Statistical analysis of mortars with DRMS Cordless 1
DRMS: PORTABLE DEVICE FOR THE DRILLING RESISTANCE MEASUREMENT The Drilling Resistance Measurement System (DRMS) is a tool for the determination of the mechanical properties of the materials used in historic masonry buildings. Statistical analysis of mortars 2
DRMS: PORTABLE DEVICE FOR THE DRILLING RESISTANCE MEASUREMENT • Suitable for both laboratory and “ in situ ” tests • It measures the Force necessary to drill the material • The mean value of the Drilling Resistance can be correlated with the Uniaxial Compression Strenght (UCS) • Works at constant operating conditions: Rotation speed (20-1000 RPM) and Penetration rate (5-80 mm/min) • Records the resistance profile of the first layer of a stone material (up to 50 mm depth) • Uses diamond drill bits to reduce the wear effect Statistical analysis of mortars 3
THE DRILLING RESISTANCE TEST METHOD The Drilling Resistance Test Method can be used for the characterization of historic masonry materials, to obtain information concerning the mechanical properties of materials and to evaluate the performance of consolidation treatments. The test consists in drilling a small hole at a set constant rotational speed and penetration rate, and in measuring the penetration force versus depth. Statistical analysis of mortars 4
Statistical analysis of mortars Some materials (e.g. mortars and concrete) present high fluctuations in the drilling resistance around the mean value, due to their intrinsic non homogeneity. These materials need to be characterized not only with average parameters but also through statistical indices that take into account the non uniformity of the material. Statistical analysis of mortars 5
Main statistical indices Parameter Symbol Formula/Definition 𝑜 σ 𝑗=1 𝑦 𝑗 Mean 𝑦 𝑜 𝑜 (𝑦 𝑗 − 𝑦) 2 σ 𝑗=1 𝑡 2 = Variance 𝑡 2 𝑜 𝑜 (𝑦 𝑗 − 𝑦) 2 σ 𝑗=1 Standard Deviation 𝑡 𝑡 = 𝑜 − 1 𝐷𝑊 = 𝑡 𝑦 ∗ 100 Coefficient of Variation 𝐷𝑊% 𝑌 𝑛𝑗𝑜 Minimum Value 𝑌 𝑛𝑏𝑦 Maximum Value Range 𝑆 𝑆 = 𝑌 𝑛𝑏𝑦 − 𝑌 𝑛𝑗𝑜 3 𝑦𝑗−𝑦 𝑜 σ 𝑗=1 𝑡 Skewness γ 1 𝑜 Measure of the asymmetry of the probability distribution 4 𝑦𝑗−𝑦 𝑜 σ 𝑗=1 𝑡 γ 2 Kurtosis 𝑜 Indicate hether the shape of the distribution of the data corresponds to the Gaussian distribution number below which lies 25 percent of the bottom data 𝑅 1 First Quartile number below which lies 50 percent of the bottom data 𝑅 2 Second Quartile number below which lies 75 percent of the bottom data 𝑅 3 Third Quartile 𝑁 Median 𝑁 = 𝑅 2 𝐽𝑅𝑆 = 𝑅 3 − 𝑅 1 IQR Interquartile Range Statistical analysis of mortars 6
Test procedure 1. Repeat tests on the same material (at least 10 holes) 2. Use the same penetration rate in all the tests 3. Use the same revolution speed in all the tests 4. Acquire data in Streaming mode (300 Hz) 5. Apply a software filter to reduce the noise related to drill bit vibration (low pass filter at 3Hz) 6. Discard the first mm of penetration data to remove drill bit surface penetration effect 7. Discard the last mm of penetration data to reduce the effect of the drilling swarf 8. Post-elaboration with DRMS software to extract a set of statistical indices 9. Graphical representation with box-plot, histogram, Qqplot and trend 10. Repeat the post-process elaboration without the data beyond the outliers Statistical analysis of mortars 7
Test parameters In this case, the tests were carried out for two different types of mortars: N2/04 and N2/01 with the following drilling parameters: Penetration speed of 40 mm/min • Rotational speed of 300 rpm • Diamond drill bit with 5 mm diameter • Low pass filter at 1.5 Hz • Statistical analysis of mortars 8
Mortar N2/04: Mean curves Statistical analysis of mortars 9
Mortar N2/04: Histogram and box-plot Statistical analysis of mortars 10
Mortar N2/01: Mean curves Statistical analysis of mortars 11
Mortar N2/01 : Histogram and box-plot Statistical analysis of mortars 12
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