4.1 Physical and Chemical Properties
The physical and chemical properties of the air dried F-GFA(AD-F-GFA), oven dried F-GFA(OD-F-GFA), air dried G-GFA(AD-G-GFA), oven dried G-GFA(OD-G-GFA) and natural sand(NS) were analyzed conforming to IS 2386-Part III(1963) and listed out below (Table 4.1.1)
Table 4.1.1 Physiochemical properties of the GFA’s compared with natural sand
Parameter
|
AD-F-GFA
|
OD-F-GFA
|
AD-G-GFA
|
OD-G-GFA
|
NS
|
Water adsorption ratio
|
7.67%
|
7.02%
|
6.96%
|
6.25%
|
0.99%
|
Specific Gravity
|
1.98
|
1.96
|
2.4
|
2.2
|
2.62
|
pH value
|
10.9
|
10.7
|
11.5
|
11.7
|
8.2
|
Zone as per IS 383:2016
|
Zone I
|
Zone I
|
Zone I
|
Zone I
|
Zone I
|
4.2 Particle size Distribution
The particle size distribution curve for the G-GFA and F-GFA were developed (Fig 4.2.1) which is then compared with that of the natural sand as per the standards of IS 383:2016[16]. Three of the curves were noted to be within the limits of zone I with poor grading of the soil. The co-efficient of curvature (Cc) and the co-efficient of Uniformity (Cu) were evaluated for G-GFA, F-GFA and natural sand conforming to IS 1498:1970[17]. For the normal river sand, the values were Cu=1.59 and Cc =0.82. In case of the F-GFA, the observations were recorded as Cu=3.97 and Cc =1.09.Similiar but slightly higher values were noted in G-GFA with Cu=4.52 and Cc =1.32.Thus all the three types of fine aggregates were noted to be categorized as poorly graded soil(well graded soil: Cu>6 and Cc =1-3) as per IS 1498:1970 much similar to the earlier studies[Rao et al, 2014; Wanjari et al, 2011]
4.3 Optical Microscopy Analysis
In order to visualize the microstructure of the agglomerated particles of the fly ash (Fig 4.3.1) and GGBS (Fig 4.3.2), the optical microscopy testing is conducted for the GFA developed and thus the polymerization in the GFA was corroborated. The samples of fly ash, GGBS, F-GFA and G-GFA were visualized with the help of optical microscope that generates the micrograph under visible light and an arrangement of system of lenses. The images seen in Optical microscope were captured by ordinary photosensitive camera to obtain the micrograph. The micrographs thus obtained clearly substantiate the agglomerated particles formed from the fly ash and GGBS along with the alkaline solution under the suitable conditions.
4.4 X-Ray Diffraction Analysis
The XRD patterns of the F-GFA and G-GFA (Fig 4.4.1) were obtained using X- ray diffractometer D8 Advance ECO XRCD systems with SSD160 1 D Detector and upon the further analysis of the results with the recent version of JCPDS software, the implications were procured accordingly. The XRD pattern of F-GFA showcased a high peak between 25.81˚ to 26.98˚ which is attributed to the presence of glassy phase [Ward et al, 2006]. Few other multiple average peaks were noted at 16.53˚, 20.95˚, 30.86˚, 33.29˚, 35.23˚,39.34˚, 40.91˚,45.92˚, 50.31˚, 60.69˚ and 66.94˚ indicating the presence of silica, sodium, aluminum, hydrogen & carbon compounds (plumbonacrite) and compounds of chlorides & oxides(chloranil) imparting the crystalline nature for the F-GFA and consequently initiates geopolymerization process in the same.
Whereas the XRD pattern of G-GFA exposed a broad hump between 24.50˚ and 34.90˚concentrated with calcium oxides, Alumina, Oxides, Iron and Sodium traces. The same traces were found throughout the diffraction pattern in lower peaks also depicting the amorphous nature in more portion. Few traces of Titanium, Calcined Alumina and Berilium were also noted in the G-GFA samples. Altogether, the G-GFA was noted to inhibit a crystalline combined with amorphous microstructure indicating the incomplete dissolution of the parent material which later imparts the hardened property in the developed mortar samples [Agrawal et al, 2017; Sharma et al, 2019].
4.5 SEM Analysis of the GFA
The GFA thus developed were analyzed for surface morphology with Scanning Electron Microscope EVO 18(CARL ZEISS) to corroborate the microstructure which can be further adapted to analyze the mechanical and durability studies of the mortar and concrete specimens. The samples of flyash, GGBS, F-GFA, G-GFA and NS were analyzed and presented in Fig 4.5.1 to Fig 4.5.5. Both F-GFA and G-GFA showcased the agglomerated crystal-like structures formed due to the polymerization process in the micrograph. In F-GFA, the glassy phase is turned out into crystal like grain structures whereas higher version of crystal-like grain structures with better pore structure is noted in the G-GFA ascertaining the formation of the geopolymerized sand through polymerization reaction. Few unreacted particles of fly ash as well as GGBS were noted in the F-GFA and G-GFA that remained as it is without reacting with the alkaline solution. These unreacted particles act as nucleation sites and as fillers also thereby contributing better binding nature due to the heterogeneous structure of the micrographs of F-GFA and G-GFA. These nucleation sites allow the reacted particles to amass it in the surroundings developed by the interlocking of the aluminum and silicon ions with the alkaline solution which apparently polymerize into aluminosilicate networks promoting the glassy phase into crystal like structure[Sharma et al, 2019]. Nevertheless, significantly similar micrographs were obtained in the GFA developed by both oven drying and air drying.
4.6 Compressive strength
Mortar cubes were casted to experimentally determine the compressive strength of the OD-F-GFA, AD-F-GFA, OD-G-GFA and AD-G-GFA which can be compared with the results (Fig 4.6.1) of the mortar specimens casted with NS. 15 mortar cubes were casted with a w/c ratio of 0.9, 0.85, 0.75, 0.7 and 0.4 for OD-F-GFA, AD-F-GFA, OD-G-GFA, AD-G-GFA and NS respectively. The higher water absorption of the F-GFA and G-GFA particles effectuated the respective mortar specimen to exhibit higher w/c ratio for the mortar mix. The compressive strength of the mortar samples was determined conforming to IS 2386(part 6):1986 by casting three replicate cubes of size 70.7mm×70.7mm×70.7mm. These specimens were allowed for ambient curing(32˚C) for a duration of 24 hours followed by water curing in a tank of tap water. Thus, the specimens were cured for 28 days.
A compressive strength of 19.9 N/mm2 , 17.6N/mm2, 20.11 N/mm2 ,21.16 N/mm2, and 23.5 N/mm2 were obtained for OD-F-GFA, AD-F-GFA, OD-G-GFA, AD-G-GFA and NS respectively. The strength attained in F-GFA and G-GFA samples can be owed to the un reacted particles [Agrawal et al,2017] in fly ash and GGBS which later on reacts with the lime discharged from the hydration process of cement particles thus counterbalancing the effects of higher w/c ratio in the mortar samples[Rao et al, 2014]