Ozkul, Tarik (Computer Engineering Department, P.O Box American University of Sharja, Sharjah 26666, 26666, AE)
| 1. | A method of measuring surface roughness, comprising: pumping air to an air reservoir which is interfaced to a surface through a rigid skirt; measuring air pressure inside the said air reservoir; and determining a roughness value of said surface which corresponds to the roughness of closest reference sample number. |
| 2. | The method of claim 1 , where said step of determining a surface roughness value comprises: taking said air pressure readings from said differential air pressure sensor repeatedly until no substantial change of said air pressure occurs between said samples; determining the steady state value of said air pressure which is not changing anymore, given a sequence of readings (Δi ΔN) where I= (1...N) where dΔ/dl is about zero. This is called the steady state value Δs ; determining a surface roughness figure from it. |
| 3. | The method of claim 2, wherein the surface roughness is found by matching Δs to the closest value of reference sample surface values where Δsi corresponds to measurement of sample surface 1, ΔS2 corresponds to measurement of sample surface 2, Δs3 corresponds to measurement of sample surface 3, ΔS4 corresponds to measurement of sample surface 4, Δs5 corresponds to measurement of sample surface 5, Δs6 corresponds to measurement of sample surface 6, Δs7 corresponds to measurement of sample surface 7, Δs8 corresponds to measurement of sample surface 8, Δs9 corresponds to measurement of sample surface 9, where, Δs9 > Δs8 > Δs7 >Δs6 >Δs5 >Δs4 >Δs3>Δs2 >Δsi . |
| 4. | The method of claim 2 wherein number of reference samples can be anywhere from 1 to N. |
| 5. | The method of claim 2 wherein different reference samples can be used. |
| 6. | The method of claim 1 , wherein said air pump is used for building air pressure inside said air reservoir. |
| 7. | The method of claim 1 , wherein said differential pressure sensor is used for measurement. |
| 8. | An apparatus for measuring surface roughness, comprising: pumping air to an air reservoir which is interfaced to a surface through a rigid skirt; measuring air pressure inside the said air reservoir; reading air pressure value repeatedly using a processing unit, and determining a roughness value corresponding to reference sample number of said surface. |
| 9. | An apparatus of claim 8, where said processing unit determines the surface roughness of an unknown surface by taking said air pressure readings from said differential air pressure sensor repeatedly until no substantial change of said air pressure occurs between said samples; determining the steady state value of said air pressure which is not changing anymore, given a sequence of readings (Δi ΔN) where I= (1...N) where dΔ/dl is about zero. This is called the steady state value Δs ;. |
| 10. | An apparatus of claim 8, where said processing unit determines the surface roughness of an unknown surface by matching Δs to the closest value of reference sample surface values where Δsi corresponds to measurement of reference sample surface 1, Δs2 corresponds to measurement of reference sample surface 2, Δs3 corresponds to measurement of reference sample surface 3, Δs4 corresponds to measurement of reference sample surface 4, Δs5 corresponds to measurement of reference sample surface 5, Δs6 corresponds to measurement of reference sample surface 6, Δs7 corresponds to measurement of reference sample surface 7, Δs8 corresponds to measurement of reference sample surface 8, Δs9 corresponds to measurement of reference sample surface 9, where, Δs9 > Δs8 > Δs7 >Δs6 >Δs5 >Δs4 >Δs3>Δs2 >Δsi. |
The present invention relates to devices and methods for measuring surface roughness. More specifically, the present invention relates to measuring arrangements characterised by the use of fluids, additionally, for measuring roughness or irregularity of surfaces. The suggested apparatus is to be used by external reinforcement specialists who specialise in repairing ailing concrete structures by wrapping them externally with fibre-reinforced plastics (FRP) and by the quality control specialist who check the work of contractors.
BACKGROUND
External reinforcement of concrete structures using fiber reinforced plastic sheets (FRP) is a powerful tool for rehabilitation of buildings and infrastructures, which are damaged due to earthquake or corrosion. This type of reinforcement is quick and practical when compared to classical steel and concrete jacketing methods of rehabilitation. This type of repair is not only considerably faster and less labor intensive, but also in some cases, provides solution where no other method works. As a result, FRP repair is considered as a modern tool of structural rehabilitation.
In this technique, concrete surfaces first coated with a special resin and then wrapped with FRP sheets soaked in different kind of resin designed for this purpose. When both resins get cured the FRP sheet gets attached to the concrete surface with a strong bond. High tensile stress of the bonded FRP sheet aids the steel reinforcement bars inside the concrete resulting in increased service life and strength of the concrete member.
Studies indicated that the bond strength between concrete surface and the FRP sheet is very important in external reinforcement applications and this bond ultimately determines how successful the rehabilitation project is. Norbert H. Maerz, et. al. reported in Concrete Repair Bulletin, May/June 2001 pp. 4-8 article titled "Laser Profilometry for Concrete Substrate Characterization Prior to FRP laminate Application" that, "Externally applied FRP sheets or laminates are impregnated in-situ and bonded directly to a concrete surface with an epoxy. These FRP materials are often applied to provide additional flexural or shear strength capacity for deficient
structures or structures where a change in the occupancy or usage occurs. The overall performance of the system and the parameters that affect delamination depend highly upon the quality of the bond between the concrete and the laminate. Experience has shown that when delamination of the FRP sheets occur at the substrate level, the load- bearing capability of the strengthened member is compromised except when FRP laminates are used to confine members in axial compression. Research has indicated that the bond strength between the epoxy adhesive and the concrete depends on a number of factors, including the material properties of the epoxy as well as the properties of the concrete substrate.".
The studies further indicated that, the roughness of the concrete surface is one of the major factors that determine the quality of the bond. Norbert H. Maertz continues in the same article mentioned above that, " The epoxy-concrete bond strength is affected by the strength, roughness, and cleanliness of the prepared concrete surface.".
Many other researchers come up with the same conclusion. A. Momayez at. al reported in Cement and Concrete Research Vol. 35, page 756 that " Rough surface preparation leads to higher bond strength. These increases ranged from 9% for pull- off to 25% for slant shear tests. The influence of surface roughness is more pronounced when the repair materials have low adhesion, e.g. cementitious materials."
Although it is clearly understood that surface roughness improves adhesion to concrete surface, excessive roughness of the surface causes different kind of problems like tearing of FRP sheet under stress which result in failure of the reinforcement. When the surface is extremely rough, protrusions on the surface act like hooks and uneven distribution of stress ruptures the sheet. Obviously there is an optimum value of surface roughness desired which maximizes the surface adhesion without causing rupture of FRP sheet.
Determination of the optimum surface roughness necessitates measurement of the roughness of the concrete surface. Problem arises when it comes to measuring the surface roughness. Measuring surface roughness is a common and well studied problem for smooth surfaces. Many methods and tools are available for surface roughness measurement of steel, glass and paper surfaces. These methods are not suitable for the level of roughness encountered for concrete surfaces.
There are also methods for measuring roughness of coarser surfaces like road surfaces. One of these methods is mentioned in international patent document WO 01/81861 for measuring roughness of road surface. Road surface roughness is closer to concrete surface roughness.
Current state of the art in measurement of the concrete surface roughness is as follows:
1. International Concrete Repair Institute, (ICRI) has developed set of reference plastic rough surfaces. The model exhibits nine different surfaces with surface roughness varying from smooth to very coarse. The user subjectively compares concrete surface profiles of the prepared concrete surface to those models provided by ICRI and judges the roughness of the prepared surface. The details of the technique is provided in an article published by ICRI titled "Selecting and specifying concrete surface preparation for sealers, coating and polymer overlays. Technical guideline No. 03732", 1997.
2. An optical apparatus designed by Norbert Maerz et. al. which is reported in May/June 2001 issue of Concrete Repair Bulletin titled "Laser Profilometry for Concrete Substrate Characterization Prior to FRP laminate Application". The device directs a laser line beam at an angle to the concrete surface and the resultant image with line projected over it is captured and digitized by a camera. A computer analyzes the line image digitally and determines the surface roughness.
SUMMARY
Present invention is intended to provide a practical tool for measuring surface roughness of concrete. Preparation of surface is considered a difficult and important phase of external reinforcement procedure.
During the surface preparation phase of the reinforcement project, the roughness of the concrete surface needs to be checked by the contractor and by the inspecting authority to make sure that optimum surface roughness condition is achieved before the FRP wrapping stage. The measurement device for checking the surface roughness is desired to be lightweight, handheld and portable so that it can be operated easily by one hand by a worker standing on a scaffold. Columns of a structure are relatively easily accessible but beams of structure are more challenging because one needs to work on a scaffold. The measurement device should not only be
portable and lightweight but also should provide the measurement in a reasonable time e.g. several seconds. The present invention is intended to fulfill such requirements.
The invention is a battery operated portable device which uses a small compressor and measurement electronics which measures the air leakage between the device and the surface. Upon operation, it provides a digital readout of the surface roughness value within several seconds. Since the roughness of the concrete surface may change from location to location on the same column or the beam, the device should be used to take several readings from different locations of the concrete surface.
BRIEF DESCRIPTION OF DRAWINGS
FIGURE 1 shows a schematic representation of the surface roughness measurement apparatus.
FIGURE 2 shows the cross sectional view of the apparatus. FIGURE 3 shows the bottom view of the apparatus.
DESCRIPTION
The operation of the concrete surface roughness measurement will now be described.
In one embodiment, the invention includes an apparatus for measuring surface roughness. In this embodiment, the invention includes an apparatus comprises of an air compressor which blows air to an internal reservoir, a skirt interfaced to concrete surface and a processing unit for recording and converting air pressure value of said reservoir.
The apparatus may further comprise a differential pressure sensor sensitive enough to sense pressure ranges involved in measurement.
The processing unit may be any processing unit capable of converting pressure readings from said differential pressure sensor. The processing unit should be capable of executing a sequence of operations and taking repetitive measurements to determine the steady state value of pressure and display the said steady state value on a digital display.
An embodiment of the apparatus is shown in Figure 1. As shown in Figure 1 , in one embodiment the apparatus for surface roughness measurement includes an air
pump 1, an air reservoir 2, a differential pressure sensor 3, a rigid skirt 4, a processing unit 5 and the surface to be measured 6.
The operational principle of the present invention id further described with reference to Figure 1. The air reservoir 2 is disposed between the air pump 1 and a rigid skirt 4. Air reservoir 2 contacts the measured rough surface 6 through a rigid skirt 4. Differential pressure sensor 3 is connected to the side of the air reservoir 2. Processing unit 5 takes pressure readings from differential pressure sensor 3 and generates roughness value. The values read are a sequence of values (Δi Δ N ) where
I= (1...N). The processing unit 5 employs an algorithm to continue reading pressure value from differential pressure sensor 3 until no substantial change of pressure reading from differential pressure sensor 3 occurs anymore, where dΔ/dl is about zero. This is called the steady state value Δs.
Air pump 1 is any pump which pumps enough air output to fill the air reservoir 2 in a matter of few seconds. The higher the throughput of the pump, the faster the measurement will be completed. When the surface to be measured is very smooth, the air leakage will be less and pressure will built up quickly. Higher roughness values will require longer time by the air pump to built up steady pressure inside.
Differential pressure sensor 3 is any sensor that can sense air pressure built up inside the air reservoir 2. It should be sensitive enough to generate substantial enough reading of pressure to distinguish smooth sample from rough one when the samples are placed under the embodiment.
Air chamber 2 and rigid skirt 4 are made from any rigid material possible. Metal, wood, plastic are possible alternatives for building these components.
The processing unit is any programmable or non-programmable logical piece capable of taking readings from differential sensor and displaying on a digital display. In one embodiment processing unit 5 is a single chip controller or any microprocessor.
The calibration of embodiment is done by measuring the surface roughness of standard samples provided by International Concrete Research Institute (ICRI). (Although ICRI provides sample surfaces for comparison, in the absence of it alternatives are possible. Desired surface should have mean surface roughness of 0.5- 1.00 mm. This value corresponds to surface roughness of 60 grit size sandpaper. Higher and lower deviations from grit size 60 can be used as more or less rough
surface standards.) The samples are placed under the skirt 4 of the embodiment and pressure readings from differential pressure sensor 3 are taken. Processing unit 5, then associates the pressure measurement with the sample number of the ICRI. Since ICRI samples are arranged from smooth to rough in increasing order, 1 meaning smooth surface and 9 meaning roughest surface.
Δsi corresponds to measurement of sample surface 1,
Δs 2 corresponds to measurement of sample surface 2,
Δs 3 corresponds to measurement of sample surface 3,
Δs 4 corresponds to measurement of sample surface 4,
Δs 5 corresponds to measurement of sample surface 5,
ΔSO corresponds to measurement of sample surface 6,
Δs 7 corresponds to measurement of sample surface 7,
Δs 8 corresponds to measurement of sample surface 8,
Δs 9 corresponds to measurement of sample surface 9, where,
Δs9 > Δs8 > Δs7 >Δs6 >Δs5 >Δs4 >Δs3>Δs2 >Δs 1
When an unknown surface is measured, processing unit determines the Δs value of the sample and displays the closest matching sample number on the display. For example if the surface of a column is tested and the measured value is 2, that means the surface has similar characteristics as sample surface 2. If the desired surface sample is sample number 6, then the column surface should be roughened more to achieve desired value.
Next Patent: ACCESS CONTROL ARRANGEMENT