Method of and device for improving the quality of fresh concrete and preventing adhesion and hardening of the fresh concrete in a mixer drum of a concrete mixer truck or of a concrete mixing plant

A method of and device for improving the quality of fresh concrete and preventing adhesion and hardening of the mixed fresh concrete in a rotary mixer drum of a concrete mixer truck or a stationary mixer drum of a concrete mixer plant which involves delivering selectively and continuously either cold or warm air into the mixed fresh concrete in the rotary or stationary concrete mixer drum in order to delay the hardening time of the mixed fresh concrete, and to avoid adhesion and hardening of the mixed fresh concrete on a plurality of blades and an inner periphery of the mixer drum.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of and device for improving the quality 
of fresh concrete in a rotary mixer drum of a concrete mixer truck or of a 
concrete mixing plant. Cold or warm air is selectively and continuously 
delivered into a rotary mixer drum of a concrete mixer truck or into a 
stationary mixer drum of a concrete mixing plant during, just before, or 
just after unloading the fresh concrete and also just before washing the 
inside of the rotary mixer drum. This is done to maintain the temperature 
of the fresh concrete at a required temperature, and to delay a hardening 
time of the fresh concrete. Subsequently, water is sprayed into the rotary 
or stationary mixer drum, after having finished discharging the remaining 
fresh concrete, to wash it away before it has hardened. 
2. Description of the Prior Art 
Concrete is an artificial stony material which is used for foundations, 
etc. made by mixing cement, sand and broken stones, etc. with water, and 
allowing the mixture to harden. Quick hardening and solid concrete is 
indispensable as a building material. These solid and quick hardening 
properties of concrete may be disadvantageous sometimes. 
As shown in FIG. 1, a conventional rotary mixer drum 20 is rotatably 
mounted on a chassis 10a of a mixer truck 10 with a hydraulic motor 12 
which is linked to a gear 16 by a roller chain 14, the gear 16 being 
provided at a central portion of a bottom portion of the rotary mixer drum 
20. 
There has been an annoying problem in the conventional concrete mixer truck 
10 and in the concrete mixing plant when the chemical reaction of the 
mixed fresh concrete advances to adhere on the plurality of rotary blades 
and around the inner periphery of the rotary concrete drum, etc. and 
hardens thereon. The concrete, once adhered and hardened on the rotary 
blades and the inner periphery of the rotary mixer drum 20 of the concrete 
mixer truck 10 and in the concrete mixing plant, is hard to scrape off. 
It has been customary in the art that the remaining fresh concrete in a 
bottom portion of the rotary mixer drum 20 of a concrete mixer truck 10 in 
a concrete mixing plant is washed away by water after the fresh concrete 
has been discharged or unloaded out of the rotary mixer drum 20. 
The temperature in the rotary mixer drum 20 rises to a range between 40-50 
degrees Celsius under the blazing sun in summer, resulting in a shortened 
hardening time and delivery range of the fresh concrete and also 
decreasing the strength of the hardened concrete. In addition, when the 
mixed fresh concrete is unloaded out of the conventional rotary mixer drum 
20 of the concrete mixer truck 10, the temperature in the rotary mixer 
drum 20 rises suddenly so that the remaining fresh concrete hardens in 
shorter time. 
Moreover, inasmuch as the temperature in the rotary mixer drum 20 itself is 
rather high, the fact that the fresh concrete is not continuously agitated 
and gathers at the bottom portion of the rotary mixer drum 20 before it is 
unloaded, further accelerates the adhesion and hardening of the fresh 
concrete. To this end, even when water is sprayed into the rotary mixer 
drum 20 immediately after the fresh concrete has been unloaded, the 
remaining fresh concrete, once hardened, cannot be washed away. 
Accordingly, it is required that an operator must enter the rotary mixer 
drum 20 to scrape or tear away the hardened concrete with a hammer. 
Washing by water is usually carried out immediately after the fresh 
concrete has been unloaded from the batcher concrete mixer, but even if 
washing by water is carried out, a certain amount of the adhered concrete 
builds up. In practice, it is necessary for the operator to scrape the 
adhered concrete off of the mixer drum of both the concrete mixer truck 
and of the concrete mixing plant once a week. 
It is very dangerous for the operator to enter the mixer drum of the 
concrete mixer truck 10 and of the concrete mixing plant in order to 
scrape the adhered and hardened concrete off the mixer drum. Regrettably, 
a number of fatal accidents are reported every year when the rotary mixer 
drum 20 is carelessly rotated without knowing that the operator is within 
the rotary mixer drum 20 mounted on the concrete mixer truck. In order to 
avoid such an accident, a safety device with a sensor for detecting when 
the operator is within the rotary mixer drum 20 has been proposed. 
However, washing by water and the scraping operation by the operator 
within the rotary mixer drum 20 would still be required, leaving open the 
possibility for accidents. 
It is stipulated under the JIS (the Japanese Industrial Standards) that the 
time between mixing fresh concrete to beginning to unload the fresh 
concrete must be within 90 minutes. When the time has passed 90 minutes, 
the temperature of the mixed fresh concrete has risen, causing the fresh 
concrete to deteriorate due to the high temperature and shortening the 
delivery range. Accordingly, the fresh concrete, thus mixed, is likely to 
be refused by a user as the product is below the standards. It is said 
that concrete mixing and transporting are a battle against time. 
In another embodiment, cooling systems or refrigerators using liquified gas 
have been proposed to cool the fresh concrete temporarily so that the 
strength of the placed concrete is increased, cracking of the deposited 
concrete is prevented and the quality of the concrete is maintained. Among 
them are many cooling systems in which the fresh concrete is directly 
cooled prior to transportation. One of the conventional cooling systems is 
characterized in that the fresh concrete is cooled at a building site or a 
construction field. 
Mounted on the concrete mixer truck 10 is another conventional cooling 
system in which liquified gas is directly injected into the fresh concrete 
(see Japanese Patent Publication No. 2295-07/1986, not-examined). It 
should be appreciated, however, that liquified gas is very expensive, and 
although it may be suitable for a temporary cooling of fresh concrete, a 
large amount of liquified gas is required for continuous cooling during 
transportation. 
Another embodiment has been proposed, wherein flakes of crushed ice are 
mixed into fresh concrete in a rotary mixer drum, but there is a 
disadvantage. When the flakes of crushed ice remain in the fresh concrete 
at the time of placing the fresh concrete, openings or gaps occur in the 
fresh concrete as a result of the crushed ice, thus deteriorating the 
strength of the hardened concrete. 
On the other hand, when the rotary mixer drum 20 is exposed to the open air 
in a cold season, dropping the temperature in the rotary mixer drum, the 
strength of the mixed fresh concrete decreases. In order to eliminate this 
disadvantage, a countermeasure has been worked out in which the mixture 
ratio of the cement is changed in accordance with the temperature of the 
open air. However, the mixing adjustment is very troublesome, and the 
material costs increase as well. Adhesion and hardening of the remaining 
cement in the rotary mixer drum also occurs in the cold season even though 
the temperature is low. 
SUMMARY OF THE INVENTION 
A principal object of this invention is to provide a method of improving 
the quality of fresh concrete and preventing adhesion and hardening of 
fresh concrete on a plurality of rotary blades and around an inner 
periphery of a mixer drum of a concrete mixer truck and/or of a concrete 
mixing plant. Cold or warm air is selectively and continuously delivered 
into the rotary mixer drum to maintain the temperature of the fresh 
concrete at a required temperature range, to delay the hardening time of 
the fresh concrete and to extend the delivery range thereof. 
Another object of this invention is to provide a device for improving the 
quality of fresh concrete and preventing adhesion and hardening of fresh 
concrete on a plurality of rotary blades and around an inner periphery of 
a mixer drum of a concrete mixer truck and/or of a concrete mixing plant. 
Cold or warm air is selectively and continuously delivered into the mixer 
drum to maintain the temperature of the fresh concrete within a required 
temperature range, to delay the hardening time of the fresh concrete and 
to extend the delivery range thereof. 
Another object of this invention is to provide a method for improving the 
quality of fresh concrete and preventing adhesion and hardening of fresh 
concrete on a plurality of rotary blades and around an inner periphery of 
a mixer drum of a concrete mixer truck and/or of a concrete mixing plant. 
Cold or warm air is continuously delivered into the mixer drum to maintain 
the temperature of the fresh concrete at a required low temperature range, 
to delay the hardening time of the fresh concrete and to extend the 
delivery range thereof. 
Another object of this invention is to provide a device whereby long 
distance transportation of the fresh concrete can be carried out easily 
without deteriorating the quality of fresh concrete and preventing 
adhesion and hardening of the fresh concrete on an inner periphery of a 
mixer drum of a concrete mixer truck and/or of a concrete mixing plant. 
Another object of this invention is to provide a device whereby the amount 
of time for transporting the fresh concrete in the rotary mixer drum can 
be increased for as long as possible without using a concrete mixing relay 
base. 
Another object of this invention is to provide a device whereby washing by 
water of the remaining fresh concrete in a mixer drum of a concrete mixer 
truck and/or a concrete mixing plant can be carried out easily and safely 
so that a scraping operation of the adhered concrete by an operator in the 
rotary mixer drum can be discontinued, thus avoiding a potentially fatal 
accident. 
Another object of this invention is to provide a device for manufacturing 
fresh concrete in a rotary mixer drum of a concrete mixer truck whereby 
the fresh concrete can be manufactured even in a region where neither a 
fresh mixing plant nor a concrete mixing relay base is located, thus 
enabling the manufacturing of fresh concrete effectively, without needing 
to bring concrete material such as sand, cement and water separately. 
Another object of this invention is to provide a device whereby only cold 
air is delivered into a rotary mixer drum of a concrete mixer truck to 
prevent adhesion of the remaining fresh concrete after most of the fresh 
concrete has been discharged. 
Another object of this invention is to provide a device whereby the placing 
of fresh concrete can be carried out at either high or low temperature. 
Another object of this invention is to provide a device for preventing 
adhesion and hardening of fresh concrete in a rotary mixer drum of a 
concrete mixer truck wherein a part or whole portion of the exterior 
casing of the rotary mixer drum is covered with removable heat insulating 
material. 
Still another object of this invention is to provide a device for 
preventing adhesion and hardening of fresh concrete in a rotary mixer drum 
of a concrete mixer truck having a compact and simple hot and cold air 
blower which can be easily manufactured and mounted on a rotary mixer 
truck at a reasonable price.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
This invention is concerned with a method and device for preventing 
adhesion and hardening of fresh concrete in a rotary mixer drum of a 
concrete mixer truck. 
Referring to FIGS. 2-4, a blower 24 is mounted on a chassis 10a of a 
concrete mixer truck 10 located between a driver's cab 10b and a rotary 
mixer drum 20 for continuously blowing cold air in the mixed fresh 
concrete in the rotary mixer drum 20. A water tank 22 is provided on the 
chassis boa to wash the inner periphery of the rotary mixer drum 20. 
Located above and adjacent to the rotary mixer drum 20 is a blower duct 26, 
one end portion 26a of which is connected to the blower 24 and another end 
portion 26b of which partially enters the hopper 20a of the rotary mixer 
drum 20. A temperature sensor or thermometer (not shown) is provided at 
one end portion 26b of the air duct 26 in order to take the inner 
temperature of the rotary mixer drum 20. When detected by the temperature 
sensor that the temperature of the mixed fresh concrete in the rotary 
mixer drum 20 has risen over the predetermined range, the blower 24 is 
driven to deliver cold air to reduce the temperature and to maintain the 
predetermined range (between about 1 degree C. and about 15 degrees C.). 
It should be understood that when the open air temperature outside the 
rotary mixer drum 20 is 28 degrees C. and the temperature in the rotary 
mixer drum 20 rises to about 15 degrees C., the air blower 24 is driven to 
deliver cold air for dropping the temperature by about 3 degrees C., thus 
maintaining the temperature in the rotary mixer drum 20 at about 12 
degrees C. When the open air temperature outside the rotary mixer drum 20 
is about 12 degrees C., and the temperature in the rotary mixer drum 20 
rises over that of the open air, and unless any measure is taken, the 
temperature in the rotary mixer drum 20 will rise over 15 degrees C., so 
that even if the open air temperature is below 15 degrees C., the air 
blower 24 is driven to deliver cold air into the rotary mixer drum 20. 
In the summer, the daytime open air temperature outside the rotary drum 
mixer 20 is usually higher than 15 degrees C. On the other hand, the open 
air temperature outside the rotary mixer drum 20 is likely to be lower 
than inside the rotary mixer drum 20 in the winter. Accordingly, the 
cooling temperature of the air blower 24 is mechanically set to -10 
degrees C. during the season between May and October with the rotary mixer 
drum 20 covered with a heat insulating material without using a 
temperature control such as the temperature sensor, and the set cooling 
temperature may be set to -5 degrees C. during the season between November 
and April. It is also possible to choose a more detailed temperature 
setting. 
The one end portion 26b of the air duct 26 must be located in the upper 
portion of the rotary mixer drum 20 so that cold air flows downwardly into 
the rotary mixer drum 20 in order to cool the whole inner periphery 
thereof. It should be appreciated that when cold air is delivered into the 
fresh concrete in the rotary mixer drum 20 of the conventional agitator 
type concrete mixer truck (see the Japanese Patent Publication No. 
229507/1986, not examined), air bubbles may be introduced into the fresh 
concrete, thus deteriorating the strength of the fresh concrete. 
Therefore, the one end portion 26b of the air duct 26 must not be located 
at the intermediate or bottom portion of the rotary mixer drum 20. 
The air blower 24 can be driven by a domestic electric power source or by 
an automobile engine so that continuous cooling may be carried out. The 
cost of producing cold air by using an electric power source or automobile 
engine is substantially less than that of using liquified gas. As a 
result, it becomes possible to carry out long term continuous cooling for 
the fresh concrete in accordance with the agitation type concrete mixer 
truck where the rotary mixer drum 20 is rotatably mounted and driven by 
the truck engine (not shown). 
The invention brings about another advantage, in that even if the mixed 
fresh concrete is transported for a number of hours, deterioration of the 
fresh concrete can be prevented. Without cooling, the temperature in the 
rotary mixer drum 20 can rise above 40 degrees C. under direct sunlight in 
the summer. 
As shown in FIGS. 5-8, a heat insulating material 28 covering the outer 
periphery of the rotary mixer drum 20 will prevent the temperature from 
rising, help decrease the load on the motor of the air blower 24 and 
decrease energy consumption as well. The heat insulating material 28 is 
not required for the rotary mixer drum 20 during the low temperatures of 
winter. As a result, it is preferable to detachably wind the heat 
insulating material 28 around the rotary mixer drum 20. In order to apply 
the heat insulating material, a monkey belt including a vinyl sheet 28b, a 
plurality of long and narrow heat insulating material pieces 28c made of 
polystyrol pasted on the vinyl sheet 28b, and several fixing means such as 
hooks or adhesive tape 28d provided along one end portion of the vinyl 
sheet 28b, is wound around the rotary mixer drum 20. A bottom portion of 
the rotary mixer drum 20, which is not exposed to the sunlight, is not 
covered with the heat insulating material 28, but a side peripheral 
portion and an upper peripheral portion are covered with the heat 
insulating material to have a remarkable heat insulating effect. 
As shown in FIGS. 7 and 8, the heat insulating material 28 made of 
polystyrol is wound around the air duct 26 in order to prevent a rise in 
temperature and to increase energy efficiency. A water tank 22 is mounted 
on the concrete mixer truck 10 to wash away the inner periphery of the 
rotary mixer drum 20. 
In accordance with this invention, cold air is continuously delivered into 
the rotary mixer drum 20 to maintain the inside temperature less than 15 
degrees C. so that the hardening time of the mixed fresh concrete may be 
remarkably delayed. 
In FIG. 9, there is shown another embodiment of a cold and warm air blower 
30 instead of the blower 24 described in the foregoing paragraphs. More 
particularly, the cold and warm air blower 30 is rotatably mounted on an 
agitation rotary concrete mixer 10 which includes a casing 30a comprising 
a dehumidifier 34 located in a casing 32 and having a rotary dehumidifying 
plate 36 driven by a pulley 36a engaged with the plate 36 and a driving 
gear 38a of a motor 38. 
The casing 32 also contains a heater 40 located near the rotary 
dehumidifying plate 36. An intake pipe 42 having a compressor 44 at its 
middle portion and an exhaust pipe 46 are both connected to an outside 
plate of the casing 32. Another intake pipe 54 is connected to another 
outside plate of the casing 32 to face the heater 40. 
The dehumifidier 34 is connected through a duct 48 to a casing 52 of an air 
conditioner 50 which comprises a heat exchanger 54 located at an upper 
portion of the casing 52 and a base operating unit 56 provided at a lower 
portion of the casing 52, both the heat exchanger 54 and the base 
operating unit 56 being connected with each other by a duct 58. The base 
operating unit 56 comprises a compressor, motor, and refrigerant container 
(not shown). A control panel 60 is connected to the base operating unit 56 
by an electrical wire 68. A duct fan 62 is provided at a connected portion 
of the duct 48 and the casing 52. 
One end portion 26a of the blower duct 26 penetrates through the casing 32 
to connect with the casing 52 of the air conditioner 50. Another duct fan 
62a is provided at a connected portion of the casing 52 and the blower 
duct 26, and a damper 66 is provided into the blower duct 26 to locate 
near the duct fan 62a. Another end portion 26b of the blower duct 26 is 
extended to enter partially a hopper 20a of the rotary mixer drum 20. 
A drain cock 64 is provided at a bottom portion of the casing 52. The 
control panel 60 is also connected to the driving unit 20b, duct fans 62, 
62a, motor 38, heater 40 and compressor 44 by electrical wire 68. 
In FIG. 10, another cold and warm air blower 30 is mounted on a batcher 
plant (not shown) which includes a dehumidifier 34, an air conditioner 50 
and other units which are the same as those of the example shown in FIG. 
9, but a stationary concrete mixing tank 70 is mounted on the batcher 
plant. 
It can be understood from the drawing that a rotatable shaft 72 having a 
plurality of agitators 74 around the shaft 72 extends horizontally near a 
bottom portion 70a of the stationary concrete mixing tank 70 to penetrate 
its outer end portions 72a, 72b through a pair of openings 78, one end 
portion 72a being linked to a driving unit 76 provided on the bottom 
portion 70a and linked to the control panel 60 by the electrical wire 68. 
Owing to the season and local outer temperature, either cold or warm air is 
selectively delivered into the rotary concrete mixer drum 20 of the 
agitation concrete mixer truck 10 or the stationary mixer tank 70 of the 
batcher plant, thus maintaining the temperature of the mixed fresh 
concrete within a predetermined range, maintaining the quality of the 
mixed fresh concrete, and delaying the hardening time of the mixed fresh 
concrete. 
The method and device of this invention can increase the time for 
transporting the fresh concrete without using a concrete mixing relay 
base, and at the same time, the ordinary scraping operation of the adhered 
concrete by the operator in the rotary mixer drum 20 can be discontinued. 
It should be understood that changes and modifications to the preferred 
embodiment described above will be apparent to those skilled in the art. 
It is intended that the foregoing description be regarded as illustrative 
rather than limiting, and that it is the following claims, including all 
equivalents thereof, which are intended to define the scope of the 
invention.