ISU evaluates lignin as additive in asphalt manufacturing
Of the 2.3 million miles of hard-surfaced roads in the United States, approximately 96 percent of those are covered with asphalt. That's quite a market. Recent studies at Iowa State University (ISU), sponsored by the Iowa Department of Transportation, have been evaluating the lignin/phenol content of bio-oil and distillers grains as a manufacturing component of hot-mix asphalt (HMA). HMA is used to build new roads, but is used most prolifically in patches and repairs.
Including a low-cost antioxidant in the mix would increase the service life of low-volume roadways since asphalt is susceptible to oxidative degradation. The antioxidant characteristics of lignin make it an attractive additive for asphalt producers, according to Nicolaus McCready, graduate student at ISU. In the past, researchers have found that the addition of lignin increases the stiffness of asphalt, therefore increasing the high and intermediate temperatures at which asphalt can perform satisfactorily as pavement. In addition, lignin derived from wood products has been shown to act as an antioxidant in asphalt.
Little research has been done to evaluate the performance of lignin derived from bio-oil in this application, which ISU said can be extracted using a simple technique. ISU tested asphalt mixtures that had different lignin contents for elasticity and viscosity, and compared them with samples of pavement made with other ingredients. The lignin from bio-oil was found to be is insoluble in water and mixed well into asphalt.
Including a low-cost antioxidant in the mix would increase the service life of low-volume roadways since asphalt is susceptible to oxidative degradation. The antioxidant characteristics of lignin make it an attractive additive for asphalt producers, according to Nicolaus McCready, graduate student at ISU. In the past, researchers have found that the addition of lignin increases the stiffness of asphalt, therefore increasing the high and intermediate temperatures at which asphalt can perform satisfactorily as pavement. In addition, lignin derived from wood products has been shown to act as an antioxidant in asphalt.
Little research has been done to evaluate the performance of lignin derived from bio-oil in this application, which ISU said can be extracted using a simple technique. ISU tested asphalt mixtures that had different lignin contents for elasticity and viscosity, and compared them with samples of pavement made with other ingredients. The lignin from bio-oil was found to be is insoluble in water and mixed well into asphalt.
Many different additives, such as elastomers, rubbers and plastomers, are available for asphalt binders and are commonly used to pave high-volume roadways. However, these are expensive, increasing the cost of HMA by up to $10 per ton. Many asphalt antioxidants have been studied in the past, but because of the toxicity of compounds like hydrated lime and zinc diabutyldithiocarbamate (ZDBC), their use has been limited. McCready said it is ISU's goal to find a "low-cost, environmentally friendly antioxidant for use in HMA pavements."
Since lignin can be obtained from the minimal further processing of distillers grains, a coproduct of ethanol production, McCready said distillers grains is a readily available feedstock for asphalt pavement that would be considerably cheaper than existing additives. Modifiers used in asphalt binders are currently selling for approximately $6,000 per ton. The ethanol industry is constantly looking for additional applications for its coproducts. Since the market for asphalt is so vast—about 500 million tons of HMA are produced every year with a cost of about $11 billion—this could be a welcome source of revenue for ethanol companies.
Since lignin can be obtained from the minimal further processing of distillers grains, a coproduct of ethanol production, McCready said distillers grains is a readily available feedstock for asphalt pavement that would be considerably cheaper than existing additives. Modifiers used in asphalt binders are currently selling for approximately $6,000 per ton. The ethanol industry is constantly looking for additional applications for its coproducts. Since the market for asphalt is so vast—about 500 million tons of HMA are produced every year with a cost of about $11 billion—this could be a welcome source of revenue for ethanol companies.
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