Mechanical Properties and Microstructure of CaSO₄ Whisker Reinforced Cement Mortar

Abstract

Calcium sulfate whisker (CaSO₄ whiskers), a new type of microfiber material, was used in cement matrix to increase the strength of the cement based composites. Effect of CaSO₄ whiskers on the mechanical properties of the resulting cement mortar was also studied. The results showed that the flexural strength and compressive strength of the mortar specimen was improved as high as 28.3% and 8.5% by incorporating 5 wt% CaSO₄ whiskers. Also, the chemical composition and structural transformation of the hardened cement matrix with CaSO₄ whiskers were identified by X-ray diffraction (XRD) and scanning electron microscope (SEM). Conclusion can be drawn that CaSO₄ whiskers can effectively retard the formation and restrict the coalescence of micro-crack expansion. The interaction mechanism of CaSO₄ whisker on the reinforcement is mainly on three aspects: whisker pullout, crack deflection, and crack bridging. Mercury intrusion porosimetry (MIP) tests have confirmed that for 28 d cement mortar, the harmless pores increased from 9.33% to 10.62%, and the harmful pores decreased from 2.08% to 1.90%. Therefore, the whisker can optimize the pore size distribution of the resulting cement mortar.

Keywords

calcium sulfate whisker / reinforcement / mechanical properties / microstructure / toughening mechanism / cement paste

References

[1] Dawood E T, Ramli M. Development of High Strength Flowable Mortar with Hybrid Fiber[J].. Constr. Build. Mater., 2010, 24: 1 043-1 050.

[2] Park S H, Kim D J, Ryu G S, et al. Tensile Behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete[J]. Cem. Concr. Comp., 2012, 34: 172-184.

[3] Cao M, Zhang C, Wei J. Microscopic Reinforcement for Cement Based Composite Materials[J].. Constr. Build. Mater., 2013, 40: 14-25.

[4] Cao M, Zhang C, Lv H, et al. Characterization of Mechanical Behavior and Mechanism of Calcium Carbonate Whisker-reinforced Cement Mortar[J]. Constr. Build. Mater., 2014, 66: 89-97.

[5] Cao M, Wei J. Microstructure and Mechanical Properties of CaCO₃ Whisker-reinforced Cement[J].. Journal of Wuhan University of Technology-Mater. Sci. Ed., 2011, 26: 1 004-1 009.

[6] Sanchez F, Sobolev K. Nanotechnology in Concrete-a Review[J].. Con-str. Build. Mater., 2010, 24: 2 060-2 071.

[7] Konsta-Gdoutos M S, Metaxa Z, Shah S P. Highly Dispersed Carbon Nanotube Reinforced Cement Based Materials[J].. Cem. Concr. Res., 2010, 40: 1 052-1 059.

[8] Betterman L R, Ouyang C, Shah S P. Fiber-matrix Interaction in Mi-crofiber-reinforced Mortar[J].. Advanced Cement Based Materials, 1995, 2: 53-61.

[9] Yao W, Li J, Wu K. Mechanical Properties of Hybrid Fiber-reinforced Concrete at Low Fiber Volume Fraction[J].. Cem. Concr. Res., 2003, 33: 27-30.

[10] Lawler J S, Wilhelm T, Zampini D, et al. Fracture Processes of Hybrid Fiber-reinforced Mortar[J].. Mater. Struct., 2003, 36: 197-208.

[11] Parveen S, Rana S, Fangueiro R, et al. Microstructure and Mechanical Properties of Carbon Nanotube Reinforced Cementitious Composites Developed Using a Novel Dispersion Technique[J].. Cem. Concr. Res., 2015, 73: 215-227.

[12] Hu Y, Luo D, Li P, et al. Fracture Toughness Enhancement of Cement Paste with Multi-walled Carbon Nanotubes[J].. Constr. Build. Mater., 2014, 70: 332-338.

[13] Xu S, Liu J, Li Q. Fangueiro Mechanical Properties and Microstructure of Multi-walled Carbon Nanotube-reinforced Cement Paste[J].. Constr. Build. Mater., 2015, 76: 16-23.

[14] Li G Y, Wang P M, Zhao X. Fangueiro Pressure-sensitive Properties and Microstructure of Carbon Nanotube Reinforced Cement Composites[J].. Cem. Concr. Comp., 2007, 29: 377-382.

[15] Loos M R, Schulte K. Is It Worth The Effort to Reinforce Polymers with Carbon Nanotubes?[J].. Macromol. Theor. Simul., 2011, 20: 350-362.

[16] Yuan W, Cui J, Xu S. Mechanical Properties and Interfacial Interaction of Modified Calcium Sulfate Whisker/poly(vinyl chloride) Compos-ites[J].. J. Mater. Sci. Technol., 2016, 32: 1 352-1 360.

[17] Cwirzen A, Habermehl-Cwirzen K, Penttala V. Surface Decoration of Carbon Nanotubes and Mechanical Properties of Cement/Carbon Nanotube Composites[J].. Adv. Cem. Res., 2008, 20: 65-73.

[18] Konsta-Gdoutos M S, Metaxa Z S, Shah S P. Multi-scale Mechanical and Fracture Characteristics and Early-age Strain Capacity of High Performance Carbon Nanotube/Cement Nanocomposites[J].. Cem. Concr. Comp., 2010, 32: 110-115.

[19] Tyson B M, Abu Al-Rub R K, Yazdanbakhsh A, et al. Carbon Nano-tubes and Carbon Nanofbers for Enhancing the Mechanical Properties of Nanocomposite Cementitious Materials[J].. J. Mater. Civil. Eng., 2011, 23: 1 028-1 035.

[20] Cranmer D C. Fiber Coating and Characterization[J].. Am. Ceram. Soc. Bull., 1989, 68: 415-419.

[21] Kumar S, Singh R N. Effects of Fiber Coating Properties on The Crack Defection and Penetration in Fiber-reinforced Ceramic Composites[J].. Acta. Mater., 1997, 45: 4 721-4 731.

[22] Chen E, Chen D. The Development of Whisker-reinforced Polymer Composites Mechanisms[J].. Polymer Materials Science & Engineering, 2006, 22: 20-24.

[23] Mueller F A, Gbureck U, Kasuga T, et al. Whisker-reinforced Calcium Phosphate Cements[J].. J. Am. Ceram. Soc., 2007, 90: 3 694-3 697.

[24] Faber K T, Evans A G. Crack Defection Processes 1. Theory[J].. Acta. Metallurgica, 1983, 31: 565-576.

[25] Becher P F, Hsueh C H, Angelini P, et al. Toughening Behavior in Whisker-reinforced Ceramic Matrix Composites[J].. J. Am. Ceram. Soc., 1988, 71: 1 050-1 061.

[26] Becher P F. Microstructural Design of Toughened Ceramics[J].. J. Am. Ceram. Soc., 1991, 74: 255-269.

[27] Mehta P, Monteiro P. Concrete Microstructure, Properties, and Materials[M], 2006 McGraw-Hill: Berkeley.

[28] Scrivener K L, Juilland P, Monteiro P J M. Advances in Understanding Hydration of Portland Cement[J].. Cem. Concr. Res., 2015, 78: 38-56.