GB2158591A

GB2158591A - Durability testing

Info

Publication number: GB2158591A
Application number: GB08412120A
Authority: GB
Inventors: Adrian Ernest Long
Original assignee: NAT RES DEV; National Research Development Corp UK
Current assignee: NAT RES DEV; National Research Development Corp UK
Priority date: 1984-05-11
Filing date: 1984-05-11
Publication date: 1985-11-13
Also published as: GB8412120D0

Abstract

The rim of a cup-shaped body 7, 6 is bonded to the surface of a specimen (22 fig 4) to be non-destructively tested, (eg in-situ concrete or other porous material), and the interior of the cup and a communicating hydraulic cylinder 4 are filled with fluid through an inlet 10. A micrometer 1 is then turned to cause a piston 3 to descend within the cylinder, closing the inlet and so creating an enclosed volume of of pressurised fluid. The pressure of that volume (indicated by a gauge 8) now tends to fall gradually because fluid escapes from the enclosed volume by permeating through the specimen 22. At intervals the micrometer is turned to progress the piston, to make up the volume and restore the pressure to its original value. Durability is calculated from the amount of turn required on each occasion, and the time intervals between successive occasions. An automated version of such apparatus is also disclosed, as is the facility to acquire further useful information at the end of each test by increasing the fluid pressure to a value at which the cup parts from the specimen, by reason of failure either of the bond between the specimen and the rim 6, or of the structure of the specimen itself in the vicinity of the bond. <IMAGE>

Description

SPECIFICATION Improvements in or relating to durability testing This invention relates to durability testing, and in particular to apparatus and methods for the nondestructive testing of the durability of in-situ concrete and other porous materials by reference to their permeability to fluids.

Although a number of non-destructivetests have been developed to yield an estimate of the strength of in-situ concrete, nevertheless strength is only an indirect measure of durability. Other parameters governing the ease of movement of fluids through the concrete could provide a better measure. Permeability is a good measure of durability because it largely determines the vulnerability of the concrete which permits the passage of a fluid, subject to pressure, through the concrete.

Existing techniques for determining the permeability of in-situ concrete are not completely satisfactory. They are mainly destructive in nature, involving sample cores or disc specimens being cut on site and then transported to a laboratory for testing.

Present test rigs are often bulky and somewhat cumbersome. This makes testing difficult and slow, and test times between 24 hours and several days are typical. There is a need for a new test procedure which is non-destructive, quick and easy to operate, enabling a number of in-situ permeability tests to be carried out on different parts of a structure within several hours, and using a test rig which can be portable, light and robust.

The present invention seeks to provide such a procedure, and according to the invention apparatus to test the durability of a solid specimen by reference to its permeability to fluid comprises means defining an apertured container for the fluid; a sealing device associated with the aperture and adapted to seal against a face of the specimen, whereby that face completes the container to form a closed chamber; means to fill the volume of the chamber with fluid and to pressurise that fluid; and means to contract the chamber volume, and maintain the pressure of the fluid within it, as fluid leaves the chamber by permeating the specimen.

The sealing device may be ring-shaped and adapted to receive adhesive by which it may be bonded to the face of the specimen.

The means to fill the chamber with fluid may also be adapted to generate pressure within that fluid, and may be in the form of a syringe or other piston-and-cylinder device.

The means to contract the volume of the chamber may be in the form of a plunger movable relative to a graduated scale; the plunger may be driven by a micrometer-type device which provides the scale.

The filling means and the plunger-type device may be so relatively arranged that the connection of the chamber to the filling means is open when the plunger is fully withdrawn, that is to say when the chamber is at maximum volume, and is then closed substantially at once when the plunger is advanced from that position so as to diminish the chamber volume.

The invention includes a method of testing the durability of a porous specimen, using apparatus as just described, and the test by reference to permeability may be succeeded by raising the pressure of the fluid within the chamber until the reactive force between the specimen and the apparatus causes the specimen to fail, so that other measures of the durability of the specimen may then be derived from the value of the pressure at which the failure occurred.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure lisa diagrammatic elevation of one apparatus; Figure2 is a plan view; Figure 3 shows the filling means and their connection to the apparatus, and Figure 4 is a section through parts of the apparatus.

The apparatus includes a circular body 7, one end face of which is recessed at 5. A ring 6 engages with that end face and is held to the body 7 by bolts 12, and in use the exposed face 20 of the ring is coated with adhesive and bonded to a flat face 21 of a specimen 22 - for instance of in-situ concrete - that is to be tested. The face 21, ring 6 and body 7 then co-operate to enclose a chamber which is connected, by way of a drilling 23 in body 7, to a hydraulic cylinder 4, the threaded end 24 of which engages with a threaded recess in the upper surface of body 7. As Figure 3 shows, a radial inlet 10 to cylinder 4 may be connected by way of a flexible hose 25 to a syringe 26, and the upper end of cylinder 4 receives the piston 3 of a micrometer 1 which is mounted in a yoke 2 supported by guide rails 9 mounted on body 7.A pressure gauge 8 is also mounted on body 7, and senses the pressure within the enclosed chamber to which it is connected by way of a conduit 27 and a drilling 28 through the body 7.

In operation, the ring 6 is first bonded to the specimen 22. The body 7 is then secured to the ring 6 by means of the screws 12. The micrometer screw gauge 1 is then secured in the yoke 2 and positioned nearthetop of the guide rails 9to allow the maximum possible travel on the screw. The piston 3 is positioned within cylinder so that it rests above the level of the inlet 10 which is connected to syringe 26, and the syringe is charged with water or whatever fluid - the invention applies to gases as well as liquids - is appropriate. Syringe 26 is then discharged so that the liquid enters the recess 5 and the rest of the enclosed chamber, a bleed valve 11 being opened to allow air to escape as the chamber fills. This process continues until there is a constant flow of liquid from the valve 11 without any sign of air bubbles.Valve 11 is then closed and syringe 26 is used to pressurise the liquid within the chamber to a pressure comparable to that required for the test, usually of the order of 25 psi to 100 psi. This pressure, recorded by gauge 8, is then held constant as screw gauge 1 is turned down. As the piston 3 travels from Ato A' (Figure 3) the inlet 10 is closed off and any air that should remain in the cylinder 4 is then forced through the liquid-tight seal 29 carried by the piston. The screw gauge 1 is then turned, at predetermined intervals, so as to diminish the total enclosed volume available to the liquid within the system and restore the pressure of that liquid to its original value.The amounts of turn required are of .course related to the quantity of liquid that has left the chamber by permeating through the specimen 22, and the permeability of the specimen may be calculated, in a manner known to those skilled in the art, by reference to known quantities including the time intervals and the amounts of turn of the screw that are required on each occasion.

While an essentially manual apparatus and method has been described, the invention also includes an automated version in which there is a servo link between the pressure gauge 8 and the screw gauge 1 or its equivalent, in which case it might be possible for the system to work so that a predetermined drop in pressure of the liquid always triggered the same increment of turn of the screw. In such a case, the only variable in the calculation of the permeability of the specimen would be the time interval between each increment of turn.

On completion of the permeability test the press ure of the fluid within the chamber may be increased until the reactive force between the specimen 22 and the ring 6 is sufficient to cause failure in the region of the interface. Normally the strength of the bond between ring 6 and face 21 is greater than the tensile strength of the specimen material, so that the failure occurs within the latter. Such failure enables further measures of the durability of the specimen to be obtained, because the tensile strength of the speci men can be derived from the fluid pressure at which failure occurred, and the compressive strength can be derived from the tensile strength as explained for instance in UK patent no.1549842.

Claims

1 Apparatus to test the durability of a solid specimen by reference to its permeability to fluid and comprising: means defining an apertured containerforthe fluid; a sealing device associated with the aperture and adapted to seal against a face of the specimen, whereby that face completes the containerto form a closed chamber; means to fill the volume of the chamber with fluid and to pressurised that fluid, and means to contract the volume of the chamber, and to maintain the pressure of the fluid within it, as fluid leaves the chamber by permeating the specimen.

2. Apparatus according to claim 1 in which the sealing device is ring-shaped and adapted to receive adhesive by which it may be bonded to the face of the specimen.

3. Apparatus according to claim 1 in which the means to fill the chamber with fluid is also adapted to generate above-ambient pressure within that fluid.

4. Apparatus according to claim 3 in which the means to fill the chamber is in the form of a syringe.

5. Apparatus according to claim 1 in which the means to contract the volume of the chamber is in the form of a plunger movable relative to a graduated scale.

6. Apparatus according to claim 5 in which the graduated scale is in the form of a micrometer screw connected to the plunger.

7. Apparatus according to claims 5 and 3 in which the connection of the filling means to the chamber is open when the chamber is at maximum volume, and is closed substantially at once when the plunger is moved to diminish that maximum volume.

8. A method of testing the durability of a solid specimen by reference to its permeability to fluid, using apparatus according to any of the preceding claims, in which the container is sealed to the specimen, in which the chamber is filled with fluid and that fluid is pressurised, in which the volume of the chamber is contracted and the pressure is maintained as fluid passes out of the chamber by permeating the specimen, and in which the durability is calculated by reference to the passage of the fluid.

9. A method of testing the durability of a solid specimen according to claim 8, in which the test by reference to permeability is succeeded by raising the pressure of the fluid within the chamber until the reactive force between the specimen and the apparatus cause failure of the specimen, whereby a further measure of the durability of the specimen is derived from the fluid pressure at which failure occurred.

10. Apparatus to test the durability of a solid specimen by reference to its permeability to fluid, according to claim 1 and substantially as described with reference to the accompanying drawings.

11. A method of testing the durability of a solid specimen, according to claim 8 and substantially as described with reference to the accompanying drawings.