Cellulose-based industrial plant stalks and pyrolytic biochar for use as a modifier and stabilizer in stone mastic asphalt mixtures

Abstract

The invention relates to cellulose-based industrial plant stalks, from which the fibers have been removed, and the pyrolytic biochar obtained from these stalks, which function as stabilizers to improve the drain-down characteristics and as modifiers to enhance the performance properties of Stone Mastic Asphalt (SMA) mixtures.

Description

[0001] DESCRIPTION

[0002] CELLULOSE-BASED INDUSTRIAL PLANT STALKS AND PYROLYTIC BIOCHAR FOR USE AS A MODIFIER AND STABILIZER IN STONE MASTIC ASPHALT MIXTURES

[0003] TECHNICAL FIELD

[0004] The invention relates to the fibers of cellulose-based industrial plant stalks and the pyrolytic biochar derived from these stalks, which function as stabilizers to improve the drain-down characteristics and as modifiers to enhance the performance properties of Stone Mastic Asphalt (SMA) mixtures.

[0005] PRIOR ART

[0006] Stone Mastic Asphalt (SMA) mixtures, developed to prevent rutting, one of the most common types of pavement distress, are a type of hot mix asphalt that stands out with its coarse aggregate skeleton and high bitumen content. The high bitumen content can cause the bituminous binder to drain off the aggregate during production, storage, transportation, and placement. According to the SMA mixture design criteria, to prevent the bitumen from draining off the aggregate, it is mandatory to add at least 0.3% fiber stabilizer by the weight of the mixture, and the drain-down must not exceed 0.3% according to the Schellenberger bitumen drain-down test. Various materials such as cellulose fiber, mineral fiber, plant-based fiber, and similar materials are used as fiber stabilizers. In addition, in SMA mixtures used in hot climate regions, polymer- modified bituminous binders are typically employed alongside fiber stabilizers to improve the performance characteristics of the pavement.

[0007] Ongoing research continues to investigate the effectiveness of materials to be used as stabilizers and modifiers in SMA mixtures to prevent the drain-down of the bituminous binder and improve the performance properties of the mixtures.

[0008] In a study investigating the use of natural hemp fiber as an alternative to commercial cellulose fiber in SMA mixtures, it was reported that hemp fibers were more effective in minimizing the drain-down of the bituminous binder compared to commercial cellulose fibers (Aslan, 2020).

[0009] In a study by Oner and Ozda§ (2022), which focused on the problem of bituminous binder drain-down in SMA mixtures, the use of waste materials obtained from textile factories as a replacement for traditionally used mineral and cellulose fibers was examined. Within the scope of the study, Marshall stability tests, Schellenberg bitumen drain-down tests, and sand patch tests were performed on samples containing varying amounts of textile waste and cellulose fiber. The results showed that textile waste contributed more to asphalt stability and significantly reduced bituminous binder drain-down compared to cellulose fibers.

[0010] Panda et al. (2013) used coconut fibers as an additive to improve the engineering properties of SMA mixtures and prevent the drain-down of the binder on the aggregate. Experimental findings showed that the use of coconut fiber at a rate of 0.3% resulted in improved engineering properties of the SMA mixture.

[0011] Vale et al. (2013) used coconut fiber as an additive material in SMA mixtures and indicated that this fiber could be used as a substitute for commercial cellulose fibers.

[0012] In a study conducted by Muniandy and Huat (2006), palm fiber was used to modify the bituminous binder for use in SMA mixtures. The researchers reported that the rheological properties of the fiber-modified binder improved, the high-temperature performance grade increased by one level, and the fatigue performance of the SMA mixtures containing fibers improved.

[0013] Behbahani et al. (2009) used rock wool as a fiber stabilizer in SMA mixtures and compared its effectiveness with commercial cellulose fibers. The authors reported positive results for the use of rock wool as an additive material in SMA mixtures.

[0014] Nazir et al. (2019) evaluated jute fiber as an alternative solution to the bituminous binder drain-down problem in SMA mixtures and observed that jute fiber reduced the binder drain-down value to 0.025%, which complies with specification limits.

[0015] In a review study by Razahi and Chopra (2020), studies were reported where sisal fiber was used as an additive material in SMA mixtures. The study stated that sisal fiber prevented binder drain-down.

[0016] Munda (2013), in a study using bamboo fiber as an additive material in SMA mixtures, reported that bamboo fiber produced favorable results compared to cellulose fiber.

[0017] The patent study numbered EP1520932 relates to the use of flax and hemp fibers, as well as their mixtures, as stabilizing additives in SMA mixtures.

[0018] The patent study numbered RU2620825 relates to the use of paper pulp and waste paper as stabilizing additives in SMA mixtures. As summarized in the state of the art, the fiber parts of natural plants are used as alternative additive materials for asphalt mixtures; however, these fibers are utilized industrially in various sectors as high-value-added materials. This situation is regarded as a disadvantage.

[0019] OBJECTIVE OF THE INVENTION

[0020] The objective of the invention is to process the ground material obtained from the waste stalk portions of plants and the biochar derived from these stalks into stabilizers and modifiers for use in SMA mixtures, enabling their utilization in high- value-added sectors.

[0021] Another objective of the invention is to utilize the ground material and biochar obtained from the waste stalk portions of flax and hemp plants, after their valuable fiber parts have been removed, as stabilizers and modifiers in SMA mixtures, which differentiates this invention from the known state of the art.

[0022] Another objective of the invention is to use, for the first time, the material obtained by grinding the low-economic-value stalks of hemp and flax (from which primary / core fibers have been removed) in SMA mixtures. This purpose is particularly prominent due to its low cost.

[0023] In the known state of the art, studies have been conducted on biochar obtained from various biomasses in relation to bituminous binders and traditional bituminous mixtures; however, there have been no studies on SMA mixtures containing biochar as a replacement for polymer stabilizers and modifiers. Specifically, no information exists in the literature regarding the production of biochar through the pyrolysis of hemp / flax stalks and its activation with potassium hydroxide (KOH) for use as a stabilizer and modifier in SMA mixtures. Additionally, there is no known information on the use of biochar derived from any biomass and activated with potassium hydroxide (KOH) as a stabilizer / modifier in SMA mixtures.

[0024] Another objective of the invention is to promote the use of biochar as a stabilizer and modifier in utilizing various plant, animal, and natural waste materials. This leads to lower costs, the production of high-value-added products from waste, and environmental benefits by reducing waste disposal issues. DETAILED DESCRIPTION OF THE INVENTION

[0025] In one embodiment of the invention, the material obtained by grinding industrial hemp and flax stalks, after their fibers have been removed, is used in SMA (Stone Mastic Asphalt) mixtures as a stabilizer to prevent the drain-down of the binder from the aggregate.

[0026] In the mentioned embodiment, flax and hemp stalks were ground to a size of <0.075 mm and added to SMA mixtures. The material obtained by grinding the flax and hemp stalks and its combinations were added to the SMA mixtures in such proportions as to comply with the Schellenberger limit (it is mandatory to add at least 0.3% of fiber stabilizer by the weight of the mixture in SMA to prevent bitumen draindown, and the Schellenberger bitumen drain-down test result must not exceed 0.3%).

[0027] In another embodiment of the invention, traditional biochar (biochar produced without an activation agent, defined as traditional biochar in this patent) and biochar with high surface area and pore volume, obtained through potassium hydroxide (KOH) activation, were used as stabilizers to prevent drain-down from the aggregate and as modifiers to enhance the performance of SMA mixtures similar to polymers. The difference between KOH-activated biochar and traditional biochar lies in the principle of initially mixing biomass with KOH in certain proportions, with activation achieved by adding KOH in amounts ranging between 1 to 4 times the biomass. The resulting biochar was treated in a 1 M HCI solution for 24 hours to remove inorganic compounds and washed with distilled water until the pH reached 7. In this embodiment, biochar produced through the pyrolysis of industrial hemp stalks, flax stalks, or a combination of hemp / flax stalks, and treated to remove inorganic compounds through KOH activation, was ground or sieved to a size of <0.075 mm (a size corresponding to the No. 200 sieve, with material passing through this sieve defined as mineral filler. Biochar in the mineral filler size exhibits a more homogeneous distribution in the bituminous binder, and literature indicates that biochar at this size has a more significant effect on binder performance. Therefore, in this patent, biochar of <0.075 mm size was added to the SMA mixture) and used in SMA mixtures for two distinct purposes: as a stabilizer and as a modifier. During the pyrolysis process, nitrogen gas was introduced into the reactor for 15 minutes at the start of the process to ensure an oxygen-free environment for obtaining solid products. Literature studies indicate that the total surface area of biochar increases up to pyrolysis temperatures of 500 °C and decreases beyond this point. Based on this, the pyrolysis temperature was set at 500 °C. In SMA mixtures used in hot climate regions, polymer-modified bituminous binders are typically used alongside fiber stabilizers. This involves a two-stage modification where the bituminous binder is first modified with a polymer, and then a fiber stabilizer is added. In this invention, the developed product (hemp / flax-based biochar) was directly added to the mixture, replacing both the fiber stabilizer and the polymer, thus enabling single-stage modification. Biochar, in proportions that comply with the Schellenberger limit (maximum drain-down below 0.3%) as a fiber stabilizer, was added to the dry mixture (before adding the bituminous binder) at 0.3% of the mixture weight. Additionally, in line with literature recommendations (where polymer is generally added at 4% of the bituminous binder weight), biochar was added to the dry mixture at 0.3%, followed by the addition of the bituminous binder to produce the SMA mixture. The biochar thus acted as both a stabilizer and a modifier in the SMA mixture.

[0028] The developed stabilizers / modifiers not only affect the bituminous binder's drain-down values in SMA mixtures but also contribute to the resistance of SMA mixtures to short- and long-term aging, water damage, rutting, and fatigue.

Claims

CLAIMS1 . A pyrolytic biochar for use as a modifier and stabilizer in Stone Mastic Asphalt (SMA) mixtures, characterized in that it comprises material obtained by grinding the stalks of industrial hemp and flax after the fibers have been removed.

2. The industrial hemp and flax stalks according to Claim 1 , characterized in that the ground material has a particle size of less than 0.075 mm.

3. The pyrolytic biochar for use as a modifier and stabilizer in Stone Mastic Asphalt (SMA) mixtures according to Claim 1 , characterized in that it comprises material obtained by grinding the stalks of industrial hemp and flax after the fibers have been removed, in an amount of at least 0.3% by the weight of the mixture.

4. The pyrolytic biochar for use as a modifier and stabilizer in Stone Mastic Asphalt (SMA) mixtures according to Claim 1 , characterized in that the mixture contains potassium hydroxide (KOH) in an amount of 1 to 4 times the biomass.

5. A method for producing pyrolytic biochar for use as a modifier and stabilizer in Stone Mastic Asphalt (SMA) mixtures with KOH activation, characterized by the process steps of: o Grinding the flax and hemp stalks to a particle size of less than 0.075 mm and adding them to SMA mixtures; o Adding potassium hydroxide (KOH) as an activation agent; o Soaking the resulting biochar in a 1 M HCI solution for 24 hours to remove inorganic compounds, followed by washing with distilled water until the pH reaches 7; o Grinding / sieving the biochar, with the inorganic compounds removed, to a particle size of less than 0.075 mm to prepare it for use.