Study on the Performance of Grouting Material for Shilangtan Cliff Carving Group

Study on the Performance of Grouting Material for Shilangtan Cliff Carving Group

Zheng Liu

Faculty of Architecture and Civil Engineering Huaiyin Institute of Technology, Huaian, China

Ningbo Peng

Faculty of Architecture and Civil Engineering Huaiyin Institute of Technology, Huaian, China

Jiabao Liu

Faculty of Architecture and Civil Engineering Huaiyin Institute of Technology, Huaian, China

Dongxu Jiang

Faculty of Architecture and Civil Engineering Huaiyin Institute of Technology, Huaian, China

Jianwei Wang

Faculty of Architecture and Civil Engineering Huaiyin Institute of Technology, Huaian, China

Bo Sun

Northwest Research Institute Co. Ltd. of China Railway Engineering Corporation, Lanzhou, China

Dong Jiang

Faculty of Architecture and Civil Engineering Huaiyin Institute of Technology, Huaian, China

Abstract – In this study, the rock powder, inorganic mineral polymer and low alkali sulphoaluminate cement were selected to design the ratio of A, B and C grouting materials for the dangerous rock mass of Shilangtan cliff carving group. The undisturbed rock, pure grouting material and the combination of original rock and grouting material were prepared, and the wave velocity, shear and tensile strength under 3d, 7d, 14d and 28d curing ages were tested. The results show that the mechanical indexes of each sample increase first fast and then slow with the increase of curing age, and tend to be stable after 28 days. The performance of the original rock-grouting material combination is significantly improved compared with the original rock. The ratio of A and B is suitable for large crack repair. The ratio of A has better shear performance, and the ratio of B has better tensile performance, less polymer dosage and higher cost performance. The research provides experimental basis for the grouting repair of the stone carving group, and also provides theoretical support for the selection of stone cultural relics repair materials.

Keywords – Shilangtan Cliff Carving Group; grouting materials; Heritage conservation;

1. INTRODUCTION

   The Shilangtan Cliff Carving Group is located in Yongxing County, Chenzhou City, Hunan Province, China. In 2013, it was announced by the State Council as the seventh batch of national key cultural relics protection units [1]. It is one of the representatives of China ‘s cliff stone culture, with a unique historical, cultural and artistic value. However, due to the influence of natural environment and man-made destruction and other factors, the safety protection of the Shilangtan Cliff Rock Carvings has attracted more and more attention. In order

   to protect and repair the dangerous rock mass above the Shilangtan Cliff Carving Group, grouting technology is adopted as the repair method.

   Fig 1 The geographical location of the Shilangtan stone carving group

   In 2013, it was announced by the State Council as the seventh batch of national key cultural relics protection units.

   Fig 2 Panoramic facade photos of Shilangtan cliff carving group

   In the field of cultural relics protection and restoration, grouting technology has attracted much attention because of its accuracy, reliability and economy. In order to achieve specific engineering purposes, a variety of special grouting materials have been developed at home and abroad. Wu Z [2] compared the optimized loess residual soil grouting material with the traditional grouting material for practical engineering. Hasan H M [3] studied the effect and progress of adding auxiliary cementitious materials to grouting materials. Liu Yawei [4] studied the effect of silica fume and aluminum powder paste content on the properties of grouting materials. Gao Shengmiao [5]analyzes the characteristics of groundwater leakage in hard rock strata, and improves the performance of grouting materials by adding admixtures. Miao Hechao [6] studied the characteristics of fly ash-based anti-seepage grouting materials with different proportions, and provided an optimal mix ratio for a grouting project. Zhang Cong [7] studied a new type of clay cement composite grouting material, which can be used for karst treatment below the water surface. Zhang Yi [8] prepared a new type of high expansion grouting material for cave filling by using the red clay waste residue produced by field leveling and pile hole excavation at the construction site. Zhao [9] found that microbial induced carbonate precipitation ( MICP ) repair technology can improve the shear properties of rocks.

   Fig 3 Original rock

   1. Grouting Material

      According to literature research, expert interviews, combined with fracture development and climate impact in the area where the project is located, in view of the relatively small weight of the block, mainly spalling failure, belonging to the surface plated dangerous rock mass, it is proposed to use inorganic mineral polymer, low alkali cement and rock powder for grouting.The specific ratio of grouting materials is shown in Table I.

      TABLE I. Mix Proportions for grouting material

2. EXPERIMENTAL
   1. Experimental Purpose
      • Test the mechanical properties of undisturbed rock ( Shilangtan cliff carving group ).
      • To determine the mechanical properties of grouting materials, clarify the influence of material ratio on mechanical properties, and carry out material degradation test to determine the development of mechanical properties of materials under environmental degradation.
      • Preparation of the ‘ original rock-reinforcement material ‘ combination, and explore the mechanical properties of the bonding surface and the combination.
   2. Experimental Contents

      In order to ensure the applicability of grouting materials in the emergency reinforcement project of dangerous rock mass, the final ratio and process of grouting materials in different curing ages were determined by experiments. The wave velocity, shear strength and tensile strength of the samples before and after grouting were compared, and the reinforcement materials more suitable for grouting bonding were obtained.

   3. Material Proportions
   1. Original Rock

      Due to the particularity of the stone carving relics of Shilangtan Cliff, the local cultural relics authorities suggest that drilling and trenching should not be used. Therefore, the rock samples were taken from the Cretaceous purple-red pebbly sandstone of the Shilang Formation in Xiangzhou Village, Bianjiang Town, Yongxing County, Chenzhou City, outside the cultural relics control zone.

      For grouting material samples with different proportions, they are represented by A, and combined with the naming method of grouting materials with different proportions. For example, AA is a grouting material sample under A ratio.

      mater ial	type	inorg anic mineral polymer	low alkalinity sulphoaluminate cement	meal	water
      propor tions	A	1.9	0	0.6	0.6
      	B	1	0.9	0.6	0.6
      	C	0.4	1.5	0.	0.6

       

      Fig 4 Grouting material sample diagram

      1. Preparation of ‘ original rock-grouting material ‘ combination

      Inorganic mineral polymers and low-alkali cement are mainly used in macropores ( > 8mm ). For different original rock-grouting material combination samples, it is represented by B, and combined with different ratio of grouting material naming method, for example, AB is the original rock-grouting material combination sample under A ratio.

      Taking the shear strength as an example, the rock sample is prepared into a cube with a bottom surface of 50mm × 50mm and a height of 25mm. The tensile strength is considered to be directly stretched. The total height of the prepared sample is 160mm, which is 80mm for sandstone, 80mm for grouting material and 30mm for convex part.

      Fig 5 Grouting material-original rock sample schematic diagram. a. shear specimen model and size diagram, b. prepared shear specimens, c. tensile model and size diagram, d. the prepared tensile specimen.

3. RESULTS

   This study mainly analyzes the influence of material ratio and curing age on the performance of adhesive materials. Firstly, according to the order of wave velocity test, shear test and tensile test, the attenuation law and variation range of various indexes of undisturbed samples, grouting material samples with different proportions and original rock-grouting material samples at different curing ages are introduced one by one. Analyze the changes of grouting materials with different proportions under the same conditions, and explore the most suitable grouting material ratio for the protection of rock cultural relics..

   1. Wave Velocity Test Data Analysis

      The wave velocity is an important index to reflect the physical and mechanical properties of engineering materials. Because the mineral composition, joints and cracks contained in the rock are different, the influence on the acoustic velocity is also different. Therefore, acoustic wave testing is widely used in the fields of macroscopic parameter measurement and quality evaluation of rock and rock engineering.

      Fig 6 Wave velocity test diagram. a. non-metallic ultrasonic tester, b. wave

      velocity test photos.

      1. Original Rock

         For the wave velocity measurement data of the undisturbed sample as shown in Table II, it can be seen that the average wave velocity of the undisturbed sample is 2.840 km / s.

         TABLE II. Wave velocity test data table of original rock

         No.	Wave velocity(km/s)					average
         	1	2	3	4	5
         1	2.455	2.463	2.463	2.686	2.686	2.551	2.840
         2	2.996	3.046	3.016	2.990	2.899	2.990
         3	3.000	2.988	3.016	2.965	2.926	2.979

      2. Different Ratio Of Grouting Material Samples

         According to Figure 7, the change of wave velocity of grouting material samples with different ratios can be obtained

         : Under the same curing conditions, the variation law of wave velocity of grouting materials with different ratios is basically similar, showing an upward trend, but the change rate and change range of different grouting material indexes are different. During 3-28 days, BA and CA increased rapidly, while AA increased slowly. AA growth rate is small, from 2.715 km / s to 2.780 km / s, an increase of 0.065 km / s, while BA from 2.510 km / s to 2.771 km / s, an increase of 0.261 km

         / s, CA from 2.316 km / s to 2.515 km / s, an increase of 0.199 km / s . For the wave velocity index of grouting materials with different ratios, under the same curing conditions, the change order of wave velocity index is : AA > BA > CA.

         Fig 7 Wave velocity variation curves of grouting material samples with

         different proportions.

      3. Original Rock-Grouting Material Combination

         According to Figure 8, the wave velocity changes of different original rock-grouting material combinations can be obtained : Different original rock-grouting material combination specimens within 28 days of normal maintenance, the change law of the wave velocity of each sample is the same, showing an upward trend ; when the curing time is 3d- 7d, the change trend of the wave velocity of the samples is different. The growth rate of BB is fast, while AB and CB are less than BB. At 14d-28d, the growth rates of AB and BB were roughly the same, and CB was lower than AB and BB. Compared with the original rock sample, the wave velocity index of different original rock-grouting material combination samples has a higher improvement, so its effect on the improvement of the original rock performance is obvious, and it can be used as a repair material to repair large cracks. Due to the high content of polymer in AB and BB, and less in CB, combined with the change trend of wave velocity index, it can be seen that the polymer has a good repair effect on the interior of the material, and there is a certain growth trend with the growth of the age, so it can be considered as an important part of grouting repair material . For the wave velocity index of different original rock-grouting material combinations, under the same curing conditions, the change order of the wave velocity index is : AB > BB > CB.

         Fig 8 Wave velocity variation curve of original rock-grouting material

         combination specimen.

   2. Analysis Of Shear Test Data

      The variable angle plate method is to use the press to apply the vertical load, through a set of special fixture to make the specimen produce shear failure along a certain shear surface, and then analyze the shear surface through the static equilibrium condition. The normal stress and shear stress on are used to draw the relationship curve between the normal compressive stress and the shear stress , and the cohesion and internal friction angle of the rock are obtained.

      The variable angle shear test can evaluate the fracture morphology and characteristics of the material, measure the performance parameters such as the shear strength of the material, and better reflect the fracture behavior of the material under the shear stress.

      Fig 10 Shear curve of original rock

      1. Different Ratio Of Grouting Material Samples

         According to Figure 3-6, the change of shear strength of grouting material samples with different proportions can be obtained : The shear strength index of grouting material samples with different ratios has the same trend with the increase of curing age, showing an upward trend, but the specific change rate and size are different. The increase of internal friction angle of AA and BA is consistent, but the increase of cohesion is different. The increase of BA is obviously smaller than that of AA at 7d-28d. The change range of internal friction angle of both is within 2.5 °, and the change of cohesion is within 0.4MPa. The internal friction angle and cohesion of CA change little during the curing period. The change of friction angle does not exceed 1 °, and the change of cohesion does not exceed 0.2 MPa. For the shear index of grouting materials with different proportions, under the same curing conditions, the order of shear index change is : AA > BA > CA.

         Fig 9 Variable angle shear test schematic diagram.

         1) Original Rock

         The original rock shear test data are shown in Table III below. Fom the analysis of Figure 10, the internal friction angle of the original rock is 45.7017 °, and the cohesion is 6.0514 MPa.

         No.	Diameter(cm)	Area(cm2)	F/ N	Angle(°)
         1	55.00	2374.63	115.34	50	31.22	37.21
         2	55.00	2374.63	75.31	55	18.19	25.98
         3	55.00	2374.63	44.16	60	9.30	16.11
         4	55.00	2374.63	31.54	65	5.61	12.04
         5	55.00	2374.63	19.53	70	2.81	7.73

          

         TABLE III. Shear test data table of original rock

         Fig 11 Shear strength change curve of grouting material samples with different proportions. a. internal friction angle variation curve, b. cohesiveness variation curve.

      2. Original Rock-Grouting Material Combination

      According to Figure 12, the shear strength changes of different original rock-grouting material combinations can be obtained : With the increase of age, the shear strength index of different original rock-grouting material combination samples shows an upward trend, but the specific increase range is different. The variation range of internal friction angle of AB is 2 °, and the cohesion increases from 5.775 MPa to 6.382 MPa, which increases by 0.607 MPa. The shear strength index of BB was lower than that of AB at different ages, but it was better than that of CB. The internal friction angle increased from

      39.98 ° to 41.75 °, increased by 1.77 °, and the cohesion increased from 5.401 MPa to 5.994 MPa, increased by 0.593 MPa. The shear index of CB is much lower than that of AB and BB.Compared with the index at 3d, the internal friction angle increased by 0.55 ° and the cohesion increased by 0.32 MPa at 28 d. The order of shear strength index of different original rock-grouting material combination samples at 28 d is : AB > BB > CB.

      Fig 12 The shear strength change curve of the original rock-grouting material combination sample with different proportions. a. internal friction angle variation

      curve, b. cohesiveness variation curve.

   3. Tensile Test Data Analysis

   The indoor measurement method of rock tensile strength generally adopts direct tensile method and splitting method. The tensile strength of rock refers to the maximum stress value that rock can withstand under tensile conditions. Because the Brazilian splitting method is simple, the measured tensile strength is very close to the tensile strength measured by the direct tensile method, so this method is commonly used to determine the tensile strength of rock.

   In this test, the Brazilian splitting method was used to measure the tensile strength of the grouting material samples with different proportions, and the direct tensile method was used to measure the tensile strength of the original rock- grouting material combination sample.

   Fig 12 The variation curve of tensile strength of grouting materials with

   different proportions

   3) Original Rock-Grouting Material Combination

   According to Figure 13, the tensile strength of different original rock-grouting material combination samples at 28 days of curing can be obtained : At 28 d, the tensile strength shows : BB > AB > CB, and the tensile strength of AB and BB is higher, which is 0.98 MPa, 1.2 MPa and 0.68 MPa. That is to say, the grouting materials with two ratios of A and B are more suitable for bonding materials. Compared with the change of shear strength index, the tensile performance of B ratio is better than that of A ratio, so two kinds of grouting materials can be selected according to the actual situation of the site, the shear performance of A ratio is better than that of B ratio, while the tensile performance is the opposite.

   Fig 11 Tensile test apparatus schematic diagram. a. brazil splitting test apparatus, b. direct tensile test apparatus.

   1. Original Rock

      The tensile test data of the original sample are shown in Table IV below. From the analysis of table 3-3, the average tensile strength of the original sample is 1.96 MPa.

      No.	d	h	Fn	P
      6	55.00	50.00	8.36	1.935
      7	55.00	50.00	7.87	1.822
      8	55.00	50.00	9.15	2.118

       

      TABLE IV. Original rock tensile test data table

   2. Different Ratio Of Grouting Material Samples

   According to Figure 12, the change of tensile strength of grouting material samples with different proportions can be obtained :The tensile strength of grouting material samples with different proportions is on the rise, but the rising rate and rising range of grouting materials with different proportions are not the same. The increase rate of AA tensile strength index is greater than that of BA and CA at 3d-14d, but after 14d, the growth rate of the three materials is basically the same.The tensile strength growth range of AA, BA and CA is 0.42 MPa,

   0.176 MPa and 0.2 MPa, respectively.Under the same curing conditions, the change order of tensile strength index is : AA > BA > CA.

   Fig 13 The tensile strength diagram of different original rock-grouting

   materials at 28d

4. CONCLUSION

Based on the rock mass near the cliff carving group of Shilangtan, this study explores the repair materials that have been applied in the protection of cultural relics in combination with various bonding materials in the field of cultural protection, especially the performance of bonding materials, and then analyzes the performance changes of different types of bonding materials, and clarifies the ratio of different materials and mineral composition. Secondly, familiar with the construction process and working conditions of bonding materials, and prepare different proportions of bonding materials to test the changes of mechanical properties such as shear strength and tensile strength at different curing ages. By testing and comparing the properties of the materials, the conclusions are as follows :

• By measuring the physical indexes of grouting materials and different original rock-grouting material combination samples, it is found that with the increase of curing time, the wave velocity of the sample generally shows a continuous increase and maintains a stable trend after 28 days of curing.
• By measuring the mechanical indexes of grouting materials and different original rock-grouting material combination samples, it is found that with the increase of curing time, the shear strength and tensile strength of the samples show a rapid increase in the early stage of curing, and the increase rate slows down in the later stage, and maintains a steady upward trend after 28 days of curing.
• Both grouting materials A and B are suitable for the repair and reinforcement of large cracks, and from the perspective of engineering economic rationality, B grouting material is recommended because B is more cost-effective. Although its performance indicators are slightly lower than A, it uses less polymer, which greatly reduce the project cost.

This study provides a reliable experimental basis for the grouting repair of the Shilangtan Cliff Carving Group, and provides a reference for the selection of grouting materials. It provides important support for the preventive protection of the Shilangtan Cliff Stone Inscriptions Group and guarantees the long-term preservation of cultural heritage. It also deepens the understanding of different proportion bonding materials, provides more material selection and

application schemes for the field of cultural relics protection, provides theoretical basis and scientific basis for the restoration of stone cultural relics, and promotes the efficient restoration work.

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