MXPA98008248A - Vehicle arresting units and fabrication methods - Google Patents

Abstract

Vehicle arresting blocks of cellular concrete (70) are usable to safely slow travel of an object and may be used to construct an aircraft arresting bed at the end of an airport runway. For such purposes, cellular concrete blocks (70) must be fabricated to exhibit compressive gradient strengths of predetermined values to provide sufficient, but not excessive, deceleration forces on an object. Material uniformity characteristics must be met to avoid unacceptable drag force variations, so that arresting blocks desirably exhibit a predetermined compressive gradient strength (e.g., a 60/80 CGS) over a depth of penetration of 10 to 66 percent of block thickness (Fig. 7). A 60/80 CGS will typically represent an average compressive strength of 70 pounds per square inch over such depth of penetration. Prior applications of cellular concrete typically involved meeting minimum strength values and the production methods did not meet uniformity or compressive gradient strength predictability as required for arresting blocks. Described methods include parameter, ingredient and process controls and ranges effective to enable fabrication of arresting blocks having dry densities and compressive gradient strengths which can be specified in order to provide limited deceleration of aircraft and other objects. Limited deceleration can avoid destructive effects inherent in excess rates of deceleration.

Description

VEHICLE DETENTION UNITS AND MANUFACTURING METHODS THEREOF FIELD OF THE INVENTION This invention refers to slowing the movement of vehicles »and more particularly» to cellular concrete units suitable for use in detention bed systems to safely decelerate an airplane leaving the end of a take-off and landing runway »and methods to produce said units.

BACKGROUND OF THE INVENTION An airplane can (and indeed does) bypass the ends of the take-off and landing lanes, increasing the possibility of damage to passengers and destruction or severe damage to the airplane. These invasions have occurred during aborted takeoffs or during landing "with the airplane traveling at speeds of 80 knots. To minimize the dangers of invasions »the Federal Aviation Administration (FAA) of the United States generally requires a safety area of 305 m in length beyond the end of the take-off and landing runway. Although this security area is currently a standard of the FFA »many runways in the United States were built before their adoption and are located in such a way that water» roads and other obstacles prevent them from economic compliance with the invasion requirement of 305 m. Several materials »have been analyzed including the existing ground surfaces beyond the take-off and landing runway to determine their ability to decelerate the airplane. Soil surfaces are very unpredictable in their ability to stop »because their properties are predictable. For example, 'a very dry clay can be hard and almost impenetrable' but wet clay can cause the airplane to get stuck quickly 'causing the landing gear to collapse and causing potential damage to the passenger and crew' as well as greater damage to the airplane. A report of 1988 handles an investigation of the port authority of New York and New Jersey »E.U. on the feasibility of developing a plastic stop foam for a take-off and landing runway at JFK International Airport in the United States. The report "states that the analyzes indicated that such a stopping design is feasible and can safely stop a 45-tonne airplane that invades the take-off and landing runway at an output speed of up to BO knots" and a 3S9 airplane. tons invading at an exit speed of up to SO knots. The report states that the performance of an appropriate detention plastic foam configuration is potentially "superior to a paved invasion area of 305" particularly when the arrest is not effective and reverse thrust is not available. " As it is known, the effectiveness of detention can be limited under wet or icy conditions (report of the University of Dayton UDR-TR-88-07 »January 19BB). More recently »an airplane stopping system has been described in US Pat. No. 5,193,7S4 by Larrett et al. According to the description of that patent "an airplane stopping area is formed by adhering a plurality of thin layers of flame retardant and fragile fire-resistant foam" stacked together "with the lowermost layer of foam adhered to a support surface. The stacked layers are designed in such a way that the compressive strength of the combined layers of rigid plastic foam is less than the force exerted by the landing gear of any airplane of the type intended to be stopped when moving in the area of stopping a runway and landing »in such a way that the foam is crushed when it makes contact with the airplane. The preferred material is phenolic foam used with a compatible adhesive such as a latex adhesive. System tests of detention based on phenolic foam indicate that "although these systems can work to reach an airplane stop" the use of foam material has disadvantages. The main one among the disadvantages is the fact that the foam »depending on its properties» can typically exhibit a rebound property. Thus, it was observed that in the stool bed tests with phenol foam there is a certain forward thrust to the wheels of the airplane as it moves through the foamed material as a result of the bounce of the foam material on its own. Foamed or cellular concrete has been suggested as a material for use in detention bed systems and has undergone a limited field analysis in the prior art. These tests have indicated that cellular concrete has good potential for use in detention bed systems »based on the provision of many of the advantages of phenolic foam» while avoiding some of the disadvantages of phenol foams . However, the requirements for a crushing resistance and uniformity of material controlled exactly on the entire bed of detention, they are critical and as far as is known »the production of cellular concrete of appropriate characteristics and uniformity» has not been achieved or described previously. The production of structural concrete for building purposes is an old technique that includes relatively simple treatment steps. The production of cellular concrete »although it usually includes simple ingredients» is complicated by the nature and effect of the aeration »mixed and hydrated» aspects which must be specified closely »and accurately controlled if a uniform final product is to be produced that is neither too weak nor too strong for present purposes. Discontinuities - including weaker and stronger areas of cellular concrete - can actually cause damage to the vehicle that decelerates if, for example, deceleration forces exceed the strength of the wheel support structure. This lack of uniformity also results in an inability to accurately predict the deceleration performance and the total stopping distance. In a recent feasibility test using commercial grade cellular concrete, an airplane equipped to record run test data overland was acquired through a bed section and load data. Although actions have been taken to try to provide uniformity of production, the samples taken and the airplane load data from the test stopping bed showed significant variations between the areas where the resistance to the crushing was excessively high and areas in the which was excessively low. Obviously, the potential benefit of a detention system is compromised if the airplane is exposed to forces that could damage or crush the main landing gear. A 1995 report prepared by the Federal Aviation Administration entitled "Preliminary Soft Ground Arrestor Design for JFK International Airport" describes a proposed airplane stopper. This report discusses the potential use of phenol foam or cellular concrete. As for the phenolic foam, reference is made to the disadvantage of a "bounce" characteristic which results in the return of some energy after compression. As for cellular concrete »called« foam concrete »» it is noted that "a constant density (strength parameter) of foam concrete is difficult to maintain" in production. It is indicated that foam concrete seems to be a good candidate for the construction of the stopper »if it can be produced in large quantities with constant density and compressive strength. The flat-plate test is glossed and uniform compressive strength values of 4,218 Kg / cm 2 and 5,624 kg / cm 2 are described on a deformation scale of 5 to 80% as objectives based on the level of information then available in the technique. The report thus indicates the inaccessibility of both existing materials that have acceptable characteristics "and of the methods of production of said material" and suggests on a somewhat hypothetical basis "the characteristics and possible testing of said materials if they become available. In this way »although the detention bed systems have been considered» and some real tests of various materials have been explored for the same, the production and practical implementation of a detention bed system has not been achieved which » of the specified distances »safely detain the airplane of known size and weight that moves at a speed regime projected outside a runway and landing» nor suitable materials to be used in the same. The amount of material and the geometry in which it is formed to provide an effective stopping bed for vehicles of predetermined size, weight and speed "directly depends on the physical properties of the material and» in particular, of the level of drag that will be applied to the vehicle as it moves through the bed compressing or otherwise deforming the material. Computer programming models or other techniques can be used to develop entrainment or deceleration objectives for detention beds, based on calculated forces and absorption energy for an airplane of particular size and weight, in view of the corresponding strength specifications of the landing gear for said airplane. However, the models must assume that the detention bed is constructed of a material that has a uniformity of characteristics from section to section and from batch to batch, such as strength, durability, etc. to produce uniform results with a predictable amount of energy absorption (drag) when it makes contact with the portions of the airplane <or another vehicle) that carries the load of the vehicle through the bed (for example, the wheels of an airplane as it moves through the bed after having invaded the take-off and landing runway). One of the potential benefits of the use of cellular or foamed concrete in detention bed systems is that the B Same material is capable of being produced in a variety of different ways using numerous different starting materials. For previous types of applications unrelated to vehicle deceleration, concrete has been produced using a particular type of cement (usually Portland) that combines with water, a foaming agent, and air to produce a cellular concrete. However, a distinctive signifi- cant requirement separates these earlier applications for cellular concrete from the production of a product suitable for use in a detention bed. In previous applications "the targets are typically reduced weight or cost" or both "while providing a predetermined minimum resistance" with better resistance being better. Previous applications typically have not required the production of cellular concrete at strict standards of both maximum strength and minimum strength. In the same way, previous applications have not required a high degree of material uniformity, provided that the basic resistance objectives are met. Even for previous applications of cellular concrete, it is known that the quantity and type of cement, the water / cement ratio, the amount and type of foaming agent, the manner in which the materials are combined, the treatment conditions and the conditions of Curing »have all critical effects on the resulting properties of cellular concrete. The need to refine production to the levels required to produce adequate cellular concrete for vehicle stowage beds has not been presented in the above applications. Thus »an object is to specify the objectives in terms of the mechanical properties of the appropriate materials to obtain the desired deceleration during the arrival of an airplane or other vehicle in the detention bed. However, it is not known that the ability has been previously achieved to consistently produce cellular concrete material that actually has the required properties of predetermined strength and uniformity. A substantial problem in the art is the lack of established techniques to produce cellular concrete in the low resistance scale "in a uniform form for very narrow tolerances" that allow the construction of a complete stopping bed having consistently the desired mechanical properties to along its geometry. The objects of the invention are to provide new and improved vehicle stopping units and methods for their production which provide one or more of the following characteristics and capabilities: units produced in block form of suitable sizes for various applications; - units produced to provide predefined characteristics of compression resistance gradient »- units that have uniformity of suitable characteristics to safely brake the vehicle's journey; - methods that allow repetitive production with predetermined characteristics; - methods that allow production control based on scales of established parameters "and - methods that allow a high level of quality control in the production of cellular concrete having a predetermined compression strength gradient suitable for several applications. .

BRIEF DESCRIPTION OF THE INVENTION According to the invention, a vehicle stopping unit comprises a vehicle stopping block made to provide a compression resistance gradient without effective rebound to retard the travel of the wheel of a vehicle without failure of any asated support structure. of the wheel. The block is manufactured from cellular concrete »preferably having a dry density on the scale of 192.24 g / l to 352.44 g / l» formed from a combination of a water and cement suspension having a temperature not exceeding 31. S ° C »a foam prepared from water and an agent foaming "and a form of healing. The curing form is arranged to provide three-dimensional support with controlled evaporation for a mixture of the slurry and the foam that mixes after the suspension has experienced a temperature increase in the range of -15 ° C to -11.1 ° C. of its initial temperature. For the purposes of the invention, a vehicle stop block has a predetermined compression resistance gradient (CGS). For example, "an SO / 80 CGS equals approximately 4,921 kg / cm2" when averaged over a penetration depth of 10 to 66% of the block thickness. Also in accordance with the invention, a method for forming a section of detention material, characterized by a gradient of effective compressive strength to provide limited deceleration of a moving object "such as an airplane" includes the steps of: (a) forming a cement suspension and water »including inducing mixing of the suspension by high shear stress» (b) allowing the suspension to suffer a temperature increase related to hydration in the range of -15 to -11.1 ° C »until the suspension reaches a temperature Not more than 31.S ° C; (c) preparing a foam from water and a foaming agent; (d) mixing the suspension and foam to provide cellular concrete; (e) placing a portion of the cellular concrete in a form representative of the shape of the section; and (f) curing cellular concrete under controlled evaporation conditions to provide the 1Z material section detention in an independent three-dimensional shape and having a density on the scale of 192.24 g / l to 352.44 g / l. For a better understanding of the invention "together with other additional objects" reference is made to the accompanying drawings and the scope of the invention will be indicated in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A »IB and 1C are» respectively »a longitudinal plan view and cross-sectional and cross-sectional views of a vehicle stopping bed system. Figure 2 shows a deceleration block form of cellular concrete using the invention. Figures 3 »4 and 5 show alternative constructions of deceleration blocks in accordance with the invention. Figure G illustrates a controlled evaporative curing form for use in accordance with the invention. Figures 7 and 8 show test results in terms of compressive strength versus percent peation for cellular concrete samples of two different resstences.

DETAILED DESCRIPTION OF THE INVENTION The use of cellular concrete in detention bed applications requires that the material is generally uniform in its resistance to deformation "since it is the prediction of the resistance forces acting on the surface of the contact members of the vehicle being decelerated »which allows the bed to be designed» sized and constructed in a way that will guarantee acceptable performance. To obtain such uniformity "there must be a careful selection and control of the ingredients used to prepare the cellular concrete" the conditions under which it is processed "and its cure regime. The ingredients of cellular concrete are usually a cement, preferably Portland cement, a foaming agent and water. In some circumstances "relatively fine sand or other materials may also be used" but these are not used in the currently preferred modes. In addition to the common types of materials used in various concrete applications »according to the invention» hollow glass or ceramic spheres »or other crushable materials» can be embedded in cellular concrete. The type of cement currently preferred for the application of the detention bed is Type III Portland cement. For the present purposes, the term "cellular concrete" is used as a generic term that encompasses concrete with relatively small internal cells or bubbles of a fluid "such as air" and which may include sand or other material "as well as formulations that They do not include said sand or other material. Numerous foaming agents as known and used in the cellular concrete industry are classified as natural or synthetic foams. It is generally considered that natural foams are more robust in the sense that they will not degrade as quickly as synthetic foams. On the other hand »synthetic foams are generally more uniform in quality and, therefore» more predictable in their performance. While any type of foam can be used, "it is currently preferred to use a synthetic foam with suitable foaming and setting characteristics" because the consistency and uniformity of the resulting cellular concrete is of primary interest in the application of the detention bed. There are many known methods for producing cellular concrete. In general »the procedure includes the steps of mixing the foam concentrate with water» generating foam medium with inductive air »adding the resulting foam to the cement suspension or the cement / aggregate suspension mixture» and thoroughly mixing the foam and the cement suspension in a controlled manner that results in a homogeneous mixture with a significant amount of voids or "cells" that keep the material density relatively low. comparatively with other types of concrete. Because the application of cellular concrete in applications of the detention bed requires a general uniformity of properties of the material - the foamUniform mixing and setting of materials is extremely important. The preferred method for producing the cellular concrete is to use a procedure that comes as close as possible to a steady state continuous process. By controlling pressures, mixing speeds, raw material temperatures and other processing variables to be as constant as possible, higher levels of uniformity of the cellular concrete product are achieved »and the variations usually associated with interprocessed processing are avoided. . However, "the amount of material produced at any time in an intermittent or other procedure" will determine the duration of the procedure "and how much an approximation to the operation similar to a" steady state "is practical under the circumstances of production. for a particular installation of the detention bed. The preferred process includes the steps of creating a cement suspension »creating the foam» and then mixing the cement suspension and the foam to form the foamed or cellular concrete. The foam is prepared by mixing the foam concentrate with water to form a foaming solution. As an example »a preferred water relationship: ÍS foam concentrate for the synthetic foam material described above »is about 39: 1 on a volume basis. Then »the foam is formed by any suitable means of capturing air such as» for example »by passing the foam solution through a pump adapted with an adjustable air inlet. Preferably, the foam density produced by this process step will be from about 35.24 g / l to about 41. = 5 g / l »and more preferably from about 3S.84 g / l to about 38.44 g / l. According to the invention, the cement suspension is produced by mixing water with Type III Portland cement. It has been found that the preferred water: cement ratios are on the scale of about 0.5 to about 0.7, finding that an O.54 ratio provides excellent results. The cement is mixed thoroughly with the water and it has been found to be particularly advantageous to impart a very high shear stress to the suspension. Passing the mixture through a high shear pump is the currently preferred method for imparting a high shear stress to the cement suspension. It is preferred that the ambient temperature during the preparation of the cellular concrete is at least about 18.3 ° C. It has also been determined that the preferred method includes allowing a sufficient time of partial hydration to elapse so that the cement slurry before it is mixed with the foam forms the foamed concrete. While the partial hydration times may vary given different cement and cement / water ratios, it has been found that a certain degree of hydration of the suspension, for example as it is circulated through a device that imparts shear stress. helps to obtain an acceptable final product. Since the hydration reaction releases heat into the suspension, a measure of hydration is an increase in temperature. Thus, it has been found to be particularly effective to sufficiently mix water and cement to provide a temperature increase related to hydration of about -15 ° C to about -11.1 ° C. In a preferred embodiment "a period of about 4 minutes is used" to provide a temperature increase related to hydration within a scale of -14.4 ° C to approximately -13.3 ° C »before introducing the foam into the suspension of the suspension. cement. For example »a high-speed pump with temperature sensors can be adapted» and the mixing of the cement suspension can be carried out in recirculating form until the rise in temperature related to hydration has occurred (and »accordingly» the appropriate level of hydration for the present purposes). The partially hydrated cement suspension can then be passed to a low shear environment or a relatively moderate mixing environment such as a paddle mixer where the foam combines to form the cellular concrete. The wet densities of the foam concrete should be controlled very closely if you want to obtain the necessary uniformity of the product. The preferred wet densities are from about 224.28 to about 3S8.4S g / l. A currently preferred wet density that has been used to obtain a specified compressive strength gradient or "CGS" (as defined below) of about SO / 80"is about 288.3S g / l. Foamed concrete must be allowed to cure in a way that reduces low water regimes. Preferably, only the self-drying healing effects will be responsible for most of the water loss. This can be accomplished by casting sections of cellular concrete in wood forms coated with a plastic sheet material that also extends over the top of the concrete cel lar. Figure S is a simplified illustration of an open top wooden form 90 suitable for use in methods in accordance with the invention. The shape 90 may typically have respective inner length and width dimensions of 2.44 m and 1.22 m "and an appropriate internal height for the particular thickness of the block to be fabricated using the shape. As shown »a plastic coating 92» covering the inner surfaces and having a covering portion or portions for overlapping the upper surface of the cellular concrete introduced in the form, is included and placed within the form 90. The combination of the shape 90 and the coating 92 of plastic or other suitable material allows the provision of controlled evaporation conditions during the curing period for stop blocks produced in accordance with the invention. Preferred curing conditions include ambient temperatures near room temperature (approximately 21.1 ° C). The curing process will vary with the materials and the mixture, but it usually ends in approximately 21 days. The construction of a detention bed system can be achieved by producing the cellular concrete in a central production facility or in the bed site and by pouring the concrete into shapes of appropriate dimensions to achieve the desired geometry for the system. However, for the interests of uniformity of material characteristics and general quality control, it has been found preferable to cast sections of the general bed using appropriately sized shapes and then transport the sections to the site and install them to form the general configuration of the bed. In the latter case, said units or sections »in the form of blocks of predetermined sizes» can be produced and kept until the end of the quality control test. The blocks can then be placed on the site and adhered to the safety area of the runway and landing using asphalt »cement paste or other suitable adhesive material» depending on the construction materials of the security area itself. In any case, a hard coating material is preferably applied to the exposed surfaces of each block of the assembled stop bed to provide a stronger surface that is not as easily deformed as the main structure of the bed itself, allowing maintenance to be carried away. out without serious deformation damage to the main structure. A preferred hard coating material comprises foamed concrete, wherein the wet density is a little higher, for example, on the scale of about 352.44 g / l at 41S.52 g / l. In order to provide a greater context for the description of the stopping blocks according to the invention, an example of a complete stopping bed system using said blocks is illustrated in FIGS. 1A-IB and 1C. As shown »the stopping bed basically includes a first section 52 assembled from side rows of stop blocks of a first compression strength gradient (eg, a SO / 80 CGS)» and a section 54 assembled from rows of blocks of arrest of a gradient of superior compressive strength. In the shown mode »an initial row of stop blocks has a thickness or height of 22.86 cm» with subsequent rows increasing in height in increments of 1,905 cm. Certain successive rows of stop blocks in section 54 have increasing height differences of 7.62 cm. The combination of increasing height and different CGS provides an increasing drag effect for the deceleration of an airplane entering the detention bed. The detention bed will be described in more detail later. Referring to FIG. 2, an example of a vehicle stop block or deceleration block 70 formed of cellular concrete according to the invention is illustrated. Block 70 is suitable for uses such as vehicle detention bed systems installed at the end of an airport take-off and landing runway »to stop the journey of an airplane leaving behind the end of the take-off and landing runway» as well as similar types of facilities to stop trucks or other vehicles. In other applications, blocks or other units of cellular concrete of various sizes and configurations are used to stop the movement of various types of projectiles and other objects in motion. As shown in Fig. 2, the vehicle stopping block 70 generally has a height or thickness 72 that is less than the free space of the body of a vehicle to be decelerated. The block 70 can thus be placed in the path of a vehicle »such as an airplane» which will be decelerated »with the aim of interacting with the landing gear (for example, the wheels) of the airplane "without coming directly into contact with the fuselage. As an exception to the above »where the use is intended to be provided by several large and small airplanes» it may not be possible to secure the fuselage clearance for smaller airplanes »due to the need to provide a desired deceleration capability for a Largest airplane. In accordance with the invention, the block 70 is made to provide a compression resistance gradient without effective rebound to decelerate or retard the travel of the wheel of a vehicle. An important but secondary objective is to achieve this without resulting in failure of a support structure associated with the wheel in the nose of the airplane "if possible. To achieve these objectives, block 70 comprises a block of pre-established freestanding concrete having a dry density in the range of 192.24 to 352.44 g / l. For use in a typical airplane stop-bed assembly as illustrated in Figures 1A-IB and 1C, the cellular concrete blocks can be manufactured in the manner shown in Figure 2, with an even width 74 (nominally 1.22 m) and length 76 (nominally 2.44 m) and a thickness 72 (typically 22.86 cm to 76.2 cm), which can vary in increments (typically from 1,905 cm to 7.62 cm) to allow the provision of front tapering bed configurations. or later ones capable of providing predetermined increasing increases in towing forces. As illustrated in FIG. 2, the stop block 70 includes two transverse grooves 78 and 80 configured to facilitate handling and positioning of the block. In a currently preferred mode »two tubular plastic pieces of 1.22 m in length» and each having a rectangular opening of approximately 3.81 cm in height by 10.16 cm in width »are located on the inner lower surface of a curing form before a suspension of cellular concrete is introduced into the foam. In this mode, the tubular pieces are thus molded into the block and are embedded in the lower part of the resulting stop block when it is removed from the shape after the cure has ended. Tubular plastic parts are economically constructed and only need to be strong enough to prevent their collapse during the introduction and curing of cellular concrete in the form. When cured, the resulting stop block 70 includes the two transverse grooves 78 and 80 formed structurally in the block. It will be appreciated that a relatively lightweight cellular concrete block "which can have dimensions of 1.22 m x 2.44 m x 20.32 cm in thickness" will be a relatively fragile structure »in terms of handling» movement and placement of the block. This means that the attempt to select the block without care "may tend to cause cracking or fracture of the block. According to the invention, the fracture problem is greatly reduced while allowing the blocks to be easily moved and placed in a stopping bed. Slots 78 and 80 are typically located about one sixth of the length of the block from each end. Then, a load-lifting vehicle or apparatus having two approximately dimensioned and spaced projections that can be inserted into slots 78 and 80, can be easily used to lift, move and transport a block from one position to another. Various other arrangements can be used, such as the use of raised flange portions that remain in the shape to provide suitable transverse grooves comparable to slots 78 and 80. More particularly, the block 70 comprises cellular concrete formed of a combination that includes: - a suspension of water and cement, typically on a ratio scale of 0.5: 1 to 0.6: 1 »- a foam prepared from water and a foaming agent, typically having a density on the scale of 35.24 to 41.65 g / l; and - a curing form arranged to provide three-dimensional support with controlled evaporation for a suspension and mixture of foam having a wet density in the range of 224.28 to 368.46 g / l. Said combination is effective to provide a cellular concrete block for deceleration having a gradient of continuous compressive strength in the range of 2812 kg / cm3 to 9,842 kg / cm2 over at least GO% of its thickness. The specific compressive strength gradient for a particular block can be selected or specified within a much narrower scale, as appropriate for a particular application, more particularly specifying the particular parameters within the established scales. To enable the manufacture of vehicle stopping blocks having specified and repeatable compressive strength gradients for particular applications and a high degree of uniformity of said resistance along the cellular concrete forming the block, the deceleration blocks »And more particularly the vehicle stopping blocks» are conveniently formed of materials that meet the following specifications. The suspension of water and cement has been subjected to high shear mixing, and has been allowed to suffer a temperature increase related to the hydration in the scale of -15 ° C to -11.1 ° C until reaching a temperature not exceeding 31.6 ° C, before being mixed with the foam. In a presently preferred method, a hydration-related temperature increase in the range of -14.4 ° C to -13.3 ° C is used until a maximum preblending temperature not exceeding 30.5 ° C is reached. Figures 3, 4 and 5 illustrate particular embodiments of cellular concrete blocks usable in detention bed systems according to the invention. The block of Figure 3 is a mixed block that includes an upper portion 100 of cellular concrete having a convenient CGS and a thin lower layer 102 of stronger cellular concrete or other material to provide additional strength »particularly during transport and installation of the block. Figure 4 shows a block of cellular concrete 104 that includes within its lower portion reinforcing members illustrated in the form of a fiber reinforcing grid »metal or other suitable material. In other embodiments, wires or rods or other suitable material configurations may be used. Figure 5 illustrates a block 108 of cellular concrete containing within it pieces or crushable forms of another material. As represented in a somewhat idealized form, said material may comprise one or more of: regular or irregular pieces of crushable material; glass or ceramic spheres »hollow articles of selected material and shape» or other suitable parts. These configurations of the block can be made by placing the articles in the casting forms "or in the wet cellular concrete" in order to be embedded in a vehicle stopping block. It will be appreciated that the articles or materials added to the block will typically be located near the bottom of the block adjacent to the land surface (Figures 3 and 4) or distributed through it (Figure 5). Such articles or materials will thus have a minor effect on the deceleration of a vehicle or other object »taken into account to determine the CGS» or both.

It will be appreciated that while the prior art recognized, for example, "the potential advantages of an airplane stopping bed constructed of a foam material" there was no adequate formulation of cellular concrete. Thus »while there was cellular concrete for various uses that required light weight and at least a minimum strength before the material failed or collapsed» the characteristics of uniformity of resistance and resistance to compression failure within a narrow predictable scale »And continued on a scale of thickness, they were not required nor were they attainable. According to the invention, a method for forming a section of stop material, characterized by a gradient of effective compressive strength to stop the movement of a moving object without destroying the object, includes the following steps: (a) forming a suspension of cement and water, including projecting the suspension in a high shear current to induce high shear mixing; (b) allow the suspension to suffer a temperature increase related to hydration in the range of -15 to -11.1 ° C »without the suspension exceeding a final temperature of 31.6 ° C; (c) preparing a foam from water and a foaming agent, having a density in the range of 35.24 to 41.65 g / l; (d) mixing the suspension and foam to provide cellular concrete; (e) placing a portion of said cellular concrete in a shape representative of the three-dimensional shape of the desired section; and (f) curing the cellular concrete under controlled evaporation conditions to provide the detention material section in an independent three-dimensional form and having a dry density in the range of 192.24 g / l to 352.44 g / l. By adjusting the relevant parameters, which can be fine-tuned on a results-based basis, blocks of cellular concrete stopping and other forms of deceleration blocks having uniformity and appropriate compressive strength gradients can be provided for detention bed of airplanes and other uses. Typically, compression gradients in the range of 2,812 kg / cmß to 9,842 kg / cm58 are appropriate for these purposes. According to the invention, it has been determined that cellular concrete manufactured to have a dry density in the range of 160.2 to 400.5 g / l is suitable for said purposes.

DEFINITION OF "GRADIENT OF RESISTANCE TO COMPRESSION", OR "CGS" It is commonly understood that the term "compressive strength" (non-CGS) »means the amount of force (conventional measure in kilograms per square meter) that» when applied to a normal vector to the surface of a standardized sample »will do that the sample fails. Most conventional test methods specify testing apparatus, sampling procedures, test specimen requirements (including size requirements, molding and curing), loading regimes and record keeping requirements. An example is ASTM C 495-86"Standard Method for Compressive Strength of Lightweight Insulating Concrete". While such conventional test methods are useful when designing structures that are required to maintain structural integrity under preloaded load conditions (ie, having at least a minimum resistance) the object of the detention bed systems it is to fail in a predictable specified way "thus providing predictable controlled resistance force as the vehicle deforms the cellular concrete (ie, a specific compressive strength gradient). Thus, said conventional test focuses on determining the resistance to a point of failure, not the resistance during compression failure. Put more simply, know how much force will crash a specimen of cellular concrete material, does not answer the critical question of what amount of drag or deceleration will be experienced by a vehicle moving through a detention bed system. In contrast to a "punctual" fracture resistance as in the prior art, for the present purposes the test should evaluate a continuous mode of compression failure as a portion of a specimen is continuously compressed to approximately 20% of its original thickness. Generally, there have not previously been adequate equipment and methods for such continuous testing appropriate for the present purposes. Due to the wide range of available variables in the materials and processing of cellular concretes, and the magnitude and cost to construct detention beds for testing, it is imperative that there is accurate test information to predict the amount of resistance force a A particular variety of cellular concrete, processed and cured in some form, will provide when used in a detention bed system. Through the development of new test methodology to focus the resulting data on the measurement of the strength of resistance that occurs during the failure to continuous compression of a sample "instead of" point resistance "simple point" have developed new Test methods and apparatus to allow reliable testing and confirmation of cellular concrete materials and appropriate process variables.

As a result, it has been determined that the compression force needed to crush cellular concrete up to 20% of its original thickness varies with the penetration width. This characteristic, which the present inventors termed "compression resistance gradient" or "CGS", must be precisely specified to construct a vehicle stopping bed made of cellular concrete having known deceleration characteristics for safely slow down an airplane. Thus »a penetration type test method» where the compressive strength of a sample of cellular concrete is measured by not applying a force that will fracture a sample »but rather it will continuously report information about the resistance forces generated as a head of Test probe that has a specified compressive contact surface moves through a volume of cellular concrete »is key to obtaining the data needed to formulate and use cellular concrete in detention bed applications. As measured thus »the CGS will fluctuate on a scale with depth of penetration» resulting in a gradient value (such as CGS of 60/80) »more than a simple singular fracture value as in the previous tests. For the present purposes "the term" compression strength gradient "(or" CGS ") is used to refer to the compressive strength of a section of cellular concrete from a surface and continuing to an internal depth of penetration that typically It can be 66 percent of the thickness of the section. As defined »the CGS does not correspond to the compressive strength determined by standard ASTM test methods. Figure 7 illustrates the CGS characteristics of a cellular concrete sample representative of a block of section 52 of Figure 1 determined by test. In figure 7, the lower scale represents the penetration percentage of the test probe expressed in tenths of thickness or height of the sample. The vertical scale represents the compressive strength of the test probe expressed in kilograms per square centimeter. The test data of interest are typically within the penetration scale of 10 to SS percent of the sample thickness. Data that is outside of this scale may be less reliable »occurring effects of accumulation of crushed material beyond a penetration of approximately 70 percent. As illustrated in Figure 7, the resistance of cellular concrete to failure exhibits a gradient with resistance to compression that increases with depth of penetration. The line passing through points A and B in Figure 7 represents a generalized CGS of 60/80, that is to say »a CGS characterized by a compressive strength that changes from around 4,218 kg / cmz to approximately 5,624 kg / cm2 on a penetration scale of 10 to 66 percent. The average, on this scale »is thus nominally equal to 4,921 kg / cmz at midpoint C. Lines D and E represent quality control limits» and line F represents actual test data recorded for a specific test sample of cellular concrete. In this example »a test sample for which test data on a penetration scale of 10 to 66 percent fall within lines D and E of the quality control limit» represents a stop block manufactured within tolerances acceptable Figure 8 is a similar illustration of CGS characteristics of the deceleration block »with a CGS of 80/100 which is nominally equal to 6327 kg / cmz» when averaging over a selected depth of penetration (eg »a penetration scale) from 10 to 66 percent). For the present purposes, the terms "nominal" or "nominally" are defined in relation to a value or relation that is within approximately 15% of a value or relationship indicated. Suitable methods and test apparatus for determining the CGS are described in the serial application No. 08/796 »968» filed concurrently with it »having a common proxy» and incorporated herein by reference.

DETENTION BED OF FIGURES 1A, IB AND 1C Referring to FIG. 1 (including FIGS. 1A, IB and 1C as a whole), "one embodiment of a vehicle stopping bed system" is illustrated which utilizes stopping units as described above. Basically »the system of Figure 1 is constructed of pre-cast blocks of cellular concrete that have two different compressive strength gradients and several different thicknesses» with an installation intended for the end of the take-off and landing runway of an airport. The subsurface 50 supporting the system should typically be relatively flat and leveled (subject to having an appropriate slope for water inflow requirements) and capable of supporting an airplane leaving the take-off and landing runway. The subsurface 50 must be in good condition and must be cleaned satisfactorily to place and adhere the detention bed system. To show the vertical details »the vertical dimensions of Figures IB and 1C are enlarged with respect to the dimensions of Figure 1A (for example) the width of the bed in Figure 1A can typically be 45.75m, while the maximum thickness of the bed in Figures IB and 1C can typically be 76.2 cm). In the same way, "certain dimensions such as block size" have been altered to facilitate lustration (for example) rather than showing the thousands of blocks actually included in a typical detention bed. As shown »the vehicle stopping bed system of Figure 1 includes a first section 52» comprising an assembly of blocks having a first CGS and a first dry density »and a second section 54, comprising an assembly of blocks that have a second CGS and a second dry density. As shown in the side sectional view of Figure IB, sections 52 and 54 partially overlap (in what could be considered section 52/54) "indicating a dark line the junction where certain blocks of section 52 are they support blocks of section 54 in a transition region. In a particular embodiment, the blocks of section 52/54 may actually be mixed blocks (ie, individual blocks that include a portion 52 having a first CGS and also a portion 54 having a second CGS). In other modalities, separate blocks of different CGS may be stacked for section 52/54. More particularly, vehicle stop bed systems of the type illustrated in Figure 1 include at least a first block side row (eg, row 52a) of cellular concrete having a first dry density on the 208.26 scale. to 296.37 g / l. Each of the blocks in the first row 52a has a first height and is made to be vertically collapsible to a compressed height (eg, typically about 80 percent of the initial thickness). These blocks can be manufactured to exhibit a CGS feature of 60/80 »as shown in Figure 7. As shown in Figures 1A and IB» the first section 52 includes a plurality of additional side rows illustrated as rows 52b a 52n »formed of cellular concrete that have the same basic characteristics as row blocks 52a» but some of which differ from row to row by a differential of increasing height. Similarly »as discussed in relation to overlap section 52/54, certain rows of blocks» such as row 52n »rest on row blocks 54d on a mixed block or stacked block basis. In this modality »successive changes of 1,905 cm thickness were used in section 52 for. providing tapered or tilting features that result in gradually increasing vehicle stopping capabilities. In this particular design, corresponding 7.62 cm thick changes were used in section 54. Stop bed systems of the illustrated type also include at least one side row 54 g of cellular concrete blocks having a second dry density which can be at a higher level on the same scale as the blocks in section 52. As shown, the side row 54g is located parallel to and behind the first side row 52a. In turn, row 54g is followed by a side row 54h of increasing height. The blocks of section 54 are manufactured to be vertically collapsible to a second gradient of compressive strength "which will generally be specified to exceed the CGS of the blocks of section 52. These blocks may be fabricated to exhibit a CGS of BO / 100 characteristic represented in figure B »and a dry density in the scale from 256.32 to 344.43 g / l. In the illustrated embodiment, the first row of blocks 54a of section 54 includes only one individual course or layer of the second CGS. The successive rows of section 54 include increasing thicknesses of the material of the second CGS »until the blocks of section 54 reach the total height of the stopping bed beyond section 52. The successive rows of section 54 then increase in thickness in increments of 7.62 cm in advance until reaching the total height in a subsequent level portion that comprises rows of the same thickness that continue until the final rear row 54n. The rows of increased height »such as the row 54n» can be formed of two or three superposed blocks of reduced thickness »or of blocks of relatively dense individual blocks» depending on the considerations of manufacture »management and release on the site. As shown, the system of FIG. 1 further includes an inclined entry ramp 56 located across the vehicle entry front side of the first lateral line 52a. The ramp »which may be formed of a mixture of asphalt or other permanent type material» tapers to a height adjacent to the blocks of row 52a >; which is typically greater than the compressed height of the blocks of the row 52a. In a particular embodiment, a ramp height of 7.62 c adjacent to blocks of 22.B6 cm having an estimated minimum compressed height of 4.572 cm was used. The 5S ramp is thus effective to gradually raise an airplane above the general level of the take-off and landing runway "so that the airplane can enter the stopping bed on a relatively uniform basis" as the wheels leave the ramp 56 and begin to compress the blocks of row 52a. Also included in the system of Figure 1 is a hard coating layer 62 »in the form of a relatively thin protective layer of cellular concrete material» resting on the blocks of section 52 and section 54 (represented by the lower limit). top of the bed in figure IB). In a preferred embodiment, the hard coating layer 62 comprises a relatively thin layer of cellular concrete having a higher dry density (sufficient to support people walking on the stopping bed, for example) and which can be covered by paint or similar coating resnt to the weather. The layer 62 is applied to the detention bed after all the blocks of sections 52 and 54 are placed and adhere properly to the support surface SO. As illustrated »the detention bed system also has associated with it a barrier against carry 5B and entry ramps for service vehicles SO. The barrier 58 can be formed of relatively light weight aluminum sheet supply material suitable for deflecting the blown particles by the jet exhaust "etc." but quite fragile to easily yield to the wheels of an airplane. Ramps 60 are provided and constructed to allow airport fire or rescue vehicles to reach the detention bed to asspassengers in an airplane that has had to stop within the limits of the detention bed. The ramps 60 can be constructed of cellular concrete of appropriate strength or other suitable material. In a typical detention bed facility »suitable for stopping the travel of various types of airplane» the blocks of section 52 can typically have thicknesses that vary in increments of 1,905 cm from 20.32 cm to 60.96 cm and provide a CGS of 60 / B0 that average 4,921 kg / cm2 over a penetration depth "as described above. Correspondingly, the blocks of section 54 can have thicknesses that vary in increments of 7.62 cm from 60.96 cm to 76.2 cm "and provide a CGS of 8O / 10O that averages S.327 kg / cm2 over a depth of penetration. In the manufacture of the blocks, the blocks of section 52 can be formulated from cellular concrete having a wet density towards the lower portion of a scale of approximately 224.28 to 368.46 g / l »where the blocks of the section 54 made of cellular concrete have a wet density towards the upper portion of said scale. The mixed blocks in section 52/54 would correspondingly conspartly of CGS material of 60/80 and partly of CGS material of BO / IOO. In total, sections 52 and 54 can have an aggregate length of 122 m »45.75 m wide and thicknesses of the front and rear ends of 22.86 cm and 7S.2 cm, respectively. It will be appreciated that for any particular implementation of the invention, the performance achieved will depend on the charactercs of the materials and the design of the detention system. specified and manufactured to meet specific on-site performance objectives identified. The parameters relating to the materials or systems for any specific implementation are beyond the scope of the present purposes, and the specific values they are discussed only as general examples of magnitudes of possible parameters. The nature of a cellular concrete detention bed system is such that its construction will be time consuming and relatively costly. Therefore »it is important that the method and information used to design the system be quite reliable to correlate with and predict» the performance under real conditions of use. The present invention allows the manufacture of vehicle stopping blocks suitable for use in aircraft bed arrest systems and automotive applications on tracks and roads, as well as other forms of deceleration blocks suitable for various other object deceleration purposes and applications. Although the presently preferred embodiments of the invention have been described, those skilled in the art will recognize that other additional modifications may be made without departing from the invention, and that they are intended to claim all modifications and variations that are within the scope of the invention. same

Claims (13)

NOVELTY OF THE INVENTION CLAIMS

1. - A vehicle stopping unit, characterized in that it comprises: a three-dimensional block of cellular concrete having a combination of thickness and gradient of compressive strength over an effective depth of penetration to provide limited deceleration of the wheel of a vehicle, said block comprising cellular concrete having a dry density in the range of 192.24 to 352.44 g / l.

2. A vehicle stopping unit according to re-indication 1, characterized in that said three-dimensional block is formed of a combination that includes: a suspension of water and cement; a foam prepared from water and a foaming agent; and a curing form arranged to provide three dimensional support with controlled evaporation for a mixture of said suspension and said foam during a curing period.

3. A vehicle stopping unit according to claim 1 or 2, characterized in that said three-dimensional block has a gradient of compressive strength of 60/80 nominally equal to 4,921 kg / cm2 »when averaging over a depth of penetration of said block.

4. - A vehicle stopping unit according to claim 1 or 2 »characterized in that said three-dimensional block has a gradient of compressive strength of 80/100 nominally equal to 6327 kg / cm2» when averaged over a depth of penetration of said block.

5. A vehicle stopping unit according to claims 1 »2» 3 or 4 »characterized in that said three-dimensional block is formed using a suspension that has undergone a temperature increase related to hydration in the scale of -15 to -11.1 ° C »before mixing with said foam.

6. A vehicle stopping unit according to claims 1, 2, 3 or 4, characterized in that said three-dimensional block is formed using a suspension that has undergone a temperature increase related to hydration in the scale of -14.4 to -13.3 ° C, before mixing with said foam.

A vehicle stopping unit according to any of the preceding claims, characterized in that said three-dimensional block is formed using a suspension that has undergone a temperature increase related to hydration until reaching a temperature no higher than 30.5 ° C before of mixing with said foam.

8. A vehicle stopping unit according to any of the preceding claims, characterized in that said three-dimensional block is formed using a suspension that has been projected in a stream to produce shear forces before being mixed with said foam.

9.- A detention unit "characterized in that it comprises: a deceleration block manufactured to provide limited deceleration without rebounding of an object, said block comprising cellular concrete having a dry density in the range of 192.24 to 352.44 g / l and a resistance effective to limit the maximum deceleration of said object.

10. A detention unit according to claim 9, characterized in that said deceleration block is formed of a combination that includes: a suspension of water and cement; a foam prepared from water and a foaming agent; and a curing form arranged to provide three dimensional support with controlled evaporation for a mixture of said suspension and said foam during a curing period.

11. A stopping unit in accordance with the rei indications 9 or 10 »characterized in that said deceleration block has a gradient of compressive strength predetermined over a penetration depth of 10 to 60% of the thickness of the block.

12. A vehicle stopping unit according to claims 9 or 10 »characterized in that said Deceleration block includes a first layer of cellular concrete that has a first gradient of compressive strength and a second layer of cellular concrete that has a gradient of superior compressive strength. 13. A detention unit according to claims 9 »10» 11 or 12 »characterized in that said deceleration block is formed using a suspension that has undergone a temperature increase related to hydration in the scale of -15 to - 11.1 ° C without exceeding a final temperature of 31.S ° C. 14.- A detention unit in accordance with the instructions 9 »10» 11, 12 or 13, characterized in that said deceleration block is formed using a suspension projected in a stream to produce shearing forces before being mixed with said foam. 15. A vehicle stopping unit according to claims 9 »10, 11» 12 »13 or 14, characterized in that said block additionally includes at least two transverse grooves to facilitate the handling of said block. 16. A detention unit according to claims 9, 10, 11, 12, 13, 14 or 15, characterized in that said detention unit additionally comprises collapsible pieces of a different cellular concrete material embedded in said block. 17. A vehicle stopping unit according to claims 9 »10» 11 »12» 13 »14» 15 »or 16, characterized in that said stopping unit additionally comprises a layer of superior resistance material to increase the structural stability of said block. 18. A vehicle stopping unit in accordance with claims 9, 10 »11» 12 »13» 14 »15» or 16 »characterized in that said stopping unit additionally comprises one or more reinforcement members embedded in said block . 19. A method for forming a section of detention material "characterized by a gradient of effective compressive strength to provide limited deceleration of a moving object, comprising the steps of: (a) forming a suspension of cement and water; (b) allow said suspension to suffer a temperature increase related to hydration in the range of -15 to -11.1 ° C »until the suspension reaches a temperature no higher than 31.6 ° C; (c) preparing a foam from water and a foaming agent; (d) mixing said suspension and said foam to provide cellular concrete; (e) placing a portion of said cellular concrete in a shape representing the shape of said section; and (f) curing said cellular concrete under conditions of controlled evaporation to provide said section of detention material in an independent three-dimensional form suitable to provide deceleration of a moving object. 20. A method according to claim 19, characterized in that step (a) includes projecting said suspension into a stream to induce high shear mixing. 21. A method according to claim 19 or 20 »characterized in that in step (a) said suspension is formed from water and cement in a ratio scale of 0.5: 1 to 0.6: 1. 22. A method according to claims 19, 20 or 21, characterized in that in step (b) said suspension undergoes an increase in temperature related to hydration in the scale of -14.4 ° C to -

13. 3 ° C. 23. A method according to the rei indications 19"20" 21 or 22"characterized in that in step (d) said cell concrete has a wet density in the range of 224.28 to 368.46 g / l. 24. A method according to claims 19, 20 »21» 22 or 23 »characterized in that in step (f) said cellular concrete when cured has a dry density of 192.24 to 352.44 g / l. 25. A method for forming a deceleration block usable to provide limited deceleration of a moving object "characterized in that it comprises the steps of: (a) forming a suspension of cement and water" (b) preparing a foam from water and a foaming agent .; (O) mixing said suspension and said foam to provide cellular concrete, and (d) placing a portion of said cellular concrete in a suitable manner to provide said deceleration block in a suitable shape and size for use in the deceleration of a moving object. 26.- A method in accordance with the claim 25 »characterized in that it further comprises the step of: including within said form» crushable pieces of a different cellular concrete material. 27.- A method according to claim 25 or 26 »characterized in that it additionally comprises the step of: including within said form» a layer of higher resistance material that said cellular concrete will have after being cured. 28. A method according to claim 25 »26 or 27» characterized in that it additionally comprises the step of: including within said form »one or more reinforcing members. SUMMARY OF THE INVENTION Cellular concrete blocks for stopping vehicles are used to safely delay the travel of an object, and can be used to construct an airplane stopping bed at the end of an airport take-off and landing runway; for these purposes »cellular concrete blocks should be manufactured which exhibit compression strength gradients of predetermined values to provide sufficient, but not excessive, deceleration forces of an object» material uniformity characteristics must be satisfied »to avoid variations of unacceptable drag force "so that the stop blocks conveniently exhibit a predetermined compressive strength gradient" for example "a 60/80" CGS over a penetration depth of 10 to 66% of the block thickness » as shown in figure 7 »a 60/80 CGS will typically represent an average compressive strength of 4,921 kg / cm2 over said penetration depth; Previous applications of cellular concrete typically included meeting minimum resistance values, and the production methods did not meet the prediction of the compression strength gradient or uniformity required for the detention blocks. The described methods include parameter controls, ingredients and procedures, as well as effective scales to enable the manufacture of stop blocks having dry densities and compression resis- tance gradients that can be specified to provide limited deceleration of airplanes and other objects; Limited deceleration can avoid destructive effects inherent in excessive deceleration rates. MG / ehp asg amm * xal. P98-1087F.