Method, apparatus and system for testing the self-sealing capabilities of a concrete sample

A method, apparatus and system for testing the self-sealing properties of a concrete sample. The method may include providing an apparatus for creating a consistent and reproducible crack in a concrete sample and creating a consistent and reproducible crack in the concrete sample with the apparatus. The method may further include providing a fluidic delivery system that provides a consistent flow of fluid for testing the self-sealing properties of the concrete sample and testing the self-sealing properties of the concrete sample with the system.

FIELD OF THE INVENTION

The invention relates to the field of testing methodology and in particular in relation to a method for testing the self-sealing capabilities of a concrete sample and an apparatus and system used in the method.

BACKGROUND OF THE INVENTION

Concrete is a common building material that is prized for its versatility, strength and durability. However, strength and durability are both compromised in concrete due to damage as a result of water intrusion through cracks, which in turn leads to various destructive processes within concrete—especially concrete containing steel reinforcement. Since concrete is a mixture of various components, including water, and is weak under tension, it is common for concrete to develop cracks due to tension forces caused by shrinking and/or loading. Such resulting cracks provide paths for the easy intrusion of water and waterborne chemicals, which commonly lead to damaging chemical and physical processes and premature deterioration of the concrete.

It has been observed that some cracks in concrete may initially allow the passage of water, but then over time, the flow of water may be reduced and eventually stopped completely. A crack, that formerly allowed the passage of water and subsequently sealed so as to no longer allow the passage of water, is said to have “self-sealed”.

Chemical agents are commercially available which claim to enhance the ability of concrete to self-seal. These agents further claim that they allow concrete to self-seal more quickly and also allow self-sealing of cracks that are much wider than those cracks that may self-seal in concrete that do not contain these agents.

Accordingly, a need exists for a method for testing the self-sealing properties of a concrete sample in order to prove or disprove the claims made about these agents. In addition, a reliable test method would allow for the comparison of concrete mixtures, which vary in their ingredients, proportions and other factors contributing to their hardened properties, in so far as these relate to the self-sealing ability of the concrete.

A suitable method for testing the self-sealing properties of a concrete sample has not previously existed. Prior art relating to this subject has failed to achieve acceptable results due to two major missing elements:1. The ability to produce a concrete sample with consistent, predictable and repeatable crack size and shape. The ability to produce a crack with the same size and shape in each concrete sample is critical to the comparability and validity of test results measured and compared between samples; and2. The ability to produce a suitable flow of water through a crack in a concrete sample that is consistent between comparable samples, can be accurately measured over time and maintains a constant vertical head pressure over time, independent of flow.

It is an object of the present invention to address these two missing elements. Other objects of the invention will be apparent from the description that follows.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method, apparatus and system for testing the self-sealing properties of a concrete sample. The method may include providing an apparatus for creating a consistent and reproducible crack in the concrete sample and then creating a consistent and reproducible crack in the concrete sample with the apparatus. The method may also include providing a fluidic delivery system that provides a consistent flow of fluid for testing the self-sealing properties of the concrete sample and then testing the self-sealing properties of the concrete sample with the system.

The apparatus for creating a consistent and reproducible crack in a concrete sample may include a base member and first and second opposed support structures connectable to the base. A top member moveable relative to the support structures and being opposed to the base member may be included as part of the apparatus. First and second opposed stabilizer members, each of which are connectable to the first and second opposed support structures, may also be included. Finally, the apparatus may include a first force member connectable to the base and a second force member connectable to the top member.

The method of creating a consistent and reproducible crack in a concrete sample may include placing the concrete sample in the apparatus and aligning the concrete sample in the apparatus so that the first and second force members are centered along a middle-line of the concrete sample. The first and second stabilizer members may then be connected to the first and second opposed support structures to snugly engage the concrete sample. The apparatus may then be placed into a hydraulic press so that said press engages the top member and the press is then operated until a crack is created in the concrete sample.

The fluidic delivery system for testing the self-sealing properties of the concrete sample may include a tank filled with a constant head of fluid and a fluidic distribution device connected to the tank. A fluidic transport device connectable to the distribution device and to the concrete sample may also be included as well as a platform for holding the concrete sample, and fluidic collection means disposed underneath the platform.

The method of testing the self-sealing properties of a concrete sample may include applying a continuous bead of waterproof substance down the outside cracks of the sides of the concrete sample. A waterproof jacket may be secured around the sides of the concrete sample and the sample may be stood upright. A fluidic coupling may be secured to the waterproof jacket adjacent a top portion of the concrete sample and the fluidic coupling may be affixed to the fluidic delivery system. The fluidic delivery system may be operated and a flow rate may be recorded as fluid passes through the concrete sample.

Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims that follow.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The invention relates to a method for testing the self-sealing properties of a concrete sample. To initiate the test, an apparatus for creating a consistent and reproducible crack in the concrete sample is provided.

Referring toFIGS. 1 and 2, the apparatus includes a jig frame10which includes a base12and first14and second16opposed support structures emanating from the base. First14and second16opposed support structures may be integrally formed with the base12or may be connectable to the base via fasteners18, as depicted. Preferably as depicted, each of the first14and second16opposed support structures include a notched section20adjacent the respective top portion22of the support structures. A top member24is disposed and is moveable within the frame10. Preferably, top member24is dimensioned to fit within the notched sections22of the first14and second16opposed support structures. First26and second28opposed stabilizer members are each connectable to the first14and second16support structures via fasteners30, as depicted.

The apparatus also includes a first force member32connectable to the base12and a second force member34connectable to the top member24. As depicted inFIG. 1, the first32and second34force members are merely ball bearings whereas depicted inFIG. 2, the first and second force members are cutting blades.FIG. 1shows the jig10in its direct compression cracking configuration with a concrete sample40placed upright. The direct compression configuration uses ball bearings to create high pressure point loads on the upper and lower faces of a concrete sample40. The crack patterns here, could be radial or linear, passing though the center of the sample40.FIG. 2shows the jig10in its indirect tension configuration with the concrete sample40placed on its side. The indirect tension configuration uses the cutting edges to create a line of high stress concentration on each side of the sample40. This causes a single linear crack from one face of the sample40to the other.

Once the apparatus is constructed, a consistent and reproducible crack may be created in the concrete sample40. Referring toFIG. 3, after the sample40and first32and second34force members have been wiped clean of any excess concrete debris or dust, the sample is placed within the jig10either upright, as depicted inFIG. 1, or on its side as depicted inFIG. 2. Care is taken to align the concrete sample40in the jig10so that the first32and second force34members are centered along a middle-line of the concrete sample40. Care is also taken to ensure that the first32and second34force members are not aligned over any large void or aggregate pieces in the sample40. The first26and second28opposed stabilizer members may further be connected to the first14and second16opposed support structures to snugly engage the concrete sample40. To aid in the engagement of the first26and second28opposed stabilizer members to the sample40, each of the stabilizer members may include a resilient material (not depicted), such as foam, attached to the engaging sides of the stabilizer members. Alternatively, the fasteners30may be a biasing device such as by including a spring as shown inFIGS. 1 to 3. Once the sample40is snugly placed into the jig10and properly aligned, the jig may then be placed into a hydraulic press42so that the press engages the top member24. Once engaged, the press42is then operated to plunge the top member24and second34force member into the sample40until a crack is created. To disperse the force created by the press42more evenly across the top member24and hence the sample40, a steel plate (not depicted) may be inserted between the press and top member. Preferably, a loading rate of 20 kN/min should be applied with the press42onto the sample40.

Once a consistent and reproducible crack in the sample40has been created with the jig10, a fluidic delivery system for testing the self-sealing properties of the sample is provided.

Referring toFIG. 4, a fluidic delivery system50that provides a consistent flow of fluid for testing the self-sealing properties of the sample40includes a tank52filled with a constant head of fluid54. A fluidic distribution device56is connected to the tank50. The distribution device56is conventionally constructed and includes a reservoir and distribution manifold (not depicted)—each of which must be elevated above the concrete sample so as to produce a consistent hydraulic head. The reservoir must be kept filled to a constant height by using a common float valve connected to a water supply, similar to what you find in a toilet reservoir. The distribution device56also includes a valve58to control the volumetric flow of the fluid54to the sample40. A fluidic transport device60, such a hose or other conduit device, is connectable to the valve58and to the sample40. To hold the sample40in place during testing, the system50also includes a platform62which is adapted to allow the fluid54to pass through; for example, platform62may simply be a wire rack. Finally, the system50includes fluidic collection means64disposed underneath the platform62. Preferably, the fluidic collection means64is a device that enables the user to measure the volume of fluid that passes through the sample40, such as a graduated cylinder or other measured container.

Once the fluidic delivery system50has been provided, testing the self-sealing properties of the sample40may commence. A continuous bead of waterproof substance, such as silicone, is applied down the outside cracks of the longitudinal sides of the concrete sample40. The waterproof substance is preferably void free and the sample40should sit for some time after application of the waterproof substance to enable the substance to cure. Once the substance has cured, the sample40is secured with a waterproof jacket72around its sides. The sample40is then stood upright and secured to a fluidic coupling74adjacent a top portion of the sample40. The fluidic coupling74may then be affixed to the fluidic transport device60and operation of the system50may commence. Finally, the flow rate of fluid as it passes through the sample40may then be recorded.

Referring toFIG. 5, jacket72includes a waterproof sleeve76(preferably made of rubber) secured around the sample40with a lower clamp78. Jacket72also includes a fluidic coupling80(preferably constructed from PVC) which covers the top portion of the sample40and is adapted to engage with the fluidic transport device60using conventional means. To install coupling80onto the sample40, it is first slid over the top portion of the sample40and underneath the top of portion of sleeve76. Both the top portion of the sleeve76and coupling80may then be secured to the sample40with an upper clamp82.

To achieve the goal of creating a method for testing the self-sealing properties of the concrete sample40it is important that the crack has a constant width throughout the sample40and be small enough to allow for self-sealing to occur. Generally, concrete is weakest in tension; therefore a smaller load is required to crack the sample40. Given the consistency of application and low load requirements, preferably a jig10configuration as depicted inFIG. 2is used for testing the self sealing properties of the sample40.

The following table gives the mix proportions used to prepare the samples40.

For comparison testing, some samples include a substance known commercially as KIM®. In these instances, the samples40were made using the same mix design, except 2% of the cement was substituted with an equivalent weight of KIM®. KIM® is a cement-based admixture that is added to fresh concrete before placement. KIM® has been in commercial use for over 35 years as waterproofing protection in concrete structures. The addition of KIM® in a concrete mix eliminates the need for external waterproofing membranes. When exposed to water, KIM® reacts with unhydrated cement to form a crystalline structure that fills the voids and pores in hardened concrete. The crystals form a tight matrix that turns the concrete into an impermeable barrier that prevents water intrusion. When concrete cracks due to shrinkage, settlement, etc., KIM® reactivates and crystal growth resumes until the crack seals. This unique property gives KIM® concrete the ability to “self-seal”.

Following completion of the sample40mix, a sample may be molded into shape. Preferably the sample40is in the shape of a cylinder having a 4″ diameter with a length of 6″. As those skilled in the art will appreciate, any suitable sample shape will suffice. As those skilled in the art will also appreciate, the sample40may also includes regions to allow for the first32and second force members32to engage the sample. For example, when the first32and second force members34are cutting blades, the regions may be longitudinal notches made into the sample40. To construct a notched sample, a mold may consist of angles that are attached to the sides of a standard 4″×6″ mold. Preferably, samples older than 2 days and less than 7 days are used in the self-sealing test.

Flow measurements may be taken in real time using flow meters and manual measurements. The flow meters may have a flow range of 100-2000 ml/min. Samples40with smaller cracks, less than 0.4 mm, may have smaller flows that require manual measurement. Optionally, instead of measuring the volume of the fluid in the fluidic collection means64, it may be advantageous to physically measure the flow using a graduated cylinder and a stopwatch. Using this measurement approach may eliminate the lost volume due to evaporation and can provide an exact flow at one instance instead of an average across hours of flow.

It is recommended that a FLR-1618A-V2 Omega Engineering™ flow meter or suitable substitute be used to measure the flow. This type of meter measures flows from 4-200 ml/min. Alternatively, a FTB601-B Omega Engineering™ flow meter or suitable substitute may be used to measure the flow. This type of meter measures flows from 100-2000 ml/min.

To process the flow meter output frequencies, it is possible to use a National Instruments™ USB-6210 multifunction data acquisition board (DAQ). A flow meter produces a unique frequency corresponding to the actual flow. The DAQ can take as input the raw digital frequency, count the incoming pulses, and output a scaled number via a task to DASYlab 10.

It will thus be seen that a new and novel method, apparatus and system for testing the self-sealing properties of a concrete sample has been illustrated and described and it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.