Effects of cementitious grout components on rheological properties

Construction and Building Materials 227 (2019) 116654

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Effects of cementitious grout components on rheological properties Jie Liu a,b, Yi Li b,c,⇑, Guijin Zhang b, Yaning Liu d a

School of Traffic & Transportation Engineering, Changsha University of Science & Technology, Changsha 410114, Hunan, China School of Hydraulic Engineering, Changsha University of Science & Technology, Changsha 410114, Hunan, China c Key Laboratory of Dongting Lake Aquatic Eco-Environmental Control and Restoration of Hunan Province, Changsha 410114, Hunan, China d Department of Mathematical and Statistical Sciences, University of Colorado Denver, Denver, CO 80204, USA b

h i g h l i g h t s
The effects of cementitious grout components on the rheological properties are investigated.
The performance of scouring resistance of cementitious grouts with different components is studied.
The rheological mechanism and engineering applicability of cementitious grouts are analyzed.

a r t i c l e

i n f o

Article history: Received 2 April 2019 Received in revised form 5 July 2019 Accepted 3 August 2019

Keywords: Cementitious grouts Curtain grouting Rheological properties Rheological mechanism Applicable formation

a b s t r a c t The impacts of rheological properties of cementitious grouts on the quality of curtain and consolidation grouting cannot be ignored. A series of experiments are carried out to investigate the effects of the components of cementitious grouts on the rheological properties. Moreover, the rheological mechanism and applicable formations of the slurries are discussed. The results show that the rheological properties of clay-cement slurry (CCS) are related to the water/solid ratio and clay dosage. Using CCS to form grouting curtain in strata with large porosity can solve the problem of slurry leakage and dramatically reduce costs. The rheological properties of clay-cement pasty slurry (CCPS) are mainly related to the modifier dosage. With the increase of modifier dosage, the rheological phenomenon of the CCPS shifts from rheopexy to thixotropy. The fact that CCPS has a strong scouring resistance makes it applicable in strata that are rushed by dynamic water. The rheological properties of clay-cement-sand pasty slurry (CCSPS) are related to the sand/cement ratio and modifier dosage. Adding sand can remarkably increase the initial yield stress and viscosity. CCSPS can be the optimal grouting material for impervious grouting in strata where there is a high consumption of slurry or high velocity of groundwater flow. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Soft and loose strata with three permeable structures (i.e., layered, banded and shelled structures) are widely encountered in hydraulic engineering, civil engineering and mining engineering [1–3]. The dynamic flow of groundwater in those grounds is one of the harmful factors damaging the foundations. Flowing water carries fine particles away from the ground, resulting in a worse engineering geological condition [4]. To ensure the safety of projects with soft and loose strata, it is worth implementing antiseepage and reinforcement measures. Grouting is the injection of pumpable materials into a soil or rock formation to change the physical characteristics of the formation [5,6]. Not only can it reduce leakage through the foundation ⇑ Corresponding author. E-mail address: [email protected] (Y. Li). https://doi.org/10.1016/j.conbuildmat.2019.08.035 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

and potential seepage erosion, but also it can improve mechanical properties, integrity and compactibility of rock and soil [7,8]. As an effective measure for seepage prevention or reinforcement of foundation, grouting has been widely used in anti-seepage of reservoir, foundation reinforcement, cavern filling and landfill protection [9– 11]. However, there are many problems with grouting in soft and loose strata, such as the difficulties of construction and controlling diffusion range, high material consumption and poor grouting effects [12–14]. Cementitious materials must have desirable rheological properties (i.e., fluidity, stability and initial viscosity), which directly determine the workability such as the pumpability, selfleveling and compacting, and the ability to penetrate into voids of the materials in engineering practice [15,16]. Only in this way can the slurry be successfully pumped to the target aquifers [17]. In addition, the highly stable grouting slurry can effectively resist water dilution and form a high-quality solidified grout stone in the target aquifers with large voids. For this purpose, clay, sand,

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J. Liu et al. / Construction and Building Materials 227 (2019) 116654

and accelerator were mixed with cement slurry to further improve the grouting effects [18–20]. However, the impacts of the amount of clay, sand and accelerator on the rheological properties of cementitious grouts are not very clear, and therefore it should be studied comprehensively. Many studies have been performed on the rheological properties of a series of slurries. Warner et al. [21] studied the influence of additives on the rheological properties, and showed that proper rheological behavior can improve grouting quality. Nguyen et al. [22] studied the effects of water/cement (w/c) ratio and viscosity modifier on the rheological properties of Herschel-Bulkley fluid. Rahman et al. [23] measured the yield stress of cement slurry by conventional rheometer. It showed that the rheological properties of cementitious grouts are very complicated because of their unpredictable thixotropy and yield stress. Zhang et al. [24] investigated the rheological properties of a new type of pasty cement slurry, and it showed that the initial fluidity and viscosity of the slurry vary with time. Hoang et al. [25] analyzed the rheological properties of unstable slurry during the process of water bleeding, with the conclusion that the rheological properties of the slurry during the layered process are mainly determined by the lower slurry and the shear rate. Zhang et al. [4] studied the rheological model, viscosity and thixotropy of a pasty clay-cement grouting material that is suitable for curtain grouting in soft and loose strata under the condition of dynamic groundwater scouring. The existing literature provides a wide variety of admixtures to shorten the setting time of cement slurries and improve the early strength of slurries. Lachemi et al. [26] investigated the performances of four different types of new viscosity modifying admixtures based on various tests of rheological properties, fluidity, segregation and washout resistance of the cement pastes. Güllü et al. [27] studied the rheological properties (e.g., shear stress, apparent viscosity, shear rate, yield stress, and plastic viscosity) of geopolymer grout in comparison with the cement-based grouts including fly ash and cold bonded fly ash. Tregger et al. [28] investigated how clay admixtures affect the microstructure of cement pastes from a rheological stand point. The results are consistent with the green strength tests performed on concrete mixes derived from the cement paste mixes. Therefore, the modifier can be used as long as it meets the practical needs of grouting engineering. The modifier studied in this paper has been successfully implemented to solve the anti-seepage problem in the Tuokou hydropower project (located in Huaihua City, Hunan Province, China) and the prereinforcement problem in the Luodala tunnel project (located in Lijiang City, Yunnan Province, China) [4,29]. Though the above works have promoted the development and application of grouts, there are still a few problems worth further exploring. The existing research mainly focuses on conventional cement slurry, rarely involving clay-cement slurry and pasty slurry. However, the rheological properties and the ranges of engineering applications of the latter two are significantly distinct from the former. In addition, previous studies only focused on single slurry or just one aspect of rheological properties. There is still a lack of comprehensive and systematic study on rheological properties of grouts. There are limited reports on rheological mechanism, and the mechanisms of rheological behavior of grouts are not clear so far. Therefore, it is necessary to study the rheological properties and mechanism of cementitious grouts with different components in a comprehensive and systematic way to verify the full engineering applicability. The main objective of the current work is to systematically study the rheological properties of cementitious grouts with different components. A series of experiments are carried out to investigate the effects of the components, such as clay, sand and modifier, on the rheological properties of slurries. The rheological mechanism of cementitious grouts is analyzed, followed by analysis of

the engineering applicability of the slurries. The results will serve as a guide and reference to the relevant theoretical research and engineering applications. 2. Experimental details Rheological properties refer to the shear deformation and flow of slurries when subjected to the external force. It is well known that the rheological properties of the slurry have a strong impact on its fluidity, degree of perfusion and grouting effect. The dosages of clay, sand and modifier can influence the rheological properties of cementitious grouts. 2.1. Materials In this paper, the rheological properties of CCS, CCPS and CCSPS are studied. The main components of the three types of cementitious grouts are cement, clay, sand and a modifier. 2.1.1. Cement Cement mainly serves to enhance the strength of the solidified grout stone. The cement used in the tests is grade 42.5 ordinary Portland cement. The quality of the cement conforms to the national standard for Portland cement [30]. Its chemical constituents and main performance indices are shown in Table 1 and Table 2. 2.1.2. Clay Clay, with a stable chemical properties and a large viscosity, plays a major role in the viscosity of grouts. The mineral constituents, consistency limits, content and types of ions, pH values, relative density and particle size of clay from Huaihua, a southwest city of Hunan Province, China, are measured. This acidic clay has a natural water content of 20–30%, a plastic limit greater than 14, a liquid index of 0.30–0.45 and an average specific gravity of 2.73. The mineral components and chemical constituents of clay are shown in Table 3. 2.1.3. Sand Mixing an appropriate amount of sand can improve the cohesion and internal friction angle of the slurry, and then enhance the strength of the solidified grout stone. The sand used in the test is natural river sand with a fine modulus of 2.56, a sediment percentage of 1.6%, a stacking density of 1465 kg/m3, an apparent density of 2645 kg/m3, and a natural water content of 1.99%. The gradation of natural river sand does not meet the requirement of rheological experiments, so it needs to be sieved before the test. Accordingly, equal amounts of grit (diameter >0.5 mm), medium sand (diameter of 0.25–0.50 mm) and fine sand (diameter of 0.1– 0.25 mm) are mixed uniformly. The grading diagram of sand is shown in Fig. 1. 2.1.4. Modifier The modifier is made in-door, which contains a coagulationpromoting additive. The main function of modifier is to shorten the setting time of slurries [31]. The dosage of such modifier meets the technical requirements of Chinese Standard [32]. The main component of the modifier is meta-aluminate. The modifier needs to be stored in dry environment because it is hygroscopic and can react with water. 2.2. Experimental instrument and principles Rheological experiments are conducted using an R/S Plus rheometer (Brookfield Engineering, MA, USA). The R/S Plus

3

J. Liu et al. / Construction and Building Materials 227 (2019) 116654 Table 1 Chemical constituents of Portland cement. Chemical constituents

SiO2

Al2O3

Fe2O3

MgO

CaO

SO3

Loss on ignition

Dosage/%

22.7

7.7

4.7

2.7

56.8

2.7

2.3

Table 2 Performance indices of Portland cement. Indices

Cement

Density (g/cm3)

3.06

Consistence (%)

29.5

>80 lm (%)

Stability

Qualified

1.9

Setting time (min)

Compressive strength (MPa)

Initial set

Final set

3d

28d

90

325

19.1

48.6

Table 3 Mineral components and chemical constituents of clay. Mineral components

Kaolinite

Illite

Montmorillonite

Quartz

Albite

Albite Chlorite

Dosage/% Chemical constituents Dosage/%

62 SiO2 45.80

12 Al2O3 37.30

10 Fe2O3 0.50

8 K2O 0.11

5 CaO2 <0.01

3 MgO <0.01

Loss on ignition 14.50

Fig. 1. Grading diagram of sand.

rheometer measurement sensing system consists of two parts, a variety of spindles and a dial, connected with a specific torque coefficient calibrated spring. The spindle rotates in the sample driven by a synchronous motor. The fluid resists the rotating spindle, and then the calibrated spring connected to a rotation shaft is distorted. Eventually, the resistance can keep balance with the torque force of the calibrated spring. The schematic diagram of the rheometer is shown in Fig. 2. The experimental system includes a vane spindle (V30-15-3tol) (Fig. 3) for date testing and software (Rheo3000) for data analysis and processing. The radius of the vane spindle is 15 mm, and the length is 60 mm. The ranges of the vane spindle (V30-15-3tol) are shown in Table 4. The Rheo3000 software is proprietary software designed by BROOKFIELD for automatic testing, data collection and analysis, which can save time and maximize the utility of the rheometer. According to the operating manuals, the sample container is a beaker with a measuring range of 600 ml, an external diameter of 90 mm and a height of 130 mm [33]. Viscosity, cohesion and flow resistance are related to the shear rate and shape of the spindles. The rheometer can measure different ranges of viscosity by adjusting the shear rate or using different

Fig. 2. Schematic diagram of the rheometer.

Fig. 3. Vane spindles.

spindles. The viscous force increases when shear rate rises or the superficial area of the spindles increases. Therefore, the minimum viscosity can be measured by the maximum superficial area of the spindles at the highest shear rate, and the maximum viscosity can be measured with the smallest superficial area of the spindles at the lowest shear rate.

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J. Liu et al. / Construction and Building Materials 227 (2019) 116654

g¼

Table 4 Ranges of the vane spindle (V30-15-3tol). Vane spindle

Viscosity range/Pas

Shear rate/s1

Shear stress/Pa

V30-15-3tol

0.039–3390000

0–306.15

0–8000

2.3. Experimental schemes The water/cement ratio, clay, modifier and sand are the dominating factors to control the rheological properties of slurries [34,35]. According to the Chinese Standard DLT_5418-2012 [36], the water/cement ratio of cement slurry can generally be 2.0, 1.5, 1.0, and 0.6. Moreover, the clay dosage should be less than 50% by cement mass. Therefore, in the study of the rheological properties of CCS, the water/solid ratios (by mass) are 0.6:1, 1.0:1 and 1.5: 1, and the clay dosages are 0%, 10%, 30% and 50% by cement mass. The dosage of sodium aluminate ranges from 0.5% to 3.0% by cement mass when used as a cement slurry additive [37]. In the study of the rheological properties of CCPS, the water/clay/cement ratio (by mass) is 2:1:1, and the modifier dosages are 0.5%, 0.75%, 1.0%, 1.25% and 1.5% by cement mass. According to previous engineering experience from both the laboratory tests and field practice [38–41], for CCSPS, the water/clay/cement ratio (by mass) is also 2:1:1, the modifier dosages are 0.5%, 1.0% and 1.5% by cement mass, and the sand/cement ratios (by mass) are 1:1, 1.5:1, 2:1. The specific experimental schemes are shown in Tables 5–7. To minimize experimental error, three comparative tests are conducted for each scheme. The intermediate results of the three comparative tests are taken for final analyses.

s t

ð3Þ

where s is the shear stress, t is the shear rate, g the is viscosity, M is the torque acting on the surface of the spindle (instrument reading), x is the angular velocity of the spindle, Rc is the radius of the container (outer boundary), Rb is the radius of the spindle (bob), and L is the effective spindle side length (Fig. 4). According to previous experimental experience, operating manuals [33], and the results reported in the literature [42,43], for the rheological model test, the shear rate is raised from 0 to 60 s1 over a period of 120 s. For viscosity tests, the shear rate is kept at a constant level of 30 s1 and the viscosity data are gathered over a period of 60 min. For the thixotropy test, the shear rate increases from 0 to 60 s1 over a period of 120 s and then decreases from 60 to 0 s1 over another 120 s. 2.5. Experimental procedure The operational schematic of the rheological experiment of slurries is shown in Fig. 5. First, the impurities (including sand, stones and small wood pieces from tree stumps, etc.) are removed from the clay by sieving (270 lm) and drying, and then the clay is ground with a grinder and sieved through a mesh (75 lm). Second, the clay is soaked in water for 24 h. Afterwards, appropriate amounts of water, cement, modifier or sand are thoroughly mixed by a rotating mixer at 1000 rpm for 5 min [36,44]. After that, 600 ml of the slurry is quickly added into a beaker (measuring range of 600 ml). Finally, the rheological experiments begin within two minutes after the slurry is mixed. All the processes in this study are performed under room temperature (25 ± 2 °C).

2.4. Experimental methods

2.6. Scouring resistance test

The formulae for calculating the shear rate, viscosity and shear stress in the rheometer are as follows:

The slurry should perform well in resisting water rushing or dilution. To keep stable in dynamic water, it should be solidified rapidly in such circumstances. CCPS (B3) and CCSPS (C2) have the same water/cement/clay ratio (2:1:1) and modifier dosage (1%). The cement/clay ratio of CCS (A4) is also 1:1, and its water/solid ratio of 60% is the closest to that of CCPS (B3) and CCSPS (C2). Therefore, the scouring resistance tests of CCS (A4), CCPS (B3) and CCSPS (C2) are conducted under different flow velocities in the water flume to verify their scouring resistances. According to pre-

s¼ t¼

M

ð1Þ

2pR2b L 2xR2c R2b R2b ðR2c

ð2Þ

 R2b Þ

Table 5 Experimental schemes of CCS. Number

A1

A2

A3

A4

A5

A6

A7

A8

A9

A10

A11

A12

Water/solid ratio Clay dosage

0.6:1 0%

0.6:1 10%

0.6:1 30%

0.6:1 50%

1:1 0%

1:1 10%

1:1 30%

1:1 50%

1.5:1 0%

1.5:1 10%

1.5:1 30%

1.5:1 50%

Table 6 Experimental schemes of CCPS. Number

B1

B2

B3

B4

B5

Water/cement/clay Modifier dosage

2:1:1 0.5%

2:1:1 0.75%

2:1:1 1.0%

2:1:1 1.25%

2:1:1 1.5%

Table 7 Experimental schemes of CCSPS. Number

C1

C2

C3

C4

C5

C6

C7

C8

C9

Water/cement/clay Sand/cement ratio Modifier dosage

2:1:1 1:1 0.5%

2:1:1 1:1 1.0%

2:1:1 1:1 1.5%

2:1:1 1.5:1 0.5%

2:1:1 1.5:1 1.0%

2:1:1 1.5:1 1.5%

2:1:1 2:1 0.5%

2:1:1 2:1 1.0%

2:1:1 2:1 1.5%

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J. Liu et al. / Construction and Building Materials 227 (2019) 116654

0. 35 m

4.00 m

1.00 m

Slurry

Fig. 6. Scouring resistance experiment in the flume.

Fig. 4. Geometry diagram of the spindle.

vious works [4,41], the water flow velocities are designed as 0.2, 0.5, 0.8 and 1.2 m/s. The scouring time is 60 s. The length, width and height of the flume are 4.00 m, 0.35 m and 1.00 m, respectively. A water pump is used to control the flow velocities. The test procedure is as follows: first, adjust the flow velocity to the certain value; second, when the flow velocity is stable, place 2.5 kg slurry in the flume and then starts the scouring resistance experiment; third, stop scouring the slurry and weigh the residual slurry at the flushing time of 60 s; finally, calculate the flushing rate. The experimental model is illustrated in Fig. 6.

3. Results and discussion 3.1. Rheological properties of CCSs 3.1.1. Rheological curves The rheological curves of CCSs with different water/solid ratios are shown in Fig. 7. It is clear that the CCSs with a water/solid ratio of 0.6: 1 belong to the Bingham fluid [26,45]. The yield stress increases with the increase of clay dosage. When the water/solid

ratio is 1:1 and clay dosages are 0% and 10%, the rheological models of slurries are similar, which are power-law fluids with shear dilatancy (Dilatant fluid) [40]. The shear stress increases with the shear rate. When the clay dosage reaches 30% and 50%, the slurries are Bingham fluids, and the phenomenon of shearing dilatation only exists at the clay dosage of 30% in the designed schemes. When the water/solid ratio is 1.5: 1, the CCSs are Bingham fluids. Though, the clay dosage significantly changes the rheological curves of the slurries, they are still Bingham fluids. When the shear rate is less than 15 s1, the shear stresses of the slurries are 0 Pa since the high water/solid ratio causes the initial viscosities of the slurries to be close to 0 Pa·s (water). As the slurries coagulate, the viscosities and shear stresses gradually increase.

3.1.2. Viscosity The viscosity curves of CCSs with different water/solid ratios are shown in Fig. 8. When the water/solid ratio is 0.6:1 and clay dosages are 0% and 10%, the viscosities of the slurries vary slightly with time. When the clay dosages are 30% and 50%, the viscosities of the slurries increase with time rapidly, followed by staying stable after 40 min. When the water/solid ratio is 1:1, the viscosities of the slurries first decrease and then increase. With the increase of clay dosage, the initial viscosity of a slurry also increases. When the water/solid ratio is 1.5:1, the viscosity of the slurry with clay dosage of 0% first remains zero, and then increases gradually. The viscosities of the other slurries decrease first and then increase. Except for the slurry with clay dosage of 50%, the initial viscosities of the other slurries are 0. The explanation for the viscosity of a slurry decreasing first and then increasing with time

Fig. 5. Operational schematic of the rheological experiment of slurries.

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J. Liu et al. / Construction and Building Materials 227 (2019) 116654

(a) water/solid ratio 0.6:1

(a) water/solid ratio 0.6:1

(b) water/solid ratio 1:1

(b) water/solid ratio 1:1

(c) water/solid ratio 1.5:1 Fig. 8. Viscosity curves over time of CCSs with different water/solid ratios.

(c) water/solid ratio 1.5:1 Fig. 7. Rheological curves of CCSs with different water-solid ratios.

is that the slurry is unstable and can be separated into water and slurry quickly when the water/solid ratio is high. The viscosity of the slurry decreases in the water bleeding process. After the water bleeds completely, the slurry is cemented and its viscosity increases gradually.

3.2. Rheological properties of CCPSs CCPS, mainly composed of clay, cement and coagulationpromoting modifier, has a yield stress more than 20 Pa. It is widely used in large porous strata suffering from water soaking or scouring [46]. The modifier dosage strongly affects the rheological properties of the slurry.

J. Liu et al. / Construction and Building Materials 227 (2019) 116654

3.2.1. Rheological curves As shown in Fig. 9, the rheological model of CCPS is affected by the modifier dosage. The slurries are Bingham fluids with the modifier dosage of 0.50% and 0.75%. While the modifier dosages are 1%, 1.25% and 1.50%, the slurries are a pseudo-plastic fluid (i.e. Herschel–Bulkley fluid) with an initial shear yield value more than 20 Pa [23,47]. When the modifier dosage is higher than 1%, the shear stresses of the slurries first decrease and then remain stable with the increase of shear rate. The reason for this phenomenon may be that the slurry structure is gradually destroyed as the shear rate increases. Furthermore, the structural resistance is reduced, resulting in a decrease in the viscosity of the slurry. When the structure of the paste is completely destroyed, the shear stress of the system maintains a stable value. Therefore, the shear stress tends to be stable eventually. A comparison of static and dynamic yield stresses can be a good example for the phenomenon [48]. The stable shear stresses are similar in value when the modifier dosages are higher than 1%. At a given shear rate, the shear stress first increases and then almost stops changing with the increase of modifier dosage. 3.2.2. Viscosity The viscosity curves of CCPSs with different modifier dosages are shown in Fig. 10. The viscosities of the CCPSs first increase with time and then remain stable. With regard to the variation of the viscosity with elapsed time, it is clearly seen that the viscosities of all CCPSs continuously increase with hydration time due to the continuous production of hydration products [49]. The time point at which the viscosity tends to be stable increases with the increase of the modifier dosage. The result shows that the time point of stabilization is related to the hydration time. In addition, the CCPSs with different modifier dosages but the same clay dosages exhibit similar viscosities, which indicates that the clay dosage is the main factor determining the viscosity of a slurry. 3.2.3. Thixotropy When a suspension is at rest, particles collide due to the shear force and Brownian motion, and flocs eventually agglomerate [50]. However, when the material is sheared, the flocs break and their size decreases at an increasing shear rate, and thus the apparent viscosity decreases [51]. This phenomenon is known as thixotropy and has been shown earlier for other fluids [52]. The thixotropies of CCPSs with different modifiers are shown in Fig. 11. Modifier dosage has a strong influence on the thixotropy of CCPS, and it makes the change in thixotropy very complicated.

Fig. 9. Rheological curves of CCPSs with different modifier dosages.

7

Fig. 10. Viscosity change curves over time of CCPSs with different modifier dosages.

When the modifier dosages are 0.5% and 1.0%, the rising curves of the slurries are below the decreasing curves, and they show different rheopexy behavior. When the modifier dosage is 1.5%, the rising curve of the slurry is above the decreasing curve, and they show overt thixotropy. Overall, with the increase of modifier dosage, the properties of the CCPSs switch from rheopexy to thixotropy. The effects of modifier dosage on thixotropy of CCPS are as follows. When modifier dosage is high (i.e. larger than or equal to1.5%), the coagulability of the slurry appears and it is at plastic state. The internal structure of the slurry can be destroyed when it is subjected to external forces (e.g. sustaining shear forces), because of the weakness or disappearance of its intermolecular forces. Finally, the strength and consistency of the slurry decrease. If the external forces are terminated, the molecules spontaneously coagulate again. However, the strength of the slurry is lower than before, which shows thixotropy. On the other hand, the slurry with low modifier dosage (i.e. smaller than 1.0%) has a larger Brownian motion range due to the weaker bonding forces among molecules. The consistency of the slurry increases with the hydration of the cement. Under the same shear rate, the shear stress of the rising rheological curve is always less than the shear stress of the dropping rheological curve, and it shows rheopexy. 3.3. Rheological properties of CCSPSs CCSPS is made by adding a suitable amount of sand on the basis of CCPS. It is usually applied to the grouting of large cavities and wide cracks. In order to ensure the grouting effect, the rheological properties of the slurry should be studied before application. 3.3.1. Rheological curves The rheological curves of CCSPSs with different sand/cement ratios are shown in Fig. 12. The results show that modifier dosage has remarkable impacts on the rheological model and yield stress of CCSPS. When the modifier dosage is 0.5%, the rheological curve of CCSPS is a straight line without going through the origin (0, 0), so the slurry belongs to Bingham fluid. When the modifier dosages are 1.0% and 1.5%, the shear stresses of the slurries initially decrease with increasing shear rate, and finally become stable. The slurry is a pseudo-plastic fluid with a yield value larger than 30 Pa. The yield stress is dependent on both the flocculation strength and structure of the suspension [53]. When the shear stress exceeds the yield stress, flow is initiated and flocs begin to break down into smaller ones. This microstructural process releases liquid entrapped within the flocs, producing more free liquid for lubrication between sand particles. As a result, the shear

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J. Liu et al. / Construction and Building Materials 227 (2019) 116654

(a) sand/cement ratio 1:1 Fig. 11. Thixotropies of CCPSs with different modifier dosages.

stress decreases with increasing shear rate, which explains the shear-thinning behavior of the slurry [54,55]. Under the same shear rate, the higher the modifier dosage is, the greater the yield stress becomes. The change in sand/cement ratio alters the yield stresses of slurries, while the varying yield stresses of slurries with different proportions show similar behavior. Under the same modifier dosage, the yield stresses of slurries with the sand/cement ratio of 1.5:1 are much higher than those of slurries with sand/ cement ratios of 1:1 and 2:1. 3.3.2. Viscosity The changes in the viscosities of CCSPSs with time are shown in Fig. 13. The modifier dosage has impacts on the viscosity curves of CCSPSs. Fig. 13(a) shows that when the modifier dosage is 0.5%, the viscosity of the slurry slowly increases with time and the fluctuation of the slurry viscosity is less than 0.5 Pas. However, when the modifier dosages are 1.0% and 1.5%, the viscosities of the slurries are initially larger than 2.5 Pas, then decrease sharply with time and finally remain stable. The differences of stabilized viscosities of slurries with different modifier dosages are less than 1 Pas. The reason for the viscosity variation of the slurry with modifier dosage is due to the fact that the modifier can promote the hydration reaction of cement; the higher the amount of curing agent is, the more significant the promotion effect becomes. The test results are consistent with those reported in [56]. The viscosity sharply decreases with time is probably because the slurry quickly solidifies into a soft solid under the action of modifier, and the internal structure of the soft solid is destroyed at a certain shear rate. Fig. 13(b) shows that the change in sand/cement ratio alters the initial viscosity of CCSPS, while the variation tendencies of the viscosities with different component proportions are also similar. With the same modifier dosage, the initial viscosity of the slurry with the sand/cement ratio of 2:1 is higher than those of the slurries with sand/cement ratios of 1:1 and 1.5:1. In addition, the final viscosities of the slurries are less than 0.5 Pa·s. Based on the analysis of the data, it can be concluded that the increase of sand/ cement ratio increases the initial viscosity of the slurry, but the effect on the viscosity of the slurry after stabilization is not obvious. When the sand/cement ratio increases, the amount of sand increases at a constant amount of cement, so more water in the slurry is consumed. This leads to a reduction of the slurry that can be used to enwrap sand particles and an increase of the friction between the sand particles. Therefore, the initial viscosity of the slurry increases [57–59].

(b) sand/cement ratio 1.5:1

(c) sand/cement ratio 2:1 Fig. 12. Rheological curves of CCSPSs with different sand/cement ratios.

3.3.3. Thixotropy The thixotropy of CCSPS is shown in Fig. 14. The results show that the rising curves of CCSPSs are above the descending ones. These properties of CCSPSs are thixotropy, and the thixotropy increases with increasing modifier dosage. However, the sand/

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J. Liu et al. / Construction and Building Materials 227 (2019) 116654

(a) sand/cement ratio 1:1 (a) sand/cement ratio 1:1

(b) sand/cement ratio 1.5:1 (b) modifier dosage 1.0% Fig. 13. Viscosity curves of CCSPSs.

cement ratio has little effect on the thixotropy of the slurry, which is consistent with the results published in [60]. 3.4. Effects of rheological properties of slurries on scouring resistance performance Scouring resistance performance of the slurries has a strong impact on the grouting effect in soft and loose strata under dynamic groundwater scouring. The grouting material in such condition should have the specific performance of resisting water rushing and diluting. Moreover, it should have the performance of stably filling the large porosity of the formations with water rushing. The results of scouring resistance experiments are shown in Table 8. The maximum and minimum scouring resistance performances of the tested slurries are CCS (A4) and CCSPS (C2) respectively. Even though the flow rate increases to 1.2 m/s, the flushing rates of CCPS (B3) and CCSPS (C2) are at low levels of 34% and 26%, respectively. It can be concluded that both CCPS (B3) and CCSPS (C2) have excellent water rushing resistance. Viscosity and yield stress have important effects on the scouring resistance performance of a slurry as well. When the shear force is less than the yield strength of a slurry, the slurry will remain stationary. Only when the shear force exceeds the yield strength does the slurry begin to flow. In addition, the viscosity becomes the

(c) sand/cement ratio 2:1 Fig. 14. Thixotropy of CCSPSs with different sand/cement ratios.

main internal factor that affects the diffusion distance of the slurry when the slurry begins to move [44]. Therefore, the viscosity and yield stress of the slurry are important parameters that influence the diffusion distance and grouting effect. Figs. 15 and 16 are the bar diagrams of the initial yield stresses and viscosities of three types of slurries respectively. The initial yield stresses and viscosities of the three types of slurries are dif-

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J. Liu et al. / Construction and Building Materials 227 (2019) 116654

Table 8 Results of anti-rush experiment. Number

Flow velocity/ms1

Flushing rate/%

Flushing time/s

A4 A4 A4 A4 B3 B3 B3 B3 C2 C2 C2 C2

0.2 0.5 0.8 1.2 0.2 0.5 0.8 1.2 0.2 0.5 0.8 1.2

37 43 51 68 13 20 29 34 11 15 19 26

60 60 60 60 60 60 60 60 60 60 60 60

Fig.15. Yield stresses of the slurries.

ferent. CCS has the largest values, CCPS has the intermediate ones, and clay-cement-sand slurry has the smallest ones. Due to the difference in viscosities and yield stresses of the three types of slurries, their scouring resistance performances are also distinguishing.

4. Analysis of the rheological mechanism of grouts CCS, CCPS and CCSPS are all stable slurries, which have the advantages of less bleeding and better integrity [61]. Because the main components of the three types of slurries are cement and clay, the yield stresses and viscosities are larger than those of the conventional cement slurry. However, the rheological mechanisms of the three slurries are different because of their different components. A schematic of the microstructures of the slurries is presented in Fig. 17 [62–64]. It shows that clay particles are evenly distributed in the slurries. The reaction products of the modifier wrap the cement particles. The sand serves as a skeleton in the slurry, which greatly reduces the water/solid ratio of the slurry. The change in rheological properties of the CCS compared with the pure cement slurry is mainly due to the amount of clay. Clay has more stable chemical properties and finer particles than cement. Besides, it has a larger viscosity and also contributes to the viscosity of the slurry. Therefore, the initial yield stress and viscosity of CCS are larger than those of cement slurry. In addition, thanks to the clay component, the slurry owns a controlled thixotropy and a better stability. During the grouting process, when the diffusion rate of the slurry slows down or even decreases to zero, the slurry structure will recover so quickly that the cement particles cannot be layered or precipitated. When the slurry is grouted in large fissures or karst caves, the thixotropy of it can prevent the slurry from diffusing far away, and it therefore can reduce the consumption of slurry. Furthermore, thixotropy can improve scouring resistance of slurries in soft and loose strata under dynamic groundwater condition. CCPS is a type of cementing material based on ordinary CCS with a suitable amount of modifier mixed. It can be hardened in both the air and water. CCPS can firmly bond sand, stone and other materials together to form the grouted stone. The rheological mechanism of the grouting material is mainly due to the interaction among cement, water and modifier. By adding the modifier into the slurry, the inorganic salt in the modifier hydrolyzes, followed by the generation of a large amount of aluminate anions, sulfate ions and hydroxyl ions [65]. Then, the aluminate anions react with calcium ions. The main hydration reaction equations are as follows: 3-

1. 2AlO3 Fig. 16. Viscosities of the slurries.

þ 3Ca2 þ þ 6H2 O ! 3CaO  Al2 O3  6H2 O

þ

2. 6H þ 3SO24 - þ 3CaðOHÞ2 þ 3CaO  Al2 O3  6H2 O þ 20H2 O ! 3CaO  Al2 O3  3CaSO4  32H2 O

Fig. 17. Schematic of the microstructures of the slurries.

J. Liu et al. / Construction and Building Materials 227 (2019) 116654

The tricalcium aluminate hydrate produced in the abovementioned reactions reduces the concentration of calcium ions. Subsequently, the two reactions of Eqs. (1) and (2) are strongly promoted [66]. Tricalcium aluminate hydrate forms a type of crystal nucleus that contributes to the growing crystal nucleus of subsequent reaction. The produced crystal nucleus can accelerate the growth of various hydration products and the hydration reaction of cement. As a result, the initial setting time of the slurry is reduced. Finally, the early viscosity and yield stress of the slurry are enhanced. CCSPS is made up of CCPS and an appropriate amount of sand. Adding an appropriate amount of sand into the CCPS is to improve the particle filling degree, which can effectively reduce the porosity of the slurry. Furthermore, the slurry can better facilitate the replacement of sand particles and the cementation of cement hydrates. Thus, an aggregate structure that sand particles are in the center and cement-hydrate wraps around them is formed. As a result, the initial viscosity and yield stress of the slurry are increased, and the scouring resistance of the slurry is enhanced. At the same time, adding an appropriate amount of sand into the slurry can improve the cohesive force and internal friction angle, and therefore improve the strength of the slurry. 5. Discussion on the applicability of the grouts The conventional cement slurry has a poor stability and a weak scouring resistance. Therefore, when the slurry is grouted in soft and loose strata, the diffusion range is uncontrollable, and the phenomena of slurry leakage and pressure loss are serious, which is unbeneficial to construction duration and cost [67,68]. The shortcomings of low early strength and poor durability of cementsodium silicate grout make it difficult to be widely applied. Cementitious grouts with different components have large initial viscosity, adjustable thixotropy, and strong scouring resistance, and therefore they can effectively reduce the mass and pressure loss in soft and loose strata. According to previous grouting engineering experience and the test results of this paper, the cement slurry with a modifier dosage of 1.0% by cement mass has the optimal rheological properties [4,29]. Furthermore, clay and sand can be obtained locally, and the cost of grouting can be significantly reduced [40,69]. It is difficult to raise pressure and control the grouting process for grouting in strata with large porosity, which leads to a large amount of ineffective perfusion [70]. CCS has good coagulability and is more likely to fill the voids completely. In addition, thanks to the low water bleeding rate, the voids formed between the solidified slurry and grouted stone are limited. In addition, larger initial viscosity and yield stress make the range of grouting diffusion controllable. The application of CCS to impervious grouting in strata with large porosity not only significantly solves the problem of slurry leakage but also greatly reduces the cost. The CCPS can quickly solidify into a whole under the dynamic water environment due to the rapid setting of the modifier. The fact that the yield stress of CCPS is greater than 20 Pa ensures that the dynamic water cannot enter the slurry solidified body easily [71]. Simultaneously, cement particles and clay particles, in the slurry, are not segregated. After rapid solidification, the CCPS with a high strength cannot be washed away by dynamic water. Therefore, the leakage problem of the strata with dynamic water can be solved by CCPS. The test and engineering applications show that CCPS with large initial viscosity and strong scouring resistance performance can be applied in the strata that suffers from dynamic water scouring. The anti-seepage Tuokou hydropower project shows that compared with the conventional cement slurry, 1 m3 CCPS can be about 100 RMB cheaper [72]. Statistical results revealed that the average grouting volume of the CCPS is 0.31 m3

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per meter for each grouting hole and the cost is about 400 RMB/ m3, which is very competitive compared with other grouting materials [31]. CCSPS can be used for impervious grouting in the strata with high consumption of slurry or high velocity of groundwater (e.g. wide fissures, karst caves). It is difficult to lose the CCSPS due to its large viscosity, small fluidity and high stability. Its grouting range is also easy to control. Sand in the slurry can be used as the filling material for the cavern, and it enhances the strength of the solidified grout stone as well [73]. In addition, the cost of impervious grouting can be reduced because sand can be obtained locally.

6. Conclusion 1) The rheological properties of CCSs are related to the water/solid ratio and clay dosage. The CCS with a water-solid ratio of 0.6:1 belongs to the Bingham fluid and its viscosity increases with the increase of clay dosage. When the water/solid ratio is 1:1 and the clay dosages are 0% and 10% by cement mass, the rheological models of the slurries show that they are power-law fluids with shear dilatancy. However, when the clay dosages are 30% and 50%, they are Bingham fluids. When the water-solid ratio is 1.5:1, the slurry is Bingham fluid. The viscosities of the slurries first decrease and then increase with time when the water/solid ratios are 1:1 and 1.5:1. 2) The rheological properties of CCPSs mainly depend on the modifier dosage. The slurries are Bingham fluids when the modifier dosages are 0.5% and 0.75%. While the modifier dosages are 1%, 1.25% and 1.50%, the slurries are HerschelBulkley fluids. The viscosities first increase with time and then remain stable. The time point, when the viscosity tends to be stable, increases with the increase of modifier dosage. The properties of the CCPSs switch from rheopexy to thixotropy when the modifier dosage increases to 1.5%. 3) The rheological properties of CCSPSs are related to the modifier dosage and sand/cement ratio. When the modifier dosage is 0.5%, the slurry belongs to Bingham fluid. When the modifier dosages are 1.0% and 1.5%, the slurries are Herschel-Bulkley fluids. The viscosities decrease sharply with time, and finally tend to be stable. Thixotropy increases with the increase of modifier dosage. The higher the sand/ cement ratio is, the greater the yield stress and viscosity of the slurry are. 4) The initial viscosity of CCS is larger than that of ordinary cement slurry, and the diffusion area is controllable. This type of slurries has been widely used in strata with large voids to solve the problems of running slurry and grout leaking. The CCPS, with large initial yield stress and viscosity, has a strong scouring resistance, so it can be used for blocking leakage and anti-seepage under groundwater condition. The CCSPS, which has a better performance due to its large viscosity, small fluidity and high stability, is hard to be scoured by dynamic underground water. It is the preferred material for anti-seepage grouting in strata with high consumption of slurry or high velocity of groundwater flow.

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Acknowledgments The financial supports from the National Natural Science Foundation of China (Nos. 51509022 and 51579188) and the Natural Science Foundation of Hunan Province, China (No. 2019JJ50661) are gratefully acknowledged. The financial supports are also from Hunan Province Water Resources Technology Project of China (Nos. 2017-230-4 and 2018-179-04). References [1] Q.L. Cui, H.N. Wu, Y.S. Xu, S.L. Shen, Construction measures to prevent hazards in karst cave ground under soft sand strata, Japanese Geotechnical Society Special Publication 1 (7) (2015) 52–55. [2] H. Güllü, A factorial experimental approach for effective dosage rate of stabilizer: an application for fine-grained soil treated with bottom ash, Soils Found. 54 (3) (2014) 462–477. [3] Y. Li, Y.F. Chen, G.J. Zhang, Y. Liu, C.B. Zhou, A numerical procedure for modeling the seepage field of water-sealed underground oil and gas storage caverns, Tunn. Undergr. Space Technol. 66 (2017) 56–63. [4] G.J. Zhang, J. Liu, Y. Li, J.W. Liang, A pasty clay-cement grouting material for soft and loose ground under groundwater conditions, Adv. Cem. Res. 29 (1) (2016) 1–9. [5] D. Feys, A. Asghari, Influence of maximum applied shear rate on the measured rheological properties of flowable cement pastes, Cem. Concr. Res. 117 (2019) 69–81. [6] T. Kasper, G. Meschke, On the influence of face pressure, grouting pressure and TBM design in soft ground tunnelling, Tunn. Undergr. Space Technol. 21 (2) (2006) 160–171. [7] K. Komiya, K. Soga, H. Agaki, M.R. Jafari, M.D. Bolton, Discussion: soil consolidation associated with grouting during shield tunnelling in soft clayey ground, Géotechnique 53 (4) (2003) 447–448. [8] B. Nikbakhtan, M. Osanloo, Effect of grout pressure and grout flow on soil physical and mechanical properties in jet grouting operations, Int. J. Rock Mech. Min. Sci. 46 (3) (2009) 498–505. [9] D. Battaglia, F. Birindelli, M. Rinaldi, E. Vettraino, A. Bezzi, Fluorescent tracer tests for detection of dam leakages: the case of the Bumbuna dam – Sierra Leone, Eng. Geol. 205 (2016) 30–39. [10] S.L. Shen, Z.F. Wang, W.J. Sun, L.B. Wang, S. Horpibulsuk, A field trial of horizontal jet grouting using the composite-pipe method in the soft deposits of Shanghai, Tunn. Undergr. Space Technol. 35 (4) (2013) 142–151. [11] H. Güllü, S. Girisken, Performance of fine-grained soil treated with industrial wastewater sludge, Environ. Earth Sci. 70 (2013) 777–788. [12] S. Turkmen, Treatment of the seepage problems at the Kalecik Dam (Turkey), Eng. Geol. 68 (3) (2003) 159–169. [13] R. Gothäll, H. Stille, Fracture dilation during grouting, Tunn. Undergr. Space Technol. 24 (2) (2009) 126–135. [14] G.C. Yang, X.H. Wang, X.G. Wang, Y.G. Cao, Analyses of seepage problems in a subsea tunnel considering effects of grouting and lining structure, Mar. Geotechnol. 34 (1) (2016) 65–70. [15] M. Lekkam, A. Benmounah, E.H. Kadri, H. Soualhi, A. Kaci, Influence of saturated activated carbon on the rheological and mechanical properties of cementitious materials, Constr. Build. Mater. 198 (2019) 411–422. [16] M. Aziminezhad, M. Mahdikhani, M.M. Memarpour, RSM-based modeling and optimization of self-consolidating mortar to predict acceptable ranges of rheological properties, Constr. Build. Mater. 189 (2018) 1200–1213. [17] J.J. Assaad, Y. Daou, Cementitious grouts with adapted rheological properties for injection by vacuum techniques, Cem. Concr. Res. 59 (5) (2014) 43–54. [18] S.T. Kang, J. Kim, B. Lee, Effects of water reducing admixture on rheological properties, fiber distribution, and mechanical behavior of UHPFRC, Appl. Sci. 9 (1) (2019) 29. [19] H. Güllü, Unconfined compressive strength and freeze-thaw resistance of finegrained soil stabilised with bottom ash, lime and superplasticiser, Road Mater. Pavement Des. 16 (3) (2015) 608–634. [20] M. Saric-Coric, K.H. Khayat, A. Tagnit-Hamou, Performance characteristics of cement grouts made with various combinations of high-range water reducer and cellulose-based viscosity modifier, Cem. Concr. Res. 33 (12) (2003) 1999– 2008. [21] J. Warner, P.E. Fellow, Geo-institute, proper grout rheology assures quality work, Grouting for Ground Improvement 168 (2007) 1–11. [22] V.H. Nguyen, S. Remond, J.L. Gallias, Influence of cement grouts composition on the rheological behaviour, Cem. Concr. Res. 41 (3) (2011) 292–300. [23] M. Rahman, J. Wiklund, R. Kotzé, U. Håkansson, Yield stress of cement grouts, Tunn. Undergr. Space Technol. 61 (2017) 50–60. [24] J.X. Zhang, X.J. Pei, W.C. Wang, Z.H. He, Hydration process and rheological properties of cementitious grouting material, Constr. Build. Mater. 139 (2017) 221–231. [25] Q.G. Hoang, A. Kaci, E.H. Kadri, J.L. Gallias, A new methodology for characterizing segregation of cement grouts during rheological tests, Constr. Build. Mater. 96 (2015) 119–126.

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