Specification, guidelines and directives in building and construction materials play a vital role in any organization for better performance of road and highway or any infrastructure construction and development.

These instructions and specifications should be followed and mandated for road and highway construction sectors to check and evaluate the degree of quality and adjustment of works that have been carried out.

These provisions obtained characterize the desired materials for concrete pavement mixes, such as cement type, water for mixing and curing, mineral and liquid additives, aggregates and granulation materials, fiber reinforcement that may be required to improve the performance of concrete mixtures. In addition, construction conditions are provided, which are necessary for mixing, transporting, placing of paving concrete pavements.

However, these limitations need to be enhanced and the quality of the concrete pavement has to be increased. The proposed amendments often include the maximum size of aggregates, the range of grading and optimization techniques, that could have a definite favorable effect on the concrete pavement performance and they are briefly discussed.

Increasing the Maximum Nominal Size (MNS) of aggregates in the cement concrete pavement mixtures creates many important deviations from the specification. The aim of the recent study is to estimate and evaluate these amendments and its effect on the quality and cost of the concrete mixtures, which mainly includes the following:

• To propose the new constraints for cement concrete pavement (CCP) with combined aggregates gradation.
• To achieve the maximum density, coarseness factor, and retained percentage of cement concrete pavement ingredient by using the maximum size of coarse aggregates.
• To evaluate the compressive and flexural strength of CCP by suing the maximum nominal size 38 mm coarse aggregates.

The gradation is one of the most influential aggregate characteristics to determining how it will perform as a pavement material. In the pavement design, gradation helps govern almost every important property either for flexible or rigid pavement. Because of this, gradation is a primary concern in a pavement mix design and accordingly most agencies specify permissible aggregate gradations for pavement mixtures (Khazaei&Sravana, 2019).

In the cement concrete pavement, the particle size of coarse aggregates influences the paste requirement for coating through the surface area. The larger aggregates have a smaller surface area than smaller aggregates with the same volume. Subsequently, the amount of the paste available for lubrication is increased for concrete with large aggregates, and consistency is improved. Hence, for a given w/c ratio, as the maximum size of aggregate increases, the fluidity of fresh concrete increases.

Ministry of Road Transport & Highways government of India MoRTH specification-chapter 6 (Indian Road Congress, 2013), considering the certain constraints for cement concrete pavement which could ensure the quality of concrete mixtures during construction. But the weakness is limited to the maximum nominal size of 25 mm for the coarse aggregate (Indian Road Congress, 2017). While this nominal size can be increased more than 31.5 mm by considering certain steps (Bureau of Indian Standards, 2000).

To provide the optimal mixture design, it is necessary to choose the accurate components proportioning in the concrete mixtures. So that, fine and medium size of aggregates can be placed in the voids between coarse aggregates to achieve the maximum density of the concrete as compacted mixtures (Richardson, 2005). The desired maximum density can be a moral criterion for improving the quality of concrete and ultimately leads to maximum compressive strength and lowest cost effect. Therefore, aggregates characteristics containing the maximum nominal size of aggregates could have significant impact on the quality of cement concrete pavement (Issa et al., 2000).

Specification needs to be enhanced, in order to improve the quality of the concrete pavement. The proposed amendments often include the maximum size of aggregates, the range of grading, and optimization techniques, that could have a definite favorable effect on the concrete pavement performance.

The present study considers the necessity of investigating on cement concrete pavement constraints for given combined gradation by increasing the maximum nominal size of coarse aggregates and evaluate the effect of size changes between control samples with the nominal aggregates 20 to 26.5 mm and proposed gradation with a maximum nominal size of 38 mm.

The effect of aggregates size on the properties of fresh and hardened concrete specifically, in compressive and flexural strength has been investigated by many researchers with the different orientations in consolations.

In these studies, there is no comprehensive consensus on the overall properties of hardened concrete. The consequences of a literature review in general can be summarized as follows.

• When the maximum size of the aggregates decreases, the compressive strength increases (Albarwary et al., 2017; Yaqub&Bukhari, 2006; Jimoh, 2007; Neville, 1997; Shetty, 2000; Tumidajski& Gong, 2006; Woodeet al., 2015).
• As the size of the aggregates increases, the compressive strength increases (Ajamu&Ige, 2015; Ekwulo&Eme, 2017; Issa et al., 2000; Kozul& Darwin, 1997; Krishna et al., 2010; Musa & Bin Saim, 2017).
• The coarse aggregates gradation had little effect on the properties of concrete (Ioannides& Mills, 2006).
• MoRTH specification recommends that the maximum size of coarse aggregate should not exceed 25 mm (Indian Road Congress, 2013). While the Indian Road Congress (2017) assumed that, the maximum nominal size of 38 mm for cement concrete pavement can be employed. Precautions may be taken to reduce the segregation in concrete mixtures and an attempt should be made to limit the maximum particle size of 31.5 mm, respectively, according to Bureau of Indian Standards (2000).

The proposed amendments often contain increasing the max size of coarse aggregates, the new constraint of gradations and optimization techniques which have a favorable effect on the cement concrete pavements performance that are considered below.

4.1 Change in the Maximum Nominal Size (MNS) of Coarse Aggregates

Like other inherent properties of coarse aggregate, the size can have a huge impact on fresh and hardened concrete that might not be ignored. Indian Road Congress (2017) limited the maximum size of coarse aggregates for cement concrete pavement up to 31.5 mm.

With respect to the ratio of a maximum size of aggregate to the clear cover and thickness of the section, it seems that the nominal size of the coarse aggregate is limited to 31.5 mm. While the minimum thickness of cement concrete pavement can vary from 150 mm to 300 mm depending upon design parameters, thickness to aggregates size ratio will vary between 3 to 7.9 times. Thus, due to the adequate thickness of pavement concrete, using the nominal size of aggregates with 38 mm could not be a problem, if it can maintain the technical specification and standard code of practice as shown in Table 1.

Using the coarse size aggregates, the following advantage might be expected in the concrete mixes (Shetty, 2000).

• Less Specific Surface Area and More Work ability: Specific surface increases with the reduction in the size of aggregates particles. Fine aggregates contribute much more to the surface area than does the coarse aggregates. A great surface area requires more water for the same workability of the mix. Hence increasing the size of coarse aggregates for the same mix enhance the workability.
• Less Cement and Low Water Cement Ratio: Coarse aggregates have less specific surface, water absorption, and need less water for concrete mixes.
• Less Drying Shrinkage: Due to point content between coarse and fine aggregates and also on account of lower cement and matrix content, the drying shrinkage is reduced.
• Good Inter Locking: The coarser aggregates have better interlock and bound strength than does the fine aggregates.

4.2 Change in the Combined Gradation of Aggregates Limit

The MoRTH specification defined that the range of combined gradation can be much smoother in the upper and lower limit in the cement concrete pavement gradation. Those points can be in closer range with acceptable curvature in the target area, which is presented in Figure 1.

Figure 1. Illustration of Proposed Aggregates Gradation

Grading has a heavy impact on materials performance according to the materials and its desirable characteristics, structural, loading, environmental, material mix property inputs. Thus, proper aggregates size and those blending requirements for certain pavement mixes are important. To optimize the maximum density of the concrete mixtures, the selection of appropriate proportioning, and max nominal size of aggregates is very important. The fine and medium-size aggregates get placed in the available void between coarser aggregates to form a denser and harder particle structure. Early researchers, proposed various methods, for designing the ideal aggregates size distribution. The power chart as discarded in the next section is one of the aides that can be employed to optimize the components of the concrete mixture.

5.1 Proportioning of Aggregates by Maximum Density Line (MDL) Method

Formulae, symbols, and all subscripts, superscripts, Greek letters, and other characters must be legible and carefully checked. Standard mathematical notation should be used. All symbols used in manuscript must be explained.

Fuller and Thompson (1907) developed an equation to describe maximum density gradation for a given maximum aggregate size as given in the following Equation.

(1)

where,

D = Maximum size of aggregate

P = Percentage of finer than diameter d (by weight)

d = Maximum size of fine aggregate

n = Parameter which adjusts curve for fineness or coarseness (for maximum particle density n ≈ 0.5 according to Fuller and Thompson)

In the early 1960s, the Federal Highway Administration (FHWA) presented the standard gradation used in the hot mix asphalt industry today. This equation with n = 0.45 is convenient for determining the MDL and for adjusting gradation it uses the sieve size raised to the nth power on the x-axis units. Thus, a plot of maximum density equation with n = 0.45 appears as a straight diagonal line generates from zero to the maximum aggregates size gradation being considered as shown in the Figure 2 for the proposed cement concrete pavement mix design with the maximum size of 20 and 38 mm.

Figure 2. Illustration of Proposed Power Chart Aggregates Gradation

In the present study attempts have been made to optimize the coarse and fine aggregates proportioning in order to achieve the maximum bulk density and investigate the effect of coarse aggregate size and gradation on the compressive strength of cement concrete pavement. Thus, power chart, 0.45 are developed for all in aggregates combination, to obtain a dense and stiff particle structure in concrete mixes. Regardless of its practical use, a maximum density gradation provides a convenient reference. The higher degree of particle packing leads to minimum voids, maximum density, less cement and water requirement.

5.2 Proportioning and Optimization of Aggregates

In order to optimize the blending of coarse and fine aggregates, two distinct mix designs have been proposed. Mix PQC-20 contains coarse aggregates of 10 and 20 mm and Mix PQC-40 consists of coarse aggregates of 10, 20, and 38 mm and the same identical sources of materials were used. In both mixtures, fine aggregates including river and mine sand have been employed with optimum proportions as given in the following steps.

• Indicate the coarse aggregates to fine aggregatesratio (CA/FA).
• Initially, for proportion of coarse/fine aggregates which will be selected.

• Proportioning of coarse aggregates.
• Selection of individual fraction ratio of coarse aggregates.
• Selection of individual fraction ratio of coarse aggregates.
• Mix PQC-20: the ratio of fraction 10 and 20 mm have been selected by different value.
• Mix PQC-40: the ratio of fraction 10, 20, and 38 mm ware have been selected in a similar way.

• Proportioning of fine aggregates.
• Fine aggregates consist of the river and mine sand. The ratio of this fraction has been selected with a different proportion from 0 to 100%.
• For all above steps, an attempt has been made to develop a rational method for predicting aggregate blending related to the MDL by the using the Graphical Approach to achieve the maximum density and minimum air voids. Now the combined gradation is well-graded and full fit to the zone and closer to the MDL as shown in the Figure 3 and Figure 4.
• The PQC-20 with the maximum nominal size of 20 mm coarse aggregate, is positioned outside the upper limit in combined gradation and is far from the MDL. While the coarse mixture PQC-40 with maximum nominal size of 38 mm is very close to MDL compared to the Mix PQC-20 as shown in Figure 2.
• FA plays an important role in determining air voids, packing and density of the mix. The bulk density and specific gravity test for various mixes with CA/FA ratio of (90: 10, 80: 20, 70: 30, 60: 40, 55: 45, 50:50) are tested to obtained the optimum proportion.

5.3 Determination of the Bulk Density and Air Voids Content of Mixtures

The void and packing density of aggregate mixtures can be expressed as per the following equation. The packing density of combined individual aggregate represents the maximum bulk density of the mixtures with respect to the overall specific gravity. The purpose of packing density is to minimize the porosity of the mixtures (Kwan et al., 2012; Raj et al., 2014; Wong & Kwan, 2005), which allows using the minimum possible amount of binder.

(2)

Figure 3. Maximum Loose and Compacted Density of Mixes

Figure 4. Minimum Air Voids in Loose and Compacted Density

The air voids content is the percentage volume of the aggregate or mixture of combined aggregates and is determined from its bulk density from Equation (2).

5.4 Reconfirming the mix fractions

To reconfirm the selected mix proportions of coarse aggregates in the Mix PQC-20 and PQC-40 by the power chart method, fine aggregate percentages have been increased in the various mixes from 25% to 55% gradually. The specific gravity, air voids, and bulk density tests were carried out according to the Bureau of Indian Standards (1963), and the test results are listed in Table 2 accordingly. The bulk density and voids ratio are plotted against the mass fraction of coarse aggregate are presented in the Figure 3 and Figure 4 respectively.

Table 2. Bulk Density, Specific Gravity and Air Voids of Proposed Mixes

5.5 Pavement Quality Concrete Mix Design

Concrete mixes have been carried out by the Indian code of standard (Indian Road Congress, 2017) with the recommendation of MoRTH 5th revision Indian Road Congress, 2013. Two different concrete mix designs with the various proportions of aggregates are made and sampled. Then fresh and hardened concrete performance had been checked and compared. The experimental investigation of mixes is briefly summarized in Table 3. Hence, 325 Kg 425Kg, is accepted.

Table 3. Summary of Experimental Investigation

5.6 Mix Proportions for Trial Mix Based on Aggregates

Gradation of selected concrete mix design proportions in dry condition is given as in Table 4.

Table 4. Mix Proportions for One Cum Trial Mix

5.7 Mix Design Strength Summary

The compressive strength test has been performed on cubes sample 150 mm × 150 mm and flexural strength of beam specimens with 150 mm × 150 mm × 700 mm standard size after the desired curing period. The samples weredemolded after 24 hours of casting time and were o placed in a fixed temperature tank at 25± 2 C. The specimens were removed from water at 7th , 28th , 42th and th 90 days and were tested in surface dried condition as per Bureau of Indian Standards (2004).

5.8 Comparing the Mix Proportions and Flexural/ Compressive Strength

The relativity of flexural and compressive strength at different curing days is presented in Table 5. The graph in Figure 5 and Figure 6 shows the comparison of mix proportion on compressive and flexural strength respectively and the relationship is compared.

Table 5. Compressive and Flexural Strength of Mixes

Figure 5. Compressive Strength Development of Concrete Mixes

Figure 6. Flexural Strength Development of Concrete Mixes

5.9 The Effect of Aggregates Size on the Cost of Concrete

There are several factors that can influence the price of pavement quality concrete. The main important factors are materials, machinery, fuel, manpower quality, and quantity of concrete. One of the factors is the materials, including the coarse and fine aggregates, cement, water, steel rebar, and admixtures, which are a few ingredients whose prices fluctuate.

More than 70% of the volume of concrete is made up by aggregates (Shetty, 2000). To this end, there is a serious need to address the issues of characteristics of aggregates including size that can affect the quality and cost of concrete significantly. In this study, the effect of increasing the maximum nominal size of coarse aggregates on the price of concrete in two mix designs with different sizes of aggregates have been investigated and the results have been summarized as given in Table 6.

Table 6. Net Cost of PQC Concrete Mix Per One Cum IRs

As stated in the Table 6, the unit price of the PQC-20 mix is above 3% than the PQC-40 mix. Thus, this mix has an economic and environmental reason as well.

6. Results and Discussions

In the current study, based on the laboratory investigations and data analysis, the following results can be drawn.

It has been observed that by using the coarser aggregates in pavement quality concrete, the values of bulk density and air voids in the concrete mixtures significantly have been changed.

PQC-20 with CA/FA ratio of 65:35, resulted in loose bulk 3 density of 1.960 kg/m and compacted bulk density of 3 2.001 kg/m . Air voids are 31.389 for loose and 29.674 for compacted density.

In the case of PQC-40 with CA/FA ratio of 60:40, loose 3 bulk density is 1.9367 kg/m and compacted density is 3 2.013 kg/m . Air voids are 30.089 for loose and 29.564 for compacted density.

By implementation of the Fuller curve in aggregates blending, the loose and a compacted bulk density of PQC-40 is higher than PQC-20 as well as the air voids of PQC-40 is less than PQC-20 as illustrated in Figure 3 and Figure 4.

The compressive and flexural strength of concrete mixtures as well as the fluidity of fresh concrete have been influenced by the coarser size of aggregates. Mix PQC-40 with the same W/C ratio, gave better results as shown in Table 4.

Although the C/A ratio in the PQC-20 mix is higher than the PQC-40, which is about 3% to 5% more costlier. From the cost point of view, the production of the PQC- 40 concrete mix has economic and environmental benefits.

• The Indian Road Congress (2013) limited the maximum nominal size to 20 mm coarse aggregates for cement concrete pavement. Though The Indian Road Congress (2017) allows the use of aggregates with a maximum nominal size of 31.5 mm. This might be used in the PQC in order to improve the quality and cost reduction in concrete industries.
• The density and compaction of mixtures can have a significant impact on the performance and quality of mixtures. The Fuller curve provide a higher density to the mixture (Richardson, 2005), resulting improvement in the qualities and performances of concrete mixtures.
• In respect to the PQC grading requirement and transformation to the Fuller curve, the 20 mm size of aggregate cannot attain the maximum density and will be far away from the Maximum Density Line (Khazaei&Sravana, 2019) as shown in the Figure 2. To achieve the maximum density and better mechanical properties, it is desirable to optimize aggregate proportioning by using the 30~40 mm nominal size of aggregates for the jointed plain concrete pavement.

Conclusion

For both mixes, maximum density and lesser air voids have been achieved. The w/c ratio of 0.38 had been obtained and the strength development of the hardened concrete samples has been checked at various curing ages. It has been observed that the coarser mix (PQC-40) had more compressive and flexural strength at all ages. The compressive strength at the age of 28 days is more than 10%, flexural strength is more than 4% when compared to PQC-20 mix with maximum nominal size of 20 mm. The unit cost of concrete will reduce more than 3%.

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