Patent Application
20130263673
The method of the present invention pertains to the testing of compressive strength of multiple molds filled with a liquid settable grout. The method of the present invention is particularly applicable for quality control for determining the compressive strength of support columns formed by pumpable grout bags in mining operations in order to support the roof or hanging wall.
Conventional grout bags or pumpable cribbing bags are essentially closed geotextile containers which typically have some means of suspending them on support structures. The bags are inflated by pumping a liquid settable grout into the bags, wherein the grout is permitted to cure or set to develop sufficient strength to carry load. This invention pertains to a new process for testing compressive strength of such pumpable cribs or other molds.
Because of preparation and handling, it is not feasible to make traditional three by six inch compressive strength cylinders for crush tests underground in a coal mine when installing pumpable cribs.
The present invention provides a method for testing compressive strength of multiple molds, such as pumpable cribbing bags for mines, filled with a liquid settable grout. First a series of molds, such as pumpable cribs, are filled with liquid settable grout. At selected mold filling intervals, samples of the liquid settable grout are poured into a container and the container is sealed and the time, date and location information regarding the mold then being filled is recorded on the container. The sample container is subjected to the same environment as the mold being sampled is subjected to.
A curve is generated or established which projects a final compressive strength based on compressive strengths at various cure times. The sample is removed from its container after a selected cure time and the sample is subjected to a series of Schmidt rebound hammer tests, thereby obtaining a series of compressive strength readings. The projected final compressive strength of the samples is then determined based on the cure time of the sample from the established curve.
If desired, a core sample from the cured grout sample may be taken and subjected to a crush test to thereby confirm the projected compressive strength results. It is also preferable that the container be selected to provide a flat smooth surface on the cured sample for conducting the Schmidt hammer test.
The method is repeated over and over again on multiple grout samples taken at different selected intervals from different molds or pumpable cribs.
Other objects and advantages appear hereinafter in the following description and claims. The accompanying drawing shows, for the purpose of exemplification, without limiting the scope of the invention or the accompanying claims, certain practical embodiments of the present invention wherein
The method of the present invention for providing quality control to determine the compressive strengths of liquid settable grout being used to fill molds will be discussed in regard to pumpable cribs for providing roof support in underground mines.
First, a series of pumpable mine crib bags which are supported in place in the mine are filled with liquid settable grout. At selected crib bag filling intervals, samples of the liquid settable grout are poured into a container and the container is sealed and the time, date and location information regarding the particular crib bag is then recorded on the container. The sample container may for example consist of a five gallon plastic bucket, and the selected interval for testing or sampling may for example be selected as every tenth crib bag. Pouring of the sample is accomplished by taking the injection nozzle for pumping the pumpable grout into the crib bags off the inlet port of the crib bag and the disconnected nozzle is used to fill the test or sample container.
After the lid has been placed on the bucket and the time, date and location of the crib bag being filled is recorded on the bucket or bucket lid, the bucket is then left in the same area as the pumpable crib bag being pumped or filled so that the crib bag and the sample will both be subject to the same environment. The time from when the sample is poured and when it is tested can vary since the inventors have established a curve projecting a final compressive strength based on compressive strengths taken at various cure times. This curve is shown in
The curve of
If, for example, one were to decide to test the samples after 24 hours of cure time, the bucket lid is removed and the bucket is turned upside down. The bucket walls taper inward from top to bottom and thus allow the sample to be easily removed with no damage to the sample. The bottom of the bucket is smooth and therefore provides a smooth flat surface on the sample which eliminates the need to cut and polish the sample in order to achieve a suitable surface for testing and allows accurate testing on site. A Schmidt rebound hammer, sometimes also referred to as a Swiss hammer or simply a rebound hammer, is then used to obtain a series of readings, say for example 10. The Schmidt hammer is a device commonly used to measure the elastic properties or compressive strength of concrete or rock, mainly surface hardness and penetration resistance.
The Schmidt hammer is previously programmed to convert the readings into a compressive strength of the grout.
At this stage, the inventors then go to their chart as illustrated in
This application claims the benefit of U.S. Provisional Patent Application No. 61/686,287, filed Apr. 4, 2012, and entitled METHOD OF QUALITY CONTROL FOR DETERMINING THE COMPRESSIVE STRENGTHS OF GROUT IN PUMPABLE MINE CRIBS, the contents of which are incorporated herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61686287 | Apr 2012 | US |
