Design of Air-Entrained Concrete for Airport Pavements Through Local Aggregate Utilization

2.1. Cement

Type IV Portland cement conforming to ASTM C150 [16] was selected for this investigation due to its low heat of hydration characteristics and reduced tricalcium aluminate (C3 A) content. The cement was procured from a local Pakistani manufacturing facility and stored in moisture-controlled conditions to prevent hydration prior to testing. Chemical analysis was conducted to verify compliance with ASTM specifications, with particular attention to the total equivalent alkalies (Na2 O + 0.658K2 O) content which was maintained below 0.6%. The chemical composition and physical properties were determined and are presented in Table 1 and Table 2.

2.2. Fine aggregate

Lawrencepur sand sourced from the Indus River was used as fine aggregate throughout this study. Petrographic examination was performed according to ASTM C295 [17] to determine mineralogical composition and assess potential alkali-aggregate reactivity, with microscopic analysis conducted

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Table 1. Chemical composition of Type-IV cement. Constituent

Fineness (cm2 /g) Standard consistency (%) Initial setting time (min) Final setting time (min) Autoclave expansion (%) Heat of hydration (kJ/kg) Heat of hydration (kJ/kg) Compressive strength (MPa) Compressive strength (MPa) Compressive strength (MPa)

under plane-polarized light conditions with 10x scale bar length as shown in Fig. 1. Sand equivalence testing was conducted following ASTM D2419 [18] procedures using standard measuring cylinders and clay reading measurements. Sieve analysis was performed according to ASTM C117 [19] with washing procedures to determine particle size distribution and fineness modulus. The testing procedures and results are documented in Table 3 and Table 4.

2.3. Water

Potable water meeting drinking water standards was utilized for both concrete mixing and curing

operations. Water quality analysis was performed according to BS 3148:1980 [20] specifications to evaluate total alkalinity, chloride content, sulfate content, total dissolved solids, and organic matter content. The test procedures and acceptance criteria are summarized in Table 5.

2.4. Coarse aggregates

Three gradations of crushed stone aggregate were obtained from Sargodha quarry sources (Mountain #116 and #127), comprising size fractions of 510mm, 10-20mm, and 20-38mm as shown in Fig. 2. Aggregate blending was performed using proportions of 15% (5-10mm), 50% (10-20mm), and 35% (2038mm) to optimize particle packing density. Sieve analysis was conducted according to ASTM C33 [21] for each size fraction and the combined gradation, with procedures detailed in Table 6. The combined gradation curve was plotted to verify compliance with specification limits as shown in Fig. 3. Physical property testing was conducted following standard ASTM procedures. Specific gravity and water absorption were determined according to ASTM C127 [22] using the saturated surface-dry method. Flat and elongated particle analysis was conducted

Fig. 1. Petrography test for fine grains in Lawrencepur Sand; (a) Plagioclase and Quartz with Biotite grains, (b) Quartz with Biotite grains, (c) Magnetite grains with strained Quartz, (d) Lithic fragment, Epidote and Biotite grains.

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Table 4. Fine aggregates sieve analysis test (ASTM C117). Initial Wt. of Dry Sample (g)

3/8 in 9.5 Nil #4 4.75 22.8 #8 2.36 80 #16 1.18 282.9 #30 0.60 705.8 #50 0.30 1091.2 #100 0.15 1380 #200 0.075 1412.4 Fineness Modulus Percentage of Material Passing #200 Sieve C=[(A-B)/A] x 100 A Original Dry Wt. of Sample (g) B Dry Wt. of Sample after Washing (g) C % of Material Finer than #200 Sieve by Washing

and polarized light microscopy. Modal analysis was performed to determine mineral composition percentages using point counting techniques. Sample preparation involved standard thin section preparation with 30-micron thickness, and examination was conducted using polarized light microscopy at 100x and 400x magnifications under both plane-polarized and cross-polarized light conditions.

Total alkalinity as CaCO3 Chloride Sulphate Total dissolved solids Organic matter

97.9. ppm

according to ASTM D4791 [23] using proportional calipers. Los Angeles abrasion testing was performed according to ASTM C131 [24] using the standard grading and 500 revolutions. Test results are summarized in Table 7.

2.5. Alkali-aggregate reactivity testing

2.5.1. Accelerated mortar bar test Accelerated mortar bar testing was conducted according to ASTM C1260 [25] to evaluate potential alkali-silica reaction. Standard mortar bars (25×25×285 mm) were prepared using 1:2.25 cement-to-aggregate ratio with 0.47 water-cement ratio. Specimens were stored at 80°C in 1N NaOH solution with length measurements recorded at 1, 7, 14, and 28 days using a length comparator. Expansion calculations were performed using the standard formula for percentage length change. 2.5.2. Petrographic analysis of coarse aggregates Petrographic analysis was conducted according to ASTM C295 [17] using thin section preparation

2.6. Chemical admixtures

High-range water-reducing admixture (Sikament HRM) conforming to ASTM C494 [26] Type G specifications was incorporated. This dual-action superplasticizer was selected for water reduction capabilities of 12-25% and set retardation properties suitable for hot climate conditions. Dosage rates were established through trial mixing to achieve target slump values. Air-entraining admixture (Sika-Aer) complying with ASTM C260 [27] was added to achieve target air content of 3-6%. Dosage rates of 0.03-0.15% by cement mass were evaluated through systematic testing. Regular air content measurements were performed using the pressure method to ensure consistent entrainment levels.

2.7. Concrete mix design

Mix designs were developed using the absolute volume method for cement contents ranging from 360 to 450 kg/m3 . Water-cement ratios were maintained

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Table 6. Sieve analysis test for coarse aggregates (ASTM C33). Blending of Aggregates Sr. #

1) 05∼10mm 2) 10∼20mm 3) 20∼38mm Combined Gradation 1) 05∼10mm 2) 10∼20mm 3) 20∼38mm Total Mid-Point Specification Limits

through superplasticizer optimization. Target slump was established at 50mm in accordance with ACI 211.1-9.1 [28] recommendations for pavement applications, which specify 25-70mm range for slabs and pavements. For each cement content, fine aggregate content was calculated to fill remaining volume after coarse aggregate, cement, water, and air. Superplasticizer dosage was adjusted to maintain 50mm slump while

air-entraining admixture was dosed to achieve 3-6% air content. Water content was adjusted based on admixture interactions to maintain workability requirements. The complete mix proportions for 1m3 concrete including material costs are presented in Table 8. The economic assessment of 1 m3 of concrete was performed based on prevailing local market rates for the year 2026. All costs were initially calculated in Pakistani Rupees (PKR) and subsequently converted into US Dollars (USD) using an exchange rate of 1 USD = 280 PKR. The unit prices of constituent materials and associated production costs were obtained from local suppliers and market surveys. Table 9 summarizes the local market rates (2026) of the materials considered in the cost analysis.

2.8. Specimen preparation and curing

Test specimens were prepared for flexural strength testing using 500mm × 150mm × 150mm beam specimens, while compressive and split tensile strength evaluations utilized ø150mm × 300mm cylindrical specimens. For each mix proportion and testing age,

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Table 7. Physical characteristics of coarse aggregates used in this research. Properties

2.9. Mechanical testing procedure

Flexural strength tests were conducted according to ASTM C78 [29] using third-point loading on simply supported beam specimens. Loading rate was maintained at 1.0 MPa/min until failure, with maximum load recorded and flexural strength calculated using standard beam theory. Compressive strength tests were performed on cylindrical specimens with loading rate of 0.25 MPa/s, with end preparation including sulphur capping to ensure uniform load distribution throughout the cross-sectional area. Split tensile strength tests were conducted according to ASTM C496 [30] using diametral loading on cylindrical specimens, where loading strips were placed along the specimen length and load applied at constant rate until splitting failure occurred along the loaded diameter. For each mechanical test, three replicate specimens were evaluated and the reported strength values correspond to the mean results.

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Fig. 4. Testing setup; (a) Flexural strength test (b) Compressive strength test (c) Split tensile strength test.

3.1. Material characterization results

3.1.1. Cement properties The chemical composition and physical properties of the Type IV cement used in this study are presented in Table 1. The cement exhibited silica content of 22.09% and calcium oxide content of 61.76%, conforming to ASTM C150 requirements for Type IV cement. The total equivalent alkalies content was 0.53%, well below the 0.6% specification limit for low-alkali cement. Physical testing revealed a fineness of 3055 cm2 /g, standard consistency of 24.4%, and setting times of 140 and 190 minutes for initial and final set, respectively. Compressive strength development showed values of 2416 psi at 3 days, increasing to 4609 psi at 28 days, which satisfied the minimum requirements for Type IV cement applications. 3.1.2. Fine aggregate characterization Petrographic examination of Lawrencepur sand revealed a predominantly quartz composition (57%) with subordinate feldspar (14%), amphibole (8%), rock fragments (6%), and biotite (6%), as illustrated in the photomicrographs presented in Fig. 1. The mineral grains exhibited predominantly sub-rounded morphology, indicating moderate transport distance and suitable surface characteristics for cement paste bonding [4]. Sand equivalence testing according to ASTM D2419 indicated an average value of 78%, demonstrating low clay content and minimal plastic fines that could adversely affect concrete workability or strength development. Sieve analysis, confirmed a fineness modulus of 2.456, falling within the acceptable range of 2.3-3.1 for concrete applications. The gradation curve indicated good particle distribution with 2.6% material passing the #200 sieve, meeting ASTM C33 specifications for concrete aggregates.

3.1.3. Water quality test Water quality analysis performed according to BS 3148:1980 standards confirmed the suitability of the potable water used for concrete mixing and curing operations. As shown in Table 5, total alkalinity measured 469.8 ppm, chloride content was 29.7 ppm, and sulphate content was 17.2 ppm, all values falling well within acceptable limits for concrete production. Total dissolved solids content of 846.3 ppm remained substantially below the 2000 ppm maximum allowable limit, ensuring no adverse effects on cement hydration or concrete durability. 3.1.4. Coarse aggregate properties The physical characteristics of the blended coarse aggregates from Sargodha quarries are summarized in Table 7. Specific gravity values ranged from 2.92 to 2.93 for all size fractions, indicating consistent mineralogy and density characteristics suitable for structural concrete applications. Water absorption values were consistently low, ranging from 0.21% for the 20-38mm fraction to 0.51% for the 5-10mm fraction, all well below the 2% maximum specification limit. Flat and elongated particle content remained below 5% for all size fractions, ensuring good workability and strength characteristics. The Los Angeles abrasion test result of 18.6% for the blended aggregates demonstrated excellent toughness and resistance to mechanical degradation, comfortably meeting the 30% specification limit for structural applications. The combined gradation curve presented in Fig. 3 shows that the blended aggregate proportions produced a well-graded material that fell within ASTM C33 specification limits. The aggregate blending strategy successfully achieved optimal particle packing with the mid-point curve closely following the specification band, which contributed to reduced cement paste requirements and improved concrete economy.

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3.2. Alkali-aggregate reactivity assessment

3.2.1. Accelerated mortar bar test The accelerated mortar bar test results are presented in Fig. 5, showing the expansion characteristics of mortar bars prepared with Sargodha aggregates over the 28-day test period. The average expansion at 28 days was 0.099%, falling well within the safe limits established by ASTM C1260 for non-reactive aggregate classification. The expansion curve demonstrated low initial expansion in the first 14 days, followed by minimal additional expansion through 28 days, indicating stable behaviour and low potential for deleterious alkali-silica reaction. These results confirmed that the selected aggregates posed no risk for long-term expansion or deterioration in concrete applications. 3.2.2. Petrographic analysis results Petrographic examination (scale bar length 10x) of the coarse aggregates revealed the mineral composition presented in Fig. 6 through representative photomicrographs. The modal analysis indicated plagioclase content of 39.4%, followed by chlorite (23%), calcite (21.9%), magnetite/limonite (7.6%), amphibole (2.2%), and quartz (2.1%). The remaining constituents included K-feldspar (1.6%), hydromica/illite (0.9%), epidote (0.9%), and sphene/leucoxene (0.4%). The low quartz content and absence of strained quartz or other potentially reactive silica phases confirmed the non-deleterious nature of these aggregates. The analysis demonstrated that both fine and coarse aggregates could be safely used with ordinary Portland cement and high-alkali cement without risk of alkali-silica or alkali-carbonate reactions.

3.3. Mechanical properties development

Each data point presented in Figs. 7 to 12 represents the average of three specimens (n = 3), and corresponding standard deviation values are included in Figs. 8 and 10 and Fig. 12 to indicate experimental variability, which remained within acceptable limits for structural concrete testing. 3.3.1. Flexural strength performance Flexural strength test results for the various mix designs are presented in Fig. 7, while Fig. 8 shows the corresponding error bars (± standard deviation). The strength development at 3, 7, 28, and 90 days for cement contents ranging from 360 to 450 kg/m3 . The maximum flexural strength achieved was 8.0 MPa at 28 days and 9.2 MPa at 90 days for the 450 kg/m3 cement content mix, representing significant improvements over the minimum 4.1 MPa requirement specified by FAA guidelines [31] and the 4.5 MPa requirement specified by military standards [32]. The strength development pattern showed consistent improvement with increased cement content, with flexural strength increases averaging 1.04 times from 28 to 90 days across all mix designs. Analysis of the flexural-to-compressive strength relationship revealed that flexural strength represented 11-23% of compressive strength at 3 days, 14-24% at 7 days, 13-18% at 28 days, and 13-16% at 90 days. These ratios fell within the typical range of 1015% reported in literature for well-designed concrete mixes, with the higher ratios at early ages reflecting the different hydration kinetics affecting tensile versus compressive strength development.

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Fig. 6. Petrography test for Sargodha coarse aggregates; (a) Plagioclase with Chlorite and Calcite grains, (b) Plagioclase with Calcite grains, (c) Plagioclase with Chlorite, Calcite, Magnetite and some Quartz grains, (d) Plagioclase with Chlorite, Calcite, and Magnetite grains.

Fig. 7. Flexural strength test results (3, 7, 28 and 90 days).

3.3.2. Compressive strength development Compressive strength test results for the various mix designs are presented in Fig. 9, while Fig. 10 shows the corresponding error bars (± standard deviation).

33.4. MPa at 28 days for the 360 kg/m3 cement

content, increasing to 45.2 MPa for the 450 kg/m3 mix. At 90 days, compressive strengths ranged from approximately 40 MPa to 57.0 MPa for the same

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Fig. 8. Flexural strength test results (3, 7, 28 and 90 days) with error bars ± SD (n = 3).

Fig. 9. Compressive strength test results (3,7, 28 and 90 days).

cement content range. These values exceeded the requirements specified in military guidelines UFC 3250-01 [32] for heavy-duty pavement applications. The strength gain from 28 to 90 days showed an average increase factor of 1.02, indicating continued hydration and strength development beyond the standard 28-day testing age, which was beneficial for long-term pavement performance. 3.3.3. Split tensile strength characteristics Split tensile strength test results for the various mix designs are displayed in Fig. 11, while Fig. 12 shows the corresponding error bars (± standard deviation).

The minimum split tensile strength of 2.70 MPa was achieved with 360 kg/m3 cement content at 28 days, while the maximum value of 3.90 MPa was obtained with 450 kg/m3 cement content. At 90 days, the maximum split tensile strength reached

5.9. MPa, demonstrating substantial improvement in

tensile characteristics with extended curing. The split tensile strength represented approximately 6-8% of compressive strength at 3 days, 9-11% at 7 days, 7-9% at 28 days, and 9-10% at 90 days, which aligned well with established relationships between these properties in high-quality concrete.

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Fig. 10. Compressive strength test results (3, 7, 28 and 90 days) with error bars ± SD (n = 3).

Fig. 11. Split tensile strength test results (3,7, 28 and 90 days).

3.4. Economic analysis

The cost analysis summarized in Table 8 evaluates the economic feasibility of the developed concrete mixtures using current local market prices (2026). This assessment accounts for both material expenses, batching and transportation, offering a practical estimate of the overall cost for field scale production.

The material cost per cubic meter ranged from $80.61 for the 360 kg/m3 cement content mix to $88.94 for the 450 kg/m3 mix, representing an approximate 9.4 % increase in cost relative to the baseline mix (360 kg/m3 ). However, this increase in cost corresponds to comparatively smaller gains in mechanical performance, particularly beyond 420 kg/m3 cement content.

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Fig. 12. Split Tensile strength test results (3, 7, 28 and 90 days) with error bars ± SD (n = 3).

The analysis indicates that mixtures within the 400-420 kg/m3 range provide an optimal balance between mechanical performance and economic efficiency. These mix designs achieved flexural strengths exceeding 7.0 MPa at 28 days while maintaining material costs below $86.25 per cubic meter, making them attractive options for airport pavement projects requiring both structural performance and economic viability.

3.5. Performance optimization discussion

The optimization of air-entrained concrete mixtures for airport pavements was carried out by analysing the relationship between cement content, mechanical performance, and material cost. The findings show that increasing the cement content leads to improvements in flexural, compressive, and tensile strengths; however, beyond approximately 420 kg/m3 , the rate of improvement decreases, indicating diminishing returns in strength relative to cost. This identifies an optimal cement content in the range of 400–420 kg/m3 , where adequate structural performance is achieved without excessive material cost. The dosage of air-entraining admixtures was regulated to maintain an air content between 3-6%, which enhanced workability and potential durability benefits without significantly compromising strength. Furthermore, the use of optimized aggregate gradation improved particle packing efficiency, thereby reducing paste demand and contributing to overall mix efficiency.

It should be noted that, although alkali–aggregate reactivity tests confirmed the aggregates to be nonreactive, durability was not directly assessed through freeze–thaw resistance, or corrosion tests, representing a limitation of this study.