The SiCC Column Improved the Expansive Clay Agus Setyo Muntohar 1, a, and Siswoko Adi Saputro 1,b

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3 The SiCC Column Improved the Expansive Clay Agus Setyo Muntohar 1, a, and Siswoko Adi Saputro 1,b 1 Department of Civil Engineering, Faculty of Engineering, Universitas Muhammadiyah Yogyakarta, Indonesia a muntohar@umy.ac.id, b siswoko.adi.s@student.umy.ac.id Keywords: expansive clay, soil improvement, flexible pavement, column technique. Abstract. In Indonesia, many roads were constructed over the expansive clay that caused road deficiencies as the result of the heaving and shrinking effects of the expansive soil during the seasonal period. Soil improvement using lime and cement is the common method of soil improvement. However, uses of industrial wastes such as carbide and rice husk ash are advantage method to improve the shear strength of expansive soil. This paper is aimed to investigate the compressive strength of the columns of carbide lime/rice husk ash mixtures for improving performance of expansive soil. The carbide lime and rice husk ash was mixed to form a SiCC column in expansive soil. Unconfined compression strength (UCS) test was conducted to establish a general trend for the gain in strength. For the UCS test, the specimen size is 50 mm diameter and 100 mm height and the column size is 0.5 inch diameter. The specimen was compacted in optimum (OMC) and optimum-wet (OW) of compaction. The investigations resulted that the compressive strength of soil-column of carbide lime/rice husk ash mixtures increased with the increasing age of the column from 11 kpa to 127 kpa at 28 days of curing time. At the earlier age, the strength gain of the soil-column prepared at OW side was higher than the soil-column at OMC side. But after 14 days of curing, the strength of soil-column at OMC side is higher than the soil-column at OW side. Thus, the secant modulus of elasticity (E 50 ) of the soil-column at OMC side is generally higher than the soil-column at OW side. Introduction In tropical regions such as Indonesia, problematical expansive behaviour generally occurs in clays of high plasticity. Either way, expansive soils demonstrate the potential significant volume change in direct response to changes in water content. The soil behaves to swell in a humid environment, but the soil tends to shrink in a dry condition. The swell and shrink behavior causes a detrimental effect on the structures laid on the soil. As the result, the potential of economic lost is the possible impact that should be considered in many countries. Muntohar [1] stated that pavement deterioration was found at national highway Yogyakarta - Wates because of constructed on high expansive soil. In practice, pavement overlay was the common method the recover the flexible pavement distresses. The overlay was the quick method, but unfortunately this method was ineffective to overcome the expansiveness problem of subgrade. Soil improvement was the common method to enhance the performance of subgrade and pavement. The principal materials used for the soil stabilization are lime and cement. The common technique of lime or cement stabilization was by replacing and mixing the materials with soil. However, the mixing limited at very shallow depth. In fact, the expansive soil deposit can be very deep. Hence, a column-like pile method can be introduced to improve the soil. Lime-column or lime pile and lime/cement column reinforced expansive soil has been studied by several investigators [2-3]. The technique was adopted from mini pile foundation to control the heave and deformation [4]. The knowledge on the use of column treated soils is not enough and should be investigated. Utilization industrial waste enriched lime e.g. carbide waste is a benefit for environment and construction. Abundant of another solid waste such as rice husk ash (RHA), can be mixed with carbide lime to form cementitious materials. The shear strength properties of the carbide lime and rice husk mixture to improve expansive clay has been studied intensively by Muntohar et al. [5]. Page 38

4 In this paper, the utilization of the carbide waste and RHA was investigated to improve the longterm compressive strength of the expansive clay. A column technique made of the carbide waste and RHA was applied in this research. The objective of the research is to investigate the effect of column technique on the unconfined compressive strength of the expansive clay. Experimental Program Materials. The soil was collected from the Kasihan area in Bantul, Yogyakarta. The soil predominantly consists of fines particle about 78% - 92%. The montmorilonite mineral was the main composition of the clay particles as shown in X-ray diffraction test (Fig. 1). The properties of soil are presented in Table 1. According the plasticity indices relationship given by some researchers [6], the swelling potential of the soil range from 8% to 24%, thus it can be classified as medium to very high swelling. The SiCC column was made of microsilica and microcalcium mixtures which were blended with the rice hush ask and carbide waste materials. The mineralogical of the SiCC is presented in X-ray diffractograph as illustrated in Fig. 2. The SiCC was mainly composed of portlandite and calcium silicate hydrate which were similar to the cement elements. Parameter Table 1 Properties of the soil Value Spesific gravity Consistency limits: Liquid limit, LL (%) Plastic limit, PL (%) Plasticity Index, PI (%) Particle sizes : Silt/clay: < 75 m (%) Sand: 75 m 4.75 mm USCS symbol Stanard Proctor compaction : Maximum dry density, MDD (kn/m 3 ) Optimum moisture content, OMC (%) Swelling potential (%) CH Counts M (15Å) V (8.40Å) M (4.49Å) M (4.49Å) M (3.76Å) M (3.21Å) Q (3.35Å) M = montmorillonite (85%) V = Vermiculite Q = Quartz Diffraction angle, 2 (degree) Fig. 1 The X-ray diffractograph of the soil Page 39

5 Counts Ca 2.SiO 4 CaCO 3 Ca 2.SiO 4 CaCO 3 ;CaCO 3 Ca 2.SiO ;CaCO 3 CaCO 3 = portlandite (35%) CaCO 3 = calcite (16%) = cristobalite- (17%) Ca 2.(SiO 4 ) = calcium silicate (31%) ; Ca(OH) CaCO 2 3 ; Difraction angle, 2 (deg.) Fig. 2 The X-ray diffractograph of the SiCC Preparation of Test Specimens. Unconfined compression strength (UCS) test was conducted to establish a general trend for the gain in strength. The specimen size was 50 mm diameter and 100 mm height and the column size was 0.5 inch diameter (Fig. 3a). The specimen was compacted in two moisture content conditions at optimum (OMC) and optimum-wet (OW) of compaction. The oven-dry soils about 250 g were initially mixed with the predetermined quantity of water so that the mix acquired the intended moisture content. The mixing was carried out in a laboratory mixer for at least 2 min and the mix was subsequently put into plastic bags for 5 minutes. The soil was then divided into three portions. Each portion was placed into the split-metal mold and subsequently compacted by applying static compaction. This method was adopted to have a constant density (about 12 kn/m 3 ) for all specimens. The compacted soil was drilled by 0.5 inch drilling machine to make column hole. SiCC paste was prepared by mixing 10 g microsilica and 10 g microcalcium with 10 ml water. The paste was poured into the hole by gentle compaction to form a column. The paste was left for about 5 minutes to allow hardening in the mold. The specimen was extruded from the mold. The diameter, height and weight of the specimen were measured subsequently. Finally to prevent moisture change, then the specimen was kept in a sealed-plastic bag and stored at a controlled room temperature about 28 o C±2 o C. The set of specimens was cured for 3 days, 7 days, 14 days, and 28 days. UCS Testing Procedure. The UCS test was conducted after the curing period for each set of specimens. The test procedure was in accordance with the standard ASTM D [7]. The mass of the specimen was weighted to determine the change in mass. The dimension was remeasured and recorded before the test. The specimen was placed in the loading device so it was centered on the bottom platen (Fig. 3b). The axial deformation rate was approximately 1% per min. The load (axial force), deformation, and time values were recorded at intervals sufficient to define the shape of the stress-strain curve. The maximum axial force applied to the specimen was recorded along with its deformation. The loading was continued until load values decrease with increasing strain or until 5 % strain was exceeded the specimen. The compressive stress for a given applied axial force was calculated to three significant digits by Eq. (1). P A (1) where, = compressive stress (kpa), P = axial force applied to the specimen (kn), and A = corresponding cross-sectional area (m 2 ). Page 40

6 50 mm 12.7 mm SiCC column Load dial indicator Proving ring Plunger 100 mm Soil Upper platen Specimen Bottom platen (a) Fig. 3 (a) The compacted soil and SiCC column specimen, (b) The universal compression testing machine (b) Results and Discussion Unconfined compressive strength. The average value of the unconfined compressive (q u ) and odulus of deformation (E 50 ) of each two specimens is presented in Table 2. In this study, the strength measured the compressive strength of the SiCC column and soil composite. In general, the compressive strength increases with the increasing of curing time. The characteristic indicates that a pozzolanic reaction possibly occurred in SiCC column. At an early age up to 14 days of curing, the compressive strength of the specimen compacted at OW side was higher than the compacted at OMC. Whereas, the compressive strength of the specimen prepared at OMC condition was higher than the specimen at OW condition after 14 days of curing time. This result shows that the water content of the compacted soil affects the compressive strength. Table 2 The unconfined compressive strength and modulus deformation of the SiCC column soil composite Age Unconfined compressive strength, q u (kpa) Modulus of deformation, E 50 (kpa) (days) at OW at OMC at OW at OMC The hardening of SiCC paste probably occurred as a result of combined hydration, pozzolanic reaction and carbonation. Initial strength development of the SiCC pastes was governed by the hydration of cementitious material. After the addition of SiCC column, hydration begins by consuming water, which produces an increase in the shear strength of soil. The water in the soil surrounding SiCC column was needed to maintain the hydration process. In fact, at an early age of curing the moisture of the soil was relatively high as shown in Figure 4a. It was probably the reason of the faster strength gain at an early age up to 14 days of the specimen at OW condition. This behavior was also explained by Walker and Pavia [8]. At low water content (OMC), the hydration possible slowly occurred since the humidity of the soil surrounding SiCC column was low as shown Page 41

7 in Figure 4b. The water penetrates at a slow rate into SiCC column interface. Hence, the hardening took place slowly at an early age. This phenomenon was also explained by the Thomas et al. [9] and Cizer et al. [10] (a) (b) Moisture (%) Moisture (%) Curing time (days) Curing time (days) Fig. 4 Measured moisture in the soil surrounding SiCC column before test (a) at OW condition, (b) at OMC condition. Fig. 5a shows the relationship between the unconfined compressive strength and the curing time of the SiCC column soil composite. The solid lines in the figure stand for the hyperbolic trendline of each data. The compressive strength tends to increase marginally for the OW specimen but the increase was significantly for the OMC specimen after 14 days of curing. Principally, longterm strength development is governed by the pozzolanic reaction and carbonation. Eventhough there was neither microstructure nor mineralogy tests, Ajorloo [11] indicated that the pozzolanic process can be defined by the strength development with the time. In this study, the higher strength of the OMC specimens was probably affected by the remaining water content in the soil (Fig. 4b). The water was consumed by the SiCC column for further reaction. Modulus of deformation. The behavior of soil due to compressive loading can be identified from the soil modulus which is obtained from stress and strain curve. For a typical concrete unconfined compression test on a soil, the soil modulus can be defined as the slope of the stress strain curve. In soil mechanics, the soil modulus is commonly stated as secant modulus at 50% of strength which is denoted as E 50 or modulus of deformation. Kivelo [12] and Ekstrom [13] stated that the compression of ground improved with lime columns under an axial load is governed by stiffness, or modulus of elasticity, of the columns and of the base soil between the columns. As presented in Table 2, the E 50 increased with the increasing of curing time. Since the E 50 is a function of the q u /2, then the relationship can be plotted as in Fig. 5b. The figure indicates that the E 50 tends to increase linearly with the unconfined compressive strength. In general, the E 50 of the SiCC column soil composite lay on the 35 to 200 time of the q u /2. The E 50 of the OMC specimens were laid on the equation E 50 = 200(q u /2), whereas the OW specimens were approached by the equation E 50 = 122(q u /2). The correlation indicates that the OMC specimens have higher E 50 than that of OW specimens. The modulus of soil is one of the most difficult soil parameters to estimate because it depends on so many factors. But in this research, two factors that are the water content and the chemical cementation can explain the characteristics illustrated in Fig. 5b. At low water contents the water binds the particles and increases the effective stress between the particles through the suction and tensile skin of water phenomenon. Therefore in this case low water contents lead to high soil modulus. The second reason was due to the chemical cementation which can develop at the interface between the column and soil. Such cementation leads to a significant increase in modulus. Page 42

8 Unconfined Compressive Strength, q u (kpa) Optimum-wet (OW) Optimum mositure content (OMC) Age (days) Modulus of deformation, E 50 (kpa) E 50 = 200(q u /2) (1) (7) (28) (14) (7) (3) (7) (3) (3) (3) (28) (7) (1) (14) (14) (28) q u /2 (kpa) E 50 = 70.5(q u /2) (28) E 50 = 35(q u /2) (14) Note: the number in bracket indicates the age of specimens Optimum-wet (OW) Optimum moisture content (OMC) (a) (b) Fig. 5 (a) Variation of unconfined compressive strength with curing time, (b) Relationship between the unconfined compressive strength (q u /2) and modulus of deformation (E 50 )of the SiCC column soil composite Conclusion Laboratory test on the unconfined compressive strength of SiCC column improved expansive clay has been successfully performed. In general, the compressive strength increases with the increasing of age or curing time. The characteristic indicates that a pozzolanic reaction take place in SiCC column. At an early age up to 14 days of curing, the compressive strength of the specimen compacted at OW side was higher than the compacted at OMC. Whereas, the compressive strength of the specimen prepared at OMC condition was higher than the specimen at OW condition after 14 days of curing time. Acknowledgment This paper is part of the research project under a scheme of Penelitian Unggulan Perguruan Tinggi in 2014 according to the contract number 1314/K5/KM/2014 on 6 May Authors thank to the Ministry of Education and Culture, the Republic of Indonesia for the research fund provided in References [1] A.S. Muntohar: Dimensi Teknik Sipil 8(2), (2006), p [2] V.B. Swamy. Stabilisation of Black Cotton Soil By Lime Piles. M.Sc.(Eng.) Thesis, Indian Institute of Science, 2000 (unpublished). [3] M.C. Tonoz, C. Gokceoglu, and R. Ulusay: Bull. Eng. Geol. Environ., Vol. 62 (2003), p [4] E. Hewayde, H. El Naggar, and N. Khorshid: Proc. Inst. Civ. Eng. Ground Improv., Vol. 9, No. 2, (2005), p [5] A.S. Muntohar, S.A.P Rosyidi, W. Diana, and Iswanto. Pengembangan Fondasi Perkerasan Lentur Jalan Dengan Kolom Eco Si-CC Pada Tanah Ekspansif. Research Report 1 st Year 2014 Penelitian Unggulan Perguruan Tinggi, Department of Civil Engineering, Universitas Muhammadiyah Yogyakarta, Yogyakarta, (2014). (unpublished) Page 43

9 [6] H.B. Seed, R.J. Woodward, and R. Lundgren : J Soil Mech. Found. Div. ASCE, Vol. 88, No. SM3, (1962), p [7] ASTM D , Standard Test Method for Unconfined Compressive Strength of Compacted Soil-Lime Mixtures. ASTM International, West Conshohocken, PA. (2009) [8] R. Walker, and S. Pavia, Behaviour and Properties of Lime-Pozzolan Pastes. Proc. 8 th Int. Mason. Conf. 2010, 4-7 July 2010, Dresden, p , (2010) [9] J.J. Thomas, A.J. Allen, and H.M. Jennings : J. Am. Ceram. Soc., Vol. 91 No. 10, (2008), p [10] O. Cizer, K. Van Balen, D. Van Gemert, and J. Elsen : Proc. Inst. Civ. Eng. Constr. Mater., Vol. 162, (2009), p [11] A.M. Ajorloo. Characterization of the Mechanical Behavior of Improved Loose Sand for Application in Soil-Cement Deep Mixing. Thèse Docteur, Université Lille 1 Sciences et Technologies, (2010) [12] M. Kivelo. Stabilization of embankments on soft soils with lime/cement columns, Doctoral Thesis, Royal Institute of Technology, Sweden, (1998). [13] J.C. Ekstrom Checking of lime and lime/cement columns A method under development, Swedish Geotechnical Society, Stockholm, Sweden. (1994) Page 44