Behaviour of an emulsion treated base (ETB) layer as determined … · 2016. 4. 12. · 10 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA - 1 - BEHAVIOUR OF AN EMULSION TREATED

10th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA

- 1 -

BEHAVIOUR OF AN EMULSION TREATED BASE (ETB) LAYER AS DETERMINED FROM HEAVY VEHICLE SIMULATOR (HVS) TESTING. Prof G.J. Jordaan, Pr Eng Tshepega Engineering (Pty) Ltd, Highgrove Office Park, Building No 10, 50 Tegel Avenue, Highveld Techno Park, Centurion, 0046, South Africa. Professor Extraordinaire, University of Pretoria, Pretoria, South Africa.. Abstract Bituminous materials and, more specifically, emulsions are often used as an additive to layers during the rehabilitation of road pavements. However, the Mechanistic analysis and economic justification of emulsion stabilization often presents engineers with challenges. This paper reports on the development of a fatigue relationship to be used for the Mechanistic analyses of emulsion treated layers using Heavy Vehicle Simulator (HVS) test results. It is shown that the rehabilitated road pavement is capable of carrying relatively high traffic loads under a condition of relatively high surface deflection measurements. The resultant fatigue line is compared to other existing fatigue lines which are shown to be comparatively conservative. The verification of these results in practice could assist engineers in the economic justification of the use of emulsion as an additive for the in-situ recycling of road pavement layers.


- 2 -

1. INTRODUCTION Bituminous materials and, more specific to this paper, emulsions (usually with cement to (mainly) facilitate the breaking of the emulsion) are often used in South Africa as an additive to existing pavement layers during the rehabilitation of road pavements. However, the Mechanistic analysis and economic justification of the addition of emulsion (a relatively expensive product) often presents engineers with challenges. As a result, a series of Heavy Vehicle Simulator (HVS) (Freeme et al, 1982) were conducted over a number of years to obtain real field behaviour data from typical roads where rehabilitation was done using emulsion as an additive. This paper reports on the use of the data of such an HVS test (done on National Route N2 near East London, in the eastern Cape in South Africa) (Jordaan and Nienaber, 1988) to develop a fatigue relationship for the Emulsion Treated Base (ETB) layer (also referred to in South Africa as a Bituminous Stabilized Material (BSM) using emulsion (BSM-emulsion). The test site proved to be ideal for the assessment of the behaviour of treated layers, due to relatively weak supporting layers in the pavement which allowed for the detailed monitoring of the field fatigue behaviour of the ETB layer. The details of this HVS test, the materials and the various measurements and pavement behaviour as seen, have been discussed in detail before (Jordaan Van der Walt and Horak, 1989) (Jordaan and Horak, 1991) and will not be repeated in full. Only data crucial to the purpose of this paper is repeated. Reference to the previously published papers should be made to fully understand the initial testing and the rationale behind the processing of the data to prevent contamination due to high wheel loads applied and the addition of water. Never-the-less, it should be emphasised that water was only added to the test after the stabilized layers had already broken down and hence, the water added had no influence on the data used to derive the fatigue life of the ETB layer. The HVS test has shown that the rehabilitated pavement with the Emulsion Treated Base (ETB) layer is capable of carrying relatively high traffic loads (about 30 million equivalent 80 kN single axle wheel loads (E80s)) in the dry state under conditions with relatively high measured static surface deflections of about 0.6 mm (varying) under a dual wheel load of 40 kN (520 kPa wheel pressure) before fracturing (end of fatigue life)of the ETB layer occurred. The addition of emulsion (with cement to assist in the breaking of the emulsion) in the base layer proved effective and resulted in a layer capable of withstanding high traffic loads under relatively high surface deflections. The ETB behaviour is dependent on the early detection of initial cracking that occurred and reflect to the pavement surface and the sealing of these cracks to prevent the ingress of water that will cause early damage to the treated base layer (as observed on site in the field at the time of the HVS test in the wheel tracts of the same road). The HVS test site was selected to be between the wheel tracks with no visible cracking at the start of the test. These HVS test results (including the results from three Multi Depth Deflectometer (MDD) measuring points) were used to develop a fatigue relationship to be used in the Mechanistic Design and Analyses of


- 3 -

Emulsion Treated Base (ETB) layers (Jordaan and De Bruin, 1998). The resultant fatigue relationship is compared to other existing fatigue lines. It is shown that, according to the fatigue relationship developed from this HVS test, ETB layers may be able to withstand a higher than previously reported number of equivalent wheel loadings before “fracturing” or serious damage occurs. This relationship has since been used on a number of roads in practice to successfully motivate both structurally and economically, the addition of emulsion (with cement to assist breaking) during the rehabilitation of existing roads. The implementation and verification of these results will, without doubt, assist engineers in the economic justification of the use of emulsion as an additive to layers during rehabilitation design. 2. BACKGROUND

2.1 Pavement details and HVS testing

Results used for the modelling of the structural behaviour of the ETB layers were obtained from a HVS test done on the N2, Section 116 near Kwelera, East London, South Africa in 1987 (Jordaan and Nienaber, 1988). The pavement tested was rehabilitated in 1979-1980 and consisted of (material classification according to TRH14, 1983):

• 60 mm gap graded wearing course (AG),

• 100 mm quartzite sandstone base stabilised with 1 per cent cement and 1 per cent residual bitumen by mass (ETB),

• 130 mm sub-base consisting of a mixture of decomposed dolerite, old wearing course and base course material stabilised with 1,5 per cent lime and 1,5 per cent slagment (C4),

• 100 mm selected sub-grade layer (SSG) of sandstone (G6); and

• in situ material containing clay (G8). During the HVS test behaviour of the pavement section was closely monitored under accelerated loading conditions. Monitoring included permanent deformation (rut depth), the formation of visible cracks, crack movement (CAM), elastic deformation (surface deflection bowl measurements), in depth-deflections (multi depth deflectometer (MDD) measurements), i.e. the elastic deformation within each of the pavement layers at three separate points. At the time of the accelerated testing, a considerable amount of cracking was present on the road. The cracking mainly consisted of longitudinal cracking in the wheel paths (C2-C3 severity) (pavement condition according to TRH 6, 1985) and some randomly spaced transverse cracking (Jordaan & Nienaber, 1988). The HVS test section was selected between the wheel paths with no cracking on the test section, representing as close as possible, a section with no (or very little) previous loading. In total about 1,36 million repetitions were applied with the HVS on the test site. These repetitions were applied at various wheel loads under both dry and wet pavement surface conditions. The effect of water on the


- 4 -

behaviour of the pavement was assessed by allowing the water to flow freely over the cracked test site towards the end of the testing. Water was only added after considerable damage had already been done under the effect of the accelerated testing (fatigue life of the stabilised layers have been exceeded) in order not to contaminate the behaviour data of the individual pavement layers. Table 1 gives a summary of the test and the rate of deformation obtained under the various wheel loads and different conditions (Jordaan & Nienaber, 1988). Table 1: Summary of the loading, rate of deformation and pavement surface condition during HVS testing

Repetitions (REPS) REPS at

wheel load

Dual wheel

load (kN)

Rate of deformation (mm/1 x 10

6

REPS)

Pavement surface

Condition

0 - 552 710 552710 60 1,5 Dry surface

552 710 - 854 435 301725 80 14,4 Dry surface

854 435 - 1 056 253 201818 100 70,6 Dry surface

1 056 253 - 1 203 070 146817 60 18,2 Dry surface

1 203 070 - 1 283 802 80732 60 48,5 Water on surface

1 283 802 - 1 360 403 76601 40 83,8 Water on surface

Multi-depth deflectometers (MDDs) were installed at three points with measurements taken at various pavement layer interfaces. The positions of the MDD modules were varied between the three tests in order to enable the back calculation of the effective in-situ elastic moduli of up to 6 layers to a depth of 2 meters (depth at which the MDDs were anchored). Figures 1 and 2 give a summary of the rut depth measurements and number of cracks visible on the surface during HVS testing. Figures 3(a), 3(b) and 3(c) give the In Depth MDD deflection measurements at Points 3, 7 and 13 on the HVS test section.

Figure 1


- 5 -

Rut depth measurements during HVS testing

Figure 2 Number of cracks counted during HVS testing

Initially, the stabilised layers (base and sub-base) prevented the formation of serious permanent deformation (more than 10 mm) within the pavement. However, during trafficking at a dual wheel load of 100 kN the sub-base failed first followed, at a later stage, by the base which reached the end of its fatigue life and cracked into small blocks, becoming an effective granular layer. The cracks reflected through to the surface, resulting in an increase in the number of cracks appearing on the surface of the road (Figure 2). Subsequently, continued trafficking caused the selected layer to consolidate, resulting in a decrease in deflection measured on the surface as shown in Figures 3a), 3(b) and 3(c). In addition, the cracking of the base resulted in an increase in the load transferred to the lower layers and allowed the pavement to deform freely, causing a steep increase in the permanent deformation (Figure 1). 2.1 Pavement behaviour

The results show that the state of the pavement changed considerably during the HVS testing. More detailed analyses of the in-depth deflections showed that the selected layer formed a relatively "weak" layer in the pavement structure. Most of the increase in deflection originated within the selected layer during HVS testing. This aspect made this test perfect for the more detailed analysis of the behaviour of the treated layers to failure. 2.1 Pavement life The life of the pavement is usually given as the number of equivalent 80 kN single axle loads (E80s) which can be applied to a pavement before it will reach a specified level of distress. The levels of distress usually applied to a pavement, which will, inter alia, also be used for the analysis


- 6 -

of this pavement, are initial crack appearance on the pavement surface and 10 mm rut depth. a) (b) (c)

Figure 3(a), 4(b) and 4 (c)


- 7 -

MDD measurements during HVS testing at three measuring points

The wheel loads applied to the pavement are converted to E80s by means of an equivalency factor (F), where: F = (P/80)d (Eq. 1) Where F = equivalency factor for load P P = axle load in k d = damage coefficient, which is dependent on the pavement type

and material state The damage coefficient “d” is the equivalent of the “n” value ranging from4 to 4.2 as established during the AASHO road test (Hveem and Sherman, 1963). HVS testing has shown that many factors such as the type and state of the pavement layers can influence the value of “n”. Hence, to prevent confusion between the AASHO established “n” value and the value determined through HVS testing, the coefficient “d” is used in the latter case (Jordaan, Van der Walt and Horak, 1989) (Jordaan and Horak, 1991). The rate of an increase in deformation during testing at various wheel loads is used to calculate the damage coefficient “d”, which is applicable to the pavement in terms of deformation during the different phases of behaviour. The “d” coefficient is also used to determine the effective standard E80s that could have caused the same damage as the increased wheel loads. The following calculated damage factors are used to calculate the life of the pavement to a certain level of distress, i.e. cracking and deformation. The data as given in Table 1 are used to calculate the various values of d applicable to the HVS test:

• trafficking at a 60 kN dual wheel load : d = 7,2,

• trafficking at a 80 kN dual wheel load : d = 6,0,

• trafficking at a 100 kN dual wheel load : d = 2,7; and

• trafficking at a 60 kN dual wheel load : d = 2,7. It is clear that the pavement experienced a change in its state of behaviour (changes in the “d” coefficient) and that the base of the pavement is in an equivalent granular state after cracking (low “d” coefficient of 2.7). The variation in the life of the pavement at the test site is calculated so that there is a 95 per cent probability that at least 95 per cent of all possible measurements giving an indication of life as defined would indicate a life within the limits shown. This variation in life is shown as follows: Nx = 95[L; H]95 E80s Where


- 8 -

Nx = variation in the life of the pavement as defined by x in E80s x = distress and level of distress L = lower limit of the variation in pavement life as defined by x H = higher limit of the variation in pavement life as defined by x Furthermore, the measurements are also used to calculate the mean expected life (Nx) of the pavement as defined by a certain level of distress in terms of E80s. In addition, the 95th percentile value of expected life, i.e. the expected life for a maximum of 5 per cent of the test site to have reached a certain level of distress, is also calculated. These calculations of pavement life are shown in Table 2. Table 2: Life of the pavement to various levels of distress as tested during HVS testing.

Expected remaining pavement life (n) IN E80s Distress

(x)

Level of

distress Nx =

95[L; H]

95 Nx 95Nx

Cracking

(visible)

Initial

Increase

0,87 x 106; 4,9 x 10

6

26,0 x 106; 35,4 x 10

6

2,9 x 106

30,7 x 106

1,9 x 106

28,4 x 106

Deformation

(rut depth)

10 mm

20 mm

27,8 x 106; 33,8 x 10

6

28,9 x 106; 34,0 x 10

6

30,8 x 106

31,4 x 106

29,9 x 106

30,1 x 106

2.1 Life to cracking Figure 2 shows that cracking started during the early stages of testing. However, this initial cracking did not seriously affect the behaviour of the pavement in the dry state, and the stabilised base still behaved as an intact layer. However, these open cracks could allow water to get into the pavement and cause premature distress. Therefore, the life of the pavement to initial cracking is important from the point of view of possible early maintenance. More important to the general behaviour of this pavement is the life to a meaningful increase in the cracking which occurred as a result of the breaking down of the stabilised base layer. Hence, it is relevant to calculate the life of the pavement up to both initial cracking and up to a meaningful increase in cracking. In the latter case, this was defined as the life of the pavement to ten and more cracks per one metre section of the test site over the middle 6 meters of the test area. 2.2.2 Life to deformation The life of a pavement is usually calculated as the number of E80s load repetitions it can carry before reaching a certain level of distress. In this case the numbers of E80s to a rut depth of 10 mm and 20 mm are calculated. For national roads the 95th percentile values of measurements are usually used to calculate the "life" of a pavement.


- 9 -

3.0 ETB BEHAVIOUR MODELLING

3.1 Rigid layer

The MMDs were anchored at a depth of 2.0m. Hence, all calculations are based on a rigid layer depth of 2.0m.

3.2 Elastic moduli

The MDD measurements are shown in Figure 3 for the three measuring points. The effective elastic moduli for the pavement layers were determined from the three MDD’s using the CHEV15 (CHEVRON linear elastic computer programme), an example of which is shown in Tables 3, as determined for MDD measuring Point 3.

3.3 ETB layer behaviour

The effective E-modulus of the ETB layer was calculated for the first million repetitions to be on average just below 200 MPa at 196 MPa. After about 1,05 million repetitions the layer failed and the effective modulus reduced quikly to below 90 MPa and continued to reduce. The observed behaviour is typically that of a layer failing in fatigue with a sudden increase in observed cracking and surface rut depth. These trends are confirmed by the similar calculated life to cracking, 10mm rutting and 20mm rutting as shown in Table 2.

Table 3: E-moduli calculated from MDD Point 3 measurements

4.0 DETERMINING DESIGN CRITERIA FOR THE FATIGUE CRACKING OF

THE ETB LAYER

The following methodology was used to determine a fatigue behaviour relationship for the ETB layer using the HVS test results:

Layer 1:

0 - 60

Layer 2:

60 - 160

Layer 3:

160 - 390

Layer 4:

390 - 590

Layer 5:

590 - 800

Layer 6

800 - 2000

HVS

Repetitions

Asphalt ETB base Sub-base + selected

In-situ In-situ In-situ

10 1500 167 395 425 410 110

59559 1500 205 196 135 475 65

118845 1500 230 166 119 325 59

241709 1000 171 132 88 359 45

346045

455974 1000 171 105 78 405 40

552710 1000 179 103 84 430 37

667567 1000 183 85 71 315 32

760613 1000 213 64 69 161 33

896709 700 206 49 67 155 32

1056253 500 235 20 56 77 34

1218408 500 85 55 53 83 31

1360403 250 49 70 103 153 31


- 10 -

• It is reasonable to assume that the ETB layer failed in fatigue. Hence, the assumption is made that the criteria for failure of the layer will be the maximum horizontal tensile strain (εh) in the layer.

• In order to get an indication of the maximum εh, the strains against the number of repetitions are calculated and plotted in depth through the layer, an example of which is shown in Figure 4. (It is seen that the maximum εh is not always at the bottom of the layer. Substantial errors are possible if the maximum εh is assumed to be always at the bottom of the layer.)

• The results are used to do detailed analyses of the layer behaviour as measured at all three MDD points to obtain the number of repetitions to the end of the fatigue life of the pavement. As previously shown, the rate of distress varied during the HVS testing. The detailed analyses show that the average rate of distress to fracture, as defined in Eq 1 for the MDD at Point 3, is d = 4.92 and for the MDD at point 7 d = 4.77 to failure (after failure of the sub-base the coefficient is reduced to d = 4.64).

• The resultant analyses give three points on the fatigue line applicable to strain calculations near the top of the layer (depth at 80mm) and three points on the line applicable to the bottom of the layer (depth of 160mm).

• An objective of this paper is also to compare the newly derived fatigue line to existing approaches such as those for bituminous treated base (BTB) layers in the South African Mechanistic Pavement Rehabilitation Design Method (SAMPRDM) (Jordaan, 1994) and the fatigue lines developed by Santucci (Santucci, 1997). (The Santucci fatigue lines were used as a basis for the recommendations contained in the Sabita Manual 14.) (Sabita, 1993). Both these approaches give the fatigue life to crack initiation. Hence, the derived fatigue lines were adjusted to represent the life to crack initiation. It is assumed that the approach recommended in the SAMPRDM (Jordaan, 1994) for BTB layers to allow for crack propagation through the layer, is also applicable to the ETB layer and the results adjusted accordingly. Hence, using the adjusted results, two fatigue lines (top and bottom of the layer) are obtained as shown in Figure 5.

•


- 11 -

Figure 4

Strains through the depth on the ETB layer

Figure 5 Tensile strain criteria for crack initiation in the ETB layer (BSM-emulsion)

as determined from HVS testing

The relationships shown in Figure 5 are of the following format:

10 = Nf

Eh - 1

βα

Log

(Eq. 2)

Where Nf = number of repetitions to crack initiation εh = horizontal tensile strain in the ETB layer α and ß = constants The values for α and ß as determined from the HVS data are given in Table 6 below. Table 6: Constants for α and ß for the Fatigue Relationship shown in Figure 85 for the ETB Layer to crack initiation

Depth (mm)

α

ß

80 mm (top)

23,496

3,975

160 mm (bottom)

22,923

4,204

The fatigue line near the top of the layer is based (depth of 80mm) is where the maximum horizontal tensile strain is occurring (critical line) and hence, is used further on in this paper.


- 12 -

5.0 COMPARISON OF THE NEWLY DERIVED FATIGUE LINE TO

FATIGUE LINES IN SOME EXISTING METHODS

5.1 Comparison with the fatigue lines recommended for BTB layers in the SAMPRDM

The new fatigue line (near the top of the ETB layer) is shown together with the BTB fatigue lines as recommended in the SAMPRDM (Jordaan, 1994) in Figure 6. In comparison, it is seen that the main difference is that the slope of deterioration of the BTB lines is higher than that of the newly derived ETB fatigue line to crack initiation. The new ETB fatigue line allows for more repetitions to be carried before crack initiation, especially at lower tensile strain values. Never-the-less, considerable agreement between the two approaches, at the same elastic modulus, is apparent. 5.2 Comparison with the fatigue lines recommended by Santucci

for ETB layers

The newly derived fatigue line for the ETB layer is shown together with the fatigue lines recommended for ETB layers by Santucci (Santucci, 1997) in Figure 7. It is shown that the fatigue lines recommended by Santucci are considerably more conservative than the newly derived fatigue line. The horizontal tensile strains, measured in Santucci's method are based on laboratory values. Although done in a controlled environment, the crack propagation which influences the strain within the layer is much faster than crack propagation encountered in the field. This could be a reason why the Santucci lines are more conservative than the newly developed fatigue line developed from HVS testing.


- 13 -

Figure 6 Comparison of the tensile strain criteria to crack initiation of the ETB

layer (BSM-emulsion) and the BTB fatigue lines (SAMPRDM)

Figure 7 Comparison of the derived fatigue line to crack initiation of the ETB

(BSM – emulsion) layer and the fatigue lines recommended by Santucci

The slopes for the two different fatigue lines are almost identical. The data from the Santucci's laboratory based tests and those obtained from the HVS test indicate, that the rates to which the fatigue and/or deformation develop in the ETB layers tend to be the same. 5.3 Comparison with the fatigue lines for ETB layers obtained from

HVS testing by De Beer and Grobler (De Beer and Grobler, 1994)

The newly derived ETB fatigue line curve together with ETB fatigue lines published by De Beer & Marais (1994) is shown in Figure 8. The fatigue lines from De Beer and Grobler are based on maximum horizontal strains at the bottom of the layer. In comparison, the De beer and Grobler fatigue lines are considerably more conservative than the fatigue lines shown in Figure 5. It is noted that although relatively high E-moduli were initially obtained during the testing by De Beer and Grobler (1994), the layer stabilised quickly during testing at E-moduli (100 – 300 MPa)), which is comparable to that measured by Jordaan and Nienaber(1988). The test done by Jordaan and Nienaber was done on a pavement which was already 7 years old and it is postulated that, in this case, the ETB layer has already gone through the initial phase of “settling in” (De Beer and Grobler, 1994) to reach a stage of relative balance for the type of layer. (A process similar


- 14 -

to that as also previously described for cement treated layers (Jordaan, 1992).)

Figure 8 Comparison of the newly developed fatigue line (tensile strain

criteria) for crack initiation of the ETB (BSM – emulsion) layer and the fatigue lines derived by De beer and Grobler (1994)

6.0 DEVELOPMENT OF RECOMMENDATIONS TOWARDS THE

MECHANISTIC ANALYSIS OF ETB (BSM – emulsion) LAYERS

The preceding comparison between the various recommended fatigue lines are used to make some recommendations with regard to the mechanistic analysis of ETB layers and a generally applied fatigue relationship based on the HVS testing as discussed.

• It is clear that the maximum horizontal tensile strain (εh) is not always at the bottom of the layer. As shown, considerable errors can be made in fatigue predictions if a wrong assumption is made in terms of the position of the maximum εh . The method to determine the position of the maximum εh as developed for cement treated layers (Jordaan, 1992) can also be applied to other types of base layers, ie:

The position of the maximum horizontal tensile strain (εh) is at the bottom of the layer when: (E3/E2)

2 hc< K (Jordaan, 1992) With hc = (h1 (E1/E3)

1/3 + h2 (E2/E3)1/3)

Where: E1 = elastic modulus of the asphalt layer (MPa) E2 = elastic modulus of the base layer (MPa)

Crack initiation - new

Crack Initiation, De Beer & Grobler

“Fracturing”


- 15 -

E3 = elastic modulus of the sub-base layer (MPa) h1 = thickness of the asphalt layer (mm) h2 = thickness of the cement-treated base layer (mm) K = constant = 128

• The fatigue lines recommended for use in the analyses of BTB layers and the Santucci fatigue lines were used to develop the following relationships (r2 > 0.98 in both cases): SAMPRDM (BTB) εh = 171034 E-0.4803 Nf

-0.226 (Eq. 3) Santucci (ETB) εh = 7612 E-0.1407 Nf

-0.1814 (Eq. 4) Where εh = maximum horizontal tensile strength. E = effective elastic modulus of the layer. Nf = number of repetitions to crack initiation.

• Equations 3 and 4 indicate that a direct relationship exists between the E modulus of the bitumen bound layer (E), the number of load repetition to crack initiation (Nf) and the maximum horizontal tensile strain (εh) within the bitumen bound layer. It is concluded that the same principle would apply to the relationship developed for the ETB layer (Eq.2 and Table 6). Hence, the ETB fatigue relationship developed from the HVS measured data discussed in this paper can be further develop to include the same variable. The following relationship is found applicable to the HVS data and recommended for use: ETB (newly derived) εt = 124208 E-0.488 Nf

-0.169 (Eq. 5)

Where

εh = maximum horizontal tensile strength. E = effective elastic modulus of the layer. Nf = number of repetitions to crack initiation.

7.0 VERIFICATION OF THE ETB FATIGUE RELATIONSHIP The relationship as shown in Eq.5 had, over the last decade, been used for the rehabilitation of several roads in South Africa for the design of the emulsion stabilization of existing base layers trough in-situ recycling (with a small percentage of cement to facilitate breaking of the emulsion). The mechanistic analysis of in-situ emulsion stabilization using the relationship as given in Eq. 5, in a life cycle comparison with alternative rehabilitation options, has shown that emulsion stabilization can be economically feasible. These materials used for the construction of these ETB layers varied considerably, as did the traffic loading conditions and pavement compositions. Some of these roads have, by now, almost carried the design traffic loading.


- 16 -

Detailed records about the pavement design, materials, pre-rehabilitation condition and traffic loading are available. It follows that the opportunity exists to verify the use of Eq. 5 for the mechanistic analysis of ETB layers in the field through the behavioural assessment of these roads. 8.0 CONCLUSIONS A new relationship for the mechanistic analysis of ETB layers to the initiation of fatigue cracking has been developed. This relationship is based on the detailed post-analysis of an HVS test done on a pavement structure containing an ETB (BSM-emulsion) layer. The HVS showed that the layer can carry a relative high traffic loading (± 30 Million E80s) under relative high surface deflection measurements (in the order of 0.6mm). This pavement section was found to be ideal for the detailed analysis of the fatigue characteristics of the stabilised layers as it contained relatively poor support in the existing selected layers. Observations indicated that the ETB layer failed in fatigue. The detailed analyses of the horizontal strains in depth through the ETB layer were made possible through the input of three MDD measuring points. It is shown that the maximum horizontal strain is not always found at the bottom of the layer. A method for determining the position of the maximum horizontal tensile strain is given. The derived relationship for the mechanistic analysis of ETB layers to determine the number of load repetitions to crack initiation is compared to several previously published fatigue lines. It is shown that the previously published fatigue relationships are comparatively conservative. Hence, the newly developed fatigue relationship has the potential to considerably assist with the economical motivation for the use and design of the in-situ emulsion stabilization of existing road pavement layers. Relationships were also derived for some of the previously published fatigue lines in order to determine the influence of the effective modulus of the stabilised layer on the fatigue characteristics of the layer. These relationships and correlations between the methods were used to refine the newly derived fatigue relationship for the analyses of ETB (BSM - emulsion) layers. Several roads have over the last decade been rehabilitated using the newly derived fatigue relationship for ETB layers. These roads have the potential to be used for the practical verification of the derived relationship using field measurements. 9.0 ACKNOWLEDGEMENTS

The HVS work used in this paper was done at the then Division of Roads and Transport Technology (DRTT) of the CSIR and the analyses thereof funded by the South African Department of Transport. The opinions are those of the author and do not reflect official policy of any nature. 10.0 REFERENCES


- 17 -

De Beer, M, Grobler, I E. Towards improved structural design criteria for granular emulsion mixes (GEMS), Paper presented at CAPSA 1994, CSIR, 1994. Freeme, CR, Walker, R N and Kuhn, S H. User experience with the South African Heavy Vehicle Simulators. Proceedings of the Annual Transportation Convention (ATC ’82), Session: Transportation Infrastructure – Accelerated Pavement Testing, Pretoria, 1982. Hveem, F H and Sherman, G B. Thickness of flexible Pavements by the California Formula compared to AASHO road test data. HRR Nr 13, Flexible Pavement Design, HRB, Washington DC, 1963. Jordaan, G J and Nienaber, C J. HVS Testing on a Rehabilitated Pavement containing a Cold Mix Recycled layer: National route N2 near Kwelera, East London. Research done for and on behalf of the Department of Transport, Transportek, CSIR, Pretoria,1988. Jordaan, G J, Van der Walt, N, Horak, E. Accelerated testing of a rehabilitated pavement containing a cold mix recycled layer, Second International Symposium on pavement evaluation and overlay design, Rio de Janero, Brazil, 1989. Jordaan, G J and Horak, E. The behaviour and analysis of a rehabilitated pavement containing a bituminous and cement treated cold-mix recycled layer. Proceedings of the Eleventh Annual Transportation Convention (ATC ‘1991, Pretoria, 1991. Jordaan, G J. Towards improved procedures for the mechanistic analysis of cement treated layers in pavements. Proceedings of the Seventh International Conference on Asphalt Pavements, Nottingham, 1992. Jordaan, G J. The South African Mechanistic Pavement Rehabilitation Design Method. Research Report RR 91/242. Research done for and on behalf of the Department of Transport by Jordaan & Joubert Inc, Pretoria, 1994. Jordaan, G J and De Bruin, P W. Mechanistic Analysis Procedure for the Analysis of Emulsion Treated Layers in Pavements. Research report RR 91/238, Research done for and on behalf of the Department of Transport by African Consulting Engineers, Pretoria, 1998. SABITA, GEMS - The design and use of granular emulsion mixes, Manual 14, Roggebaai, 1993. Santucci, L E. Thickness design procedure for Asphalt and Emulsified Asphalt Mixes, Fourth International Conference on Structural Design of Asphalt Pavements, Ann Arbour, pp 424-456, 1997


- 18 -

Technical Recommendations for Highways Manual no 14 (TRH14): Guidelines for Road Construction Materials. Published by The National Institute for Road and Transport Research, CSIR, Pretoria, 1985. Technical Recommendations for Highways Manual no 6 (TRH6): Nomenclature and methods for describing the condition of Asphalt Pavements. Published by The National Institute for Road and Transport Research, CSIR, Pretoria, 1985.

Documents

Behaviour of an emulsion treated base (ETB) layer as determined … · 2016. 4. 12. · 10 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA - 1 - BEHAVIOUR OF AN EMULSION TREATED