Conclusions

curing time to study the effects of long-term condition on strength of the modified-sludge. For failure strain, it seemed that the failure strain of two conditions decreased with increasing of curing time from 7 days to 365 days. However, the failure strains were still far greater than target value (more than 5%). it could conclude that the roughness surface of fiber is the key effecting parameter on strength and strain of RS fiber-cement-reinforced sludge. Moreover, the RS in in-soil condition has slightly deterioration compared with those in-solution even if they have same pH value (or alkaline environment effect). Therefore, the RS fiber in cemented-sludge could keep its strength for longer time than those exposed outside. In the other ways, the RS fiber in soil has longer supporting life for rice straw-cement-soil composites. In the other hand, to test long-term durability of RS fiber-cement-reinforced sludge, it is better to test the RS within cemented-sludge, not in simulated alkaline environment (such as alkaline solution even if they have same pH value).

Finally, the durability in repeated drying-wetting condition of optimum mixing conditions of RS fiber-cement-reinforced sludge were carried out. The results showed that most of specimens constantly keep rank-A respect to increasing of cycle numbers.

Only the one condition was reduced to rank-B at 10^th cycle. However, its soundness was still good enough to apply. Thus, it could conclude that RS fiber-cement-reinforced sludge did not deteriorate within 10 cycles of repeated drying-wetting. Therefore, all of the optimum conditions satisfied the target values for failure strength, failure strain, and durability in repeating drying-wetting. The results of specimens’ soundness performances of cement-reinforced sludge showed that all of specimens greatly reduced to rank-F to rank-H (the worst) once they were submerged into water at the 1^st wetting phase.

References

[1] H. Takahashi, Topical Themes in Energy and Resources. Japan: Springer, 2014.

[2] A. N. Nguyen and X. L. Luu, “Study on strength and durability of fiber-cement-stabilized soils by using rice straw,” in Proceeding of the 1st Vietnam/Japan Joint Symposium on Saigon River Bank Erosion, 2011.

[3] A. N. Nguyen, “Study on strength properties of fiber-cement-stabilized soils by using rice straw,” Tohoku University, 2011.

[4] N. U. Sumi S, “Natural fibers in engineering applications: an overview,” Int. J. Sci.

Eng. Res., vol. 5, no. 7, pp. 260–265, 2014.

[5] G. Bogoeva-Gaceva et al., “Natural fiber eco-composites,” Polym. Compos., vol. 28, no. 1, pp. 98–107, 2007.

[6] M. Rose Marie Garay, B. Mónica Rallo de la, C. René Carmona, and C. Jaime Araya,

“Characterization of anatomical, chemical, and biodegradable properties of fibers from corn, wheat, and rice residues,” Chil. J. Agric. Res., vol. 69, no. 3, pp.

406–415, 2008.

[7] J. Atkinson, The Mechanics of Soils and Foundations, 2nd ed. CRC Press, 2007.

[8] L. Gao, G. Hu, N. Xu, J. Fu, C. Xiang, and C. Yang, “Experimental Study on Unconfined Compressive Strength of Basalt Fiber Reinforced Clay Soil,” Adv.

Mater. Sci. Eng., vol. 2015, pp. 1–8, 2015.

[9] ASTM-D2166/D2166M−13, “Standard Test Method for Unconfined Compressive Strength of Cohesive Soil.” ASTM International, West Conshohocken, PA, 2013.

[10] T. Satomi and H. Takahashi, “Setting optimum conditions for creating fiber-cement-stabilized soil by recycling tsunami sludge,” J. Japanese Soc. Exp. Mech., vol. 15, no. 3, pp. 225–230, 2015.

[11] M. Mori and H. Takahashi, “A proposal of new recycling system for high-water content muds by using paper debris and polymer and strength property of recycled soils,” J. MMIJ, vol. 119, pp. 155–160, 2003.

[12] P. T. Chien, T. Satomi, and H. Takahashi, “Study on sludge recycling with compaction type and placing type by rice husk-cement-stabilized soil method,”

Adv. Exp. Mech., vol. 2, pp. 159–167, 2017.

[13] H. Takahashi and T. Satomi, “Study on Durability for Drying and Wetting of Cover Soil for Radiation-Contaminated Soil Made of Tsunami Sludge,” J. JSEM, vol. 14, pp. s309–s313, 2014.

[14] M. Mori, H. Takahashi, and K. Kumakura, “An Experimental Study on Strength of Fiber-Cement-Stabilized Mud by use of Paper Sludge and Durability for Drying and Wetting Tests,” J. MMIJ, vol. 122, pp. 353–361, 2006.

[15] H. Takahashi and M. Mori, “Creation of artificial ground by recycling tsunami sludge,” in Proceedings of the 6th Symposium on Sediment-Related Disasters, 2012.

[16] T. Satomi and H. Takahashi, “Evaluation of Failure Strength Property and Permeability of Fiber-Cement-Stabilized Soil Made of Tsunami Sludge,” J. JSEM, vol. 14, pp. s303–s308, 2014.

[17] R. L. King, Fibre-reinforced composites materials, manufacturing and design, vol.

20, no. 2. CRC Press, 1989.

[18] R. N. Swamy, “Influence of slow crack growth on the fracture resistance of fibre cement composites,” Int. J. Cem. Compos., vol. 2, no. 1, pp. 43–53, 1980.

[19] G. Ramakrishna, T. Sundararajan, and S. Kothandaraman, “Evaluation of Durability of Natural Fibre Reinforced Cement Motar Composite-A New Approach,” ARPN J. Eng. Appl. Sci., vol. 6, no. 6, pp. 44–51, 2010.

[20] N. Shafiq, L. Robles-Austriaco, and P. Nimityongskul, “Durability of Natural Fiber in RHA Mortar,” J. Ferrocem., vol. 18, no. 3, pp. 249–262, 1988.

[21] H. E. Gram, “Natural Fibre Concrete Roofing,” Nat. fibre Reinf. Cem. Concr., vol. 5, pp. 256–285, 1988.

[22] R. D. T. Filho, K. Joseph, K. Ghavami, and G. L. England, “The Use of Sisal Fibre as Reinforcement in Cement Based Composites,” Rev. Bras. Eng. Agrícola e Ambient., vol. 3, no. 2, pp. 245–256, 1999.

[23] H. S. Ramaswamy, B. M. Ahuja, and S. Krishnamoorthy, “Behaviour of concrete reinforced with jute, coir and bamboo fibres,” Int. J. Cem. Compos. Light. Concr., vol. 5, no. 1, pp. 3–13, 1983.

alkali-sensitive sisal and coconut fibres in cement mortar composites,” Cem.

Concr. Compos., vol. 22, no. 2, pp. 127–143, 2000.

[25] V. John, M. Cincotto, C. Sjöström, V. Agopyan, and C. T. A. Oliveira, Durability of slag mortar reinforced with coconut fibre, vol. 27. 2005.

[26] H. H. Abdel-Rahman, R. Al-Juruf, F. Ahmad, and I. Alam, “Physical, mechanical and durability characteristics of date palm frond stalks as reinforcement in structural concrete,” Int. J. Cem. Compos. Light. Concr., vol. 10, no. 3, pp. 175–181, 1988.

[27] R. MacVicar, L. M. Matuana, and J. J. Balatinecz, “Aging mechanisms in cellulose fiber reinforced cement composites,” Cem. Concr. Compos., vol. 21, no. 3, pp. 189–

196, 1999.

[28] R. MacVicar, “Mechanical and physical changes associated with aging of cellulose fiber reinforced cement composites,” University of Toronto, Canada, 1997.

[29] A. Bentur and S. A. S. Akers, “The microstructure and ageing of cellulose fibre reinforced cement composites cured in a normal environment,” Int. J. Cem.

Compos. Light. Concr., vol. 11, no. 2, pp. 99–109, 1989.

[30] P. Soroushian, Z. Shah, J.-P. Won, and J.-W. Hsu, “Durability and moisture sensitivity of recycled wastepaper-fiber-cement composites,” Cem. Concr.

Compos., vol. 16, no. 2, pp. 115–128, 1994.

[31] S. G. Bergström and H.-E. Gram, “Durability of alkali-sensitive fibres in concrete,”

Int. J. Cem. Compos. Light. Concr., vol. 6, no. 2, pp. 75–80, 1984.

[32] L. E. Rogers and S. G. Wright, “The effects of wetting and drying on the long-term shear strength parameters for compacted Beaumont clay,” Center for Transportation Research, The University of Texas at Austin, Texas, , 1986.

[33] G. S. Wright, G. Zomberg, and J. E. Aguettant, “The Fully Softened Shear Strength of High Plasticity Clays,” Texas Department of Transportation, Research and Technology Implementation Office, 2007.

[34] A. T. Al Zubaydi, “Swell Potential, Collapse Potential, Wetting and Drying Cycles, Cracks, Number of Segment,” Tikrit J. Eng. Sci., vol. 18, no. 4, pp. 71–79, 2011.

4.1 Permeability characteristics 4.1.1 Introductions

The property of soil to transmit water is known as soil permeability. It is one of fundamental processes in geotechnical and geo-environmental engineering. The pore-water pressure, whether positive or negative, is an integral component of the stress state within the soil and consequently has a direct bearing on the shear strength and volume change behavior of soil [1]. In general, it is driven by an energy which associated with the total head of water (or pore water pressure) and elevation.

When soil is in unsaturated state, hydraulic conductivity becomes a function of the negative pore-water pressure in the soil. It is a complex processing. As a non-linear problem, it is difficult and no meaning to determine the permeability coefficient at unsaturated stage of soil. Therefore, the study is carrying out the experiments to determine the permeability with saturated soil. Figure 4-1 shows a sketch of water go through a soil structure. The knowledge of soil permeability is necessary for:

 Estimating the quantity of underground seepage.