J. Cent. South Univ. (2020) 27: 2999-3012
DOI: https://doi.org/10.1007/s11771-020-4524-6
Effects of temperature and age on physico-mechanical properties of cemented gravel sand backfills
JIANG Fei-fei(江飞飞)1, 2, ZHOU Hui(周辉)1, 2, SHENG Jia(盛佳)3, 4,KOU Yong-yuan(寇永渊)5, LI Xiang-dong(李向东)3
1. State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and
Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China;
3. National Engineering Research Center for Metal Mining, Changsha Institute of Mining Research Co., Ltd., Changsha 410012, China;
4. School of Resource & Environment and Safety Engineering, Hunan University of Science and Technology, Xiangtan 411201, China;
5. Jinchuan Group Co., Ltd., Jinchang 737104, China
Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract:
Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20-60 °C in the next few decades. In this paper, two types of cemented gravel sand backfills, cemented rod-mill sand backfill (CRB) and cemented gobi sand backfill (CGB), were prepared and cured at various temperatures (20, 40, 60 °C) and ages (3, 7, 28 d), and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests. Results show that: 1) the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures. The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages. 2) The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB. With the increase of temperature, the compressive failure modes changed from X-conjugate shear failure to tensile failure, and the integrity of specimens was significantly improved. 3) Similarly, the shear performance of CGB is generally better than that of CRB. The temperature has a weaker effect on shear strength than age, but the shear deformation and shear plane morphology are closely related to temperature.
Key words:
Cite this article as:
JIANG Fei-fei, ZHOU Hui, SHENG Jia, KOU Yong-yuan, LI Xiang-dong. Effects of temperature and age on physico-mechanical properties of cemented gravel sand backfills [J]. Journal of Central South University, 2020, 27(10): 2999-3012.
DOI:https://dx.doi.org/https://doi.org/10.1007/s11771-020-4524-61 Introduction
Over the past decades, the backfill mining method has been widely used in underground mines due to its advantages in dealing with mined-out voids, managing ground pressure, improving mining environment and increasing ore-recovery ratio [1-4]. One of the critical issues in deep backfill mining is the increasing ambient temperature, in terms of safety and stability of backfill [5-8].
Cemented backfill (CB) is a homogeneous mixture of aggregate, hydraulic binder, water and necessary additives [9, 10]. The physico- mechanical properties of CB directly affect the safety and stability of mining disturbed area, and there are many factors influencing the performance of CB. In addition to the characteristics of filling materials (e.g., density, particle size, and chemical composition) and mixing proportion [11-14], the ambient conditions (e.g., temperature, humidity, and age) can also greatly influence their properties [15]. Previous studies revealed that the behaviour of CB is temperature-dependent [16, 17], and a higher curing temperature can facilitate the strength of CB for shorter ages because of the rapid hydration process [15, 18]. The age can also influence the hydration degree and consolidation process, thus causing significant changes in physical and mechanical characteristics [19-21]. However, the effects of temperature and age on the physico-mechanical properties and its variation laws of CB are often quite different due to the difference in types and characteristics of aggregates.
The rod-mill sand (RMS) and gobi sand (GS) are two types of gravel sand (i.e., aggregate) that are widely distributed and abundant in northwest China. The CBs prepared by these two types of gravel sand have been used in some underground backfill mines in northwest China due to their advantages in strength performance and cost [22]. Previous studies mainly focus on the properties of cemented gravel sand backfill at room temperature [23-25]. However, with the increase of mining depth, the CB would inevitably be exposed to the ambient temperature of 20-60 °C in the next few decades. At present, the effect of temperature on the characteristics of cemented gravel sand backfill has not been well-investigated.
In this paper, the RMS and GS produced in Gansu province, northwest China, were used as filling aggregate to prepare the specimens of cemented rod-mill sand backfill (CRB) and cemented gobi sand backfill (CGB) with a cement-sand ratio of 1:4 and slurry concentration of 78%. The specimens were continuously cured at three different temperatures (20, 40 and 60°C). Laboratory tests were carried out for the physico- mechanical properties (including thermal expansion rate, ultrasonic properties, compressive and shear strength) of CRB and CGB at different ages (3, 7, 28 d) that are closely related to the temperature and of particular concern in deep mining. The influence of temperature on the physico-mechanical properties of CBs is discussed emphatically, and the performance difference between CRB and CGB at various temperatures and ages is compared. The experimental results can contribute to a better understanding of the effects of temperature and age on the physico-mechanical properties of cemented gravel sand backfills, and can also provide positive guidance for the performance optimization of CB in deep backfill mines in northwest China.
2 Experimental
2.1 Materials
The RMS and GS produced in Gansu province, northwest China were used in the experimental study. The RMS was obtained from open-pit mining, which underwent the processes of crushing, sieving, and rod milling. In contrast, the GS was acquired from the sieved gobi aggregate in the Gobi Desert, which is a relatively simple process. The ordinary Portland cement (OPC) was used as the hydraulic binder in the experimental investigation.
The particle size distribution of gravel sands is shown in Figure 1 and Table 1, and the median particle sizes of RMS and GS are 1.434 mm and 0.807 mm, respectively. The gradation of RMS matches a more obvious normal distribution than GS, indicating that the multi-process techniques are beneficial to gradation control of aggregate. The chemical compositions of RMS, GS and OPC were examined using a D8 Advance X-ray diffractometer with the results shown in Table 2. The contents of SiO2 in RMS and GS are 71.47% and 72.97%, respectively; while the contents of SO3 are low (1.13% and 0.32%, respectively. It is conducive to improving the strength of CB [26, 27]. The chemical compositions of RMS and GS are similar, and the main difference between them is the particle size distribution.
Figure 1 Particle size sieving results of RMS and GS
Table 1 Particle size characteristics of RMS and GS
Table 2 Main physical properties and chemical compositions of gravel sands and binder
2.2 Specimen preparation and testing program
Two types of dismountable transparent acrylic moulds were designed and manufactured for the laboratory tests. Mould type I was a cylindrical mould that had dimensions of 50 mm×100 mm (diameter×height), and type II was a cube mould with a side length of 100 mm. In the test, the cement to sand ratio was 1/4, and the filling slurry concentration was 78%. First, the required solid masses of OPC and gravel sand were put into a mixing container and stirred for 5 min. Then, the required amount of water was added to the blender and stirred for another 10 min. Next, the well-mixed slurry was poured into the moulds slowly, waiting for 12 h for initial setting at room temperature (20 °C). Finally, the moulds were removed, and the specimens were put into a constant-temperature and humidity-curing box.
A total of 102 specimens of CRB and CGB, including 36 cube specimens and 66 cylindrical specimens, were prepared using the procedures mentioned above, as per the experimental purpose and program (see Table 3). Two types of specimens were cured in a constant humidity of (95±1)% at various temperatures (20, 40 and 60 °C) and ages (3, 7 and 28 d). After the curing process was completed, the weight and size of all specimens were measured, and the physical parameters such as coefficient of linear thermal expansion (CLTE) and ultrasonic pulse velocity (UPV) were tested. Next, the unconfined compressive test (UCT) and direct shear test (DST) were conducted. Each test was repeated at least twice, and the average was considered the needed value of the tested specimen. The specific testing program is shown in Table 3.
Table 3 Laboratory testing program
2.3 Testing apparatuses and procedures
1) Linear thermal expansion test. An XPZ-300 linear expansion coefficient tester was adopted to measure the CLTE. The target temperature of the test was set to 80 °C and the temperature gradient was 5 °C/min. The test can be started after the cylindrical specimen was put into the furnace chamber. Data were automatically recorded by internal strain gauge in the top in real-time, and the data can be exported to the computer for further processing after tests were completed. The CLTE can be calculated by
(1)
where T0 and T are initial temperature and target temperature, respectively; L0 is the length of specimen at the initial temperature; LT is the length of specimen at the target temperature; ΔL is the difference value between LT and L0.
2) Ultrasonic pulse velocity test. An apparatus of RSM-SY5(T) non-metallic acoustic detector was adopted to measure the ultrasonic pulse velocity (UPV), and the ultrasonic variation laws of CRB and CGB at various and ages were compared and analyzed. The UPV value can be calculated by
(2)
where L is the interval length to be tested between two parallel planes of the standard specimen; t is the propagation time tested when the transducers are well coupled with the specimen at both ends; and t0 is the net transmission time between transmitter and receiver.
3) Unconfined compressive test and direct shear test. An RJST-616 multifunctional tester (developed by Institute of Rock and Soil Mechanics, Chinese Academy of Sciences) was used for the mechanical tests. The maximum normal and shear loading forces of this apparatus are 150 and 200 kN, respectively. The tests can be conducted as follows: i) Cylindrical specimens were adopted for UCT. In this test, only the displacement-control mode was used to apply the normal load at a rate of 0.5 mm/min, until the specimens were destroyed by compressive stress. ii) Cube specimens were used in DST. First, the force-control mode was used to load the normal force to 5 kN at a rate of 0.1 kN/s and kept the force constant. Then, the displacement-control mode was adopted to load the shear force at a rate of 0.3 mm/min, and the test could be stopped automatically when the shear displacement reached 15 mm.
3 Results and analysis
3.1 Linear thermal expansibility
The test results of CLTE at various ages (3, 7, and 28 d) are shown in Figure 2. It displays that the temperature and age have significant effects on the thermal expansion properties of CBs. The CLTEs of both CRB and CGB increase linearly with increasing temperature, while the growth rate of CLTE at ages varies differently with increasing temperature. The growth rate of CLTE of CRB and CGB with 7 d is the fastest, while that with 28 d is the slowest. In the early stage of the test, the CLTE value with 3 d is generally the maximum, while that with 28 d is the minimum. However, the CLTE with 7 d exceeds the value with 3 d when the temperature rises to a specific value (point 1 in Figure 2).
Figure 2 Relationship between CLTE and temperature of CRB and CGB
By comparing the CLTE values between CRB and CGB at the same age, it can be seen that the CLTE of CGB is generally higher than that of CRB at the beginning of the test, and this situation will change with the increasing temperature. For example, there is a turning point (i.e., point 2 in Figure 2) between CRB and CGB at the age of 3 d, the temperature at point 2 is 65°C and the CLTE3d is 1.4649×10-6 K-1, which is evident that the CLTE value of CRB is higher than that of CGB after this point. Similar trends were also observed at the age of 7 d and 28 d; the difference between CGB and CRB gradually decreases with increasing temperature in the whole testing process. At 80°C, the differences between CGB and CRB are reduced to 0.0555×10-6 K-1 at the age of 7 d and 0.2185×10-6 K-1 at the age of 28 d, respectively. It suggests that the temperature has a more significant effect on the thermal expansibility of backfill at early ages (e.g., 3 d), and the expansion rate of CGB is slower than that of CRB.
During the test, the axial strain value of the specimens and the corresponding temperatures can be checked through the control screen in real-time, so the initial expansion temperature (IET) of the specimens can be obtained directly from the screen. Figure 3 shows IET testing results of CRB and CGB at various ages, indicating that the IET increases with the growth of age. The IET of CRB is higher than that of CGB at the same age, suggesting that CGB begins to expand and deform at a relatively lower temperature.
Figure 3 Initial expansion temperature (IET) comparison between CRB and CGB
3.2 Ultrasonic performance
Figure 4 shows the UPV test results of CRB and CGB at various temperatures and ages. It is obvious that the ultrasonic performance of CRB and CGB is positively correlated with temperature and age, and the UPV of CGB is higher than that of CRB under the same conditions. The effects of age and temperature on the UPV are interdependent. According to the test results, the UPV values of CRB and CGB at 60 °C are substantially higher than those at 40 °C and 20 °C at early ages (e.g.,3 d). In contrast, the UPV at 20 °C increases relatively faster with ages than those at 40 °C and 60 °C, so the effect of age on UPV is stronger at a lower temperature (e.g., 20 °C). The above analysis indicates that appropriate growth of temperature and age is helpful to improving the ultrasonic performance of CRB and CGB.
Figure 4 Effects of temperature and age on UPV of CRB and CGB
Based on the above analysis of UPV test results, it can be concluded that there are significant differences in cementation structures between CRB and CGB at various temperatures. Thus the hydration products and microstructure of CRB and CGB at various temperatures need to be further tested and analyzed.
3.3 Hydration products and microstructure
Figures 5 and 6 show the X-ray diffraction (XRD) phase quantitative analysis results of CRB and CGB at various temperatures for 28 d, respectively. The diffraction pattern shows that the distribution area of diffraction peaks is mainly within the diffraction angle (2θ) of 20°-30°. The main phase compositions of CRB and CGB at various temperatures include quartz, albite and microcline, which account for more than 74% of the total phase. When the temperature increased from 20 °C to 40 °C or 60 °C, the content of portlandite increased, while the content of ettringite decreased, which are beneficial to improving the strength of CRB and CGB [28-30]. The increase in temperature can improve the amount of hydration products to some extent, thus affecting the strength characteristics of CRB and CGB. The SEM micrographs present the interaction among particles, calcium silicate hydrate (C-S-H), and air voids inside the CBs. The voids inside the cementation structure of CRB and CGB were reduced obviously with the increase of temperature (as shown in Table 4), indicating that the temperature can improve the hydration degree of binder and refine the cementation structures to some extent, thus improving the strength and integrity of CBs [31].
The main reasons for the above phenomenon are as follows: i) the temperature can affect the rate of hydration. Generally, the self-hydration of backfill takes a longer time at a lower curing temperature, which directly affects the amount of hydration products and the cementation degree of CB [17, 32, 33]. With the increase of temperature, the hydration processes of both CRB and CGB were intensified. There was an increase in the amount of hydration products (mainly C-S-H), the internal cementation structure of CBs was improved and refined. ii) The comparison of CRB and CGB microstructures shows that there is a correlation between the amount of hydration products and the particle size. Larger particles have more hydration products attached to their surface at a higher temperature (e.g., 60 °C), and the internal cementation structure of CB is more compact than that at a lower temperature (e.g., 20 °C).
Figure 5 Hydration products and cementation structures of CRB at various temperatures
Figure 6 Hydration products and cementation structures of CGB at various temperatures
Table 4 Statistical results of porosity based on SEM micrographs (at 100 μm)
3.4 Compressive strength and deformation characteristics
Figure 7 presents the effects of temperature and age on the compressive strength of CRB and CGB. The results show that the compressive strengths of CRB and CGB are positively correlated with temperature and age except for a few cases, such as the compressive strength of CRB at 60 °C for 28 d (2908.78 kPa) is slightly lower than that of 7 d (3183.28 kPa). The compressive strength of CGB is higher than that of CRB under the same conditions, and the difference between them tends to increase with the increasing temperature and the growth of age. For example, the compressive strength ratio of CGB to CRB for 28 d is 1.03 at 20 °C, and increases to 1.96 at 40 °C and 2.01 at 60 °C, as region A and region B shown in Figure 7. The analysis shows that the temperature and age can facilitate the growth of compressive strength, and the facilitating effect on the compressive strength of CGB is higher than that on CRB.
Figure 7 Effects of temperature and age on compressive strength of CRB and CGB:
Figure 8 shows the compressive deformation processes and failure modes of CRB and CGB at various temperatures. The overall variation trends of compressive deformation of both CRB and CGB at various temperatures are consistent. The compressive deformation process generally can be divided into five stages: initial compaction stage (0A), elastic deformation stage (AB), micro- fracture stable development stage (BC), unstable fracture development stage (CD), and post-peak fracture stage (DE). The point C is the yield point, and the corresponding yield stress increases significantly with the increasing temperature, indicating that the temperature is beneficial to improving the resistance to compressive plastic deformation. Furthermore, the compressive failure mode of the specimens is closely related to temperature. At 20 °C, the CRB and CGB specimens are severely damaged, the failure modes are mainly the shear failure of X-conjugate inclined plane, and the fragmentation at failure is dominated by large pieces and a small amount of debris. At 40 °C and 60 °C, the overall integrity of specimens is relatively good, the failure modes of CRB and CGB specimens are mainly the tensile failure, and the failure fragmentation is mainly small debris. The amount of debris decreases with the increasing temperature, thereinto the CGB at 60 °C has the best integrity and the least amount of debris. The failure modes of CRB and CGB specimens differ, indicating that the increase of temperature is conducive to improving the integrity and stability of both CRB and CGB, and the overall stability of CGB is better than that of CRB.
Figure 8 Compressive deformation and failure modes of CRB and CGB at various temperatures after curing for 7 d:
3.5 Shear strength and deformation characteristics
Figure 9 displays the effects of temperature and age on the peak shear strength (PSS) of CRB and CGB. It is clear that the PSS of CGB is generally higher than that of CRB under the same conditions, the PSS is positively correlated with temperature and age, and the temperature has a weaker effect on PSS than age. The PSS of CRB and CGB increases significantly at 40 °C compared with 20 °C, while the PSS at 60 °C remains the same compared with that at 40 °C. For example, the PSSs of CRB at 20, 40 and 60 °C for 28 d are 1179.06, 1987.15 and 2008.20 kPa, respectively.
Figure 9 Effects of temperature and age on PSS of CRB and CGB:
Figure 10 displays the effects of temperature and age on the residual shear strength (RSS) of CRB and CGB. It is obvious that age has a significant influence on the RSS of CRB and CGB, and the RSS decreases with the growth of age. Except a few cases (e.g. the RSS of CRB at 40 °C is higher than that of CGB for the same age of 28 d), the RSS of CGB is generally higher than that of CRB under the same conditions. There are significant differences between CRB and CGB in the variation trends of RSS with increasing temperature. For CRB, the RSS first increased and then decreased, and reached its maximum value at 40 °C. For CGB, the RSS first decreased and then slightly increased, but the overall variation range is limited. The analysis indicates that the temperature also has a weaker effect on RSS than age.
Figure 11 presents the shear deformation processes of CRB and CGB at various temperatures, respectively. The overall variation trends of shear deformation of CRB and CGB at variation temperatures are consistent. The shear deformation process can be roughly divided into four stages: initial compaction stage (I), pre-peak elastic deformation stage (II), post-peak plastic deformation stage (III), and residual deformation stage (IV). The PSS can be achieved within the shear displacement range of 1-2 mm, the shear performance of CGB is better than that of CRB at the same temperature in the whole shearing process. When the shear displacement reaches 6 mm, the shear stress changes gently, and then the residual deformation stage (IV) can be achieved. According to the technical codes [34, 35], the RSS can be considered to be reached with a larger shear displacement (generally no less than 10 mm), as shown in Figure 11, it is obvious that the RSS difference of CRB and CGB is insignificant at various temperatures.
Figure 10 Effects of temperature and age on RSS of CRB and CGB:
Figure 11 Shear deformation of CRB (a) and CGB (b) at various temperatures after curing for 7 d
By comparing the shear failure features of CRB and CGB at various temperatures, it can be concluded that there is an obvious relationship between the shear plane morphology and temperature. The higher the temperature, the greater the undulation and roughness of failure surface, as shown in Figure 11. Furthermore, there is an obvious correlation between the normal displacement and temperature in the shearing process. The higher the temperature, the larger the normal displacement in the residual stage at the constant normal stress and the same shear displacement. When the normal displacement is constrained effectively, the shear stress will increase accordingly. Besides, the normal displacement of CGB at the residual stage is larger than that of CRB, indicating that the shear resistance capability of CGB is better than that of CRB. For example, the normal displacement of CGB is the maximum at 60 °C, so its peak strength and shear resistance capability are relatively optimal.
4 Discussion
The above experimental results show that the temperature has a significant influence on the physico-mechanical properties of cemented gravel sand backfills. When the temperature increases from 20 °C to 60 °C, the temperature effect on the performance of CB is mainly reflected in the following aspects: i) The thermal expansibility and ultrasonic characteristics can reflect the structural changes of CB. The increase of temperature can lead to favourable variations in the hydration products, such as the amount of portlandite increased, and the internal cementation and pore structures are refined, which can prompt the expansion and ultrasonic performance of CB. ii) The increase in temperature generally has a facilitating effect on the strength of CB. The temperature has a significant influence on compressive strength. In contrast, the effect on shear strength, especially the residual shear strength, is relatively weak, as shown in Figures 7(b), 9(b) and 10(b), indicating that the temperature effect on mechanical properties of cemented gravel sand backfills is directional. iii) Temperature can affect the deformation characteristics and failure modes of CB. Although the overall variation trends of backfill deformation at various temperatures are consistent, there are apparent differences in the deformation process. For example, the displacements corresponding to the compressive strength present a delayed tendency, as shown in Figures 8, indicating that the increase of temperature can enhance the resistance to deformation of CB to some extent.
The effect of temperature on the strength of CB is age-dependent, and the temperature has a more significant effect on the physico-mechanical properties of CB at early ages (e.g., 3 d). The temperature and age often act together on the CB in the actual deep backfill mining. When the filling slurry enters into the stopes, the ambient temperature in deep mining can effectively promote the early strength of CB, and the influence of temperature would be gradually weakened with the growth of age. This process is always in a state of dynamic change and eventually tends to a relative equilibrium state. Besides, the difference between CRB and CGB in physico-mechanical properties is mainly caused by the difference in the particle size distribution. A high proportion of large particle size aggregate is conducive to the improvement of CB strength, which is similar to concrete [36, 37]. Thus, the performance of CGB is generally better than CRB under the same conditions, and CGB has a higher temperature resistance and is conducive to maintaining its strength and stability, compared with CRB.
The experimental results have practical significance for understanding the properties of cemented gravel sand backfills in deep mining in northwest China and can provide some ideas for optimizing the performance of deep backfill. It should be noted that this experimental research mainly focuses on the physical properties and short-term strength of cemented gravel sand backfills. However, the influence of temperature on the long-term mechanical properties should also be paid attention to, as well as the rheological properties and pipeline transport performance of filling slurry in the process of deep backfill mining. Relevant researches will continue to be performed in the near future.
5 Conclusions
1) The temperature has a more significant effect on the thermal expansibility and ultrasonic performance of cemented gravel sand backfills at early ages (e.g., 3 d), and the effect of age on UPV is stronger at a lower temperature (e.g., 20 °C). Temperature and age mainly affect the amount of hydration products and refine the cementation structures, thus affecting the physico-mechanical properties of backfills.
2) The compressive strength of CRB and CGB is positively correlated with temperature and age, and the facilitating effect on CGB strength is greater than that of CRB. The overall variation trends of compressive deformation of both CRB and CGB at various temperatures are consistent, and the yield stress increases with increasing temperature, indicating that the temperature is beneficial to improving the resistance to compressive plastic deformation. With the temperature increased from 20 °C to 40 °C or 60 °C, the failure mode of specimens changed from X-conjugate shear failure to tensile failure, and the integrity of the specimens can be significantly improved.
3) The shear performance of CGB is generally better than that of CRB. The PSS of CRB and CGB is positively correlated with age, while the RSS is negatively correlated with age, and the temperature has a weaker effect on PSS and RSS than age. The overall variation trends of shear deformation of CRB and CGB at variation temperatures are consistent, and the peak strength can be achieved within the shear displacement range of 1-2 mm. The shear deformation and shear plane morphology are closely related to temperature.
4) There are significant differences in physico- mechanical properties between CRB and CGB due to the difference in the particle size distribution of gravel sands, and the performance of CGB is generally better than CRB. The strength and resistance capability to deformation of both CRB and CGB are greatly improved at 40 °C and 60 °C, compared with 20 °C. The findings presented in this paper can contribute to a better understanding and optimizing the physico-mechanical properties of cemented gravel sand backfills in deep backfill mines in northwest China.
Contributors
The overarching research goals were developed by ZHOU Hui and JIANG Fei-fei. JIANG Fei-fei, SHENG Jia, and KOU Yong-yuan conducted the laboratory tests and analyzed the experimental results. JIANG Fei-fei, ZHOU Hui, and LI Xiang-dong conducted the literature review and wrote the first draft of the manuscript. All authors replied to reviewers’ comments and revised the final version.
Conflict of interest
JIANG Fei-fei, ZHOU Hui, SHENG Jia, KOU Yong-yuan, and LI Xiang-dong declare that they have no conflict of interest.
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(Edited by HE Yun-bin)
中文导读
温度和龄期对砾石砂胶结充填体物理力学性能的影响
摘要：深部矿山胶结充填体在未来数十年里将不可避免地会暴露在20~60 °C的环境温度中。本文制备了两种砾石砂胶结充填体，即棒磨砂胶结充填体(CRB)和戈壁砂胶结充填体(CGB)，并分别在不同温度(20 °C、40 °C、60 °C)和龄期(3 d、7 d、28 d)条件下进行了养护；然后，基于室内试验探索了温度和龄期对CRB和CGB物理力学特性的影响效应。结果表明：1) 温度和龄期对充填体物理力学特性的影响主要取决于水化产物量和胶结结构密实度，温度对早期充填体热膨胀性和超声性能的影响更为显著；2) 温度和龄期对CGB抗压强度的促进作用要强于CRB，随着温度的升高，试样的压缩破坏形式由X-共轭剪切破坏转变为拉伸破坏，试样的完整性得到了显著改善；3) 同样CGB的抗剪性能普遍优于CRB，温度对充填体抗剪强度的影响较龄期要弱，但剪切变形和剪切面破坏形态与温度密切相关。
关键词：胶结充填体；砾石砂；温度；物理力学特性；变形特征
Foundation item: Project(P2018G045) supported by the Science & Technology Research and Development Program of China Railway; Project(2018CFA013) supported by the Hubei Provincial Natural Science Foundation Innovation Group, China; Project(KFJ-STS-QYZD-174) supported by the Science and Technology Service Network Initiative of the Chinese Academy of Sciences; Project(51709257) supported by the National Natural Science Foundation of China
Received date: 2020-06-27; Accepted date: 2020-09-03
Corresponding author: ZHOU Hui, PhD, Professor; Tel: +86-27-87197913; E-mail: hzhou@whrsm.ac.cn; ORCID: https://orcid.org/ 0000-0002-9255-0178
Abstract: Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20-60 °C in the next few decades. In this paper, two types of cemented gravel sand backfills, cemented rod-mill sand backfill (CRB) and cemented gobi sand backfill (CGB), were prepared and cured at various temperatures (20, 40, 60 °C) and ages (3, 7, 28 d), and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests. Results show that: 1) the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures. The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages. 2) The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB. With the increase of temperature, the compressive failure modes changed from X-conjugate shear failure to tensile failure, and the integrity of specimens was significantly improved. 3) Similarly, the shear performance of CGB is generally better than that of CRB. The temperature has a weaker effect on shear strength than age, but the shear deformation and shear plane morphology are closely related to temperature.
