Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
2001-03-26
2003-01-28
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
Reexamination Certificate
active
06510743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates generally to equipment and methods for testing material specimens, and more specifically to an apparatus and method for forming concrete specimens for comprehensive strength testing of ACI (American Concrete Institute) “field cured” cylinders. These cylinders are used primarily to insure proper concrete curing for the initiation of early form work removal (i. e., stripping of forms) during construction. The present equipment or apparatus is set into the concrete being poured, and forms a plurality of specimen cylinders meeting the requirements for ASTM testing. The test specimens formed by the present apparatus and method cure in situ, thus providing accurate and representative specimens of the remainder of the concrete from which the specimens were taken. Nearly all of the present apparatus is reusable, thus cutting testing expenses considerably.
2. DESCRIPTION OF THE RELATED ART
It is a standard practice in the construction industry, to test samples of various materials used during construction. This is especially true of concrete, where many field cured specimens are generally required when structural concrete is poured. These specimens are taken from a number of locations across the element or slab when it is poured.
The testing of such specimens is such a standard practice, and so regulated, that the American Society for Testing and Materials (ASTM) has developed certain criteria for the formation and testing of such concrete test specimens. One of the most critical criterion is that the field cured test specimens represent accurate samples of the cured concrete slab. This is critical, as concrete is exothermic (i. e., gives off heat) as it is curing, due to the heat of the hydration reaction which occurs. Accordingly, ASTM requires that field cured specimens which are cast separately from the slab, be treated during curing to closely approximate the heat developed during the curing process in the more massive slab. If the specimens are not in situ, this is difficult to achieve. Also, the specimens must be kept moist until the cure is complete, just as in the case of the poured slab. Any significant variation in the procedure can result in the specimens being an inaccurate representation of the actual qualities of the cast slab they are supposed to represent.
Accordingly, a need will be seen for a means of providing in situ concrete test specimens by means of a largely reusable apparatus. The only portion of the apparatus which is not reusable, comprises an inexpensive plastic cylinder in which the test specimens are cast. The remainder of the device, including the larger container used to encapsulate the smaller test specimen containers during pouring and curing, is removable from the poured slab or foundation after curing. Yet, the sample cylinders formed by means of the present apparatus, are surrounded by the concrete slab during the cure and receive the same heat from the exothermic reaction as does the remainder of the concrete in the slab. The result is a very accurate representation of the actual condition of the concrete of the cured slab, with the largely reusable apparatus resulting in relatively low costs for the test specimens. A method of forming such test specimens in accordance with the apparatus of the present invention, is also disclosed.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 3,176,053 issued on Mar. 30, 1965 to Joseph R. Di Stasio, titled “Method For Obtaining Test Cores,” describes an apparatus much like that described in ASTM C873-94, in which outer and inner cylinders are set in the concrete slab at the time of pouring the slab. The outer cylinder remains in place in the concrete after it cures, with the single inner cylinder and its specimen being removed from the outer cylinder. Di Stasio describes his outer cylinder as being formed of materials such as galvanized sheet steel or plastic, and while a very few such cylinders would not add appreciably to the cost of a project, a very large poured concrete project could require thousands of specimens spread throughout the slab. Leaving a major part of the test apparatus buried in the concrete in such a situation where thousands of tests may be required, obviously adds considerably to the cost of the project. Moreover, it is noted that Di Stasio configures his outer and inner containers to leave an air gap between the two. The inner container is thus somewhat insulated from the larger exterior mass of concrete, and the heat of its hydration reaction. The present apparatus and method does not provide any air gaps between the concrete slab and the test specimen apparatus, thus providing a more representative cure and a more accurate specimen.
U.S. Pat. No. 3,541,845 issued on Nov. 24, 1970 to Peter Kierkegaard-Hansen, titled “Method For Testing The Strength Of The Material Of Cast Structures, Particularly Concrete Structures,” describes a reusable test device in which a portion of the device is cast into the concrete and a tension rod is threaded into the device through a hole formed in the concrete. The rod is used to apply tension to the part which is cast into the concrete, until the assembly breaks loose. The tensile force required to break the cast-in part loose, indicates the strength of the concrete. This test method is opposite that described in ASTM C873-94 and the present disclosure, in which compressive force is applied to a specimen removed from the slab after curing.
U.S. Pat. No. 3,595,072 issued on Jul. 27, 1971 to Owen Richards, titled “Concrete Testing Means,” describes another tensile testing method and apparatus, similar to that of the Kierkegaard-Hansen U.S. Patent discussed immediately above. Richards uses a hydraulically actuated tension device to pull a rod which has been threaded into an anchor device in the concrete. While the entire apparatus is recoverable from the concrete (assuming the test is continued to destruction), the tensile test is not in accordance with ASTM methods for compressively testing specimens removed from a concrete slab, whereas the present invention provides a means for forming specimens which are accurate representations of the remainder of the concrete slab and which comply dimensionally with current ASTM test equipment.
U.S. Pat. No. 3,861,201 issued on Jan. 21, 1975 to Franz Kaindl, titled “Method And Apparatus For Early Strength Testing Of In-Place Concrete,” describes the use of a screen installed before the concrete is poured, for screening large aggregate pieces in order to provide a more uniform specimen. A base may be imbedded in the concrete into which a tension rod is installed for tensile strength testing, or the specimen may be compressively tested in place as desired. The test specimen is not cast in place and then removed for testing, as provided by the present invention. While the goal of the Kaindl apparatus, i.e., to provide a uniform representative specimen free of large aggregate pieces which would produce large variation in the results, is appreciated, the test resulting from the Kandl device may not be truly representative.
U.S. Pat. No. 3,974,679 issued on Aug. 17, 1976 to Karim W. Nasser, titled “Accelerated Concrete Strength Testing,” describes a testing apparatus which applies pressure and heat to a cylinder(s) of wet concrete. The heating and pressure result in a cure equivalent to a 28 day aging period, in a time of only about five hours. The apparatus is quite complex and costly in comparison to the present in situ specimen apparatus, and in any event, some of the wet concrete mix of the slab being poured must be placed in the mold(s) of the Nasser apparatus in order to have a truly representative sample. Thus, the Nasser apparatus must be located on, or very near, the actual job site; this would appear to pose some problems regarding portability and operation. The present in situ specimen apparatus is placed direc
Carpenter, Jr. Robert E.
McAfee Ralph Glenn
Litman Richard C.
Noori Max
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