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Influence of mineral nano-fibers on the physical properties of road cement concrete material
Construction and Building Materials 190 (2018) 287–293
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of mineral nano-fibers on the physical properties of road cement concrete material Jingyi Liu ⇑, Huaxin Chen, Bowen Guan, Kaiping Liu, Jiuran Wen, Zhihua Sun School of Material Science and Engineering, Chang’an University, Xi’an, Shaan Xi 710054, PR China
h i g h l i g h t s Waste brucite short fibers processed to nano diameter level with a simple way. The physical properties of brucite nano-fiber reinforced concrete have been improved. Nano-fiber concrete superior to ordinary concrete in cost performance. 8 years traffic practice proves the practicability of nano-fiber concrete.
a r t i c l e
i n f o
Article history: Received 30 April 2018 Received in revised form 4 September 2018 Accepted 7 September 2018 Available online 25 September 2018 Keywords: Mineral nano-fibers Brucite Cement concrete Road Physical properties
a b s t r a c t In this paper, brucite nano-fiber is processed and used as reinforcement to improve the toughness of road cement concrete material. The brucite nano-fiber is obtained by soaking the natural low-coat brucite short fibers in the superplasticizer solution and then agitating in a forced mixer to refine it to the nano meter level. The mechanical properties as elastic modulus, dry shrinkage, anti-frost, thermal expansion, and flexural fatigue performance of the nano-fiber concrete are investigated. The nano-fiber reinforced cement concrete was also put into practice in highway. Results show that nano-fiber concrete has better toughness. Its flexural strength is 7.4% and 17.7% higher than that of the ordinary fiber concrete and the plain concrete, respectively. Its ratio of compression to flexural strengths is 6.4% and 16.1% lower than that of the rest two. Nano-fiber concrete has lower static modulus and higher dynamic modulus. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 41.0% and 61.3% lower in flexural elastic modulus, and is 1.12 and 1.24 times higher in dynamic modulus of elasticity. Nano-fiber concrete has stronger capability to resist dry shrinkage, freeze-thaw damage, thermal expansion and bending fatigue stresses. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 35.7% and 55.9% lower in dry linear shrinkage; 3.2% and 7.9% less loss rate in compression strength, and 1.9% and 4.5% less loss rate in flexural strength after 50 cycles freezing-thawing; 13.9% and 28.7% lower in coefficient of thermal expansion; and 15% and 50% more longer in bending fatigue service life. Nano-fiber concrete is comprehensively superior to ordinary fiber concrete and plain concrete in cost performance. After more than 8 years traffic practice, the nano-fiber concrete test road is still in good condition. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Cement concrete pavement has good qualities of high strength and stiffness, strong water-resistance and stable high-temperature property, and exhibits obvious advantage in the heavy load and weak roadbed areas [1,2]. However, cement concrete is a brittle material due to its feature of heterogeneous, multiple defects, low tensile strength, and low deformation capacity, it is ease to fracture under tension, bending and impact load, which leads to ⇑ Corresponding author. E-mail address: [email protected] (J. Liu). https://doi.org/10.1016/j.conbuildmat.2018.09.025 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
a premature failure [3,4]. It is significant to strengthen the tensile strength and toughness of cement concrete for prolonging its service life. In general, the effective approach to enhance the anti-bending performance of the road concrete is to employ fibers as the reinforcement to strengthen it [5,6]. Brucite fiber, or fibrous brucite (FB), is a kind of natural mineral fiber rich in China. It is mainly composed of Mg(OH)2 and has strong alkali resistance, good compatibility and strong binding force with cement concrete. It is also harmless to the human health [7,8]. The aim of this paper is trying to use a simple way to process the low-cost ordinary brucite fibers into nano-diameter fibers,
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and then using them as reinforcements in the road concrete to improve the properties of the cement concrete. 2. Experimental 2.1. Raw materials and properties 2.1.1. Mineral fibers Grade 7-X brucite fibers [9] from Shaanxi province were used. They are short fibers from the dust collector and mill tailings in the mine. The optical photo is shown in Fig. 1. The fiber parameters are shown in Table 1. The fibers are usually used as fillers simply instead of reinforcing phase due to their very short length. 2.1.2. Superplasticizer Based on the results of our previous work [9–11], compound admixture of different chemicals was used as the superplasticizer in the test, so as to both improve the properties of concrete and split brucite fiber bundles as well as disperse fibers in concrete. The superplasticizer admixture is prepared by mixing the materials with the mass ratio of naphthalene water reducer: aliphatic water reducer: Amino sulfonate reducer: sodium gluconate: methanol: water = 1: 1.5: 3: 0.05: 0.15: 2. The measured solid content of the result admixture is 29%, and its performance index meets the requirement of quality standards of Concrete Admixture(GB8076-2008). 2.1.3. Coarse aggregate The coarse aggregate is the 4.75–26.5 mm fabricated continuous grading limestone gravel, which is prepared by the mass proportion of gravel 1#(size 26.5 mm-19 mm): gravel 2# (size 19– 9.5 mm): gravel 3#(size 9.5–4.75 mm) =0.5: 0.4: 0.1. The screen analyst result is shown in Fig. 2 and meets the 4.75–26.5 mm nominal diameter of the Technical Specification for Construction of Highway Cement Concrete Pavements(JTG F30-2003).
Fig. 1. Brucite fibers.
Table 1 Parameters of brucite fibers. Aspect ratio Range
Average
14–143
53
Specific surface area, cm2/g
Sieve analysis, wt% +1.4 mm
+0.4 mm
Sieve bottom
239
12
35
53
Fig. 2. Screen analysis result of the coarse aggregate.
2.1.4. Other raw materials Other raw materials include P.O.42.5# Portland cement, fineness modulus 2.9 river sand and water. They all meet the Technical Specification for Construction of Highway Cement Concrete Pavements (JTG F30-2003). 2.2. Processes of mineral nano-fibers The brucite fibers were processed as follows: mixed the brucite fiber, superplasticizer and water at the mass ratio of 1: 0.96: 0.54 homogeneously, and stood for 24 h in order that the fibers could be soaked by the superplasticizer solution, then mechanically agitated inside a forced mixer for 10 min, aging the paste for 0.5 h, then collected and packed up the fiber paste for future use. Fig. 3 shows the comparative SEM(Scanning Electron Microscope) photos of fibers before and after processing. Fig. 3-A shows the original fibers, while Fig. 3-B presents the processed ones. The original fibers are in the state of closely combined fiber bundles with the diameters of about 1.5–46.3 lm. The diameters of processed fibers are about 45–110 nm, mostly are around 60 nm. The aspect ratio becomes march larger than the original fibers. Fig. 3 reveals that the original micro-diameter fibers become nano-diameter fibers after processed by the simple way of soaking with superplasticizer solution and agitating in forced mixers. To understand the mechanism of the naturally produced ordinary brucite fiber changing to the nano-fibers, further tests were conducted. Fig. 4-A and B show SEM photos of the enlarged original brucite fiber and the fibers soaked by superplasticizer solution for 24 h. Table 2 is the surface Zeta Potentials of original and processed brucite fibers in deionized water measured with JS94G + type electrophoresis apparatus under condition of 25D°C, 1.4A, 30 V, PH7 and voltage switching period 1000 ms. Fig. 4-A indicates that brucite fiber, as a natural fibrous mineral, is produced in the forms of closely bonded bundles. In fact, a single macro fiber is actually composed of much more finer fibers. It is an aggregation of many thinner fibers. After soaked in superplaticizer solution, the brucite fiber bundles are loosened (Fig. 4-B). Under the action of mechanical force of the mixer, the loosened fiber bundles are split into single fine fibers (Fig. 3-B). From Table2, it shows that the surface of the original brucite fibers brings positive charges, while the processed brucite fiber presents negative charges. This phenomenon should be related with the chemical adsorption of surfactant [12,13]. We all know that, water reducers are indispensable chemical agents in the modern concrete industry. They play some important parts in the concrete, such as, reducing the water content, enhancing the workability, improving the mechanical properties, etc. Since different water reducers have different functions, usually admixtures of water reducers were used for a better performance of the concrete. While in this paper, water reducers have the additional function of splitting the fiber bundles, as shown in Fig. 5.
J. Liu et al. / Construction and Building Materials 190 (2018) 287–293
289
Fig. 3. SEM photos of brucite fibers (A-original, B-processed).
Fig. 4. SEM photo of original brucite fiber (A) and fibers in splitting (B).
Table 2 Zeta potentials of the brucite fibers. State of brucite fibers
Original
Processed
Zeta potential, mV
+8.2
44.1
In the test, the water reducers in the superplasticizer were all anionic type surfactants. In the solution, the negative hydrophilic heads of the water reducer molecules would be absorbed toward
to the positive surface of the minerals due to the action of electrostatic attraction, and the hydrophobic tails would stretch into water, forming an absorption layer of the water reducers on the mineral surface. For stability, the hydrophobic tails of the molecules of water reducers in the solution would absorb towards the hydrophobic tails of the first absorbed layers, leaving their hydrophilic ends towards the outer. Second absorption layer of surfactants thus formed on the mineral surface. At the edge or head of the fiber bundle, the adjacent single fibers would also have two
Fig. 5. Diagrammatic sketch of chemical splitting of fiber bundles.
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layers of surfactant molecules on their surfaces. Since the hydrophilic ends of water reducers presented electronegative, so the adjacent single fibers in fiber bundle would have the same charges on their surface and would repel each other. Moreover, since surfactants have the strong ability to penetrate into the fiber bundle, the bond between the thin fibers in the bundle would be weakened, and the bundle were loosened after soaking. At the action of penetration of surfactants and the repulsive force of adjacent fibers, in addition to the auxiliary mechanical blending force of the mixer, the fiber bundles were split to single fibers, and negative charge would display on the surface of each single fibers. 2.3. Concrete specimen preparation and evaluation In order to get the designing target of flexural strength 5.5 MPa, slumps 30 mm, and according to Specifications of Cement and Concrete Pavement Design for Highway (JTG D40-2002) and Technical Specification for Construction of Highway Cement Concrete Pavement (JTG F30-2003), as well as the preliminary trial, 367 kg/m3 cement dosage was used. The raw material mix proportion for fiber concrete was: cement: water: sand: course aggregate: fiber: superplasticizer = 1: 0.38: 2.02: 3.30: 0.04: 0.011, and that for reference concrete (plain concrete) was cement: water: sand: course aggregates: superplasticizer = 1: 0.35: 2.02: 3.30: 0.008. The proportion of fiber concrete samples have a slight higher water/cement ratio and superplasticizer dosage, for the fibers have a larger specific surface area and will absorb more water. Fresh nano-fiber concrete was made by putting the sand, course aggregate and fiber paste to the concrete mixer first, agitating for 30 s, then adding the cement and rest water, blending for 1 min. Fresh ordinary-diameter fiber concrete and plain concrete were made by putting all the raw materials (including dry fibers for fiber concrete) to the mixer simultaneously, then blending them for 1.5 min. After fresh concrete was made, the mold casting, vibrating, and curing, as well as the detecting of physical properties (compression strength, flexural strength, splitting-tensile strength, static and dynamic modulus of elasticity, dry shrinkage, anti-frost) of concrete samples were conducted as per the Test Methods of Cement and Concrete for Highway Engineering (JTG E30-2005). The thermal expansion coefficient test of concrete was done as follows: putting the 28d aged 100 mm 100 mm 515 mm samples in oven for 4 h at different temperatures, then measuring the lengths according to the dry shrinkage test method with the mechanical comparator, calculating the expansion rate, then determining the thermal expansion coefficient through the relationship between expansion rate and temperature. The fatigue bending test was conducted by 4-poit bending and stress control sine wave loading method with the 90d aged 100 mm 100 mm 400 mm beam specimen. 3. Test result and analysis 3.1. Strengths of concrete Table 3 shows the comparison of strengths for nano-fiber concrete, ordinary fiber concrete and plain concrete, therein the Table 3 Strengths of concrete. Samples
Nano-fiber concrete
Ordinary fiber concrete
Plain concrete
28 d flexural strength, MPa 28 d splitting tensile strength, MPa 28 d compressive strength, MPa 28 d strengths ratio of compression/flexural
7.3 5.6 53.5 7.3
6.8 5.1 53.3 7.8
6.2 4.8 54.2 8.7
strengths ratio of compression to flexural generally presents the ductility of the concrete. The lower the ratio of compression to flexural, the more ductile the concrete. From Table 3, at the condition of almost the same compressive strengths, the fiber concrete samples have the higher flexural strengths and splitting tensile strengths, and lower ratios of compress to flexual strength than the plain concrete sample. This is accordance with the general rule of fiber-reinforcing materials [1–3]. Meanwhile, the nano-fiber concrete sample is higher than the ordinary fiber concrete in both the flexural strength and splitting tensile strength, and is lower in the ratio of compress to flexural strengths. Compared with ordinary fiber concrete and plain concrete from Table 3, the nano-fiber concrete is 7.4% and 17.7% higher in flexural strengths, 6.4% and 16.1% lower in the ratio of compress to flexural strengths. This indicates that the nano-fiber concrete has better toughness. The increase of the toughness in nano-fiber concrete is probably due to the strengthening role and the homogeneous distribution of the fibers in concrete. From Fig. 6, ordinary fibers are existed in concrete in the forms of micro-diameter, while nano-fibers are distributed in concrete in the forms of nano-diameter. Since the ratio of length to diameter of nano-fibers is much larger than that of the ordinary fibers in the same fiber length, nano-fibers have better enhancement function in concrete. Furthermore, at the condition of same weight quantity dosage, there are much more numbers of single fiber in the concrete for nano-fibers than for ordinary fibers. Consequently, nano-fibers form a uniformly combined fiber-binding material network structure, which has stronger toughening effect to the concrete than the sporadic scattered fiber structure formed by ordinary fibers. Therefore, nano-fiber concrete displays a higher toughness. 3.2. Modulus of elasticity Table 4 lists the elastic modulus of fiber concrete and plain concrete after aged 28d. The static modulus values of elasticity of fiber concrete are obviously lower than that of the plain concrete from Table 4, especially the flexural modulus values. Among them the nano-fiber concrete has the lowest flexural modulus value of elasticity. The flexural elastic modulus of nano-fiber concrete is 41.0% and 61.3% lower than that of the ordinary fiber concrete and the plain concrete. This also means that the nano-fiber concrete has greater strain and deformability than the ordinary fiber concrete and the plain concrete under the same bending stress. Fig. 7 is the cross section SEM photo of nano-fiber concrete bending sample. From Fig. 7, the phenomenon of fiber pull-out and bridge can be clearly observed. So we have reasons to believe that toughening mechanism of fiber dominates the load-deformation for nanofiber concrete. This is apparently different from the plain concrete. As we know, generally in plain concrete, cracks produce and brittle fracture occurs quickly under load because of its weak ability to prevent crack propagation. While in nano-fiber concrete, the debond, pull-out and break of the fibers would need larger force and consume more energy. Therefore, the nano-fiber concrete has higher bending and tensile strength, larger deformation capacity and lower static modulus of elasticity. The dynamic modulus of elasticity of nano-fiber concrete is higher than not only the static compression modulus of elasticity of itself (this is consistent with the general rule), but also the dynamic modulus of elasticity of the ordinary fiber concrete and the plain concrete. From Table 4, the dynamic modulus of elasticity of nano-fiber concrete is 1.12 and 1.24 times that of the ordinary fiber concrete and the plain concrete. Since the dynamic modulus
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Fig. 6. SEM photos of ordinary fiber concrete (A) and nano-fiber concrete (B).
Table 4 Elastic modulus of concrete, GPa. Concrete samples
Nano-fiber concrete
Ordinary fiber concrete
Plain concrete
Compressive modulus of elasticity Flexural modulus of elasticity Dynamic modulus of elasticity
34.5 7.2 48.1
36.9 12.2 43.1
41.1 18.6 38.8
Fig. 8. Line shrinkage rate of concrete samples over time.
Fig. 8 shows that, the dry shrinkage of concrete samples takes place mainly in the early ages. The nano-fiber concrete sample has the lowest dry shrinkage rate in the three. The dry line shrinkage rate of nano-fiber concrete is approximately 35.7% and 55.9% lower than that of the ordinary fiber concrete and the plain concrete after 7 day ages. The cause of this behavior should also be derived from the restriction of fibers to the contractions of concrete. 3.4. Freezing resistance
Fig. 7. Cross section SEM photo of nano-fiber concrete bending sample.
of elasticity represents the Young’s modulus under very low stress and approximately equals to the initial tangent slope on the stressstrain curve, this demonstrates that the initial deformation of nano-fiber concrete is very small and the initial tangent modulus of nano-fiber concrete is large under load. The reason for this should also be related to the role of fiber in concrete. As we have seen in Fig. 6-B and Fig. 7, nano-fiber and cement slurry in the concrete forms a network structure in cement stone after hardening. In the early stage of concrete stress, cement stone and aggregates are tightly combined together as a whole due to the bond and load transfer of fibers, it is not easy to be deformed. So the early strain of the nano-fiber concrete is smaller and the dynamic modulus of elasticity is higher than that of the ordinary fiber concrete and the plain concrete.
Table 5 is the strength decrease percentage of concrete samples after 50 cycles freezing and thawing. It is clear that the nano-fiber concrete has less strength loss after 50 cycles freezing and thawing than the ordinary fiber concrete and the plain concrete. The loss rate of compression strength is 3.2% and 7.9% less, and the loss rate of flexural strength is 1.9% and 4.5% less, respectively. This tells us that nano-fiber concrete has better freezing resistance, on approximately account of the confinement of the nano-fibers. 3.5. Thermal expansivity Fig. 9 is the variation of linear expansion rate of nano-fiber concrete, ordinary fiber concrete and plain concrete with the rising of temperature based on the specimen size of 10 °C. Table 5 Strength reduction after freezing-thawing test. Concrete samples
Nano-fiber concrete
Ordinary fiber concrete
Plain concrete
Reduction of Compression strength, % Reduction of splitting tensile strength, %
3.9
7.1
11.8
2.6
4.5
7.1
3.3. Dry shrinkage Fig. 8 is the change of line shrinkage rate of nano-fiber concrete, ordinary fiber concrete and plain concrete samples over time dried at room temperature.
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Fig. 9. The linear expansion rate varies with temperature.
From Fig. 9, the linear expansion rate of nano-fiber concrete is notably lower than that of the ordinary fiber concrete and the plain concrete. The regression equations of linear expansion rate versus the temperature are respectively as follows:
Ynanofiber ¼ 0:0087t 0:1006; R2 ¼ 0:9654
ð1Þ
Yplain ¼ 0:0122t 0:149; R2 ¼ 0:9944
ð2Þ
Yordinary ¼ 0:0105t 0:1248; R2 ¼ 0:99
ð3Þ
Herein, t is the temperature, °C; Ynano-fiber, Yordinary and Yplain are the linear expansion rates of the nano-fiber concrete, the ordinary fiber concrete, and the plain concrete, respectively. From the correlation coefficient R2, we know that the equations are linear highly significant. So the coefficient of thermal expansion a of each is:
Plain concrete : aplain 12:2E 6 = C
ð4Þ
Nano fiber concrete : ananofiber 8:7E 6 = C
ð5Þ
Ordinary fiber concrete : aordinary 10:5E 6 = C
ð6Þ
The coefficient of thermal expansion of nano-fiber concrete is approximately 13.9% and 28.7% lower than that of the ordinary fiber concrete and the plain concrete, that is to say, nano-fiber concrete has stronger capacity to resist heat deformation, which is also probably due to the restraining action of the fiber network structure.
3.6. Flexural fatigue performance Fig. 10 is the relationship between the bending fatigue life of the concrete and the stress level after the statistics. The Fig. 10 makes it clear that, the fiber concrete samples have longer bending fatigue life than the plain concrete, especially in the lower bending fatigue stress level (<0.80) (this is the common application situation), showing that the reinforcing effect of the fibers. Therein the bending fatigue life cycle of nano-fiber concrete is 15% and 50% more higher than that of the ordinary fiber concrete and the plain concrete, displaying that the nano-fiber concrete has more longer service life.
4. Engineering application of nano-fiber concrete in highway pavement Nano-fiber concrete has been applied in several highway test pavement engineering projects. Fig. 11 shows the road photos of brucite nano-fiber concrete in An-Kang Highway section, Shaan Xi province. The road section is located in the middle of BaoTou MaoMing expressway, one of the south-north key highways of China. After more than 8 years traffic practice, the road is still in good condition. There is no visible cracks or damage. Economically, although the addition of brucite nano-fiber into concrete raised the cost of the concrete by about 3.8%, the whole cost performance of brucite nano-fiber concrete road was 1.21 times that of the plain concrete road, owing to the dramatic increase of concrete properties and lifespan, which shows the
Fig. 10. Relationship between bending fatigue life and stress level.
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2017.5.30
2009.8.1 Fig. 11. Highway road photos of brucite nano-fiber concrete.
cost-income ratio superiority of brucite nano-fiber concrete over the plain concrete. 5. Conclusions (1) The low-cost naturally produced ordinary micro-diameter brucite short fibers were split into 45–110 nm diameter fibers by the simple way of soaking with superplasticizer solution and agitating in forced mixers; (2) Nano-fiber concrete has better toughness. Its flexural strength is 7.4% and 17.7% higher than that of the ordinary fiber concrete and the plain concrete, respectively. Its ratio of compression to flexural strengths is 6.4% and 16.1% lower than that of the latter two. (3) Nano-fiber concrete has lower static modulus and higher dynamic modulus. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 41.0% and 61.3% lower in flexural elastic modulus, and is 1.12 and 1.24 times higher in dynamic modulus of elasticity. (4) Nano-fiber concrete has stronger capability to resist dry shrinkage, freeze-thaw damage, thermal expansion and bending fatigue stresses. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 35.7% and 55.9% lower in dry linear shrinkage; 3.2% and 7.9% less in compression strength loss rate, and 1.9% and 4.5% less in flexural strength loss rate after 50 cycles freezing-thawing; 13.9% and 28.7% lower in coefficient of thermal expansion, and 15% and 50% more longer in bending fatigue service life. (5) Nano-fiber concrete is comprehensively superior to ordinary fiber concrete and plain concrete in cost performance. 6. Conflict of interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influ-
ence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled ‘‘Influence of Mineral Nanofibers on the Performance of Highway Cement Concrete”. References [1] S.Y. Choi, J.S. Park, W.T. Jung, A study on the shrinkage control of fiber reinforced concrete pavement, Procedia Eng. 14 (2011) 2815–2822. [2] A. Nobilia, L. Lanzoniab, A.M. Tarantino, Experimental investigation and monitoring of a polypropylene-based fiber reinforced concrete road pavement, Constr. Build. Mater. 47 (10) (2013) 888–895. [3] Zhong-Xian Lia, Chang-Hui Lia, Yun-Dong Shi, etc, Experimental investigation on mechanical properties of Hybrid Fibre Reinforced Concrete, Constr. Build. Mater. 157 (30) (2017) 930–942. [4] T.F. Fwa, P. Paramasivam, Thin steel fibre cement mortar overlay for concrete pavement, Cem. Concr. Compos. 12 (3) (1990) 175–184. [5] Katerina Krayushkina, Tetiana Khymerik, Oleksandra Skrypchenko, et al., Investigation of fiber concrete for road and bridge building, Procedia Eng. 187 (2017) 620–627. [6] José A. Fuente-Alonso, Vanesa Ortega-López, Marta Skaf, et al., Performance of fiber-reinforced EAF slag concrete for use in pavements, Constr. Build. Mater. 149 (9) (2017) 629–638. [7] Dong Faqin, Pu. Wan, Zhou Kaican, et al., The environmental safety investigation on brucite fiber in Shannan, China Environ. Sci. 18 (1) (1998) 29–33. [8] Dong Faqin, Pan Zhaolu, Pu. Wan, etc, Physical properties investigation of fibrous brucite(FB)in the south of shaanxi, J. Southwest Instit. Technol. 10 (4) (1995) 5–15. [9] Liu Kaiping, Cheng Hewei, Zhou Jing’en, Investigation of brucite fiber reinforced concrete, Cem. Concr. Res. 34 (11) (2004) 1981–1986. [10] Liu Kaiping, Zhao Chongyang, Yang Xuegui, et al., Dispersing effects of superplsticizer to brucite fibers, Mining Res. Dev. 25 (5) (2005) 46–49. [11] Zhang Yan, Liu Kaiping, Guan Bowen, et al., Research on the influence of short fiber brucite on the performance of cement based composites, Appl. Chem. Industry 38 (9) (2009) 1267–1269. [12] Somen Mondal, Tarasankar Das, Prasun Ghosh, etc, Surfactant chain length controls photoinduced electron transfer in surfactant bilayer protected carbon nanoparticles, Mater. Lett. 141 (2) (2015) 252–254. [13] H.N. Atahan, C. Carlos Jr., S. Chae, P.J.M. Monteiro, et al., The morphology of entrained air voids in hardened cement paste generated with different anionic surfactants, Cem. Concr. Compos. 30 (7) (2008) 566–575.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Influence of mineral nano-fibers on the physical properties of road cement concrete material Jingyi Liu ⇑, Huaxin Chen, Bowen Guan, Kaiping Liu, Jiuran Wen, Zhihua Sun School of Material Science and Engineering, Chang’an University, Xi’an, Shaan Xi 710054, PR China
h i g h l i g h t s Waste brucite short fibers processed to nano diameter level with a simple way. The physical properties of brucite nano-fiber reinforced concrete have been improved. Nano-fiber concrete superior to ordinary concrete in cost performance. 8 years traffic practice proves the practicability of nano-fiber concrete.
a r t i c l e
i n f o
Article history: Received 30 April 2018 Received in revised form 4 September 2018 Accepted 7 September 2018 Available online 25 September 2018 Keywords: Mineral nano-fibers Brucite Cement concrete Road Physical properties
a b s t r a c t In this paper, brucite nano-fiber is processed and used as reinforcement to improve the toughness of road cement concrete material. The brucite nano-fiber is obtained by soaking the natural low-coat brucite short fibers in the superplasticizer solution and then agitating in a forced mixer to refine it to the nano meter level. The mechanical properties as elastic modulus, dry shrinkage, anti-frost, thermal expansion, and flexural fatigue performance of the nano-fiber concrete are investigated. The nano-fiber reinforced cement concrete was also put into practice in highway. Results show that nano-fiber concrete has better toughness. Its flexural strength is 7.4% and 17.7% higher than that of the ordinary fiber concrete and the plain concrete, respectively. Its ratio of compression to flexural strengths is 6.4% and 16.1% lower than that of the rest two. Nano-fiber concrete has lower static modulus and higher dynamic modulus. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 41.0% and 61.3% lower in flexural elastic modulus, and is 1.12 and 1.24 times higher in dynamic modulus of elasticity. Nano-fiber concrete has stronger capability to resist dry shrinkage, freeze-thaw damage, thermal expansion and bending fatigue stresses. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 35.7% and 55.9% lower in dry linear shrinkage; 3.2% and 7.9% less loss rate in compression strength, and 1.9% and 4.5% less loss rate in flexural strength after 50 cycles freezing-thawing; 13.9% and 28.7% lower in coefficient of thermal expansion; and 15% and 50% more longer in bending fatigue service life. Nano-fiber concrete is comprehensively superior to ordinary fiber concrete and plain concrete in cost performance. After more than 8 years traffic practice, the nano-fiber concrete test road is still in good condition. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Cement concrete pavement has good qualities of high strength and stiffness, strong water-resistance and stable high-temperature property, and exhibits obvious advantage in the heavy load and weak roadbed areas [1,2]. However, cement concrete is a brittle material due to its feature of heterogeneous, multiple defects, low tensile strength, and low deformation capacity, it is ease to fracture under tension, bending and impact load, which leads to ⇑ Corresponding author. E-mail address: [email protected] (J. Liu). https://doi.org/10.1016/j.conbuildmat.2018.09.025 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
a premature failure [3,4]. It is significant to strengthen the tensile strength and toughness of cement concrete for prolonging its service life. In general, the effective approach to enhance the anti-bending performance of the road concrete is to employ fibers as the reinforcement to strengthen it [5,6]. Brucite fiber, or fibrous brucite (FB), is a kind of natural mineral fiber rich in China. It is mainly composed of Mg(OH)2 and has strong alkali resistance, good compatibility and strong binding force with cement concrete. It is also harmless to the human health [7,8]. The aim of this paper is trying to use a simple way to process the low-cost ordinary brucite fibers into nano-diameter fibers,
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and then using them as reinforcements in the road concrete to improve the properties of the cement concrete. 2. Experimental 2.1. Raw materials and properties 2.1.1. Mineral fibers Grade 7-X brucite fibers [9] from Shaanxi province were used. They are short fibers from the dust collector and mill tailings in the mine. The optical photo is shown in Fig. 1. The fiber parameters are shown in Table 1. The fibers are usually used as fillers simply instead of reinforcing phase due to their very short length. 2.1.2. Superplasticizer Based on the results of our previous work [9–11], compound admixture of different chemicals was used as the superplasticizer in the test, so as to both improve the properties of concrete and split brucite fiber bundles as well as disperse fibers in concrete. The superplasticizer admixture is prepared by mixing the materials with the mass ratio of naphthalene water reducer: aliphatic water reducer: Amino sulfonate reducer: sodium gluconate: methanol: water = 1: 1.5: 3: 0.05: 0.15: 2. The measured solid content of the result admixture is 29%, and its performance index meets the requirement of quality standards of Concrete Admixture(GB8076-2008). 2.1.3. Coarse aggregate The coarse aggregate is the 4.75–26.5 mm fabricated continuous grading limestone gravel, which is prepared by the mass proportion of gravel 1#(size 26.5 mm-19 mm): gravel 2# (size 19– 9.5 mm): gravel 3#(size 9.5–4.75 mm) =0.5: 0.4: 0.1. The screen analyst result is shown in Fig. 2 and meets the 4.75–26.5 mm nominal diameter of the Technical Specification for Construction of Highway Cement Concrete Pavements(JTG F30-2003).
Fig. 1. Brucite fibers.
Table 1 Parameters of brucite fibers. Aspect ratio Range
Average
14–143
53
Specific surface area, cm2/g
Sieve analysis, wt% +1.4 mm
+0.4 mm
Sieve bottom
239
12
35
53
Fig. 2. Screen analysis result of the coarse aggregate.
2.1.4. Other raw materials Other raw materials include P.O.42.5# Portland cement, fineness modulus 2.9 river sand and water. They all meet the Technical Specification for Construction of Highway Cement Concrete Pavements (JTG F30-2003). 2.2. Processes of mineral nano-fibers The brucite fibers were processed as follows: mixed the brucite fiber, superplasticizer and water at the mass ratio of 1: 0.96: 0.54 homogeneously, and stood for 24 h in order that the fibers could be soaked by the superplasticizer solution, then mechanically agitated inside a forced mixer for 10 min, aging the paste for 0.5 h, then collected and packed up the fiber paste for future use. Fig. 3 shows the comparative SEM(Scanning Electron Microscope) photos of fibers before and after processing. Fig. 3-A shows the original fibers, while Fig. 3-B presents the processed ones. The original fibers are in the state of closely combined fiber bundles with the diameters of about 1.5–46.3 lm. The diameters of processed fibers are about 45–110 nm, mostly are around 60 nm. The aspect ratio becomes march larger than the original fibers. Fig. 3 reveals that the original micro-diameter fibers become nano-diameter fibers after processed by the simple way of soaking with superplasticizer solution and agitating in forced mixers. To understand the mechanism of the naturally produced ordinary brucite fiber changing to the nano-fibers, further tests were conducted. Fig. 4-A and B show SEM photos of the enlarged original brucite fiber and the fibers soaked by superplasticizer solution for 24 h. Table 2 is the surface Zeta Potentials of original and processed brucite fibers in deionized water measured with JS94G + type electrophoresis apparatus under condition of 25D°C, 1.4A, 30 V, PH7 and voltage switching period 1000 ms. Fig. 4-A indicates that brucite fiber, as a natural fibrous mineral, is produced in the forms of closely bonded bundles. In fact, a single macro fiber is actually composed of much more finer fibers. It is an aggregation of many thinner fibers. After soaked in superplaticizer solution, the brucite fiber bundles are loosened (Fig. 4-B). Under the action of mechanical force of the mixer, the loosened fiber bundles are split into single fine fibers (Fig. 3-B). From Table2, it shows that the surface of the original brucite fibers brings positive charges, while the processed brucite fiber presents negative charges. This phenomenon should be related with the chemical adsorption of surfactant [12,13]. We all know that, water reducers are indispensable chemical agents in the modern concrete industry. They play some important parts in the concrete, such as, reducing the water content, enhancing the workability, improving the mechanical properties, etc. Since different water reducers have different functions, usually admixtures of water reducers were used for a better performance of the concrete. While in this paper, water reducers have the additional function of splitting the fiber bundles, as shown in Fig. 5.
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289
Fig. 3. SEM photos of brucite fibers (A-original, B-processed).
Fig. 4. SEM photo of original brucite fiber (A) and fibers in splitting (B).
Table 2 Zeta potentials of the brucite fibers. State of brucite fibers
Original
Processed
Zeta potential, mV
+8.2
44.1
In the test, the water reducers in the superplasticizer were all anionic type surfactants. In the solution, the negative hydrophilic heads of the water reducer molecules would be absorbed toward
to the positive surface of the minerals due to the action of electrostatic attraction, and the hydrophobic tails would stretch into water, forming an absorption layer of the water reducers on the mineral surface. For stability, the hydrophobic tails of the molecules of water reducers in the solution would absorb towards the hydrophobic tails of the first absorbed layers, leaving their hydrophilic ends towards the outer. Second absorption layer of surfactants thus formed on the mineral surface. At the edge or head of the fiber bundle, the adjacent single fibers would also have two
Fig. 5. Diagrammatic sketch of chemical splitting of fiber bundles.
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layers of surfactant molecules on their surfaces. Since the hydrophilic ends of water reducers presented electronegative, so the adjacent single fibers in fiber bundle would have the same charges on their surface and would repel each other. Moreover, since surfactants have the strong ability to penetrate into the fiber bundle, the bond between the thin fibers in the bundle would be weakened, and the bundle were loosened after soaking. At the action of penetration of surfactants and the repulsive force of adjacent fibers, in addition to the auxiliary mechanical blending force of the mixer, the fiber bundles were split to single fibers, and negative charge would display on the surface of each single fibers. 2.3. Concrete specimen preparation and evaluation In order to get the designing target of flexural strength 5.5 MPa, slumps 30 mm, and according to Specifications of Cement and Concrete Pavement Design for Highway (JTG D40-2002) and Technical Specification for Construction of Highway Cement Concrete Pavement (JTG F30-2003), as well as the preliminary trial, 367 kg/m3 cement dosage was used. The raw material mix proportion for fiber concrete was: cement: water: sand: course aggregate: fiber: superplasticizer = 1: 0.38: 2.02: 3.30: 0.04: 0.011, and that for reference concrete (plain concrete) was cement: water: sand: course aggregates: superplasticizer = 1: 0.35: 2.02: 3.30: 0.008. The proportion of fiber concrete samples have a slight higher water/cement ratio and superplasticizer dosage, for the fibers have a larger specific surface area and will absorb more water. Fresh nano-fiber concrete was made by putting the sand, course aggregate and fiber paste to the concrete mixer first, agitating for 30 s, then adding the cement and rest water, blending for 1 min. Fresh ordinary-diameter fiber concrete and plain concrete were made by putting all the raw materials (including dry fibers for fiber concrete) to the mixer simultaneously, then blending them for 1.5 min. After fresh concrete was made, the mold casting, vibrating, and curing, as well as the detecting of physical properties (compression strength, flexural strength, splitting-tensile strength, static and dynamic modulus of elasticity, dry shrinkage, anti-frost) of concrete samples were conducted as per the Test Methods of Cement and Concrete for Highway Engineering (JTG E30-2005). The thermal expansion coefficient test of concrete was done as follows: putting the 28d aged 100 mm 100 mm 515 mm samples in oven for 4 h at different temperatures, then measuring the lengths according to the dry shrinkage test method with the mechanical comparator, calculating the expansion rate, then determining the thermal expansion coefficient through the relationship between expansion rate and temperature. The fatigue bending test was conducted by 4-poit bending and stress control sine wave loading method with the 90d aged 100 mm 100 mm 400 mm beam specimen. 3. Test result and analysis 3.1. Strengths of concrete Table 3 shows the comparison of strengths for nano-fiber concrete, ordinary fiber concrete and plain concrete, therein the Table 3 Strengths of concrete. Samples
Nano-fiber concrete
Ordinary fiber concrete
Plain concrete
28 d flexural strength, MPa 28 d splitting tensile strength, MPa 28 d compressive strength, MPa 28 d strengths ratio of compression/flexural
7.3 5.6 53.5 7.3
6.8 5.1 53.3 7.8
6.2 4.8 54.2 8.7
strengths ratio of compression to flexural generally presents the ductility of the concrete. The lower the ratio of compression to flexural, the more ductile the concrete. From Table 3, at the condition of almost the same compressive strengths, the fiber concrete samples have the higher flexural strengths and splitting tensile strengths, and lower ratios of compress to flexual strength than the plain concrete sample. This is accordance with the general rule of fiber-reinforcing materials [1–3]. Meanwhile, the nano-fiber concrete sample is higher than the ordinary fiber concrete in both the flexural strength and splitting tensile strength, and is lower in the ratio of compress to flexural strengths. Compared with ordinary fiber concrete and plain concrete from Table 3, the nano-fiber concrete is 7.4% and 17.7% higher in flexural strengths, 6.4% and 16.1% lower in the ratio of compress to flexural strengths. This indicates that the nano-fiber concrete has better toughness. The increase of the toughness in nano-fiber concrete is probably due to the strengthening role and the homogeneous distribution of the fibers in concrete. From Fig. 6, ordinary fibers are existed in concrete in the forms of micro-diameter, while nano-fibers are distributed in concrete in the forms of nano-diameter. Since the ratio of length to diameter of nano-fibers is much larger than that of the ordinary fibers in the same fiber length, nano-fibers have better enhancement function in concrete. Furthermore, at the condition of same weight quantity dosage, there are much more numbers of single fiber in the concrete for nano-fibers than for ordinary fibers. Consequently, nano-fibers form a uniformly combined fiber-binding material network structure, which has stronger toughening effect to the concrete than the sporadic scattered fiber structure formed by ordinary fibers. Therefore, nano-fiber concrete displays a higher toughness. 3.2. Modulus of elasticity Table 4 lists the elastic modulus of fiber concrete and plain concrete after aged 28d. The static modulus values of elasticity of fiber concrete are obviously lower than that of the plain concrete from Table 4, especially the flexural modulus values. Among them the nano-fiber concrete has the lowest flexural modulus value of elasticity. The flexural elastic modulus of nano-fiber concrete is 41.0% and 61.3% lower than that of the ordinary fiber concrete and the plain concrete. This also means that the nano-fiber concrete has greater strain and deformability than the ordinary fiber concrete and the plain concrete under the same bending stress. Fig. 7 is the cross section SEM photo of nano-fiber concrete bending sample. From Fig. 7, the phenomenon of fiber pull-out and bridge can be clearly observed. So we have reasons to believe that toughening mechanism of fiber dominates the load-deformation for nanofiber concrete. This is apparently different from the plain concrete. As we know, generally in plain concrete, cracks produce and brittle fracture occurs quickly under load because of its weak ability to prevent crack propagation. While in nano-fiber concrete, the debond, pull-out and break of the fibers would need larger force and consume more energy. Therefore, the nano-fiber concrete has higher bending and tensile strength, larger deformation capacity and lower static modulus of elasticity. The dynamic modulus of elasticity of nano-fiber concrete is higher than not only the static compression modulus of elasticity of itself (this is consistent with the general rule), but also the dynamic modulus of elasticity of the ordinary fiber concrete and the plain concrete. From Table 4, the dynamic modulus of elasticity of nano-fiber concrete is 1.12 and 1.24 times that of the ordinary fiber concrete and the plain concrete. Since the dynamic modulus
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Fig. 6. SEM photos of ordinary fiber concrete (A) and nano-fiber concrete (B).
Table 4 Elastic modulus of concrete, GPa. Concrete samples
Nano-fiber concrete
Ordinary fiber concrete
Plain concrete
Compressive modulus of elasticity Flexural modulus of elasticity Dynamic modulus of elasticity
34.5 7.2 48.1
36.9 12.2 43.1
41.1 18.6 38.8
Fig. 8. Line shrinkage rate of concrete samples over time.
Fig. 8 shows that, the dry shrinkage of concrete samples takes place mainly in the early ages. The nano-fiber concrete sample has the lowest dry shrinkage rate in the three. The dry line shrinkage rate of nano-fiber concrete is approximately 35.7% and 55.9% lower than that of the ordinary fiber concrete and the plain concrete after 7 day ages. The cause of this behavior should also be derived from the restriction of fibers to the contractions of concrete. 3.4. Freezing resistance
Fig. 7. Cross section SEM photo of nano-fiber concrete bending sample.
of elasticity represents the Young’s modulus under very low stress and approximately equals to the initial tangent slope on the stressstrain curve, this demonstrates that the initial deformation of nano-fiber concrete is very small and the initial tangent modulus of nano-fiber concrete is large under load. The reason for this should also be related to the role of fiber in concrete. As we have seen in Fig. 6-B and Fig. 7, nano-fiber and cement slurry in the concrete forms a network structure in cement stone after hardening. In the early stage of concrete stress, cement stone and aggregates are tightly combined together as a whole due to the bond and load transfer of fibers, it is not easy to be deformed. So the early strain of the nano-fiber concrete is smaller and the dynamic modulus of elasticity is higher than that of the ordinary fiber concrete and the plain concrete.
Table 5 is the strength decrease percentage of concrete samples after 50 cycles freezing and thawing. It is clear that the nano-fiber concrete has less strength loss after 50 cycles freezing and thawing than the ordinary fiber concrete and the plain concrete. The loss rate of compression strength is 3.2% and 7.9% less, and the loss rate of flexural strength is 1.9% and 4.5% less, respectively. This tells us that nano-fiber concrete has better freezing resistance, on approximately account of the confinement of the nano-fibers. 3.5. Thermal expansivity Fig. 9 is the variation of linear expansion rate of nano-fiber concrete, ordinary fiber concrete and plain concrete with the rising of temperature based on the specimen size of 10 °C. Table 5 Strength reduction after freezing-thawing test. Concrete samples
Nano-fiber concrete
Ordinary fiber concrete
Plain concrete
Reduction of Compression strength, % Reduction of splitting tensile strength, %
3.9
7.1
11.8
2.6
4.5
7.1
3.3. Dry shrinkage Fig. 8 is the change of line shrinkage rate of nano-fiber concrete, ordinary fiber concrete and plain concrete samples over time dried at room temperature.
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Fig. 9. The linear expansion rate varies with temperature.
From Fig. 9, the linear expansion rate of nano-fiber concrete is notably lower than that of the ordinary fiber concrete and the plain concrete. The regression equations of linear expansion rate versus the temperature are respectively as follows:
Ynanofiber ¼ 0:0087t 0:1006; R2 ¼ 0:9654
ð1Þ
Yplain ¼ 0:0122t 0:149; R2 ¼ 0:9944
ð2Þ
Yordinary ¼ 0:0105t 0:1248; R2 ¼ 0:99
ð3Þ
Herein, t is the temperature, °C; Ynano-fiber, Yordinary and Yplain are the linear expansion rates of the nano-fiber concrete, the ordinary fiber concrete, and the plain concrete, respectively. From the correlation coefficient R2, we know that the equations are linear highly significant. So the coefficient of thermal expansion a of each is:
Plain concrete : aplain 12:2E 6 = C
ð4Þ
Nano fiber concrete : ananofiber 8:7E 6 = C
ð5Þ
Ordinary fiber concrete : aordinary 10:5E 6 = C
ð6Þ
The coefficient of thermal expansion of nano-fiber concrete is approximately 13.9% and 28.7% lower than that of the ordinary fiber concrete and the plain concrete, that is to say, nano-fiber concrete has stronger capacity to resist heat deformation, which is also probably due to the restraining action of the fiber network structure.
3.6. Flexural fatigue performance Fig. 10 is the relationship between the bending fatigue life of the concrete and the stress level after the statistics. The Fig. 10 makes it clear that, the fiber concrete samples have longer bending fatigue life than the plain concrete, especially in the lower bending fatigue stress level (<0.80) (this is the common application situation), showing that the reinforcing effect of the fibers. Therein the bending fatigue life cycle of nano-fiber concrete is 15% and 50% more higher than that of the ordinary fiber concrete and the plain concrete, displaying that the nano-fiber concrete has more longer service life.
4. Engineering application of nano-fiber concrete in highway pavement Nano-fiber concrete has been applied in several highway test pavement engineering projects. Fig. 11 shows the road photos of brucite nano-fiber concrete in An-Kang Highway section, Shaan Xi province. The road section is located in the middle of BaoTou MaoMing expressway, one of the south-north key highways of China. After more than 8 years traffic practice, the road is still in good condition. There is no visible cracks or damage. Economically, although the addition of brucite nano-fiber into concrete raised the cost of the concrete by about 3.8%, the whole cost performance of brucite nano-fiber concrete road was 1.21 times that of the plain concrete road, owing to the dramatic increase of concrete properties and lifespan, which shows the
Fig. 10. Relationship between bending fatigue life and stress level.
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2017.5.30
2009.8.1 Fig. 11. Highway road photos of brucite nano-fiber concrete.
cost-income ratio superiority of brucite nano-fiber concrete over the plain concrete. 5. Conclusions (1) The low-cost naturally produced ordinary micro-diameter brucite short fibers were split into 45–110 nm diameter fibers by the simple way of soaking with superplasticizer solution and agitating in forced mixers; (2) Nano-fiber concrete has better toughness. Its flexural strength is 7.4% and 17.7% higher than that of the ordinary fiber concrete and the plain concrete, respectively. Its ratio of compression to flexural strengths is 6.4% and 16.1% lower than that of the latter two. (3) Nano-fiber concrete has lower static modulus and higher dynamic modulus. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 41.0% and 61.3% lower in flexural elastic modulus, and is 1.12 and 1.24 times higher in dynamic modulus of elasticity. (4) Nano-fiber concrete has stronger capability to resist dry shrinkage, freeze-thaw damage, thermal expansion and bending fatigue stresses. Compared with ordinary fiber concrete and plain concrete, nano-fiber concrete is 35.7% and 55.9% lower in dry linear shrinkage; 3.2% and 7.9% less in compression strength loss rate, and 1.9% and 4.5% less in flexural strength loss rate after 50 cycles freezing-thawing; 13.9% and 28.7% lower in coefficient of thermal expansion, and 15% and 50% more longer in bending fatigue service life. (5) Nano-fiber concrete is comprehensively superior to ordinary fiber concrete and plain concrete in cost performance. 6. Conflict of interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influ-
ence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled ‘‘Influence of Mineral Nanofibers on the Performance of Highway Cement Concrete”. References [1] S.Y. Choi, J.S. Park, W.T. Jung, A study on the shrinkage control of fiber reinforced concrete pavement, Procedia Eng. 14 (2011) 2815–2822. [2] A. Nobilia, L. Lanzoniab, A.M. Tarantino, Experimental investigation and monitoring of a polypropylene-based fiber reinforced concrete road pavement, Constr. Build. Mater. 47 (10) (2013) 888–895. [3] Zhong-Xian Lia, Chang-Hui Lia, Yun-Dong Shi, etc, Experimental investigation on mechanical properties of Hybrid Fibre Reinforced Concrete, Constr. Build. Mater. 157 (30) (2017) 930–942. [4] T.F. Fwa, P. Paramasivam, Thin steel fibre cement mortar overlay for concrete pavement, Cem. Concr. Compos. 12 (3) (1990) 175–184. [5] Katerina Krayushkina, Tetiana Khymerik, Oleksandra Skrypchenko, et al., Investigation of fiber concrete for road and bridge building, Procedia Eng. 187 (2017) 620–627. [6] José A. Fuente-Alonso, Vanesa Ortega-López, Marta Skaf, et al., Performance of fiber-reinforced EAF slag concrete for use in pavements, Constr. Build. Mater. 149 (9) (2017) 629–638. [7] Dong Faqin, Pu. Wan, Zhou Kaican, et al., The environmental safety investigation on brucite fiber in Shannan, China Environ. Sci. 18 (1) (1998) 29–33. [8] Dong Faqin, Pan Zhaolu, Pu. Wan, etc, Physical properties investigation of fibrous brucite(FB)in the south of shaanxi, J. Southwest Instit. Technol. 10 (4) (1995) 5–15. [9] Liu Kaiping, Cheng Hewei, Zhou Jing’en, Investigation of brucite fiber reinforced concrete, Cem. Concr. Res. 34 (11) (2004) 1981–1986. [10] Liu Kaiping, Zhao Chongyang, Yang Xuegui, et al., Dispersing effects of superplsticizer to brucite fibers, Mining Res. Dev. 25 (5) (2005) 46–49. [11] Zhang Yan, Liu Kaiping, Guan Bowen, et al., Research on the influence of short fiber brucite on the performance of cement based composites, Appl. Chem. Industry 38 (9) (2009) 1267–1269. [12] Somen Mondal, Tarasankar Das, Prasun Ghosh, etc, Surfactant chain length controls photoinduced electron transfer in surfactant bilayer protected carbon nanoparticles, Mater. Lett. 141 (2) (2015) 252–254. [13] H.N. Atahan, C. Carlos Jr., S. Chae, P.J.M. Monteiro, et al., The morphology of entrained air voids in hardened cement paste generated with different anionic surfactants, Cem. Concr. Compos. 30 (7) (2008) 566–575.