Modified Superpave Mix-Design for Cold In-Place Recycling (CIR)  

Mix Design Method for Cold In-Place Recycling of Asphalt Mixtures

1.      1.      Scope

1.1     1.1     This method covers the design of mixtures for cold in-place recycling (CIR) using the Superpave Gyratory Compactor.  The procedures presented are applicable only for mixtures containing asphalt emulsion and reclaimed asphalt pavement (RAP).  This method consists of two parts.  The first is the determination of the optimum emulsion content and the second is the determination of the optimum mixing water content.

2.      2.      Apparatus

2.1     2.1     See AASHTO TP4

3.      3.      Test Specimens

3.1     3.1     Preparation of RAP

3.1.1        3.1.1        RAP samples shall be obtained from the roadway that will be recycled by taking cores to the specified depth.  These cores will then be crushed in order to have representative samples.

3.1.2        3.1.2        Dry a portion of the RAP to a constant mass at 110⁰ C (230⁰ F) to determine the moisture content.  Dry the remainder of the RAP to a constant mass at 60⁰ C (140⁰F) to remove the existing water.

3.1.3        3.1.3        Separate the RAP into particle sizes according to Table 1, by screening through a series of sieves.  Eliminate the material retained on the 31.75 mm (1 ¼”) sieve either by removing or crushing the material such that excess fines are not produced.

                                          Table 1  Sizes for Separation

3.2     3.2     Mixing and Compacting Temperatures

3.2.1        3.2.1        The mixing temperatures shall be 25⁰ C +/- 2⁰ C (77⁰ F +/- 4⁰ F) for the RAP and mixing water.  The mixing temperature for the emulsion varies depending on the emulsion.  Obtain the correct mixing temperature from the emulsion manufacturer.

3.2.2        3.2.2        The compaction temperature shall be 25⁰ C +/- 2⁰ C (77⁰ F +/- 4⁰ F).

3.3     3.3     Preparation of Mixtures

3.3.1        3.3.1        The first part of the mix design involves the determination of the optimum emulsion content, while keeping the mixing water content constant.  A minimum of two specimens shall be prepared for a minimum of four emulsion contents in 0.5 % increments.  All specimens will be prepared with 3.0% mixing water (different water contents can be used based on experience).  In addition, one loose sample shall be prepared for each additive content for determination of maximum theoretical specific gravity

3.3.2        3.3.2        Weigh into individual pans a sufficient amount of RAP (~ 4000 grams) based on the gradation determined in section 3.1.3 to fabricate specimens 150mm (6 in) in diameter and 115 mm (4.5 in) in height.

3.3.3        3.3.3        Heat RAP samples at 25⁰ C +/- 2⁰ C (77⁰ F +/- 4⁰ F) for a minimum of one hour.  In addition, heat emulsion at the specified temperature (Section 3.2.1) for one hour.

3.3.4        3.3.4        Add mixing water to each sample and mix thoroughly for one minute.  Mixing may be performed either by hand or through the use of a mechanical mixer.

3.3.5        3.3.5        Add emulsion to each sample according to section 3.3.1 and mix thoroughly until the emulsion is uniformly dispersed but for no longer than two minutes.  If the sample is not uniformly mixed after two minutes, additional mixing water may be required to improve emulsion dispersion.  Otherwise, another emulsion type may be required.

3.3.6        3.3.6        Spread the mixture in a pan and allow the sample to cure until it “breaks” (when sample changes from a brown to a black color).

3.4     3.4     Compaction of Specimens

3.4.1        3.4.1        Preheat the molds at 60⁰ C (140⁰ F) for a minimum of one hour.

3.4.2        3.4.2        Apply load using the Superpave Gyratory Compactor (SGC).  The loading pressure shall be 600 kPa at an angle of gyration of 1 ¼ degrees.  The load shall be applied for the number of gyrations that will result in achieving densities similar to those found in the field.

3.4.3        3.4.3        Remove specimens from their molds immediately after compaction.

3.4.4        3.4.4        Oven cure the specimens at 60⁰ C (140⁰ F) for 24 hours.

3.4.5        3.4.5        Remove the specimens from the oven and allow to cool to room temperature.

3.5     3.5     Bulk Specific Gravity, G_mb

3.5.1    (ASTM D2726 or AASHTO T166)

This test method should be used when the samples absorb less than 2 % of water by volume as determined by section 10.4 of ASTM D2726.  Otherwise use ASTM D1188 (Section 3.5.2).

3.5.1.1  3.5.1.1   Record the dry mass, A, of the specimen.

3.5.1.2  3.5.1.2   Immerse the specimen in water at 25⁰ C (77⁰ F) for five minutes and record the

             immersed mass, C.

3.5.1.3  3.5.1.3   Remove the specimen from the water, surface dry with a damp towel and record 

             the surface-dry mass, B.

3.5.1.4  3.5.1.4   Calculate the bulk specific gravity as follows:

3.5.2       3.5.2       (ASTM D1188)

This test method should be used when the samples absorb more than 2 % of water by volume as determined by section 10.4 of ASTM D2726.  Otherwise use ASTM D2726 (Section 3.5.1).

3.5.2.1  3.5.2.1   Record the dry mass, A, of the specimen

3.5.2.2  3.5.2.2   Coat specimen with parafilm and record the coated mass, D.

3.5.2.3  3.5.2.3   Immerse the specimen in water at 25⁰ C (77⁰ F) and record the

 immersed mass, E.

3.5.2.4  3.5.2.4   Determine the specific gravity of the parafilm at 25⁰ C (77⁰ F), F.

3.5.2.5  3.5.2.5   Calculate the bulk specific gravity as follows:

3.5.3        3.5.3        Determine maximum theoretical specific gravity for each emulsion content using AASHTO T209.

3.6     3.6     Determine Optimum Emulsion Content (OEC)

3.6.1        3.6.1        Plot unit weight versus percent emulsion content for each emulsion content.

3.6.2        3.6.2        Plot percent air voids versus percent emulsion content for each emulsion content.

3.6.3        3.6.3        OEC is the emulsion content at which the unit weight is at its maximum value.

3.6.4        3.6.4        If a maximum unit weight is not achieved, the OEC should be the emulsion content at which the unit weight is the same as that found in the field.

3.7     3.7     Determine Optimum Mixing Water Content (OWC)

3.7.1        3.7.1        OWC is determined by following steps 3.1 through 3.5, with the following exceptions.

3.7.2        3.7.2        A minimum of two specimens will be prepared at the Optimum Emulsion Content (OEC) with each of four varying water contents, 0.5 % and 1.0 % above and below the mixing water content used in step 3.3.1.

3.7.3        3.7.3        Plot unit weight versus percent water content for each water content.

3.7.4        3.7.4        Plot percent air voids versus percent water content for each water content.

3.7.5        3.7.5        OWC is the water content at which the unit weight is at its maximum value.

3.7.6        3.7.6        If a maximum unit weight is not achieved, the OWC should be the water content at which the unit weight is the same as that found in the field.

3.8     3.8     Moisture Sensitivity

3.8.1        3.8.1        Prepare six specimens at OEC and OWC, three for dry testing and three for conditioned testing and determine moisture sensitivity of the specimens in accordance with AASHTO T283.

4        4        Report

4.1  4.1        The report shall include the following:

4.1.1        4.1.1        Type of Emulsion Used

4.1.2        4.1.2        RAP Gradation

4.1.3        4.1.3        Specimen Height

4.1.4        4.1.4        Specimen Mass

4.1.5        4.1.5        Specimen Bulk Specific Gravity

4.1.6        4.1.6        Specimen Unit Weight

4.1.7        4.1.7        Specimen Air Void Content

4.1.8        4.1.8        Optimum Emulsion Content

4.1.9        4.1.9        Optimum Mixing Water Content

4.1.10    4.1.10    Moisture Sensitivity Results