DE3442171A1 - Process for improving the incorporation behaviour of bituminous mixtures in accordance with TV-bit 3/72 technical regulations and guidelines for the construction of bituminous road surfaces - Google Patents

Abstract

The filler proportion determined by TV-bit 3/72 is formed by a mixed filler comprising rock meal and silicic acid, it originally being proposed to use the natural product kieselguhr, whose relatively broad scattering range with respect to the SiO2 content of between 70 and 90% and the maximum bulk density of 0.3 kg/dm<3> prevents precise establishment of the results to be expected. Together with the further development, the aim was to reverse the dependencies of the known quality parameters in so far as high deformation resistance, even in summer temperatures, is obtained at the same time as high compactability together with a reduction in the roll openings. This has been achieved by preparing the mixed filler quasi-homogeneously from rock meal having a bulk density of 1 kg/dm<3> and from synthetic silicic acid having a mean bulk density of 0.2 kg/dm<3>, and introducing this mixed filler and the binder into the preheated aggregates and mixing the components. Within the further definition, it has been determined that the rock meal filler about 0.5 m<2>/g measured by the BET method, and the synthetic silicic acid filler having a surface area of 250 m<2>/g, likewise measured by the BET method, are combined and ... Original abstract incomplete.

Description

PATENT ADVOCATE PAUL MUNDERICH

D 1 P L. - I N G.

EUROPEAN PATENT ATTORNEY

• "* * *.. * Β *» ββ 'Ct R.Ü.N DAU-

ROTHENBERGEN FRANKFURTER 8TRA88E BA

TELEPHONE O6O51 / 3703

Ί A A? 1 7 1 KREI88PARKA8SE GELNHAUSEN

> 3 H 4 ^ I / I _{KTOi 2ββ8 (BLZ 507 B00 Μ)}

POST CHECK ACCOUNT. FFM. 33 «726 · 80S

• ^{9 NOV 1984}

Mu / Lo
29/3/84

Patent application

Central German hard stone industry GmbH

Mainzer Landstr. 27-31
6000 Frankfurt 1

'Process to improve the paving behavior of bituminous mix according to the "technical Regulations and guidelines for the construction of bituminous road surfaces - TV-bit 3/72 - "

(Inner priority. P 33 42 669.4 of November 2, 19Ö3)

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The invention relates to a method for improving the installation behavior of stable, bituminous mix for road construction, the mix according to the "technical regulations and guidelines for the construction of bituminous road surfaces" ~ TV-bit 3/72 - is composed and prepared, and the filler portion determined from this is replaced by a mixed filler portion consisting of stone powder and silica, reference being made to the method according to DK-I ³ S 29 19 444 below.

The criteria resulting from today's traffic load, which are specially designed for heavily frequented Set road or motorway guides are well known.

The quality of the pavement is placed in the order of priority of the claims in front positions. If one considers the extent of the federal German road network alone, then from an economic point of view emphasizes the durability of the road surface. If one further illuminates the demands of road users in a targeted manner, this is how the steadily increasing rates of heavy traffic and the advancing traffic crystallize Growth in the number of passenger cars means the need for durable, resilient road surfaces out, whereby from the generic term "quality" the durability with the stability in close relation can be brought.

The properties of a stable or deformation-stable Road surface -

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especially if it is rolled asphalt With the state of the art, they can only be bought through compromises.

Stable coverings require a high level of compaction, which is usually only from the properties of the Haitetein grain, a high one Brechsandante ^ l, stiffening filler, harder binder and lower binder content can be determined.

The method mentioned at the beginning was based on the task of processing asphalt concrete with residual voids of known size remaining in the ceiling, while maintaining a conventional filler volume, the production of flowable or quasi-flowable, particularly easily compactable asphalt concrete, in particular fine asphalt concrete. The criterion of this process is the preparation and use of a mixed filler made of lime, basalt or slate powder with a bulk density between 0.9 and 1.1 kg / dm ³ , with a filler made of powdered amorphous silica with a bulk density between 0.1 and 0, 2 kg / dm ³ or kieselguhr (70 to 90% SiO ₂ ) with a bulk density between 0.15 and 0.3 kg / dm ³ in a predetermined volume ratio.

The further processing takes place according to TV-bit 3/72, whereby the usual volume fraction corresponds to that of a rock flour with a bulk density of 1 kg / dm ³ .

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The proportion of binder is increased approximately in accordance with the enlarged surface.

The asphalt-concrete mix prepared in this way has a significant amount due to its higher proportion of binding agent "smoother" character and is in terms of the requirements of its processing Similar to mastic asphalt.

In principle, this procedure has proven to be suitable for the task at hand. Have the relatively broad scatter range of the SiO component between 70 and 90% and that of the bulk weight however, a sufficiently exact setting of the expected result is difficult. This situation inevitably leads to the demand for a standardization of the silica product its physical and chemical definition. Because the natural product "kieselguhr" is always used for this can only offer broad areas, it is for these reasons alone to be excluded and further development to use synthetic amorphous silica.

In this context, methods such as those described, for example, by RÖMPP 7th edition, volume 1, page 66 and Volume 3, page 17 69 mentioned are offered.

According to the procedure developed by DEGUSSA Silicic acid prepared by hydrolysis of silicon tetrachloride in an oxyhydrogen flame.

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The criterion for this product is an SiO ~ content of up to 99.8% and the formation of spherical particles with a surface area of up to 400 m ² / g.

In addition to this pyrogenic manufacturing process, there are also precipitation processes, in some cases with subsequent ones Spray drying, became known.

The products are used, among other things, to control the viscosity of paints, adhesives, plastics, etc. as fillers known in rubber, ointments, toothpastes, etc. Even small admixtures improve the flow behavior of powders, fertilizers, etc.

Coming back to the qualitative ones explained at the beginning and resulting from today's traffic load Criteria - durability, stability, deformation stability etc. - which, according to today's possibilities, are usually not in a satisfactory degree let meet jointly, and with appreciation of the state of the art described in the introduction, as well as the outlined process for the synthetic preparation of amorphous, powdery silica, it is therefore the task this invention to call a method of the type described above, the experience gained since of asphalt technology, according to which

- a high degree of compaction a low resistance to deformation,

- a low willingness to compress a high resistance to deformation and

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- a high resistance to deformation, an unfavorable flexural behavior for the service life

should mean, to the extent reversed / that with a high willingness to compress, combined with a reduction the roller passages, a high deformation resistance - even given in summer temperatures is. ——

The inventive solution to this problem provides that the mixed filler made of stone meal with an average bulk density of 1.0 kg / dm ³ and synthetic silica with an average bulk density of 0.2 kg / dm ³ prepared virtually homogeneously with a stable distribution of the two components and this and the bituminous binder are supplied to the already heated aggregates and mixed with them.

The use of this mixing filler not only leads to a substantial increase in the active, i. Surfaces of the filler that can be wetted by binding agents and thus to a temporary increase in the plasticity of the mortar during installation, but also to a stiffening of the between the aggregate arranged mortar framework.

With regard to the selection and the proportion of silica in the mixed filler, it has been found to be expedient that, for the production of a mixed filler, stone meal fillers with a surface area of about 0.5 m ² / g - measured according to BET surface area - and synthetic silica fillers in a proportion of 0, 1 to 2% by weight, based on the weight of the material to be mixed, and with a surface area of about 250 m ² / g

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- also according to BET - combined and mixed will.

As a rule, it is appropriate that the volume of the both filler components is matched so that the ratio of a maximum of 1: 1 is not exceeded, with A particularly advantageous result is obtained when 0.5 to 0.6% by weight of silica, based on the weight of the mix is admitted.

Independent of these statements and confirmed on a case-by-case basis by the results of investigations described below, it can be assumed to be safe that further parameters, in particular those in the interrelationships between the types of filler and Binders can be seen to be effective, since only the enlargement of the active surfaces and the possible increase in the proportion of binder, probably not that confirmed by the tests Can justify results. So it can already be recognized today as certain that the use of the mixed filler in the context of the preparation of mixed material according to TV-bit 3/72 increases the willingness to compact the mixed material significantly, so that the number of roll transitions required after installation can be greatly reduced to the prescribed density of at least 97% Reach Marshall.

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The deformation resistance and the associated stability are also shown by the use of the Mixing filler has considerably higher values, even at relatively high outside temperatures.

This behavior clearly contradicts previous experience, according to which easily compressible masses have a lower resistance to deformation. A negative influence on the stress reduction - i.e. on the relaxation behavior with comparable mortar consistencies is not given.

In connection with the increased resistance to deformation, the properties of the mix can also be improved be adjusted when using softer binders.

Finally, it should be noted that the favorable properties of the mixed filler described Modified asphalt mix allows alternative, otherwise necessary, more complex types of pavement to be replaced.

In this context, the replacement of mastic asphalt with a TV-bit 3/72 mixture can be considered in particular be thought.

The invention is further illustrated by the following Description of experiments, for example, explained.

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1. Preliminary remark

By using the method according to the invention Benefits achieved in practice are provided by excerpts or evaluations from the Research Institute for Roads of the Technical University of Darmstadt on behalf of the applicant on "Investigations on the Earning / deformation and flexural tensile behavior of Asphalt concrete with conventional fillers and special fillers "confirmed, with the special filler being part of the entry Mixing filler mentioned above, contains a synthetic silica with the following characteristics:

Bulk weight = 0.2 kg / dm ³

Average grain size = 0.08 mm

Surface approx. 250 m ² / g

SiO ₂ ~ share = 93%,

where in the following the synthetic silica for short as "Silicic Acid" is referred to.

The stone meal portion of the filler is either limestone meal or basalt meal with a bulk density of 1 kg / dm ³ and a surface area of about 0.5 m ² / g.

The evaluation of the results of this scientific Investigation is not yet fully completed. However, the findings that have already been made confirm this the complete solution of the task mentioned at the beginning.

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Regardless of the test materials used, fillers can also be used in addition to basalt or lime flour other hard rocks such as diabase, gabbro, etc. can be used.

Test materials and test arrangement

2.1 Test materials

A gravel-rich asphalt concrete 0/11 mm was examined with road construction bitumen B 80. The grain size distribution de] Mineral mix is shown in Figure 1. The mineral components were:

55.0% by weight of high-grade basalt chippings, 36.0% by weight of high-grade basalt crushed sand 9.0 wt% filler

The filler type was varied and included

Limestone powder and
Basalt flour with and without silica

used.

The silica content was in both filler mixtures 6.7% based on the filler content.

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The binder content was determined so that the air-filled cavity in the Marshall test specimen was approx. 3% by volume.

The void _{content (H R} ) of the filler according to Ridgen and the characteristic data of the mixed material variants examined are compiled in Table 1.

description Filler type Hollow-
space-
gchalt
¹¹ R
Vol% Bandage
nd, ttel-
salary
Gevi .-% Hollow
space
salary
H, ..
bit
Vol% A. limestone
flour 36.6 5.8 3.1 B. limestone
flour with 51, 8 6.4 3.3 Silica C. basalt
flour 37.4 6.1 3.0 D. basalt
flour with
Silica 52.4 6.4 3.2

Table 1 : Mixture variants

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2.2 Test arrangement

The investigations of the compression and deformation ver holding were carried out with the gyrator test and the bending tensile behavior with the bending tensile test.

The gyrator is a kind of kneading compressor in the test specimen from bituminous mix by simultaneous vertical pressure and gyrating movement of a horizontal pusher be exposed to stress. It gives the possibility of changing the density of the mineral and the hollow space To record the conditions under the compaction by rollers and the redensification under traffic metrologically ur to register continuously. The compression mechanism of the gyrator is shown graphically in Figure 2.

The mixed material is introduced into the mold (8) with an initial void content of 25% by volume and subjected ^{to a vertical punch pressure of 0.7 N / mm 2.} During the test, the roller carrier (2) rotates at a constant angular speed of 20 revolutions per minute and a default angle of 1 °. The resulting deformation causes the test specimen to stand wide. The actual inclination of the specimen is always greater than the specified angle. It is called the gyrator angle. designated. During the test, the specimen height h, the gyrator angle *. and the roller bearing force P measured with the help of an analog-digital conversion developed in Darmstadt and registered on punched tape for the computational evaluation.

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The following parameters can be calculated from the distribution of forces in the entire gyrator system:

τ The phase shift φ which is identical to the caster angle that occurs under dynamic loads.

- The specific compression work A "related to the unit of mass of the test material.

- The complex shear stress t with the elastic Portion and the viscous portion.

The compaction behavior of the mix variants was examined at a test temperature of 135 ° C. The mixes were compressed to a degree of compression of 98% of the bulk density of the test specimen according to Marshall. Afterward the specimens were stored in a heating cabinet at a temperature of 60 ° C. for 24 hours. The specimens were re-compacted at 60 ° C in the gyrator and thus the deformation behavior was tested.

For the dynamic flexural tensile tests, based on DIN 1164, sheet 7, test specimens with the dimensions 4 cm χ 4 cm χ 16 cm made. The bituminous Mixture with a temperature of 135 ° C in a three-part mold for the production of three test specimens is filled and heated to 98% under static pressure the density of the probo body according to Marshall condensed.

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The molded test specimens were installed in the bending tensile device and at a temperature of 20 ° C one force-regulated and the other one regulated away Dynamic bending tensile test with the RE 16 hydraulic press.

The experiments were carried out with sinusoidal oscillations at 5 Hz.

For the force-controlled dynamic flexural tensile tests, the was

Upper load 0.7 kN and the
Underload 0.3 kN.

The displacement-controlled dynamic flexural tensile tests were carried out with a

upper deformation of 0.5 mm and one
lower deformation of 0.1mm.

During the tests, the central deflection of the bending beam and the force were each dependent on
the loading time was recorded with the Bryans XY Recorder 2600C A 2.

Examples of the recorded curves are shown in Figures 3 and 4. An envelope is plotted in Figure 4 because the resolution of the recorder was too low to absorb the force oscillation. the
Oscillation runs between the envelope and the
Timeline.

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3. Presentation and discussion of the test results

For the statistical description of the relationship between the cavity filled with air and the specific compression work A the following relation was brought to the approach:

bxt bit

b
e ν

with H _bit

= 25 vol

b _v = compression number

A_ = Specific compaction work in 0.1 Nm / kg

After taking the logarithm, the value pairs obtained on the basis of the measurements for A_, and H, Perform linear single regression and calculate the compression ratio. The compression figures obtained in this way are included in Table 2.

Filler type number of
Value pairs
η Correlation
coefficient
r Compaction
digit, Limestone powder 43 0.986 -0.0130 Limestone powder
with silica 17th 0.982 -0.0198 Basalt flour 20th 0.988 -0.0196 Basalt flour
with silica 24 0.9802 -0.0168

TaLc I Lu 2: May dl chLun <jH / .l I for L boi varied filling type ν

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The mixtures with basalt filler and those with limestone powder and silica turned out to be comparatively easy to compress with almost the same compression ratios.

Basalt flour made it difficult to compress. The mixture with limestone powder required the greatest compaction effort.

The caster angle φ is an influencing factor of the compressibility. If the caster angle is 0 °, the mix to be compacted behaves elastically. The mixed material ve: holds like a viscous liquid at a wake angle of 90 °. In the range 0 ° < φ * 90 °, the behavior of the mixed material corresponds to that of a visco-elastic material. The viscous component predominates in the range φ> 45 °, in the range φ <■ 45 ° the elastic component predominates.

The compaction process can be divided into three phases depending on the compaction work applied will. In the first phase, the compaction of the cavities is due to the quasi-viscosity of the bituminous mortar certainly. In the second phase, the quasi-viscosity of the bituminous mortar influences the internal friction the grain structure the course of compaction. At the transition ve of the first to the second phase, the lag angle has a minimum. With further compaction, the supporting effect of the mineral structure is reduced by increasing the amount of filling dej Cavities with mortar as well as broken edges and abrasion removed.

As the cavity is increasingly filled with mortar, the direct contact between the support grains is reduced. the Shear stresses cause increasingly viscous displacement ^ within the mortar. The caster angle is greater than aJ 45 °. The compression process enters the third phase in which a quasi-viscous flow takes place.

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The course of the caster angle described qualitatively above as a function of the compaction work can can be described with the following equation:

tan (90 ° -φ) = a * A_ ^b 'e ^C *

with φ = caster angle

A _G = Specific compression work in 0.1 Nm / kg

After a regression calculation, the coefficients given in Table 3 were obtained on the basis of the measured values.

Filler type number of
Value pairs
η Correlation
coefficient
r ₄ Coefficients a b C. Limestone powder
Limestone mehi
with silica
Basalt flour
Basalt flour with
Silica 15th
9
7th
8th 0.982
0.962
1.0
0 r9 ⁷⁴ 0.3283
0.2764
0.3483
0.3342 0.4135
0.4762
0.3833
0.3875 -0.0048
-0.0098
ί
-0.0043!
-o.oofiir.

Table 3: Coefficients a, b and c for different types of filler

The qualitative curve of the dependencies described is shown graphically in Figure 5. The curve has a maximum at point A and a point of inflection at point C. The coordinates of these points were calculated and for the individual variants compared. Figure 6 shows the percentage comparison of the compaction work and the caster angle φ.

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The bituminous mixtures with limestone powder and basalt powder have compared to the mixtures with silicic acid at point A lower caster angles. The internal friction of the grain structure affects the Mixtures without silica have a stronger effect on the compression process. The type of filler (basalt flour or limestone flour) does not affect the compaction process when compacting these mixtures, which is caused by the sewing same specific compression work is documented wij The specific compression work is trots in point A. approximately the same lag angle when mixed with basalt flour and silica compared to the mixture with Limestone powder and silica larger. The addition of silica to the limestone powder promotes compaction The mixtures without silica are more reluctant to compress than the mixtures with silica. The same relationships tend to arise for point C.

Deformation behavior

If the temperature of the bituminous mass is still high enough for compaction, the compaction reaches a kind of limiting void content under the roller, which as a result of a momentary isotropic pressure a further compression not possible. After the built-in layer has cooled down on the street and the Bound contraction of compressed air and binder relaxes the system; there will be additional Free cavities under the action of traffic can be "redensified". The redensification is in winter because of the high viscosity of the material as good as not possible. Rather, a certain heat content generated by solar radiation is used for this purpose bituminous mass required.

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However, this not only causes a reduction in viscosity, but also an increase at the same time of the mortar volume.

The recompaction on the road under traffic was carried out on the mix samples with a degree of compaction of 98% mimicked in the gyrator at a temperature of 60 ° C. The change in the cavity filled with air Η, .. via the applied deformation energy Ay, analogous to the compression in section 3.1 expressed mathematically by the following relationship.

^H bit ~ ^H bit

bw

"o, w

The index w was introduced here to denote a resistance to deformation, while A ₁ ,, .. die

GV

Applied deformation energy means. Table 4 shows the values calculated on the basis of the measurement results Coefficients included.

Filler type number of
Value pairs
η Correlation
coefficient
r Starting
cavity
^H bit
O, W Verfor
mungs
number Limestone powder
Limestone powder
with silica
Basalt flour
Basalt flour
with silica 22nd
: 23
24
22nd 0.972
0.959
0.975
0.968 4.373
4.094
3.733
4.211 -7.4323
-4.9400
-10.45 69
-6.6729

Table 4; Deformation numbers b for a varied filler type

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The deformation factor b is with the mixtures with

Silica addition significantly smaller than with the mixtures without addition of silica. The mixes with Limestone powder and silica as well as basalt powder and silica therefore have a greater resistance to deformation than the mixtures without silica. "The mixture exhibits the greatest resistance to deformation with limestone powder and silica-on.

Another possibility for assessing the deformation resistance results from an analysis of the shear stresses. The elastic part of the shear stress The expressed deformation quantity indicates that part of the applied deformation energy, which causes elastic reactions during stress. The elastic reactions set the deformation opposition to; they can therefore be viewed as resistance to deformation. The during the elastic shear stress component of the deformation process can be used as a measure of the deformation resistance will. The change in the elastic shear stress component T "over the applied deformation

Ji

energy A -,., is also used with a regression approach

IaV

the form

_{x E} = a. A _GV ^b . e ^c · ^A GV.

After an interim calculation and the equations for the elastic shear stress component, a caster angle of 45 °, i.e. the limit from which the viscous behavior then predominates upwards calculate elastic shear stress.

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In Figure 7, a percentage comparison has been made for the filler variants. The absolute highest value (^ 100%) is T-, = 0.367 N / mm ² .

The greatest resistance to deformation, expressed by the shear stress 7 , is therefore found in the bituminous ones

do

Mixtures with the filler type limestone powder with silica as well as the filler type basalt flour with silica.

3.3. Dynamic flexural behavior

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In one supported on two supports and through the middle The following deformations and bending tensile stresses occur on the underside of the beam subject to a single force Beam at the point of application of the load on:

- Bending tensile stress: . P. 1 1
E. in N / l he - ϊ b * h ² ° bz - 2 - deformation P * 1 ³ * in mm * · \ ■ b * h ³

In these equations:

P = force in N

b = width of the bar in mm

h = height of the bar in mm

1 = distance between the supports in mm K · - Iiliujl i /. 11. "IUiiuoilu 1 i η N / mm"

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The tensions caused by the traffic load can be without or in conjunction with temperature-related Stresses lead to crack formation when the size of the locally available strength of the building material is reached will. The speed with which the forced tension in a visco-elastic building material is broken down, is determined by the relaxation time. Small relation times result in a very fast voltage connection construction, with extremely long relaxation times, the behavior of the substance approaches that of a purely elast see fabric. During relaxation, the dei decreases elastic stress component in favor of a viscous flow deformation.

The test specimen becomes dynamic when the position is regulated Bending tensile test with the following deformation stressed:

Deflection in the middle of the beam:

^f o * ^f u + f - f. sin («t -

with upper deformation f = 0.5 mm

f _u = 0.1 mm ω = 2 * T>' f = 31, 42

■ for _r = 5 Hz

This deformation causes a tensile bending stress in the specimen. The tension over time corresponds to a damped harmonic sinusoidal oscillation

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This oscillation oscillates between the time axis and the envelope curve (see Figure 4). The envelope forms the connecting line between the maximum values of the amplitudes. You can use the following equation mathematically to be discribed:

ο: = σ bz ο

-D

in N / now ²

with <3 _Q = voltage ordinate of the envelope curve at time t = 0

D = damping constant

With the measured values, the calculation resulted in the characteristic values contained in Table 6.

Filler type number of
Value pairs Correlation
coefficient tension Damping
constant η r ^σ ο D. Limestone powder 11th 0.939 0.261 0.0097 Limestone powder
with silica 11th 0.963 0.405 0.0069 Basalt flour 11th 0.966 0.329 0.0104 Basalt flour
with silica 11th 0.992 0.380 0.0091

Table 6: Er and D coefficients for the relationship

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The time t in seconds is inserted into this equation. The reciprocal of the damping constant is called Denotes relaxation time t_. A percentage comparison Figure 9 shows the calculated relaxation values. The greatest time was absolute 144.9 see.

The relaxation time is greater for the mixtures with added silica than for the mixtures without added silica. This means / that the forced tension in the mixtures with added silica as a result of more viscous Flow deformation is degraded more slowly than in the mixtures without the addition of silica.

3 _Λ 3.3 ^ Load change behavior

The forces introduced into the road structure via the contact area between the wheel and the road surface occur, apart from that of parked vehicles, not statically but dynamically. For the force-controlled dynamic Bending tensile tests were selected as the upper load 0.7 kN and the lower load 0.3 kN.

The test specimens were loaded with the following sinusoidal bending tensile stress in the center of the beam:

^ö bz ⁼ ° ^{ob +} ° ^{un +} ° ^oh "° ^un · ^{sin {ω} ' ^t ~ 2 2 2

with upper bending tensile stress σ = 1.45 N / mm ² lower bending tensile stress Cf = 0.62 N / mm ²

Frequency f = 5 Hz

Angular frequency *** = 31.42

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This stress causes a deflection in the test specimen. The course of the deflection over time has already been shown as an example in Figure 3. The curve has a turning point and a maximum. This course can be described with the following function:

t = a

with t

f a, b, c

= Load time in seconds

= Deflection in mm = constants

The coefficients given in Table 7 were obtained with the measured values.

Filler type number of
Value pairs
η Correlation
coefficient
r Coefficients b C. Limestone flour *
Limestone powder
with silica
Basalt flour
Basalt flour
with silica 20th
17th
30th
18th 0.996
0.994
0.994
0.996 a 1, 618
1, 766
1, 419
1,319 -0.307
-0.354
-0.186
-0.143 8.403
10.816
5.847
5.601

Table 7: Coefficients a, b and c with different types of filler

The turning point can be defined as the beginning of the break phase. The percentage comparison of the coordinates of this point is shown in Figure 10. The greatest deflection for the four mixtures with!, «! 7 mm and Uiu l« 'inqnl <? '/.oil with 10.2 s «.; c ιι <μικ · ι;:; ι · μ.

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The bituminous mixtures with the addition of silicic acid can be subjected to longer loads until the start of the breakage phase are considered to be the mixtures without added silica. Also, the deflection is at this point larger for mixtures with added silica.

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For the compression behavior, at a compression temperature of 135 ° C, the lag angle φ is a characteristic feature. On the basis of the results in Section 2.1 it can be stated that the bituminous mixtures with the addition of silica to the limestone powder or to the basalt powder more compact were as bituminous mixes with fillers without additive.

The elastic shear stress component T at the caster angle 45 ° is a measure of the deformation resistance of the bituminous mass at 60 ° C. Due to the Results in Section 2.2 can be stated that the addition of silica both in the case of the filler from limestone powder as well as from basalt powder have a greater deformation resistance in the asphalt concrete acted as the filler with no additive.

The addition of silica in the filler fraction therefore promoted the compressibility and increased the Deformation resistance of the examined asphalt concrete. This behavior contradicts previous experience with asphalt concrete, since easily compactable compounds show a lower resistance to deformation.

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The question of the relationship between compression and flexural tensile behavior must be taken into account the air-filled cavities H, .. the test specimen for the dynamic flexural tensile tests answered will. For this purpose, the slightly different ones found on the test specimens were used - Void content based on the void content achieved at 98% degree of compaction and in percentages the associated characteristics of the compression in the gyrator are calculated.

A comparison of these percentages with the calculated relaxation times indicates a hyperbolic Context on. From this it can be concluded that the relaxation behavior of the four mixtures approximates is equal to. The same statement can be made for the period up to the beginning of the break phase. To what extent the addition of silica influences the flexural tensile behavior under dynamic loading, was carried out in Section 2.3.

The relaxation time and the time to the start of the fracture phase is for the four bituminous mixes at a degree of compression of 98% approximately the same, while the deformation resistance of the mixtures with Silica is greater than that of the mixtures without added silica. The "stiffening effect" of silica therefore does not have a negative impact on the flexural tensile behavior of asphalt concrete. This result contradicts the general experience that deformation-resistant bituminous mixtures are one for the service life exhibit unfavorable flexural tensile behavior.

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4 ^ Summarize} 2_and_Conclusion

In the case of a grit-rich asphalt concrete, 0/11 was now the pen varies. Limestone powder and basalt powder were used with and without additives a synthetic silica. The compressibility at 135 ° C, the resistance to Deformations at 60 ° C / the flexural behavior of displacement and force-controlled dynamic loading 20 ° C.

The addition of synthetic silica to the filler resulted in a, despite the fact that it was easier to compress higher resistance to deformation in summer temperatures.

Which, according to general experience, has been disadvantageously changed in asphalt concrete with high resistance to deformation Fatigue did not occur. All tested mixtures showed in the flexural tensile tests under dynamic Load at 2 0 ° C and a degree of compression of 98% approximately the same relaxation time and the Time until the beginning of the break phase.

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Claims (4)

29/3/84 - »- ■ '" ■' "''" '' claims 1. Process to improve the installation behavior of stable / bituminous mix for road construction, the mix according to the "Technical regulations and guidelines for the construction of bituminous road surfaces" - TV-bit 3/72 composed and is processed, and the filler share determined from this by a mixed filler share, consisting of stone powder and silica is replaced .. characterized by, • 'Uh-i' ..-! ^: '■ "..r that the mixed filler' made of stone flour with an average bulk density of 1.0 kg / dm ³ and synthetic silica with an average bulk weight of 0.2 kg / dm ^{3 is} prepared almost homogeneously with a stable distribution of the two components and this and the bituminous binder are fed to the already heated aggregates and mixed with them. 2. The method according to claim 1, characterized in that that to produce a mixed filler stone flour filler with a surface area of about 0.5 m ² / g - measured according to BET surface area - and synthetic silica filler in a proportion of 0.1 to 2% by weight, based on the weight of the mixed material, and with a surface area of about 250 m ² / g - also according to BET - are brought together and mixed. - 40 - EPOCOPY JJ 29/3/84 -> β - 3. The method according to claims 1 and 2, characterized in that that the volume of the two filler components of the mixing filler is adjusted so that the ratio of a maximum of 1: 1 is not exceeded 4. The method according to claims 1 to 3, characterized in that that 0.5 to 0.6% by weight of silica, based on the weight of the mix is added. IPO COPY