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The Effect of the Portland and Eco-Cement Stabilization on the Physical and Mechanical Behaviour of the Bahlui Clay
Abstract:
The research program developed by the authors and presented in this paper designate the Bahlui clay Romania fitting the clays with specific behaviour such as the Addis Ababa clay, London clay, Dharwad clay, New Yorkshire clay, Ankara clay and Weald clay. Its behaviour is mainly characterized by high swells and shrinkages at moisture variations. The utilization of the Bahlui clay as good foundation soil or material for compacted soil cushion required the determination of the parameters characterizing its behaviour during moisture variation: swell-shrinkage, compressibility and respectively shear strength. The research experiments to define the physical and mechanical behaviour of the Bahlui clay were performed on both natural and remoulded samples with 2.5÷10% mix from the dry soil mass with Portland with/or eco-cement. The paper presents graphs and tables displaying the Portland/eco-cement stabilization influence on the main physical and mechanical indices characterizing the Bahlui clay behaviour during moisture variations as well as conclusions its usage.
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June 2013
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[16] .
[14] Experimental program. The objective of this program is to reduce the swell potential of the Bahlui clay – Romania and to improve the behaviour of the stabilized soil as foundation soil, by analyzing comparatively the effect of the cement percentage increase (using both Portland cement as well as a 1: 1 mix, Portland cement and eco-cement) for the chemical stabilization of this clay. Results and Discussion The influences of expansive clay Eco cement stabilization on the physical properties. The cement stabilization effect on the physical properties of the Bahlui clay has been studied in these two options (Portland cement stabilization and 1: 1 mix of Portland and eco-cement stabilization). The binder content has been 0%, 2. 5%, 5%, 7. 5% and 10% of the dry soil mass. The obtained results for the grain size distribution, Atterberg limits and linear shrinkage are presented in Table 4. Diagrams in Figure 2 a ÷ d emphasize the effect of the Portland cement substitution as 50% with eco-cement as mix acting like binder in the Bahlui clay stabilization. Table 4. The influence of the ecologic/Portland cements on the main geotechnical indices of the Bahlui clay-Romania S. no. Mix wL.
[86] 1.
[57] 8 - 89.
[20] 1 0 2.
[2] 5% (EC+PC).
[86] 2 0.
[41] 9.
[27] 51 63.
[29] 21.
[19] 4.
[3] 48 3 5% (EC+PC).
[75] 1.
[12] 78.
[30] 4.
[47] 40 55.
[38] 20.
[14] 7.
[26] 87 4.
[7] 5% (EC+PC) * 75.
[12] 89.
[30] 8.
[46] 71 48.
[46] 07.
[14] 3.
[28] 85 5 10% (EC+PC).
[65] 6.
[23] 93.
[22] 6.
[60] 90 26.
[70] 79.
[10] 3.
[48] 75 6.
[2] 5% (PC).
[88] 3 0.
[52] 8.
[8] 65 78.
[12] 36.
[20] 8 0 7 5% (PC).
[79] 7.
[7] 43.
[42] 1.
[27] 16 51.
[42] 70.
[16] 4.
[18] 41 8.
[7] 5% (PC).
[69] 6.
[19] 16.
[25] 1.
[56] 57 47.
[47] 19.
[15] 0.
[25] 37 9 10% (PC).
[63] 2.
[26] 6.
[22] 9.
[60] 38 23.
[74] 16.
[9] 8.
[51] 24 wL – liquid limit; IP – plasticity index; A2µ- colloidal clay fraction; LS – linear shrinkage; (*) 50% eco-cement (EC) and 50% Portland cement (PC) Fig. 2. Variation of the geotechnical indices with the chemical stabilizing agent Figure 2 a ÷ d presents the percentage decrease of the geotechnical indices: liquid limit (wL), plasticity index (IP), colloidal clay fraction (A2µ) and linear shrinkage (LS) with the increase of the PC and PC+EC mix. The evaluation of the swell potential for the stabilized expansive soil is made indirectly based on the following geotechnical indices: liquid limit, plasticity index, colloidal clay fraction and linear shrinkage. Using this empirical correlation, the Bahlui clay – Romania develops a very high swell potential (Table 5). By the chemical stabilization of the Bahlui clay with Portland cement and 1: 1 mix of Portland and ecological cement, the swell potential is constantly decreased with the increase of the cement percentage, from very high for the natural clay to medium for 10% cement (PC or PC+EC mix). Van der Merwe [15] developed the correlation between the swell potential and heave per meter of the expansive (Table 5). Thus, the natural clay would display a heave of 80mm/m while being used as cushion material that can induce degradation for light structures founded on this soil without chemical stabilization. The Bahlui clay would reduce the potential heave from 80mm/m to 40mm/m by chemical stabilization with a binder mix of PC and EC. Table 5. The swell potential of the stabilized Bahlui clay with Portland and eco-cement Swell potential depending on Heave/meter of soil profile [mm] S. no. Mixes wL [%] IP [%] A2µ [%] LS [%] 1 Natural clay High Very high Very high Very high 80 2.
[2] 5% (EC+PC) * High Very high Very high High 80 3 5% (EC+PC) * High High Very high Medium 40 4.
[7] 5% (EC+PC) * High High Very high Medium 40 5 10% (EC+PC) * High Medium Medium Low 40 6.
[2] 5% (PC) High Very high Very high High 80 7 5% (PC) High Very high Very high Medium 40 8.
[7] 5% (PC) High High Very high Medium 40 9 10% (PC) High Medium Medium Low 40 References: wL [17]; IP [18, 19]; A2µ [20]; LS [21]; Heave/m meter of soil profile [15] The requirements imposed for the soil cushion as values for the geotechnical indices presented in Table 1, are not fully satisfied by the chemical stabilization with cement (Portland cement (PC) and Eco-cement-Portland cement (EC+PC). For 10% cement, for both cases of stabilization, with Portland cement and ecological/Portland cement mix, the colloidal clay content and the plasticity index decrease sufficiently to meet the requirements for a soil cushion (Table 1), but the other parameters, plastic limit and liquid limit develop still higher values than the demanded ones for the use of the material in cushion compaction (Table 1 and Table 4). The influences of expansive clay Eco cement stabilization on the mechanical properties. The value increase of the shear strength parameters with the necessary binder addition for chemical stabilization can be designated to the initiated cation exchange by the chemical composition of the Portland and ecological cements. Clays consisting predominantly of montmorillonite present a residual internal friction angle decreasing with the increase of the liquid limit, approximated by the following function [22]: (1) where: Φr is the predicted value of the residual internal friction angle, wL – the liquid limit of the investigated clay (the correlation coefficient is R =0. 837 and it was determined using 142 soil samples). Using this correlation for the Bahlui clay both natural and stabilized with cement (PC and PC+EC mix) one can notice (Table 6) an increase of the residual internal friction angle with the increase of the utilized cement. For percentages of 7. 5% and 10% of PC, the stabilized clay will display higher values of the residual internal friction angle, by comparison with the PC+EC binder mix. Regarding the compressibility determined by oedometer laboratory tests and following the value of the compressibility index (Cc - Table 6), the natural Bahlui clay displays a high compressibility (Cc>0. 4), while by stabilization with 10 % cement PC and PC+EC mix the compressibility decrease to medium (Cc=0. 2÷0. 4). Table 6. The mechanical properties of the stabilized Bahlui clay with cement (PC and EC+PC) S. no. Parameters Natural clay (EC+PC) stabilization PC stabilization.
[2] 5% 5.
[7] 5% 10.
[2] 5% 5.
[7] 5% 10% 1 Φr [0].
[9] 65.
[9] 64.
[11] 17.
[11] 19.
[12] 9.
[9] 39.
[10] 48.
[12] 11.
[13] 41 2 Cc.
573.
54.
457.
424.
385.
552.
498.
456.
399 Φr - residual friction angle; Cc – compression index; EC – eco-cement; PC- Portland cement Swelling properties of treated expansive soil. The literature presents correlation techniques of the geotechnical properties indices to obtain an estimation of the swell potential S and the swell pressure Ps [19]. Eq. 2 is proposed for the swell pressure and Eq. 3 for the swell potential, both obtained by the method of least squares applied on the results from the laboratory tests, with a very high coefficient of correlation, R, of the fitted regression lines (R>0. 8) [23]: (2) where: Ps is the predicted value of the swell potential in psi, utilizing the initial value of the moisture content for the soil sample, wi. (3) in which: S is the predicted value of the swell potential, expressed as percentage, using the natural moisture content of the soil sample wi. The predicted swell pressure for the natural Bahlui clay using the equation (2) resulted in Ps = 177. 85 kPa, which is approximately the same value obtained by oedometer tests performed according to ASTM D 4546-90, method A, Ps = 187kPa. The swell pressure and swell potential values for the stabilized Bahlui clay with 2. 5% ÷ 10% PC and PC+EC mix are presented in Table 7. The 75% decrease of the swell pressure (Ps) (Table 7) for only 2. 5% EC+PC cement mix or just PC, continues at a smaller rate with the increase of cement participation to the stabilization process, recording decreases up to 10% for 10% cement percentage. Table 7. The swelling potential of the stabilized Bahlui clay with Portland and eco-cement S. no. Mixes Swell potential (S) [%] Decrease in swell potential [%] Swell pressure (Ps) [kPa] Decrease in swell pressure [%] 1 Natural clay.
[31] 16465 - 177. 85 - 2.
[2] 5% (EC+PC).
[18] 97018.
[39] 12917.
[75] 55118.
[57] 51973 3 5% (EC+PC).
[16] 82514.
[46] 01208.
[67] 99937.
[61] 7659 4.
[7] 5% (EC+PC).
[16] 62094.
[46] 66733.
[66] 96804.
[62] 34578 5 10% (EC+PC).
[15] 33897.
[50] 78085.
[63] 57446.
[64] 25389 6.
[2] 5% (PC).
[24] 53638.
[21] 26854 110. 0464.
[38] 12403 7 5% (PC).
[18] 80752.
[39] 65112.
[74] 51216.
[58] 10394 8.
[7] 5% (PC).
[16] 01555.
[48] 60987.
[65] 48824.
[63] 17783 9 10% (PC).
[15] 31787.
[50] 84858.
[63] 51405.
[64] 28786 S - Swell potential; Ps - Swell pressure kPa; (*) 50% eco-cement (EC)+50% Portland cement (PC) The initial moisture content of the soil (wi) plays an important role in the estimation of the swell pressure. In Figure 4 a ÷ d the variations of the swell pressure and swell potential are presented depending on the natural moisture content of the soil. Fig. 3. Variations of a), b) swelling pressure and c), d) swelling potential, with the moisture content, for the Bahlui clay - Romania Conclusions The Bahlui clay – Romania is spread on a relatively large zone within the city of Iasi area. Founding construction on this clay as well as its utilization as material for soil cushions required the necessity to develop an extensive research program to obtain its main physical and mechanical properties. This research work performed by the authors classified this clay as being an expansive one, similar with other representative clays in the world (Addis Ababa clay – Ethiopia, London clay – U.K.; Dharwad clay –India; New Yorkshire clay – U.K.; Ankara clay – Turkey and the Weald clay from the U.K. ). The Bahlui clay has been investigated to build without any structural risk exposure, establishing its behaviour and potential improvement based on the physical and mechanical characteristics, by chemical stabilization with Portland cement or cement mix, Portland and eco-cement. It is noted based on the laboratory test results that stabilization by 10% cement (PC and PC+EC mix) reduces the swell potential from very high to medium. The very high swell pressure of the natural Bahlui clay (177. 85kPa) decreases as well by 57. 52% for only 2. 5% cement (PC+EC mix) and with only 38. 12% for 2. 5% stabilization with Portland cement (PC). The influence of the eco-cement participation in the binder mix utilized in the stabilization is more pronounced at small values (up to 2. 5%) while the increase from 2. 5% to 10% cement is not providing significant decreases of the swell pressure and swell potential. The partial substitution of the Portland cement with eco-cement lead to a significant influence on the environment protection by consequence of the reduction of non-renewable resources and CO2 emissions resulted from the manufacturing process. ACKNOWLEDGMENT: This paper was supported by the project Development and support of multidisciplinary postdoctoral programmes in major technical areas of national strategy of Research - Development - Innovation, 4D-POSTDOC, contract no. POSDRU/89/1. 5/S/52603, project co-funded by the European Social Fund through Sectoral Operational Programme Human Resources Development 2007-2013. ACKNOWLEDGMENT: Thank to ECOCEM Ireland, for the eco-cement support provided during the research study. References.
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