Binder blending estimation method in hot mix asphalt with reclaimed asphalt

Abstract

Current road construction technologies includes the use of recycled materials increasingly. High quality of hot mix asphalt with high content of reclaimed asphalt pavement (RAP) requires the use of virgin binder or rejuvenator agent additive(gilsonite). This phenomenon has not been fully investigated. This paper discuses procedure which allow asses blending level between virgin binder and also binder film in RAP. In this essay we presented the preliminary tests results of the research concerning binder blending estimation. Degree of partial blending was estimated based on the rheological tests such as complex modulus and phase angle conducted in Dynamic Shear Rheometer. The Multiple Stress Creep Recovery test method was used to examine how virgin binder blends with polymer modified RAP binder.

 

  1. Introduction

Currently the use of recycled materials for road construction are increasing because of ecological reasons and preserve natural resources. The hot mixed asphalt (HMA) is a material which can be recycled in 100% and could be totally reuse to construct new asphalt layers in flexible pavements. Now, there is a tendency to use RAP for HMA in amount as much as possible. There are many technological solution to produce asphalt mixture with RAP addition like bypass and double drum production into asphalt plant or production in construction site such as remixing and foamed asphalt. Recycled asphalt pavements material properties depend on its original properties such as type of aggregate, binder and on deterioration of the service properties resulting from aging and weather condition. RAP properties also depend on milling asphalt pavement process. Obtaining appropriate properties of new asphalt mixtures contains high percent of RAP requires the application a new softer binder or special additive – rejuvenators to refresh aged binder from RAP. Besides during asphalt mixes process design the correction of aggregate gradation which is achieved by adding selected fraction of virgin aggregate may be required.

The problem of blending degree between virgin binder and RAP binder is still unresolved. Previous studies have shown that virgin binder and RAP binder blends only partially and to a limited extent. There is also no clear answer whether and how the partial blending of the binder film affects the properties of HMA. There is need to develop the method allows easily determine how two binders mix each other.

This paper shows results of using one of the laboratory method based on the method proposed by the Carpenter and Wolosick (1980) which allows to assess the degree of binders miscibility based on the gradual extraction of binders from aggregate.

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  1. Binder miscibility

During HMA with high content of RAP is designed, influence of aged RAP binder on HMA properties should be take into consideration. Improvement of aged binder properties is obtained e.g. by adding softer virgin binder during HMA production process.

Theoretically, it is assumed that the parameters of the equal binder are resulting from parameters of virgin binder and from aged RAP binder. Actually this equal binders are only partial blended. Previous studies shown that virgin binder additive makes new binder film covering RAP aged binder surface. Hypothetically, in extremely unfavorable case, only virgin binder creates a new layer covering the RAP and there is possible no interaction between these binders.

 

  1. Objective

The objective of this preeliminary tests was identify miscibility opportunity of RAP aged binder and virgin binder. Effectiveness of multistep extraction method proposed by the Carpenter and Wolosick was adopted and verified.

 

  1. Experimental procedure

4.1. Materials

In this study the asphalt mixture consisting of 100% RAP was used. RAP which was used in this tests came from stone mastic asphalt (SMA) wearing course. Basic properties of SMA RAP materials are shown in table 1.

 

Table 1. RAP properties

 

property unit result
Binder penetration in 25°C

 

[0,1mm] 25
Binder softening point [°C] 60
Soluble binder conten [%] 5.4
Content of aggregate < 0,063 mm [%] 12.0
Content of aggregate from 0,063 to 2,0 mm [%] 34.6

 

4.2. Specimen preparation

Asphalt mixture was prepared in laboratory mixer. The amount of 15,000 gram of RAP and 300 gram of virgin binder was used. RAP was heated to temperature of 150°C before mixing. Virgin binder was accounted for 2% of total mixture (27% of total binder). The time of 60 s of mixing was used counted form adding the whole binder. Mixing temperature was adjusted to 150°C. After mixing process the asphalt mixture was spread on metal trays to facilitate subsequent granulation.

4.3. HMA extraction procedure

In this study multistep extraction method was applied. Before the extraction, natural bitumen mixture was heated to 100°C and granulated for separate grains to allow solvent filtration through their surface. Then weighed specimen of mixture was placed onto the 1 mm sieve. After twenty seconds sieve was removed and after draining was immersed in next vessel with clear solvent. In total the HMA specimen was treated by solvent three times. Scheme of multistep extraction method was shown on Fig. 1.

From each of three vessels for extraction, about 1, 5 liter of binder solution was obtained. Next the binder was recovered in rotavapor (Fig. 3.b.). From each layer about 50 gram of binder was recovered.

 

4.4. Rheological tests

To investigate the rheological parameters of recovered binder the Dynamic Shear Rheometer (DSR) was used. Six binder specimens have been studied. Three recovered binders from external, middle and internal layer of HMA with RAP. As a reference specimens the virgin binder 160/220 and RAP binder have been tested. Moreover specimen prepared in laboratory of recovered binder from RAP mixed with virgin binder was used to compare as a total (100%) blended binder.

  1. Results

Phase angle and complex modulus were obtained from dynamic share tests in temperature range from 46°C to 82°C.

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