J. Cent. South Univ. (2019) 26: 3114-3125

DOI: https://doi.org/10.1007/s11771-019-4240-2

Property changes of anchor grout calcined ginger nuts admixed with fly ash and quartz sand after accelerated ageing tests

ZHANG Jing-ke(张景科)^{1, 2}, ZHANG Li-xiang(张理想)^{1, 2}, ZHAO Lin-yi(赵林毅)³,

LIU Dun(刘盾)^{1, 2}, GUO Qing-lin(郭青林)³, PEI Qiang-qiang(裴强强)³

1. School of Civil Engineering and Mechanics, Lanzhou University, Lanzhou 730000, China;

2. Key Laboratory of Mechanics on Disaster and Environment in Western China, Ministry of Education, Lanzhou 730000, China;

3. National Research Center for Conservation of Ancient Wall Paintings and Earthen Sites, Dunhuang Academy, Dunhuang 736200, China

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract: Calcined ginger nuts admixed by fly ash and quartz sand (CGN-(F+S)) has been validated to be basically compatible to earthen sites as an anchor grout. Accelerated ageing tests including water stability test, temperature and humidity cycling test, soundness test and alkali resistance test are conducted with the objective to further research the property changes of CGN-(F+S) grout. Density, surface hardness, water penetration capacity, water permeability capacity, soluble salt, scanning electron microscopy (SEM) images and energy dispersive spectrometry (EDS) spectrum of these samples have been tested after accelerated ageing tests. The results show that densities of samples decrease, surface hardness, water penetration capacity and water permeability capacity of samples increase generally. Besides, soluble salt analysis, SEM and EDS results well corroborate the changes. Based on the results it can be concluded that property changes are most serious after temperature and humidity cycling test, followed by water stability, soundness and alkali resistance test in sequence. But in general,CGN-(F+S)still has good durability.

Key words: CGN-(F+S) grout; accelerated ageing tests; physical property change; chemical property change; scanning electron microscopy; energy dispersive spectrometry

Cite this article as: ZHANG Jing-ke, ZHANG Li-xiang, ZHAO Lin-yi, LIU Dun, GUO Qing-lin, PEI Qiang-qiang. Property changes of anchor grout calcined ginger nuts admixed with fly ash and quartz sand after accelerated ageing tests [J]. Journal of Central South University, 2019, 26(11): 3114-3125. DOI: https://doi.org/10.1007/s11771-019- 4240-2.

1 Introduction

In 1970s, a large-scale excavation at the Dadiwan site in Qin’an County, Gansu Province, China was carried out by an archaeological team from Gansu Museum. A housing floor material which is confirmed as the earliest lightweight concrete in China was discovered [1, 2]. Study shows that the lightweight concrete is mainly composed of the light calcined kunkur as aggregate and the powder of calcined ginger nuts (CGN) as bonding material. The bulk specific weights of the lightweight concrete and ginger nuts are 1.74 g/cm³ and 2.41 g/cm³, respectively. Porosities of the lightweight concrete and ginger nuts are 27% and 5%, respectively, and the flexural strengths of the lightweight concrete and ginger nuts are 10 MPa and 0.61 MPa, respectively. The result of X-ray diffraction analysis shows that the main composition of ginger nuts is SiO₂, CaO, CO₂ and Al₂O₃ [2]. By calcining under specific temperature about 1000 °C, the modified materials with name of calcined ginger nuts acquire similar chemical composition with natural hydraulic lime (NHL) [2, 3], and the main compositions of calcined ginger nuts are β-CaSiO₃, CaO, SiO₂ Ca₂Al₂SiO₇. Utilization of NHL in the masonry can be dated back to Greek and Roman period [4], and nowadays, it has become a popular conservation material in historic buildings. Hence, extensive researches on NHL have been performed. LANAS et al [5] carried out contrastive studies of factors affecting the long-term mechanical behavior of NHL. SEABRA et al [6] studied the rheological behavior of hydraulic lime-based mortars used for restoration of historic buildings. HANLEY et al [7] researched the workability of natural hydraulic lime mortars and its influence on strength. KALAGRI et al [8] evaluated the designed NHL grout for strengthening of stone masonry historic structures. GULOTTA et al [9] investigated compositional and mechanical characteristics of NHL-containing mortars for the preservation of historical architecture. Meanwhile, NHL admixed by wasted textile fibre waste and dispersed graphene oxide was studied as composite material [10, 11]. Considering that durability of repair materials plays a critical role in the long-time service, MARAVELAKI- KALAITZAKI et al [12] studied the hydraulic lime mortars used for the restoration of historic masonry in Crete, Greece, and found that appropriate proportion can result in good durability. With respect to the successful application and research fruits of NHL-based mortar in the historic buildings, CGN is expected to be applied in the conservation of Chinese earthen sites.

Abundant earthen sites are preserved in northwest of China under the arid and semi-arid environment. Chinese earthen sites could be traced back to Neolithic Period [13], 6000 years ago, for instance, Banpo site and Dadiwan site. Collapse and fissures are considered major challenges for the stability of earthen sites [14, 15]. Since 1990s, anchor technology has been applied to the reinforcement of earthen sites. After nearly 25 years’ application, it has been regarded as a key method in solving the stability problems. And the anchor system consists of anchor bolt, anchor grout and surrounding soil masses.

Anchor grout currently applied in earthen sites includes potassium silicate (PS) based grout [16, 17], NHL admixed by quartz sand [18], modified glutinous rice mortar [19], SH [20] and CGN based grout. These grout materials are also generally studied by mixing with some industrial wastes and disturbed soil from earthen sites to achieve the compatibility. Since the good long-term service of anchor grout is of significant importance for anchor effect in earthen sites, its durability study is currently becoming an urgent and hot issue.

Performance study of CGN-based grout is still in its infancy as anchor grout in conservation of earthen sites. After studying the age performance of grout mixed with CGN and earthen fabric, REN et al [21] found that the penetration coefficient and density were compatible to earthen sites. Several ageing tests of CGN-based grout were carried out by LI et al [22], and the results reveal that the material has high porosity, low shrinkage and good durability. Besides, at the sintering temperature of 1100 °C, when the water cement ratio is 0.33, CGN grout mixed exhibits good ductility, mechanical properties and weathering resistance ability [1, 23]. ZHANG et al [24] studied the age properties of fissure grouting material composed of CGN and earthen site soil. It preliminarily proved that soil from the earthen sites modified with CGN is suitable for grouting the fissures in earthen sites. ZHANG et al [25] investigated the workability and durability of CGN based grout and proved that CGN grout mixed with fly ash and quartz sand (CGN-(F+S)) acquired predominant durability. Except for earthen sites, CGN has also been considered potential grouting material in the reinforcement of murals in wet conditions [26], crack grouting of grottoes [27] and kilns of the Maritime Silk Road [28].

The existing study on durability of CGN-(F+S) grout is only carried out by the comparison of compressive and flexural strength before and after accelerated ageing tests. However, other property changes, which help understanding the weathering mechanism of CGN-(F+S), are still lacking.

The aim of this paper is to conduct a deep study on the durability of CGN-(F+S) grout. Accelerated ageing tests adopted in this research are completely the same as those of previous study [25]. More comprehensive experiments including density test, surface hardness test, water penetration capacity test, water permeability capacity test, soluble salt analysis, scanning electron microscopy (SEM) and energy dispersive spetrometry (EDS) are conducted after a series of accelerated tests involving water stability test, temperature and humidity cycling test, soundness test and alkali resistance test. The results will be particularly valuable for understanding the deterioration mechanism of CGN-(F+S) grout.

2 Experimental program

2.1 Materials

The grout is composed of calcined ginger nuts (CGN), fly ash(F), quartz sand(S) and water. The mix proportion of CGN-(F+S) grout is 1:0.5:0.5 for CGN:F:S. In order to meet the requirement of slurry liquidity, 0.35 is determined as the water-to-cement ratio. CGN is produced in the material laboratory of Dunhuang Academy, Gansu Province, China. The composition of CGN derived from XRD diffraction analysis is given in Table 1. It indicates that CaO and β-CaSiO₃ dominate the composition of CGN.

Table 1 XRD semi-quantitative analysis result of CGN

Fly ash is collected from Tianshan Thermal Power Plant in Hebei province, and it’s quality is classified as F (Table 2) according to the composition of SiO₂ (54.11%), Al₂O₃ (34.44%) and Fe₂O₃ (5.34%) [29]. Quartz sand (0.02 μm, 7 in Leeb hardness and 2.65 g/cm³ in grain density) utilized in this research is purchased from building material market. The test water is distilled in this experiment.

2.2 Specimens preparation and curing condition

600 g dry CGN, 300 g quartz sand and 300 g fly ash are mixed with trowel, and the mixing process lasts for 2 min to ensure that these materials are blended sufficiently. Afterwards, the water is added within 30 s meanwhile keeping the electric mixer stirring. After all the water is added, the mix will last for 4 min to avoid the present of aggregates. With raw materials, 5 groups corresponding to the accelerated test are conducted for the research. The identification of each group is given in Table 3.

Most of Chinese earthen sites are distributing in northwest of China, especially along the Silk Road. The surviving environment can be characterized as high temperature difference, dry and rainless, and occasional extreme rainfall climate. Concentrated rainfall and intensive evaporation lead to the deterioration of earthen sites [30]. Besides, soil mass above subgrade is also affected by capillary activity [31]. Moreover, salt crystallization of sodium sulfate is another important factor for deterioration of earthen sites, which will undoubtedly damage anchoring grout [30]. Because of the alkaline nature of the soil in the northwest, the alkali resistance of the CGN-(F+S) grout is also an important index of the performance [32]. Combing with all these above into consideration, accelerated tests including water stability test, temperature and humidity cycling test,soundness test and alkali resistance test are chosen.

Table 2 Chemical component of fly ash (%)

Table 3 CGN-(F+S) grout identification

Specimen size, curing environment and regime of accelerated ageing tests are identical to the previous study [25]. All the tests are done in triplicate, but only the average values are reported in this study.

2.3 Testing methods

2.3.1 Density test

Density test is conducted based on RILEM TC 25-PEM [33]. Weight of these samples was determined by electronic scale with a precision of 0.001 g, and the measurement was conducted three times to ensure the accuracy. The volume of samples was obtained by using wax-sealing method.

2.3.2 Surface hardness test

After a series of accelerated ageing tests, the surface hardness of every specimen is measured under laboratory conditions at 22.4 °C and 49.1% relative humidity by means of Equotip 3 Leeb hardness tester produced by Proceq Company, Switzerland. For each sample, it is measured 10 times and finally the mean value is taken.

2.3.3 Water penetration capacity

The vertical Karsten tube is applied to monitor changes of water penetration capacity after accelerated ageing tests according to BS EN 16682-2017 [34]. The Karsten tube consists of a dome with a diameter of 30 mm and attached calibrated glass tube with volume graduation. Surfaces of the tested cubic samples with size of 70 mm×70 mm are carefully cleaned and the dust is blown away before the test. Afterwards, the tube is pasted onto the surface of each sample in the central position firmly using a suitable plastic cement. Before formal test, 1 mL water is penetrated in advance and then top the water up again to 10 mL. Time and volume will be recorded successively until 10 mL is completely consumed.

2.3.4 Water permeability capacity

The objective of this experiment is to determine the permeability (hydraulic conductivity) of CGN-(F+S) grout by falling head test based on ASTM D2434-68 [35]. Firstly, the cubic sample was made into cylindrical ones with diameter of 37.6 mm and 45 mm in length by running a cutter bar carefully. And it is important to soak the cylindrical sample in the water until the sample is totally saturated so as to remove the air inside. And a vacuum method is taken before the water permeability capacity experiment.

2.3.5 Soluble salt analysis

According to soluble salt analysis [36], the test is carried out to monitor the quantitative changes of anions and cations which are acquired by dissolution of soluble salt from different samples. ICS-2500 ion chromatography system produced by Dionex Company is used in this test. Soluble salts are extracted from the solution which is gained by dissolving the sample powder in a fixed volume of ultra-pure water with specific conductivity no more than 1 μS/cm. The anion and cation contents can be determined in accordance with ISO 3310.1-2000 [37].

2.3.6 Scanning electron microscopy analysis

SEM images are obtained by JSM-5910 produced by JEOL. The instrument consists of electronic optical system, signal detection and amplification system, scanning system, image display and recording system, power system and vacuum-cooling water system. The maximum resolution of the instrument is 5 nm with 5-20 kV of acceleration voltage. Firstly, the sample is made into specimen blocks with the same size as the sample holding stage, and then the block is fixed on the stage by the conductive adhesive. The prepared sample block is firstly sprayed with a conductive layer and then placed in a scanning electron microscope for observation. The energy dispersive spectrometer (EDS) spectrum is also tested for each sample.

3 Results and discussions

3.1 Density

As presented in Figure 1, there is no significant change in density, except for CGN-(F+S)-3. Densities of CGN-(F+S)-1, CGN-(F+S)-2, CGN-(F+S)-3, CGN-(F+S)-4 and CGN-(F+S)-5 are 1.64, 1.62, 1.28, 1.62 and 1.58 g/cm³, respectively. It is obvious that the temperature and humidity cycling test leads to the largest reduction by 22.18%. Moreover, densities of CGN-(F+S)-2, CGN-(F+S)-4, CGN-(F+S)-5 decrease by 1.39%, 1.14% and 3.47% when comparing with original sample correspondingly. A dramatic increase of the porosity after accelerated ageing test could be summarized based on the highest decrease of density, which reflects that samples after temperature and humidity cycling test experience the most severe deterioration.

Figure 1 Densities of CGN-(F+S) grout

3.2 Surface hardness

The results of surface hardness are shown in Figure 2. Surface hardness values of CGN-(F+S)-1, CGN-(F+S)-2, CGN-(F+S)-3, CGN-(F+S)-4 and CGN-(F+S)-5 are HLD 253, HLD 272, HLD 307, HLD 284 and HLD 229, respectively. With exception of CGN-(F+S)-5, a general increase of surface hardness can be found comparing with original samples. CGN-(F+S)-3 shows the highest value of surface hardness which increases by 21.34%. Meanwhile, surface hardness of CGN-(F+S)-2 and CGN-(F+S)-4 increases by 7.50% and 12.25%, respectively. Conversely, surface hardness of CGN-(F+S)-5 decreases by 9.48%. In terms of surface hardness, alkali is one of the most severe factors that causes surface deterioration of CGN-(F+S) grout.

Figure 2 Surface hardness of CGN-(F+S) grout

3.3 Water penetration capacity

Figure 3 shows the results of the water penetration capacity of CGN-(F+S) grout. Water penetration capacities of CGN-(F+S)-1, CGN-(F+S)-2, CGN-(F+S)-3, CGN-(F+S)-4 and CGN-(F+S)-5 are 0.01425, 0.03351, 0.08302, 0.01247 and 0.0352 mL/min, respectively. Among all the samples, CGN-(F+S)-3 obtains the highest water penetration capacity and the CGN-(F+S)-4 is characterized by the lowest value which is just slightly inferior to CGN-(F+S)-1. It is pointed out that the water penetration capacity is highly increased after temperature and humidity cycling test. CGN-(F+S)-2 and CGN-(F+S)-5 share similar water penetration capacity which increases by about 235%. Above all, the temperature and humidity cycling are still the serious factors, which leads to the surface degradation of CGN-(F+S) grout.

Figure 3 Water penetration capacity of CGN-(F+S) grout

3.4 Water permeability capacity

Figure 4 shows the water permeability capacity of CGN-(F+S) grout. Water permeability capacities of CGN-(F+S)-1, CGN-(F+S)-2, CGN-(F+S)-3, CGN-(F+S)-4 and CGN-(F+S)-5 are 5.42×10^-9, 2.91×10^-8, 8.41×10^-8, 6.42×10^-8 and 1.69×10^-8 m/s, respectively. In general, water permeability capacities increase after the accelerated ageing tests, which reflects the increase of the porosity. The results of water permeability are consistent with the density changes. When comparing with the results mentioned above,temperature and humidity cycling test affects the pore structure of CGN-(F+S) grout significantly than other factors. Besides, the permeability also increases massively after the soundness test, which shows that the phase transition of sodium sulfate plays a crucial role in deterioration. Combining with density results, it can be inferred that the decrease of densities accounts for increase of porosity, since water penetration capacity increases with porosity.

Figure 4 Water permeability capacity of CGN-(F+S) grout

3.5 Soluble salt analysis

It is widely recognized that soluble salts greatly reduce the durability of porous material [38]. Therefore, it is important to figure out the soluble salt deterioration effect on CGN-(F+S) grout. Results of soluble salt analysis are depicted in Figures 5 and 6. The main anions considered are sulfate (SO₄^2-), nitrate (NO^3-), nitrite (NO^2-), chloride (Cl^-) and fluoride (F^-). From the results it can be observed that the sulfate content of each specimen is in considerably high level than other anions. CGN-(F+S)-4 has the highest SO₄^2- content which reached 7033 mg/kg. The content of sulfate ions increased by 2855.04% after soundness test. In addition to CGN-(F+S)-4, sulfate ions contents of CGN-(F+S)-2, CGN-(F+S)-3 and CGN-(F+S)-5 decreased widely. And chloride ions content of those samples is lower than that of sulfate ions, basically.

Cations containing sodium　(Na⁺), potassium (K⁺) and calcium (Ca²⁺) are taken into account. The results in Figure 6 demonstrate that CGN-(F+S)-4 obtained the highest content of sodium which reached 3133 mg/kg and the highest content of potassium which reached 257.37 mg/kg due to samples’immersing in 14% sodium sulfate solution. CGN-(F+S)-5 is also rich in sodium ions and the value is about 800 mg/kg mainly because of the 2% solution of sodium hydroxide applied in alkali resistance test. It is evident that the calcium content of CGN-(F+S)-3 increases by 1.59% after temperature and humidity cycling test. The only decrease of calcium is detected after the alkali resistance test. It can be concluded that ions content changes of CGN-(F+S)-4 and CGN-(F+S)-5 are gained mainly due to the solution used in this research. The variation of Ca²⁺ content could reflect the product of air hardening reaction to some extent. It can also be seen that Ca²⁺ content of samples after accelerated ageing tests increases except for CGN-(F+S)-5.

Figure 5 Anions content of CGN-(F+S) grout

Figure 6 Cations content of CGN-(F+S) grout

3.6 Scanning electron microscopy analysis

SEM scanning images with various resolutions (×1000, ×2000) are obtained after accelerated ageing tests in order to monitor microstructure changes of the CGN-(F+S) grout. EDS are measured to check the composition difference of CGN-(F+S) grout. SEM and EDS results of CGN-(F+S)-5 grout are depicted in Figures 7-11. Based on the results, the following phenomenon can be observed:

1) After accelerated ageing tests, it is observed that the microstructures of these samples are different from each other (Figures 7(a), 8(a), 9(a), 10(a) and 11(a)). Sample after water stability test shares the similar microstructure with original sample. It is obvious that, except for CGN-(F+S)-4 the structure of fly ash could be distinguished, in which fly ash spherulite is wrapped by calcium carbonate gelation.

Figure 7 Different resolutions SEM images and EDS of CGN-(F+S)-1

Figure 8 Different resolutions SEM images and EDS of CGN-(F+S)-2

2) As shown in Figure 10(b), the structure of CGN-(F+S)-4 becomes denser due to the filling of pores by sodium sulfate.

3) Evident holes are obtained in CGN-(F+S)-5 (Figure 11(b)) due to the losses of fly ash. It means that the fly ash spherulite is washed away by alkali solution.

4) The microstructures of CGN-(F+S)-3 and CGN-(F+S)-4 become very grainy. Moreover, flaky gel which probably is tricalcium silicate of aluminum (3·CaO·Al₂O₃·nH₂O) could be detected in CGN-(F+S)-2.

Figure 9 Different resolutions SEM images and EDS of CGN-(F+S)-3

5) The content of gel on the surface of sample blocks could be inferred from the EDS results (Figures 7(c), 8(c), 9(c), 10(c) and 11(c)) in which the corresponding energy peak of each element is given. The spectral peaks of Ca and Si can indicate the content changes of calcium carbonate gelation after a series of accelerated ageing tests. The increase of calcium carbonate gelation to some extent demonstrates the further hydration reaction in the samples.

4 Discussion

After water stability test, density of CGN-(F+S)-2 decreases slightly than the original sample, but the surface hardness, hydraulic properties including water penetration capacity and water permeability capacity have all increased in the meantime. It can be interpreted that soluble salt content of CGN-(F+S)-2 decreases after water stability test, but the content of Ca still increases slightly. Besides, the microstructure and EDS results of CGN-(F+S)-2 support relevant evidences that more flaky and flocculent gel are detected, and the spectral peaks of Ca and Si are higher than original sample. It can be inferred that the further harden reaction takes place in CGN-(F+S)-2. LI et al [39] also found that the further hydration of hydraulic components in CGN grout results in higher mechanical property.

Figure 10 Different resolutions SEM images and EDS of CGN-(F+S)-4

After temperature and humidity cycling test, density of CGN-(F+S)-3 decreased while surface hardness increased, and water penetration capacity and water permeability capacity also increased massively. Result of soluble salt analysis, SEM and EDS results confirm the changes of physical properties. The soluble salt content of CGN-(F+S)-3 decreased, and the microstructure from SEM images becomes much grainy comparing with the floccular topological feature of original sample. More calcium carbonate gelation (CSH) can be detected in CGN-(F+S)-3 both from the SEM images and EDS. Higher content of Ca and Si may contribute to the possible further harden reaction in the samples. Studies also suggest that the harden reaction of lime materials is a long-term process, and changes of the curing environment will influence the long-term harden process [40]. Study on the carbonation of NHL3.5 hydraulic lime by EL-TURKI et al [41] has proved that a higher relative humidity (97%) can improve carbonation process of grout. Therefore, CGN-(F+S)-3 may still obtain the highest surface hardness when other properties (density, hydraulic properties) are fairly poor.

Figure 11 Different resolutions SEM images and EDS of CGN-(F+S)-5

After soundness test, density of CGN-(F+S)-4 changes slightly in general. The water penetration capacity decreases, and meanwhile, the water permeability capacity increases. Besides, the surface hardness increases, which may be attributed to the possible recrystallization of Na₂SO₄, filling the pore spaces. Some studies also suggest that the compressive strength will increase after soundness test [1,22,38] due to the recrystallization of Na₂SO₄. But in the water permeability capacity test, the recrystallized salt will dissolve and migrate again into the water. As a result, the water permeability capacity of CGN-(F+S)-4 increases while the water penetration capacity decreases. Observation of sodium sulfate from SEM images of CGN-(F+S)-4 and high content of Ca and Si also support the above explanation.

After alkali resistance test, density and surface hardness of CGN-(F+S)-5 decrease. Without the recrystallization phenomenon, water penetration capacity and permeability capacity of CGN-(F+S)-5 increases simultaneously. The content of sodium increases massively while the content of sulfate decreases. In addition, obvious changes in microstructure are obtained, and evident holes emerge due to the losses of fly ash spherulite. Although the spectral peaks of Ca and Si are in a higher level, the deterioration caused by solution of sodium hydroxide (NaOH) still has a great impact on the surface of CGN-(F+S)-5. So, the surface hardness of the samples decreases.

After comprehensive comparison, the effect of temperature and humidity cycling test is more severe than other accelerated ageing tests. The deterioration caused by single water factor is weaker than the combination of temperature and water. However, in the preservation environment of earthen sites, the effect of temperature and humidity exist simultaneous. Based on the background of arid and semi-arid climate, salt dissolved in the water will sometimes accumulate on the surface of the soil in northwest of China. Results from soundness test and alkali resistance test show that changes in physical and chemical properties are significant. Even though deterioration is detected after accelerated ageing tests, CGN-(F+S) grout still has good durability. In special, it is observed the further hardening reactions including hydraulic reactions and air hardening reactions will arises under specific test conditions. In other words, this material can guarantee the long-term service of the anchorage system in earthen sites under arid and semi-arid climate.

5 Conclusions

After these accelerated ageing experiments, a series of tests are conducted. Based on the results, the following conclusions can be made:

1) After water stability test, density of the samples decreases slightly, and meanwhile, the surface hardness and hydraulic properties increase obviously. SEM result shows that more gel could be detected, which means further harden reaction arose in the samples.

2) After temperature and humidity cycling test, density of the samples decreases massively. At the same time, the surface hardness and hydraulic properties increased apparently. The microstructure from SEM images becomes much grainy. With more CSH detected in the samples, possible further harden reaction is confirmed.

3) After soundness test, density and water penetration capacity decrease, but the water permeability capacity increases. Besides, the surface hardness is higher than original sample. This phenomenon may be attributed to the possible recrystallization of Na₂SO₄, which fills the pore spaces. Furthermore, SEM images indicate that the sample is filled with Na₂SO₄.

4) After alkali resistance test, density and surface hardness of the samples decrease. The hydraulic properties increase simultaneously. The content of sodium increases massively while the content of sulfate decreases. SEM result indicates that evident holes could be found due to the losses of fly ash spherulite.

5) As comprehensive comparison, the effect of temperature and humidity cycling test is more severe than other accelerated ageing tests, followed by water stability, soundness and alkali resistance test in sequence. But in general, CGN-(F+S) still has good durability. This material could prolong the long-term service of the anchorage system in earthen sites.

6) Based on the results in this paper, studies on the long-term hardening reaction of the material is strongly recommended. It will help understanding the long-term service of the anchorage system in earthen sites better.

Acknowledgements

Most of experiment works were finished in OxRBL, University of Oxford. We would like to express our gratitude to Prof. Heather VILES, Dr. ZHANG Hong and Dr. Mona EDWARDS for their instructions and helps.

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(Edited by ZHENG Yu-tong)

中文导读

烧料礓石拌合粉煤灰与石英砂锚固浆液加速老化试验性能研究

摘要：作为锚固浆液，烧料礓石拌合粉煤灰与石英砂(CGN-(F+S))混合浆液与土遗址之间具有良好的兼容性。为了进一步探究CGN-(F+S)浆液在加速老化试验后的性能变化，设置了水稳定性试验、温湿循环试验、安定性试验和耐碱性试验等加速老化试验。在加速老化试验后，对锚固浆液试样的密度、表面硬度、渗透系数、表面吸水率、可溶盐含量、扫描电子显微镜(SEM)图像和EDS能谱图进行了测试。结果显示，CGN-(F+S)浆液试样的密度发生了下降，表面硬度、渗透系数及表面吸水率普遍提高。可溶盐分析结果与SEM、EDS图像印证了CGN-(F+S)浆液在加速老化试验后的物理性质变化。综合分析CGN-(F+S)浆液的物理及化学性质变化，结果表明，温湿循环试验后CGN-(F+S)浆液的性能劣化最为严重，其次是水稳定性试验，安定性试验和耐碱性试验。但总的来说，CGN-(F+S)锚固浆液仍具有良好的耐久性。

关键词：CGN-(F+S)锚固浆液；加速老化试验；物理性质变化；化学性质变化；SEM；EDS

Foundation item: Project(51578272) supported by the National Natural Science Foundation of China

Received date: 2018-08-24; Accepted date: 2019-06-21

Corresponding author: ZHANG Jing-ke, PhD, Professor; Tel: +86-931-8914308; E-mail addresses: zhangjink@lzu.edu.cn; ORCID: 0000-0002-7421-3979