Advances in Materials Science and Engineering
Volume 2019 (2019), Article ID 9076760, 11 pages
https://doi.org/10.1155/2019/9076760

Research Article

Slurry and Technology Optimization for Grouting Fissures in Earthen Sites with Quicklime

Kai Cui,1,2 Fei Feng,¹ Wen-wu Chen,² Dong-hua Wang,¹ and Xiao-hai Wang¹

¹Engineering Research Center of Ministry of Education for Disaster Prevention and Mitigation of Civil Engineering in Western China, Lanzhou University of Technology, Lanzhou 730050, China
²Key Laboratory of Mechanics on Disaster and Environment in Western China, Lanzhou University, Ministry of Education, Lanzhou 730000, China

Correspondence should be addressed to Fei Feng; 824290056@qq.com

Received 13 December 2018; Revised 11 April 2019; Accepted 22 April 2019; Published 9 May 2019

Guest Editor: Alexandra Rempel

Copyright © 2019 Kai Cui et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Shrinkage differentiation and the need for multiple replenishments of slurry after fissure reinforcement are key problems for the grouting reinforcement of fissures in earthen sites. In this study, quicklime was mixed with 1.5% SH binder, clay, and fly ash in different proportions to prepare nine different mixtures and water-cement ratios of SH-(CaO + C + F) slurry. An expansibility test was performed, and based on the results, four groups of slurry were selected for a fluidity test. Ultimately, three different water-cement ratios were considered, and the mixing ratio of 3 : 2 : 5 was determined to produce the optimum slurry. The curing age was optimized according to the intensity and tensile and flexural strengths of the concretion. The selected slurry and curing age were then applied to testing traditional grouting technology and optimized grouting technology (i.e., microlime piles in the fissure) in fissure grouting field experiments. The acoustic wave, penetration resistance, and infrared thermal imaging results after fissure grouting were used to develop a preliminary explanation for the related mechanisms of slurry swelling, hardening, and lime pile compaction. The results showed that the combination of the preferred slurry and optimized grouting technology help address the problems of shrinkage differentiation on both sides of the fissure and need for multiple replenishments of the slurry after grouting.

1. Introduction

Earthen architectural sites are relics left over from production, culture, religion, and military activities in human history [1]. After hundreds of years of erosion, they have become increasingly precious because of their important historical positivism and nonrenewability [2–5]. However, in the arid areas of Northwest China, most earthen sites are exposed to adverse environmental factors for long periods of time, which results in cracking, collapse, erosion, and other damages. This poses a serious threat to the long-term preservation of earthen sites. Fissures are the most common type of damage to earthen sites and cause media discontinuities and instability [6]. Their mechanism and prevention have become the focus of research on earthen site conservation. At present, the most common treatment of fissures is grouting technology [7–9]. However, the large shrinkage and deformation of traditional grouting slurry and the limitations of grouting technology mean that the concretion formed by the slurry easily detaches from the soil on both sides of a fissure after drying. Thus, the slurry needs to be replenished multiple times to seal the fissure. Screening candidate grouting materials and optimizing the grouting process are important for developing a slurry and grouting process that are more compatible with earthen sites in different regions.

In recent years, a consensus has developed of exploring traditional building materials and techniques to find grouting materials that are more compatible with the soil of earthen sites for conservation. Quicklime is one such traditional building material that has received a great deal of attention. Its use in China can be traced back to the Qijia cultural site in the upper reaches of the Yellow River 4000 years ago, and it has played an important role in military, cultural, and religious construction [10, 11]. Studies have shown that quicklime has properties similar to those of European hydraulic lime [12–14], which has not only good expansion and bonding properties [15] but also good compatibility with earthen sites. It has been applied to anchoring [16] and crack grouting [17] in reinforcement projects, and good results have been achieved. At present, domestic scholars have carried out a series of modification studies on traditional lime materials [18, 19]. However, although hydraulic lime is widely used in the repair and reinforcement of historical buildings in Europe and the United States [20–22], China’s application of quicklime materials to soil restoration works is still lagging.

The aim of the present study was to improve the compatibility and expansibility of the slurry. In order to fully exploit the expansibility and bonding properties of quicklime (CaO), it was mixed with fly ash (F) and crushed site soil (C) with a 1.5% SH solution as a binder to make a new SH-(CaO + F + C) slurry. The expansion ratio and fluidity index of nine sample groups with different ingredient proportions and water-cement ratios were evaluated, and three groups with good fluidity and swelling properties were selected. The three preferred groups were cured for continuous but different periods of time to form concretions. The intensity and tensile and flexural strengths of the concretions were evaluated to determine the optimum curing age. The optimized slurry was then used with both traditional grouting technology and optimized grouting technology (i.e., microlime piles in the fissure) in fissure grouting field experiments. After curing for 63 d, acoustic wave, penetration resistance, and infrared thermal imaging tests were conducted to evaluate the reinforcement. The results showed that the mixture of CaO : F : C = 3 : 2 : 5 with water-cement ratios of 0.50, 0.52, and 0.54 met the expansibility and fluidity requirements for fissure grouting of earthen sites. This combination of a new grouting slurry and optimized grouting technology can solve the problems of detachment due to slurry shrinkage and the need for multiple replenishments.

2. Slurry Preparation and Selection

2.1. Materials and Methods

2.1.1. Material Properties

The main materials used in this research were quicklime, fly ash, crushed earthen site soil, and SH solution. The quicklime was industrial grade lime with a CaO content of 93.6%. The fly ash was grade II, and the main components were SiO₂ (52.2%), Al₂O₃ (31.1%), Fe₂O₃ (3.5%), CaO (2.5%), and MgO (1.7%) with other trace ingredients. The crushed earthen site soil was sampled from the collapsed Great Wall at the experimental site; the soil was silty clay with a water content of 1.53%, natural density of 1.47 g·cm⁻³, compressive strength of 3.50 MPa, tensile strength of 0.61 kPa, cohesion of 32.86 kPa, and internal friction angle of 38.36°. SH is a new type of polymer material (liquid-modified polyvinyl alcohol) developed by Lanzhou University; it has a density of 1.09 g·cm⁻³, and it is highly hydrophilic and soluble in water. Moreover, it is nontoxic and environmentally friendly, and it has good mechanical properties and a low preparation cost [23, 24].

2.1.2. Experimental Method

In order to determine a suitable grouting slurry with better expansibility and fluidity, nine slurry groups with different ingredient proportions and water-cement ratio were prepared, as given in Table 1. The slurries all used SH solution with a mass concentration of 1.5% as the binder. The proportions of quicklime (CaO), fly ash (F), and site soil (C) followed the mass ratios of CaO : F : C = 1 : 2 : 7, 2 : 2 : 6, and 3 : 2 : 5. The water-cement ratio was determined according to existing results in related research [25, 26] and controlled between 0.48 and 0.54.

Table 1: Mixture and water-cement ratios.

No.
Ingredient proportion
Water-cement ratio

1
CaO : F : C = 1 : 2 : 7
0.48, 0.50, 0.52

2
CaO : F : C = 2 : 2 : 6
0.50, 0.52, 0.54

3
CaO : F : C = 3 : 2 : 5
0.50, 0.52, 0.54

Based on JGJ/T70-2009 [27] and BS EN 1015-9:1999 [28], a comparator (standard rod reference length of 176 mm and measurement accuracy of 0.001 mm) and SC-145 pointer mortar consistency meter were used to test the volume expansion ratio and consistency, respectively, of the nine slurry groups.

2.2. Expansibility Tests

The volume expansion ratio of the concretions from the nine slurry groups after 28 d of aging was measured with the comparator. Three parallel samples were used for each group of slurry concretions, and the results were averaged for the final analysis. Table 2 presents the test results. The three water-cement ratios with CaO : F : C = 1 : 2 : 7 and two water-cement ratios of 0.52 and 0.54 with CaO : F : C = 2 : 2 : 6 show negative values for the volume expansion ratios; thus, they did not satisfy the precondition for the slurry to expand.

Table 2: Expansion ratios of different grout concretions over 28 d.

Ingredient proportion
Water-cement ratio
Volume expansion ratio (%)

1 : 2 : 7
0.48
−4.11

0.50
−4.68

0.52
−8.75

2 : 2 : 6
0.50
0.68

0.52
−2.34

0.54
−2.52

3 : 2 : 5
0.50
6.01

0.52
5.55

0.54
4.84

2.3. Fluidity Tests

After the slurries that did not satisfy the expansion ratio requirement were removed, the remaining four slurry groups were tested for their flow properties. The consistency was measured with a consistency meter, as shown in Figure 1(a), and the test results are shown in Figure 1(b).

(1)For the ingredient proportion of 2 : 2 : 6 and a water-cement ratio of 0.50, the consistency was 45 mm. Differentiation and segregation occurred after the sample was left standing for 1 h.(2)The consistencies of the three water-cement ratios with the ingredient proportion of 3 : 2 : 5 were 59, 67, and 83 mm, respectively. The fluidity of the slurry gradually increased with the water-quicklime ratio. After the samples were left standing for 1 h, no differentiation or segregation occurred.

(a)

(b)

Figure 1: Consistency index test: (a) apparatus for the consistency tests and (b) liquidity index for the four slurry groups.

Therefore, because of the gravimetric and nonpressure grouting methods used for earthen sites and the time factor, the ingredient proportion was set to 2 : 2 : 6. However, the slurry with the water-cement ratio of 0.50 did not meet the fluidity requirement.

2.4. Selection

Based on indoor testing of the nine slurry groups with different ingredient proportions and water-cement ratios, the four groups with the best expansion properties were selected for the fluidity test. Based on the required fluidity and reduced shrinkage deformation of the grouting, the final three slurry groups were selected: CaO : F : C = 3 : 2 : 5 and water-cement ratios of 0.50, 0.52, and 0.54.

3. Determination of the Curing Age

After the types of grouting slurry were determined, the concretions from the three selected groups were aged for continuous but different periods of time to determine the optimal curing age. Then, they were tested for their compressive, flexural, and tensile strengths.

3.1. Experimental Method

According to GB/T50123-1999 [29], slurries of three water-cement ratios with CaO : F : C: = 3 : 2 : 5 were used to form 7.07 cm × 7.07 cm × 7.07 cm cubic specimens and 40 mm × 40 mm × 160 mm (width × depth × length) prismatic specimens for curing. According to GB/T17671-1999 [30], the concretion samples cured for 7, 14, 28, 35, 42, 49, 56, 63, and 90 d were then subjected to compressive, tensile, and flexural strength tests [31, 32]. The cubic specimens were subjected to the compressive and tensile strength tests. The compressive strength test was carried out with a CSS-88000 electrohydraulic servo universal testing machine (range: 300 kN) at a loading rate of 1 mm/min. For the tensile strength test, a pair of parallel steel rods was added to the central axis of the upper and lower sides of the cubic specimens and fixed with rubber bands. Then, the CSS-88000 electrohydraulic servo universal testing machine was used to load the specimens at a rate of 3 mm/min until destruction. The prismatic specimens were subjected to the center-point loading flexural test, which was conducted at a fixed rate of 0.1 mm/min with Instron Testing Machine. The prismatic specimens were tested until they were broken into two halves. Then, their flexural strength was computed.

3.2. Test Results

Figure 2 plots the curves of the concretion strength against the curing age.

(1)The compressive, tensile, and flexural strengths of the concretions gradually increased with the curing time. The growth trends were basically the same for the three water-cement ratios: a fast growth rate early and a relatively slow growth rate later.(2)The pressure, tensile, and flexural strength curves all had two inflection points at curing ages of 28 and 63 d. Before 28 d, the intensity curves basically increased linearly, which indicates that the samples quickly grew stronger compared to the initial strength and had good early strength. The intensity growth gradually slowed down and showed an upper-convex curve at curing ages of 28–63 d. After 63 d, the compressive, tensile, and flexural strengths of the concretions were more stable for all specimens and the changes were very slight.(3)The sample with the highest strength had the water-cement ratio of 0.50. At 63 d, the compressive, tensile, and flexural strengths were 2.28 MPa, 271 kPa, and 1.75 MPa, respectively, which were 99.1%, 97.5%, and 98.9%, respectively, of the strength at 90 d. This indicates that the slurry had basically completed hardening after 63 d of aging, so a curing age of 63 d was selected.

(a)

(b)

(c)

Figure 2: Variations in the (a) compressive, (b) tensile, and (c) flexural strengths against the curing age.

4. Onsite Fissure Grouting Tests

4.1. Test Site

The onsite fissure grouting experiment was carried out on the rammed earth wall near the Lin-Ze Ming Great Wall in Gansu, as shown in Figure 3. The physical and mechanical properties of the wall soil were generally similar to those of the earthen site, and the rammed wall was complete and stable. Before the experiment, six artificial fissures with a width of 8 cm and depth of 10 cm were cut in the wall. Square holes on both sides of the fissures were scooped for the soundwave test.

Figure 3: Experimental site.

4.2. Experimental Materials and Methods

4.2.1. Experimental Materials

The three grouting slurries of SH-(CaO + F + C) with CaO : F : C = 3 : 2 : 5 and water-cement ratios of 0.50, 0.52, and 0.54 were used in the field experiment. The lime slurry used for the lime piles was a mixed slurry of 1.5% mass concentration SH solution and quicklime, earthen soil, and polypropylene fiber, where the water-quicklime ratio was 0.75 and the mass ratio of CaO : C was 8 : 2. The mass ratio of the propylene fiber was 0.5% of the total mass of quicklime and earthen soil.

4.2.2. Experimental Methods

The grouting experimental process was based on WW/T 0038-2012 [33]. Among the six fissures excavated in the experimental wall, the conventional grouting process was adopted for three of them, and no piles were arranged during grouting (Figure 4(a)). The other three fissures were grouted with optimized grouting technology: microlime piles were placed in the cracks during grouting (Figure 4(b)).

(a)

(b)

Figure 4: Flowcharts of grouting technologies: (a) traditional grouting and (b) optimized grouting with lime piles.

Depending on whether the grouting process involved lime piles and the water-quicklime ratio of the grouting slurry, the six cracks were labeled as YZ0.50, YZ0.52, YZ0.54, WZ0.50, WZ0.52, and WZ0.54, as listed in Table 3. YZ indicated lime piles, WZ indicated no lime piles, and the number indicated the water-cement ratio of the slurry.

Table 3: Fissure grouting field experiment data.

No.
Fissure width (cm)
Grouting slurry
Water-cement ratio
Diameter of the lime piles (cm)
Test method

WZ0.50
8.1
SH-(CaO + F + C)
0.50
No lime piles
Sonic wave monitor

WZ0.52
0.52

WZ0.54
0.54

YZ0.50
8.1
SH-(CaO + F + C)
0.50
4.5
Foundation bearing force penetration instrument, infrared thermal imager

YZ0.52
0.52

YZ0.54
0.54

The steps of the traditional grouting process were as follows:

(1)A small air compressor was used to clean up the floating soil and soil residue in fissures.(2)Osmosis reinforcement was sprayed on both sides of the fracture with 1.5% SH slurry.(3)The grouting slurry SH-(CaO + F + C) was mixed evenly according to the mixing ratio CaO : F : C = 3 : 2 : 5 and water-cement ratios of 0.50, 0.52, and 0.54.(4)Foam board was used as formwork to seal the cracked surface from air.(5)Plastic grouting pipes with a diameter of 10 mm were buried at vertical intervals of 300 mm along each crack, which was grouted through the grouting pipe in a bottom-up order. When the grouting pipe overflowed from the adjacent upper grouting pipe, the grouting was stopped and the grouting hole was blocked. Then, grouting was resumed with the above grouting pipe.(6)After the slurry had initially set, the mold was removed to allow the concretion to slowly dry.(7)The 1.5% SH solution and mud prepared by crushing site soil were used to smooth the surface of the slurry concretion.

The steps of the optimized grouting process were as follows:

(1)A small drilling machine was used to drill holes in the selected crack of about 20 cm at 10°–15°. The holes were located at the center of the crack. The diameter of a hole was exactly 1.8 times the crack width. The distance between adjacent two holes in a crack was twice the diameter of the hole from the top to bottom.(2)A small air compressor was used to clean the floating soil in the holes and crack.(3)A PVC pipe with the same diameter as the hole was slowly inserted inside. About 15 cm of the PVC pipe in the wall was exposed.(4)1.5% SH slurry was sprayed on both sides of the fracture as osmosis reinforcement.(5)The grouting slurry of SH-(CaO + F + C) was mixed evenly according to the mixing ratio of CaO : F : C = 3 : 2 : 5 and water-cement ratios of 0.50, 0.52, and 0.54.(6)Foam board was used as formwork to seal the cracked surface from air and leave only the PVC nozzles exposed.(7)Plastic grouting pipes with a diameter of 10 mm were buried at vertical intervals of 300 mm along the crack, and grouting was performed in a bottom-up order. When a grouting pipe overflowed from the adjacent grouting pipe above, the grouting was stopped, and the grouting hole was blocked. Then, the grouting pipe above was used to continue the grouting.(8)The 1.5% SH solution was mixed with quicklime, crushed site soil, and polypropylene fiber to form a lime slurry. The water-cement ratio was 0.75, the CaO : C mass ratio was 8 : 2, and the polypropylene fiber mass ratio was 0.5% of the total mass of the quicklime and site soil.(9)After the grouting slurry was initially set, the PVC pipe were gently pulled out, and the above lime slurry was injected into the holes under pressure to ensure compactness and fullness.(10)After the lime piles and slurry had initially set, the mold was removed so that the slurry concretion and lime pile could slowly dry.(11)1.5% SH solution and mud prepared by crushing site soil were used to smooth the surface of the grout concretion and lime pile.

4.2.3. Test Method

In order to achieve a more reliable quantitative evaluation of the onsite fissure grouting, a sonic wave monitor, infrared thermal imager, and ground bearing force penetration instrument were used to test the wave velocity, penetration resistance, and temperature data of the working area on the rammed wall before and after grouting.

An RSM-SY-type sonic wave monitor was used to test the wave velocity of the rammed wall before grouting, and the mixed wave velocity of the rammed wall and grouting concretion were measured after grouting. From the top to bottom, square holes with a length and width of 10 cm and depth of 7 cm were sequentially excavated on both sides of the fissure. The distance between the square holes and fissure was 5 cm. These holes were convenient for placing the sonic instrument probe. The average values of multiple tests were taken as the final results.

A WG-V-type ground bearing force penetration instrument was used to test the penetration resistance of the same area before and after grouting. The test locations were areas of 0.3 m × 0.3 m that were 5 cm away from both sides of the fissure. The measurement points were arranged to follow the piles, which were in the shape of a quincunx. Six points were measured in each area and averaged to obtain the final value.

An R-series research infrared thermal imager was used for the infrared thermal imaging tests of the six experimental fissures. The infrared thermal images were processed and analyzed with Mei-sheng infrared video processing software.

For the analysis, the unit length was selected from the middle axis of the slurry concretion area in the infrared thermal images of each fissure. Second, another unit length parallel to the first one and around 15 cm away was selected from the rammed wall area. Finally, 30 points with a stable temperature were selected from each line, and the average temperature was taken as the final value of the area.

4.3. Grouting Test Results

4.3.1. Macroscopic Morphology of Fissures after Grouting

After curing, the macroscopic morphology of the onsite fissures after grouting was observed. The slurry concretions were dense with both the traditional and optimized technologies and tightly bonded to the soil on both sides of the fissures. No detachment occurred. In addition, the grouting concretion was similar in color to the rammed soils, as shown in Figure 5.

(a)

(b)

Figure 5: Macroscopic shapes of the fissure after grouting: (a) traditional and (b) optimized.

4.3.2. Changes in the Wave Velocity

Figure 6 shows the results of the wave velocity tests.

(1)With both grouting technologies, the wave velocity clearly improved after grouting. However, the YZ group showed greater amplification at the same water-cement ratio, which indicates that the optimized grouting technology was better at enhancing the strength.(2)For the WZ group with the traditional grouting process, the mixed wave velocity of the slurry concretion and rammed wall decreased as the water-cement ratio increased after grouting and curing: 0.952, 0.921, and 0.876 km·s⁻¹. The wave velocity increased to 46.9%, 45.0%, and 32.7%, respectively, compared to that of the rammed wall soil before grouting.(3)For the YZ group with the optimized grouting process, the mixed wave velocity after grouting and curing were 0.972, 0.975, and 0.893 km·s⁻¹, which indicate increases of 50.9%, 54.3%, and 36.1%, respectively, compared to that before grouting. The YZ0.52 group had the greatest mixed wave velocity and maximal amplification. This is because the additional lime piles meant that more water was required for strength enhancement during the curing period and the water-cement ratio of 0.52 was most conducive to the strength growth.

Figure 6: Wave velocity test results.

4.3.3. Changes in the Penetration Resistance

Figure 7 shows the results of the penetration resistance test.

(1)For both grouting technologies, the penetration resistance of the rammed soil on both sides of the fissures increased significantly after grouting with different water-cement ratios. This means that the soil was compacted on both sides after grouting, and the strength was improved.(2)For the WZ group with the traditional grouting process, the extent of improvement of the penetration resistance after grouting and curing decreased with an increasing water-cement ratio: 6.4%, 6.0%, and 4.2%. The penetration resistance of the slurry concretions also decreased with an increasing water-cement ratio. This indicates that a lower water-cement ratio allows the soil on both sides of the fissure to be squeezed more easily by the slurry concretion.(3)For the YZ group with the optimized grouting process, the penetration resistance increased after grouting by 10.4%, 12.0%, and 9.0% after grouting. The amplification was greatest at a water-cement ratio of 0.52, which corresponds to the trend of the wave velocity.

Figure 7: Penetration resistance test results.

4.3.4. Changes in the Temperature

The infrared thermal imager was used to take photos of the fissures at 13:00–14:00 pm, which are shown in Figure 8. The images show no low-temperature zone between the slurry concretion and rammed soil around the fissures with both grouting technologies, and the transition was relatively gentle. Figure 9 shows the changes in the temperature parameters extracted from the images.

(1)With both grouting technologies, the average temperature of the concretion in the fissure was lower than the average temperature of the rammed soil around the fissure, but the difference was small. This indicates that the thermal conductivities of these two materials are compatible and will not produce a huge thermodynamic effect at the slurry-soil interface or cause local stress concentrations. That is, the effective bonding at the slurry-soil interface will not be destroyed.(2)For the WZ group with the traditional grouting process, the temperature of the slurry concretion decreased as the water-cement ratio increased.(3)For the YZ group with the optimized grouting process, the maximal temperature of the concretion was when the water-cement ratio was 0.52 at 25.4°C. This is because the slurry concretion with a water-cement ratio of 0.52 had the highest dry density. This is consistent with the changes in the wave velocity and penetration resistance, and the thermal conductivity of the concretion body increased with the dry density [34, 35]. Therefore, the YZ group with the water-cement ratio of 0.52 had the highest temperature and was more compatible with the thermal conductivity of the site soil.

(a)

(b)

Figure 8: Infrared thermograms: (a) traditional grouting and (b) optimized grouting.

Figure 9: Analysis results for the infrared thermograms.

5. Analysis and Discussion

The experiments on selecting the slurry and curing age indicated that slurries with an ingredient proportion of CaO : F : C = 3 : 2 : 5 and water-cement ratios of 0.50, 0.52, and 0.54 had typical swelling properties. At 28 d, the concretions experienced no shrinkage but rather volume expansion ratios of 6.01%, 5.55%, and 4.84%, respectively. This would ensure effective bonding of the slurry-soil interface after grouting and greatly mitigate the problem of large dry shrinkage in the past. The strength-age curves showed that the strengths of the three groups of concretions continued to increase after 28 d and became stable after 63 d. The strengths of the concretions increased rapidly in the first 28 d. During this stage, the hydrolysis and hydration reactions were dominant. The free silica and alumina formed by the hydrolysis and hydration of the fly ash reacted with the calcium hydroxide formed by the hydrolysis of the calcium oxide to produce hydrated calcium silicate and calcium hydrated calcium aluminate under the action of water. Both are hydraulic compounds that can make the slurry quickly turn into cement when the water content is high and produce a certain level of strength. The hydration and dissolution of the lime caused the concretion to swell to satisfy the grouting requirement and enhanced the interfacial bonding ability of the grout. At 28–63 d, the rate of increase of the strength for the slurry concretion slowed down, and the carbonization reaction mainly occurred inside the concretion. The aerobic gelling component, Ca(OH)₂ produced by the hydrolysis of calcium oxide absorbed CO₂ to produce CaCO₃, which gradually improved the strength of the concretion. After 63 d, the carbonization reaction gradually weakened, and the strength of the slurry concretion no longer improved. The three selected water-cement ratio slurries had small differences in strength at the final curing age (90 d), which indicates that they had good late mechanical strength and stable physical and mechanical properties. These two aspects indicated that the slurries with the three water-cement ratios and CaO : F : C = 3 : 2 : 5 had a typical expansion and hardening mechanism that ensured that the slurry concretion did not shrink after hardening. This solves the problem of shrinkage and detachment. The typical expansion and hardening mechanism was mainly caused by the hydration and carbonization reactions of quicklime and the hydrolysis and hydration reactions of fly ash. This is consistent with the conclusions of Chen et al. [26] and Wang and Xu [36].

The test results for the onsite fissure grouting showed that the slurry concretion could be compacted and then have good contact with soils on both sides of the crack when the optimized technology of arranging microlime piles in the crack was used. This process resulted in good reinforcement. The main functions of the lime pile were as follows:

(1)Expansion and compaction: in the experiment, the wave velocity in the YZ group with the three water-cement ratios were 4.0%, 9.3%, and 3.4% higher than that of the WZ group, respectively. The penetration resistance in the YZ group was 4.0%, 4.0%, and 4.8% higher than that in the WZ group, respectively. This close agreement showed that the optimized grouting technology is more conducive to grouting reinforcement than the traditional grouting technology. The expansion of the lime piles had an obvious compaction effect on the slurry concretion and the soil on both sides of the fissure. In addition, the width of the experimental fissures was 1.8 times the diameter of the lime piles, so the lime piles had a compacting effect on the slurries within the range of 1.8 times its diameter. This result corresponds to the findings of Mi and Gao [15].(2)Heating: when the lime piles were consolidated, along with the reactions of the quicklime, a large amount of heat was released. Then, the free water in the slurry around the lime piles was vaporized to some extent, which promoted the hardening of the slurry concretion.

After the grouting was completed, the slurry concretion and soil on both sides of the crack were effectively bonded without shrinkage and differentiation. In addition to the quicklime, the SH binder also had an effect [37]. When SH is mixed with raw lime, fly ash, and site soil as the binder, this induces adsorption, chemical reactions, and flocculation. SH not only replaces the alkali metal ions but also makes the solid particles of the slurry agglomerate. It can also form hydrogen bonds because of the carboxyl groups on the molecular chain and hydroxyl groups on the surface of the mixture to form a relatively stable structure. The polar hydroxyl group in SH can actively adsorb small particles of the mixture so that the particles are cemented together to form a large polycondensate, which increases the strength of the slurry concretion. After grouting, the SH solution penetrates the soil around the fissure, wraps the soil particles, and forms a mesh-like connection between the particles and pores so that the soil particles form an organic whole. This increases the strength of the soil around the fissure, water stability, and durability. This mesh-like coupling mechanism promotes tight meshing of the slurry particles and soil particles at the slurry-soil interface, which ensures tight bonding without shrinkage or differentiation.

In contrast, the conventional slurry and grouting process caused dry shrinkage to occur after grouting, and secondary cracks formed, as shown in Figure 10. The expansion and hardening mechanism of the optimized slurry and the microlime pile compaction and heating effects of the optimized grouting technology can solve the problems of shrinkage and differentiation at the slurry-soil interface, as shown in Figure 5(b).

Figure 10: Macroscopic morphology of fissures after conventional slurry and grouting processes.

6. Conclusions

Based on the results, the following conclusions were drawn:

(1)The SH-(CaO + F + C) slurry with the ingredient proportion CaO : F : C = 3 : 2 : 5 meets the expansibility and fluidity requirements for grouting. The resulting concretion had a typical expansion and hardening mechanism that solves the large shrinkage problem of the traditional slurry.(2)The water-cement ratio directly affects the fissure grouting reinforcement. For the WZ group with the traditional grouting technology, the water-cement ratio of 0.50 had the best reinforcement effect. For the YZ group with the optimized grouting technology, the water-cement ratio of 0.52 provided the best results.(3)The onsite fissure grouting tests showed that when the fissure width was 1.8 times the diameter of the lime piles, the piles effectively squeezed and compacted the slurry to produce closer contact with the surrounding soil.(4)The expansion and hardening mechanism of the slurry and the compaction and heating effects of the microlime piles can solve the shrinkage and separation of the slurry from the surrounding soil after drying to avoid the need for multiple replenishments.

Data Availability

The data used to support the findings of this study are included within the article.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

Acknowledgments

The research was funded by the National Natural Science Foundation of China (Grant Nos. 41562015 and 51208245). We would also like to express our gratitude for the support provided by the Program for Changjiang Scholars and Innovative Research Team in the University of Ministry of Education of China (2017IRT17-51).

References

M.-L. Sun, “Research status and development of the conservation of earthen sites,” Sciences of Conservation and Archaeology, vol. 19, no. 4, pp. 64–70, 2007, in Chinese.

E. Fodde, “Traditional earthen building techniques in central Asia,” International Journal of Architectural Heritage, vol. 3, no. 2, pp. 145–168, 2009.

A. A. Charnov, “100 years of site maintenance and repair: conservation of earthen archaeological sites in the American Southwest,” Journal of Architectural Conservation, vol. 17, no. 2, pp. 59–75, 2011.

A. R. Gallardo and J. M. L. Osorio, “Historical rammed earth structures in Eastern Andalusia: (Spain) the restoration philosophy of the architect Prieto-Moreno,” in Proceedings of the 1st International Conference on Rammed Earth Conservation, pp. 407–412, Valencia, Spain, June 2012, in Spanish.

P. A. Jaquin, C. E. Augarde, and C. M. Gerrard, “Chronological description of the spatial development of rammed earth techniques,” International Journal of Architectural Heritage, vol. 2, no. 4, pp. 377–400, 2008.

Z.-X. Li, L.-Y. Zhao, and M.-L. Sun, “Deterioration of earthen sites and consolidation with PS material along silk road of China,” Chinese Journal of Rock Mechanics and Engineering, vol. 28, no. 5, pp. 1048–1052, 2009, in Chinese.

Z.-X. Li, H.-Y. Zhang, and X.-D. Wang, “The reinforcement research of the ancient earth structure sites,” Dunhuang Research, vol. 3, p. 117, 1995, in Chinese.

X.-D. Wang, “New progresses on key technologies for the conservation of Chinese earthen sites in arid environment,” Dunhuang Research, vol. 6, pp. 6–12, 2009, in Chinese.

F.-G. He, “Study on fissure grouting reinforcement of cliff of jiaohe ancient city,” Ph.D. thesis, Lanzhou University, Lanzhou, China, 2009, in Chinese.

Gansu Qinghai Academy of Archaeology, Chinese Academy of Social Sciences, and Qinghai Institute of Cultural Relics and Archaeology, “A brief report on the excavation of the Rahab site in Min-he County, Qinghai, in 2000,” Archaeology, vol. 12, pp. 12–25, 2002, in Chinese.

L. Li and L.-Y. Zhao, Research on Lime Materials in Ancient China, Cultural Relics Press, Beijing, China, 2015, in Chinese.

A. Brás and F. M. A. Henriques, “Natural hydraulic lime based grouts—the selection of grout injection parameters for masonry consolidation,” Construction and Building Materials, vol. 26, no. 1, pp. 135–144, 2012.

A. Bras, F. M. A. Henriques, and M. T. Cidade, “Effect of environmental temperature and fly ash addition in hydraulic lime grout behaviour,” Construction and Building Materials, vol. 24, no. 8, pp. 1511–1517, 2010.

J. Grilo, P. Faria, R. Veiga, A. Santos Silva, V. Silva, and A. Velosa, “New natural hydraulic lime mortars—physical and microstructural properties in different curing conditions,” Construction and Building Materials, vol. 54, no. 11, pp. 378–384, 2014.

H.-Z. Mi and C. Gao, “Experimental study of expansive behaviors of quick lime,” Chinese Journal of Rock Mechanics and Engineering, vol. 31, no. 4, pp. 1253–1256, 2010, in Chinese.

J.-J. Huang, “Researches on selection of anchor slurry and performance mixed quick lime in earthen ruins,” Lanzhou University of Technology, Lanzhou, China, 2018, Dissertation.

J. Liu, “The study on the performance of fissure grouting material and grouting process to the soil ruins in the north-west region,” Dissertation, Lanzhou University, Lanzhou, China, 2017, in Chinese.

L. Li, L.-Y. Zhao, J.-H. Wang et al., “Study on the physical and mechanical properties of two kinds of China ancient buildings,” Chinese Journal of Rock Mechanics and Engineering, vol. 30, no. 10, pp. 2120–2127, 2011, in Chinese.

L.-Y. Zhao, L. Li, Z.-X. Li, and J.-H. Wang, “Research on two traditional silicate materials in China’s ancient building,” Journal of Inorganic Materials, vol. 26, no. 12, pp. 1327–1334, 2011.

A. Kalagri, A. Miltiadou-Fezans, and E. Vintzileou, “Design and evaluation of hydraulic lime grouts for the strengthening of stone masonry historic structures,” Materials and Structures, vol. 43, no. 8, pp. 1135–1146, 2010.

L. G. Baltazar, F. M. A. Henriques, and F. Jorne, “Optimisation of flow behaviour and stability of superplasticized fresh hydraulic lime grouts through design of experiments,” Construction and Building Materials, vol. 35, pp. 838–845, 2012.

R. A. Silva, O. Domínguez-Martínez, D. V. Oliveira, and E. B. Pereira, “Comparison of the performance of hydraulic lime- and clay-based grouts in the repair of rammed earth,” Construction and Building Materials, vol. 193, pp. 384–394, 2018.

F.-G. He, W.-W. Chen, W.-F. Han et al., “Correlation of microstructure indices and performance of sand solidified with polymer material SH,” Rock and Soil Mechanics, vol. 30, no. 12, pp. 3803–3807, 2009, in Chinese.

Y.-M. Wang, Z.-C. Yang, W.-W. Chen et al., “Strength characteristics and mechanism of loess solidified with new polymer material SH,” Chinese Journal of Rock Mechanics and Engineering, vol. 24, no. 14, pp. 2554–2559, 2005, in Chinese.

W.-W. Chen, J. Liu, K. Cui et al., “The comparative study to performance of the earthen sites fissure grouting material PS-(C + F) and SH–(C + F),” Sciences of Conservation and Archaeology, vol. 5, pp. 70–76, 2017, in Chinese.

W.-W. Chen, J. Liu, S.-Y. Gong et al., “Researches on the durability of the SH–(C + F + CaO) slurry applied to reinforce the cracks in earthen sites,” Chinese Journal of Rock Mechanics and Engineering, vol. A2, pp. 4310–4317, 2016, in Chinese.

JGJ/T70-2009, Standard for Test Method of Basic Properties of Construction Mortar, Ministry of Housing and Urban-Rural Development, Beijing, China, 2009, in Chinese.

BS EN 1015-9:1999, Methods of Test for Mortar for Masonry. Determination of Workable Life and Correction Time of Fresh Mortar, British Standards Institution, London, UK, 1999.

GB/T 50123-1999, Standard for Soil Test Method, China Planning Press, Beijing, China, 1999, in Chinese.

GB/T 17671-1999, Method of Testing Cements—Determination of Strength, China Planning Press, Beijing, China, 1999, in Chinese.

X.-R. Ren, J.-K. Zhang, N. Wang et al., “Age performance of grout mixed with calcined gingernuts and earthen fabric in anchoring conservation of earthen sites,” Journal of Materials Science and Engineering, vol. 35, no. 1, pp. 62–66, 2017, in Chinese.

J.-K. Zhang, W.-W. Chen, Z.-X. Li et al., “Laboratory tests on property and durability of PS-(C + F) slurry used in anchoring conservation of earthen sites,” Chinese Journal of Geotechnical Engineering, vol. 37, no. 10, pp. 1802–1809, 2015, in Chinese.

State Administration of Cultural Heritage, WW/T 0038-2012: Design Specification for Preservation and Reinforcement Engineering of Arid Earthen Sites, Cultural Relics Press, Beijing, China, 2012.

D.-X. Zhang, T.-R. Wang, X.-D. Wang et al., “Experimental study of the heat-conduction properties of earthen ruins soil rein forced by potassium silicate,” Chinese Journal of Rock Mechanics and Engineering, vol. 30, no. 1, pp. 202–207, 2011, in Chinese.

D. Zhang, T. Wang, X. Wang, and Q. Guo, “Laboratory experimental study of infrared imaging technology detecting the conservation effect of ancient earthen sites (Jiaohe Ruins) in China,” Engineering Geology, vol. 125, pp. 66–73, 2012.

D.-X. Wang and W.-Y. Xu, “Research on strength and durability of sediments solidified with high volume fly ash,” Rock and Soil Mechanics, vol. 33, no. 12, pp. 3659–3664, 2012, in Chinese.

S.-X. Chai, P. Wang, W.-F. Han et al., “Research on strength and microstructure feature of solidified saline soil in inshore with polymer,” Rock Mechanics and Engineering, vol. 06, pp. 1067–1072, 2007, in Chinese.