The strength of the existing and proposed materials was analyzed based on their quality by conducting various tests. The tests are as follows:
2.2 Strength analysis of existing materials
In this, the quality and lifetime of the current state of the Alamparai fort are studied. The rebound hammer test, core sample test and its water absorption property, and so on. The requirements and setup procedure of each test are explained in this section.
The basic test for the analysis is the compressive and flexural strength of material after 28 and 90 days of building brick from the sample collected from the Alamparai fort. Another method for measuring the compressive strength is the rebound hammer test. The rebound hammer test carried out as per IS 13311 (Part 2) – 1992 [33] by using a rebound hammer. This test depicts the quality of the hardened mortar by applying pressure to the building through a device [12]. The device made up of spring material, so it rebounds to the value based on the hardness of the concrete. The quality of the concrete is weak if it has a low rebound value and vice versa.
A non-destructive method for finding the compressive strength depicted in Fig. 2.a by using the Schmitt hammer. The rebound hammer test carried out in all four directions (i.e., East, west, North and South) of the Alamparai fort. The compressive strength for each direction of the wall is as follows 17.45 Mpa, 37.88 Mpa, 33.51 Mpa and 42.70 Mpa. The compressive strength varied between 11.40 Mpa and 42.70 Mpa. Among these, the east-facing wall has minimum strength; due to the bombasts and struck by high waves during cyclones and tsunamis. It indicates that the east-facing wall requires restoration to retain the shape of the Alamparai fort.
The strength of the historical materials of the Alamparai fort analysed by conducting Brazilian tests like the core-drilling test and double punch test on the materials collected from it.
2.2.1 Core- drilling test:
In this, the core drilling test carried out in a horizontal direction (i.e., perpendicular to the direction of the wall) using a core bit of size 90mm in diameter. As the drilling progresses, the bit gets hotter. To cool down the bit, the air cooling with aspirator used instead of a water- cooling system. The water- cooling system leads to the absorption of water in the building, which degrades the building strength. This degradation avoided by the air-cooling system. Another advantage of this system; it utilizes the aspirator, which cleans the dust from the drilling. Because the accumulation of dust to the specimen also degrades the evaluation process. Here, the core drilling extracts four samples from the Alamparai fort from four directions of the wall. The diameter and height of each block; are the same as 90 mm and 200 mm respectively.
The process of extracting the sample from the Alamparai fort of size 90 mm in diameter and 200 mm in height depicted in Fig. 2. (b) and it is the same for all other samples. Some of the blocks break down during the testing process displayed in Fig. 2. (d); it is due to the dust accumulation during the drilling process. The final core samples for testing displayed in Fig. 2.(c); it collected by cooling the bit step by step and clean the bit frequently using an aspirator. Then, the obtained core samples subjected to the young modulus test and water absorption test to analyse their strength.
Additional to the compressive strength, the stress- strain behavior including the post-cracking behavior was determined. Dividing the applied force by the cross-sectional area, and dividing the mean of both longitudinal displacements by the height of the test specimen, respectively, leads to the stress-strain relations of five specimens plotted in Fig. 3(a). Both the compression strength and stiffness exhibit a large dispersion, and also the ductility behavior is different for each tested specimen. While both the red and the black stress-strain relation indicate large deformation ability, the three other curves show brittle fracture. The physically meaningless decrease of the compressive strain at the end of the black curve is the result of a tipping of the specimen (note that the displayed strain is derived from the mean of two displacements recorded at opposite surface points). All test specimens show an almost linear stress-strain behavior up to the compressive strength. However, no pronounced hardening such as in concrete can be observed. Two further displacement transducers recorded the lateral displacement to obtain information on Poisson’s ratio ν, which represents the quotient of the mean lateral to the mean longitudinal deformation. In Fig. 3 (b) for five tests Poisson’s ratio is plotted against the compressive strain in the elastic range of deformation from 1–2%. For the considered brick specimens, Poisson's ratio is relatively small between 0.05 and 0.12. Table 1 presented in material parameters of the core samples.
Table 1
Material Parameters of the core samples
Samples
|
Size of the core cylinder
(mm)
|
Density (p)
(Kg/m3)
|
Young modulus (E)
(Mpa)
|
Poisson Ratio(µ)
|
Shear modulus (G)
N/mm2
|
Shear Wave velocity (Vs)
m/s
|
I
|
90 Ø &
200 H
|
2113.42
|
1460
|
0.13
|
624
|
544
|
II
|
2021.72
|
1502
|
0.14
|
626
|
557
|
III
|
1985.25
|
1400
|
0.16
|
604
|
551
|
After performing the young's modulus test on the core samples, it subjected to the water absorption test. The initial weight of the core samples before the water absorption test is 2.796 kg, 2.824 kg, 2.678 kg and 2.972 kg. The water absorption carried out by immersing the samples into the water for 3 days. At the end of each day, its weight measured to determine the amount of water absorbed by the brick. Each core samples increase its weight by 9.58%, 9.8%, 9.63% and 13.05% after 24 hours. At the end of three days, the total weight of the samples increased by 10.15%, 10.45%, 10.34% and 16.76%.
2.2.2 Small scale Masonry test
The strength of the mortar joints analysed by small scale masonry test. Here, the mortar joint between two bricks used for the testing purpose. The joint subjected to the uniaxial compression test as in the Fig. 4 (a) .
The brick-mortar joint tested by applying pressure on both sides of the bricks. Three different colours in Fig. 4 (b) indicate the Stress-displacement curve caused in the brick-mortar joint due to the uniaxial stress on the three different samples from the Alamparai fort. Both uniaxial compression tests were conducted on specimens consisting of two bricks of 4 cm edge and a mortar joint with thickness of 10mm & 20mm, respectively. The displacement is higher when the pressure applied to the joint increases. Based on the statement from [13] the cracks in the heritage structure is due to the triaxial pressure developed in the brick, it makes the joint weakens and reduces its strength; it gets a crack on the outer part of the wall.
2.2.3 Double Punch test
The double punch test is an important method to analyse the mortar strength in historical buildings by following the DIN 18555-9:1999 standard [14]. Here, the test carried out by applying a load of 4 KN cell using a compressive machine of two special punching devices to the mortar extracted from the building. It is also a uniaxial strength test and it causes cracks in the mortar as in the Fig. 4 (c). The crack occurs due to the triaxial pressure developed during the test process on a smaller area of mortar. The mortar specimen height used in the DPT tests was equal to the bed point thickness, as per DIN18555-9 standard the mortar specimen dimension were approximately 50mm. The strength (\(\sigma\)) for producing the crack during the DPT can be calculated using Eq. 1.
![](data:image/png;base64,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)
Where Fmax is the maximum experimental load and radius is ten millimetres. Based on this, the double punch test carried out on five samples extracted from four directions of the wall (i.e., East, west, north and south) from the Alamparai fort. The corresponding mortar thickness and its compression strength tabulated in Table 2 and Fig. 4 (c); shows that the sample got cracks when the maximum load applied to it.
Table 2
DPT analysis of existing mortar samples
Samples
Collection
|
No of samples (Pcs)
|
Specimen
Thickness
(mm)
|
Average Specimen
Thickness
(mm
|
Avg
Load (KN)
|
Values (Mpa)
|
Avg Value
(Mpa)
|
Standard
Deviation (values)
(Mpa)
|
Standard
Deviation
(thickness)
(Mpa)
|
COV
(Values)
|
COV
(Tk)
|
East wall
|
5
|
13.7
15.5
12.5
13.2
12.7
|
13.52 (17.52)
|
3.68
|
1.79
2.95
2.92
1.92
3.52
|
2.62
|
0.66
|
1.07
|
0.25
|
0.41
|
West wall
|
5
|
12.8
14.2
16.4
13.7
17.2
|
14.86
(19.61)
|
3.92
|
2.89
2.65
2.92
3.92
3.52
|
3.18
|
0.47
|
1.66
|
0.15
|
0.52
|
South wall
|
5
|
11.6
12.7
18.4
12.5
13.2
|
13.68
(18.43)
|
3.27
|
3.68
3.92
2.72
1.86
3.27
|
3.09
|
0.73
|
2.42
|
0.24
|
0.78
|
North wall
|
5
|
13.2
14.6
17.7
12.7
18.5
|
15.35
(19.61)
|
3.78
|
3.72
3.92
4.72
2.76
4.27
|
3.87
|
0.65
|
2.35
|
0.17
|
0.61
|
The specimens total thickness is shown in brackets (with the gypsum caps) |
The cylindrical samples of two diameters, 90 mm and 120 mm collected from the Alamparai fort using a core drilling process. These samples subjected to a load test to determine the tensile strength of the material. In this, the load varies from 0 KN to 35 KN. Then, the displacements in its length and width measured using the horizontal and vertical LVDT. Based on this displacement and the load, the tensile strength calculated using formula in [16].
The tensile strength in Table 3 indicates the strength between the mortar and the brick, while in compression strength, the mortar bonding only analysed. Due to this, there is a variation between the values in tensile strength.
Table 3
Tensile strength test on core samples
Sample Name
|
Diameter and Height (mm)
|
Area(mm2)
|
Tensile strength (N/mm2)
|
ST-1
|
90 &200
|
6362
|
0.34
|
ST-2
|
0.36
|
ST-3
|
150 &200
|
17672
|
0.57
|
ST-4
|
0.68
|
2.2.4 Marsh cone test
The cracks in the walls cured by injecting the mortar mixture into them; restore the ancient structures. This mortar mixture should have good fluidity; it also possesses greater strength to renovate the building. The mortar mixture fluid nature studied using the Marsh cone test by following ASTM C939, EN445 standard [15]. Based on the XRD analysis, the lime is the base mortar in Alamparai fort construction. Hence, in this, the lime is mixed with two solutions. One is the water; the other is the organic water. The organic water is the admixture, which improves the strength of the building. The organic water was prepared by mixing 2.5% of both Gur and Haritaki in half a litre of water and kept aside for 15 days for the fermentation process. Then, the organic water extracted from the fermented solution.
Then, both the solutions subjected to the marsh cone test by injecting the mixture into the marsh cone as in Fig. 5 (a) upper picture and it’s time for reaching the container in ; its value tabulated in Table 4.
Table 4
S. No
|
Description
|
Time taken to discharge (s)
|
1
|
Lime + Water
|
13.02
|
2
|
Lime + organic matter
|
7.68
|
As per the ASTM C939 standard, the proposed organic mixture consumes less time for discharge from the marsh cone of 7.68 s than 13.02 s for lime mixture. The minimal discharge time indicates that the proposed organic matter can fix the crack effectively in the walls of the Alamparai fort. The stability test conducted by observing zero variation in the final product between both the water and organic mixtures as per ASTM C940 standard. Because Zero variation in the mixture can exhibit the homogeneity property as it hardened in future. Based on this, the Fig. 5(a) shows that the proposed organic mixture exhibit homogeneity between both the mixtures. Therefore, the proposed organic solution can restore the Alamparai fort. Then, the proposed organic matter subjected to different tests to evaluate its strength.
2.2.5 Diagonal shear test
The proposed Gur and Haritaki mixed in different proportions with lime and sand to form a mortar mixture. By using this mixture, the square block is built up to perform the diagonal shear test. The diagonal shear test carried out on the square shape block by applying the load in vertical direction from the top side and its force transmitted to the bottom side as in Fig. 5 (b) and it has two displacement transducers attached in horizontal and vertical directions to measure the variations in length and width of the block. Based on the displacement values from the transducers and the formulas used in [16] utilized to calculate the shear stress, shear strain, rigidity modulus and tensile strength and these values tabulated in Table 5.
Table 5. Material properties of Diagonal shear test
Samples
|
Density (p)
Kg/m3
|
Young Modulus (E) N/mm2
|
Poisson Ratio (µ)
|
Shear Modulus
N/mm2 (G)
|
Shear Wave Velocity Vs
(m/s)
|
I
|
1812
|
554
|
0.17
|
237
|
361
|
II
|
1811
|
595
|
0.17
|
254
|
375
|
III
|
1792
|
527
|
0.17
|
225
|
355
|
I
|
1812
|
554
|
0.17
|
237
|
361
|
Based on these values, the deflection of the building versus load is plotted in Fig. 5 (c) and it shows that as the load progresses, the deflection of the building tends to increases and it may result in deformed state of the building. All the above strength analysis performed only on the walls of the Alamparai fort. The main block arch of the fort is not analysed. Most of the historical architecture also carried out analysis only on the walls and block of the building. Hence, in this, the arch analysis conducted by performing the seismic analysis using Ansys software.
The purpose of modal analysis to analyse the behaviour of the building under seismic conditions. During seismic conditions, the building gets excited; it gets damaged when the earthquake frequency exceeds its natural frequency. The results from the strength of the core samples (Poisson ratio, shear strain and stress and young's Modulus), the modal analysis of the conical arch carried out using Ansys software. Then, it subjected to vibrations of different frequencies as tabulated in Table 6.
Table 6
Seismic analysis of arch and Fort
|
Frequency (Hz)
|
Mode
|
Arch`
|
Fort
|
1
|
2.7783
|
0.91447
|
2
|
4.6342
|
1.6496
|
3
|
6.9002
|
2.0362
|
4
|
127.05
|
2.7328
|
5
|
135.88
|
2.8298
|
6
|
186.49
|
3.7596
|
7
|
214.33
|
3.865
|
8
|
218.94
|
4.386
|
9
|
289.7
|
4.4231
|
10
|
310.14
|
4.9585
|
The arch gets excited about each frequency, but its shape deformed when it excited two modes, mode 5 & mode 8. During these two modes, 5 and 8, the arch gets to deform towards the right or left direction, as in Fig. 6 (a) to (h). The individual responses of the building concerning the time of the vibrations displayed in Fig. 7 (a) to (f).
The above responses are the existing material-based arch response during seismic frequency ranges from 2 Hz to 310 Hz. The peaks in the response curve indicate the natural or cut-off frequency of the arch. The term cut-off frequency indicates the starting frequency for building deformation. Based on the response curve for all conditions like acceleration to stress, the building gets deform after mode 5. because the values get reduced at this point. Therefore, the strength of the arch also analyzed by this seismic analysis.
The above strength analysis determines that the Alamparai Fort requires a restoration process to restore its historical heritage for longer periods. Based on the stability tests results, the Gur and Haritaki used in mortar mixture with lime to restore the fort.