The Application of Drillability Properties in Measuring the Strength of Hardened Concrete

Transcription

1 International Journal of Applied Engineering Research ISSN Volume 9, Number 11 (2014) pp Research India Publications The Application of Drillability Properties in Measuring the Strength of Hardened Concrete Wail Asim Mohammad Hussain, M. Hanim Osman, A. Latif Saleh, Izni Shahrizal Ibrahim Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor, Malaysia Abstract The aim of this study is to establish a reliable equation to estimate the strength of in situ concrete from the results of a new non-destructive testing method that depends on measurements of the drilling penetration speed. Some previous studies used the same technique to determine the strength of other construction materials, such as rocks or marble. However, none of the previous studies attempted to use the drilling penetration speed method to estimate the strength of in situ concrete. In this study, a new drilling machine was designed, and all the factors that can affect the drilling speed were considered. In addition, the rebound hammer and ultrasonic pulse velocity tests were used to estimate the concrete strength for comparison with the new technique. Ten different concrete batches were prepared with different mix proportions; each batch consisted of twelve cubes with dimensions of 150x150x150 mm. Another thirty cubes for each mortar and cement paste with dimensions of 100x100x100 mm were cast for the calibration of the drill bit sharpness. Equations that were derived from the correlations between the drilling penetration speed and concrete strength using a 10 mm drill bit have high correlation coefficients; thus, these equations can be used to estimate the strength of concrete with high accuracy. The findings of this study show that the drilling test method can be used to estimate concrete strength in situ more accurately than the conventional non-destructive tests and without causing major structural damage to the concrete member being tested. Keywords: Concrete strength, drilling penetration rate, rebound hammer test, reliability of estimation, ultrasonic pulse velocity.

2 1766 Wail Asim Mohammad Hussain et al 1. Introduction Although concrete cubes and cylinders prepared in the laboratory have the same mix proportions, the actual in situ compressive strengths of these cubes and cylinders may be different. This result is due to the many variations that occur between field and lab conditions, such as variations in mixing, in the degree of compaction and in curing. In addition, the strength value of the existing concrete structures is sometimes required for reasons such as extending buildings or adding extra stories to an existing building. The coring test is widely used to accurately measure the strength of concrete in existing structures. However, this test lowers the strength of the tested concrete in these structures. In ancient buildings, coring may cause substantial damage to the structural units, which has led some governments to prohibit the use of this test for some buildings, as stated by Aliabdo and Elmoaty [1]. Consequently, a reliable method is required to measure the actual in situ compressive strength without coring the concrete structural member. Numerous trials have been carried out by many researchers to develop a rapid and reliable method for estimating the strength of in situ concrete by correlating the results of various non-destructive test methods, such as the Rebound Hammer test, the Ultrasonic Pulse Velocity test and the Windsor probe test, with the actual concrete compressive strength to develop a new equation that can calculate the strength of concrete in any existing structure. Because concrete is a heterogeneous material, the non-destructive tests reliability is questionable, and these formulas cannot be relied upon for estimating the compressive strength of in situ concrete. The drillability of concrete is defined as the time spent drilling to a certain depth in hardened concrete or as the ease of drilling in concrete [2], and it can be considered a non-destructive test method because the drilled holes resulting from the use of this method have a minor effect on the strength of the tested positions. The drillability test method for estimating the compressive strength of concrete is expected to be an accurate method that overcomes the heterogeneity of the concrete material. The aim of this study is to construct a reliable equation from non-destructive experiments to estimate the strength of concrete from the correlation between the drilling penetration speed and the strength of the concrete. Most of the previous studies on drillability have focused on measuring the strengths of different rocks by comparing the time needed to drill one meter into these different rocks and correlating this parameter to the actual rock strength. A few other studies have used drillability or drilling resistance techniques to assess the amount of damage over the whole depth of the concrete structural member by measuring the speed of drilling. Felicetti [3] applied drillability to assess the damage depth of concrete exposed to fire. Francisco and Paulo (2007) stated that microdrilling tests are capable of rapidly obtaining reliable data for mechanical or damage investigations of structural materials. Pamplona et al. [4] added that this method is more reliable and more sensitive in the assessment of material strength than other ordinary methods. Valentini et al. [5] and Stavropoulou [6] used the microdrilling machine for testing marble, whereas Fernandes and Lourenço [7] used the microdrilling test to measure the strength of clay bricks.

3 The Application of Drillability Properties in Measuring 1767 Although the results of these studies were reliable, none of the previous studies attempted to use the drillability method to estimate the in situ concrete strength by correlating the measured drilling penetration speed with the actual concrete compressive strength. 2. The design of the new drilling machine The drilling test machine for this study was designed after taking into consideration all the factors that affect the measurement of the drilling penetration rate. Some of these factors were controlled and adjusted as a constant value for all the drilling tests, while the other factors were measured. As illustrated in Figure 1, the designed drilling test machine has three main components connected with each other by electrical wires and air hoses. These components are the air compressor, the control box and the drilling frame. Detailed descriptions of the main components of the drilling test machine are as follows: 1. The control box shown in Figure 2 contains two main buttons, one to turn the drill on and off, and another one to turn the control box on and off. A knob is used to control the vertical movement of the drill, and the box has three digital meters to measure the time, pressure and electrical current. 2. The air compressor, which has two parts, a motor and a cylindrical air tank, is attached to a trolley for easy movement, as shown in Figure 1. The motor compresses and stores air in the air tank to increase the pressure. The air compressor has a wire connected to a power source and two air pipes; one of these pipes has an air gun attached to the end of the pipe to release the air pressure, while the other air pipe has a pressure gage that is connected to the control box. 3. The frame that holds the drill: as shown in Figure 3, the drilling machine is fixed tightly on this frame to test concrete specimens placed and fixed on the right drilling position in the base of this frame. The frame of the drill has a steel base frame that can fit concrete cubes up to 600x600x600 mm in size. The cube sample is fixed in its position at its four sides by four horizontal screws (clamps). The frame base is fixed to the rigid floor using four screws located at the corners of the base. The base of the drilling frame is connected to two vertical solid steel bars (120 cm in height) that hold two beams. The lower beam is allowed to move up and down, and this lower beam has a bracket attached to this beam to firmly fix the drilling machine. The upper beam is fixed to remain stable. As illustrated in Figure 4, the pressure cell is welded above the upper beam, and the pressure cell piston rod is fixed with the lower beam. When the knob in the control box is switched downward, the piston rod of the pressure cell pushes the lower plate and moves downward with the drill to penetrate the test sample. As shown in Figure 4, two air hoses are connected between the air cylinder and the knob controller in the control box. One of these hoses is connected to the entry on the upper cap of the air cylinder, while the other hose is connected to the lower cap of

4 1768 Wail Asim Mohammad Hussain et al the air cylinder. 4. The device for measuring the drilling rotational speed is a laser reflector sensor that is pointed on a 1 cm long piece of reflector tape that is attached to the drilling rotating part to read and record the drilling rotational speed in RPM. 5. A digital camera records the readings of the drilling rotational speed measurement device because the rotational speeds change every second. 6. A digital calliper is used to measure the depth of the drilled hole after conducting the drilling test. 7. The drill bits used in this study were 10 mm and 14 mm diameter masonry bits; the material of both bits was steel with an SDS-type shank on the end of the bit grasped by the drill. 8. The drill used in this experiment was 1-1/4 in SDS pulse rotary hammer which was manufactured in Germany by Bosch company. This drill is adjusted to drill using rotational movement only. 3. Test specimens In this study, ten concrete batches with different mix proportions were prepared to cover a wide range of concrete strengths, between 20 MPa and 50 MPa, to make the test results more generalisable to any concrete mix proportions, such as the different water-to-cement ratios shown in Table 1. For each batch, twelve cubes of concrete with dimensions of 150x150x150 mm were cast. Nine cubes from each concrete batched remained after testing three samples from each batch after seven days of curing. All the concrete samples were numbered from one to nine for each batch. For the calibration of the drill bit sharpness, mortar and cement paste were used because these materials are more homogenous than concrete, are easily available and can be tested using the drilling test machine. Therefore, thirty samples of mortar and another thirty of cement paste were cast in 100x100x100 mm cube moulds. The mix proportions of these materials are listed in Table 2 below. 4. Rebound hammer test The rebound hammer test is a device that uses the rebound technique to check the quality of the concrete in the structural members. This test depends on the potential energy of the steel ball inside the rebound hammer device after hitting the tested concrete surface. Higher strength concrete most often has greater surface hardness as a result of a larger rebound hammer number. On the other hand, the hardness of the concrete surface does not always accurately represent the concrete strength; thus, this method may not be very accurate because only the concrete surface is measured. According to ASTM C805 [8], small specimens should be rigidly fixed before the rebound hammer test. The concrete samples were fixed in a compressive testing machine by a slight pressure to ensure the stability of these samples when conducting the rebound hammer test. Each of the concrete samples was tested by a rebound hammer in twelve different points in two opposite faces.

5 The Application of Drillability Properties in Measuring 1769 The rebound numbers were correlated with the strength of the concrete, and an equation for the estimation of concrete strength was obtained. The aim of this test is to compare the reliability of the resulting formula with the formula that resulted from the correlation of drilling test parameters with the concrete compressive strength. 5. Ultrasonic pulse velocity test The Ultrasonic pulse velocity (UPV) test is another non-destructive test method that is used to measure the quality of concrete. According to ASTM C597 [9], this technique depends on measuring the time that is needed to send and receive a wave through the concrete sample between two poles on the surface of the concrete. The speed of this wave depends on the density and percentage of voids, which depend on the strength of the concrete sample; therefore, when testing concrete samples with numerous voids and low density, the traveling time of these waves is longer. In this study, the aim of the UPV test is to build a formula from the correlations of the results of this test and the compressive strength results to estimate concrete compressive strength by measuring the UPV value. The resulting formula has a regression coefficient that can be compared with the reliabilities of the formulas for compressive strength and drilling test parameter. 6. Drilling test procedure 1. The first step in the drilling test was to fix the drilling frame in the appropriate position; this step requires drilling four holes in strong ground to fit the positions of the four screws located at each corner of the drilling frame base. Then, four steel nuts were driven with a hammer into the four holes. The drill frame was placed on these holes so the screws could be fixed inside the nuts, but during the fixation process, two bubble levels were placed on each axis of the drill frame base to adjust the level of the drill frame base by increasing or decreasing the height of the four screws before fully fixing in the steel nuts. This process is important to ensure that drilling is exactly in the vertical direction. 2. The second step was placing a new drill bit, either 10 mm or 14 mm, inside the drilling machine. The drilling machine was tightly fixed in its position by two pieces of steel to avoid any horizontal or vertical displacement and to reduce vibrations due to the drilling process. 3. The third step was connecting the wires of the drill, control box and the air compressor to the electrical power source. Then, the two air pipes from the control box were connected to the air cylinder in the drill frame. In addition, a water pipe was fixed on the drill frame to pour cooling water on the drilling position. 4. The fourth step was placing the sample inside the base, making the drill bit approximately above the drilling point. After sample placement, the sample could be fixed by four horizontal screws (clamps). 5. The fifth step was to place two video cameras in the control box, one camera to record the RPM readings and another camera to record the pressure meter. The

6 1770 Wail Asim Mohammad Hussain et al purpose of using these cameras is that the readings of the RPM and the pressure meter change every second; thus, manually recording these readings is impossible. 6. The final step was switching on the compressor, after which the pressure increases gradually. Before the maximum pressure was reached, the drill was turned on to be ready to penetrate the sample. Then, the compressor stopped compressing air when the pressure reached approximately 7.5 bars, and the knob in the control box was switched downward, starting the drill, which began to penetrate the test sample. After the drilling test was finished, the sample was removed from the drill frame base and the depth of the drilled hole was measured using a digital calliper. In this study, the drilling test was performed using 10 mm and 14 mm diameter drill bits. Three concrete samples from each batch were tested using the 14 mm drill bit, and the other three samples from each batch were tested using the 10 mm drill bit. Each sample was drilled in four equally spaced positions, as shown in Figure 5. For each batch, two new drill bits were used (10 mm, 14 mm); therefore, one new drill bit was used for every three concrete samples. 7. Grouting the drilled concrete samples The aim of grouting the drilled holes was to restore the drilled concrete cubes to their original strength so that the drilling penetration speed for each cube could be related to its strength. The grout used in this study was SikaGrout-215 due to the availability of this product in the market and the suitability of this product for filling the holes in the drilled concrete samples. The grout type is a fine grey powder, which looks very similar to cement, and this powder is mixed with water before filling the holes. The amount of water depends on the workability required as listed on the SikaGrout-215 bag. The procedure for grouting all the drilled concrete cubes is as follows: 1. The dust and water were removed from all the holes using the air gun of the compressor of the drilling test machine. 2. Four litres of water was mixed with a 25 kg bag of SikaGrout-215 using the mortar-mixing machine for three minutes. The mix was divided into two mixes to fit in the mixing bowl. 3. A small amount of the grout was placed in a plastic bottle with a small opening to easily fill the holes. 4. After the grout dried, the excess grout was removed and the samples were left to cure in air for seven days, as shown in Figure 6, and then the samples were tested in the compressive test machine. 8. Calibration of drill bit sharpness A calibration method was applied to the drilling test to improve the accuracy of the

7 The Application of Drillability Properties in Measuring 1771 drilling penetration rate results. The drilling bit was used to drill once into a standard mortar cube and once into a cement paste cube each time before testing any concrete sample. First, the average values of the drilling penetration rate of all the tested mortar and cement paste cubes were calculated for both the 10 mm and 14 mm drill bits. These values were considered as reference values to compare with the drilling penetration rate results for mortar and cement paste. The differences between the reference values of the penetration rate and the resulting values of the mortar and cement paste penetration rates before testing each concrete sample were calculated, and the average of these two differences was considered as a sharpness reduction correction factor. This value was added to the drilling penetration speed of the concrete samples. 9. Results and discussion 9.1 Sharpness reduction of the drill bit From the results of the drilling test, an overall reduction in the penetration rate between the first tested sample and the second sample as well as between the second and the third sample was recorded, as shown in Tables 3 and 4. The reduction in penetration rate was due to the reduction in the sharpness of the cutting edge of the drill bit. The rate of the reduction in the drill bit sharpness or cutting ability depends on the drilling duration using the same bit and the hardness of the material being drilled. In addition, although a new drill bit was used with the same specification for each batch, either the 10 mm or 14 mm drill bit, small differences in the sharpness of the new drill bits were observed because these bits were supplied by different manufacturing companies. These differences can affect the estimation of the concrete strength, so calibrating the drill bit sharpness before conducting the drilling tests is important. The results of the calibration analysis are shown in Table 3 for the 10 mm drill bit and in Table 4 for the 14 mm drill bit. As illustrated in Table 3, the average penetration rates for mortar and cement paste are 2.8 mm/sec and 1.07 mm/sec, respectively, using the 10 mm drill bit. These values were considered as the reference penetration speeds for both the mortar and cement paste for calibrating the drill bit sharpness. Additionally, Table 3 shows that for each concrete sample, there are two penetration rate values for mortar and cement paste that were conducted before testing this concrete sample. The following are the general formulas for calibrating the drilling penetration rate of concrete samples: Mortar reference penetration rate (MRPr) = average penetration rate of all drilling tests conducted on mortar samples. Equation 1 Cement reference penetration rate (CRPr) = average penetration rate of all drilling tests conducted on cement samples. Equation 2 The following formulas were applied to the drilling results of any concrete cube: Mortar correction value (MCi) = MRPr M.Pri Equation 3 Cement correction value (CCi) = CRPr C.Pri Equation 4 Avg. correction value (ACi) = (MCi - CCi) / 2 Equation 5 Modified penetration rate (M.Cr.Pri) = Cr.Pr i + ACi Equation 6

8 1772 Wail Asim Mohammad Hussain et al Where Cr.Pri = Concrete penetration rate. M.Pri = Mortar penetration rate. C.Pri = Cement penetration rate. The same calibration procedure was applied on the concrete penetration rate for samples drilled using the 14 mm drill bit, as shown in Table 4 below. The reference penetration rates of mortar and cement paste are equal to 2.66 mm/sec and 0.89 mm/sec, respectively. As a result, the values of the modified penetration rates within the same batch, as shown in Tables 3 and 4, are more precise than the values of the unmodified penetration rates for the same concrete batch. 9.2 Linear regression analysis of the 10 mm drilled concrete samples The results of all the tests conducted on concrete cube numbers 4, 5 and 6 that were tested using the 10 mm drill bit for all the concrete batches are summarised in Table 5 below. Additionally, all the tests conducted on concrete cube numbers 7, 8 and 9 that were tested using the 14 mm drill bit for all the batches are shown in Table 6. Linear regression analysis was performed on the data in Tables 5 and 6. This analysis includes three correlation equations concerning the test results of each concrete sample by using the strength as the dependent variable with the three independent variables separately. These variables were the drilling penetration rate, the RN and the UPV. Another correlation was between the average strength at twentyeight days, which represents the strength of each concrete batch with its average penetration rate. As shown in Figure 7, a strong relationship exists between the strength of concrete and the drilling penetration rate for the concrete samples that were tested in the drilling machine using the 10 mm drill bit. This figure clearly illustrates that the penetration rate decreases when the strength increases. Linear regression results in the following equation: Concrete strength = (drilling penetration rate) Equation 7 The reliability of this equation is represented in the correlation coefficient, which equals to (R²) = Figure 8 shows the correlation coefficient and regression equation for the strength of concrete with the Rebound number for samples 4, 5 and 6. This figure illustrates that the strength of concrete increases with the increase of the rebound number. Linear regression of these data results in the following equation: Concrete strength = 1.42 (RN) Equation 8 and R² = From Figure 9, the relationship between concrete strength and UPV test results for samples 4, 5 and 6 is weaker than the previous relationships. When concrete strength increases, the UPV also increases. Linear regression of these data results in the following formula:

9 The Application of Drillability Properties in Measuring 1773 Concrete strength = (UPV) Equation 9 and R² = Figure 10 shows the correlation between the average strength of concrete tested after twenty-eight days and the average penetration speed using the 10 mm bit for each concrete batch. The resulting formula is the most reliable and has the highest correlation coefficient among the other correlation equations. Linear regression results in the following equation: Concrete strength = (penetration rate) Equation 10 and R² = Among the four first equations that resulted from data analysis of the tests results for concrete samples 4, 5 and 6 using the 10 mm drill bit, equation 10 is the most reliable equation which is resulted from the correlation of the average twentyeight days concrete strength with average penetration rate for every batch. This equation has a very high correlation coefficient of In addition, the equation resulting from linear regression of the strength and penetration speed for the concrete samples No. 4, 5 and 6 (equation 7) has a good reliability as the correlation coefficient is equal to On the other hand, this correlation coefficient suggests that this equation is slightly less reliable than the equation that resulted from linear regression of the data for the rebound hammer with concrete strength (equation 8) and more reliable than the equation resulted from linear regression of the data for UPV and concrete strength (equation 9). The resulting two equations from the drilling test using the 10 mm drill bit to estimate the concrete compressive strength have a high reliability and can be used to estimate the in situ concrete strength without any other tests. As shown in Figure 11, the strength of concrete has a negative relationship with the drilling penetration rate using the 14 mm drill bit on concrete samples number 7, 8 and 9. The resulting equation is: Concrete strength = (Penetration rate) Equation 11 and R² = The rebound hammer number is positively correlated with the strength of concrete for samples 7, 8 and 9, as illustrated in Figure 12. The resulting regression equation is: Concrete strength = 1.42 (RN) Equation 12 and R² = As shown in Figure 13, the UPV value increases when the strength of concrete increases. Linear regression results in the following equation: Concrete strength = 61.5 (UPV) Equation 13 and R² = The last relationship is illustrated in Figure 14, which is between the average twenty-eight days strength and the average drilling penetration rate using the 14 mm

10 1774 Wail Asim Mohammad Hussain et al drill bit for each batch. Linear regression indicated a negative relationship between these variables, the same result as all the penetration speed and strength relationships. The resulting equation is: Concrete strength = (penetration rate) Equation 14 and R² = Four other equations were constructed from the results of the concrete samples that were tested by the 14 mm drill bit. The most reliable equation resulted from the correlation of the average twenty-eight days strength with the average drilling speed for every batch, as shown in Figure 14. The correlation coefficient of this equation is equal to 0.866, but this value is less than the value for equation 10. The equation that resulted from linear regression of the data for concrete strength for samples 7, 8 and 9 and the drilling penetration speed (equation 11) has a good correlation coefficient of This coefficient is slightly less than the coefficient for RH of the same samples with strength after grouting as in equation 12, which is equal to 0.857, but more than the coefficient of the UPV test results of the same samples with the strength after grouting, as in equation 13, which is equal to The correlation equations from the drilling test results using the 14 mm drill bit with concrete strength have high correlation coefficients. On the other hand, the equations that resulted from the drilling test results using 10 mm drill bit are more reliable and better describe the strength of concrete. 10. Conclusions In this article, the reliability of a new method for estimating the strength of concrete was evaluated and compared with other conventional test methods to measure concrete strength. This study leads to the following conclusions: 1. All the formulas resulting from linear regression of the data for the drilling speed with the strength of concrete have high correlation coefficients; therefore, these equations can be used to accurately estimate in situ concrete strength. 2. In comparison with the other non-destructive tests for concrete strength, the drilling penetration speed results have a strong and more reliable relationship with the concrete strength because the factors that that have a negative effect on this correlation are less significant than the factors that affect the correlation of the non-destructive test with concrete strength. 3. The regression equation using the 10 mm drill bit is more reliable than the equation using the 14 mm bit; thus, the 10 mm drill bit is more appropriate for in situ estimation of concrete strength. 4. The drilling test can be conducted to estimate the compressive strength of concrete for a wide range of concrete strength values and with different concrete mix proportions. In conclusion, the drilling test method can be used to accurately measure the strength of concrete.

11 The Application of Drillability Properties in Measuring 1775 Table 1: Mix design proportions of the ten groups of concrete batches. Batch No. Grade Water (kg) Cement (kg) Fine aggregate (kg) Coarse aggregate (kg) W/C 1 C C C C C C C C C C ml SP* *SP: superplasticiser Batch No. Table 2: Standard mortar and cement paste mix proportions Material Water (kg) Cement (kg) Sand (kg) W/C Mortar Cement Table 3: Modified penetration rates for the 10 mm drill bit. Grade Sample No. Penetration rate (mm/sec) Mortar penetration rate (mm/sec) Cement penetration rate (mm/sec) Modified penetration rate (mm/sec) 1 C C C C C C

12 1776 Wail Asim Mohammad Hussain et al C C C C Average penetration rate Batch No. Table 4: Modified penetration rates for the 14 mm drill bit. Grade Sample No. Penetration rate (mm/sec) Mortar penetration rate (mm/sec) Cement penetration rate (mm/sec) Modified penetration rate (mm/sec) 1 C C C C C C C C

13 The Application of Drillability Properties in Measuring C C Average penetration rate Batch No. Grade Cube No. Table 5: Test results for the 10 mm drilled cubes. Modified Pen. rate (mm/sec) Avg. modified Pen. rate (mm/sec) Strength after grouting (Mpa) RN UPV 28 days (mm/µs) (Mpa) avg. strength 1 C C C C C C C C C C

14 1778 Wail Asim Mohammad Hussain et al Batch No. Grade Cube No. Table 6: Test results for the 14 mm drilled cubes. Modified Pen. Rate (mm/sec) Avg. modified Pen. Rate (mm/sec) Strength after grouting (Mpa) RN UPV (mm/µs) 28 days (Mpa) avg. strength 1 C C C C C C C C C C

15 The Application of Drillability Properties in Measuring 1779 Figure 1: The newly designed drilling test machine. Figure 2: Control box of the drill testing machine.

16 1780 Wail Asim Mohammad Hussain et al Figure 3: Drilling test frame. Figure 4: Air cylinder shown from two different angles.

17 The Application of Drillability Properties in Measuring 1781 Figure 5: Sketch of a concrete sample with the drilling positions (top view). Figure 6: Concrete cubes after grouting. Figure 7: Strength vs. penetration rate for samples 4, 5 and 6 from each batch.

18 1782 Wail Asim Mohammad Hussain et al Figure 8: Strength vs. RN for samples 4, 5 and 6 from each batch. Figure 9: Strength vs. UPV for samples 4, 5 and 6 from each batch.

19 The Application of Drillability Properties in Measuring 1783 Figure 10: Strength vs. penetration rate using the 10 mm drill bit for each batch. Figure 11: Strength vs. penetration rate for samples 7, 8 and 9 from each batch.

20 1784 Wail Asim Mohammad Hussain et al Figure 12: Strength vs. RN for samples 7, 8 and 9 from each batch. Figure 13: Strength vs. UPV for samples 7, 8 and 9 from each batch.

21 The Application of Drillability Properties in Measuring 1785 Figure 14: Strength vs. penetration rate using the 14 mm drill bit for each batch. References: [1] Aliabdo, A. A. E., Elmoaty, A. E. M. A., 2012, Reliability of Using Nondestructive Tests to Estimate Compressive Strength of Building Stones and Bricks, Alexandria Engineering Journal, 51, pp [2] Tanaino, A. S., 2005, Rock Classification by Drillability. Part 1: Analysis of the Available Classifications, J. Min. Sci., 41(6), pp [3] Felicetti, R., 2006, The Drilling Resistance Test for the Assessment of Fire Damaged Concrete, Cem. Concr. Compos., 28(4), pp [4] Pamplona, M., Kocher, M., Snethlage, R., and Barros, L. A., 2007, Drilling Resistance: Overview and Outlook, Z. dt. Ges. Geowiss., 158, pp [5] Valentini, E., Benincasa, A., Tiano, P., Fratini, F., Rescic, S., 2008, On Site Drilling Resistance Profiles of Natural Stones, ICVBC: Istituto per la Conservazione e la Valorizzazione dei Beni Culturali, Florance. [6] Stavropoulou, M., 2006, Modeling of Small-Diameter Rotary Drilling Tests on Marbles, Int. J. Rock Mech. Min. Sci., 43, pp [7] Fernandes, F., and Lourenço, P. B., 2007, Evaluation of the Compressive Strength of Ancient Clay Bricks Using Microdrilling, J. Mater. Civ. Eng., 19(9), [8] ASTM International, 2013, ASTM C805/C805M-13a: Standard Test Method for Rebound Number of Hardened Concrete, ASTM International, West Conshohocken, PA. [9] ASTM International, 2009, ASTM C597-09: Standard Test Method for Pulse Velocity through Concrete, ASTM International, West Conshohocken, PA.

22 1786 Wail Asim Mohammad Hussain et al Biographical sketch Wail Asim Mohammad Hussain received the BSc. degree in Civil Engineering in (2007) from Jordan University of Science and Technology, and MSc degree in Structural Engineering from the same university in (2009). He is now a PhD student of Structural engineering in the Faculty of Civil Engineering at Universiti Teknologi Malaysia. M. Hanim Osman is an Assoc. Professor at Universiti Teknologi Malaysia. He received his Diploma Engineering (Civil) in 1980 from Universiti Teknologi Malaysia and B.Eng (Hons) Civil Engineering from the same uuniversity in Master of Science (Structural Eng.) from University of Surrey, Guildford, United Kingdom in Doctor of Philosophy (Ph.D)(Structural Eng.), Univ.of Wales, Cardiff, United Kingdom in Currently, M. Hanim Osman is the Deputy Dean (Academics) in the faculty of Civil engineering in Universiti Teknologi Malaysia. A. Latif Saleh is a professor at Universiti Teknologi Malaysia. He received his Diploma in Civil Engineering from Universiti Teknologi Malaysia in 1984, B.Eng (Hons) Civil Engineering from Thames Polytechnic, London, United Kingdom in 1986; M.Eng (Struct) Civil Engineering from Universiti Teknologi Malaysia in Ph.D (Struct) from University of Portsmouth, United Kingdom in Currently, A. Latif Saleh is director of works in the office of assets and development in the Universiti Teknologi Malaysia. Izni Shahrizal Ibrahim has a Bachelor Degree (Hons.) in Civil Engineering from UTM in He then join UTM as a tutor in 1999 and completed his Master in Structural Engineering also from UTM in He obtained his PhD from the University of Nottingham, United Kingdom in 2008 and currently a Senior Lecturer at the Faculty of Civil Engineering, Universiti Teknologi Malaysia.