GB2204956A

GB2204956A - Method of and apparatus for testing the sale loading of concrete ground floor slabs

Info

Publication number: GB2204956A
Application number: GB08712253A
Authority: GB
Inventors: George Cyril Brown; Leonard Reed
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-05-23
Filing date: 1987-05-23
Publication date: 1988-11-23
Anticipated expiration: 2007-05-23
Also published as: GB8712253D0; GB2204956B

Abstract

A method of and apparatus for testing the safe-loading characteristics of an existing concrete floor slab (12) by drilling out or otherwise isolating a core (13) so that it is capable of free vertical movement relative to the remainder of the slab. The core (13) is drilled carefully so that the sub-base below the slab remains undisturbed, drilling being terminated as soon as the core starts to spin. A test rig consists of a framework (14) with platforms (15) to receive ballast. An upstanding frame (16) with cross beam (17) locates a hydraulic jack (18) which acts via probe (20) on the isolated concrete core. Upon extension of the jack, compaction of the sub-base immediately beneath the core is measured by a plate (19) reading off against a graduated scale (22). Alternatively transducers may measure force applied and compaction. The measurement of compaction is correlated with known properties of the concrete slab to determine the safe-loading characteristics of the floor in the test zone. The core may be removed and replaced by a steel probe for the compaction test. <IMAGE>

Description

METHOD OF AND APPARATUS FOR TESTING THE SAFE LOADING OF CONCRETE GROUND FLOOR SLABS THIS INVENTION concerns a method of and apparatus for testing the safe loading characteristics of an existing concrete ground floor slab and may be used to determine the safe loading of concrete floors in ,for example, industrial premises where it is intended to install additional overhead flooring or machinery, which will impose a very high loading over a small area.

Aside from the strength characteristics of the floor itself, its capacity for loading, i.e. its compressive strength, is dependent largely upon the consolidation of the ground (sub-grade) and hard core (subbase) upon which the floor has been laid. It is therefore important to determine the resistance to compaction of these sub-floor strata. This kind of testing is carried out conventionally by excavating an area of the floor during which an exploratory hole is made through the concrete, and this inevitably disturbs, to some extent, the sub-base and perhaps even the sub-grade with the result that the material below the floor is more readily compacted than would have been the case had the floor not been excavated. Consequently, a mis-leading result can be obtained in a test carried out this way.

It is an object of the present invention to provide a method of and apparatus for floor testing wherein the aforementioned inaccuracy can be avoided.

According to the present invention there is provided a method of testing the safe-loading characteristics of an existing concrete floor slab, comprising the steps of drilling out or otherwise isolating a core of the slab thus to be capable of free vertical movement relative to the remainder of the slab, whilst ensuring that the sub-base below the slab remains substantially undisturbed, applying a compressive load to the sub-base, and measuring the resultant compaction of the latter to enable such measurement to be correlated with data pertaining to-floor thickness and strength, thus to enable the safe loading characteristics of the floor to be determined.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 illustrates diagrammatically how the method is carried out; Fig. 2 is a vertical elevation of a test rig designed and constructed to carry out the method; S Fig. 3 is an end view of the rig; and Fig. 4 is a plan view of the rig.

Fig. 1 shows a floor to consist of ground or subgrade 10 on which is laid and compacted a hard core subbase 11 upon which is laid a reinforced concrete surface layer 12.

A test is carried out in accordance with the invention by initially drilling out from the concrete a core 13 such that it is isolated from the parent slab 12 and is free to move vertically with respect thereto. The core 13 is drilled carefully so that there is minimal disturbance to the sub-base 11. In practice, the drilling tool or hole cutter used to isolate the core causes the latter to spin as soon as it becomes free from the parent slab so that there is an immediate indication of breakthrough, and the drilling can be arrested before damage to the sub base occurs.

The test is advanced by subsequently applying a compressive load to the top of core 13 which causes it to bear on the sub-base 11. Resultant compaction of the latter can be measured as will be described, and this measurement in conjunction with a measurement of the characteristics of the concrete slab 12 i.e. its thickness and strength properties, may be correlated to determihe the safe loading characteristics of the floor in the test zone.

Referring now to Figs. 2 to 4, there is illustrated a simple test rig for effecting the procedure outlined above, and this consists of a framework 14 defining two platforms 15 between which is an upstanding frame 16 supporting a horizontal beam 17. Attached to beam 17 is the upper end of a hydraulic jack 18 whose ram bears against a steel plate 19 below which is a cylindrical probe 20 having a base plate 21. An edge region of plate 19 is adapted to read off against a graduated scale schematically illustrated at 22.

Extension of jack 18 causes plate 19 and probe 20 to apply a downwards force upon core 13 whilst sufficient ballast is placed on platforms 15 to ensure that the rig remains in contact with the floor and is not lifted by the upward reaction force exerted by the jack 18. The load applied to platforms 15 must be at least as great as the maximum load to be applied to the core. As the load is applied the degree of settlement i.e. compaction of the sub-base below the floor which causes core 13 to descend within the slab 12, may be measured by movement of plate 19 against graduated scale 22.

In a less simple form of the invention, the combination of plate 19 and scale 22 may be provided as a transducer, with a further transducer disposed between beam 17 and jack 18, both transducers producing electrical signals which are fed to appropriate recording instrumentation.

Compaction of the sub-base for a particular load applied by jack 18 may be correlated with the thickness of the slab 12 and its structural characteristics in order to determine the safe-loading characteristics of the floor in the test zone as has been described.

If required, the load may be applied incrementally and the compaction recorded at each stage. The test may be considered complete once substantially no further compaction is achieved with the load sustained for a predetermined period.

It will be appreciated that since isolation of the core 13 can be carried out substantially without disturbance to the sub-base 11, a true assessment of the compressive strength of the latter can be made as compared with the present method involving excavation.

In an alternative embodiment, core 13, once isolated, may be removed from the slab 12 and replaced by the steel probe 20, the latter being appropriately longer than is illustrated in the drawings so that the base plate 21 acts directly upon the sub-base 11 or on sub-grade 10 at various predetermined depths.

Claims

1. A method of testing the safe-loading characteristics of an existing concrete floor slab comprising the steps of drilling out or otherwise isolating a core of the slab thus to be capable of free vertical movement relative to the remainder of the slab, whilst ensuring that the sub-base below the slab remains substantially undisturbed, applying a compressive load to the sub-base immediately beneath the core and measuring the resultant compaction of the latter to enable such measurement to be correlated with data pertaining to floor thickness and strength, thus to enable the safe-loading characteristics of the floor to be determined.

2. A method according to Claim 1, wherein the drilling out of said core causes it to spin as soon as it becomes free from the parent slab whereby there is an immediate indication of breakthrough, and the drilling operation is arrested before damage to the sub-base can occur.

3. A method according to Claim 1 or Claim 2, wherein said compressive load is applied by a jack exerting a force downwardly onto the drilled-out core which thus bears locally on the sub-base to compact the latter, and the extension of the jack is measured to determine the degree of compaction.

4. A method according to any preceding claim, wherein compaction of the sub-base is measured by means transmitting electrical signals to appropriate recording instrumentation which enables the safe-loading characteristics of the floor to be determined.

5. A method according to Claim 1, wherein compaction of the sub-base is correlated with the thickness of the remaining slab and its structural properties in order to determine the safe-loading characteristics of the floor in the test zone.

6. A method according to any preceding claim, wherein said compressive load is applied incrementally and the compaction recorded at each stage, said applications being discontinued once substantially no further compaction is achieved with the load sustained for a pre-determined period.

7. A method according to Claim 1, wherein the core, after isolation, is removed from the remainder of the slab, and a compressive load is applied directly to the sub-base in the position from which the core has been removed.

8. Apparatus for testing the safe-loading characteristics of an existing concrete floor slab, comprising means for drilling out or otherwise isolating a core of the slab thus to be capable of free vertical movement relative to the remainder of the slab, whilst ensuring that the sub-base below the slab remains substantially undisturbed, means for applying a compressive load to the sub-base immediately beneath the core, and means for measuring the resultant compaction of the latter to enable such measurement to be correlated with data pertaining to floor thickness and strength thus to enable the safe loading characteristics of the floor to be determined.

9. Apparatus according to Claim 8, wherein said means for drilling out or otherwise isolating the core comprises a drill or hole cutter which is adapted to cause the core to spin as soon as it becomes free from the parent slab.

10. Apparatus according to Claim 8, further comprising a test rig consisting of a framework upon which ballast may be located whose mass is at least equivalent to the maximum load to be applied to the core, an upstanding frame supporting a horizontal beam, a jack, acting between the horizontal beam and a probe adapted to bear upon the floor surface to be compressed, and means providing a measurement of extension of the jack during application of the compressive load.

11. Apparatus according to ClaimlO, wherein said framework includes, on each side of said upstanding frame a platform upon which said ballast may be selectively located, and said measurement means comprises a plate adapted to move upon extension of said jack to read off against a graduated scale fixed with respect to the framework.

12. Apparatus according to Claim 8, wherein said jack, upon extension, effects downwards movement of a steel probe which in turn acts upon the concrete core, or alternatively the sub-base therebelow.

13. Apparatus according to Claim 8, including one or more transducers producing electrical signals representative of the compaction of the sub-base, and recording instrumentation adapted to receive and correlate said signals with the thickness and strength properties of the remaining concrete slab, to determine the safe-loading characteristics of the floor in the test zone.

14. Apparatus according to Claim 8, wherein said jack is hydraulically extended.