Patent Application
20090231950
1. Field of the Invention
The present invention relates to a system and apparatus for thermally treating ready mixed and/or transit mixed concrete, and, more specifically, to an apparatus for cooling or heating ready mixed and transit mixed concrete during transportation in a concrete mixer truck.
2. Description of the Background Art
Ready mixed and transit mixed concrete is a combination of fine aggregate (usually sand), coarse aggregate (usually crushed stone or gravel), cement, and water. Often chemical admixtures are added to modify aspects of the concrete design mix and or performance, such as viscosity, workability, or air content. Concrete is formed by mixing the components and allowing the mixture to harden.
The process of concrete hardening (or “setting” or “curing”) is a chemical reaction between the water and cement. This chemical reaction falls under a class of chemical reactions known as hydrolysis. A natural by-product of all hydrolysis reactions is heat. In the case of concrete curing, heat also acts to speed the rate of reaction, causing concrete to set more rapidly. The rate of setting is often in need of controlling in order to maintain desirable properties of the concrete, both in the plastic and cured states. These traits vary from workability, viscosity (called “slump”), and setting time in plastic concrete to concrete strength (measured in PSI or pounds per square inch) and durability in cured concrete. Standard concrete strengths range from 2000 PSI at an age of 28 days to 5000 PSI at 28 days. Higher and lower strengths are also available. The standard method of measuring concrete strength is to measure the strength of a test cylinder at 28 days of age from the date of concrete pouring and initial setting. This testing/measuring is done at regulated temperature and humidity conditions. Other tests are available and in use.
The American Concrete Institute (ACI) and the American Society for Testing and Materials (ASTM) are the two main academic bodies that set standards for concrete production and usage in the United States. ACI publishes the ACI Manual of Concrete Practice as a standard reference, which is revised annually. Several sections address the effects of temperature before, during and after the initial setting of the concrete. ASTM standards concentrate more on the specifications for the aggregates, water, and cement themselves, rather than with concrete.
As temperature has a direct effect on the rate at which concrete sets and the properties of plastic and cured concrete, controlling temperature becomes highly desirable. The temperature of concrete has direct effects upon setting time of concrete as well as strength development. The effects of various ambient and mix temperatures on concrete strength development are well studied and documented. While cooler and warmer mix temperatures affect strength at the standard 28 day interval when compared to a mix at 73° F., at 90 days and older, concrete strengthens to the desired design strength or very close to that mark, as far out as 365 days. ACI has sections devoted to both cold and hot weather concreting, as well as numerous subsections in various sections and chapters about concrete temperature in relation to other aspects of concrete work (such as time of transport or temperature effects on concrete in various stress conditions).
ACI 305 deals with hot weather concreting and ACI 306 deals with cold weather concreting. In order to achieve the desired concrete strength, the recommended range for the temperature of the concrete mix (at the time of concrete placement) in most applications is 40° F. through 90° F. However, the specifications for specific projects may have more stringent requirements for temperature of the concrete mix. In cases where concrete is being poured in hot weather, ACI 305 (2006 edition) has listed in Appendix B five methods for cooling concrete temperature. These include:
B1—Cooling with chilled mixing water: Using cooled water at the concrete plant as mixing water to help cool other ingredients of the concrete mix and have a lower starting temperature for the hydrolysis reaction,
B2—Liquid nitrogen cooling of mixing water: Using liquid nitrogen for the rapid cooling of water at the concrete batch plant for use in the concrete mix,
B3—Cooling water with ice: Using ice to replace up to 75% of the mixing water for the concrete mix,
B4—Cooling mixed concrete with liquid nitrogen: Using liquid nitrogen to directly cool the concrete mix either at the concrete plant or at the jobsite when concrete arrives,
B5—Cooling of coarse aggregates: Using various methods, such as spraying cooled water onto stockpiles of gravel, to cool the coarse aggregate prior to concrete batching and production.
All five of these methods are designed to be implemented either at the concrete batch plant prior to the mixer truck beginning the trip to the jobsite or at the jobsite after the mixer truck arrives.
However, a critical time for maintaining the concrete at a desirable temperature is during transportation to the jobsite. For instance, cooling during transportation is critical because it is a period of time wherein the concrete mix will begin producing heat from the hydrolysis reaction as well as absorbing ambient heat. Cooling also will have the added benefit of slowing the rate of hydrolysis down, effectively retarding concrete setting and extending the time in which concrete remains in a usable plastic state (aiding workability and slump). While ACI has no current method for cooling during the transportation period, ACI 304R-12 4.6 states:
Batch-to-batch uniformity of concrete from a mixer, particularly with regard to slump, water requirement, and air content, also depends on the uniformity of concrete temperature. Controlling the maximum and minimum concrete temperatures throughout all seasons of the year is important.
When the maximum temperature of the mix is regulated during transportation, an inspector will be less likely to reject an entire load of concrete when it arrives at the jobsite. Thus, a cost effective way of controlling temperatures during transport is highly desirable. Furthermore, the established methods for cooling concrete temperature all require highly specialized equipment with high investment, maintenance, and labor costs.
In the case of cold weather concreting, ACI 306 states that the minimum temperature of concrete at the time of placement is dependent upon the intended use of the concrete. However, ACI 306 also states that a minimum temperature at the time of placement is approximately 40° F. in the most accommodating application. With all cases of cold weather concreting, ACI has recommendations for the temperature of the concrete at the time of placement. This fact allows concrete producers to utilize the time available between loading concrete into mixers at the concrete plant and the time of placement on the jobsite to heat the concrete into the range of temperatures called for by specification. Currently, the most widely used method of warming concrete is to heat mixing water at the time of batching at the plant. Often, water is heated to near boiling point in order to aid in bringing overall concrete temperatures up.
The current invention is applicable without any adverse affects to any of the currently used methods of heating or cooling concrete. In fact, the present invention will supplement or eliminate the currently used methods. Effectively, the workload of those current, costly systems may be reduced by implementing the invention.
Accordingly, there is a need in the art for an apparatus that will effectively regulate the temperature of ready mixed and transit mixed concrete during transport thereof.
It is an object of the present invention to provide a system and apparatus for thermally treating (heating or cooling) ready mixed and transit mixed concrete, and, more specifically, to a system and apparatus for thermally treating ready mixed and transit mixed concrete during transportation in mixer trucks. The proposed method is far less labor intensive and has the added benefit of acting upon the mix during the entire time of transport, a time period up until now that was not utilized to treat concrete or maintain temperatures (and thereby desirable qualities) of concrete.
The system and apparatus for cooling ready mixed and transit mixed concrete during transportation in a concrete mixer truck solves many of the problems in the prior art. For example, the present invention provides a cost effective and labor simplified system of cooling concrete. Cooling concrete will increase workability in warm weather conditions. Cooling concrete during transport will increase the life of concrete in a plastic state. There is no adverse long term effect on concrete due to initial high temperatures. The cooled concrete will meet standard specifications for concrete on project sites, thereby reducing lost costs.
In accordance with the objectives referred to herein, the present invention provides for an apparatus for thermally treating concrete during transportation in a concrete mixer truck which includes a unit mounted on the chassis of the concrete mixer truck for providing at least one of a cooling and heating medium; a heat exchanging radiator assembly mounted adjacent to a concrete mixing drum of the concrete mixer truck and configured to receive at least one of the cooling and heating medium from the unit; and a mixing water tank mounted on the concrete mixer truck. The at least one of the cooling and heating medium may also be routed through a coil in the mixing water tank after it passes through the heat exchanging radiator assembly. The cooling medium is preferably a liquid refrigerant and the heating medium is preferably a liquid solution including hot water. A fan unit may be positioned adjacent to the heat exchanging radiator assembly. Additional elongate radiators may be positioned along a lower portion of the concrete mixer drum. Also, a shell may be formed around the heat exchanging radiator assembly wherein the shell is formed of a plastic material having insulating qualities to at least partially shield the heat exchanging radiator assembly from ambient conditions. A set of brushes and a drain plug may be positioned at the upper and lower ends of the shell, respectively, to keep the area between the shell and concrete mixing drum free of debris and condensation.
The invention is not limited to the above-described embodiments, and various changes are possible without departing from the principles set forth herein. Furthermore, the embodiments include the invention at various stages, and various inventions can be extracted by properly combining multiple disclosed constructional requirements. There are many applications of this design.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings.
The invention will become more clearly understood from the following detailed description in connection with the accompanying drawings, in which:
The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.
Referring now to the drawings in detail, and first to
With continued reference to
In accordance with the present invention, cooling/heating unit 20 includes and utilizes a compressor to compress a coolant material. Preferably, the compressor is a standard type compressor known to one having ordinary skill in the art (for example, the compressor may be of the type commonly found on refrigerated cargo trucks). The coolant material is preferably a commercially available refrigerant or coolant (for example, the coolant may be “Freon”). While the concrete mixer truck 10 is in transit, airflow in the direction indicated by arrow A in
Coolant which flows through the cooling/heating unit 20 is compressed and circulated to the heat exchanging radiator assembly 30. Heat exchanging radiator assembly 30 preferably includes an upper heat exchanging radiator section 32 and a lower heat exchanging radiator section 34. Heat exchanging radiator assembly 30 is preferably configured as a series of pie wedge shaped radiator style heat exchangers. In order to prevent concrete from falling out of the mixer drum 12 while truck 10 is in transit, the mixer drum 12 is configured and positioned such that the concrete mix is directed to a location in the drum 12 which is away from the exit location toward a first section 50 of the mixer drum 12. An end of the first section 50 of the mixer drum 12 is referred to herein as the head portion 52. Preferably, the heat exchanging radiator assembly 30 is positioned adjacent to the head portion 52 of the mixer truck's drum 12, since it is this section which will be in continuous contact with the concrete mix during transit. The heat exchanging radiator assembly 30 is preferably placed as close as possible to the outer surface of the rotating mixer drum 12. Typically, the outer surface of the rotating mixer drum is constructed of steel.
Once the coolant is circulated through the heat exchanging radiator assembly 30, the coolant is circulated back to the compressor within cooling/heating unit 20. Alternatively, the coolant is first routed through the mixing water tank 40 via a coil passing through the tank 40. Thus, the coolant will also cool or heat the water within the mixing water tank 40. The water contained in mixing water tank 40 is utilized for mixing with the concrete mix as necessary. Therefore, the result of the cooling or heating of the water within mixing water tank 40 will enhance the objective of this invention. As illustrated, the mixing water tank 40 is typically placed on the driver's side of the truck. However, it is contemplated that placement of the mixing water tank 40 may vary as design constraints vary.
Alternatively, during cold weather applications, cooling/heating unit will circulate hot fluid through the heat exchanging radiator assembly 30. The hot fluid may be, for example, a solution of water and anti-freeze. The fluid may be heated by a means know to one having ordinary skill in the art, including, but not limited to, a gas heater, an electric heater or routing the fluid through the concrete mixing truck's engine cooling system.
Referring now to
It is also contemplated that two elongate radiators 68 are positioned along the lower portion of mixer drum 12 to provide additional cooling/heating to the bottom of mixer drum 12, since it is the bottom portion of the mixer drum 12 that will be in continuous contact with the concrete mix contained therein. Preferably, the two elongate radiators 68 extend longitudinally along the lower portion of mixer drum 12. It is contemplated that any number of elongate radiators may be employed and, although the bottom portion of the drum may be the most convenient location, it is also contemplated that any number of elongate radiators may be placed at various locations around the circumference of mixer drum 12.
At the top of the radiator assembly 60, illustrated in
Referring now to
In the embodiment illustrated in
Various configurations of cooling radiator assembly 130 are contemplated for use with the present invention. For example, in
As best seen in
This process would allow the entire load of concrete to come into contact with the treated areas of the drum. The high density of concrete, particularly the aggregates, and the liquid nature of freshly mixed concrete will facilitate rapid transfer of heat across the system. As illustrated in
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiment and these variations would be within the spirit and scope of the present invention. For example, the size of the mixer drum, as well as local climate conditions, may affect the size and/or power requirements of the compressor unit and other components of the system and apparatus for thermally treating ready mixed and transit mixed concrete during transportation in a concrete mixer truck. Also, the system and apparatus may be powered by dedicated engines, dedicated batteries or the systems that provide power to the truck. When the need to cool or heat concrete is not required, whether by project specification, distance of transportation, or season of the year, the unit can just be powered down. The mixer truck can remain in operation, not taking up space or staying unproductive for the concrete supplier. Furthermore, it is contemplated that the present invention may be configured to be utilized in each of the two main types of mixer trucks, front discharge and rear discharge.
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiment and these variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the invention.
