AU2005203383A1 - Lightweight concrete block - Google Patents

Description

AUSTRALIA

Patents Act 1990 ADVANCED BUILDING SYSTEMS, INC.

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Lightweight concrete block The following statement is a full description of this invention including the best method of performing it known to us:toLIGHTWEIGHT CONCRETE BLOCK _BACKGROUND OF THE INVENTION 1. The Field of the Invention This invention relates generally to lightweight concrete building units concrete block, 00 and more particularly to lightweight concrete building units that are apable of being dry C€ stacked without the use of a mortar) and have an impact resistant outer layer.

2. Backgound The use of lightweight concrete for building construction has been known for decades. Aerated, lightweight concrete has many desirable properties for use in the building construction industry. For example, it is typically easier to handle because of its decreased weight compared to conventional concrete structures. Furthermore, aerated lightweight concrete often has an "R value" or insulative properties that eliminate or substantially decrease the need for additional insulation. Aerated lightweight concrete is also fire resistant.

so that any buildings built with such materials are less likely to be destroyed by fire.

Aerated, lightweight concrete is typically formed by one of two methods. One method involves mixing cement with an aerated foaming agent to form a cement mixture with air cells formed therein. For example, as disclosed in U.S. Patent 3,062,669 to Dilnot, a lightweight concrete is formed by combining Portland cement, ground silica, fibers, sodium silicate, water and a stable, preformed foam prepared by incorporating air into a hydrolyzed protein foaming agent. Similarly, in U.S. Patent 3,867,159 to Ergene, cellular concrete structures are made by mixing water, cement, and a foam into a foamed cement slurry which is cast into a mold and cured. Another method includes adding alumina powder to the cement mixture. The alumina powder reacts with the cement mixture to form gas bubbles causing aeration of the cement mixture. In order to form individual blocks of lightweight concrete, the aerated cement mixture is poured into a mold and allowed to harden around the air cells thus forming an aerated, lightweight concrete structure.

Several approaches in the art have been employed to form aerated, lightweight concrete structures that are suitable for building purposes. In order for the concrete structures to be suitable for building purposes, they must have sufficient structural integrity, compressive strength, to meet building code requirements and they must be uniform in size and shape to be practical for use in the construction industry. In addition, it has been difficult using the methods of the prior art to manufacture individual building blocks in an c) efficient manner and in sufficient quantities to support demands required by the building construction industry. As such, one of the more common approaches to mass produce individual blocks has been to form larger blocks of lightweight concrete and then cut the larger blocks into smaller building units while the cement is still in a partially cured or M 5 "green" state, 00 Mc, When employing cutting methods to form smaller building units, whether the initial e¢3 larger block is formed by using alumina powder to cause the cement mixture to "rise" or the t initial block is formed by forming a foamed cement slurry by adding a stable foam to the mixture, the resultant cement slurry is poured into a large mold and allowed to partially cure into a large block. For cement slurries that "rise," the height of the block within the mold is dependent upon the amount of aeration or gas generation that occurs within the cement mixture and the amount of gas that is entrained within the cement mixture when the mixture begins to harden. For cement slurries to which a stable foam has been added prior to being poured into a mold, the height of the block of the mold is determined by the amount of prefoamed cement slurry poured into the mold and the amount of air that escapes from the cement slurry before the viscosity of the cement slurry increases to a point where the air cells can no longer migrate within the mixture. Once the cement has hardened or cured to a degree where the formed block is sufficiently rigid to be handled but is still in a "green" state, the block is removed from the mold and cut into smaller blocks of a desired size and shape.

Because the height of the initially formed block is somewhat unpredictable, there is often significant amounts of scrap material produced during the cutting process. That is, it is often the case that at least a top layer of the initially formed block is wasted. Examples of cutting apparatuses for cutting larger blocks into smaller building units are described in U.S. Patents 4,174,936 to Goransson and U.S. Patent 4,528,883 to Goransson et al.

When casting aerated cement compositions, it is common to find that the density of the block formed varies from top to bottom. That is, prior to solidification of the cement slurry, the gas cells migrate to the top of the block resulting in a block that has a greater density nearer the bottom of the block. Accordingly, individual building units that are cut from a larger block will vary in density resulting in blocks of varying structural strength and weight. In order to compensate for the varying density in individual building units, the composition of the aerated slurry must have a higher density than what would otherwise be optimal.

In processes where the individual building units are cut from a larger block, a mortar or some other binding agent must be employed in order to stack the block for building purposes. Additionally, because each building unit has an outer surface that is comprised of open cells, water is easily absorbed into the building units. As such, the surface of the C 5 individual building units must typically be treated with a water repellant material to prevent 00 Mc, water from absorbing into the block. This is especially important in colder climates. That is, water that enters a building unit and freezes will expand causing fractures in the building unit t that may actually pulverize the cement.

SIn order for these types of building materials to be accepted for use in the construction industry, they are typically required to pass a "freeze/thaw test." In the freeze/thaw test, a block is submersed in water for an extended period of time and then frozen. If the block cracks, crumbles, or is otherwise structurally compromised, the block will not be approved for use as a building material. Thus, it is important that the block be formed so that water is not easily absorbed.

Another method employed to form individual building units is to cast them separately in a single mold. For example, as shown in U.S. Patent 5,522,685 to John, the building units are each formed by pouring the lightweight cement slurry into a mold to form a cast body and combining pairs of cast bodies into individual building units. In U.S. Patent 4,372,092 to Lopez, modular panels are individually formed by pouring a cement slurry into a single panel mold having desired components incorporated therein. Suchmethods for forming individual building units are typically not very efficient at producing large quantities of building units in a relatively short period of time. As such, the cost per unit is relatively high compared to conventional construction methods resulting in products that have not been very commercially successful.

One approach in the art to overcome the foregoing disadvantages with prior art systems is disclosed in U.S. Patents 5,457,926 and 5,775,047 to Jensen, the inventor of the present invention, each of which are herein incorporated by this reference. In both of these references, a lightweight interlocking building block is disclosed in which the blocks are configured to be stacked without the use of mortar. U.S. Patent 5,775,047 focused on the size of the bubbles entrained in the slurry in order to produce a block having desired compressive and shear strengths. The approach taken in forming blocks in these references, however, was to cause the air cells to coalesce to form an open cell structure within the block.

SAs such it would be advantageous to provide a building unit that has a precise dimension to be practical for dry stacking.

It would also be advantageous to provide a building unit relatively consistent densities throughout the core of the building unit.

C 5 It would be afurther advantage to provide a building unit having an impact resistant 00 Mc, outer layer.

e¢3 SIt would be yet another advantage to provide a building unit having a closed cell t structure.

It would be another advantage to provide a building unit having a relatively low density while maintaining structural integrity sufficient to meet or exceed building requirements.

It would also be advantageous to provide a building unit having more dense layers proximate the stacking surfaces.

SUMMARY OF THE INVENTION Accordingly, a building unit is provided, generally comprising a core having a first lower density and an outer layer having a second higher density. Havingsuch characteristic densities allows the block to be produced from highly aerated cement slurries to decrease the weight of the resulting building units blocks) while maintaining structural integrity, impact resistance and water repelling characteristics.

Preferably, such blocks are formed by compressing the aerated cementitious slurry in C a mold before the slurry sets. Compressing the slurry prior to setting provides several beneficial features of the formed block. First, the resulting block has superior impact resistant properties compared to lightweight concrete blocks of similar density. Second, the block can have a relatively precise volume and external dimensions since each block can be compressed to a substantially precise amount. Thus, it is preferable that the block have an outer layer defining an outer surface of the building unit and the outer surface defines a substantially precise volume. In addition, it is preferable that the block have an outer layer that forms a water barrier to inhibit absorption of water into the core.

It is also preferable that such block have an impact resistant outer layer. This is preferably accomplished by pouring the aerated lightweight concrete slurry into a heated mold that is above the critical temperature of the foam. The critical temperature of the foam Sis the temperature at which the foam destabilizes and the air cells therein collapse. Foaming agents typically have a critical temperature above which the foaming agent will fail to 0 produce a foam. In addition, there is typically a critical range of temperatures below the critical temperature at which the foaming agent will foam to some extent. For example, at a M1, 5 lower end of this critical temperature range, the foamingagent will foam quite well, while at 00 Mc, a temperature nearer but less than the critical temperature the ability of the foaming agent to foam is reduced. Preferably, the foamed cementitious slurry is mixed at a temperature at or tn near the lower end of the critical temperature range to maximize foaming efficiency.

There is also often a second critical temperature of the foaming agent in slurry above which the foam will quickly destabilize collapse). Often, but not necessarily, this second critical temperature is at or near the first critical temperature. Because, however, the foam will be mixed with the cementitious slurry, the slurry itself affects the temperature at which the foam will destabilize. In order to locally destabilize the foam at the interface between the mold and the slurry to create an outer hardened shell around each building unit produced, the mold is preferably heated above this second critical temperature or at least above the first critical temperature to obtain a desired shell thickness in the block. Knowing the temperature sensitive characteristics of the foaming agent (both alone and when mixed with a cement slurry) allows the other process parameters to be set to maximize the foaming efficiency of the foaming agent while encouraging quicker curing of the cement slurry and formation of an outer shell by the addition of heat. Those skilled in the art, will appreciate that the temperature may be kept at other temperatures depending upon the temperature sensitivity of the characteristics of the ingredients and the desired cure time. By pouring the slurry into such a mold, the slurry that contacts the outer surface or is at least contained within a layer adjacent the mold surface will become heated above the critical temperature of the foam causing the foam to destabilize and the air cells in this layer to collapse. As a result, the resulting block is formed with an outer layer of a more dense material than the core of the block which is generally unaffected by the heat of the mold as the remainder of the block will set before such cement reaches the critical temperature of the foam. Thus, the outer layer of the block has fewer air cells entrained therein than the core.

While the temperature of the mold can affect the thickness of the denser outer layer, this layer is generally smaller in thickness than the dense outer layers formed by compression oftheslurry by a mold. As such, in a preferred embodiment, the building unit includes a top side, a bottom side, a front side, a back side, a left side and a right side. The outer layer along the back side, front side, right side and left side has a first smaller thickness and the outer layer along the top side and bottom side has a second larger thickness.

Preferably, the first smaller thickness is approximately 1/8 inch and the second larger thickness is approximately 1 inch.

e¢ 5 In another preferred embodiment, the building unit of has an outer layer that includes 00 Mc, surface features for interlocking with adjacent building units when stacked.

e¢3 SIn yet another preferred embodiment, the building unit has an outer layer that t includes surface features for forming aesthetic texturing.

SIn yet another preferred embodiment, the inner core is comprised of a closed cell structure. While air cells within such a foam are of infinitely variable sizes, it is preferable that such air cells be relatively uniformly sized. That is, the average air cell size is relatively uniform such that a majority of air cells is close to the average. Such air cells may have an average size of approximately 1/16 inch. In addition, it is preferable that the core have a relatively uniform density throughout. That is, from top to bottom, side to side, the concentration of aeration of the core of the block is approximately uniform.

Because the block are formed by a method in which the cement is quickly cured before the air cells entrained therein can collapse, coalesce, or migrate to any appreciable extent, the core of the block is a closed-cell structure. In addition, the speed at which the block cures results in a block that can have a much higher cell-to-cement volumetric ration.

Preferably, such cell-to-cement volumetric ratio is approximately 1-to-1.

In yet another preferred embodiment, a lightweight building unit comprises a block having a top layer, a bottom layer and a core. The top and bottom layers have densities that are similar but substantially greater than the density of the core. The block further includes outer layers that define the outer surface of the block having a fourth density greater than the density of the core.

In still another preferred embodiment, a lightweight building unit formed from aerated concrete comprises a pair of elongate panels separated by left and right end panels that depend from and are interposed between the elongate panels effectively forming a boxlike structure with an open top and an open bottom. The building unit further includes at least one wall interposed between and depending from the elongate panels to form chambers that extend from the top to the bottom of the building unit. The top surface of the building unit is defined by a more dense top layer and the bottom of the building unit is defined by a J more dense bottom layer while the core of the building unit is fully aerated with a substantially less density than the top and bottom layers.

In another preferred embodiment, the top layer of the building unit defines a raised surface having features formed therein for mating with a second set of recessed features M* 5 formed in the bottom layer of another similarly configured building unit.

00 M In yet another preferred embodiment, the left and right ends of the building unit include substantially vertical tongue and groove features for mating with similarly configured t tongue and groove features of other building units.

In accordance with the principles of the present invention it is highly preferred that the building units include impact and water absorption resistant outer layer. This is particularly important for blocks formed from aerated concrete since such blocks in the prior art are more easily damaged by an external blow and tend to absorb water by capillary action thus preventing them from passing a freeze/thaw test.

Other objects and advantages of the present invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block flow diagram illustrating a first preferred embodiment of a process for forming lightweight concrete building units in accordance with the principles of the present invention; FIG. 2 is a schematic block flow diagram illustrating a preferred embodiment of a process for measuring ingredients for forming lightweight concrete building units in accordance with the principles of the present invention; FIG. 3 is a schematic block flow diagram illustrating a second preferred embodiment of a process for forming lightweight concrete building units in accordance with the principles of the present invention; FIG. 4 is a schematic block flow diagram illustrating a preferred embodiment of a process for transporting mixed slurry to a mold in accordance with the principles of the present invention; FIG. 5 is a partial cross-sectional view of a lightweight building unit manufactured in accordance with the principles of the present invention; J FIG. 6 is a partial cross-sectional view of cementitious slurry being compressed within a mold in accordance with the principles of the present invention; FIG. 7 is a perspective top view of a lightweight building unit manufactured in accordance with principles of the present invention; M€1 5 FIG. 8 is a top view of the building unit illustrated in FIG. 7; 00 Mc, FIG. 9 is a bottom view of the building unit illustrated in FIG. 7; FIG. 10 is a perspective top view of a wall constructed with building units in n accordance with the principles of the present invention; FIG. 11 is a perspective top view of a U-shaped building unit in accordance with the principles of the present invention; FIG. 12 is a top view of the building unit illustrated in FIG. 11; FIG. 13, is a side view of a mold in accordance with the principles of the present invention; FIG. 14 is a top view of the lid of the mold illustrated in FIG. 13; FIG. 15 is a top view of compression plates for the mold illustrated in FIG. 13 in accordance with the principles of the present invention; FIG. 16 is a top view of mold pillars for the mold illustrated in FIG. 13 in accordance with the principles of the present invention; FIG. 17 is a top view of the mold illustrated in FIG. 13; FIG. 18 is a front end view of the mold illustrated in FIG. 13; FIG. 19 is a side view of the mold illustrated in FIG. 13 in which the lid is in an opened position and the sides of the mold have been removed to show the inside of the mold; FIG. 20 is a top view of a plurality of panels assembled to form the mold illustrated in FIG. 13 in accordance with the principles of the present invention; FIG. 21 is a back side view of a mold panel in accordance with the principles of the present invention; FIG. 22 is a front side view of the mold panel illustrated in FIG. 21; FIG. 23A is a side view of a mixing device in accordance with the principles of the present invention; FIG. 23B is an end view of the mixing device illustrated in FIG. 23A; FIG. 24 is a front view of an apparatus for forming lightweight concrete building units in accordance with the principles of the present ihvention; SFIG. 25 is a top view of a hopper discharge control mechanism in accordance with the principles of the present invention; and FIG. 26 is a front view of the apparatus shown in FIG. 24 with the mixing device positioned over a mold.

00 M DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION t' Reference is now made to the drawings wherein like parts are designated with like Snumerals throughout. The present invention is directed to a lightweight cementitious building unit that is amenable to being dry stacked, that is, stacked to form buildings and other structures without the use of mortar or other such compounds known in the art. Providing an outer layer of more dense cement provides water absorption resistance and impact strength to the building unit is important in order to capture the entrained air in the cementitious slurry while the entrained air is substantially evenly dispersed throughout the slurry mixture. One problem found in the art is that the density of similar blocks vary within each block or from block to block because the entrained air was allowed to rise to the top the heavier particles settled toward the bottom) before the block sufficiently solidified. In accordance with the present invention, the ability to reach this "green" state before the individual air cells coalesce or migrate maintains the "closed-cell" characteristics of the resulting block and produces building units with consistent densities of materials throughout the building unit.

Maintaining the air cells in a closed form is important to give the blocks certain insulative, structural, and water resistant properties that may not be as good if the individual air cells are allowed to join with other adjacent air cells to form larger air cells to any appreciable extent.

For example, aerated concrete materials known in the art that are in an open cell form will allow air, heat, and water to travel into and through the material much more rapidly than similar materials having closed cells. Its somewhat like the difference between neoprene (a closed cell material) which is use for wet suits and a synthetic sponge (an open cell material).

Both are made from similar materials but they perform very differently.

The resulting block manufactured in accordance with the present invention is capable of withstanding a "freeze thaw test." Such tests are often required for certification of building materials for certain applications. The freeze thaw test requires the building material to be submersed in water for a period of time and then placed in a freezing environment for another period of time. If water has been allowed to absorb into the material, the water therein will expand when frozen causing fractures in the material. To date, there are no lightweight concrete products known other than the block manufactured in accordance with the present invention that can sufficiently pass the freeze thaw test, which have a relatively high volume of air.

3 5 Specifically, with reference to FIG. 1, a block diagram illustrating the process, generally 00 M€3 indicated at 10 for manufacturing such lightweight cementitious building units is shown in Saccordance with the principles of the present invention. As illustrated in FIG. 1, an t automated process, generally indicated at 10, for forming lightweight concrete building units Scomprises the steps of measuring 12 the ingredients necessary for forming a first batch of an aerated lightweight concrete slurry, combining 14 those ingredients in a mixer, mixing 16 the ingredients into a first batch of aerated cementitious slurry, and pouring 20 the ingredients into a mold. While the first batch is mixing 16, the "dry" ingredients cement, sand, quick setting cement) sufficient to form a second batch of aerated cementitious slurry are measured 12 and await emptying of the first batch from the mixer. As the first batch is being mixed 16, it is also being delivered transported) to the mold such that the mixing time is utilized to transport the batch to a mold. Upon delivery of the first batch to a mold, the mixer is quickly returned to receive the next batch of weighed ingredients. The second batch is then mixed 16 while the dry ingredients for a third batch of slurry are being measured 12.

Additional batches are mixed 16 and poured 18 into additional molds until the first batch has cured to a "green" state to at least a point where the resulting building unit(s) can be safely handled). As such, dry ingredients are either measured 12 or being dispensed into the mixer and combined 14 with water and foam. Likewise, the mixer is either being emptied 18 and returned for receiving additional batches of ingredients or is mixing 16 ingredients to form a batch of cementitious slurry and transporting the ingredients to a mold.

Once the first batch of cementitious slurry is cured 20 to a point where the resulting building unit(s) can be safely handled, the process further includes removing 22 the building unit(s) from the first mold, applying 24 a release agent to the mold and repeating the process for that mold. As illustrated in FIG. I, the process is divided into three main stages including dry ingredient measuring 26, mixing 28, and curing in mold 30. Each of these stages 26, 28 and 30 are repeated as quickly as possible. That is, while the mixing stage 28 is occurring for one batch of materials, the measuring and curing in mold stages 26 and 30, respectively, are being performed for other batches of materials. As such, usage of each of the physical structures to perform the process is efficiently maximized. Further, because the cost of each Smold is relatively high, increasing the speed of the process and decreasing curing time decrease the number of molds required to be able to continuously run the operation without interruption. More specifically, the number of molds necessary for continuous operation when employing a single mixer is approximately equal to the time required to pour 18 the C1 5 mixed slurry into a mold and remove 22 the building units from the mold divided by the time 00 Mc, required to combine 14 the ingredients in the mixer and pour 18 the mixed slurry into a mold 18. Thus, for example, if the cure time of each mold from the time a mold receives a batch of t mixed slurry to when the block is cured to a point where it can be safely handled is about ten minutes, and the mixing time of each batch is approximately one minute, then the number of molds per mixer for maximum efficient usage of the mixer and molds is ten. As such, when a first batch of blocks in the first mold reaches a point the resulting blocks can be safely handled, the blocks are removed from the first mold and a new batch of slurry is poured into the first mold. Each of the batches in the other nine molds should then be sufficiently cured in the sequence filled in order to remove the blocks from the molds. It is also contemplated that more than one mixing device may be employed for simultaneously mixing of multiple batches.

Referring now to FIG. 2, the method or process for measuring ingredients, generally indicated at 12, is comprised of several steps for substantially controlling the amount of each ingredient in each batch. Because the densities of most dry materials are relatively consistent, the quantity or volume of a material can be generally determined from the weight.

The present process utilizes ingredient weights in a novel manner to meter the quantity of each ingredient in each batch. The first step involves selecting 32 the first ingredient to be i )added to the mixture that will form the desired cementitious slurry. The first ingredient is then dispensed 34 at a first rate onto a scale. It should be noted that the term "scale" refers to any device that is capable of receiving a material and determining its weight. The first ingredient is weighed 36 as the ingredient is dispensed 34. When the weight of the ingredient has reached 38 an amount proximate to but not in excess of the desired weight, for example 90% of the desired weight, the rate of dispensing 40 is decreased to a second slower rate so that the scale can more accurately respond to increased weight. The ingredient is further dispensed at this second slower rate while being weighed 42 until the weight has reached 44 approximately 100% of the desired weight. By using such a method, ingredients can be dispensed in more accurate quantities without significantly decreasing overall dispensing time. In the alternative, weighing ingredients while being dispensed at a single J rate must either be dispensed at a slower rate to allow the scale to accurately measure changes in weight or likely result in inaccurately measured quantities if the rate of dispensing is too high. That is, it is difficult to control the quantity of ingredients resulting from dispensing at a single fast rate and then abruptly stopping the dispensing process when the M'C 5 desired weight is measured.

00" M€ When the weight of the dispensed ingredient reaches 44 approximately 100% of the Sdesired weight, dispensing is stopped 46 and it is determined 48 whether other ingredients t are needed for the present batch. If not, no additional ingredients are dispensed for the batch.

If so, the next ingredient is selected 50 and the measuring process 12 is repeated for the next ingredient. Multiple ingredients can be measured in this manner as the weight of the next ingredient is determined by calculating the weight added to the previously measured ingredients. This process is typically employed for measuring "dry" ingredients but may also be utilized for water, foaming agent and other liquid ingredients.

Preferably, a metered amount of water is added to the mixer before any of the dry ingredients so that the mixer can be activated with the water present to rinse the inside of the mixer between batches. The amount of water and foaming agent added to each batch are preferablymeasured by dispensing these "wet" ingredients for preselected periods of time.

By knowing the size of the orifice through which the wet ingredients pass into the mixer and the pressure at which the wet ingredients are injected, relatively precise amounts of liquid ingredients can be dispensed by controlling the dispensing time.

In order to decrease the cure time of the resulting block the time to reach a "green" state where the block is sufficiently rigid to be safely removed from the mold and f. handled), the process is performed at an elevated temperature. Preferably, this temperature is between 100 and 180 degrees Fahrenheit, which decreases the curing time of the cementitious slurry without significantly affecting its physical properties. Lower temperatures, even ambient temperatures, may be employed with the present invention, but will increase the overall cure time of the cement. Likewise, higher temperatures up to and exceeding the boiling point of water may also be employed to decrease the cure time.

Decreasing the cure time of the cement to a "green" state is important in order to properly capture the entrained air in the cementitious slurry while the entrained air is substantially evenly dispersed throughout the slurry mixture. One problem found in the art is that the density of similar blocks vary within each block or from block to block because the entrained air was allowed to migrate or rise to the top the heavier particles settled toward the Sbottom) before the block sufficiently solidified. In accordance with the present invention, the ability to reach this "green" state before the individual air cells coalesce or migrate maintains the "closed-cell" characteristics of the resulting block and produces building units with consistent densities of materials throughout the building unit. Maintaining the air cells in a Mf 5 closed form is important to give the blocks desired insulative, structural, and water resistant 00 M properties that would not otherwise be achieved if the individual air cells were allowed to join with other adjacent air cells to form larger air cells to any appreciable extent. For 'n example, aerated concrete materials known in the art that are in an open cell form will allow air, heat, and water to travel into and through the material much more rapidly than similar materials having closed cells. A good analogy is to compare the difference between neoprene (a closed cell material) which is use for wet suits and a synthetic sponge (an open cell material). Both are made from similar materials but they perform quite differently.

The resulting blocks manufactured in accordance with the present invention are capable of withstanding a "freeze thaw test." Such tests are often required for certification of building materials for certain applications. The freeze thaw test requires the building material to be submersed in water for a period of time and then placed in a freezing environment for another period of time. If water has been allowed to absorb into the material, the water therein will expand when frozen causing fractures in the material. To date, there are no lightweight concrete products known other than the block manufactured in accordance with the present invention that can sufficiently pass the freeze thaw test, that have a relatively high volume of air.

Referring now to FIG. 3, the process, generally indicated at 200, in accordance with the present invention is illustrated. In the process 200, it is preferable that cement, sand, water, and foam areutilized to form the desired cementitious slurry. Fibers, additional cements, and other aggregates may also be included in accordance with the principles of the present invention depending on the desired characteristics of the finished product. The "dry" ingredients, such as cement and sand are weighed 202 to a desired weight and dispensed 204 into a mixer. Water and foam, generated by blowing or mixing air into a foaming agent to produce a foam having a consistency similar to shaving cream with larger or smaller air cells as may be desired, are added 206 to the mixture and mixed 210 with the other ingredients for a relatively short period of time thirty seconds), sufficient to substantially evenly disperse the foam throughout the mixture. While.the ingredients are being mixed 210, the mixer itself is transported 208 to the mold, thus utilizing the mixing time to convey the slurry Sto the desired mold. Of course, those skilled in the art will appreciate that a separate transport device may be utilized in which the mixer remains stationary, dispenses a mixed batch into a transport container and allows the transport container to deliver the batch of slurry to the mold. The present embodiment, however, keeps the cementitious slurry M 5 workable in a liquid state) until it is dispensed into the mold such that the slurry is less 00 M€ likely to begin substantial solidification during the delivery or transport 208 process.

Preferably, the size of air cells within the foam are relatively consistent in size for tn producing cells within the slurry and core of the resulting block of relatively consistent sizes.

The foam is formed from a foaming agent, such as a protein-based, synthetic, or a combination protein-based/synthetic foaming agent known in the art, having properties that will result in a foam that will maintain a stable foam at elevated temperatures. Additionally, the foaming agent is selected that will break down, when foamed, at a known temperature or approximately a known temperature. To form the cementitious slurry in accordance with the present invention, heated water, preferably at approximately 100 degrees Fahrenheit is mixed with the dry ingredients. The foaming agent is then added to the mixture at a temperature preferably below about 90 degrees Fahrenheit for a foaming agent that will foam at temperatures up to 100 degrees Fahrenheit. Such a foam preferably has the ability to remain stable maintains surface tension of the air cells therein without collapsing) to at least a temperature of 120 degrees Fahrenheit.

As used herein, the surface tension of a bubble in a cementitious slurry at ambient pressure at sea level (the slurry having a selected temperature, a selected composition and components, and having a certain viscosity sufficient to resist migration of the air cells), is :IP the ability of the bubble to resist coalescing and/or collapsing. As is known in the art, there are foaming agents which produce bubbles that are more resistant to collapse and coalescing either in the presence of certain surfactants or when heat, vibration, or other means are applied to the slurry to cause bubbles to collapse or coalesce with other adjacent bubbles to form new larger bubbles. The present invention preferably utilizes a temperature sensitive foaming agent that results in a foam whose bubbles have relatively high surface tension and thus remain stable and are less likely to coalesce or collapse, unless subjected to temperatures above the critical temperature of the foam the temperature at which the foam breaks down). Those skilled in the art, however, will appreciate that various aspects of the present invention may be practiced with other types of aerated or lightweight slurries that may be Sformed by insitu chemical reaction or by adding lightweight aggregate materials, such as ;polystyrene pellets, to the mixture.

As previously discussed, it is preferable that as the slurry is being mixed 210, the slurry is simultaneously being transported 208 to a mold for delivery of the slurry. The slurry M 5 is then dispensed 212 from the mixer into a mold. Preferably, the heated slurry is poured into 00 M a mold that has been heated to an elevated temperature of approximately 180-220 degrees Fahrenheit. The heat from the mold and the fact that the slurry itself has been heated by the t addition of heated water and foam hastens hardening of the slurry to limit the amount of coalescing of adjacent air cells within the slurry and to limit the amount of migration of air cells and settling of heavier particles to the bottom of the mold during the curing process.

The elevated temperature of the slurry and mold quickly reduces the viscosity of the slurry to a point below which the air bubbles in the slurry can move or coalesce to form larger bubbles. Indeed, in accordance with the present invention, the heated ingredients utilized to form the cementitious slurry nearly immediately begin to cure much more rapidly. That is, because the slurry is heated by the combination of the dry ingredients with heated water and foam that are each at a temperature of over about at least 80 degrees Fahrenheit, the mixing and delivery of the slurry to the mold is essentially a race against the curing process. Those skilled in the art, after understanding the principles of the present invention, will appreciate that other temperatures of components and ingredient ratios may be employed depending upon the types of cement and foaming agent used as well as the desired curing time of the slurry into a solid state. For example, by modifying the cement ratios, such as decreasing the quick setting cement or calcium aluminate cement by 25% and adding 25% more standard cement, the cure time would increase by about 10 minutes compared to other embodiments discussed herein. Likewise, reducing the temperature of the water added to the mixture by 25 degrees Fahrenheit, the cure time would increase by about seven minutes compared to adding water at 140 degrees Fahrenheit.

Heating the mold to a temperature above the critical temperature of the foam produces an outer wall or shell in each block. This shell is produced because the foam breaks down the air cells collapses) in the layer adjacent the mold that exceeds the critical temperature of the foam before the slurry in this outer layer cures. One consequence of the heated mold is the formation of larger air cells adjacent the outer layer. The air cells in this region may not reach a hot enough temperature before curing of the cement to break down Sbut may coalesce to form a small layer of larger air cells between the outer layer and the core of the block.

Modifying the temperature of the mold will affect the thickness of the outer wall of each block. For example, fore each 10 degree increase of the mold temperature above 180 (cf 5 degrees Fahrenheit the thickness of the outer wall will increase by about 1/16 inch.

00 Cc Increasing the mold temperature above 180 degrees Fahrenheit to a temperature of 220 Sdegrees, for example, also helps to produce a smoother outer surface on the block. For every t decrease of 10 degrees Fahrenheit of the mold temperature, the wall thickness will decrease by about 1/32 inch down to a temperature of about 150 degrees Fahrenheit.

In accordance with the present invention, a mold is utilized to compress 214 the slurry therein to a precise dimension. Preferably, the step of compressing 214 the lightweight slurry is performed to a substantially precise degree, that degree being substantially the same for each block produced. Compressing 214 the slurry is possible in accordance with the present invention, because the slurry is a lightweight slurry preferably filled with air cells that can be forced out of or compressed within the slurry depending on the amount of compression applied. As such, when the slurry is poured into a mold, the mold is capable of squeezing the slurry a precise amount to a specific dimension. This compressing 214 performs at least two functions. First, the compressing 214 causes air cells in an outer layer of the slurry to collapse such that the density of this outer layer increases to produce a relatively hard outer shell in the finished block. Second, the compressing 214 provides a means by which the dimensions of the resulting block can be precisely controlled. That is, regardless of the quantity of slurry poured into the mold or the beginning density of the slurry prior to being poured into the mold and assuming that the batch of slurry has an adequate amount of air cells entrained therein, the slurry can be compressed to a point where the air entrained within the slurry is removed to allow the desired amount of compression.

Accordingly, each produced block will have nearly the same dimensions since each batch of slurry is compressed the same amount regardless of initial density or quantity of each batch of slurry the compression is not dependent upon force but rather compressing to a specific dimension wherein a preselected volume within the mold is achieved). As such, each lightweight concrete building unit produced has a substantially precise volume and precise dimensions. Indeed blocks produced in accordance with the principles of the present invention can achieve dimensional tolerances of 0.03 inches or less.

~J Upon curing of the slunrry into a block that is rigid enough to be handled, the blocks are removed 216 from the mold and hydrated 218 with water. That is, when the blocks reach a "green" state, the blocks are removed 216 the mold and transported for hydration 218, if necessary, during which water is sprayed or otherwise applied to the block. As is known in c 5 the art, this.supplemental water facilitates the slow curing of the block and provides adequate 00 Mc, water to complete the hydration process. The blocks may then be placed 220 in an autoclave Cc, to further aid the curing process of the blocks. The blocks may then be stacked, packaged t and allowed to completely cure prior to shipment.

As illustrated in FIG. 4, the process of pouring 18 the mixed slurry into a mold, as shown in FIG. 1, may include the steps of pouring 60 the slurry into a transport container and transporting 62 and 64 the slurry to the mold while a new batch of slurry is being mixed 16 (see FIG. The transport container may agitate the slurry during transport to keep the slurry in a workable state. The transport container then pours 66 the slurry into the mold and returns to the mixer for receiving another batch of slurry for another mold. Use of such a transport allows the mixer to continue to mix additional batches of slurry while other batches are being delivered to a mold. Of course, those skilled in the art will appreciate that multiple transports could be employed in accordance with the present invention. In order to increase the speed of transport, however, while maintaining precision of movement relative to each mold, the transport container containing a batch of slurry is accelerated to a first rate 62 or speed until the transport nears or is a relatively short distance from the mold. The transport is then decelerated to a second slower rate 64 or speed until the transport is properly positioned over the mold for pouring 66 the slurry into the mold. As such, the transport can move the slurry quickly to each mold without sacrificing precision of position over the mold.

As shown in FIG. 5, a lightweight cement block, generally indicated at 300, having a "closed cell" structure manufactured in accordance with the present invention, has a novel internal structural configuration. More specifically, the block 300 has a relatively smooth, dense, continuous outer surface 302 and a lightweight inner core 304. This outer surface 302 is preferably produced by at least two process parameters. First, the foaming agent contained in the outer surface 302 of the slurry that contacts a heated mold quickly destabilizes causing the air cells to collapse producing a layer of slurry with fewer air cells. Second, compression of the slurry within a mold further causes air cells in an outer layer being compressed to collapse and forces the air cells out of the slurry. This outer surface or shell 302 gives the block 300 unique characteristics. Preferably, the relatively smooth outer surface 302 is a J result of an outer, dense layer 306 having a width of about 1/64 inch to 1 inch, but could be larger or smaller in width depending on process parameters. The outer layer 306 gives the block 300 unique properties including the ability to resist the absorption of water by capillary action to an appreciable extent, as is required by the "freeze thaw" test, impact resistance to C- 5 external forces that would otherwise damage the block 300, better insulative values "R" 00 M€3 value). In addition, the structural strength of the block 300 is dramatically increased since e¢3 the outer layer 306 creates a hardened outer framework to support the softer, less dense core t' 304. In fact, the block 300 can have a core 304 that has a higher volumetric percentage of aeration compared to aerated concrete blocks in the art because the outer layer 306 provides the necessary structural support for the aerated core 304. Thus, the block 300 can be made lighter and use less cement per block than any other block known in the art.

As further illustrated in FIG. 6, in accordance with the present invention, when the slurry, generally indicated at 320, is placed inside a mold, indicated by surfaces 324 and 326, and compressed, as indicated by arrow 322, the surface 326 presses, as indicated by arrow 328, against the bottom 330 of the slurry 320. The slurry 320 is thus "squeezed" or compressed along this axial direction. As a result, air cells are forced from the slurry 320 and layers 332 and 334 of denser material are formed along the top 336 and bottom 330, respectively, of the slurry 320. Typically, these layers 332 and 334 are of approximately equal thickness as a result of the compression. Depending on the density of the slurry 320 during compression, however, the layers 332 and 334 may have different thicknesses. In either case, the resulting block has relatively thick layers 332 and 334 at the surfaces where the block is typically stacked. That is, additional structural rigidity is provided in the block along the surfaces that are employed to stack the block, resulting in blocks and walls formed therefrom that have better structural properties than lightweight concrete blocks known in the art.

Referring again to FIG. 5, the foregoing compression techniques may be employed in accordance with the present invention to produce textures, designs. or other aesthetic textural features 308 and 309 in the outer surface 302 of the block 300. Thus, the slurry can be compressed against the surface 302 to imprint a texture on the surface 302 while the slurry is in the mold.

The unique lightweight concrete building units of the present invention have external features for interlocking adjacent blocks toallow the-blocks to be dry stacked without the need for mortar or other binding agents interposed between building units. Such a block is illustrated in FIGS. 7, 8 and 9 in which the block, generally referred to at 110, in accordance with the present invention has a generally rectangular configuration with interlocking or mating features 112, 114, 116, 118, 120, 121, 122, 123, 124, 125 and 126, among others, that provide the ability to stack the blocks 110 in an interlocking arrangement. FIG. 8 is a view of M 5 the top of the block 1 10 showing the various mating features, such as mating features 112 00 Mc, and 114 for interlocking with mating features 116 and 118, respectively of another block 110.

¢€3 These "tongue and groove" mating features 112, 114, 116 and 118 are preferably tt substantially vertically aligned relative to the block 110 such that the blocks 110 can be vertically removed, slid, from a mold during the manufacturing process. The bottom of the block 110, as shown in FIG. 9, also has mating features 140-149 which comprise an inverse impression of the top 120 of the block 110 for mating with features such as mating features 121-126. In addition, the bottom 138 of the block 110 is recessed below the elongate sides 150 and 152 to receive the raised top portion 117 of the block 1 10. The mating features 121-126 and 140-149 are preferably relatively evenly spaced so that when the blocks 110 are stacked, they can be offset or staggered from one another as one of skill in the art would typically build a brick wall. Thus, the mating features 140-149 can receive any of the mating features 121-126 of another block 110.

As is further illustrated in FIGS. 7, 8, and 9, each block 110 is defined by a pair of elongate sides 154 and 156 separated by a plurality of interposing walls 158, 159, 160, 161 and 162 with the walls 158 and 162 forming the ends of the block 110. The walls 158-162 define a plurality of transversely extending chambers or cavities 128, 129, 130, and 131 that significantly reduce the amount of cement required per block 110 compared to a solid block that does not have such cavities. In addition, these cavities provide a means for adding structural strength to a stacked arrangement of the blocks 110.

As shown in FIG. 10, the blocks 110 in accordance with the present invention are stacked in a manner in which the mating features as described with reference to FIGS. 7, 8 and 9 properly align the stacked blocks 110 such that the cavities 128, 129, 130, and 131 align with cavities of other blocks 110 stacked above and below. Rebar 170 or other structural materials may be inserted into the cavities 128, 129, 130, and 131 and the cavities may be filled with non-aerated cement to provide columns 172 of rigid support within the blocks 110.

U-shaped blocks, generally indicated at 180, as illustrated in FIGS. 11 and 12 may also be employed to allow rows 174 of horizontal support preferably comprising non-aerated I concrete and rebar 170 (see FIG. 10) to extend through the wall of the structure being built with the block 110 of the present invention. The U-shaped block 180 includes mating or interlocking features 181-185 as well as other features similar to those found on the block 110 for mating with adjacent blocks above and below the U-shaped block 180. Such features C 5 (not shown) are provided on the bottom of the block 180 to mate with blocks 110 as well.

00 Mc, The U-shaped block 180 is similar in overall size and shape to the blocks 110, but have side walls 186 and 187 that define a longitudinal channel 188 extending the length of the block tn 180. Furthermore, the dividing or interposing walls 189-193 are similar in configuration to similar walls found in the block 110 but are of a shorter height to further define the longitudinal channel 188. Preferably, the height of the channel 188 from the top edge 194 of the wall 189 to the top edge 195 of the wall 187 is approximately equal to the width W of one of the vertical chambers 196.

The building units as described are preferably formed in a mold, generally indicated at 400, in accordance with the principles of the present invention, shown in FIG. 13. The mold 400 includes a base portion 402 forming the sides of the mold 400 and a lid 404. The lid 404 is pivotally attached to the back side 403 of the base portion 402 as with hinges 406 to allow access to the inside of the mold 400. The use of hinges 406 and 407 provide for controlled positioning of the lid 404 relative to the rest of the mold 400 in a reliably repetitive manner. Of course, those skilled in'the art will appreciate after understanding the principles of the present invention that other mechanisms may be employed to position the lid 404 relative to the rest of the mold 400. The lid 404 is pivotally actuated with actuator 408 preferably comprising a hydraulic ram controlled by hydraulic control valve 410. Sensor J 412 is provided to detect when the lid 404 is in a closed position and is positioned near the proximal end 414 of the lid 404. Sensor 416 is also provided proximate the distal end 418 of the lid 404 to detect when the lid 404 is in an open position. The lid 404 supports a slurry compression system, generally indicated at 420 which is configured for precise compression of.a slurry batch contained within the mold 400 to produce individual building units having substantially precise dimensions. The slurry compression system 420 includes an upper lifting bar 422 to which actuators 424 and 426, preferably hydraulic lifting rams are attached, guides 428 and 430 and sensors 432 and 434 for detecting top plate elevation.

A hold down device 435 is provided to lock the lid 404 to the base portion 402 of the mold 400 during the compression phase of the operation. Each hold down device 435 preferably comprises an air ram controlling a tapered hold down pin and an electronic sensor J to determine whether the hold down pin is properly engaged. An air valve controller is provided to control actuation of the air ram.

As shown in FIG. 14 the lid 404 comprises a frame having a first side 440, a second side 441, a distal end 418 and a proximal end 414. A plurality of cross-members 442-446 M* 5 depend from and are interposed between the sides 440 and 441 of the lid 404. The cross- 00 Mq members 442-446 define a plurality of apertures 448-453 corresponding to chambers within the mold 400. Four actuators 424,426, 436 and 438, preferably hydraulic or pneumatic t rams, secured to lifter bar 422 that essentially forms a rectangular frame, raise and lower the lifter bar 422 to precisely control compression of the slurry contained within the mold 400.

Referring now to FIG. 15, a plurality of compression plates 460-465 are secured to the lifter bar 422 shown in FIG. 14. Each compression plate, such as plate 460, is configured to relatively closely fit within the individual chambers of the mold 400 but have enough clearance to allow relatively easy insertion and removal therefrom without becoming jammed within the mold 400. As such, the perimeter 480 of the plate 460 includes external features 481-484 to substantially match the contour of the inner surface of the mold 400 thus keeping any substantial amount of slurry from passing between the plate 460 and the inside surface of the mold 400 during the compression process. The plate 460 includes a first elongate side member 466 and a second opposing elongate side member 467, a first end 468 and a second end 469 interposed between and depending from the sides 466 and 467 to essentially form a rectangular plate. A plurality of cross-members 470, 471 and 472 are interposed between and depend from the first and second side members 466 and 467 to define a plurality of apertures 473, 474, 475 and 476.

As further shown in FIG. 16, the apertures 473-476 of the plate 460 are sized and shaped to fit over pillars 490493 that are positioned inside the mold 400 for forming internal chambers inside the finished building units in accordance with the present invention. The other pillars, such as pillars 496-500, are similarly positioned relative to the other plates 461- 465. Each pillar, such as pillar 490 is generally rectangular in shape, but may have other geometric configurations, and is preferably tapered from proximate its proximal end 502 to proximate its distal end 504. This taper 506 allows for easier vertical removal of the building units such that as a building unit is lifted from the pillars 490-493, the building unit will effectively disengage from contacting the pillars 490-493 after a relatively small lifting displacement of the building unit relative to the pillars 490-493. Such disengagement substantially prevents the building units from becoming damaged by rubbing against the to pillars 490-493 during removal and reduces the possibility ofijamming the building unit within the mold during removal.

As further shown in FIG. 17, the plates 460-465 fit within cavities 510-515, respectively, of the mold 400 and can be raised and lowered within the cavities with the hydraulic rams or actuators 424, 426, 436 and 438 a precise amount to compress slurry 00 M€ contained within the mold 400. This precise movement of the plates creates a precise volume within each chamber or cavity 510-515 to produce building units with relatively precise outer t dimensions 0.03 inch). Producing such building units in accordance with the present invention that have such precise tolerances compared to other similar building units known in the art allows the building units to be dry stacked since there is little variance in wall height along a length of stacked building units for a given height wall.

Referring again to FIG. 13, the mold 400 also includes a block raising device, generally indicated at 520 for raising the at least partially cured building units from the mold 400. The lifting device 520 comprises a lower lifting bar 522 to which a plurality of lifting arms 526-531 are attached. The lifting arms 526-531 are secured to the lower lifting bar 522 with threaded rods 533 and thus may be adjusted relative to the lower lifting bar 522. As the lifting bar 522 is raised from a molding position, the lifting arms 526-531 move in unison to raise building units formed inside the mold 400 out of the mold for further processing. The lifting bar 522 may be raised and lowered with various devices known in the art including hydraulically or pneumatically driven actuators or, as is shown in FIG. 13, an electric motor 534 which is linked to ball screws 536 and 538. The motor 534 is coupled to a first gear box 540 which drives a pair of shafts 542 and 544. The shafts 542 and 544 are connected to a pair of right angle gear boxes 546 and 548, respectively.

As further shown in FIG. 18. the ball screws 536 and 550 are interconnected with shaft 552 and unions 554 and 556 so that the ball screws 536 and 550 are controlled and driven in unison to raise and lower the lower lifting bar 522. External boots 558 and 560 are provided over the ball screws contained therein to protect the threads from contamination that may otherwise hinder their performance. As the motor 534 causes rotation of the shafts 542, 544 and 552, the ball screws rotate relative to internally threaded collars 560 and 562 that are coupled to the lifter bar 522 causing the collars 560 and 562 to raise or lower the lower lift bar 522 depending on the direction of rotation of the ball screws. Because all four ball screws are controlled in unison by a single motor in a substantially symmetrical and uniform manner, the lifter bar 522 can be raised or lowered while staying in a level plane.

tb Control of the various components of the mold 400 are preferably computer controlled as with a PLC 564. Thus, each movement of the mold 400 can be precisely controlled and proceed in a preprogrammed and orderly manner. That is, in operation, the lid 404 of the mold 400 is in an open position to receive cementitious slurry therein. In addition, c 5 the lifter arms 526-531 have been lowered and the plates 460-465 have been raised. After 00 Mc, receiving a batch of slurry, the lid 404 of the mold 400 is closed and locked in position, and the plates 460-465 are lowered into the mold to compress the slurry contained therein. After t a few minutes when the slurry has cured to at least a "green" state whereby the now formed building units can be handled, the plates 460-465 are raised, and the lid 404 is opened. The lower lifter arms 526-531 are then raised to force the "green" blocks from the mold 400 for removal therefrom.

Referring now to FIG. 19, the mold 400 is illustrated with its sides removed and in an open position. In addition, the lifting arms 526-531 are shown in a fully extended position a position whereby the block can be removed from the mold 400). The mold 400 is comprised of a plurality of internal walls or panels 600-606, of which panels 600 and 606 form the proximal and distal ends, respectively, of the mold 400. The panels 600-606 form a plurality of internal chambers 610-615 within the mold for forming, in this example, six individual building units each time the mold 400 is filled with a slurry. Attached to the top of each arm 526-531 is a bottom mold plate 620-625 each of which fit relatively tightly within the chambers 610-615, respectively, while still allowing vertical movement of the plates 620-625 therein. Each plate 620-625 is configured to form the bottom of the building unit, such as that shown in FIG. 9. As such, the plates 620-625 include reverse impressions of the mating features of the block. In addition, as with the plates 460-465, the perimeter of each plate 620-625 is configured to match the configuration of the chambers 610-615 including the tongue and groove features. As such, the mold 400 is provided with upper actuable plate members 460-465 for compressing the slurry within the mold 400 and lower actuable plate members 620-625 for lifting the cured building units from the mold 400.

Those skilled in the art, however, will appreciate that actuation of either or both sets of plates could be employed to compress the slurry contained therein to obtain the beneficial results of compression taught by the present invention.

As further illustrated in FIG. 19, the actuators 424 and 426 are provided with longitudinally extending shafts 425 and 427, respectively. The distal ends of the shafts 524 an 427 are attached to the lid 404 while the body of the actuators 424 and 426 is attached to ~J the upper lifting bar. When the plates 460-465 are in a retracted position as is shown in FIG.

19, the shafts 425 and 427 are in an extended position. When the lid 404 of the mold 400 is in a closed position, retraction of the shafts 425 and 427 into the body of the actuators 424 and 426 cause the lifter bar 422 to lower and the upper lifting arms, such as arm 429, and 5 plates 460-465 to extend into the mold cavities 610-615 until the sensors 432 and 434 detect 00 Mc, the desired precise position of the guides 428 and 430.

As illustrated in FIG. 20, the panels 680-688 of a mold 690 in accordance with the tt present invention are provided with a plurality of heat pipes or pathways 691-699 for circulating water or another heated fluid through the mold 690. As shown in FIG. 21, the heat pipes, such as heat pipe 695, serpentine throughout the panel 680 to provide even heating throughout the mold 690. As previously discussed, the molds 690 are preferably heated to a temperature above the critical temperature of the foam in order to collapse the foam and form a dense outer layer or shell around the building units. Those skilled in the art will appreciate that the molds 690 may also be heated with electrical heating elements or other means known in the art.

As further shown in FIGS. 20, 21 and 22, the mold 690 is bolted together with a plurality of fasteners 700 that engage the panels 691, 693, 695, 696, 697, 698 and 699 through holes 702 and are secured into threaded holes in the panels. In addition, in order to define internal passageways to circulate water through each panel, each panel 691-699 is comprised of a pair of plates, such as plates 704 and 706 and plates 708 and 710. The passageways 712 and 714 are formed by cutting or milling channels in the plates 706 and 710 of the pair of plates. When the other plates 704 and 708 are attached to the first plates 706 and 710, respectively, as with rows of threaded fasteners in a patter similar to that shown with respect to panel 680, circulation passageways 714 and 712, respectively, are formed in the panels 692 and 699, respectively. Thus, with respect to plate 706, tongue and groove features 720 and 722 are formed on the front side 724 of the plate 706 while flow ways 714 are formed in the back 726 of the plate 706. For assembly purposes, recesses 728 may be formed in the plate 706 to receive the panels, such as panel 687.

Referring now to FIGS. 23A and 23B, a mixing device, generally indicated at 750, in accordance with the principles of the present invention, is illustrated. The mixer 750 is comprised of a generally cylindrical vessel 752 that is rotatably mounted proximate a longitudinal axis thereof to a support frame 754. The vessel 752 is coupled to a first drive motor 756 that may be controlled to rotate the vessel in order to dump its contents. A second drive motor 758 is coupled to the vessel 752 to rotate paddles 760 and 762 within the vessel 752 for mixing a cementitious slurry contained within the mixing vessel 752. An elongate spout 764 which preferably extends along a substantial length of the vessel 752 is provided to dispense slurry when the vessel 752 is rotated with motor 756. The spout 764 is attached to M 5 the vessel proximate to an around a perimeter of an opening 766 formed therein. The spout 00 M€ 764 is preferably tangentially offset relative to the vessel 752 such that the center line C of the spout 764 is spaced from and substantially parallel to a line defined by a diameter of the t vessel 752. This tangential offset is preferably opposite to the direction of rotation of the vessel 752. Offsetting the spout 764 helps prevent slurry contained within the vessel 752 from prematurely flowing out of the spout 764 when the vessel 752 is rotated in the direction of arrow 768 when dispensing of the slurry is desired. When dispensing the slurry is desired, the motor 756 rotates the vessel 752 to a position where the spout 764 has been rotated approximately 180 degrees from the position shown in FIG. 23B. After dispensing the slurry, the vessel 752 is preferably further rotated in the direction of arrow 768 back to the position shown in FIG. 23B for receiving another batch of ingredients to be mixed.

FIG. 24 illustrates a block manufacturing apparatus, generally indicated at 800, that utilizes the various new and novel devices described herein, for forming lightweight concrete blocks in accordance with the principles of the present invention. The apparatus 800 is comprised of a plurality of molds, two of which are indicated at 802 and 804, preferably arranged in rows or banks. A mixing device, generally indicated at 806 is suspended above the molds with an overhead truss, generally indicated at 808. The mixing device 806 can move in the direction of arrow 810 relative to the truss 808 for positioning over the molds 1 802 and 804. This is preferably accomplishedby motor driven wheel/track arrangements 809 and 811. The truss 808 is attached to an overhead mezzanine structure, generally indicated at 812, and is movable relative thereto in a direction perpendicular to the arrow 810.

Specifically, the truss 808 is coupled to tracks 814 and 816and is motor driven with motors 818 and 820 for positioning the mixing device 806 in alignment with a desired mold.

In operation, the mixing device 806 is positioned below a "dry" ingredient measuring device, generally indicated at 822, comprising a plurality of hoppers 824, 826 and 828 for receiving three separate dry ingredients, preferably standard cement, sand, and a quick setting cement. At the bottom of each hopper 824, 826 and 828 are provided computer controllable valves or discharge control mechanisms 830, 832 and 834 that can selectively control the discharge of ingredients from the hoppers 824, 826 and 828, respectively.

As shown in FIG. 25, the discharge control mechanism 830 is comprised of a plate 842 that is slidably engaged with the opening 840 of the hopper 824. The position of the plate 842 relative to the opening 840 is controlled with an actuator 842, in this example a pneumatic piston, that can be extended or retracted to at least three positions. The discharge M 5 control mechanism 830 can close the opening 840 as is shown in solid lines or partially or 00 M completely open the opening 840 as is indicated by dashed lines. In order to better control Smeasurement of the dry ingredients, the discharge control mechanism 830 can fully open the t opening 840 to allow maximum flow of ingredient until the desired amount is nearly reached, for example about 90 percent of the desired amount. The plate 842 can then be positioned to partially close the opening 840 to restrict the flow of the ingredient until 100 percent of the desired amount is reached. As such, more accurate measurement is achieved while substantially maximizing the discharge flow rate.

The dry ingredients are measured by dispensing the ingredients from each of the hoppers 824, 826 and 828 into a weighing hopper 850 that include an electronic scale. The ingredients are individually dispensed into the hopper 850 such that a first ingredient is dispensed until a first desired weight is reached. Similarly, a second ingredient is dispensed until a second desired wight is reached. The third ingredient can then be dispensed until a third weight is reached. Of course, more or less ingredients can be dispensed in this manner depending on the composition of the cement.

After the ingredients have been measured, the ingredients are gravity fed into the mixer 806 through openings 852 in the hopper that are fully opened with actuators 854 similar to that shown with respect to FIG. 25. The dry ingredients are then mixed with foam produced by a foam generator 856. The foam is preferably dispensed through a line 858 that exits between the openings 852 of the hopper 850. Heated water is also provided in the mixer 806. The amount of water is preferably controlled by opening a valve for a set period of time in order to meter the water into the mixer 806.

As shown in FIG. 26, once the ingredients are all in the mixer 806, the mixer can be moved from beneath the hopper while the mixing process occurs to efficiently utilize the slurry transport time to a mold 804. Preferably, the mixer is transported in a direction perpendicular to the arrow 860 until the mixer is aligned with the mold 804. The mixer is then moved in the direction of arrow 860 until the mixer is properly positioned above the mold 804. Preferably, this movement of the mixer occurs at two separate speeds, the first speed being faster than the second to quickly transport the mixer and thus the slurry to a Sposition near the mold and then a second speed for precise positioning over the mold at a slower rate.

Once the mixer 806 is positioned over the mold, the mixer 806 is rotated to dispense the mixed slurry into a slurry dispensing hopper 862. The slurry hopper 862 is comprised of M 5 an open top portion 864 and a plurality of individual hoppers 866 at its bottom portion 868.

00 M€ The hopper 862 is sized such that a single slurry batch fills the hopper 862 above the tops of the individual hoppers 866. As such, when a single batch of slurry is poured from the mixer t 806 into the hopper 862 the slurry is evenly distributed within the hopper 862 in the top portion 864. The hopper 862,is then lowered to the mold 804 with actuators 870 and 872.

The individual hoppers 866 are then opened and the slurry is dispensed in substantially equal amounts through each individual hopper 866 into the mold. The individual hoppers 866 are provided in equal numbers for each of the individual mold chambers within the mold 804.

The hopper 862 is then raised to a position proximate the mixer 806 and the mixer is returned to a position below the weighing hopper 850 for receiving the next batch of dry ingredients.

Preferably, the dry ingredients have been premeasured while the mixer 806 was transporting the slurry to the mold 804.

It will be appreciated that the apparatus and method of the present invention are capable of being incorporated in the form of a variety of embodiments, only a few of which have been illustrated and described above. The preferred embodiments are presented for the purpose of illustration and are not intended to limit the scope of the invention. Those skilled in the art will appreciate after understanding the principles of the present invention that the invention may be practiced and embodied in other forms without departing from its spirit or essential characteristics. Thus, the described embodiments are to be considered in all respects only as illustrative and not restrictive, and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes or modifications which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims (14)

1. A lightweight building unit, comprising: a core having a first lower density; and an outer layer having a second higher density. 00 Cc

2. The building unit of claim 1, wherein said building unit further includes a top side, a bottom side, a front side, a back side, a left side and a right side, and wherein said outer layer along said back side, said front side, said right side and said left side has a first smaller thickness and said outer layer along said top side and said bottom side has a second larger thickness.

3. The building unit of claim 2, wherein said first smaller thickness is approximately 1/8 inch and said second larger thickness is approximately I inch.

4. The building unit of claim 1, wherein said outer layer includes surface features for interlocking with adjacent building units when stacked. The building unit of claim 1, wherein said outer layer includes surface features for forming aesthetic texturing.

6. The building unit of claim 1, wherein said inner core is comprised of a closed cell structure.

7. The building unit of claim 1, wherein said closed cell structure is comprised of relatively uniformly sized cells.

8. The building unit of claim 7, wherein said uniformly sized cells have a diameter of approximately 1/16 inch.

9. The building unit of claim 6, wherein said core of said block has a cell-to- cement volumetric ratio of approximately 1-to-1. The building unit of claim 1, wherein said outer layer has fewer air cells entrained therein than said core.

11. The building unit of claim 1, wherein said core has a relatively uniform M 5 density throughout said core. 00

12. The building unit of claim 1, wherein said outer layer defines an outer tn surface of the building unit and said outer surface defines a substantially precise volume.

13. The building unit of claim 1, wherein said outer layer forms a water barrier to inhibit absorption of water into said core.

14. A lightweight building unit, comprising: a block having a top layer having a first density; a bottom layer having a second density substantially equal to said first density; and a core having a third density substantially less than the first and second densities. The building unit of claim 14, wherein said block further includes side surfaces defined by outer layers adjacent said core having a fourth density greater than said third density.

16. A lightweight building unit formed from aerated concrete, comprising: a first elongate panel and a second elongate panel; a left end and a right end depending from and interposed between said first and second panels; and at least one wall interposed between and depending from said first and second sides and positioned between said left end and said right end defining a plurality of chambers thereinbetween; said first and second panels, said left and right ends, and said at least one wall defining a top layer, a core, and a bottom layer, said top layer and said bottom layer having densities greater than the density of said core. Q) O t0 17. The building unit of claim 17, wherein said top layer defines a raised surface having a first set of features formed therein and said bottom layer defines a recessed surface having a second set of features formed therein for mating with said first set of features of another building unit. rM1 00 C 18. The building unit of claim 18, wherein said left end and said right end Sinclude substantially vertical tongue and groove features for mating with similarly configured ltt tongue and groove features of other building units.

19. The building unit of claim 17, further including an impact and water absorption resistant outer layer.