Influence of Utilization of Fly Ash as Sand Replacement Agent in Sustainable Flexible Pavement

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INTRODUCTION
The efficiency with which global transportation networks operate is directly proportional to the state of the global economy.Roads are one of the most time-tested and widely used methods for travelling from one location to another [1][2].According to a number of studies, it is necessary to validate the long-term viability and performance of such vital resources using mathematical modelling and crystallographic representations of their component parts [3][4].The wearing course, the base course, the sub base course, and the subgrade are the four layers that are often used in the construction of roadways.How efficiently axle loads are transferred from the top layer to the layers below is dependent on the types of materials, the mechanical qualities of each layer, and the thickness of each layer of pavement [5][6].The subgrade layer is the most plastic and flexible of the layers, and it also has the highest plasticity index.The CBR and MDD values for this layer are the lowest of all the layers.Moreover, environmental conditions such as a high groundwater table can make the soil beneath the subgrade far less stable [7].When conducting a feasibility study, it is essential to pay close attention to the properties of the soil that will be utilised to construct a road.For instance, the poor quality of the soils, which is especially prevalent in arid regions, makes it difficult to build the pavement and ensures that a road construction project will be profitable.Deserts suffer from a lack of water, which results in erosion, strong winds, sedimentation, and significant temperature shifts between day and night.All of these factors contribute to the transformation of rocks into sand and gravel [9].The grains that make up desert sand are often quite small, smooth, and spherical.This makes the sand relatively weak.Sand grains in a desert typically have a spherical form, which has a role in how effectively they mechanically interlock with one another.When cement is added to a mixture, it changes the qualities of the fresh concrete as well as the stability of the mixture [10].Hence, untreated desert sand does not typically fulfil the technical parameters necessary to be used as a pavement subgrade [11].Because it makes mortar stronger both physically and chemically, desert sand is gaining popularity as a building material [12].This is one of the reasons why.Desert sand concrete, often known as DSC, is on par with traditional concrete in terms of its strength [13][14][15].Yet the appearance of desert sands and the kind of minerals they contain can vary greatly depending on the location where they were formed [16].There are a variety of pozzolanic and industrial products that can be utilised to stabilise subgrade [12][13][14][15][16][17][18][19][20][21].Some examples of these materials include lime, FA, silica fume, cement, and bentonite.The utilisation of waste products from construction projects as resources for the construction of roads is another way that can be effective for waste management.In addition to the generation of FA, the use of coal results in the production of a sizeable quantity of construction material that is recyclable at a low cost.The utilisation of waste products from construction projects as resources for the construction of roads is another way that can be effective for waste management.In addition to the generation of FA, the use of coal results in the production of a sizeable quantity of construction material that is recyclable at a low cost.FA is still completely untapped as a source of important chemicals despite the fact that it is used extensively in the construction industry.In one investigation, the subgrade soil was stabilised with the help of cement, polymers, enzymes, and FA [21].By utilising a combination of FA, cement, and enzymes to increase the carrying capacity of the soil [22][23][24][25], the overall thickness of the road layer was able to be lowered.For the use of waste material in the road pavement over the past decade, there is a significant amount of literature that has been available; however, in order to make the system more condensed, there is a requirement for additional experimental inquiry.In the existing experimentation investigation the percentages of FA addition in the soil that were examined for optimal utilisation in civil application with proportion of 12%, 17%, 22%, and 27%.Also, some experimental inquiry is carried out in order to confirm that the mix proportion of the substrate is appropriate for civil application by checking the moisture content, degree of compaction and densities.

Sample Collection
The location of the soil sample collection in the Gurgaon region is 760-765 metres from the beginning of the Delhi-Mumbai highway.Despite the fact that the FA sample was collected at the Dhunela innovation centre (Gurgaon).A gradation test has been carried out on the sample in order to ascertain the size of its constituent particles.This test involved passing the sample through a series of increasingly smaller sieves, with a certain amount of dirt being retained on each sieve.The standard proctor compaction tests are carried out on the soil sample by compacting it at their respective MDD and OMC.The current investigation used a variety of values for the percentage of FA added in the sample, and those values were 12%, 17%, 22%, and 27% respectively.The specific gravity of soil can be determined by utilising a technique called the pycnometer, which involves determining the volume of the soil to be tested and then dividing the soil's weight by the weight of an equivalent volume of water.The specific gravity of a substance is never determined at any temperature other than room temperature, and the results are always given to the closest 0.01.

Physico chemical properties
In Table 1, the FA's physical characteristics are outlined for the reader.The sample is graded using standard sieves coupled to a mechanical shaker, and the results of this process are summarised in Table 2.Because more than half of the entire soil's weight is comprised of particles larger than 75 micron, the soil can be classified as having coarse grains.Gravel with a size greater than 4.75 millimetres, sand with a size between 4.75 and 0.075 millimetres, and fines with a size less than 0.075 millimetres were identified in the soil sample in the following proportions: 29.0%, 60.1%, and 10.9% correspondingly.According to the Indian Standard for soil classification (IS 1498:1970), the soil has been given the designation of "sandy soil with poor gradation," which is abbreviated as "SP."It appears that the soil does not have any plasticity in its makeup because it tests out to be a sandy soil that falls into the SP group.But in order to be certain of this, a Plastic Limit test was carried out.However, the test was unsuccessful since the soil sample could not be rolled into a 3mm thickness.Because of this, it demonstrates that the soil lacks any flexibility.
An analysis of the chemical composition of the flexible pavement was carried out so that the usage of FA could be verified.The presence of a variety of chemicals in the FA sample is illustrated in Figure 1, along with an actual picture of the sample itself.It was discovered that SiO2 has the highest proportion, whereas Al2O3 has the lowest.The sample has an approximate proportion of 57% SiO2, whereas the percentage of Al2O3 is 27%.The other components, such as Fe2O3, MgO, and Na2O, are also found.CaO was discovered as a further significant element, and it is the one that is accountable for the components' pozzolanic action.Similar type of observation has been documented in other research as well [16][17][18][19][20].

Materials and Methods
Whenever the FA was used in the processing of the samples, the oven-dried soil was combined with an amount of water that was proportional to the OMC of the soil.This was done so that the OMC could be determined.The FA addition was utilised, and the designated quantity of FA was initially mixed into the oven-dried soil by hand in small increments.This was done to ensure that all of the FA was thoroughly combined, which allowed for the formation of a relatively uniform mixture after the addition of an adequate quantity of water.The preparation of three identical samples is required for each reading, and the average of these samples is what is used to determine the value or reading.
The instrument that was invented by Casagrande is utilised in the process of determining the liquid limit via the process of cutting a groove that is 8 millimetres high, 11 millimetres broad at the top, and 2 millimetres wide at the bottom.A Proctor compaction test has been carried out in order to determine the link between the moisture content and density of soils that have been compacted in a mould of a particular size using a rammer weighing 2.5 kilogrammes that has been dropped from a height of 30 centimetres.In order to evaluate the sample's ability to support a load, a CBR test, also known as a California Bearing ratio test, was carried out.

RESULT AND DISCUSSION
. A variety of studies have been carried out in order to investigate the impact that the incorporation of FA in the flexible pavement's foundational material has had.The samples are made in accordance with the appropriate mixing proportions.For the purpose of determining whether or not there was an error in the calculation, three distinct samples were prepared for the same specification, and the average value was used as the final reading.The instrument that was invented by Casagrande is utilised in the process of determining the liquid limit.via the process of cutting a groove that is 8 millimetres high, 11 millimetres broad at the top, and 2 millimetres wide at the bottom.The values of the water content were influenced differently depending on the total number of blows.Compaction is a procedure that involves eliminating air from voids in the material that is being compacted in order to enhance the bulk density of the substance.When the soil is compacted at a moisture content that is sufficiently high and almost all of the air is forced out, the ideal moisture content is reached.This moisture content is referred to as the optimal moisture content.Figure 2(a) illustrates how the change in the total number of blows affects the amount of water in the sample, It is clear that the lesser no of blows have minimum number of water content as compared to higher no of blows.On the other hand effect on the degree of compaction with varying percentage of water addition has been shown in Figure 2(b).From the results it has been observed that degree of compaction has been increased with increase in addition of water.However this trends does not prolong exists and decreasing after a certain limit.With addition of 16% of water the degree of compaction have higher as compared to other amount of water addition.The number of blows that were delivered in order to bring the two soil samples into close contact is recorded, and a tally is kept of the total number of blows.The maximum amount of liquid allowed is equal to 35 blows taken from the graph.Similarly the variation in dry as well as bulk density of the samples has been studies and results are presented in Figure 3.It was reported that with increase in water addition the bulk and dry density increase wet up to a certain limit.However the increase in bulk density was notice more effective as compared to dry density with increase in percentage of water addition upto 16%.After this the lower trends observed with dry as well as bulk density.

Effect of addition of fly ash
A Proctor compaction test has been carried out in order to determine the link between the moisture content and density of soils that have been compacted in a mould of a particular size using a rammer weighing 2.5 kilogrammes that has been dropped from a height of 30 centimetres.Figure 4 illustrates how the addition of FA affects the degree of compaction and DD as well as BD (Bulk Density) of the sample.It was found that an addition of 12% increased the DD, and it appears that the value of DD decreases in proportion to an increase in the amount of FA added.While the dry matter indicates an upward tendency, the moisture content is going in the opposite direction as shown in Figure 5. From results presented in the figure 4 and 5, it has been reported that with the addition of fly ash in the sample, value of degree of compaction is decreases with the bulk and dry density.While the capacity of retain the water was increased or the moisture content capacity of the sample has been increased.From the results it has been clear that the decrease in BD was higher as compared DD with the addition of fly ash in the sample.Higher the as addition higher was the moisture content, with the addition of 27% fly ash the sample have higher moisture content.On the other hand for the same sample the trend BD,DD and degree of compaction shows reverse trend.Degrees of compaction have minimum value at 22% addition of fly ash as compared to other proportion [21][22].Similarly the additions of fly ash in the sample have shown its effect on the moisture content of the sample [23][24][25][26][27][28][29][30][31][32].The detailed comparison of variation of moisture content with increase in addition of fly ash in the sample has been presented in the Figure 5.It would appear that increasing the amount of FA results in a rise in the moisture content, which is indicative of the high water holding ability of the FA content [4,5,21].It was also reported that maximum rate of increase in moisture content was observed with the addition of fly ash with 22%, However, the moisture content increased with increase in percentage of addition of fly ash in the sample.Minimum increase in moisture content was observed with the minimum addition of fly ash like 12%, while Maximum value was observed for 27% of fly ash addition.

CONCLUSION
On the base of test results it was concluded that: • With the increase in percentage of water the degree of compaction, Dry density as well as bulk density has been increased up to a certain limit.Maximum value of degree of compaction, Dry density and Bulk density was found with the addition of 16% of water.• Decrease in densities has been observed throughout the addition of fly ash in the sample.However the decrease in Dry density was higher as compared to Bulk density of the sample.• After the addition of 12%, 17%, 22%, and 27% FA, respectively, the moisture content of the sample increased but the rate of increase in moisture content was optimal till the addition of 22% of fly ash.• Addition of fly ash up to a certain limit shows good agreement for utilization as sand replacement in civil application.

Fig. 2
Fig. 2 Liquid Limit with respect to different blows

Fig. 4
Fig.4 Variation of degree of compaction, dry density and bulk density with respect to addition of fly ash

Fig. 5
Fig. 5 Variation in moisture content with increase in addition of fly ash

Table 1
Properties of FA