·Table of Contents
·Conservation and Restoration in Art and Architecture
Correlation between ultrasonic measurements and mechanical testings: a methodology applied to D'Amico Palace of MilazzoV. A. M. Luprano, G. Montagna, A. Giardina, A. Rotella
PASTIS-CNRSM, - S.S. 7 'Appia' km. 714 - 72100 BRINDISI - ITALY
ISCOM-CNR - Via per Arnesano - Lecce - ITALY
Via XXIV Maggio - 60035 Jesi (Ancona) - ITALY
|Fig 1: Scheme of the ultrasonic measurements points|
2.1. Petrographycal and mineralogical study
These analysis were been carried out to distinguish the stony material championship from the columns (stem and basic) with the lithotype taken from a castle near Milazzo used for the laboratory analysis. The samples were called respectively PDAC 1, 2, 3. The material for the petrographycal observation of the last one was extracted with a cylindrical pipe of 80 mm of diameter. For the petrographycal and mineralogical characterization were carried out the following analysis
2.2. Ultrasonic measurements on the two columns
Ultrasonic measurements were performed in situ on two columns of Palazzo d'Amico of Milazzo (called A and B) at three different highs: 35, 100, 200 cm as shown in Fig.1. The frequency used for the longitudinal velocity measurements were 50 KHz, in transmission mode, by using a pulse generator SIRIO RP 4000 CSM. For the ultrasonic measurements was made reference to the NORMAL 22/86 standard . The measure points are showed in Fig. 1, for each velocity measure were taken opposite points on the column. Data acquisition was made by means of a home-made software. Accuracy of the measurements is estimated as 2% of the measured longitudinal velocity.
2.3. Tomographic reconstruction by means of ultrasonic waves on a columns
The tomographic reconstruction was realised on the column B. The considered section was at 100 cm from the column top. The paths considered are reported in Fig. 2. The measurements were performed with the same instruments of the par. 2.2. For the tomographic reconstruction was used an home made software called Tomo 2.0 .
|Fig 2: Scheme of the measurements point for the tomographic reconstruction of a section of the column B|
2.4. Ultrasonic measurements on cubic and cylindrical samples of similar material
Tests have been carried on 6 samples obtained from quarry blocks of similar material (arenaria stone) as shown in the petrographic analysis (par. 2.1), cutted in cubes (5 cm edge), taking into account the cut direction (Fig.3). Velocity measurement were performed at a frequency of 1 MHz, in transmission mode, by using a pulse receiver Panametrics 5601A/ST and an oscilloscope Philips PM3323. Both the longitudinal (Vl) and shear velocity (Vt) were measured in the three directions. Reference was made to the NORMAL 22/86 standard .
Before the compression mechanical tests was also measured the longitudinal velocity at the frequency of 50 KHz with the SIRIO instrument on 13 cylindrical samples (141mm high and with a diameter of 73,5 mm) placing the ultrasonic probes on the two opposite faces of the sample, parallel to the direction of the applied load.
2.5 Mechanical measurements on cylindrical samples
Compression mechanical tests was carried out by means of an Instron 4507 apparatus, making reference to the ASTM standard  and to the UNI 9724, on the same 13 cylindrical samples of Areanaria stone used for NDT. The samples were grinding with a 100 m diamond paste and, in order to follow the real deformation due to the increasing load, four strain-gauges have been applied around the specimen at 90° each other, perpendicularly to the direction of the load applied. The test was performed by small increase in load (0.5 Mpa) till the ultimate compressive value was reached. The elastic static modulus was also measured.
3.1. Petrographycal and mineralogical characterisation
Petrographycal observations shows that the sample PDAC 1 is mainly made of quartz; the presence of abundant feldspars of quantity, crumbs and chlorites.The fragment has a total porosity media, varying among the 24, 6% and the 27, 8%; the chemical analysis validation, the eminently silicate nature of the fragment, showing the shortage of the natural cement, it has clayey and carbonat among the granules.
Samples PDAC 2 and PDAC 3 have also a quite mineralogical-petrography characteristic with a prevalence of quartz, presence of abundant feldspathic quantity (orthoclase and plagioclases) with cement quartz. The porosimetric analysis do not also show great variations between PDAC 2 and PDAC. 3, in fact the values are understands among 19% and 22%.
The sample show a grey-clear coloration and an enough elevated porosity; considering the silic fraction-clastic and the carbonatic granule number, the rock it may define a " quartzoarenite or protoquarzite" Fig 3. Mineralogical is constituted from quartz crystals, alkaline feldspar, plagioclase, muscovite, biotite, chlorite, clayey mineral and rock fragment. In some point is possible to observe little quantity of chalk, perhaps added to animal glue from as it is suggests by the inclusion of least quantity of protein substance.
|Fig 3: PDAC 1 - thin section, Nx, 25x.||Fig 4: PDAC 2 - thin section, Nx, 25x.||Fig 5: PDAC 3 - thin section, Nx, 25x.|
The section in examination is an arenaria sandstone type " arcosic", containing an elevated percentage of granules detritus of alkaline feldspars (orthoclase and microcline) Fig. 4. The orthoclase crystals, are easily sensitive in the decay and in more accentuated manner in comparison with the quartz is often underline turbid. The feldspars are represented from orthoclase, microcline and sodic plagioclases (albite and oligoclase).
The sample PDAC 3 is similar to the sample PDAC 2. From the mineralogical point o f view. It is constituted from coherent material to clastic weaving, but with a decidedly coarse nuisance, with granules to angular to round off, cement primarily quarztic, with some calcitic points. Considering the silic-clastic fraction and the number of carbonatic granules, the rock may be definite an arcosic, giving also the contain of feldspars superior to the 50%, Fig. 5.
3.2. Ultrasonic tests
The values of the longitudinal velocity measured on the column A and B at three different highs are reported respectively in Figs 6 and 7.
|Fig 6: Longitudinal velocity measurements on column A||Fig 7: Longitudinal velocity measurements on column B|
It is possible to note as the longitudinal velocity in column B is more uniform at the three different highs then column A.
3.3 Tomographic reconstruction
On column B was carried on a tomographic reconstruction of a section of the column to verify that the velocity map was really well distribuited.
The tomographic reconstruction is showed in Fig. 8. At darker areas correspond the lower ultrasonic velocities. It can be observed that the velocity map is well distributed.
|Fig 8: Ultrasonic tomography of column B|
3.4. Ultrasonic measurements on cubic and cylindrical samples of similar material
The results of the the longitudinal (Vl) and shear (Vt) wave measurements on 6 cubes along the direction x,y,z are reported in Table 1. The first number indicated on the sample represents the carry block from which was extracted the cube. In Table 1 are also reported the calculated values of the dynamic elastic modulus (Ed) following the equation :
|Table 1: Ultrasonic velocity measurements on cubic samples|
The higher velocities of the longitudinal waves in the Z direction point out an anisotropy of the material. The shear ones seem to be less affected by an anisotropic behaviour.
The longitudinal velocity values of the 13 cylindrical samples measured before the mechanical testing are reported in Table 2:
|Sample||H(mm)||D(mm)||VL H(m/s)||VL D(m/s)||Volume(m3)||Peso(kg)||Densitא(kg/m3)
||Table 2: Ultrasonic velocity values on cylindrical samples|
The first number which is indicated on the sample represents the carry block from which was extracted the cylindrical samples. In the Table 2 the symbol * it means that the samples were obtained from the same curry block, but in the perpendicular direction with respect to the other.
3.5. Mechanical measurements on cylindrical samples
Compression test has been carried out on the same 13 cylindrical samples of the ultrasonic measurements. Values of the compressive strength (s ) and of the Stalic Elastic modulus (Estat) are reported in Table 3.
|Sample||Tension [kN]||Compressive strength [N/cm2]||Estat [N/ mm2]||e|
|Table 3: Results of the compressive mechanical testing.|
|Sample||Edyn [N/ mm2]||Estat [N/ mm2]|
|Table 4: Calculated values of the Elastic dynamic modulus and measured Elastic Static modulus|
Correlation diagram between the Dynamic Elastic Modulus (Edyn) calculated by means of non-destructive testing and the Static Elastic Modulus (Estat) measured by mechanical testing are shown in Fig.9, the estimated error was of 5%. The ratio between Estat and Edyn is estimated by a linear fit as 1,1. The correlation coefficient value is 0.97. It is quite similar to the correlation coefficient measured on rocks in laboratory measurements by other authors , that results approximately 0.99, and it is higher then the value (0.91) obtained in an other our paper . This result, obtained as a result of correlation between in situ and in laboratory tests, can be methodologically used for other in situ measurements in order to get information in a non destructive way on the mechanical properties of monuments stones.
|Fig 9: Calculated correlation between Estat and Edym Modulus|
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