Note: Descriptions are shown in the official language in which they were submitted.
The invention relates to â method of regulating
the temperature duri~g the production of building
material composition as, for example~ during the
production of cement concrete or asphalt concrete,
wherein the substances corresponding to a particular
formula are mixed with one another and heat is supplied
or removed during the preparation of the composition.
It has been found that the processing or
starting temperature of a hydraulically or thermo-
plastically setting composition, that is to say that
temperature at which the concrete mortar or a bituminous
hot plant mix, for example, leaves the mixer and is
supplied for processing, has a considerable influence
on the quality of the end product.
Thus it has been found that the starting
temperature of the concrete is proportional to the early
removal strength, that is to say that strength which the
concrete must have reached in order to be able to be
stripped.
It has further been found that adhering to a
constant temperature of the freshly mixed or hardened
concrete at all points of the structure to be erected is
of great importance. A prerequisite for this is that the
temperature of the freshly mixed concrete of each batch is
the same or in the case of large structures is the same on
the averâge. The latter is to be understood to mean that
in the case of a relatively long bridge girder for
example, in which the beginning has already cooled, the
end batch is adjusted cooler according to the cooling of
the initial section so that the temperature of the bridge
girder is practically equal over its length and so the
risk of cracking as a result of temperature differences in
the concrete which is not yet completely hardened is
largely avoided.
In the case of bituminous hot pla.nt mix, it has
likewise been found that the adhering to a specific
temperature of the plant mix has an important influence
on the quality of the bituminous pavement produced from
such a plant mix. Thus too high a temperature of the
plant mix leads to oxidation of the bitumen and hence to
embrittlement of the pavement laid and also leads to
difficulties in the compression of the surfacing,
whereas too low a temperature of the plant mix leads to
surfacings of poorer quality with numerous cavities.
It is the object of the invention to propose
a method of the ki.nd mentioned at the beginning which
ensures the production of a plant mix which can be pro-
cessed in the optimum manner.
~ccording to the invention, as broadly claimed
herein, this is achieved by a method of the above type
characterized in that during the whole preparation, the
temperature of the mix is measured at short intervals in
the region of 0.5 to 30 sec or continuously, with high
accuracy, without contact, and the amount of heat to be
added or subtracted in order to reach the required pro-
cessing temperature of the composition is calculated,
and that either an amount of heat slightly below the
calculated value is always supplied or removed, the
amount of heat to be supplied or removed approaching the
calculated value asymptotically, preferably in stages, or
the whole amount of heat corresponding to the calculated
value is supplied or removed at one time.
In this manner, the tempe~ature of the
finished mix which can be processed can be brought to a
very accurate value. In particular, by the method
according to the invention, hunting about the desired
temperature is avoided, which might lead to an unequal
temperature distribution in the finally mixed compositionO
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As a result of the very precise adherence to a
predetermined temperature of the finished mixing
according to the method of the invention, it is possible,
in the case of concrete, -to achieve a defined early
removal strength, as a result of which the possibility is
afforded of beginning the stripping of the article
produced from the concrete after a precisely pxedetermined
period of time.
In the case of a bituminous hot plant mix
(bitumen concrete) there is the advantage according to the
method of the invention that an oxidation Gf the bitumen is
reliably avoided because the necessary temperature of the
mix is never exceeded and after only a few passes a
bituminous surfacing of high quality and constant cavity
content can be achieved. In addition, as a result of the
method according to the invention, an optimum use of
energy results and because of the satisfactory
processability of the mix a considerable saving in time
during the compression of a bituminous surfacing.
The method is preferably characterized in that
in the case of a composition in which the mixing
temperature of the substances used is below the required
processing temperature of the finished composition, an
amount of heat which is less by a fractlon, for
example ~y l/lOth, is always supplied or its supply is
increased by such a fraction, than is calculated as a
result of the instantaneously measured temperature of
the composition.
As a result of this measure according to the
invention of the asymptotic supply of an amount of heat
reduced or increased by a fraction, the amount(s) of
heat necessary to achieve the required processing
temperature can be supplied with an accuracy better
than ~ ]%. In the calculation of the amount of heat to
be supp]ied, the uncertainties in the weighing in of
the aggregates, of the water etc. are included in the
total error in accordance with the error propagation law.
Now in order to reduce to a minimum the influence of
these errors which, with the necessary amounts, may
amount to more than 1%l and to prevent excessively high
processing temperatures (starting temperatures) from
resulting because of these Gaussian errors, this
reduction or increase in the amount of heat to be
supplied can be selected in fractions in the manner afore-
said.
The same advantages can be achieved in the caseof compositions in which the mixing temperature of the
substances used is above the processing temperature of
the finished composition, if the procedure is in
accordance with another preferred embodiment of the
invention. As a result, a far-reaching approximation
of the temperature to the required temperature is reached
quickly. The same effect is also achieved if, in the case
of compositions in which the mixing temperature of the
substances used is above the processing temperature of
the finished composition, an amount of heat which is less
by about 10% than is calculated on the basis of the
instantaneously measured temperature of the composition
is always removed, for example by the addition of ice
water.
The invention is also broadly claimed as an
apparatus for carrying out the method, wherein a mixer is
provided to mix the individual substances of the com-
position, to which the individual substances can be
supplied from separate storage containers and which com-
prises a discharge opening for the finished mixed com-
position and a feed device for the feed of a heat-
surrendering and/or heat-absorbing medium, for example
water vapour or ice water, characterized in that
disposed near a closable opening of the mixer at a
distance from the mix, is an infrared det~ctor which is
connected to a computer which is acted upon by a
director and is connected to at least one indicating
device, for example a printer and/or to signal devices
which can be activated on exceeding or dropping below
certain limiting values, and possibly a device for the
supply and/or removal of heat to or from the mix, and
wherein a temperature measuring instrument which is
disposed at the processing site, is possibly connected
to the computer, preferably via a transmitting and
receiving device, in order to adapt the giving of the
desired temperature in the computer to a predetermined
processing temperature of the mix.
As a result, a constant monitoring and
regulation of the temperature of the mix is possible, in
which case provision may also be made, for example, to
control a burner provided for heating the mix.
A preferred embodiment of the apparatus of the
invention is characterized in that the computer is con-
nected to control members for the control of final control
elements actuating the supply of steam or ice water to the
mix.
A very far-reaching constancy of the temperature
of the mix can be achieved by a further embodiment of the
invention characterized in that the computer is formed by
a microprocessor and delivers signals, corrected according
to the actual value of the temperature of the mix, to the
final control elements to control the supply or removal of
heat to or from the mix.
Summing up, therefore, it must be put on record
that as a result of the invention it is possible, during
the production of cement concrete, to monitor the
temperature of the freshly mixed concrete continuously mix
after mix.
It should be assumed to be known that each mix
is not absolutely like the preceding one or the following
one, except in the formula. The fractionated stockpiling
freely exposed to the weather alone brings in the course
of the day, depending on temperature, rain and air
humidity and amount, as well as speed of use, different
temperature conditions in the mixer. The water temperature
alters, the aggregate tempera-ture alters. The volume of
the thermal energy to be supplied for the reaction must
therefore be constantly adapted to these conditions.
For the starting of the hydration or of the
cement crystallization and so for the course of hardening
of the concrete, the temperature of the freshly mixed
concrete is a functional criterion. It is equally
decisive for the values of the early strength, the removal
strength, the freezing strength depending on time for
storage in the open, for the storability and ultimately for
the economy of formwork, handling and utilization of
space. The required values are fixed.
Since the temperature of the freshly mixed
concrete and the heat of hydration originating from this
basis are functionally dependent on the electrochemical
processes in the microrange, it is possible to determine
empirically which temperature of the freshly mixed concrete
leads to the most economical starting situation in the
production of cement concrete. According to the invention,
the temperature conditions of the mix can be determined
continuously and can be printed out through a recorder or
signals can be given either optically/acoustically for a
manually operated or automatically with direct pulse
delivery to a final control element. As a result, it
becomes possible not only to achieve precisely any required
temperature of the freshly mixed concrete but to adhere
to this precisely controlled from one mix to the next.
The supply of steam does not replace the mixing water but
serves to provide the starting temperature for the micro-
process in the mix. Thus the method according to the
invention requires for the starting temperature of 27C
of the freshly mixed concrete, starting from a water
temperature of 8C instead of 50C, a supply of energy
in the form of steam of up to 6700 kcal/cubic metre of
concrete, with the following concrete formula:
Quality = B 550, fresh density = 2473 kg/m3
cement = 440 kg/m3, W/Z = 0.43, water = 188 kg/m,
aggregates = 1830 kg/m3.
Once set to the temperature of the freshly mixed
concrete, the installation controls this constantly mix
after mix. With this technical equipment, therefore, it
is possible to draw the greatest possible use from the
absolute minimum amount of cement.
The increase in and precise control of the
starting temperature causes a more rapid start o~ the
concrete hardening and avoids negative effects for the
cement crystallization which occur with other techniques.
A description of a preferred embodiment of the
invention now follows with reference to the drawing wherein:
Figure 1 is a block diagram of a device which is
suitable~ in particular, for the production of hardening
compositions with relatively low processing temperature,
and Figure 2 is a device for producing hot plant mix.
In the form of embodiment shown in Figure 1,
the mix present in the mlxer 1 is monitored by an infrared
detector 2 disposed near a closable opening of the mixer 1,
the infrared detector 2 being at a distance of about 1 to
3~ 2 m from the mix. In order to eliminate influences of
water vapour or CO2 during the measurement, it has proved
particularly advantageous to operate the infrared
detector in the 8-14 ~m band. A suction device may
appropriately be provided in the vicinity of the closable
opening in order to avoid soiling of the infrared
detector 2. The accuracy of the temperature measurement
with the infrared probe should amount to about + 0.2C
with a temperature range to be detected between 30 and
50C and a measuring time of 0.5
/
~/
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3~
The infrared detector 2 is connected to a computer ~, and
a reference value indicator 3 is provided for adjusting
purposes.
The computer ~ is further connected to a director
4 and a printer 5 serving as an indicating device.
Furthermore, the computer ~ is supplied with
analogue signals which correspond to the temperatures of
the individual components of the mix to be mixed and the
computer predetermines the heat content of the mix in
accordance with the algorithm:
Q = ~i Mi * Ci * (to ~ ti~ + Mzu q
in which
Q = heat content lacking in the mix
i = component i, for example aggregates, cement, ~ater,
bitumen etc.
Mi = mass of the component i
Ci = specific heat of the component
to = aesired temperature of the mix after the end of the
mixing operation
ti = initial temperature of the component
Mzu = mass of the aggregates5 q = heat of fusion of the water (in the case of frozen
components)
Q = additional amount of heat in the case of a bituminous
mix, which takes into consideration the fact that the
temperature in the drying drum must be higher than to in0 the mixer.
The computer li delivers a signal, which is
influenced by the actual value, which is detected by the
detector 2, and the desi,red value, to the final control
elements 6, 7 which either regulate automatically the supply
of steam and/or ice water from storage devices 8 to the
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mixer 1 or permit an adjustment by hand. Particularly for
the latter case, it is provided that in the event of an
actual value differing from the desired value beyond a
certain value, signal devices S are activated by the
computer.
The form of embodiment illustrated can also be
modified in such a manner that disposed close to the dis-
charge openings of the storage containers in which the
individual substances to be processed to form the mix are
stored, are further temperature measuring instruments,
such as infrared detectors for example, which are connected
to the computer ~ and which supply signals corresponding to
the temperatures of the individual substances to the com-
puter.
This calculates the heat content lacking in the
mix, for example in a concrete mortar, in the production of
which no frozen constituents are used, according to the
formula:
Q = ~1 . Cl (tsoll - tl) + M2 . C2 (tsoll - t2) +...Mn . Cn .
(tsoll - tn).
In this Ml signifies the mass, Cl the specific
heat of cement and tl that temperature at which the cement
is supplied to the mixer, M2, C2 and t2 are the corresponding
values for the water to be added and M~, Cn, t the
corresponding values for the aggregates and tsoll that tem-
perature which the finished mix should have.
In order to cover this lacking heat content Q, a
mass of steam (mass of ice)
D - ~
heat content of the steam (ice)
is necessary.
In any case, however, the whole amount of steam
(ice) calculated is not supplied immediately, but a value
which is less by about 10% and after an appropriate waiting
time, ever smaller masses of steam Imasses of icei are
supplied. These desired values of these latter masses of
steam, that is to say those values ~MD whi.ch would be
sufficient to bri.ng the mix to the desired temperature are
calculated from the formulao
Q*
~MD = - _ ~
heat content of the steam
in which Q* signifies the heat content of the mix which is
still lacking, for which:
Q* = m . c ~ (tsoll - tgern)
in which
m = ~ass of the mix
c = average speci.fic hea-t of the mix
tsoll = desired temperature of the mix
tgem = measured temperature of the mix.
The actual values o~ the masses of steam thus
added step by step are less by about 10% than the particular
values ~MD which are valid.
The temperature of the mix therefore approaches
the required ternperature tsoll of the mix from below (or,
if the temperature vf the substances to be mixed is ab~ve
the required teMperature of the mix, from abo~e).
The particular amount of heat or masses of steam
supplied can be controlled by hand or regulated by the
computer ~ which processes the detected values a-t appro-
priate intervals of time and causes the correspondlny
influencing of the final ccntrol elements 6, 7.
In the form of embodiment shown in Figure 2,
bunkers 10 are provided for various aggregates, the dis-
charge openings 11 of which are disposed over a conveyor
belt 12. From this conveyor belt 12, the aggregates,
which are conveyed on the conveyor belt 12, pass via a
hucket elevator 13 to a drier 15 fired by a burner 14, and
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through which they are moved.
The sorted aggregates pass via a further bucket
elevator 16 into the bunker 17 from which they pass,
according to the formula of the composition to be produced,
via a further conveyor belt 18 to the mixex 4' in which they
are mixed with hot bitumen, the bitumen being supplied from
a separately heated bunker 20.
Disposed near the discharge opening or a separate
opening in the mixer 4' is an infrared detector 2 which
detects the temperature of the hot mix from a distance of 1
to 2 m and is connected to the computer ~. The accuracy of
the temperature measurement with the infrared probe should
amount to about + 1% of the detected temperature with a
temperature range to be detected of 160 - 180C and a
measuring time of 0.5 s. The computer ~ is also connected
to further temperature measuring instruments, such as
infrared detectors 2', for example, detecting the tempera-
ture of the aggregates and of the bitumen, and controls
the burner 14 and hence the supply of heat to the hot mix.
Because of the deficit in heat content of the
aggregates, heat must be supplied to the aggregates via the
burners so that Qz is present in the mixer. The
corresponding heat content is calculated from the formula:
Qzu = Mzu Czu (tsoll - tgem) + Q* ,
in which:
Mzu = mass of the aggregate i
Czu = specific heat of the ~ggregate i
tgem = measured temperature of the aggregate i ~with 2')
tsoll = desired temperature of the hot mix
Qzu = that amount of heat which the aggregates lose again
between burner and mixer, its magnitude is specific
to ~he installation and is determined by external
influences such as weather, time of day, season of
the year etc.
The computer ~ calculates this additional heat
content Q necessary, on the basis of the measured data,
with the above formula and in accordance therewith regulates
the burner output or burning period of the burner according
to the stored burner characteristic.
Furthermore, a continuous comparision of the
desired temperature of the hot mix with the actual tempera-
ture of the hot mix detected by the infrared detector 2 is
effected by the computer. If the actual temperature
deviates from the desired temperature or from a predeter-
mined tolerance range, the computer delivers correction
signals for a further burner regulation.
The desired temperature tSoll of the mix, referred
to in the above connection, can but does not have to corre-
spond to the processing temperature tv of the mix. Particu-
larly in the case of producing bituminous surfacings, there
may be a spatial distance of up to 10 km for example between
the compacting operation, that is to say the production of
the bituminous surfacing and the production of the hot mix
in an installation as shown in Figure 2. During the compact-
ing operation, however, in order to achieve optimum results,
a very specific processing temperature of 125 - 145C for
example should be adhered to. In order to ensure this, in
a further development of the invention, the compacting
machines may be e~uipped, for example in the region of the
compaction rollers, with at least one temperature measuring
instrument, for example an infrared detector for the
measurement of the temperature of the hot mix. The output
signal of this temperature measuring instrument is radioed
to the computer ~ which selects from a conformity table the
desired temperature tsoll corresponding to -this processing
temperature and uses it as a basis for the calculating
operation. In Figure 2, this additional temperature measur-
ing instrument and the associated transmitter and receiver
unit is designated by 21, 22 and 23.
Thus, through the invention, too high or too lowa temperature of the hot plant mix can be avoided, too
high a temperature, caused by the increased oxidation of
the bitumen, leading to an embrittlement of the applied
bituminous surfacing, which corresponds to a free exposure
to the weather of about 5 years, and too low a temperature
leading to difficulties in compacting the surfacing, that
is to say, to an increased cavity content and hence to a
lower quality of the surfacing.
As a result of adjusting the required optimum
processing temperature, a bituminous surfacing of high
quality and constant cavity content is achieved ~ith the
optimum use of energy and as a result of the satisfactory
compactability with a few passes.
In the same way as in the example of embodiment
sho-~n in Figure 2, it is possible with that shown in Figure
1 to adapt the desired temperature to -the actual processing
temperature. The temperature measuring instrument is there
designated by 24, the transmitting and receiving unit by
25 and 26. In this case, the temperature measuring
instrument 24 may appropriately be mounted adjacent to the
discharge opening of a transport vehicle and the measurement
is measured immediately before or during the output of the
steam-cured concrete at the building site. Measurement
via a separate opening in the transport container is
naturally possible in the same manner. As a result of
this additional possibility of adapting the desired tempera-
ture to the processing temperature of the mix, there is also
the possibility, particula-ly in the provision of structures
in which the introduction of the concrete extends over a
relatively long period of time, of taking into consideration
the lapse of time with regard to the incipient setting, that
is to say the individual batches of concrete can be intro-
duced with appropriately graduated processing temperatures
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in view of the setting ~f the first batches intr~duced,
which has already begun.