Development of steel slag composite grouts for underground engineering

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Available online at www.sciencedirect.com

www.jmrt.com.br

Original Article

Development of steel slag composite grouts for underground engineering Fei Sha, Haiyan Li ∗ , Deng Pan, Hulin Liu, Xuefeng Zhang Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, Shandong, China

a r t i c l e

i n f o

a b s t r a c t

Article history:

The grouting materials are new fields where cement clinker (CC) can be replaced by high

Received 19 November 2019

amounts of steel slag (SS). To develop steel slag composite grouts (SSCG) for constructions

Accepted 6 January 2020

and repairs in underground engineering, it is necessary to determine and optimize the per-

Available online xxx

formance of SSCG. In this study, the SS and blast furnace slag (BFS) contents in ternary grouts

Keywords:

SS and BFS contents were all 20–40%. The FA, SS and BFS contents in quinary grouts were

Grouting material

5–10%, 25–40% and 25–30%. The flue gas desulfurization gypsum (FGDG) content was 5%. The

Steel slag composite grout (SSCG)

water-solid (W/S) range was selected as 0.65–1.2. The properties investigated were: fresh-

were all 55–75%. The fly ash (FA) contents were 10% and 15% in quaternary grouts, and the

Engineering properties

state properties i.e., mini-slump, effective W/S, stone rate, flowability losing time, setting

Microstructure

time; mechanical performance i.e., flexural strength (FS), unconfined compressive strength

Underground engineering

(UCS), FS/UCS and fracture characteristic; hydration products; microstructure and pore size distribution. The results show that the SS was suggested to combine with BFS to enhance the strengths, the 3-day and 28-day UCSs of the quinary SSCG (19#) increased by 105.3% and 167.7% with 2% B + 6% AA + 0.4% SP. With the approximate activation, the bigger pores (>100 nm) have been transformed into small pores under 30 or 100 nm effectively, and the compactness of gel structure has been improved. The workability, mechanical performance, and microstructures of optimized SSCG with high amount of SS (40%) and industrial residue (80%) are acceptable, it can meet the requirements of grouting practices for underground engineering. © 2020 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.

Introduction

In underground engineering, grouting technology is applied through injecting cementitious grouts or chemical grouts into various strata, the slurries diffuse in the forms of filling, permeating, splitting, compacting, etc. [1–3]. The positions of

∗

various spatial cavities, pores, fractures and cracks are occupied by these slurries, the fractured rock masses or loose soils are consolidated into integral bodies after the setting of grouts [4–6]. The water plugging, anti-seepage and reinforcement have been achieved, and the reinforced rocks or soils have good mechanical properties, impermeability and stability [7–9]. Therefore, the complex and severe engineering hydrogeological disasters can be treated or controlled effectively. Compared with chemical grouts, the cement-based grouts are inexpensive, environmental friendliness and durable [10–13].

Corresponding author. E-mail: [email protected] (H. Li). https://doi.org/10.1016/j.jmrt.2020.01.014 2238-7854/© 2020 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

2

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

A substantial amount of cementitious grout is needed urgently in construction and repair of tunnel, rail transportation, mining, highway, high speed railway, etc. As a main industrial residue of the steel industry, steel slag (SS) is generated through the separation process of molten steel and impurities in the steel-making furnaces. The content of SS is approximately 12−20 wt.% of the generated steel [14]. Almost 100 million tons of SS have been deposited since 2007, and the amount has increased annually [15]. In China, the discharge of SS was about 63.57 million tons in 2008, however the utilization rate was approximately 20%; the cumulative storage of SS was nearly 100 million tons in 2010, and the annual emission increase reached several million tons [16]. The deposited SS causes great waste of resources and pollutes the ecological environment seriously. In recent years, many studies have been conducted to evaluate the performance of concretes or composites with high amounts of industrial residues such as fly ash (FA) and blast furnace slags (BFS) [17–20]. However, the utilization of SS in the fields of block preparation, road construction, Portland cements (PC) and concretes are limited, this is mainly because of its low hydration reactivity, low early strength, low strength development, etc. [15,21–25]. The potential cementitious reactivity of SS is mainly from minerals of silicate and calcium ferrite. After the high temperature during the formation process of SS, the sizes of crystals became larger and thicker, and they were dissolved with many impurities such as FeO, MgO, MnO and P2 O5 . There existed obvious variability of mineral composition such as C3 S, C2 S, C4 AF, C2 F, RO phase (CaO-FeO-MnO-MgO solid solution), freeCaO, etc. With the rapid cooling of slag, large numbers of vitreous minerals formed, which greatly reduced the hydration activity of SS. The calcium silicate hydrate (C-S-H) can be produced directly from the hydration of minerals such as C3 S of BFS or SS, it should be noted that the hydration efficiency is low without alkali activators (AA) such as NaOH, Na2 SiO3 , Na2 CO3 , Na2 SO4 , etc. [15,26–28]. The vitreous bodies existed mainly in forms of tetrahedra of [SiO4 ] and [AlO4 ] and polyhedral of [AlO6 ], the Si O bond of [SiO4 ] might break during the grinding process of SS, and the follow reaction occur in the alkaline environments [29,30]:

Under the effect of OH− , the [AlO4 ] also depolymerizes to form H3 AlO4 2− , the following hydration products were produced after the interaction reactions of H3 AlO4 2− , H3 SiO4 − , Ca2+ , and Na+ : − 2+ → kCaO · lAl2 O3 · mSiO2 · nH2 O H3 AlO24 + H3 SiO4 + Ca

(3)

− 2+ H3 AlO2+ Na+ → pNa2 O · kCaO · lAl2 O3 · 4 + H3 SiO4 + Ca

mSiO2 · nH2 O

(4)

The polyhedral of [AlO6 ] depolymerizes to form Al(OH)2 + , which reacts with the existed H3 SiO4 − , OH− , Ca2+ and Na+ . Also, the related hydration products are produced: +

2+ Al(OH)2 + H3 SiO− + OH− → kCaO · lAl2 O3 · mSiO2 · n2H2 O 4 + Ca

(5)

+

2+ Al(OH)2 + H3 SiO− + Na+ + OH− → pNa2 O · kCaO · 4 + Ca

lAl2 O3 · mSiO2 · nH2 O

(6)

To generate the hydration products, the tetrahedra of [SiO4 ] or [AlO4 ] and polyhedral of [AlO6 ] were depolymerized continuously, and the Si O and Al O were decomposed constantly. In conclusion, the key of alkali activation lies in the provided conditions of complete disintegration of vitreous bodies and the effective hydration. The addition of BFS and FA can increase the siliceous material in the composite system, the reasons for improving the volume stability and strength through this method may lie in [29,31–34]: (1) It can decrease the Ca/Si ratio of SS phase and increase xonotlite content, the anti-cracking ability of sample increases due to the high tensile strength of xonotlite; (2) the hydration products such as serpentine and olivine are generated by combination of SiO2 , MgO, FeO, etc., and these products have high strength themselves; (3) under certain conditions such as hydrothermal conditions, the formation of stable magnesium-containing hydrates between SiO2 and surfaces of MgO prevent the continued hydration of periclase; (4) the amount of C S H increases through the secondary reactions between the siliceous glass of FA and calcium hydroxide (CH) [35,36]. The utilization of SS in cement production has been limited, and the effective utilization of high amount of SS has been an urgent objective. Exploring new application for industrial residue has greatly environmental, social and economic significance. Meanwhile, there is a huge demand for cementitious grouting materials in grouting projects for tunnel and underground engineering, and adopting SS in the preparation of steel slag composite grout (SSCG) is one novel and suitable application. At present, many researchers have studied the cement-based grouts prepared with BFS and FA systematically [37–39]. However, there were rarely no reports related with the utilization of SS in grouting materials, and the significant advantage of utilization of SS in grouts is that the compressive strength of grout is not expected so high in grouting applications compared with that of concrete [40,41]. This is because cementitious slurries should have higher watersolid ratios (W/S) of 0.5–1.2 to be injected into soils or rocks [42]. It should be noted that the development or performance optimization of SSCG with high amounts of SS at higher W/S (0.6–1.2) has not been previously presented and it is new at present. The experimental design for this research was shown in Fig. 1. In this present study, a locally available SS was adopted to prepare and optimize SSCG with high amounts of SS. The

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

ARTICLE IN PRESS

JMRTEC-1269; No. of Pages 17

j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

3

Fig. 1 – Experimental design and approach of this research.

key issue is in the effective activation of SS, the self-developed activators were applied to enhance the hydration activity of SS. Meanwhile, the approximate combination of BFS and class F FA was adopted to improve the mechanical performance of SSCG stone bodies. Meanwhile, the flue gas desulfurization gypsum (FGDG) was added to adjust the setting time of clinker. The utilization of the above industrial residue in large quantities can ensure the low prices of grouts, meanwhile, it can reduce carbon emissions and protect the environment. The bentonite (B) is added to improve the stability, pumpability and impermeability of slurries [43], the naphthalene-based superplasticizer (SP) is applied to improve the flowability [44,45]. To ascertain and optimize the engineering performance of SSCG in grouting practices, the fresh-state properties (spreading ability, effective W/S and stone rate), mechanical strength (flexural strength (FS), unconfined compressive strength (UCS) and FS/UCS), hydration mineral, microstructure and pore size distribution are combined to analyze the major performance of SSCG. The W/S range was chosen as 0.65–1.2, and typical suspensions were studied emphatically at the common W/S of 1.0. The ternary, quaternary and quinary grouts were designed uniquely. The curing days of specimens were 3day, 7-day and 28-day. Considering that the researches about SSCG with high amounts of SS have not been presented previously, this research result will contribute to recycling of SS in large quantities, and it would provide beneficial guidance for improvements of SSCG in grouting practices for underground engineering.

2.

2.1.

Raw materials

The Portland cement clinker (CC) and FGDG were provided by Shandong Cement Group (Shandong, China). The SS and BFS were chosen from Jinan Iron and Steel Company (Shandong, China). The class F FA was from Jinan Huangtai Electricity Power Plant (Shandong, China). The B and polynaphthalenebased SP were selected from a company in Jinan. The self-developed compound activator was adopted in this study, it was acquired through mixing water glass and sodium sulfate in a certain proportion. The module of water glass is 3.0, and its Baume degree is 40. The raw materials were all from Shandong province in China, the chemical compositions of SS, CC, BFS, FA, FGDG and B were presented in Table 1. And the material composition of mix groups was shown in Table 2. According to ISO 13320-1 [46], the particle size distributions (PSD) of SS, CC + FGDG, BFS and FA were determined by the laser diffraction technique. Fig. 2 shows the SEM images of raw materials. The difference among SS, CC and BFS was not obvious, the ball morphology of the vitreous body was obvious in FA, and the “ball effect” was probably helpful for the improvement of fluidity or spreading ability of slurries. The specific PSD characteristic of raw material was presented in Fig. 3. The weight of ground raw material was 5 kg every time, and the ball mill of SM-500 was applied. Based on our previous efficiency studies on grinding ways (separate or mixed grinding), the separate grinding of SS or BFS was adopted. The grinding times of CC + FGDG and BFS were set as 45 min, that of

Materials and methods

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

ARTICLE IN PRESS

JMRTEC-1269; No. of Pages 17

4

j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Table 1 – Main chemical composition of SS, CC, BFS, FA, FGDG and B (wt%). Materials

SiO2

CaO

Al2 O3

Fe2 O3

MgO

SO3

K2 O

Na2 O

TiO2

LOI

SS CC BFS FA FGDG B

12.36 21.97 34.79 52.03 3.36 62.68

40.98 64.61 39.20 12.36 31.97 3.3

3.36 4.52 12.87 22.35 0.85 16.81

24.11 2.40 0.41 4.32 0.06 5.22

7.28 1.72 7.58 1.06 1.21 3.35

0.71 0.68 1.80 2.55 42.12 0.03

0.05 0.59 0.36 0.92 0.12 2.26

0.05 0.26 0.38 0.21 0.04 3.96

0.81 0.13 0.39 0.72 – 0.89

7.67 1.02 1.17 2.97 19.3 1.06

Table 2 – Property of Naphthalene-based SP. Type

FDN-C

Aspect

Dark brown

Bulk density (kg/m3 ) 1.2 × 10

3

pH

Solid content (%) ≥92

7–9

Recommended dosage (%) 0.5–2.0

Repulsion mechanism Electrostatic

Steric hindrance

*

—

Fig. 2 – The SEM images of raw materials. (a) Steel slag (SS); (b) Cement clinker (CC); (c) blast furnace slag (BFS); (d) Fly ash (FA).

Table 3 – The key PSD parameters of SS, BFS, CC + FGDG and FA.

SS BFS CC + FGDG FA

d10 (␮m)

d50 (␮m)

d80 (␮m)

d85 (␮m)

d90 (␮m)

d95 (␮m)

d100 (␮m)

1.53 1.93 3.19 3.91

6.28 10.82 10.10 11.01

13.63 24.15 19.54 19.33

16.15 28.34 22.61 22.22

20.55 34.74 26.98 26.22

29.10 40.07 36.44 34.73

≤115.70 ≤115.70 ≤115.70 ≤115.70

SS was approximately 60 min. The key PSD parameters were listed in Table 3. Combining Fig. 3 and Table 3, the average particle sizes (d50 ) of SS, BFS, CC + FGDG and FA were approximately 6.28, 10.82, 10.10 and 11.01 ␮m respectively. The d90

particle sizes of SS, BFS, CC + FGDG and FA were about 20.55, 34.74, 26.98 and 26.22 ␮m respectively. The improvement of long grinding time on the PSD was obvious, and the percentage passing of SS in finer size range was improved with the

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

5

cubic specimen mold for fresh slurry was 40 × 40 × 160 mm, all the possible gaps of assembled molds were sealed with Vaseline, and the size of square section is 40 mm. As shown in Fig. 4(a), the bleeding rate is tested as the ratio of (haverage )/H after the complete hardening of grout, and the effective W/S was analyzed as follows: Effective W/S = (1 − CB ) × Initial W/S

Fig. 3 – Particle size distributions of CC, SS, BFS and FA.

prolonged grinding time. However, the d100 particle size of SS, BFS, CC + FGDG or FA was almost the same. The difference of PSD values among the raw materials were not large in general.

2.2.

Preparation of SSCG suspensions

The SSCG suspension was prepared using the following steps. The raw materials and water were placed at room temperature (25 ± 2 ◦ ). To consider performance comparison, utilization amount and synergistic effect, the ternary, quaternary and quinary grouts were designed. And the material composition of mix groups was shown in Table 4. For all grouts, the FGDG content was constant and selected as 5%. For ternary grouts (SS/BFS + CC + FGDG), the amount variables of SS or BFS were 55%, 60%, 65%, 70% and 75%. For quaternary grouts (SS/BFS + FA + CC + FGDG), the FA contents were 10% and 15%, and the amount variables of SS or BFS were 25–40%. For quinary grouts (SS + BFS + FA + CC + FGDG), the FA, SS and BFS contents in quinary grouts were 5–10%, 25–40% and 25–30%. The fresh suspensions were prepared with blended solids and the required water, and suspensions were mechanically stirred at 240 rpm speed for 4 min. The W/S range was chosen as 0.65–1.2 (0.65, 0.8, 1.0 and 1.2) by weight, the W/S of 1.0 was studied emphatically because it is commonly used in grouting practices.

2.3.

Experimental approaches

The ambient temperatures of all measurements were 25 ◦ . The spreading ability was evaluated through mini-slump (mm) [47]. Based on ASTM C-143-15 [48], the mini-slump was calculated as the average of spreading diameter of fresh suspension. Moreover, the ˚bottom , ˚top and h (height) sizes of test cone were 60, 36 and 60 mm, respectively [12,39]. Fig.4(a) illustrated the calculation method of effective W/S or grout stone rate, the square section presented the cross profile of molds. The size of

(7)

Where CB is the coefficient of bleeding volume (haverage )/H. The stone rate is the value of (1-CB ), and the higher stone rate is recommended in grouting engineering [49–51]. Fig. 5(b) and (c) presented the photos of quinary SSCG (19#) stone bodies without admixture and with 2%B + 6%AA + 0.4%SP, respectively. In this study, the flowability losing time was regarded as the flowability duration of the SSCG suspension-sodium silicate double slurry. Specifically, the fresh SSCG single slurry was placed in two separate cups with the same size, then the water glass single slurry was poured into the SSCG single slurry. The newly generated double slurry was poured between the two cups continuously until the flowability of mixed double slurry lost completely. The flowability losing time of SSCG double slurry was determined to provide the key parameters for the theoretical calculation of diffusion distance and practical evaluation of grout performance. The final setting time was adopted to evaluate the engineering setting performance, because the secondary or later sequential drillings must await the final setting of grouts in the initial grouting holes and reinforced structures. The Vicat needle apparatus was used to determine the final setting time of SSCGs. The final setting time was determined when the penetration height of the needle was less than 0.5 mm. The researches about flexural strength (FS) and unconfined compressive strength (UCS) of SSCGs are few, especially for SSCGs with different composition and improvement admixture. The FSs were determined to give practical references for such SSCGs. The size of cubic specimen mold for FS and UCS was 40 × 40 × 160 mm. If there was obvious bleeding, the bleeding water was removed until there were merely hardened grout stone bodies. Based on GB/T 17671-1999 [52], the 3-day, 7-day and 28-day FS and UCS tests of hardened SSCGs were conducted, the curing environments were 25 ± 2 ◦ and 100% R.H., and the loading rate is 2 mm/min. To evaluate the brittleness of SSCG stone bodies, the FS-UCS ratio (FS/UCS) of the SSCGs was calculated and analyzed comparatively. In this study, the D8 ADVANCE type X-ray diffraction analyzer was used to measure the hydration minerals, the scanning angle and scanning speed were 5–60 degrees and 4–5 degrees/min respectively. Fourier transform infrared spectroscopy (FTIR) was performed through a spectrometer on SSCG samples. The spectral analysis was performed in the range of 400 to 4000 cm−1 , with a spectral resolution of 1 cm−1 . The microstructure of SSCGs was studied by using a scanning electron microscope (SEM). The small broken pieces of hardened SSCGs were kept in absolute ethyl alcohol for SEM measurements. The mercury intrusion porosimetry (MIP, Quantachrome, PM60GT-18, USA) technique was adopted to quantitatively evaluate the ore size distribution characteristics of different SSCG stone bodies.

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS

6

j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Table 4 – Material composition of mix groups. Group No.

Compositions (%): CC + SS + BFS + FA + FGDG

Group No.

Compositions (%): CC + SS + BFS + FA + FGDG

Group No.

Compositions (%): CC + SS + BFS + FA + FGDG

1# 2# 3# 4# 5# 6# 7#

40 + 55 + 0 + 0 + 5 35 + 60 + 0+0 + 5 30 + 65 + 0 + 0 + 5 25 + 70 + 0+0 + 5 20 + 75 + 0 + 0 + 5 40 + 0 + 55 + 0 + 5 35 + 0 + 60 + 0 + 5

8# 9# 10# 11# 12# 13# 14#

30 + 0 + 65 + 0 + 5 25 + 0 + 70 + 0 + 5 20 + 0 + 75 + 0 + 5 45 + 40 + 0 + 10 + 5 55 + 30 + 0 + 10 + 5 60 + 25 + 0 + 10 + 5 40 + 40 + 0 + 15 + 5

15# 16# 17# 18# 19# 20# 21#

55 + 25 + 0 + 15 + 5 45 + 0 + 40 + 10 + 5 35 + 25 + 25 + 10 + 5 25 + 30 + 30 + 10 + 5 20 + 40 + 25 + 10 + 5 15 + 40 + 30 + 10 + 5 20 + 35 + 25 + 15 + 5

Fig. 4 – Calculation method of grout stone rate and the photos of SSCG stone bodies (initial W/S of 1.0) after 21 h. (a) Calculation method of stone rate, (b) stone body of quinary SSCG (19#) after 21 h, (c) stone body of optimized quinary SSCG (19#) after 21 h.

Fig. 5 – The combined effects of AA, B, SP and W/S on the mini-slumps.

3.

Results and discussion

3.1.

Fresh-state property or workability

3.1.1.

Mini-slump

The spreading or propagation ability into cracks or soil pores of fresh grouts can be characterized macroscopically by the variations of mini-slump. Also, the mini-slump is an important parameter to measure the workability of grout. At the W/S of

1.0, the mini-slump results of fresh ternary, quaternary and quinary SSCG slurries were and Table 5. As presented in Table 5, the mini-slumps of ternary slurries were relatively high when the amounts of SS and BFS exceeded 65% and 70% respectively. The maximum mini-slump values of ternary slurries were 345 and 320 mm with high amount (75%) of SS and BFS (Group 5# and 10#), the increase effect of SS was more obvious. This might be that the early cementitious activity of SS or BFS was low, the related water consumption decreased and free water increased with the increase of content. As for the quaternary fresh slurries with 10% or 15% FA (Group 11# to 15#), their mini-slump values were relatively high, and the combined effects of SS and FA tended to promote the increase of mini-slumps. Most of the slurries with 15% FA were higher than those with 10% FA, and it indicated that the FA could enhance mini-slumps or spreading ability of fresh slurries with different degrees. For example, when the amounts of FA were 10% and 15%, the mini-slump ranges of quaternary fresh slurries were 345–359 and 346−365 mm with 25–40% amounts of SS. The class F FA content was controlled within 15% to avoid the prohibitively low strength especially under high SS contents. In comparison, the mini-slumps of quinary fresh SSCG slurries (Group 17# to 21#) were not very high (325−341 mm), and the spreading ability of quinary fresh SSCG slurry was probably more appropriate for W/S of 1.0 if there was no admixture. The combined effects of AA, B, SP and W/S on the mini-slumps were shown in Fig. 5. In Fig. 5, the effects of W/S on mini-slump were significant compared with those of component especially when the W/S was not over 1.0. For example, the mini-slump increase rates of 19# suspension were about 42.5%, 9.9% and 5.4% when

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS 7

j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Table 5 – Mini-slump and effective W/S or stone rate of ternary, quaternary and quinary suspensions (W/S of 1:1) without admixtures. Mix group

Mini-slump (mm)

Effective W/S or stone rate

Mix group

Mini-slump (mm)

Effective W/S or stone rate

Mix group

Mini-slump (mm)

Effective W/S or stone rate

1# 2# 3# 4# 5# 6# 7#

315 304 341 332 345 298 310

0.788 0.775 0.763 0.773 0.759 0.855 0.850

8# 9# 10# 11# 12# 13# 14#

309 311 320 359 355 345 365

0.850 0.880 0.891 0.802 0.815 0.821 0.795

15# 16# 17# 18# 19# 20# 21#

358 346 339 325 331 338 341

0.810 0.828 0.836 0.821 0.806 0.792 0.780

the initial W/S increased from 0.65 to 0.8, from 0.8 to 1.0 and from 1.0 to 1.2, respectively. The increase rate of mini-slump tended to be little especially as the W/S increased. This might be because that the mini-slump is inversely proportional to the friction between slurries and plates, and they are likely more susceptible to the resistance under low shear rates when the mini-slumps attain some certain high values. The difference between 19# and 21# suspension was little, this might be because of little difference content (5%) of FA or SS. It was observed that the 5% B or 6% AA decreased the mini-slumps of SSCG with different degrees, and the decreasing effect of 5% B was more significant at each initial W/S. The decreasing effect of 5% B on spreading ability was in accordance with the existed findings [12]. The decrease degree of 5% B on minislump of 19# suspension was about 6.5–9.9% at the initial W/S of 0.65–1.2. To improve the spreading ability, the 0.4% SP was applied in combination with 2% B, 6% AA. It can be observed that the mini-slump of 19# increased significantly under each initial W/S, the improvement effects were generally satisfied though the increase rate was little at higher initial W/S. For example, the increase rates of mini-slump of 19# suspension were 13.2%, 4.3%, 3.9 and 2.0% when the initial W/Ss were 0.65, 0.8, 1.0 and 1.2, respectively. The adverse effect of B or AA can be offset and improve with the combination of SP, B and AA. Owing to the ordinary PSD, the high amount of CC replacement and preliminary tests, the 0.4% content of SP was appropriate for such SSCG system.

3.1.2.

Effective W/S and stone rate

The effective W/S and stone rate were adopted to evaluate the effective reaction and stability of fresh SSCG slurries. In this study, the effective W/S was calculated after the complete hardening of the SSCG and it was not based on the bleeding capacity after 2 h. Therefore, at the initial of 1.0, the effective W/S equaled to the complete stone rate of SSCG. At the initial W/S of 1.0, the effective W/S and stone rate of typical SSCG slurries were shown in Table 5. In Table 5, at the initial W/S of 1.0, the effect of composition on effective W/S was not negligible. The effective W/Ss of BFS ternary slurries (BFS + FGDG + CC) were observably higher than those of SS ternary slurries (SS + FGDG + CC). This might be because that the hydration degree and water utilization of BFS was relatively efficient compared with that of SS, especially in the initial molding stage. The effective W/Ss of SS quaternary slurries (SS + FA + FGDG + CC) or SS quinary slurries (SS + BFS + FA + FGDG + CC) were generally higher than those of SS ternary slurries. It might be inferred that the quaternary

Fig. 6 – Effective W/S and stone rate of SSCG with key formulation and initial W/Ss (0.65–1.2).

or quinary SS composition is helpful for improving the effective W/S or stone rate of SSCG at the initial W/S of 1.0. The effects of FA contents on the effective W/S of quaternary slurries were not obvious, and it might be due to the relatively low amounts of FA. Although some effective W/Ss were close to 0.9, the effective W/S was generally lower than 0.90 or 0.95. Therefore, at the initial W/S of 1.0, the effective W/S or stone rate should be enhanced to ensure the high stability and high stone rate of fresh SSCG slurries. The effective W/S and stone rate of SSCG with key formulation and initial W/Ss were shown in Fig. 6. As presented in Fig. 6, without admixtures, the distinction between effective W/S and initial W/S became larger and stone rate decreased as the initial W/S increased. It was observed that the effective W/S and stone rate of quinary SSCG (Group 19#) were higher than those of ternary SSCG (Group 5# or 1#) under different initial W/Ss, though the SS content of 5# was lower than that of 19#. It could be inferred that the quinary SS composition such as 19# was helpful for improving the effective W/S and stone rate, regardless of initial W/Ss. The initial W/S was the main control factor for effective W/S and stone rate especially when the initial W/S exceeded 1.0. The addition of 5% B, 2% B + 6% AA or 2% B + 6% AA + 0.4% SP can enhance the effective W/S and stone rate with different degrees. It was observed the 0.4% SP tended to be slightly adverse for enhancing the effective W/S and stone rate, it might be due to the compatibility among admixtures and increase of free water caused by 0.4% SP. In general, the effective W/S or stone rate

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

8

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Fig. 7 – Flowability losing time of SSCG double slurries with different initial W/S and volume ratio.

of the quinary SSCG (Group 19#) with 5% B, 2% B + 6% AA or 2% B + 6% AA + 0.4% SP were over 0.9 at the initial W/S of 1.0, and the improvement effect of effective W/S was acceptable. At the initial W/S of 1.2, those effective W/Ss were approximately 1.06–1.12, the increase rate was about 29.3–36.6%, and it was also acceptable. The SSCGs with high effective W/S and stone rate ought to be preferred in good grouting practices. The enhancing of effective W/S and stone rate still needed to be combined with other performance such as spreading ability. Although the improvement effect of 2% B + 6% AA + 0.4% SP on effective W/S was not highest, it was still acceptable especially considering that the mini-slumps of quinary SSCG with 2% B + 6% AA + 0.4% SP were excellent.

3.1.3.

Flowability losing time

The double slurries are often used to block or plug the dynamic water with high water pressure and velocity. When the SSCG single slurries mixed with the water glass single slurry in the grouting holes or strata, the characteristics of quick setting and rapid flowability losing are significant. Therefore, the flowability losing time was used to evaluate the continuous flowability time of double slurries since the moments of their mixing or blending. The flowability losing time of SSCG double slurries can provide important reference for diffusion time and distance evaluation in practical grouted strata. The results are shown in Fig. 7. As shown in Fig. 7, the flowability losing times of SSCG double slurries decreased markedly as the volume ratio increased from 1:1 to 5:1, the effect of initial W/S on flowability losing time was not so obvious. For example, at the volume ratio of 3:1, the flowability losing times of 19# SSCG double slurries were determined as 21.43 s, 22.68 s and 27.03 s when the initial W/Ss were 0.8, 1.0 and 1.2. While at the initial W/S of 1.0, those were 46.57 s, 33.55 s, 22.68 s and 13.97 s for the volume ratios of 1:1, 2:1, 3:1 and 5:1. The flowability losing times of SSCG ranged within 1 min, and the volume ratio was the key controlling factor. However, the effect of component of SSCG on flowability losing time should not be neglected. For example, when

Fig. 8 – Final setting time of quinary SSCG with different SS content, admixture and initial W/S.

the SS content of quinary SSCG increased from 25% to 40% (Group 17# to 19#) at the initial W/S of 1.0, the increase rates of flowability losing time were 27.3%, 31.3%, 36.0% and 27.3% for the volume of 1:1, 2:1, 3:1 and 5:1. The flowability losing time of typical SSCG double slurries were short in general, and it can ensure the quick blocking for disasters of water and mud inrush during the constructions of tunnels and underground engineering.

3.1.4.

Final setting time

Determination of setting time is practical for grouting engineering, the practical final setting times were evaluated because the subsequent drilling must wait for the final setting of grouts in the previous grouting holes. Fig. 8 shows the final setting times of quinary SSCG with different SS content, admixture and W/S. In Fig. 8, although the addition of B can enhance the effective W/S effectively, the addition of B prolonged the final setting time and the increase rate was not large because of small amount (2%) of B. The increase degree of 0.4% SP on final setting time was relatively large compared with that of 2% B, therefore, the SP content should not be excessive to avoid the long-setting or oversaturation. The addition of 2% B or 2% B + 0.4% SP increased the final setting time within controllable degrees, and the 6% AA and initial W/S were the main control factors for final setting time. Although the final setting time increased with the increase of W/S and SS content, the addition of 6% AA ensured the variation was within controllable degrees. In conclusion, although it decreased the mini-slump with different degrees, the addition of 6% AA can shorten the difference of final setting time among different composition or initial W/S, and the 6% AA could be helpful for adjusting the final setting time. For example, with the addition of 6% AA, the final setting of quinary SSCG was controlled within the ranges of 21.2–23.9 h and 23–25.9 h at the initial W/Ss of 0.8 and 1.0, regardless of 0.2% B, 0.4% SP or/and 25–40% SS. And this range of final setting time of SSCG

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

was relatively acceptable especially for high amounts of CC replacement.

3.2.

Mechanical performance

The SSCG was developed in this study, and the researches about combined effects of composition (SS, BFS, FA, FGDG and CC), combination of admixture (B, AA and SP) and high initial W/Ss on the flexural strength (FS) and unconfined compressive strength (UCS) of SSCG were few at present.

3.2.1.

Flexural strength (FS)

Fig. 9 shows the FSs (3-day, 7-day and 28-day) of ternary, quaternary and quinary SSCG stone bodies without admixtures. The W/S was chosen as 1:1 because it was applied commonly. In Fig. 9(a), the early (3-day) FSs of ternary SSCGs with 55–75% SS contents (1#-5#) were very low, their 7-day FSs were all lower than 1.0 MPa, and the FS development was low from 7-day to 28-day. For example, when SS contents were 55–75%, the 3-day, 7-day and 28-day FS ranges of ternary SSCG were about 0.41-0.29, 0.92-0.72 and 1.29-1.00 MPa, respectively. The low early FS was in accordance with the existed reports for SS composite at low initial W/S [14,15,53]. It was found that the 7-day and 28-day FSs of ternary SSCGs with 55% (1#) and 65% (3#) SS were relatively high, and the FS decreased obviously when SS contents exceeded 65%. It was conformed that the hydration activity of SSCG with high amounts of SS should be enhanced to ensure enough FS values. In comparison, the FSs (3-day, 7-day, and 28-day) of ternary BFS composite grout with 55–75% BFS (6#-10#) were generally much higher than those of ternary SSCG. The 3-day FSs of ternary BFS composite grout with 55–65% BFS (6#-8#) were higher than all the 7-day FSs of ternary SSCG, and they were very close to the 28-day FSs of ternary SSCG with 55–65% SS (1#-3#). The FS development was not so rapid from 3-day to 7-day because the 3-day FSs were relatively high. This might be mainly because that calcium silicate hydrate (C-S-H) forms more efficiently from the hydration of BFS or the activation of BFS by CH. Although the 3-day, 7-day and 28-day FSs of ternary BFS composite decreased obviously when BFS contents exceeded 60%, 60% and 65%, they were relatively acceptable in general. Specifically, when BFS contents were 55–75% (6#-10#), the 3-day, 7-day and 28-day FS ranges of ternary BFS composite grout were about 1.06-0.64, 1.60-1.21 and 2.26-1.49 MPa, respectively. In Fig. 9(b), it was observed that the FSs of quaternary SSCG decreased when SS or FA content increased from 25% to 40% (13# to 11#) or from 10% to 15% (11# to 14#, 13# to 15#). It was found that the FS development of quaternary SSCG (11#-15#) was also low from 7-day to 28-day, and their 3-day FSs were improved compared with those of ternary SSCG. Specifically, the 28-day FSs of quaternary SSCGs with 10% (13-11#) and 15% (15-14#) FA contents were approximately 1.22–0.94 MPa and 1.11–0.84 MPa when SS contents were 25–40%. In comparison, without admixtures, the FSs (3-day, 7-day, and 28-day) of quaternary BFS composite grout (16#) were highest compared with those of quinary (17#21#) or quaternary (11#-15#) SSCGs. This might be because that the relative contents of CC, BFS, FA and FGDG were appropriate for the combined effects of hydration reactions, and pozzolanic reactions [35,36,53,54]. The 3-day, 7-day, and 28day FSs of quinary SSCG with 25% SS (17#) were 0.80, 1.32 and

9

2.03 MPa, and they were highest in all the quinary SSCGs (17#21#) without admixtures. And the FSs of quinary SSCGs were needed to enhance further. In conclusion, this part presented a mutually comparative study of FSs for SSCGs or BFS composite grout, considering multi-factors such as combination mode of raw material, relative content, curing time, high initial W/S, engineering practicality, etc.

3.2.2.

Unconfined compressive strength (UCS)

Fig. 10 shows the UCSs (3-day, 7-day and 28-day) of ternary and quaternary or quinary SSCG stone bodies. The initial W/S ratio was chosen as 1:1. As shown in Fig. 10(a), the early (3-day) UCSs of ternary SSCGs with 55–75% SS contents (1#-5#) were also very low, their 7-day UCSs were all lower than 2.1 MPa, and the UCS developments from 7-day to 28-day were low when the SS content reached or exceeded 65%. For example, the 3-day UCSs of ternary SSCG with 55–75% SS were about 1.52–2.05 MPa, and the 28-day UCSs of ternary SSCG with 65% and 70–75% SS were about 6.28 MPa and 4.27–3.87 MPa. The low early UCS was in accordance with the low early FS or the existed reports for UCS of SS composite at low initial W/S [14,15,53]. The UCSs of ternary BFS composite grout with 55–75% BFS (6#-10#) were also generally much higher than those of ternary SSCG. The 3-day UCSs of ternary BFS composite grout with 55–65% BFS (6#-8#) exceeded all the 7-day UCSs of ternary SSCG, and 7day UCSs of ternary BFS composite grout with 60–65% BFS (7#-8#) exceeded all the 28-day UCSs of ternary SSCG. The UCS development of ternary BFS composite grout was large from 7-day to 28-day, this might be mainly due to multiple interdependence of hydration of BFS and possible activation of BFS by CH. Although the UCSs of ternary BFS composite decreased obviously when BFS contents exceeded 65%, they were also relatively acceptable. For example, when BFS contents were 55–75% (6#-10#), the 3-day, 7-day and 28-day UCSs of ternary BFS composite grout were about 4.39–2.10, 6.38–4.97 and 12.05–4.17 MPa, respectively. In Fig. 10(b), the UCS difference of quaternary SSCG between 10% and 15% FA was not obvious, and the decrease effect of SS (25–40%) on UCS was obvious especially for the 28-day UCS. It was found that the UCS development of quaternary SSCG from 7-day to 28-day was low especially when the SS content exceed 30% (11#, 12#, 14#). In comparison, the UCSs (3-day, 7-day, and 28-day) of quaternary BFS composite grout (16#) were highest compared with those of quinary (17#-21#) or quaternary (11#-15#) SSCGs. This might be because that the combined effects of hydration reactions, and pozzolanic reactions be more efficient especially for the curing time of 28 days [35,36,53–55]. The 3-day, 7-day, and 28-day UCSs of quinary SSCG with 25% SS (17#) were 1.82, 3.50 and 7.92 MPa, and they were highest in the quinary SSCGs (17#21#) without admixtures. In conclusion, the UCSs of quinary SSCGs or BFS composite grouts were much higher than the FSs, the UCSs of quinary SSCGs with high amounts of SS still should be enhanced further to ensure the needed mechanical performance.

3.2.3.

FS/UCS

The FS/UCS ratios were used to evaluate the brittleness of grout stone bodies in this study. Fig. 11 shows the FS/UCS (3d,

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

10

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Fig. 9 – FSs (3-day, 7-day and 28-day) of the ternary, quaternary and quinary composite grouts. (a) Ternary composite grouts (SS/BFS + G + CC); (b) quaternary and quinary SSCG (SS/BFS + FA + G + CC, SS + BFS + FA + G + CC).

Fig. 10 – UCSs (3-day, 7-day and 28-day) of the ternary, quaternary and quinary composite grouts. (a) Ternary composite grouts (SS/BFS + G + CC); (b) quaternary and quinary SSCG (SS/BFS + FA + G + CC, SS + BFS + FA + G + CC).

Fig. 11 – FS/UCS (3-day, 7-day and 28-day) of the ternary, quaternary and quinary composite grouts. (a) Ternary composite grouts (SS/BFS + G + CC); (b) quaternary and quinary SSCG (SS/BFS + FA + G + CC, SS + BFS + FA + G + CC).

7d and 28d) results of typical SSCG, all the initial W/S ratio was 1.0. In Fig. 11(a), compared with the 28-day FS/UCS ratios of ternary SSCG (0.19–0.26), those of BFS composite grouts (6#-10#) were relatively low (0.16–0.21), and this might be attributed to their high UCS. There existed some randomness for the FS/UCS variation characteristics of ternary SSCG, this might due to the combined effects of high amounts of SS (55–75%), hydration activity, curing time, etc. In Fig. 11(b), the FS/UCS decreased with the increase of curing days in general. This might be because that the value or increase degree of UCS was higher than that of FS from 7-day to 28-day. With the

increase of FA (10–15%), the FS/UCS tended to decreased for the quaternary SSCGs (11#-15#). For example, with 10% and 15% FA, the FS/UCS ranges of quaternary SSCGs and were 0.20–0.24 and 0.19–0.22 when the SS contents were 25–40%. Although the 28-day UCSs of quaternary BFS composite grout (16#) and quinary SSCG with 25% SS (17#) were relatively high among the selected group of 17#-21#, their 28-day FS/UCS were relatively low. Combining with Fig. 11 (a) and (b), the FS/UCS ratio was influenced by the combined effects of multiple factors such as curing time, combination of raw material, relative content and initial W/S of 1.0. The lower FS/UCS ratios reflected and determined the higher fracture brittleness of grout stone bodies,

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Fig. 12 – The FS, UCS and FS/UCS of quinary SSCG (group 19#) with different admixtures.

especially for matured grouts such as the 28-day SSCG stone bodies. The effect of curing time should not be neglected, because the effect of early stage presented some randomness. The FS/UCS ratios should be combined with the real FS and UCS values in applications. Although some FS/UCS ratios were generally lower, such as 28-day FS/UCS ratios of 17# and 18#, their mechanical performance might be acceptable or satisfied because of their high UCSs. The combination of high FS/UCS ratios and low UCSs might sometimes limit their effectiveness and applications.

3.2.4.

Improvement of mechanical performance

In this part, the quinary SSCGs with high amount of SS (40% and 19#) was improved emphatically at the initial W/S of 1.0. The effects of addition of 5% B, 6% AA or 2% B + 6% AA + 0.4% SP were studied for quinary SSCG of group 19#. The results of FS, UCS and FS/UCS were shown in Fig. 12. As shown in Fig. 12, the addition of 5% B decreased the FS and UCS of the SSCG, regardless of curing time and initial W/S. And the decrease degree was not obvious due to the relatively low content (5%) of B. The 5% B increased the 28-day FS/UCS of the SSCG, this indicated the 5% were helpful for improving the brittleness though the FS and UCS were decreased slightly. It was observed that the 6% contents of selfdeveloped AA enhanced the FS and UCS obviously. Specifically, the increase rates of early (3-day) FS or UCS and 28-day FS or UCS for the SSCG (19#) were approximately 90.4% or 138.2% and 129.1% or 184.7%. Also, the increase rates of 28-day UCS were approximately 201.6% and 284.6% under initial W/S of 0.8 and 1.2. Meanwhile, the 6% AA decreased the 28-day FS/UCS with different degrees, this might be because that the 28-day UCSs were generally high at the initial W/S. To enhance the mechanical strength and improve other properties such as mini-slump, effective W/S, etc., the effect of combination of 2% B, 6% AA and 0.4% SP was studied. It was observed that this combination was also helpful for improving the FS, UCS and FS/UCS. For example, at the initial W/S of 1.0, the related increase rates of early (3-day) FS or UCS and 28-day FS or UCS were approximately 65.9% or 105.3% and 100.7% or 141.7%. Also, the increase rates of 28-day UCS were approximately

11

167.4% and 230.8% under initial W/S of 0.8 and 1.2. Meanwhile, this combination decreased the 28-day FS/UCS and improved the brittleness of the SSCG (19#). In conclusion, although the enhancing degree of 2% B + 6% AA + 0.4% SP for mechanical strength was not so obvious as that of 6% AA, the increasing degrees and specific values of FS or UCS were generally acceptable. The 28-day FS and UCS values were approximately 2.1 and 9.2 MPa at the initial W/S of 1.0. Considering the relatively high W/S of 1.0, the SSCG with high amounts of CC replacement (19#) and the admixture of 2% B + 6% AA + 0.4% SP can meet the strength requirements of grouting materials in undergrounding engineering. As presented in Fig. 13, the fracture surface characteristics of the 28-day composite grout stone bodies were also compared and analyzed, and all the initial W/S was 1.0. In in Fig. 13 (a)–(c), for ternary SSCGs with 65%, 70% and 75% SS (3#, 4# and 5#), the fracture color of ternary SSCG seemed to be dark grey-deep green, the general fracture was loose. With the increase of SS contents, the failure section of ternary SSCG seemed to become less compact, and the macroscopic holes or micro-cracks tended to increase. This might be due to the high amount of SS (65–75%), the very low hydration reactivity of SS, relatively high W/S of 1.0, etc. In Fig. 13 (d)–(f), for ternary BFS composite grouts with 65%, 70% and 75% SS (8#, 9# and 10#), the fracture color seemed to be light grey-green, there existed some heterogeneous and large holes or pores especially for 10# sample, and the pores became more obvious with the increase of BFS contents. In Fig. 13 (g) and (h), with the addition of 2% B + 6% AA + 0.4% SP, the compactness of the fracture surface of the quinary SSCG (19#) had been enhanced, and its sedimentation and fracture uniformity have more advantages compared with those without admixtures. The detailed pore size distributions of such SSCG or BFS grout stone bodies would also be analyzed in Section 3.6 in this study.

3.3.

X-ray powder diffraction analysis

Fig. 14 shows the XRD spectra of the ternary, quaternary and quinary SSCGs. The W/S was selected as 1.0, the curing time o was selected as 28d. The scanning angle of XRD test was 5–60 , o and the scanning speed was 4–5 /min. In Fig. 14, the types of hydration products of ternary or quaternary SSCGs were similar to those of quaternary SSCGs generally. Compared with the XRD pattern of ternary SSCG with 55% SS (1# and Fig. 14(a)), the diffraction peak corresponding to Portlandite crystals (2␪ = 18.07, d = 0.490 nm; 2␪ = 34.12, d = 0.263 nm; 2␪ = 47.13, d = 0.193 nm) of the SSCG with 75% SS (5# and Fig. 14(b)) were strengthened observably. It might indicate that the reaction effectiveness among Portlandite and silicon or aluminum phases decreased. This mineral composition was adverse for strength development, which was in accordance with the FS and UCS results of ternary SSCGs with 55–75% SS. The XRD pattern difference among the quaternary SSCG with 55% SS (12# and Fig. 14(c)) and the ternary SSCGs (Fig. 14 (a) and (c)) was not obvious, this might be because of the relatively low content of FA (10%). Compared with the XRD pattern of the quinary SSCG (19#) without admixture, the diffraction peak corresponding to Portlandite crystals (2␪ = 18.07, d = 0.490 nm; 2␪ = 34.12, d = 0.263 nm; 2␪ = 47.13, d = 0.193 nm) of the SSCG with 6% com-

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

12

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Fig. 13 – Fracture surface characteristics of the 28-day composite grout stone bodies (Initial W/S of 1.0), (a) 3#, (b) 4#, (c) 5#, (d) 8#, (e) 9#, (f) 10#, (g) 19#, (h) 19# + 2% B + 6% AA + 0.4% SP.

posite AA (Fig. 14(e)) were weakened. This might be implied that, with the addition of the composite AA, the Portlandite reacted with silicate or/and aluminate ions more effectively and more C-S-H or C-A-S-H could be produced [15,56,57]. With the addition of 6% AA, the characteristic peak of AFt (2␪ = 9.12, d = 0.970 nm) was slightly weakened, that of AFm (2␪ = 9.92, d = 0.891 nm) tended to become more visible, it indicated some AFt might tend to transform into AFm at the initial W/S of 1.0. Meanwhile, the characteristic peak of RO phase was weakened, this might be because that the increased C-S-H or C-A-S-H gels could be helpful for the control of RO, especially under the combined effects of composition, relative content, 6% AA, curing time (28-day), high initial W/S (1.0), etc.

3.4.

FTIR analysis

Fig. 15 shows the FTIR result of typical ternary, quaternary and quinary SSCG stone bodies (28-day and the initial W/S of 1.0). At the initial W/S of 1.0, FTIR spectra of quaternary

Fig. 14 – The XRD spectra of the ternary, quaternary and quinary SSCGs (28-day and the initial W/S of 1.0).

Fig. 15 – The FTIR result of typical ternary, quaternary and quinary SSCG stone bodies (28-day and the initial W/S of 1.0).

SSCGs were similar to those of quaternary SSCGs generally. They highlight a succession of several weak and strong bands, located at approximately 454, (550–800), 880, 960, 1420/1480, 1650, and 3642 cm−1 . The bending vibration of Si O Si and O Si O were reflected on the bands at about 454 cm−1 [58], the highly polymerized silicates were reflected on the band vibration of (550–800) cm−1 . In the above large range, the silica of the glassy phases of FA especially for 19# + 6% AA were reflected approximately on the bands of 710 and 774 cm−1 [59]. The bands at approximately 1420, 1480 and 870 cm–1 were associated to the asymmetric stretching mode of the O C O bonds of carbonates [60]. In addition, the sulfate absorption bands were usually reflected to (1100–1200) cm−1 , due to the S O stretch of v3 -SO2-4 vibration [61]. The bands at about 1650 and 3450 cm−1 were features of water vibration, and the bands at

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

13

Fig. 16 – SEM photos of 28-day typical ternary hardened grouts (a) 5#, ×5000 (b) 5#, ×2000 (c) 1#, ×5000 (d) 1#, ×2000 (e) 7#, ×5000 (f) 7#, ×2000.

around 3642 cm−1 could be attributed to the vibration of OH in Ca(OH)2 , The band between 900 and 1300 cm− was related assigned to the asymmetric stretching mode of the Si O T (T: tetrahedral Si or Al) [62,63], and the formation of C-(A)-S-H gels were reflected especially for the quinary SSCG with 6% AA. At 960 cm−1 , the shift slightly to higher frequencies was detected for the quinary SSCG (19# + 6% AA), and this might be due to the variation of Si/Al ratio. The coinstantaneous activations of SS, BFS and FA were helpful for incorporating Al phase to the kind of C-A-S-H gel [63,64], therefore, the gel reorganization has been realized under the combined effects of composition, relative content, 0.6% AA, curing time of 28-day and high initial W/S of 1.0. It was found that the absorption of ternary SSCG with 55% SS (1#) was relatively small, this might be because that sufficient concentration of Ca2+ provided by rapid hydration of high amount of CC inhibited the continuous hydration of SS [65].

3.5.

Microstructure

The typical ternary, quaternary and quinary hardened SSCGs were selected for 28-day SEM tests, and the effects of SS, BFS, FA and CC on microstructures of hardened grouts were investigated. The results of typical ternary SSCGs (5#, 1# and 7#) are shown in Fig. 16. In Fig. 16 (a) and (b), for the ternary SSCG with 75% SS (5#), the Portlandite with hexagonal plates were observed and its crystallinity developed well, which was in accordance with the XRD results in Fig. 14. Big pores and cracks among hydrated minerals were observed especially at higher magnifications (×5000) in Fig. 16 (a), meanwhile, the large cavity area in the lower left part and connective wide cracks was found at lower magnifications (×5000) in Fig. 16 (b). The above findings verified the poor mechanical performance of the ternary SSCG with 75% SS (5#). In Fig. 16 (c) and (d), when SS contents

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

14

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

Fig. 17 – SEM photos of 28-day typical quaternary hardened SSCGs (a) 12#, ×5000 (b) 12#, ×2000 (c) 15#, ×5000 (d) 15#, ×2000.

decreased to 55% (1#), the Portlandite with hexagonal plates were not so obvious. Although its microstructure became more compact compared with that of ternary SSCG with 75% SS, there still existed large pores and connective cracks, and the microstructure still needed to be improved to enhance the mechanical strengths. In Fig. 16 (e) and (f), although the obvious big pores and large cavity area of ternary BFS composite grout were found especially in the upper left corner, its overall connectivity of amorphous minerals was more compact than that of ternary SSCG with 55–75% SS. And the above microstructure characteristics were in accordance with the related results of FS and UCS in Figs. 9(a) and 10(a). In conclusion, the gelatinization interconnection among gels and other minerals of ternary SSCG with 55–75% SS were not compact or anticipative, the weak connection of CH and low hydration efficiency might be the source of micro cracks or weak area [66]. The microstructures of ternary SSCG with 55–75% SS or BFS composite grout with 75% BFS needed to be improved further. The results of typical quaternate SSCGs (12# and 15#) are shown in Fig. 17. In Fig. 17 (a) and (b), the gelatinization interconnection among gels of quaternate SSCG with 30% SS (12#) were still relatively loose. Many AFt minerals were found, it might be related with its relatively high 3-day UCS. There existed observable pores and cracks among hydrated minerals especially at lower magnifications (×2000) in Fig. 17 (b), this might cause its relatively low 28-day UCS. In Fig. 17 (c) and (d), the microstructure was loose especially at the connection transition region between FA and gels or the area around CH minerals. A small number of gels was formed on the surface of FA, and the pozzolanic reaction was not obvious due to the low alkalinity, low curing time, etc. The cracks and pores or spaces among the hydrated minerals were still large. In

conclusion, with the addition of 10% or 15% FA, the hydration and pozzolanic reactions needed to be enhanced properly to improve the microstructure and mechanical strength. The results of typical quinary SSCGs without (19#) and with admixtures (15#+2%B + 6%AA + 0.4%SP) are shown in Fig. 18. In Fig. 18 (a) and (b), the CH with good crystallinity was barely found and there were C-S-H gels generated on the surface of the class F FA. The hydration of added 25% BFS might be helpful for improving the pozzolanic reactions hydration with some certain degrees. However, the large cavity area and high amounts of pores were found obviously at lower magnifications (×5000) in Fig. 18 (b), which might determine its relatively low 28-day UCS. It can be inferred that the reaction activity of high amount of SS was very low without activator. In Fig. 18 (c) and (d), with the addition of 2%B + 6%AA + 0.4%SP, although there were some micro-cracks in the microstructures, a good deal of hydration products intertwined with each other to generate the dense network structures. More gels were produced due to the effective activation of hydration and pozzolanic reactions, the good gelatinization interconnection among C(A)-S-H gels and other minerals enhanced the compactness of microstructure, and these explained the remarkable increase of 28-day FSs and UCSs of the quinary SSCG in Fig.12. In conclusion, at the initial W/S of 1.0, the improvement of 2%B + 6%AA + 0.4%SP was acceptable for the quinary SSCG with 40% SS and 80% CC replacement.

3.6.

Pore size distribution of grout stone body

The pore size distributions of typical ternary, quaternary and quinary hardened SSCGs were studied by using MIP technique. The initial W/S was 1.0, the results are exhibited in Fig. 19.

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

15

Fig. 18 – SEM photos of 28-day typical quinary hardened grouts (a) 19#, ×5000 (b) 19#, ×2000 (c) 19#+2%B + 6% AA + 0.4%SP, ×5000 (d) 19#+2%B + 6% AA + 0.4%SP, ×2000.

Fig. 19 – The pore size distributions of typical hardened SSCGs with MIP technique.

Combining Fig. 19, the ternary SSCG with 75% SS (5#) had most pores beyond 100 or 1000 nm and a highest total volume of pores, which might due to the combined effects of high initial W/S, high amounts of SS, low hydration activity of SS, etc. This result was in accordance with the results of mechanical strength and microstructure. Although the pores beyond 100 nm of ternary BFS composite grout (10#) were lower than those of quinary SSCG (19#), its high contents of large pore determined the pore size distribution of 10# sample still needed to be improved. The pore size range of 10–100 nm was related to pores which were partially or totally

blocked by hydrated products, and these pores were probably broken open with the increasing of mercury intrusion force. The pores with smaller sizes (<10 nm) are generally classified into the gel pores [38]. Therefore, the gel pores (<10 nm) and a large number of big holes (>100 nm) of the quinary SSCG (19#) needed to be enhanced to ensure the sufficient compactness of microstructures and mechanical strengths. In contrast, the pore size distributions of quinary SSCG (19#) with 6% AA + 2%B + 0.4% SP were optimized significantly, it had a lowest total volume of harmful pores (100–1000 and >1000 nm) and more pores under 7.5, 30 or 100 nm. This improvement of pore size distribution was verified by the microstructure in Fig. 18 and the mechanical performance in Figs. 12 or 13. The pore size distributions of optimized quinary SSCG was similar to the MIP results of cementitious composite at the W/S 0.7 in other studies [67]. The pore space was initially occupied by water in the initial hydration periods, the effective hydration of quinary SSCG proceeds with the optimized activation. With the effect of approximate activators, it could be deduced that the larger pores above 100 nm were easily filled by the newly produced hydration minerals, and the larger pores transformed into the smaller ones accordingly. As a result, the network structure of the hardened grout became denser or more compact, and the obvious increase of mechanical strength was realized correspondingly.

4.

Conclusions

1 The initial W/S was the control influence factor for spreading ability, effective W/S and stone rate, however the effects of high amounts of CC replacement, relative content and

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

16

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

admixtures should not be neglected. The combinations of 5% B, 2% B + 6% AA or 2% B + 6% AA + 0.4% SP is helpful for improving the effective W/S and stone rate of SSCG, and the 0.4% SP can offset the adverse effect of B or AA for spreading ability. 2 The FS and UCS of ternary SSCG decreased obviously when SS contents exceeded 65%, the SS were suggested to combine with BFS to optimize the strengths. With the improvement of 2% B + 6% AA + 0.4% SP, the 3-day UCS, 28day FS and 28-day UCS of the quinary SSCG (19#) increased by 105.3%, 100.7% and 167.7%, respectively. They exceeded 3.1, 2.1 and 10.2 MPa, and they are acceptable or relatively satisfied at the initial W/S of 1.0. 3 With the effect of approximate activators, the optimized quinary SSCG (19#) had a lower total volume of harmful pores (>100 nm) and more pores under 30 or 100 nm. It can be deduced that the newly produced hydration minerals filled the larger pores and the smaller ones increased accordingly, and the network structure of the hardened grout became more compact. These were in accordance with the related mineral composition and mechanical strengths. 4 With the high addition (40%) of SS and high utilization (80%) of industrial residue, the workability, mechanical performance, mineral composition and microstructure of the optimized quinary SSCG (19#) are acceptable, and it can meet the requirements of grouting practices for underground engineering.

[4] [5]

[6] [7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

Conflict of interest The authors declare no conflicts of interest.

Acknowledgements This study was financially supported by the National Natural Science Foundation of China (Grant Nos. 51909140, 51709158) and China Postdoctoral Science Foundation (2018M642658).

Appendix A. Supplementary data

[15]

[16]

[17]

[18]

[19]

Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j. jmrt.2020.01.014.

[20]

references

[22]

[21]

[23] [1] Li SC, Liu RT, Zhang QS, Zhang X. Protection against water or mud inrush in tunnels by grouting: a review. J Rock Mech Geotech Eng 2016;8(5):753–66 (In Chinese). [2] Zhang X, Li SC, Zhang QS, et al. Study of key-hole grouting method to harness high pressure water gushing in fractured rock mass. Chin J Rock Mech Eng 2011;30(7):1414–21 (In Chinese). [3] Li SC, Xu ZH, Huang X, et al. Classification, geological identification, hazard mode and typical case studies of hazard-causing structures for water and mud inrush in

[24]

[25]

[26]

tunnels. Chin J Rock Mech Eng 2018;37(5):1041–69 (In Chinese). Tani ME. Grouting rock fractures with cement grout. Rock Mech Rock Eng 2012;45(4):547–61. Saleh S, Yunus NZM, Ahmad K, et al. Improving the strength of weak soil using polyurethane grouts: a review. Constr Build Mater 2019;16(6):738–52. Marchi M, Gottardi G, Soga AK. Fracturing pressure in clay. J Geotech Geoenvironmental Eng 2014;140(2):1–9. Sha F, Li SC, Lin CJ, et al. Research on penetration grouting diffusion experiment and reinforcement mechanism for sandy soil porous media. Rock Soil Mech 2019, http://dx.doi.org/10.16285/j.rsm.2019.0133 (In Chinese). Baker WH, Cording EJ, Macpherson HH. Compaction grouting to control ground movements during tunneling [J]. Int J Rock Mech Min 1983;20(5):205–12. Lee JS, Bang CS, Mok YJ, et al. Numerical and experimental analysis of penetration grouting in jointed rock masses. Int J Rock Mech Min 2000;37(7):1027–37. AFTES (Association Franc¸aise des Travaux En Souterrain). Recommendations concerning grouting for underground structures rehabilitation. Tunnels et Ouvrages Souterrains 1998;146:103–34 (in French). Perret S, Palardy D, Ballivy G. Rheological behavior and setting time of microfine cement-based grouts. ACI Mater J 2000;97(4):472–8. Sha F, Li SC, Liu RT, et al. Experimental study on performance of cement-based grouts admixed with fly ash, bentonite, superplasticizer and sodium silicate. Constr Build Mater 2018;161:282–91. Li SC, Sha F, Liu RT, et al. Investigation on fundamental properties of microfine cement and cement-slag grouts. Constr Build Mater 2017;153:965–74. Zhang TS, Liu FT, Wang JW. Recent development of steel slag stability and activating activity. B Chin Ceram Soc 2007;26(5):980–4 (In Chinese). Zhang TS, Liu FT, Liu SQ, et al. Factors influencing the properties of a steel slag composite cement. Adv Cem Res 2008;20(4):145–50. Gao R, Cheng FQ. The comprehensive utilization of steel slag from metallurgical industry. Recy Resour Circ Econ 2010;3(11):38–41 (In Chinese). Bilodeau A, Malhotra VM. High-volume fly ash system: concrete solution for sustainable development. ACI Mater J 2000;97(1):41–8. Kuder K, Lehman D, Berman J, et al. Mechanical properties of self-consolidating concrete blended with high volumes of fly ash and slag. Constr Build Mater 2012;34:285–95. Zhang YM, Sun W, Yan HD. Hydration of high-volume fly ash cement pastes. Cement Concr Compos 2000;22(6):445–52. Wu X, Zhu H, Hou XK. Study on steel slag and fly ash composite Portland cement. Cem Concr Res 1999;29(7):983–7. Altun IA, Yilmaz I. Study on steel furnace slags with high MgO as additive in Portland cement. Cem Concr Res 2002;32(8):1247–9. Wu X, Zhu H, Hou XK. Study on steel slag and fly ash composite Portland cement. Cem Concr Res 1999;29(7):983–7. Nuno C, Joao C, Tiago M. Alkali activated composites – An innovative concept using iron and steel slag as both precursor and aggregate. Cem Concr Res 2019;103:11–21. Shi CJ, Qian JS. High performance cementing materials from industrial slags a review. Resour Conserv Recy 2000;29(2):195–207. Hu SG, He YJ, Lu LN. Effect of fine steel slag power on the early hydration process of Portland cement. J Wuhan Univ Technol Sci Ed 2006;21(1):147–9. Song S, Sohn D, Jennings HM, et al. Hydration of alkali-activated ground granulated blast furnace slag. J Mater Sci 2000;35(1):249–57.

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014

JMRTEC-1269; No. of Pages 17

ARTICLE IN PRESS j m a t e r r e s t e c h n o l . 2 0 2 0;x x x(x x):xxx–xxx

[27] Lin ZS, Tao HZ, Tu CH. Research for increasing the activation of steel slag and fly ash. J Wuhan Univ Technol Sci Ed 2001;23(2):4–7. [28] Hu SG, Jiang CS, Wei JX. Research on hydration of steel slag cement activated with water-glass. J Wuhan Univ Technol Sci Ed 2001;16(1):37–9. [29] Zhu M, Hu SG, Ding QJ. Investigation on applying steel slag to cement-based materials. J Wuhan Univ Technol Sci Ed 2005;27(6):48–51. [30] Li ZF, Zhou ZH, Liu FT, et al. Research on the hydrating mechanism of clinker-poor steel slag cement. J Wuhan Univ Technol Sci Ed 2009;31(4):139–43. [31] Shi CJ, Day RL. Early strength development and hydration of alkali-activated blast furnace slag/fly ash blends. Adv Cem Res 1999;11(4):189–96. [32] Tang M. Investigation of mineral compositions of steel slags for cement production, research report. Nanjing: Nanjing Institute of Chemical Technology; 1973 (in Chinese). [33] Sun S. Investigations on steel slag cements. Collections of achievements on the treatment and applications of metallurgical industrial wastes, 1. Beijing: Chinese Metallurgical Industry Press; 1983. p. 1–71. [34] Xiao QZ. Expansion and its inhibition of steel slag. J Chin Ceram Soc 1996;24(6):635–40 (in Chinese). [35] Fu XH, Hou WP, Yang CX, et al. Studies on high-strength slag and fly ash compound cement. Cem Concr Res 2000;30(8):1239–43. [36] Li DX, Shen JL, Chen YM, et al. Study of properties on fly ash—slag complex cement. Cem Concr Res 2000;30(9):1381–7. [37] Li SC, Sha F, Liu RT, et al. Properties of cement-based grouts with high amounts of ground granulated blast-furnace slag and fly ash. J Mater Civil Eng 2017;29(11):04017219. [38] Mirza J, Mirza MS, Roy V, et al. Basic rheological and mechanical properties of high-volume fly ash grouts. Constr Build Mater 2002;16:353–63. [39] Li SC, Sha F, Liu RT, et al. Investigation on viscous behavior and strength of microfine cement-based grout mixed with microfine fly ash (MFA) and superplasticizer (SP). Adv Cem Res 2017;29(5):206–15. [40] Hausmann MR. Engineering principles of ground modification. McGraw-Hill Publishing Company; 1990. ISBN: 0-07-027279-4. [41] Celik F, Canakci H. An investigation of rheological properties of cement-based grout mixed with rice husk ash (RHA). Constr Build Mater 2015;91:187–94. [42] Rosquoe F, Alexis A, Khelidj A, et al. Experimental study of cement grout: rheological behavior and sedimentation. Cem Concr Res 2003;33:713–22. [43] Huang WH. Properties of cement-fly ash grout admixed with bentonite, silica fume, or organic fiber. Cem Concr Res 1997;27(3):395–406. [44] Uchikawa H, Hanebar S, Sawaki S. The role of steric repulsive force in the dispersion of cement particles in fresh paste prepared with organic admixtures. Cem Concr Res 1997;27(1):37–50. [45] Liu RT, Li SC, Zhang QS, et al. Experiment and application research on a new type of dynamic water grouting material. Chin Rock Mech Eng 2011;30(7):1454–9 (In Chinese). [46] ISO 13320-1. Particle size analysis - Laser diffraction methods - Part 1 General principles. Geneva, Switzerland: International Organization for Standardization, ISO13320-1; 1999.

17

[47] Kantro DL. Influence of water reducing admixtures on properties of cement paste a miniature slump test. Cem Concr Aggr 1980;2(2):95–102. [48] ASTM. Standard test method for slump of hydraulic-cement concrete. West Conshohocken, PA: ASTM C143/C143M-15a; 2015. [49] BS. Execution of special geotechnical work-grouting, EN 12715. BS 389 Chiswick High Road, London; 2000. [50] Saleh K, Mirza J, Ballivy G. Selection criteria for Portland and microfine cement-based injection grouts. In: Proceedings International Conference on Grouting in Rock and Concrete, Salzburg. 1993. p. 97–105. [51] Bras A, Gião R, Lúcio V, et al. Development of an injectable grout for concrete repair and strengthening. Cement Concrete Comp 2013;37:185–95. [52] GB/T 17671-1999. Method of testing cements-Determination of strength. BJ: Chinese National Quality and Technical Supervision & Chinese Ministry of Construction; 1999. [53] Song S, Sohn D, Jennings HM, et al. Hydration of alkali-activated ground granulated blast furnace slag. J Mater Sci 2000;35(1):249–57. [54] Wang XY, Lee HS. Modeling the hydration of concrete incorporating fly ash or slag. Cem Concr Res 2010;40(7):984–96. [55] Shi CJ, Day RL. Selectivity of alkaline activators for the activation of slags. Cem Concr Aggregate 1996;18(1):8–14. [56] Wang JB, Du P, Zhou ZH, et al. Effect of nano-silica on hydration, microstructure of alkali-activated slag. Constr Build Mater 2019;220:110–8. [57] Wang JB, Zhou TT, Xu DY, et al. Effect of nano-silica on the efflorescence of waste based alkali-activated inorganic binder. Constr Build Mater 2018;167:381–90. [58] Nath SK, Kumar S. Influence of granulated silico-manganese slag on compressive strength and microstructure of ambient cured alkali-activated fly ash binder. Waste Biomass Valori 2019;10(7):2045–55. [59] Nath SK, Kumar S. Reaction kinetics, microstructure and strength behavior of alkali activated silico-manganese (SiMn) slag – fly ash blends. Constr Build Mater 2017;147:371–9. [60] Aydın S, Baradan B. Engineering properties of reactive powder concrete without Portland cement. ACI Mater J 2013;110(6):619–27. [61] Wang JB, Niu DT, Wang Y. Durability performance of brine-exposed shotcrete in salt lake environment. Constr Build Mater 2018;188:520–36. [62] Puertas F, Fernández-Jiménez A. Mineralogical and Microstructural Characterization of alkali-activated fly ash/slag pastes. Cement Concrete Comp 2003;25(3):287–92. [63] Ismail I, Bernal SA, Provis JL, et al. Microstructural changes in alkali activated fly ash/slag geopolymers with sulfate exposure. Mater Struct Constr 2013;46(3):361–73. [64] Shi CJ, Day RL, Wu X, et al. Microstructure and performances of alkali-slag cement pastes. In: Proc., 9th Int. Congress on Chemistry of Cements, National Council for Cement and Building Material. 1992. p. 98–304. [65] Zhao XG, Zhao SY, Li N, et al. The development of high strength steel slag cement with high content of steel slag. J Wuhan Univ Technol Sci Ed 2004;26(1):38–41. [66] Yuan RZ. Cementitious materials. Wuhan, China: Wuhan University of Technology Press; 1996. [67] Cook R, Hover K. Mercury porosimetry of hardened cement pastes. Cem Concr Res 1999;29:933–43.

Please cite this article in press as: Sha F, et al. Development of steel slag composite grouts for underground engineering. J Mater Res Technol. 2020. https://doi.org/10.1016/j.jmrt.2020.01.014