Analysis of fibre reinforced concrete for road pavements on very weak soils

In this paper, the effects of steel fibre usage on concrete pavement thickness and cost were investigated. Prepared fibrous concrete specimens were subjected to physical and mechanical tests. From the experiments, it was determined that as the steel fibre ratio increased, the workability and compressive strength of the specimens decreased, but the flexural and splitting tensile strengths increased. In addition, according to calculations made using the AASHTO 1993 design method, the concrete pavement thickness decreased in the range of 4.35 to 18.66 % with an increase in steel fibre, but the pavement cost increased by 56.50 to 74.07 %.


Introduction
Owing to rapid developments in concrete technology in recent years, researchers have investigated the effects of additives that can be used in concrete for the high-strength properties of concrete and different materials to be substituted for concrete on the physical and mechanical properties of concrete.In light of these studies, artificial pozzolans, such as fly ash, silica fume, blast furnace slag, and steel fibre, have become quite common as additives in concrete road pavements [1,2].Artificially used pozzolans protect natural resources and the environment, and reduce the cost of concrete [3,4].Among them, fly ash is a mineral-derived thermal power plant waste material with pozzolanic features.Fly ash grains are generally preferred because of their spherical structure, as well as the fact that they improve the workability of concrete, reduce bleeding in fresh concrete, and reduce the hydration heat of concrete [5].Silica fume is an industrial waste material containing a large amount of silica, generally comprising glassy and smoothsurfaced spherical particles.Silica fume grains fill the voids in the mixture, reduce the number of C a (OH) 2 crystals, and increase the compressive strength of cement and concrete.Blast furnace slag is a waste product generated during iron production; it also has some binding properties, as it contains high amounts of calcium oxide.This waste material not only increases the compressive strength and workability of fresh concrete, but also reduces sweating [6,7].The steel fibres used in concrete significantly improve its properties, such as flexural strength, toughness, energy absorption capacity, and durability, and prevent crack formation.However, steel fibres make concrete more durable by slowing down the progress of these cracks in the concrete and transferring the stresses at the end of the crack to themselves and solid areas, preventing the loss of strength that the crack would cause in the concrete [8,9].The amount of fibre used in the mixture and the fibre slenderness also have significant effects on the flexural strength, fracture energy, and toughness of steel fibre concrete.The extent to which steel fibres can be used when mixed into concrete depends on the geometric shape of the fibre and the interlock distribution between the fibre and the concrete matrix.Therefore, steel fibres are produced and used in many different geometric forms.In studies examining the effect of fibre size, it has been observed that short-length fibres increase the tensile strength by delaying the first crack formation in concrete, whereas long fibres significantly increase the final rupture strength by providing load transfer and ductility in concrete [10].Owing to these advantages, fibrous concrete has a wider range of applications than conventional concrete [11].Fibrous concrete continues to be increasingly used in tunnels, shotcrete pavements, road pavements in airport runways and highways, and industrial and water structures owing to its high abrasive and tensile strengths, stabilisation of slopes and retaining wall construction, earthquake-resistant structures, and repair and reinforcement of bearing elements of buildings and engineering structures [12].In particular, steel fibre reinforced concrete pavement roads have high fatigue and impact strength, as well as sufficient strength against repeated loads and impacts from vehicle wheels.Therefore, steel fibres make brittle concrete structures flexible and durable because they act as bridges between microcracks and transfer stress over a large area.As a result, the stress distribution within the concrete changes, and the load-carrying capacity significantly increases [13][14][15].In studies on steel fibre concrete, it has been determined that fibres have an effect of approximately ±25 % on the compressive strength of concrete; however, the effect of fibres on flexural strength is higher than that on tensile and compressive strengths.The final flexural strength becomes up to 50 % higher than that of normal concrete, and the tensile strength is also higher than that of conventional concrete [16][17][18].Similarly, it has been determined that fibres do not have a significant effect on the compressive strength of concrete and decrease strength by 5.10 % to 9.59 %, and increase the flexural strength by up to 21.15 % [19,20].In addition, in very few studies in the literature, it has been observed that steel fibre reinforced concrete reduces the concrete pavement thickness by up to 20.50 % with the addition of 0.5 % steel fibre depending on the project traffic load, reliability coefficient, and bearing strength of the soil [21].Most existing studies using steel fibre only aimed to improve the strength properties of concrete.However, these studies failed to apply a multidisciplinary approach or ignored the use of steel fibre concrete as road pavement.For this reason, the potential for the use of steel fibre reinforced concrete as road pavement for different traffic and soils and the thickness-cost effect have not been thoroughly addressed until today.In this study, unlike in the limited number of previous studies, the use of concretes containing different ratios of steel fibre on very weak soils such as plastic clay under different traffic loads was investigated.For this purpose, specimens of fibrous concrete were subjected to a series of tests, including workability, compressive, flexural, splitting tensile strength, and freezethaw tests, under a variety of curing conditions.In addition, using the AASHTO 1993 design method, the thicknesses of the road pavements for steel fibre reinforced concrete were determined, and current cost analyses were performed according to these thicknesses.

Materials
In this study, the concrete mixture was composed of crushed sand, crushed stone, Portland cement, mixing water, steel fibres, and a superplasticiser.In all mixtures, 0-5 mm crushed sand (specific gravity 2.77 kg/m 3 ), 5-11 mm crushed stone-I (specific gravity 2.79 kg/m 3 ), and 11-22 mm crushed stone-II (specific gravity 2.80 kg/m 3 ) were used at rates of 22 %, 38 % and 40 %, respectively.The particle size distribution of the aggregate mixture according to the TS EN 933-1 [22] standard limits is shown in Figure 1.Portland cement (CEM I 42.5R) with a specific gravity of 3.08 g/cm 3 , specific surface of 3.720.00cm 2 /g, SiO 2 content of 19.41 %, and 7-day compressive strength of 57.40 % was used in the mixtures.Tap water of Tekirdağ/Çorlu country was used as the mortar mixing water.Steel fibres with a length of 60 mm, diameter of 0.90 mm, and slenderness of (L/d) 65 with hook ends were used in the production of concrete (Figure 2).The tensile strength of the steel fibres with a density of 7.85 gr/cm 3 was 1150 N/mm 2 according to the TS EN 14889-1 [23] standard.As a chemical additive, 1.34 % superplasticiser with a specific gravity of 1.11 g/cm 3 was used to increase the workability of fresh concrete, which became harder with the addition of steel fibres and to provide ideal performance.

Preparation of concrete mix specimens
The water/cement ratio was taken as 0.40 in all mixtures with and without steel fibres, and this ratio was kept constant.Steel fibres were added to the concrete at rates of 0, 0.75 %, 1.00 %, 1.25 %, and 1.50 % by weight, and five series of mixtures were produced with four different fibre-volume ratios of steel fibres and fibre-free control concrete.The control and steel fibre reinforced mixture specimens produced were coded as follows, and the material ratios in the mixtures are listed in Table 1.The mixing process was initiated by dry mixing of cement, sand, and crushed stones based on the mixing ratios listed in Table 1; then, half of the plasticiser and half of the water were added after being mixed in another place.The remaining amounts of plasticiser and water were added in a controlled manner to ensure the homogeneity of the mixture.After the concrete entered a flowing state, steel fibres were added to the mixture and sprinkled in the last stage, and the mixing was continued until they were homogeneously dispersed.The mixing was completed after 15 min.An image of the fresh steel fibre concrete mixture is shown in Figure 3.The produced concrete specimens were compacted after being placed in moulds of different sizes for each experiment (Figure 4).After approximately 24 hours, the specimens were removed from the moulds and cured by being kept in a water-filled curing pool at 23±2°C for 7, 28, and 90 days.At the end of the curing process, all specimens were kept in a laboratory environment and turned into saturated surface dry (SSD).Hardened concrete experiments were performed on the SSD specimens.

Workability and fluidity properties of concrete
A slump test was applied to the mixture specimens according to the TS EN 12350-2 [24] standard to determine the consistency and workability of the fresh concrete.The experiment was conducted by measuring the amount of collapse of the fresh concrete placed in the cone after the cone was lifted in the vertical direction under its own weight (Figure 5).

Compressive strength
The compressive strength of concrete is its ability to resist the influence of an axial compressive load before breaking.An experiment was performed to determine the load that a unit area of the specimen could carry.The compressive strength of concrete specimens is determined by selecting the loading rate in the range of 0.2-1.0MPa/s (N/mm 2 .s), according to the TS EN 12390-4 [25] standard.The compressive strength test setup is shown in Figure 6.

Flexural strength test
Flexural strength is a measure of the tensile strength of the outer fibres of a material.This property is determined by applying loads to cylindrical or prismatic specimens until the material breaks, using installing mechanisms that apply loads at three or four points.The experiment was performed at a loading rate of 0.04-0.06MPa/s (N/mm 2 •s) in accordance with the TS EN 12390-5 [26] standard.The flexural strength test setup is shown in Figure 7.The flexural strengths of the concrete specimens were calculated using equation (2). where:

Splitting tensile strength test
Knowledge of the splitting-tensile strength of concrete is critical for crack and structural analysis.Tensile strength is important for preventing cracks in mass concrete, water tanks, nuclear power plants, airports, prestressed concrete, and road construction.Based on the TS EN 12390-6 [27], a load was applied to the specimen placed in the test device, as shown in Figure 8. Tensile strengths were formed perpendicularly to the compressive stresses along the linear load applied to the specimen.The concrete specimen underwent shortening where the load was applied and elongation along the horizontal axis in the middle region.The applied load was continued until the specimen broke parallel to the loading direction, and the fracture load was measured [19].The splitting tensile strengths of the concrete specimens were calculated using equation ( 3):

Freeze-thaw resistance test
This experiment was conducted to determine the performance of concrete against the environmental conditions to which it will be exposed during its service life.Specimens produced within the scope of the experiment were tested for freeze-thaw resistance according to the TSE CEN/TS 12390-9 [28] standard.The freeze-thaw cabinet in which the specimens were placed and the test cycles are shown in Figure 9.According to the standard, the resistance of specimens to the effect of freeze-thaw is determined by weighing the mass loss caused by flaking after 28 freeze-thaw cycles at -20°C for 4 hours and at +20°C for 4 hours.The particles separated from the specimen mass were weighed and their count per square meter of the specimen surface was calculated using equation (4) to measure the amount of flaking. where:

Design methods
In highway pavement design, many parameters, such as traffic load, bearing capacity of the subgrade, properties of the materials used, regional climatic conditions, service life of the road, and service quality, are considered.Because the AASHTO 1993 method has been used for rigid and flexible pavements and road design on Turkish highways for years, this study included calculations based on the AASHTO 1993 method for rigid pavement design.In this context, the AASHTO 1993 equation for the performance of a concrete pavement, which is obtained by considering the effect of the   Analysis of fibre reinforced concrete for road pavements on very weak soils

Slump test results
The consistency and workability properties of the fresh concrete mixture specimens were determined by a slump test according to the TS EN 12350-2 [24] standard, and the slump values of the specimens are shown in Figure 10. Figure 10 shows that the slump value decreases as the steel fibre content in the concrete mixtures increases; in other words, the workability decreases.It was determined that the workability of concrete reinforced with fibres decreases with an increase in fibre volume, especially after the rate of 0.75 % steel fibre, and the degree of slump entered the S3 consistency class at the rate of 1.50 % steel fibre.The results of the current study are compatible with those in the literature [31], as it has been observed in the literature that the workability of concrete mixtures decreases after a 0.8 % steel fibre ratio in studies using different ratios of steel fibres [32,33].

Compressive strength test results
The control and fibre-added mixtures were placed in cubic moulds measuring 150×150×150 mm and kept in the laboratory for 24 h.Afterwards, the hardened specimens were removed from the moulds and kept in the curing pool at 23±2°C for 7, 28, and 90 days.All specimens were removed from the pool at the end of the curing period and turned into saturated surface dry (SSD) in a laboratory environment.These specimens were tested using a 300-ton compression capacity press with a loading speed of 0.50 MPa/s.The variation in the compressive strength of the specimens, which were prepared in triplicate for each ratio, together with the steel fibre additive ratio and curing time, is shown in Figure 11.As shown in Figure 11, the compressive strength values of the concrete specimens decreased compared to those of the control specimens for all curing times, depending on the amount of steel fibre.These reductions in compressive strength were 2.07 %, 4.16 %, 8.33 %, and 12.49 % for the specimens subjected to curing for 28 days, respectively.This can be attributed to steel fibres having a higher specific gravity compared to aggregates within the scope of this study.Similarly, Soroushian and Bayasi [34] stated that fibres with a high slenderness rate negatively affect workability.In the literature, it has been stated that the use of steel fibres with three different slenderness (L/d) values such as 80, 65, and 55 in concrete production, as well as steel fibre with hook ends with different slenderness values and proportions, reduces the compressive strength of concrete.However, it has been reported that it significantly increases tensile and flexural strengths, and when up to 1.5 % steel fibre is used in concrete, the compressive strength of concrete varies by up to ±25 % compared to that of non-fibre concrete [35][36][37][38][39][40][41].  Figure 12 shows that at the end of the 28-day compressive strength test, all specimens met the minimum characteristic compressive strength (C 30/37) requirement according to the TCK Specifications.

Flexural strength test results
The prepared 150×150×525 mm concrete beam specimens were subjected to a four-point flexural strength test after 7, 28, and 90 days of curing.The test was conducted in a 20-ton bending capacity press at a loading speed of 0.05 MPa/s.The variation in the flexural strengths of the control and steel fibre reinforced specimens with the additive ratio is shown in Figure 13.

Tacettin Geçkil, Mehmet Mahmut Tanyıldızı, Ceren Beyza İnce
As shown in Figure 13, the flexural strength values of the concrete specimens with the steel fibre additive were higher than those of the control specimens.Considering the 28-day curing period of the concrete, it was observed that this increase in flexural strength occurred at higher rates of 9.77 %, 17.48 %, 28.37 %, and 39.10 %, respectively, compared to the control concrete.The reason for this is thought to be the ductile behaviour under bending, which is the most important feature of steel fibre reinforced concrete.In previous studies, it was observed that the addition of steel fibres to concrete increased its flexural strength by 31.75 % [42].

Figure 13. Flexural strengths of control and steel fibre reinforced specimens
According to the TCK Concrete Road Pavements Technical Specifications [43], the 28-day flexural strength of concrete roads must be higher than 4.50 N/mm 2 .In this study, flexural strengths of the 28-day-old specimens were compared with the specifications, and the results are shown in Figure 14.

Load-deflection curves and flexural toughness test results
The mid-load-span deflection curves obtained from the fourpoint flexural test of steel fibre reinforced specimens were prepared using the data obtained after recording with the image recorder at the time of the test.The toughness values obtained by calculating the areas under these curves shown in Figure 15 are shown in Figure 16.

Splitting tensile strength test results
To determine the splitting tensile strength of the control and steel fibre reinforced mixtures at the end of 7, 28, and 90 days of curing, three cylindrical specimens with dimensions of Ø150x300 mm were tested for each ratio.The experiment was conducted at a loading speed of 1.6 kN/s using a press with a compression capacity of 300 tons.The variation in the splitting tensile strength of the specimen with the steel fibre additive ratio is shown in Figure 17.
As shown in Figure 17, there was a significant increase in the splitting tensile strength values of the concrete specimens with Analysis of fibre reinforced concrete for road pavements on very weak soils the steel fibre additive compared to the control specimens.This increase in the 28-day splitting tensile strength occurred at rates of 10.96 %, 21.71 %, 25.50 %, and 29.08 %, respectively, compared to the control concrete.It is thought that the reason for this is that long fibres have a higher adherence to the cement matrix and transfer the tensile stresses formed in the concrete more effectively compared to short fibres.In the literature, it has been observed that the splitting tensile strength increases by up to 35 % compared to the control concrete with the use of steel fibres, and this increase varies in parallel with the increase in the rate of steel fibres added to the concrete [14,44].According to the TCK Technical Specifications, the 28-day splitting tensile strength values of the concrete pavement specimens were compared based on a minimum value of 3.30 N/mm 2 , and the results are shown in Figure 18.
Figure 18 shows that the 28-day splitting tensile strength of the fibrous specimens meets the minimum characteristic splitting tensile strength (3.30N/mm 2 ) required by the TCK Technical Specifications.

Freeze-thaw resistance test results
A freeze-thaw experiment was conducted to determine the resistance of the steel fibre reinforced concrete pavement as a result of freeze-thaw periods during its service life.Control and steel fibre reinforced concrete specimens were subjected to a freeze-thaw resistance test based on the Capillary suction of deicing solution and freeze-thaw test (CDF) method, according to the TSE CEN/TS 12390-9 [28] standard.According to Table 3, specified in accordance with the TCK Technical Specifications [43] in Turkey, the freeze-thaw resistance category was taken as FT2, depending on the climatic conditions of the region where the study was conducted.Before the experiment, after the fresh concrete was placed in the moulds, the moulds were protected against drying at 20±2°C for one day, and after 24±2 hours, the specimens were removed from the moulds and placed in a curing pool filled with tap water at a temperature of 20±2°C.Specimens were removed from the curing pool on the 7 th day and kept in a curing room at 20±2°C and 65±5 % relative humidity for 21 days until testing began.Specimens cured for 28 days were saturated with a test liquid (97 % tap water and 3 % NaCl by mass) capillary for 7 days, and the experiment started when the specimens were 35 days old.At the end of 28 freeze-thaw cycles, entailing freezing for 4 hours at -20°C and thawing for 4 hours at +20°C, the specimens produced were evaluated by scaling the  Tacettin Geçkil, Mehmet Mahmut Tanyıldızı, Ceren Beyza İnce masses they lost.The mass loss values of the specimens were calculated using Equation ( 4), and the results are given in Table 4.The changes in mass loss are shown in Figure 19.Table 4 shows that according to the specification [43], the requirement for all specimens to have a mass loss of less than 0.50 kg/m 2 after 28 cycles was met.The highest mass loss among the specimens occurred in concrete containing 1.50 % steel fibre (1.50SF+C).Compared to the control specimens, it was observed that the mass losses decreased by 0.88 %, 0.29 %, 0.88 % and 2.34 %, respectively, and thus the freeze resistance increased.This is considered to have occurred because of the lower internal stress that occurs in concrete as a result of freezing due to the higher bond strength of steel fibre reinforced specimens.However, in previous studies, it has been reported that specimens with steel fibre do not have a positive effect in terms of compressive strength, but the mass loss of specimens decreases (freeze-thaw resistance increases) as the amount of steel fibre increases according to the freeze-thaw test [45].

Concrete pavement thickness design results using the AASHTO method
Highway concrete pavement design was carried out according to the AASHTO 1993 design guide, based on 0 %, 0.75 %, 1.00 %, 1.25 %, and 1.50 % steel fibre reinforced concrete specimens.The traffic of four different projects for soil with a very low bearing capacity (plastic clay) was considered in the calculations.In traffic selection, 1×10 6 standard axle load repetitions were considered as light vehicle traffic, where the annual average daily heavy vehicle traffic (AADHVT) is less than 500; in other words, W 8.2 was less than 3,1×10 6 .For heavy vehicle traffic, 10×10 6 , 100×10 6 , and 200×10 6 standard axle load repetitions with AADHVT values greater than 500 were used.
In accordance with the TCK Concrete Road Technical Specifications, the minimum strength requirements used in the design of concrete road pavements are listed in Table 5 [43].
The S' c and E c values used in the design of the control and fibre reinforced specimens are listed in Table 6.
In soils with a very weak bearing capacity (k=150 pci), the pavement thicknesses for different project traffic loads were determined using Equation 5, and the results are shown in Figure 20. Figure 20 shows that in soils with a very low bearing capacity, steel fibre reinforced specimens showed a decrease in concrete pavement thickness compared to the control specimens.This reduction is as follows for the Analysis of fibre reinforced concrete for road pavements on very weak soils 1×10 6 , 10×10 6 , 100×10 It was determined that the experimentally calculated compressive, flexural, and splitting tensile strength results met the concrete pavement design criteria, and the steel fibres added to the concrete increased the flexural strength of the concrete compared to that of the control concrete, resulting in a decrease in the concrete pavement thickness.In very few studies in the literature, it has been determined that the addition of 0.5 % steel fibre reduces the concrete pavement thickness by 20.50 %, depending on variable criteria such as project traffic and bearing strength of the soil [21].

Cost analysis
Because construction cost prices are constantly changing globally, the US dollar was used for cost calculation for road concrete pavement thickness of the control and steel fibre reinforced specimens.Because the 20 cm thick plant mix foundation (PMF) application recommended by AASHTO under the concrete slab was performed for all specimens, it was not included in the scope of this cost analysis.The unit prices used in the cost analysis are listed in Table 7.In the cost analysis, only the effect of steel fibre on the cost of concrete pavement material was considered, and the cost and environmental impact of construction activities were not considered.
The unit prices of the control and steel fibre reinforced specimens were calculated using Table 7 and are listed in Table 8.
The costs of the control and steel fibre specimens within the scope of this study are shown in Figure 21.As Figure 21 shows, if steel fibre reinforced concrete is used instead of control specimens in the design of the concrete pavement thickness, a cost increase of 56.50-74.07% can be obtained according to the pavement layer thickness for different project traffic loads.In previous studies, it was determined that the addition of steel fibre to concrete at a rate of 0.25 % to 1.00 % by volume increases the unit cost of the concrete by 60.10-139.80 % [21].In another study, it was observed that the service life of steel fibre reinforced concrete was 6.5 times longer than that of concrete without additives.However, considering the same service life, it has been determined that even when the Tacettin Geçkil, Mehmet Mahmut Tanyıldızı, Ceren Beyza İnce pavement thickness of concrete is decreased by approximately 50 % with the addition of steel fibres, its cost increases by 41 % [46].Because concrete pavement roads are often exposed to harsh environmental conditions throughout their service life, it is thought that the addition of steel fibre to concrete will be more cost effective in the long run because it increases the resistance and ductility of concrete against crack development; has a significant effect on flexural strength, fracture energy, and toughness; increases wear strength depending on the increased fibre content; and increases the durability of the pavement.

Conclusions
In this study, the effects of using different ratios of steel fibres in concrete pavements built on soils (plastic clays) with a very weak bearing capacity on the pavement thickness and cost were investigated, and the following results were obtained: -It was observed that the slump value of the concrete mixes decreased, which indicated that the concrete became less workable as the percentage of steel fibres in the mixture increased.-Depending on the amount of steel fibre, the compressive strength values of the concrete specimens decreased compared to those of the control specimens.The reductions in compressive strength were 2.07 %, 4.16 %, 8.33 %, and 12.49 % for the 0.75 %, 1.00 %, 1.25 %, and 1.5 % steel fibre reinforced specimens, respectively.These results are due to the use of steel fibres with a specific gravity higher than that of the aggregate in the scope of this study.
-The flexural strength values of the concrete specimens were higher than those of the control concrete.Considering the 28-day curing period of the concrete, these increases in flexural strength were found to occur at high rates of 9.77 %, 17.48 %, 28.37 %, and 39.10 % for specimens with steel fibre additives of %, 1.00 %, 1.25 %, and 1.5 %, respectively, compared to the control concrete.This can be explained by the fact that the steel fibres added to the mixtures prevented and delayed crack initiation and growth by bridging the cracks in the matrix.
-There was an increase in the splitting tensile strength values of the concrete specimens with the steel fibre additive compared to the control concrete.These increases in the 28day splitting tensile strength were 10.96 %, 21.71 %, 25.50 %, and 29.08 % for specimens with steel fibre additives of 0.75 %, 1.00 %, 1.25 %, and 1.5 %, respectively, compared to the control concrete.This is thought to be because long fibres have a stronger bond with the cement matrix compared to short fibres, and transfer the tensile strength formed in concrete more effectively than short fibres.
-The calculations showed that the concrete pavement thickness of the steel fibre reinforced specimens to be built on soils with a very low bearing capacity (plastic clay) decreased by an average of 4.37-18.66% at different traffic loads (1×10 6 , 10×10 6 , 100×10 6 , and 200×10 6 ), but as a result, the costs increased within the range of 56.50-74.07%.Thus, it was observed that the physical and mechanical requirements required for the design of concrete pavements are met when steel fibres are added to concrete built on very weak soils.In addition, rigid road pavement layer thicknesses decreased, but construction costs increased.However, considering the curative effect of steel fibre additives on the properties of concrete and the fact that concrete pavements are often exposed to harsh environmental conditions during their long service life, it is considered that the cost increase will not have a negative impact.

Figure 1 .
Figure 1.The particle size distribution of the aggregate mixture

Figure 3
Figure 3. Fresh concrete mixture with steel fibre

Figure 5 .
Figure 5. Determination of the slump size of fresh concrete

Figure 6 .
Figure 6.Compressive strength test Analysis of fibre reinforced concrete for road pavements on very weak soils L -Distance between two supports [mm] b -Width of the specimen [mm] h -Height of the specimen [mm].

Figure 8 .
Figure 8. Splitting tensile strength test ) where: σ -Splitting tensile strength [MPa] P c -Fracture load [N] L -Distance between specimen contact line and loading section [mm] d -Cross-sectional size of the specimen [mm]

Figure 9 .
Figure 9. a) Freeze-thaw cabinet; b) cycle time 8950 • 10 3 Pa) Modulus of elasticity of concrete It has been suggested by AASHTO to calculate this using the equation E c ' value may vary depending on the bearing capacity, density, moisture content, and type of the soil.Commonly used values for 'k' are in the range of 150≤k≤550.The 'k' value was taken as 150 in calculations in accordance with the AASHTO 1993 Design Guidelines.

Figure 10 .
Figure 10.Effect of steel fibre on the slump values of fresh concrete

Figure 11 .
Figure 11.Compressive strengths of control and steel fibre reinforced specimens

Figure 12 .
Figure 12.Compressive strength design criterion of specimens

Figure 14 .
Figure 14.Flexural strength design criteria chart of specimens

Figure 17 .Figure 18 .
Figure 17.Splitting tensile strengths of control and steel fibre reinforced specimens

Figure 19 .
Figure 19.Freeze-thaw mass loss graph of the specimens

Figure 20 .
Figure 20.Concrete pavement thickness values for mixture specimens

Figure 21 .
Figure 21.Cost analyses for concrete specimens

Table 1 . Material ratios in mixtures
[29]ton standard equivalent single-axle load repetition number (W 8,2 ) on the performance of the pavement, is given in equation 5. Concrete pavement thickness (d) is calculated with the help of this equation[29].The meanings of the parameters given in Equation5and the values selected in this study in accordance with the AASHTO 1993 design criteria are listed in Table2.According to the AASHTO 1993 method, the (p o ) value was determined as 4.5 for rigid pavements.In the calculations made for the study, p 0 = 4.5 and p t = 2.5 were selected.