Moreover, the hybridization leads to improvement in the mechanical as well as the tribological properties of the PMCs (Praveenkumara et al., 2021).
It is understood that a good amount of work is already completed on the incorporation of diverse filler materials for preparing composites with varied matrix material (epoxy/polypropylene) including the mechanical, thermal, tribological and the water absorption characterization. Several studies have been conducted on carbon capture potential of FA and FA has been proven to be a potential feedstock for the permanent CO2 sequestration and storage in ex-situ mineral carbonation (regarded as the CFA). The CFA has been successfully used as the partial replacement of cement in concrete but, the use of CFA as filler material for the fabrication of GFRP composite and exploring its potential use is yet to be investigated. In view of this, the present research aims to analyze the potential applicability of a new class of GFRP composite filled with CFA. Firstly, CFA is prepared by indirect carbonation via chemical activation technique. Then, GFRP composites with five different weight percentage of CFA have been prepared and their physical properties are evaluated. Subsequently, the dry abrasion wear behavior of these composites was investigated and the effect of process parameters are reported.
II. EXPERIMENTAL PROGRAM
The scope of the present study is initially, to prepare the carbonated fly ash via indirect carbonation technique. Then, to fabricate GFRP composite plates filled with five different weight percentage (0%, 5%, 10%, 15% and 20%) of CFA by hand lay-up technique. Subsequently, to evaluate the physical properties of the aforementioned composites and study the dry sliding wear behaviour using statistical techniques.
A. Carbonated Fly Ash (CFA)Preparation
Sample raw Fly ash was collected in small crystal form Hindalco, Hirakud, India. The fly ash was dried for 2 days under the sun and then crushed and sieved up to below 90-micron sizes using a sieve shaker of make Aimil Ltd., as per IS:460. Around 10 kg of normal fly ash is sieved to get the desired size of material which weights 200gm. Then, the fly ash has been carbonated by chemical activation technique and the process is shown in Fig. 1. The fly ash as raw crystal and in powder form after carbonation (CFA) is shown in Fig. 2 and 3, respectively.
B. Specimen Preparation
The epoxy (LAPOX L-12) with density 1.1gm/cm3 and hardener (K-6) procured from Harippa Industries, Kolkata, India was thoroughly mixed (in 10:1 ratio) with gentle stirring to minimize air entrapment. Then, required CFA powder were added to the mug with different weight ratios and mixed thoroughly. In this analysis, composite plates with 5 different wt.% of CFA as filler material are prepared. The mixture of epoxy, hardener and filler was applied uniformly above each sheet of E-glass fiber layer by layer for all the 10 sheets. For quick and easy removal of composite sheets, silicon spray was applied at the lower and upper surface of the composite plate on the Teflon sheet. To avoid formation of air bubbles care is taken. The total set up was allowed curing at room temperature for 24 hours with load (approximately 25 to 30 kgs) applied uniformly on the composite plate. After 24 hours the plate was taken out. The composition of 5 different types of composites prepared in the present analysis is depicted in Table 1.
Figure 1: Process flow diagram for CFA preparation by chemical activation.
C. Density and Dry Sliding Wear test
Density Test:
The densities of the above five types of composite specimen were
obtained by the Archimedes’s principle. The composite samples (20mm×20mm×5mm)
were taken for the measurement of the density of the different samples. First,
the specimens were measured for weight. The specimens were tied with a string
having negligible mass. Then, the particular samples were slowly dipped into
distilled water and measured in a digital weighing machine. The measured values
with water were recorded manually. Then the ratio of the specimen weight and
the floating weight gives the result of the relative experimental density. To
get the value of theoretical density, the dimensions of the specimen were
measured. The ratio of mass and the corresponding volume gives the
numerical/theoretical density value. The volume fraction of voids (
) present in
the composites is calculated as per Eq. 1.
(1)
where 
= Theoretical
density and 
= Experimental
density.
Dry sliding wear test:
In general, the GFRP composite materials have
insufficient wear resistance in unlike abrasive wear environment. Therefore,
the assessment and enhancement of wear properties of these composites is very
much necessary for justifying their structural application in abrasive wear
environment. The wear behaviour of the currently developed composite samples is
evaluated utilizing a pin-on-disc tribometer of 20kg capacity (TR-20LE,
(a)
(b)
Figure 4: (a) Wear test specimens, (b) Dry sliding wear test rig (DUCOM; TR-20LE).
DUCOM, Novus Tribo Solutions, Bengaluru 165F; En31 hardened to 60 HRC wear disc ground to 1.6Ra and 8mm thickness). Using the above-mentioned equipment, the current CFA composites are employed as the pin material to determine the dry sliding wear behaviour at room temperature. Wear test is performed as per ASTM G65 standard. The wear test specimens (Cylindrical specimen with 10mm diameter and 5mm length) for three different types of composites and the sliding wear machine are shown in Fig. 4 (a) and (b), respectively.
Before each experiment, a load is applied manually by placing the
necessary weight discs. The disc is rotated with the help of an AC motor, while
the flat sample surface remains stationary. The mass loss is obtained and the
Specific Wear Rate (
) was
calculated by using the equation:
(2)
where 
, 
, 
, 
and 
are the mass
loss (g), density (g-mm-3), test duration (s) applied load (N) and
sliding velocity (ms-1), respectively.
D. Experimental Design
In order to avoid time consuming and expensive test procedures during experimentation, a design of experiment (DOE) approach based on Taguchi’s orthogonal array is implemented for recognizing the control factors those have significant impact on the wear characteristic of presently prepared composites. The most crucial stage in the DOE is the selection of control parameters. As a result, a number of variables are added to the equation in order to quickly identify and eliminate non-significant factors. Wear tests on composites are conducted under various working conditions based on machine capacity, taking into consideration three parameters (wt. % of filler material, load, and speed in rpm) with three levels as given in the table below (Table 2). The disc of diameter 165 mm, made up of stainless steel is cleaned with acetone before and after each test performed at different experimental conditions.
Table 2. Process parameters and their selected levels for dry sliding wear test of CFA composite
Table3. Density data for carbonated fly ash (CFA) based composite.
The L9 orthogonal array is used to investigate the
effects of these three parameters, and the experiments are carried out at room
temperature. The experimental data are then used to calculate the signal to
noise (
) ratios. The ratio is a
technical term that compares the amount of background noise to the level of a
desired signal (output). The ratio for the
lowest wear rate can be described as a smaller is better characteristic because
the purpose of this study is to minimize the wear rate. A high ratio equates
to improved performance with the least degree of instability and variability,
regardless of performance criteria. The S/N ratio (loss function logarithmic
transformation) for smaller-is-better criteria is calculated as follows:
(3)
where, 
is the number
of observations and 
is the
observed data.
III. RESULTS AND DISCUSSION
The densities and volume fraction of voids (%) for each type of CFA composites are provided in Table 3. Lower values of void percentage indicate the reliability in preparation of the composite samples. It is interesting to note that the volume fractions of voids are reduced considerably for higher weight percentage of filler. This may be due to good packing characteristics of the CFA with the matrix material.
Sliding wear tests are conducted as per Taguchi’s L9 orthogonal array. MINITAB 17, a software designed primarily for DOE applications, was utilized to conduct the study. The experimental design, test circumstances and results of dry sliding wear of CFA composites (Specific Wear Rate (SWR)) along with the corresponding S/N ratios values as obtained in the statistical analysis are provided in Table 4.
The influence of the control parameters on SWR is graphically
depicted in Fig. 5 (a) and (b). The graphs demonstrate how the ratio changed as
the control factor's setting was modified from one level to the next. The main
effects plot can be used to examine the impact of each
