Binder extraction methods

6 METHODS FOR DETERMINATION OF BINDER CONTENT 9.6.1 Binder extraction methods 

The determination of binder content of asphalts and reclaimed asphalts by the binder extraction method consists of the following steps  

Binder extraction with hot or cold solvent can be conducted with various devices, which characterise the binder extraction method used (hot extraction or cold extraction). 

The separation of the mineral matter from the binder solution is conducted with various ways, depending on the selected extraction method. 

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Binder content is determined using one of the following methods (a) binder extraction method, (b) ignition method or (c) nuclear method. 

The binder extraction method is the most common and widely used method for determining the binder content in the mixture. It uses hydrocarbon solvents capable of dissolving bitumen and a binder extraction apparatus. Because of the high purchase and disposal costs of solvents, the risk to the operator s personal health and safety and the environmentally unfriendly nature of the hydrocarbon solvents, this test method was started to be replaced with the ignition method. The binder extraction method by European standards is conducted in accordance with CEN EN 12697-1 (2012), whereas that by American standards is in accordance with ASTM D 2172 (2011) or AASHTO T 164 (2013) and AASHTO T 319 (2008). A detailed description of the binder extraction test method is given in Section 9.6.1. 

As mentioned above, after the extraction of the binder, the aggregates are dried and sieved for aggregate gradation determination. With some, the binder extraction method is also capable of determining the possible water contained in the mix. Of course, the determination of water content (if any) can be carried out before the binder extraction procedure by weight loss, after heating the mix in an oven for 2 to 3 h at 150-160 C (until a constant mass is obtained). The above presupposes the fact that no further tests are going to be carried out on the extracted bitumen. 

The cold extraction method using a centrifuge extractor (centrifugal filter paper method) is perhaps the most common method worldwide for the determination of the soluble binder content. 

When a continuous-flow centrifuge or pressure filter apparatus is used, the determination of the soluble binder content is conducted by the weight difference method, as in the case of the extraction method with a centrifugal extractor (see Section 9.6.1.1). 

The incineration method for determining the residual matter in the binder extract is used by some extraction methods for residual binder content as an alternative method (see Figure 9.1). 

The solubility of the polymer-modified binders depends largely on the temperature of the solvent. This can lead to considerable differences between the results of cold and hot extraction methods. 

The binder extraction is carried out by washing the asphalt with solvent and filtering the solution, repeatedly in an extraction/filtration vessel. The extraction is carried out by rotating the vessel for 5 min at 30 rpm, while the vessel is positioned vertically (unlike the rotating bottle extraction method). The extraction vessel is equipped with three cloth sieves (2.00 cm, 300 mm and 75 mm). 

Lime mortar radiocarbon dating will result ambiguous because of CO2 contamination from inherited carbonates and, burial and/or weathering modifications. Therefore, an effective extraction method of binder is necessary in order to prevent the determination of older or younger ages. 

Figure 7.2 shows a typical TLC plate. Some components are visible to the naked eye, but others may need to be visualized. Commonly this can be achieved under a UV light if the compounds themselves fluoresce, or if they alter the behavior of the fluorescent binder. It is also possible to spray the plate with dye or oxidize the compounds with sulfuric acid to make them visible, although the last method will result in the destruction of the sample. Once identified, areas of the stationary phase can be scraped from the inert plate and solvent extracted to yield the separated components for further analysis, if needed. 

The form of the dissolved sulfur has not been characterized properly yet. While stable at ambient temperatures, a substantial amount can be converted to crystalline sulfur at elevated temperatures or by solvent separation. This observation led to the development of a rapid liquid chromatography method to determine elemental sulfur in SA binders. The procedure which has been described previously by Cassidy (17) is based on gel permeation principle and uses a Styragel column and a uv detector. Results showed that 2-14% of the elemental sulfur added reacted chemically with the asphalt. Petrossi (18) and Lee (19), who determined free sulfur by extraction with sodium sulfite followed by titration with iodine, calculated a higher percent of bonded sulfur in sulfur-asphalt compositions. The observed differences are most likely caused by variations in the asphalt composition with regard to polar aromatics and naphthene components as well as by reaction temperature and contact time. 

The SA binder is tested for dispersion and particle size prior to mix production with a microscope. The binder level of the mix is constantly measured with a Troxler model 2226 asphalt content gauge. Hot solvent extraction (ASTM D2172) using tetrachloroethylene solvent can also be used to measure the binder content of a SA mix. The sulfur—asphalt ratio of the binder is monitored in the field with the Troxler or by density measurements. Other methods that can be used to measure SA ratios are x-ray fluorescence of solutions of sulfur-asphalt in tetrachloroethylene, liquid chromatography, and differential scanning calorimetry. X-ray fluorescence measures total sulfur, liquid chromatography determines elemental sulfur, and DSC monitors crystalline sulfur. 

In the TLC analysis of dry extracts prepared from medicinal plants, the sample preparation is performed in a different way from that prescribed in the monographs for the drugs in the pharmacopoeias. Also, there is no binder in the recommended solvent system, and in these cases a validation of the new in-house method is certainly necessary. 

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