WO2010079384A1

WO2010079384A1 - Apparatus for measuring bughole rating of concrete surface

Info

Publication number: WO2010079384A1
Application number: PCT/IB2009/050106
Authority: WO
Inventors: Tarik Ozkul; Ismail Kucuk
Original assignee: American University Of Sharjah
Priority date: 2009-01-12
Filing date: 2009-01-12
Publication date: 2010-07-15

Abstract

This invention provides a way of classifying bughole rating of concrete surfaces. The apparatus uses air leakage method for classification and rating of bugholes on the surface of concrete (6) and comprises of an air pump (1), differential pressure sensor (3), measurement electronics (5) and resiliently flexible skirt (4) that comes in contact with the concrete surface (6). Air pumped by the pump (1) fills the internal cavity (2) which leaks through the bugholes that skirt lip crosses over. The air pressure inside the cavity (2) indicates the amount and the size of the bugholes on the concrete surface (6).

Description

Description Title of Invention: APPARATUS FOR MEASURING BUGHOLE

RATING OF CONCRETE SURFACE

APPARATUS FOR MEASURING BUGHOLE RATING OF CONCRETE SURFACE [1] FIELD

[2] The present invention relates to devices and methods for measuring irregularities of surface or contours. More specifically, the present invention relates to measuring arrangements characterized by the use of fluids, additionally, for measuring roughness or irregularity of surfaces. The apparatus is designed to measure the amount of bugholes (surface cavities) present on concrete surfaces and assign a 'bughole rating' to the surface in question. The suggested apparatus is to be used by architects, contractors and quality control specialists who specialize in fabrication of concrete surfaces and control of surface quality.

[3] BACKGROUND

[4] Surface imperfections that appear as small pits and craters on concrete surface after the casting process are called 'bugholes'. Manufacturing of concrete surfaces with no bugholes is highly desired because of cosmetic as well as cost reasons since existence of bugholes increase cost due to surface preparations needed for painting or finishing the concrete surface. Concrete surfaces ideally, are desired to be flat and free of surface voids.

[5] Surface imperfections are caused by air or water bubbles trapped at form/concrete junction during the curing process and appear as voids after the form is removed. These voids are called 'bugholes'. They are also called 'pinholes', 'blowholes' or simply called 'surface voids'. These imperfections appear as regular or irregular pits with diameters ranging from few millimeters to 15 mm in diameter and they are usually scattered randomly on the concrete surface. Bugholes do not affect the structural strength of concrete but considered a nuisance since these voids need to be filled before paint is applied to the concrete surface. Since this process is considered a labor- intensive, therefore costly, there is great desire to have concrete surfaces with least amount of bugholes.

[6] Bugholes are recognized as a major problem in construction industry. Reading T. J. has elaborated this problem in detail in his 1998 dated article titled "The Bughole Problem" which is published in Volume 36, 1998, page 1119-1134 of ACI Journal. Vikan H. has authored a report titled "Quality of Concrete Surfaces, State of the Art", (SINTEF Report, Nov. 2008) where he mentioned that 'bugholes is one of the primary influences that affect the quality of the concrete'. Even though bugholes do not affect the structural integrity of the concrete, they are considered source of aesthetic problems.

[7] It is understood that bughole problem is a manufacturing defect which is very difficult to eradicate and one should not expect to manufacture a concrete surface completely free of bugholes. However, it is possible to reduce the number of bugholes, and reduce the sizes of them by using various techniques.

[8] Being considered a major problem, construction industry paid careful attention to bughole reduction. Number of procedures and recommendations are developed to reduce sources of bugholes during the manufacturing process. Recommendations ranged from the effective use of vibrators to addition of admixtures and usage of special liners inside concrete forms.

[9] Although the methods mentioned above are effective in reducing the number of bugholes, none of the methods are really expected to get rid of 'bughole' problem completely. In most cases, reducing the surface void area contributed by the bugholes to 1% is considered successful in terms of bughole reduction.

[10] Concrete surface quality is a major source of litigation between building owners, architects and contractors. Architects demand best quality surface possible, building owners do not want the extra cost of surface preparation in order to finish the surface. Contractors want to optimize the time and labor spends on use of vibrators and form preparations. These conflicting demands usually end up causing legal problems between parties. A 'measuring yardstick' to describe and communicate 'acceptable amount of bugholes' to both parties is desired.

[11] During 1970's construction professionals tried to rate surface quality by counting number of bugholes and calculating percentage of holed areas on the surface ( Samuelsson, P., "Voids in concrete surfaces", ACI Journal, Proceedings, v. 67, no. 11, Nov. 1970, p. 868-874). This approach of counting number of bugholes in a unit area, and measuring the cumulative area of bugholes used to be done manually and it was found impractical. Additionally, some professionals argued that this method does not reflect the essence of surface quality since the size of bugholes is not uniform. Argument was that bigger diameter bugholes are much harder to deal than smaller ones.

[12] Current state of the art for measuring bughole rating of concrete surfaces are as follows:

1. This technique was first suggested by Thomson where the actual surface was compared to photos of reference samples with different degrees of bughole coverage (Thomson, M. S., "Blowholes in Concrete Surfaces", Concrete, Vol. 3, No: 2, February 1969, pp. 64-66). This approach was found acceptable by the industry and current method of bug hole rating developed by American Concrete Institute (ACI) is based on this method (CIB Report no. 24, commission W29, Tolerances on blemishes of concrete, 1973). In ACI method of rating, the sample surface to be rated is compared to set of seven standard photos of concrete surfaces with different degrees of bughole voids. Surface number 1 has the least bughole problem and surface number 7 has the worst bughole problem. The expert who is doing the comparison decides which reference photo of concrete surface resembles the sample surface with bugholes in question. D

2. Another method of bughole measurement uses camera and image processing to measure the bughole rating of concrete surfaces. Lemaire et al. developed a setup which acquires images of the sample surface and calculates void ratio automatically through image processing ( Lemaire, G. , Escadeillas, G., Ringot, E. "Evaluating concrete surfaces using an image analysis process", Construction and Building Materials, Volume 19, Issue 8, 2005, pp. 604-611). Even though the method is exactly the same as the original method suggested in 1970, measurement process became more practical since processing is done by computer. However, since method requires image processing and camera, the resultant equipment tends to be bulky and costly. D [13] SUMMARY

[14] Present invention is intended to provide a practical tool for measuring bughole rating of concrete surface. Bughole rating of the concrete surface will be classified by finding the percentage void area per unit area of concrete surface. The outcome of measurement is supposed to be an objective indication of bughole rating of the concrete surface.

[15] The measurement device for checking the bughole rating is desired to be lightweight, handheld and portable so that it can be operated easily by single person. Additionally it is desired that measurement process is done in a reasonably short amount of time. Typically several measurements are supposed to be taken from concrete surface from different random locations and the average of these measurements can be taken as the final value of measurement.

[16] The invention presented in this document uses air leakage and differential pressure measurement technique for measuring bughole rating. A small compressor pumps air into a reservoir where the accumulated pressurized air is leaked through a resiliently deformable skirt which mates with the concrete surface flush. The air escapes through the bugholes situated right under the skirt lips. Skirt is designed with a wavy shape to extend the linear length of contact between the skirt lip and the concrete surface. Since bugholes are relatively small and few, it is important to pattern the skirt in a way to maximize the contact area between the skirt and the concrete surface. In order to maximize the amount of contact area between the skirt and the concrete surface, the skirt is shaped in a zigzag/wavy pattern.

[17] Comparison of air pressure inside the reservoir and the outside pressure is indicative of the amount of bugholes situated under the skirt contact area. This information is converted to bughole rating by the electronics of the apparatus.

[18] Air leakage method is used for measuring roughness of paper surfaces in GB-

A-1063657, GB-A-1389947 and WO 01/36907 Al. The said method is also used for measuring roughness of concrete surfaces in WO 2006/111795 Al. In these applications air leaks through the interface where skirt of the instrument meets the surface being measured. Imperfections on the surface cause a fluidic impedance to escaping air which the device measures.

[19] In this particular application of bughole measurement, the voids are embedded in the surface and the concrete surface is smooth. Unlike surface roughness measurement applications where the imperfections rise over the surface like hills rise on a flat surface of earth, in bughole detection application bugholes appear as voids, like wells dug on flat surface of earth. The air leakage method mentioned in the above patents need to be modified for this particular application in order to detect the existence of those voids properly. In this invention, the skirt of the instrument is designed specifically to detect bugholes. The skirt length is extended through a zigzag shaped design, skirt is made out of resiliently flexible material with tapered edges and the whole instrument is designed to detect the bugholes by forcing pressurized air to leak through the bughole voids.

[20] BRIEF DESCRIPTION OF DRAWINGS

[21] FIGURE 1 shows a schematic representation of the surface roughness measurement apparatus resting on concrete surface with bugholes.

[22] FIGURE 2 shows the cross sectional view of the apparatus resting on concrete surface with bugholes.

[23] FIGURE 3 shows the bottom view of the apparatus.

[24] FIGURE 4 shows the top view of the skirt of apparatus while resting on concrete surface with bugholes present.

[25] DESCRIPTION

[26] The operation of the concrete bughole rating measurement device will now be described.

[27] In one embodiment, the invention includes an apparatus for measuring bughole rating of concrete surface. In this embodiment, the invention includes an apparatus comprises of an air compressor or similar means which blows air to an internal reservoir, a resiliently deformable skirt interfaced to concrete surface and a processing unit for measuring and processing air pressure value of said reservoir.

[28] The apparatus may further comprise a differential pressure sensor sensitive enough to sense pressure ranges involved in measurement.

[29] The apparatus further comprises a processing unit capable of measuring pressure readings from said differential pressure sensor. The said processing unit should be capable of executing a sequence of operations and taking repetitive measurements from said differential pressure sensor to determine the steady state value of pressure and display the said steady state value on a digital display.

[30] An embodiment of the apparatus is shown in Figure 1. As shown in Figure 1, in one embodiment the apparatus for bughole rating measurement includes an air pump 1, an air reservoir 2, a differential pressure sensor 3, a resiliency deformable skirt 4, a processing unit 5 and the concrete surface to be measured 6. Concrete surface 6 has bugholes 7, 8, 9 and 10 present on the surface. Bughole 7 is situated partially under the lip of the resiliently deformable skirt, bughole 7 and 8 under completely under the skirt area and bughole 10 is completely outside the skirt area.

[31] The operational principle of the present invention is further described with reference to Figure 2. The air reservoir 2 is placed between the air pump 1 and resiliently deformable skirt 4. Air reservoir 2 contacts the concrete surface with bugholes 6 through resiliently deformable skirt 4. The edges of the resiliently deformable skirt 4 may be placed right across some bughole 7, it may be over some bughole 8, 9. Some bughole 10 may be outside the skirt area of the apparatus.

[32] The shape of the resiliently deformable skirt is described with reference to Figure 3.

This Figure 3 shows the bottom view of the resiliently deformable skirt 4 which makes contact with concrete surface 6. The resiliently deformable skirt 4 is designed to serpentine over the concrete surface 6 by making wavy lines. This is done to increase the contact area between the skirt 4 and the concrete surface 6. The contact area between skirt 4 and the concrete surface 6 can be increased by making shape like a zigzag as shown in Figure 3, however other alternative shapes are possible as long as contact area is increased.

[33] The purpose of such shaping resiliently deformable skirt is explained with reference to Figure 4. When resiliently deformable skirt edge 4 mates with the concrete surface 6, some bugholes like 7, 8, 9 are covered by skirt 4. Some bugholes like 10 are outside the coverage area of the skirt. The described apparatus is designed to sense the existence of bugholes like 7 which are located right under the resiliently deformable skirt 4 edge. Bugholes like 7, 8 which are under the skirt area and bugholes like 10 which is outside the skirt area do not affect the measurement process. In order to maximize number of bugholes like 7 that coincide with skirt edge 4, the skirt 4 is shaped in wavy pattern. [34] Now the operation of the apparatus will be further described with reference to Figure

2. Once the apparatus is turned on, air pump 1 pumps air to fill the air reservoir 2 in a matter of few seconds. Air pump 1 can be a pump or any other means for pumping fluid like air or gas. The higher the throughput of the air pump 1, the faster the measurement will be completed. The resiliently deformable skirt mates with the concrete surface and forms a sealed cavity underneath the skirt area 11. The edge 12 of the resiliently deformable skirt 4 deforms slightly to conform to the shape of the concrete surface 6. The cavity 11 now covers bugholes like 7, 8, 9. Bughole 7 is the only source of air leakage through cavity 11. Bughole 8, 9 do not cause air to leak and do not affect the measurement. Likewise bughole 10 do not cause any air leakage so it does not affect measurement. Resiliently deformable skirt 4 is shaped to serpentine over the concrete surface in order to maximize the number of bugholes like bughole 7 that coincides with the skirt edge 12. Edge of skirt 4 is tapered to a thin edge 12 to ensure partial coverage of bughole void 7 and to ensure proper seal between skirt 4 and concrete surface 6. When the surface to be measured has few bugholes, the air leakage will be less and pressure inside cavity 11 will be high. Higher number of bugholes like bughole 7 means more leakage through the bughole and reduced pressure inside the reservoir cavity. The steady state value of pressure inside reservoir is indicative of amount of bugholes on the concrete surface 6.

[35] Processing unit 5 takes pressure readings from differential pressure sensor 3 to determine pressure inside reservoir 2. The values read are a sequence of values (D₁ D_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 dD/dl is about zero). This is called the steady state measurement value D_s.

[36] 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.

[37] Air chamber 2 and resiliently deformable skirt 4 are made from suitable material which is pliable enough to mate the concrete surface but not soft enough to fill bughole voids. The processing unit is any programmable or non-programmable logical piece capable of taking readings from differential sensor and displaying on a suitable analogue or digital display. In one embodiment processing unit 5 is a single chip controller or any microprocessor.

[38] Calibration of embodiment is done by placing the apparatus over seven different sample surfaces mentioned in CIB report 24 (CIB Report no. 24, commission W29, Tolerances on blemishes of concrete, 1973.) and measuring the output of differential pressure sensor 5. Samples are arranged with surface #1 with least amount and smallest bugholes and surface # 7 with most and biggest number of bugholes. [39] D₈₁ corresponds to measurement of sample surface 1,

[40] D₈₂ corresponds to measurement of sample surface 2,

[41] D₈₃ corresponds to measurement of sample surface 3,

[42] D₈₄ corresponds to measurement of sample surface 4,

[43] D₈₅ corresponds to measurement of sample surface 5,

[44] D₈₆ corresponds to measurement of sample surface 6,

[45] D₈₇ corresponds to measurement of sample surface 7,

[46] where,

[47] D_{81 >}D_{82 >}D_{83 >}D_{84 >}D_85>D_{86 >}D₈₇

[48] When an unknown surface is measured, processing unit determines the D₈ value of the sample and displays the closest matching sample number on the display. [49] For example if an unknown concrete surface with bugholes is tested and the measured value is closest to D₈₄, that means the surface has bughole rating similar to sample surface 4.

Claims

[Claim 1] An instrument measuring bughole rating of a concrete surface comprising; means to pump gas to an air reservoir which is interfaced to said concrete surface through a resiliently deformable skirt; differential pressure sensor measuring gas pressure inside the said air reservoir; electronic controller which controls the sequence of operations; and display to indicate result of measurement.

[Claim 2] A method of claim 1, where said bughole rating of concrete surface is determined by: letting the accumulated gas in the said air reservoir leak through bugholes of said concrete surface that are positioned under the said resiliently deformable skirt; taking pressure readings from said differential air pressure sensor repeatedly until there is no substantial change between readings; determining the category of bughole rating using said reading.

[Claim 3] The instrument of claim 1 where the said resiliently deformable skirt shaped to serpentine over the concrete surface to increase the contact area between the said resiliently deformable skirt and the said concrete surface.

[Claim 4] The instrument of claim 1 where the said resiliently deformable skirt has tapered edge that meets concrete surface.