Reinforced mastic asphalt Reinforcing of mastic asphalt with carbon fibres

Transcription

1 Reinforced mastic asphalt Reinforcing of mastic asphalt with carbon fibres Josef Scherer, S&P Clever Reinforcement Company AG ( (CH) 1. Introduction Since some years a new generation of asphalt grating of carbon fibres (C-fibres) is available. These in polymer bitumen pre-saturated arming gratings are scattered on the surface with quartz sand and provided with a burning film on the underside. The application is comparable with the laying of polymer bituminous sheeting. Any movement of the asphalt reinforcement during application of the superstructure is prevented thanks to the optimal bond of the gratings at the bearing ground. The additional polymer bitumen that is applied with the presaturated asphalt reinforcement, guarantees the layer bound. The assemblage point holding of the gratings that occurs through the bitumen saturation is dissolved by the high temperature during the bituminous application. Thus, no grating structure is there anymore during the application. The single fibre ropes are opened by the aggregates in the mixture. The fibre ropes let thus optimally pass coarse aggregates and lay on the bearing ground in an optimal way. During the cooling process the fibre ropes are bound into the paving matrix. During the last five years different experimental as well as numeric investigations were made at C- armed hot rolled coverings. The investigation results will be presented. In 2005 already about a million square metres of C-armed hot rolled coverings were laid out in Europe successfully. To what extent the positive experiences of C-armed hot rolled coverings are also applicable for mastic asphalt was examined in investigation programmes at the EMPA Dübendorf CH as well as at the TU Munich D in the spring In the paper the investigation results will be shown. 2. Carbon reinforcement (C-reinforcement) in asphalt layers Carbon fibres (C-fibres) are well-proved construction materials in the flight industry and space travel. Through their raw density (approx. 1'700 kg/m³) and the high tensile strength (approx. 3'000 to 5'000 N/mm²) they opened interesting field of application already long before their use in the building industry. Aesthetically pretentious space load-bearing structures as well as hybrid constructions experience through the reinforced plastics an innovation push. Carbon fibres are suitable as internal as well as external arming of concrete structures in different combinations. Due to their flexibility and their mechanical properties they are used increasingly in the building preservation and structure renewal. Especially the building preservation and renewal develops above average. In Europe in few years the building renewal will predominate and the new building will fall under the 50 percent limit of the entire building activity. Through a successful practice introduction S&P put important corner-stones for further C fibre developments and evolutions in the asphalt construction industry. Reinforcement fibres with a high tension modulus of elasticity can accept forces at little expansions and are thus suitable as asphalt reinforcement. Fibres with a little tension modulus of elasticity give way to the extensions before forces can be accepted. Fibres that are not able to accept lateral forces are additionally recyclable and are fundamentally suitable for asphalt reinforcement. Josef Scherer page 1

2 fibre type modulus of elasticity (N/mm²) breaking elongation fibre is recyclable (no ability of acceptance of lateral force) comment carbon fibre (C-fibre) aramid (A-fibre) glass (G-fibre) polyester (PES-fibre) polypropylene (PP-fibre) % yes ideal as asphalt reinforcement % no unsuitable as asphalt insert % yes ideal as asphalt reinforcement or as non-woven fabric for coverings % no unsuitable as asphalt insert % yes ideal as non-woven fabric for coverings steel (comparison) elastic/ plastic no little suitable as asphalt reinforcement Table 1: Overview E-modulus / possibility to recycle the reinforcement fibres / comment Table 1 shows that the coal fibre is fundamentally suitable as an asphalt reinforcement. Nonwoven fabrics for coverings are manufactured ideally of glass or polypropylene fibres. The glass fibre is usable as a reinforcement as well as a non-woven fabric for coverings. The initial fibres for the design of an asphalt reinforcement are optimised purposefully. Parallel to the axis economical glass fibres are fit in while in the cross direction the C-fibre with its high modulus is being used. 3. Bond building material reinforced asphalt The bond construction material best known in the building industry is reinforced concrete. In the reinforced concrete the reinforcing element (reinforcement) is inserted connection-stiffly into a matrix (concrete). In table 2 the E-modulus are compared in the bond construction material reinforced concrete. E-modulus matrix E-modulus tension element relation E-modulus matrix tension element concrete steel reinforced concrete 30 kn/mm² 210 kn/mm² ~ 1 : 7 Table 2: Relation E-modulus matrix / tension element in the reinforced concrete In table 4 the relevant E-modulus of differently reinforced fibre asphalt coverings are compared. The E-modulus of an asphalt layer is according to ambient temperature 3 to 15 kn/mm². The E-modulus of a fibre grating is always deeper than the theoretical modulus of elasticity of the fibre. Through the production of the grating, the fibres are not arranged optimally. Correspondingly, the theoretical modulus of elasticity of the fibre is to reduce by a reduction factor for the dimensioning (Table 3). Recommended reduction factor by S&P = 1.5 Josef Scherer page 2

3 E-modulus fibre E-modulus fibre grating carbon fibre glass fibre polyester fibre Table 3: Reduced fibre E-modulus With the reduced fibre E-modulus the comparison table can now be drawn up. E-modulus matrix E-modulus tension element relation E-modulus matrix tension element Asphalt covering complex carbon fibre grating 160 kn/mm² ~ 1 : 26 modulus CAST at 0 C (5 Hz) glass grating 47 kn/mm² ~ 1 : 7.5 (average 6 kn/mm²) polyester grating 10 kn/mm² ~ 1 : 1.6 Table 4: Relation E-modulus matrix / tension element in reinforced asphalt covering The comparison table 4 shows clearly that the polyester fibre can not cause virtually any additional bending strength in a reinforced asphalt covering. The glass grating is only minimally effective as some bending tensile reinforcement. The carbon fibre reinforcement, however, increases the bending tensile stiffness in the asphalt covering and in this way the bearing capacity of the bond construction material. Of course a bearing capacity improvement is only to be expected if the tensile element is incorporated shear-resistant in the multi-layer asphalt covering. The shear bond layer bond of a multi-layer reinforced asphalt covering must be correspondingly flawless. The layer bond is supposed to be stipulated through the building contractor (or owner) and to be controlled through the construction supervision. For the structural analysis respectively modelling of reinforced asphalt coverings one quotes the theoretical fibre cross-section. theoretical thickness of a C-fibre grating = fibre weight (in lateral direction) (lateral direction) density of the fibre In the S&P carbon fibre reinforcement S&P Carbophalt G there are 85 g/m² C-fibres in lateral direction. so: theoretical fibre thickness = 85 g/m² = mm 1.7 g/cm³ out of it follows: out of it follows: theoretical fibre cross-section for a C-fibre grating of 1'000 mm breadth, 1'000 x = 50 mm²/m relevant structural analysis specifications for carbon fibre reinforcements in lateral direction: cross-section: 50 mm²/m tensile strength: ~ 4'000 N/mm² tensile force lateral direction 200 kn/m E-modulus for structural analysis: 160 kn/mm² (reduction factor 1.5) Josef Scherer page 3

4 4. Layer bond of reinforced asphalt coverings The effect of an asphalt reinforcement is only guaranteed if the occurring strengths can be introduced into the reinforcement insertion. The layer bond of the asphalt reinforcement with the higher and lower covering layer, is corresponding of decisive importance. For multi-layer asphalt coverings a bounding shearing force of >12-15 kn (Ø 150 mm test core) according to Leutner is demanded depending on country regulation. The criterion is valid also for reinforced multi-layer asphalt coverings. This criterion is already component of the Polish Standard and will become for the time being also component of the European Standard. In Switzerland the layer bond of asphalt layers is checked regularly with the Leutner shearing test. The practice shows, that with C fibre reinforced hot rolled coverings the demanded layer bond is reached. Depending on whether the existing bond layer is milled off, roughens off or provided only with an adhesive emulsion, a layer bond is reached for C-reinforced hot rolled coverings of 15 to 30 kn according to Leutner. 5. Test results of C-fibre reinforced hot rolled coverings 5.1 C-reinforcement against thermal cracks Thermal cracks are caused by the daily temperature variations. Particularly the frost-/dewcycles strain the asphalt layers intensively. While the streets were being formerly exposed to a constant temperature under a snow layer damming up, the demand of snow-free streets is in the winter months enormous. Frost-/dew-cycles can occur repeatedly daily. The Belgium Road Research Centre examined in several investigations the influence of different asphalt reinforcements against crack reflection of existing old covering cracks into the new covering layers due to frost-/dew-cycles. In a standardized test method the effects of the following asphalt intermediate layer were compared: - non-woven fabric for coverings made of polypropylene PP - covering grating made of polyester PES - with bitumen precoated grating made of glass S&P Glasphalt G - with bitumen precoated grating made of carbon fibres S&P Carbophalt G The results were compared with a reference sample without intermediate insert but with identical cross-section. In the test an existing cracked bearing course is over built and covered with a bonding wearing course of 7 cm thickness. The samples are compacted practically and after that sawed out from the asphalt surface. The existing crack in the old bearing course is simulated as a shaping-cut from the underside into the sample. At a test temperature of -10 ºC the frost-/dew-changes are dumped into the bearing course (graphic 1). The crack opening (1 mm per cycle) corresponds to the theoretical expansion volume of the water which is in the old covering crack (shaping-cut). The control of the crack opening is done by a control-liquid which freezes and again thaws. On the occasion of the test the crack prolongation starting from the existing crack in the bearing course (shaping-cut) into the new wearing course in dependence of the load cycles is recorded (graphic 2). Josef Scherer page 4

5 new wearing course --- layer reinforcement --- existing layer Graphic 1: Test results: Test arrangement Belgium Road Research Centre crack opening Graphic 2: Test results Belgium Road Research Centre At the non-reinforced asphalt sample, the crack went through to the surface after 6 frost- /dew-cycles. The grating insertion made of polyester, as well as the non-woven fabric for coverings, could not prevent due to the little modulus of tension elasticity the coming through of the crack. While the polypropylene-non-woven reinforced asphalt went through after 10 cycles, the polyester-reinforced asphalt sample stood firm 18 load cycles. The bitumen- precoated glass grating on the other hand prevented the coming through of the old covering crack through the new wearing covering. The old crack penetrated 3-4 cm deep into the new wearing course, after that the occurring tensions could be absorbed through the glass fibre reinforcement. A further crack prolongation was prevented. In the practice it is recommended correspondingly, to over-build grating insertions of glass with a 4 cm strong new bituminous wearing course respectively covering layer in the minimum. The bitumen-precoated carbon fibre reinforcement prevents virtually any crack prolongation into the upper asphalt layer. The tensions are absorbed immediately through the asphalt reinforcement and the stress is removed as shear tension over the bond joint. Over-building (superstructure) with small strength as micro-coatings is also possible on bitumen-precoated carbon fibre insertions. Josef Scherer page 5

6 The experimental setup (Graphic 3) realized at the Belgium Road Research Centre was modelled with the Finite Element Programme LUSAS. The modelling was reduced into a twodimensional model with approved, flat extensions. 402 Ueberasphalt Horizontale Abloesung a = 0.02 m bis 0.04 m y Bestehender Belag x Riss (Breite m) im bestehenden Asphalt mit Wasser gefuellt Graphic 3: Geometry of the Finite Element Model for checking the tests about the effects of frost. Existing cracks are marked with thick black lines. Measuring indications in [mm]. The vertical crack in the existing asphalt is filled with water which will extend through the change of the phase (liquid to solid). In the modelling a certain temperature coefficient of expansion is assigned to this material which causes together with a forced temperature cooling the wanted crack extension. Table 5 shows the values for the materials which were used in the different models. material cross-section A [m2] stiffness E [kn/m2] Poisson s ratio ν [-] coefficient of expansion α [1/0C] carbon fibres ' asphalt -- 12' water -- 10' Table 5: Characteristic material values for the two-dimensional frost-models. The carbon fibre layer is modelled in the two-dimensional model as a stick with a related cross-sectional surface. The asphalt and the water are modelled as surface segments with a unit width of b = 1.0 m. During the crossing from the liquid one to the solid phase the water gets a volume extension of 9.0 %. One takes this circumstance into consideration by assigning this material an expansion coefficient of α = / 0 C as well as a temperature cooling of ΔT = 10 0 C. Firstly, linear elastic parameters are assigned to the materials. The existing crack will be transmitted in the over-layer with and without inserted carbon fibre reinforcement. It is supposed to be the effect of the carbon fibre reinforcement to prevent a complete coming through of the crack up to the surface. Josef Scherer page 6

7 A first model is created under the assumption of a completely uncracked state of the asphalt over-layer. With that it becomes clear due to the calculated results which assemblage points of the model must take over high tensile stresses. The bond of those assemblage points of the asphalt, which have to support tensions that are higher than the tensile strength of asphalt, is solved in a second model. For the present calculations the tensile strength of asphalt is defined with approx. ft = 3.5 N/mm 2. Models without carbon fibre reinforcement The models without carbon fibre reinforcement are created in order to show that as consequence of the resultant tensions the crack will come through up to the surface of the asphalt over-layer. Uncracked initial model The first model represents the uncracked initial state. Graphic 4 shows the resultant tensions in the 0.07 m thick asphalt over-layer due to the extension of the water included in the vertical crack. LOAD CASE = 1 Delta T = -10 RESULTS FILE = 1 STRESS CONTOURS OF SX E E E E E E E E E E E E E E E3 Max E+05 at Node Min at Node 2259 Graphic 4: Resulted tensions in the asphalt over-layer in the uncracked initial state due to the extension of the water included in the crack (existing asphalt). The horizontal removal is 0.02 m. The maximum tensile stress at the bottom edge of the asphalt over-layer is σ x = 46.8 N/mm 2. The existing covering as well as the vertical crack is not represented in the figure. It clearly shows that the asphalt over-layer in the middle range can not incorporate the tensile stresses. It will crack at the spots with the highest tensions. Josef Scherer page 7

8 Models with carbon fibre reinforcement The model with carbon fibre strengthening was created in order to be able to show the effect of the carbon fibre reinforcement. Six vertical cracks are defined for this model. In table 6 the tensions in the crack peaks are represented in dependence of the crack length. At a crack length of 0.02 m each the resultant tensions in the crack peaks are still significantly larger than the defined tensile strength of the asphalt. At a crack length of 0.06 m on the other hand the tensions in the crack peaks are smaller than the tensile strength of the material. Consequently the cracks will not prolongate up to the surface of the asphalt over-layer. number of cracks crack length [m] resultant tension σ x in the crack peaks [N/mm 2 ] Table 6: Resultant tension σ x in the crack peaks in dependence of the crack lengths. In table 7 the resultant tensile force as well as the maximum tension in the carbon fibre reinforcement is represented. The tensile strength of this material is f t = 3'000 N/mm 2. This value is not reached. number of cracks crack length [m] tensile force in carbon fibres [kn] maximum tension carbon fibres [N/mm 2 ] Table 7: Resultant tensile forces and maximum tensions σ x in the carbon fibres gratings in dependence of the number of cracks and the crack length. Graphic 5 shows the resultant tensions in the 0.07 m thick asphalt over-layer with six vertical 0.06 m long cracks due to the extension of the water included in the vertical crack. Josef Scherer page 8

9 LOAD CASE = 1 Delta T = -10 RESULTS FILE = 1 STRESS CONTOURS OF SX E E E E E E E E E E E E E E E3 Max E+05 at Node 4 Min at Node 151 Graphic 5: Resultant tensions in the asphalt over-layer in the model with six vertical cracks (crack length 0.06 m) due to the extension of the water included in the crack (existing asphalt). The maximum tensile stress at the crack peaks is σ x = 3.4 N/mm 2. The horizontal removal is 0.04 m. The tensile stresses at the bottom edge of the asphalt over-layer are higher on the whole length between the cracks than the tensile strength of the asphalt is. 5.2 C-reinforcements against fatigue cracks Through S&P a research programme was commissioned in the winter 2005/06 at the EMPA Duebendorf CH. In an experimental programme the effect of S&P carbon fibre reinforcements laid at different positions between two coverings were compared. Test assembly: Two-layer test samples are made of asphalt with the measurements 1'800 mm x 870 mm x 60 mm and checked in the wheel rutting test apparatus with approx. 0.5 million tyre-runovers. In this case the groove depths were periodically measured with a profile-meter; the deformations at different positions on the underside as well as on the upper surface of the test sample were periodically measured with an expansion-stripe-measure. To simulate the softness of the subsoil a rubber pad is attached under the test sample. 0.5 Mio. tyre run-overs Graphic 6: Test assembly EMPA Dübendorf CH different positions of the S&P carbon fibre reinforcement Josef Scherer page 9

10 Sample K1: Sample K2: Sample K3: Sample K4: two-layer covering without asphalt reinforcement two-layer covering S&P Carbophalt applied on the underside two-layer covering S&P Carbophalt applied in a depth of 4 cm two-layer covering S&P Carbophalt applied in a depth of 3 cm After the testing procedure one modelled with a linear-elastic finite element calculation the mechanical behaviour of the coating structure reinforced with carbon fibres for every test sample and compared it with the results of the DMS measurements. The results of the experimental and numeric investigations agreed quantitatively. In addition one did shear tests according to Leutner before and after the load of the test sample in the wheel rutting test apparatus. In the groove zone, directly under the wheel load, a drastic decrease of the bond shear force was determined. The 0.5 million tyre-run-overs on the samples only 60 mm thick led to oscillations of the test samples and corresponding extreme loads. The force diversion between carbon fibre reinforcement and asphalt layers manifested itself as loosening (reduced layer bond) at the boundary layer. The tests show clearly that only with a flawless layer bond the positive effect of asphalt reinforcement can be guaranteed. Overview of the results experimental: average deformation in the DMS (underside wheel groove) position of the carbon sample fibre reinforcement K1 without K2 underside K3 4 cm depth reduction of the deformation in % K4 3 cm depth Table 8: Analysis of the results EMPA Dübendorf CH Overview of the results numerical: a) Without reinforcement insert Explanation: In non-reinforced asphalt bodies (less stiff system), the wheel load acts on a larger influence surface. The rolling wheel leads to tensile stresses (red) below the strength introduction zone. Before and after the roll-over compressive stresses (blue) arise due to a covering coving. Graphic 7: Tensions identified numerically in the bottom asphalt covering (without carbon fibres reinforcement) Josef Scherer page 10

11 b) With carbon fibres reinforcement Explanation: In a reinforced asphalt body (stiffer system), the tensile stresses are increasingly accepted by the carbon fibre reinforcement. The covering coving and the compressive stresses arising from that are reduced. Graphic 8: Tensions identified numerically in the bottom asphalt covering with carbon fibre reinforcement The test sample with bottom situated reinforcement (test sample K2) shows an increased deformation compared with the test samples K3 as well as K4 where the reinforcements were applied between two asphalt layers. This is due to the lacking layer bond on the covering underside. The C-fibre grating must correspondingly always be applied between two covering layers in bond. The application of the C-fibre grating onto the street support (between planing and paving) does not make any sense. Thanks to the S&P carbon fibre reinforcement the deformations and corresponding tensions in the reinforced asphalt layer under the high wheel load can be reduced decisively. The deeper the carbon fibre reinforcement is situated and applied the better its effect is. For carbon fibre reinforced asphalt layers a longer lifecycle is to be expected thus. destruction of the covering decisively less destruction Wheel load (tension in the asphalt Lower tension peak Graphic 9: Influence of the wheel load on the destruction of the bituminous coverings The destruction of the bituminous coverings in dependence of the wheel load is shown in graphic 9. Thanks to the S&P carbon fibre reinforcement tensions peaks in the asphalt can be reduced decisively. The durability of carbon fibre reinforced coverings layers is increased thus in a leading way. Josef Scherer page 11

12 6. Pre-tests EMPA Dübendorf/CH C-reinforcement in mastic asphalt The assignment for two series of experiments with C-fibre-reinforced mastic asphalt layers was issued to the EMPA Dübendorf/CH by the companies Aeschlimann AG, Zofingen/CH and S&P Clever Reinforcement Company AG, Brunnen/CH in the summer The test results are subsequently presented. 6.1 Prevention of thermal cracks The test samples with the measurements of 2600 x 500 x 70 mm, see graphic 10, were made up of two mastic asphalt layers (MA-layers) with the thickness of 35 mm each. Between the bottom MA-layer and the reinforced concrete blocks of the support polymer bitumen sheeting were applied (PDB SBS). Between the MA-layers a layer of S&P Carbophalt G was incorporated. The carbon fibres of the reinforcement grating were positioned lengthways (perpendicularly to the joint). Table 9 summarises the properties of the manufactured test samples. Mastic asphalt S+P Carbophalt Gussasphalt 150 S+P Carbophalt Dichtungsbahn 10 Stahlbetonblock Prüfkörperbreite: 500 mm. Width of test sample: 500 mm Fugenüberdeckung (t = 3 mm) Sheeting Reinforced concrete block Joint covering Graphic 10: Principle of the test samples (sectional elevation) (measures in mm) Test sample TS1 TS2 TS3 Table 9: Mixture type MA11 TSP spec. Mesh size of the reinforcement grating [mm] 20 (S&P normal version) 40 (light version) Thickness of the bottom MA-layer [mm] Thickness of the upper MA-layer [mm] no reinforcement Properties of the test samples Josef Scherer page 12

13 Picture 1/2: Production of the MA test-sample Picture 2 Tests in the cold Specific test equipment was used for the investigation of the mechanical behaviour of the test samples in the cold through a horizontal, repeated opening and straining of the joint (graphic 11). One side of the test sample was immovably positioned over the concrete support on the test equipment; the bottom side was movably used through a spindle motor in horizontal direction. The periodic stress was produced distance-driven at a constant test temperature. The average speed of the joint opening (distance between the concrete supports, measured on both sides of the test sample with the distance pickup W1, see graphic 11) was 5 mm/h. For the measurement of the deformations of the asphalt in the joint area two distance pickups W2 were placed in the average height of the bottom MA-layer on both sides of the test sample. In order to examine the stretching-behaviour of the test sample qualitatively, vertical lines were placed on the facets at intervals of 20 mm, picture 3. Table 10 summarises the test conditions and some decisive values of the test equipment. Base length L2 in the table 10 was used for the calculation of the extensions in the asphalt, see formula (1). 500 Base length L2 Distance pickup W2 MA-layers Basislänge L2 Weggeber W2 GA-Schichten Belastungsrichtung Fester Teil Weggeber W1 Beweglicher Teil Fixed part Distance pickup W1 Movable part Stress direction Graphic 11: Scheme of the test design (measures in mm) Josef Scherer page 13

14 Picture 3: Test sample TS1 in the test design (side face) Test sample Table 10: Test temperature [ C] TS1-5 TS2-5 Amplitude of the joint opening W1 Number of [mm] load cycles (until fail) (until fail) Base length L2 [mm] TS (until fail) 250 Test conditions and decisive values of the test design Table 11 summarises the most important test results: maximum values of the measured and calculated values per load cycle, the decrease of the modulus of elasticity in the course of the cyclical load of the test samples TS1 and TS2 as well as the initial value of the modulus of elasticity for the test sample TS3 which was loaded monotonously up to the failure. The maximum values indicated for the test sample TS1 correspond to the time shortly before the beginning of the continuous cracks. The values mentioned in table 11 were calculated according the following formulas: ε = W 2 / L2 (1) σ = F / A, (2) Josef Scherer page 14

15 where: W2 - the distance measured with the distance pickup W2 [mm]; L2 - base length L2 [mm]; F - force [N]; A - cross-section of the test sample without bituminous sheeting [mm 2 ] (A = 500 mm x 70 mm = mm 2 ). The modulus of elasticity (in MPa) was calculated according the formula: E = σ / ε (3) l l The values of σ l and ε l in (3) correspond for all test samples to the linear sections of the force-distance-diagrams for the first cycle of a load phase in each case. Test sample TS1 TS2 Maximum joint opening W1 [mm] Maximum force F [kn] Maximum expansion in the asphalt ε [%] Maximum tension in the asphalt σ [MPa] Modulus of elasticity E [MPa] (until fail) (until fail) TS (until fail) Table 11: Summary of the test results Review of the results In table 11 it is clearly showed that the use of the reinforcement grating S&P Carbophalt G leads on the one hand to a stiffening of the mastic asphalt coating (rise of the initial modulus of elasticity) and on the other hand to a rise of its crack expansion and crack tension. Table 12 shows the comparison of the mentioned values for all test samples. Test sample Crack expansion [%] Crack tension [%] Initial modulus of elasticity [%] TS TS TS Table 12: Comparison of the test results (related to the values of TS3) Table 12 shows that the use of the S&P standard grating in comparison to a slight grating version leads to an essential rise of the crack expansion (224.2 percent for TS1 opposite % for TS2). The rise of the crack tension on the other hand remained small (114.7% for TS1 opposite to 110.1% for TS2). No rise of the original-stiffness was found (125.6% for TS1 opposite to 132.2% for TS2). Josef Scherer page 15

16 6.2 Reduction of wheel rutting building During the last years deflection measurements were executed at several carbon fibrereinforced hot rolled asphalt coverings. The practice showed that the C-fibre reinforcement S&P Carbophalt corresponds to a structure value of 3 to 4 cm thick hot rolled asphalt layer. Whether a C-fibre reinforcement can also reduce the wheel rutting building on hot rolled asphalt coverings was not checked up to now. This is the reason why a test series with C-fibre reinforced MA-layers was carried out at the EMPA Dübendorf/CH. In the test, the reinforcement was inserted as high as possible in the two-layer mastic asphalt covering. As expected the C-fibre reinforcement could not reduce the wheel rutting building of the reinforced MA-layer. The grating structure can not stop the plastic deformation (flow) of the MAlayer. Thus, a reduction of the wheel rutting building has to be aimed for with other measures. As a possibility, the modification of the binder is to discuss (polymer coated bitumen). 7. Pre-tests TU Munich/D C-reinforcement in mastic asphalt The test results there are not yet available at the deadline of the present paper and will be handed out at the annual meeting in Stockholm. 8. Summary Different experimental and numeric tests certify the C-fibre reinforced hot rolled asphalt coverings excellent properties against thermal crack reflection as well as against fatigue cracks under dynamic sustained loading. At the EMPA Dübendorf/CH tests were carried out for the first time with C-fibre reinforced MA-coverings against thermal cracking. The experimental results show that the positive effect of the carbon fibre reinforcement exists also in the mastic asphalt. The positive effects of carbon fibre reinforced hot rolled asphalt coverings as - less thermal crack reflection - fewer fatigue cracks - improvement of the structure value are also to be expected in tendency for MA-coverings. In practice one has higher durability of the asphalt coverings thanks to the C-fibre reinforcement. That automatically manifests itself in smaller maintenance works. 9. Recommendations for further reading - EMPA Dübendorf/CH, Prüfbericht Nr EMPA Dübendorf/CH, Prüfbericht Nr Studie Nr , November 2003, Kt. Uri/Schwyz - Belgian Road Research Centre, Brussels, EP 3765/ Belgian Road Research Centre, Brussels, EP Diverse Prüfberichte Consultest AG, Ohringen/CH - Tragfähigkeitsverbesserungen infolge Asphaltarmierungen, Dr. sc. techn. ETH A. Faeh - Vorbituminierte S&P Armierungsgitter für Asphaltbeläge, Josef Scherer page 16