Use of diatomite as a performance enhancing additive in asphalt pavements

Abstract

This invention relates to asphalt pavements modified with diatomite in different sizes and addition rates to improve the mechanical characteristics of asphalt pavements.

Description

[0001] DESCRIPTION

[0002] USE OF DIATOMITE AS A PERFORMANCE ENHANCING ADDITIVE IN ASPHALT PAVEMENTS

[0003] TECHNICAL FIELD

[0004] The invention relates to diatomite modified asphalt pavements and the overall performance of the diatomite additive on the asphalt pavement when used in different proportions and with different grind sizes.

[0005] PRIOR ART

[0006] Most of the transportation activities are carried out via highways. Asphalt mixtures are the most widely used construction material for road pavement. Modification of asphalt mixtures has become almost mandatory today due to increasing stresses in pavements, shortening load cycle times, and declining binder quality. Materials such as polymers, filler materials, and fibers can be used as additives to modify asphalt mixtures.

[0007] Filler type additives can generally be added to asphalt mixtures in two different ways. In the first method, called the wet method, the filler additive is first added to the bituminous binder and then the modified bitumen and aggregate are mixed. In the second method, called the dry method, the additive is added directly into the aggregate mix. It is considered that there is no significant difference between the two methods in terms of final asphalt mix performance for addition rates considerably lower than the appropriate normal utilization rate.

[0008] Diatomite is a low-cost mineral that is easy to produce and does not cause environmental pollution. Turkey has the largest diatomite reserves after United States and China. The distinctive characteristics of diatomite have led to its adoption in a variety of industrial uses, with primary applications in liquid filtration and serving as a bulking agent, as well as in the production of dyes. Furthermore, diatomite has also been used in insulation, especially in the production of fireproof bricks, and in fine abrasion applications such as toothpaste and various polishing products. In patent application no, CN113213817A, special polymer fibers were used in some mixtures and lignocellulose fibers were used in others during the preparation of diatomite modified asphalt mixtures. The use of special polymer fibers showed 1.1 times more resistance to water damage than lignocellulose fibers, and the high temperature resistance, water damage resistance, and low temperature cracking resistance of diatomite modified asphalt mixture increased with the continuous increase of SiO2 content in diatomite.

[0009] Application no. CN102219442A concerns the construction process of diatomite modified asphalt pavements. Diatomite modified asphalt pavement contains 4-5 parts asphalt and diatomite and 95-96 parts aggregate by weight. It is stated that the weight of diatomite should be between 12-15% of the weight of asphalt and diatomite. The diatomite rate of 15% can only be taken as an upper rate under special conditions.

[0010] Application no. CN105907115A mentions diatomite modified asphalts produced using diatomite with a particle size of 5-22 pm at 15% of the asphalt mass. It is stated that when asphalt cement is modified with diatomite, the softening point and high temperature performance increases, the temperature sensitivity decreases and the adherence of the asphalt with the aggregate increases. It is also stated that the modified asphalt has increased waterproofing characteristics and improved performance against aging.

[0011] OBJECTIVE OF THE INVENTION

[0012] Research involving a comparison of the use of different diatomite grind sizes and different rates in asphalt pavements in the present inventions is extremely limited.

[0013] Bitumen and aggregates used in asphalt mixtures are especially sensitive to repeated traffic loads, loading time, and temperature. Therefore, road pavements may deteriorate for various reasons even before their calculated service life. The primary way to prevent this deterioration is to improve the engineering properties of the mix using additives.

[0014] The potential of diatomite modification to improve the performance of asphalt mixtures has been demonstrated in many studies. However, the level of differentiation between different types of diatomite in these studies is considered limited. There are no patents on the effect of selected diatomite grind sizes and addition rates on the performance of asphalt mixtures.

[0015] The structural and characteristic features of the invention and all advantages thereof will be understood more clearly with the figures given below and the detailed written description provided with reference to these figures. Therefore, evaluation must be made by taking these figures and detailed description into account.

[0016] LIST OF DRAWINGS

[0017] Fig. 1 - Perspective view of high speed shear mixer

[0018] Fig. 2 - Laboratory type oven

[0019] Fig. 3 - Indirect tensile strength test results of control and diatomite asphalt mixtures at 0 °C

[0020] Fig. 4 - Indirect tensile strength test results of unconditioned control and diatomite modified asphalt mixtures at 25 °C

[0021] Fig. 5 - Indirect tensile strength test results of conditioned control and diatomite modified asphalt mixtures at 25 °C

[0022] Fig. 6 - Tensile strength rates of control and diatomite modified asphalt mixtures Fig. 7 - Deformation curves of conditioned control and 5% diatomite modified asphalt mixtures

[0023] Fig. 8 - Deformation curves of conditioned control and 10% diatomite modified asphalt mixtures

[0024] Fig. 9 - Deformation curves of conditioned control and 15% diatomite modified asphalt mixtures

[0025] DESCRIPTION OF TABLES

[0026] Table 1 - Gradation curves of diatomite additives

[0027] Table 2 - Penetration and softening point test results of control and diatomite modified bitumen

[0028] (1 ) : Command display of the high speed shear mixer

[0029] (2) : The knob for setting the revolutions per minute (rpm) of the device

[0030] (3) : Button for moving the device upwards

[0031] (4) : Button for moving the device downwards

[0032] (5) : Mixer grinder

[0033] (6) : Adjustable mini heater

[0034] (7) : Heater screen

[0035] (8) : Heater temperature control knob

[0036] (9) : Oven screen

[0037] (10) : Glass beaker

[0038] (11 ) : Steel container

[0039] (12) : Marshall sample molds

[0040] (13) : Steel shovel

[0041] DETAILED DESCRIPTION OF THE INVENTION

[0042] The invention provides originality by considering both the diatomite size and the addition rate when using diatomite as an additive in asphalt mixtures. Existing patents usually only consider the addition rate of the diatomite additive or the diatomite size. However, when the rate of diatomite addition into the asphalt mixture is changed, the effective grinding size also changes.

[0043] The high speed shear mixer device (Fig. 1 ) consists of a display indicator (1), speed adjustment knob (2), upward movement knob (3), downward movement knob (4), mixer blades (5). A mini heater (6) is placed externally at the bottom of the device to keep the bitumen warm. The mini heater has a display panel (7) and a temperature control knob (8). For bitumen modification, the glass beaker (10) previously filled with bitumen in a laboratory type oven (Fig. 2) is heated at 160 °C for 6 hours and then placed on the mini heater (6) in (Fig. 1), after checking the temperature and lowering the mixer blades (5) into the glass beaker (10), the shear mixing process is started. This process is performed at a shear rate of 4000 rpm with a shear time of 40 minutes. Wet or dry methods can be used to prepare the diatomite-modified asphalt mix. In the dry mixing method, diatomite is added to the asphalt and aggregate mix as a filler instead of natural filler material. When the wet method is used, diatomite modified asphalt binder is prepared before the mixture is prepared. Wet method was used in our invention. Diatomite additives were added to the bitumen at rates of 5%, 10% and 15% by weight (0.243%, 0.485% and 0.728%, respectively, based on total aggregateasphalt mixture weight) and diatomite modified bitumen and asphalt mixtures were prepared.

[0044] Gradation analysis results of the diatomite additives used are given in Table 1. Table 1 shows that D1 diatomite is the finest grade and D3 diatomite is the coarsest grade. 50% of D1 , D2 and D3 diatomite are finer than 9.46 microns, 111 .35 microns and 190 microns, respectively. Table 2 shows the penetration, softening point, and penetration index values of control (pure) and diatomite modified asphalts. The size of diatomite in the cement mixture can be up to 390 microns size and up to 390 microns size. It was observed that the penetration values of diatomite modified asphalts decreased by a minimum of 9.36% and a maximum of 21.81% compared to the control asphalt mixtures. Penetration values decreased with increasing diatomite content in all diatomite modified asphalt mixtures. When the softening point values given in Table 2 are analyzed, it is seen that all of the diatomite modified asphalt mixtures have higher softening point values than the control mixtures. The reason why diatomite additive generally increases softening point values and causes a decrease in penetration values is that the lightweight components of asphalt cement are absorbed by the porous structure of diatomite.

[0045] When the penetration index values are analyzed in Table 2, it is seen that the penetration index values of all diatomite modified asphalts are higher than the control bitumen, thus diatomite modification reduces the temperature sensitivity of asphalt cement. It was observed that increasing diatomite size and addition rate decreased the temperature sensitivity. It was observed that the highest penetration index value and the least sensitive to temperature were observed in 15% D3 mixtures with 1 .681 .

[0046] Dense graded asphalt concrete was designed in accordance with the Highways Technical Specifications and the bitumen content giving 4% air void was calculated as the optimum bitumen content and determined as 5.10%. It was observed that the asphalt mix at the specified rate met the other specification requirements. Standard Marshall briquettes were prepared with asphalt cement modified with D1 , D2 and D3 diatomite additives at optimum bitumen content and diatomite addition rates of 5-10- 15%. The prepared mixtures were subjected to an indirect tensile strength test at 0 °C, the results of which are shown in Fig. 3. The experimental results showed that the tensile strength of the modified mixtures increased with increasing amounts of diatomite in the mixtures modified with diatomite. The smallest tensile strengths were obtained with 15% addition of D1 diatomite (2494 kPa). When the diatomite content was increased to 10%, a 9.7% improvement in the cracking resistance of D3 modified mixtures was observed compared to the control mixtures. The low temperature tensile strengths of asphalt mixtures modified with D1 are lower than those of D2 and D3 diatomite used at the same addition rates.

[0047] The higher surface area of D1 diatomite may have increased the hardness of the mix by absorbing more bitumen. This may have resulted in a negative effect on the low temperature resistance of asphalt mixtures. The higher tensile strength of D2 and D3 diatomite confirms this idea. The resistance of the diatomite modified asphalt mixtures to water damage was determined according to AASHTO T283 method. The indirect tensile strength test was performed on three identical briquettes at 25 °C and the tensile strength values were averaged and given in Fig. 4 for unconditioned samples and Fig. 5 for conditioned samples. When Fig. 4 and Fig. 5 are examined together, although there is no significant difference between diatomite types in terms of tensile strength, asphalt mix samples modified with D3 showed the highest tensile strength at 10% addition rate in both conditioned and unconditioned samples.

[0048] In the conditioned mixtures, the highest tensile strength was obtained with D3 diatomite and the lowest tensile strength was obtained with D1 diatomite at the same addition rates. When the conditioned mixtures were evaluated, it was observed that the tensile strength of D3 modified asphalt mixtures increased by 22% or more at all addition rates compared to the control mixtures. This increase remained at 13% in D2 modified asphalt mixtures. Tensile strength rates of asphalt mixture samples are given in Fig. 6. All diatomite modified asphalt mixtures showed tensile strengths more than 80% higher than the control mixtures. It was observed that the TSR value of asphalt mixture could be increased by 22% with diatomite modification. D2 and D3 diatomite showed higher water damage resistance than D1 diatomite. Deformation curves of the conditioned samples are given in Fig. 7 - Fig. 9. According to Fig. 7 - Fig. 9, the amount of deformation decreased as the diatomite rate increased. While the highest deformation resistance was obtained with D2 diatomite at low (5%) addition rate, the highest deformation resistance was obtained with D3 diatomite at medium (10%) and high (15%) addition rates. A 37% reduction in deformation was obtained at D3 (15%) usage rate compared to the control mixtures.

[0049] D1 , D2 and D3 diatomite used within the scope of the invention show similar characteristics in terms of chemical composition. However, D1 diatomite has been ground to the finest grade, while D3 diatomite has been ground to the coarsest grade. When the mechanical test results of asphalt mixtures are evaluated, it is understood that D2 and D3 diatomite show better results than D1 diatomite. D1 diatomite creates a larger surface area with its fine structure and requires higher amounts of bitumen to coat the particles. The bitumen film around the particles becomes thinner for the same amount of bitumen. The thinness of the bitumen film reduces the flexibility of the mix and results in stiffer mixes. The lower cracking resistance of the D1 -modified asphalt mixture at low temperature seems to be related to the size of the surface area of the diatomite. The increase in surface area and slight decrease in tensile strength as the diatomite rate increases confirms this idea. s

[0050] The invention provides asphalt mixtures modified with diatomite in different proportions and sizes for use in the construction of highway pavements in different regions. The high cost of polymer materials currently used as asphalt additives raises concerns about economic sustainability. Since diatomite additive is generally produced as fillersized waste material in Turkey, its use in asphalt plants is considered important for the country in the context of sustainable future and clean energy.

[0051] Industrial Application of the Invention

[0052] Diatomite modified asphalt pavements can be applied by the same methods as bituminous hot mixes. Since it is economical and practical, it can be used in asphalt plants by mass production in road construction in industrial environments. Therefore, there is no need for additional application at the asphalt plant.

Claims

CLAIMS1. An asphalt cement pavement modified with diatomite for modifying asphalt pavements, characterized in that it comprises diatomite in an amount of 5% - 15% by weight of the total asphalt cement and having a size of up to 300 microns.

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