Category Stone Matrix Asphalt. Theory and Practice

The recommended temperatures of SMA mixtures with road bitumens accord­ing to EN 12591 are given in the standard EN 13108-5. The minimum tempera­ture of delivery to a laydown site and the maximum production temperature in an asphalt plant are provided there. When using a modified or special binder, one should follow the information passed on by its producer or as determined in other documents.

Example temperatures for two of the most common road bitumens (EN 12591) used for SMA are as follows:

• 50/70— minimum temperature 150°C, maximum temperature 190°C

• 70/100— minimum temperature 140°C, maximum temperature 180°C

This requirement regarding resistance to fuel exclusively applies to SMA mixes for airfields. The method of testing this property of SMA is elaborated in the standard EN 12697-43. The categories of the requirements are good, moderate, poor, or NR (no requirement).

14.5.11 Resistance to Deicing Fluids for Application on Airfields

This requirement concerning resistance to deicing fluids applies to SMA mixes for airfields only. The method of testing this property of SMA is described in the stan­dard EN 12697-41. The test is conducted using the pull-off method on samples sub­jected to conditioning in a deicing fluid and on nonconditioned, comparable samples. The categories of requirements are marked with the indexed symbol в: P100, в 85, P70, P55, and PNR, where PNR means no requirement. The в is a ratio of conditioned to unconditioned sample result.

The SMA wheel tracking test is carried out on samples (slabs) prepared in a labora­tory or cut out of a pavement. Additional requirements for samples may be deter­mined in the following two ways:

• Requiring a void content in the slab; in this case the requirement has a range of 3% (v/v), (e. g., 3-6% [v/v]).

• Requiring the compaction factor; in this instance a requirement with a range of 2% (e. g., 98-100%) should be imposed.

All the aforementioned requirements actually specify the quality of the prepared sample (slab) before testing.

14.5.10 Reaction to Fire

When an SMA mix has to meet requirements for resistance against fire specified in other regulations, this property should be tested and classified according to the method described in EN 13501-1.

Resistance to abrasion by studded tires is determined according to EN 13108-20, Clause D.4, and testing after EN 12697-16, Procedure A. The available categories of requirements are AbrA20, AbrA24, AbrA28, AbrA32, AbrA36, AbrA40, AbrA45, AbrA50, AbrA55, AbrA60, and AbrNR, where AbrNR means no requirement.

• Table 13—for results from the small device; Procedure B, testing in air, categorizes the following requirements marked with the symbol WTSAIR as the maximum wheel tracking slope (mm/1000 load cycles): WTSAIR 0.03, WTSAIR 0.05, WTSAIR 0.07, WTSAIR 0.10, WTSAIR 0.15, WTSAIR 0.30, WTSAIR 0.40, WTSAIR 0.50, WTSAIR 0.60, WTSAIR 0.80, WTSAIR 1.00, and WTSAIR NR, where WTSAIR NR means no requirement.

• Table 14—for results from the small device; Procedure B, testing in air, cat­egorizes the following requirements marked with the symbol PRDAIR as the maximum proportional rut depth (percent of slab’s thickness): PRDair 1.0, PRDaiR 1.5, PRDaiR 2.0, PRDaiR 3.0, PRDaiR 4.0, PRDaiR 5.0, and PRDaiR NR, where PRDaiR means no requirement.

Water sensitivity, denoted as indirect tensile strength ratio (ITSR), is determined according to EN 13108-20, Clause D.3. Water sensitivity is determined by test method after EN 12697-12 at a test temperature of 15°C. The available categories of requirements ITSR are ITSR90, ITSR80, ITSR70, ITSR60, and ITSRNR, where ITSRNR means no requirement.

The standard categorizes minimum and maximum percentages of voids filled with binder (VFB). The following are the available categories of requirements and their denotations:

• Minimum percentage of VFB range from 71 to 86% in increments of 3% (i. e., VFBmin= 71, 74, 77….)[78] plus VFBminNR, where VFBminNR means no requirement.

• Maximum percentage of VFB range from 77 to 92% in increments of 3% (i. e., VFBmax= 77, 80, 83.)f plus VFBmaxNR, where VFBmaxNR means no requirement.

14.5.5 Binder Draindown

Tests of binder draindown should be performed according to EN 12697-18. Available categories of the maximum permitted binder draindown from the SMA mixtures are D03, D06, D10, and DNR, where DNR means no requirement. However, EN 13108-20 does not indicate directly which method of EN 12697-18 should be used—basket or Schellenberg (see Chapter 8).

The determination of the void content in compacted samples should be evaluated according to the standard EN 13108-20, Table D.2, as follows:

• Bulk density of a sample should be determined according to EN 12697-6, Procedure B (Saturated Surface Dry [SSD]).

• Maximum density of sample should be determined according to EN 12697-5, Procedure A (with the use of water).

•

Calculating the void contents in compacted samples should be conducted according to EN 12697-8 (based on formulae given there).

VmaxNR.

If determining the void contents in a gyratory compactor at a set value of gyra­tions is required, testing should be conducted according EN 12697-31. In this case, methods of direct measurements of density should not be employed.

The method of preparing SMA samples in the laboratory to determine the void content is specified in the standard EN 13108-20, Item 6.5, with details in Annex C (Table C.1). The NAD should provide values of compactive efforts. Permissible methods include the following:

• Impact compaction according to EN 12697-30, with possible energies or 2 x 25 blows, 2 x 50 blows, 2 x 75 blows, or 2 x 100 blows

• Gyratory compactor according to EN 12697-31, with different numbers of gyrations

The standard EN 13108-20 also states that the JMF should clearly state the adopted method and prevailing conditions of the sample preparation.

The SMA mixture should be homogenous and completely coated with binder when discharged from the pugmill. There should be no evidence of agglomeration (balling) of the fine aggregate.

14.5.4 Void Content

Void content is one of the essential properties of a compacted SMA mix. Much attention was paid to this subject in the previous chapters, particularly in Chapters 6 and 7. Establishing the method of sample preparation and suitable conditions (compactive effort and compaction temperature) is necessary for the proper deter­mination of air voids in compacted samples. The standard categorizes of minimum and maximum void contents in SMA samples to be selected in an NAD are as follows:

• Minimum void content in SMA samples range from 1.5 to 6% in increments of 0.5% (i. e., Vmin= 1.5, 2. 2.5…)[77] plus VminNR, where VminNR means no requirement.

• Maximum void contents in SMA samples range between 3 and 8% in 0.5% increments (i. e., Vmax= 3, 3.5, 4,.)t plus VmaxNR, where VmaxNR means no requirement.

A series of categories of minimum binder contents in SMA mixes, denoted Bmin, is detailed in the standard. However, maximum binder contents are not defined; therefore an appropriate category of Bmin should be matched with each SMA specification.

The categories given in the standard have been adopted for a reference density of an aggregate mix equal to 2.650 Mg/m3. For aggregate mixtures with other den­sities, the required lower limit of the binder content should be modified using the factor a

2.650 a =

FIGURE 14.3 The position of boundary points of SMA 8S gradation envelopes according to EN 13108-5 and German final gradation limits for this mixture according to TL Asphalt – StB 07.

FIGURE 14.4 The position of overall limits to a target composition of SMA 10 accord­ing to EN 13108-5 and British final gradation limits for this mixture according to BS PD 6691:2007.

a

a

FIGURE 14.5 The position of overall limits to a target composition of SMA 14 accord­ing to EN 13108-5 and British final gradation limits for this mixture according to BS PD 6691:2007.

where pa is the particle density of the aggregate mix in megagrams per cubic meter, according to EN 1097-6.

The binder content determined for an SMA mixture should be the sum of all pos­sible sources of binder in it, which includes the following:

• Added binder

• Binder from the RAP (when added)

• Natural asphalt (when added)

Available categories of the minimum binder content in SMA (to be chosen in an NAD or a contract specification) range from 5.0 to 7.6% in 0.2% increments (i. e., Bmin= 5.0, 5.2, 5.4, 5.6 …).[76]