The Reaction Products of Lime Treated Tropical Clay Soils and Their Impact on Strength Development

The Reaction Products of Lime Treated Tropical Clay Soils and Their Impact on Strength Development Adil A. M Elhassan Sudan University of Science and Technology, Faculty of Engineering, Department of Civil Engineering e-mail: adilabdallah01@gmail.com Corresponding author Ahmed M. Elsharief Building and Road Research Institute, University of Khartoum Address: Khartoum, P.O.Box 321, Sudan e-mail: aelsharief@yahoo.com Awad E. M. Mohamed Building and Road Research Institute, University of Khartoum Address: Khartoum, P.O.Box 321, Sudan e-mail: d.a.mohamed@windowslive.com ABSTRACT Comprehensive laboratory investigations have been performed to study the mineralogy, microstructure and reaction products of three tropical clay soils treated with hydrated lime and their impact on the development of the treated soils strength with time. Soil 1 is a highly plastic montmorillonitic clay soil; Soil 2 is a low plastic lateritic clay soil whereas Soil 3 is highly plastic clay of mixed clay minerals. Optimum lime content (OLC) was added to the three soils and the tests conducted on the natural and treated soils included Atterberg limits, 1-dimensional consolidation, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Unconfined Compression Strength (UCS). The XRD was performed after 1 day, 7 days and 360 days of curing, The SEM after 360 days and the UCS in the short and long term (from 0.5 hours to 360 days). The three soils reacted with lime causing aggregation of the mix and formation of new reaction products. The reaction products formed depended on the clay mineralogy and curing time. Calcium silicate hydrates (CSH) was formed in the short and long term for Soil 1. Calcium aluminates hydrates (CAH) was the main reaction product after 7 days of curing for the kaolinitic clay (Soil 2) and CSH appeared in small quantity later (360 days). The reaction products CSH, CAH and calcium aluminates silicate hydrates (CASH) appeared in the mixed clay mineral (Soil 3). An evaluation of the reaction products and strength data has shown that the contribution of CSH to strength development seized after 56 days. The increase of strength with time was noticed for Soil 2 and Soil 3 and was attributed to the compound CAH. KEYWORDS: Hydrated Lime, XRD, SEM, reaction products, strength development. - 5483 -

Vol. 18 [2013], Bund. X 5484 INTRODUCTION Hydrated lime, here termed lime, is used as an effective additive to improve various engineering properties of cohesive soils. Many studies report that lime treatment enhances the clay soil properties by decreasing the soil plasticity and volume changes, increasing particle size, permeability, strength, and improving compressibility. [1-4]. When lime is added to a clay soil two stages of chemical reactions occur; immediate reaction and long-term reaction. The immediate reaction starts with the cation exchange between the ions associated with the surfaces of the clay particles and the calcium ions of the lime[5-7]. During this stage; improvements and changes occur immediately in soil plasticity, workability, swell and shrinkage properties, and permeability [8, 9]. Long-term stabilization aims to improve the mechanical properties of a soil with the objective to reach a permanent state of stability [2, 10]. This process is the consequence of the pozzolanic reactions engaged between lime, water, silica and alumina from the clayey particles. During the stabilization process, the highly alkaline environment resulted from the addition of lime causes silica and alumina to be dissolved out of the clay mineral structure and to combine with calcium cations from the lime producing new cementitious compounds. These compounds were reported as calcium silicate hydrate (CSH), calcium aluminates hydrates (CAH), and calcium alumino-silicate hydrates (CASH) [11, 12]. The ph value of the pore fluids should remain at around 12.4 [13] to have maximum reactivity between lime and clay. The solubility of silicate and aluminum ions is very high at this value of the ph. These reactions, known as pozzolanic reactions, are curing time and temperature-dependent and as time progresses, they contribute to strengthen the soil [11, 14]. The lime-soil reaction depends on soil and lime. The soil factors are mineralogical and chemical composition whereas the lime factors are quality and amount of lime. Tropical clays cover extensive plains in the southern, central and eastern Sudan [15-17]. Previous investigations have shown that these clay plains are covered by montmorillonitic clays known as black cotton soils and red tropical clays (lateritic clays) [17]. The dominant clays are the black cotton soils. Large projects, such as highways airports are constructed on these clay plains which offer very poor trafficability during the rainy season and lack proper construction materials, especially for road pavement construction. It is well known that lime is a suitable stabilizer for clay soils. However, the interaction of lime with soils of different mineralogical constituents is still under more investigation. This study is concerned with the mineralogy, microstructure and reaction products of lime treated tropical clay soils and their impact on strength development with time. THE PROGRAM OF TESTING This experimental program intends to study the mineralogy and microstructure of three tropical clays from Sudan, with different mineralogical constituents, treated with lime and their impact on strength development during short term and long term curing times.

Vol. 18 [2013], Bund. X 5485 Materials The Soil samples Three soils representing the main types of tropical clay soils encountered in Sudan were selected for this study. Soil 1 is highly plastic montmorillonitic silty clay obtained from Alfao town in eastern Sudan; Soil 2 is low plastic red lateritic clay soil from Tumbora in the Republic of South Sudan and Soil 3 is an alluvial, highly plastic clay with mixed clay minerals from Khartoum. Soil classification test results are presented in Table 1. The results of the cation exchange capacity, CEC, tests show Soil 1 to be the most active whereas Soil 2 is the less active clay soil. X-Ray diffraction micro-graphs of the un-treated clays are presented in Figure 1. Semiquantitative analysis of the X-Ray micrographs using X Pert Organizer software has shown that; the clay fraction of Soil 1 has about 90% montmorillonite content and 10% kaolinite content; Soil 2 is basically kaolinitic (~ 90%) mixed with about 10% of chlorite whereas for Soil 3 montmorillonite is still the dominant mineral (~ 70%), kaolinite (~ 20 %) and illite (~10%). Hydrated lime The hydrated lime used in this study was produced by heating raw limestone obtained from a local source in eastern Sudan at 900 0 C in the laboratory to produce quick lime. Water was added to the quick lime to produce hydrated lime (Ca (OH) 2 ). The produced hydrated lime satisfies ASTM C977 [18]. Table 1: Classification test results Sample CEC LL PI Specific gravity Particle Size % Clay Silt Sand Gravel USCS Classification Soil 1 83 66 37 2.7 24 65 9 0 CH Soil 2 13 48 20 Soil 3 69 73 41 2.78 2.68 20 47 17 16 CL 54 34 11.5 0.5 CH

Vol. 18 [2013], Bund. X 5486 Figure 1: XRD micrographs for the untreated soil samples Specimen Preparation, Test Methods and Results The three tropical soil samples were treated with the Optimum Hydrated Lime content (OLC). The OLC obtained using Eades and Grim (1960) test procedure [6] were about 6.5%, 4.0% and 7% (based on dry mass of soil) for soil 1, soil 2 and soil 3 respectively. The OLC was selected to ensure that enough reaction products would be generated to ease XRD and Scanning Electron Microscopy (SEM) investigations. Sample preparation involved air drying, crushing the samples and passing them through No. 40 BS sieve size and then lime was added by weight of the dry sample. The treated soils were kept in sealed plastic bags for two hours before being tested. Basic classification tests (specific gravity, Atterberg limits, clay content etc) were carried out on the treated soil samples. The results are given in Table 2.

Vol. 18 [2013], Bund. X 5487 Table 2: Physical test results Sample Lime % Atterberge limits LL PL PI CC S.G Soil 1 Soil 2 Soil 3 0 66 29 37 24 2.7 6.5 55 45 10 0 48 28 20 20 2.78 4 43 36 7 0 73 32 41 54 2.68 7 58 47 11 X-ray diffraction was performed on the treated soil samples. The treated soil samples were kept in laboratory temperature (~23 C⁰) and examined after curing periods (1, 7 and 360 days) to examine the reaction products and micro-structure of the treated soils through short and long term reactions. The X-Ray micrographs are presented in Figures 2, 3 and 4 for 1 day, 7 days and one year curing times. Figure 2: XRD test for treated soil samples (after one day)

Vol. 18 [2013], Bund. X 5488 Figure 3: XRD test for treated soil samples (after 7 days) Figure 4: XRD test for treated soil samples (after 360 days)

Vol. 18 [2013], Bund. X 5489 The Scanning Electron Microscopy (SEM) technique was used to observe the nature of clay particles in the soil before and after treatment. In this paper, the changes of the micro-structure of the three tropical clay soils before and after addition of hydrated lime (after 360 days) were investigated using JSM-6380 LA scanning electron microscope. A small piece of sample was cut with an iron wire before freeze drying to minimize the volume change. The fractured surfaces of samples were coated after freeze drying with silicate before scanning. The test results for untreated and treated soil samples are given in Figures 5-10 for X300 and X5000 magnifications. Computer programs Philips X Pert Organizer and X Pert high score plus were used for the analysis of the data for the un-treated and treated soils, respectively. The outcome of the analysis is presented in Table 3 for the treated soil samples. Table 3: Results from XRD analysis by X Pert high score plus for the treated soil samples after different curing days (1, 7 and 360 days) Samples chemical analysis (after one day) Samples 2Theta d-values (I/Io chemical Composition Compositions factor) Soil 1+ 6.5%L 26.90 3.3117 - CSH 3CaO 2 SiO 2 3H 2 O Soil 2+ 4.0% L - - - NIL NIL Soil 3+7.0% L - - - NIL NIL Samples chemical analysis (after 7 days) Soil 1+ 6.5%L 26.90 3.3117 - CSH 3CaO 2 SiO 2 3H 2 O 50.0 1.917 - Calcite CaCO 3 Soil 2+ 4.0% L 21.0 4.2268 - CAH 3CaO AL 2 O 3 Ca (OH 2 ) 12H 2 O 50.0 1.917 - Calcite CaCO 3 Soil 3+7.0% L 26.90 3.3117 - CSH 3CaO 2 SiO 2 3H 2 O 50.0 1.917 - Calcite CaCO 3 Samples chemical analysis (after 360 days) Soil 1+ 6.5%L 26.54 3.5558 15 100% CSH 3CaO 2 SiO 2 3H 2 O Soil 2+ 4.0% L 26.9 3.3117 77 8.1% CSH 3CaO 2 SiO 2 3H 2 O 21.0 4.2268 24 91.9% CAH 3CaO AL 2 O 3 Ca (OH 2 ) 12H 2 O Soil 3+7.0% L 26.92 3.3092 95 39.5% CSH 3CaO 2 SiO 2 3H 2 O 21.160 4.1952 15 37.8% CAH 3CaO AL 2 O 3 Ca (OH 2 ) 12H 2 O 24.740 2.1139 22 22.7% CASH Ca Al 2 Si 3 O103H 2 O * (where I/I O % is a chemical correction factor)

Vol. 18 [2013], Bund. X Figure 5: SEM of untreated Soil 1 Figure 6: SEM of untreated Soil 2 Figure 7: SEM of untreated Soil 3 5490

Vol. 18 [2013], Bund. X 5491 Figure 8: SEM of treated Soil 1 after one year Figure 9: SEM of treated Soil 2 after one year Figure 10: SEM of treated Soil 3 after one

Vol. 18 [2013], Bund. X 5492 The optimum lime content was added to the three soils to evaluate their stiffness, after treatment with lime, utilizing the one-dimensional consolidation test results. The constrained modulus, obtained from the test will give indirect understanding of the rigidity and bond strength of the treated soils. The test procedure, for the consolidation tests, followed BS 1377: 1990. The tests were performed on compacted samples extracted from Proctor compaction moulds, after being compacted using Normal compaction energy. The extracted samples were allowed to saturate in distilled water in the oedometer ring under a nominal applied load for 24 hours. They were subjected to successive consolidation stresses ranging from 100 to 1000 kn/m 2. The values of the constrained modulus (Ec) determined from the results of the three soil samples are summarized in Table 4 for pressure range from 1120 to 2240 kn/m 2. Table 4: Consolidation test results for natural and treated soil samples Samples Lime % Pressure ranges (kn/m 2 Constrained modulus Ec ) (kn/m 2 ) 0.0 1120 to 2240 55 Soil 1 6.5 1120 to 2240 290 0.0 1120 to 2240 234 Soil 2 4.0 1120 to 2240 560 0.0 1120 to 2240 175 Soil 3 7.0 1120 to 2240 325 To study the development of strength with time, the unconfined compression test was carried out at OLC on untreated and treated soil specimens after curing times 0.5 hour to 360 days. Mechanical dry mixing was used for mixing lime with soil. The Optimum Moisture Content (OMC) was added and the samples were carefully mixed and left two hours to cure and obtain homogeneous mix. After mixing, the sample was compacted into cylindrical moulds and put in sealed plastic bags and left 0.50 hour to 360 days for each test to cure before the test. The test results are summarized in Table 5. Location Lime % Table 5: Summary of Unconfined Compressive strength (UCS) kn/m 2 test for natural and treated soil samples (different curing). 0 days 0.50 Hour 1.0 Days 4 days 7 days 14 Days 28 days 56 Days 112 Days 168 days 224 days 360 days Soil 1 Soil 2 Soil 3 0 283 6.5-313 462 690 1560 2676 4026 5374 5417 5441 5452 5462 0 238 4.0-239 287 959 2010 3781 4554 6180 7127 8767 9346 9797 0 237 7.0-256 358 791 1920 2527 3214 4213 5111 5896 6445 6669

Vol. 18 [2013], Bund. X 5493 DISCUSSION OF THE RESULTS Background The three studied soils are tropical clays of different origin. Soil 1 and Soil 3 are black cotton highly plastic clays and are known to be highly expansive whereas Soil 2 is residual red lateritic clay. Soil 1 and Soil 2 have clay content 20 and 24 % whereas Soil 3 has high clay content (54%). Soil 2 has 33% of sand and gravel whereas the other two black clay soils have sand content of about 10%. Soil 3 has the highest value of plasticity index (41) whereas Soil 2 has the lowest value (20). Although Soil 1 and Soil 2 have about the same amount of clay fraction (<2.0 micron), the OLC is higher for Soil 1 (6.5%) compared to Soil 2 (4%). The OLC is function of the plasticity index which is dependent on the mineralogy of the clay fraction [19]. Mineralogy, Microstructure and Reaction Products The XRD was conducted on treated soil samples after 1, 7 and 360 days to evaluate the mineral s transformation and to identify the reaction products formed on the addition of OLC. Figures 1 to 4 show the XRD of the untreated and treated clay soil samples with OLC. New reflections were visible in all soil samples after addition of the OLC. The intensities characteristic of soil 1 and soil 3 peaks increased, while Soil 2 peak decreased. Montmorillonite is the dominant clay mineral detected in the untreated Soil 1 (Figure 1) from three principal lines at d- spacing of 14.7, 4.42 and 1.49 A0. After addition of the optimum hydrated lime, new reaction products with a different percentage appeared after 1, 7 and 360 days (Figures 2, 3 and 4) of curing. These reaction products were calcite detected on 7th day and calcium silicate hydrates (CSH) formed as 3CaO 2 SiO 2 3H 2 O and detected after 1 day, 7 days and 360 days. Kaolinite is the dominant clay mineral in the untreated Soil 2 (Figure 1). This is evident by the three measured peaks at d- spacing of 7.15, 3.566 and 2.331 A0. Chlorite was detected at d- spacing of 3.59 A0. When Soil 2 was treated with OLC, the intensities of the characteristic kaolinite peaks were both decreased and broadened (Figure 4). The reduced intensities were previously observed by the kaolinite clays [6]. The broadening of the peaks suggests either a slight expansion of some of the layers or a change in the orientation of the particles, as may perhaps occur due to the flocculating effects of the hydrated lime on the kaolinite. Calcium aluminates hydrate (CAH) and calcites (CaCO 3 ) were observed after 7 days of reaction in Soil 2. Two reaction products reflections were visible at d-spacing's of 3.3117 and 4.2268 A0 shown after 360 days. However, these reaction products are calcium silicate hydrates (8.1% CSH) and calcium aluminate hydrates (91.9% CAH). Previous studies confirm that the reaction product CAH is the main chemical reaction formed as a result of the reaction of lime with Kaolinite [5, 20], therefore the CSH is probably formed due to reaction with the chlorite in the soil. Soil 3 is formed of different clay minerals, montmorillonite, kaolinite and illite. These clay minerals were observed by X- ray diffraction from different measured peaks at d- spacing of 4.42, 3.566 and 1.89 A0 respectively. When Soil 3 was treated with optimum hydrated lime, the intensities of the peaks were both increased and broadened. Calcium silicate hydrate (CSH) and calcite (CaCO3) were observed on the 7th day. New reflections were found after 360 days at d- spacing s of 3.3092, 4.1952 and 2.1139 A0. The three reactions products which appeared were CSH, CAH and CASH. It is noticed that, although Soil 3 contains appreciable amount of kaolinite clay mineral the CAH did not appear on the seventh day.

Vol. 18 [2013], Bund. X 5494 It may be concluded from this section that the reaction products formed when OLC was added to the tropical clays are dependent on the mineralogical composition and curing time. Only CSH was formed for montmorillonitic clays (Alfao). It appeared after one day and was also detected after 7 and 360 days. CAH was the main reaction product after 7 days of curing for kaolinitic clays. CSH appeared in small quantity later and was detected after 360 days. This could probably be due to presence of small amounts of chlorite. CSH, CAH & CASH appeared in the mixed clay mineral of Khartoum. CSH is high in quantity (~ 40%), followed by CAH (~38%) and remainder is CASH. These amounts agree with the percentages of montmorillonite, kaolinite and illite in the untreated soil sample. Therefore, the CASH could be related to the presence of illite in this sample. The SEM of untreated and treated Soil 1, Soil 2 and Soil 3 are shown in Figures 5 to 10. Figures 5, 6 and 7 present the SEM photographs of the natural clay soils. The micro-fabric is still open and individual particles and aggregates can be seen. Addition of OLC to the natural soil flocculates the soil into larger lumps, as seen in Figure 8 to 10 after 360 days of curing. These lumps were more or less cemented together by the reaction products (Figures 8, 9 and 10). Networks of needle-like crystals were observed in the SEM images. The aggregation of the clay particles and the reaction products are thought to be the main sources and cause of the stabilization and long term strength development. The increase in stiffness as depicted in the one dimension consolidation test (Table 4) together with the very high increase of permeability of the treated soils [19] (~ 1000 times) are support the microfabric observation and reasoning. Strength Development The increase in strength of the lime treated clays when compared to the strength of the untreated clays can be attributed to the aggregation of the treated clays and to the contribution of the new reaction products formed due to the stabilization process. The new compounds formed were identified as carbonates and calcium silicate hydrates (CSH) in the short term, calcium aluminates hydrate (CAH) and calcium aluminum silicate hydrate (CASH) formed later (Table 3). The compressibility test results show that the lime treated samples experienced high increase in the constrained modulus during the first week of treatment. This increase is supported by the mineralogical and micro-structural changes. The results obviously shows that the bonds resulted from the reaction of lime with the lateritic soil kaolinitic clays are stronger than those formed by the reaction with the swelling soils. The treated kaolinitic clay soil (Soil 2) recorded the highest strength and rigidity compared to the Soil 1 and soil 3. The UCS strength of Soil2 increased by more than 40 times after one year of curing compared to about 20 times increase for Soil1, for the same period of curing (Table 5). Consequently, it can be concluded that the addition of OLC changed the behavior of the three relatively flexible soils towards rigid materials. The strength of the lime treated soils was assessed at various curing ages (from 0.5 hour to 360 days) by the unconfined compression test (UCS). The results are presented in Table 5 and Figure 11. The strength of Soil 1 showed fast increase for the first 56 days and then increased at a very slow rate for the remaining period up, to 360 days. The other two soils showed continuous increase in strength with time up to one year. It should be noted that Soil 1 formed only one

Vol. 18 [2013], Bund. X 5495 reaction product detected by X-ray diffraction which is CSH. Therefore the CSH was not contributing to the long term pozzolanic reaction. The very small increase after 56 days may be attributed to the small amount of kaolinite (~10% of the clay) in Soil 1. 12000 10000 8000 UCS (kpa) 6000 4000 2000 0 0 40 80 120 160 200 240 280 320 360 400 Curing Duration (days) Soil1+6.5% Lime Soil2 +4% Lime Soil3 +7% Lime Figure 11: UCS for soil samples at mix design with various curing days Soil 2 when treated with 4% hydrated lime has higher soil strength compared to soil 1 and soil 3. The clay fraction of Soil 2 contains about 90% of kaolinite mineral and the reaction product is mainly CAH. The continuous increase in strength, i.e., pozzolanic reaction, is therefore attributed to the formation and presence of CAH. Soil 3, when treated with the OLC (7%), has generally lower soil strength when compared to Soil 2 and higher soil strength when compared to soil 1. Soil 3 contains different mineralogical composition when analyzed with XRD test. The reason behind the continous increase in soil strength up to 365 days would depend on the presence of two chemical reaction compounds, CAH and CASH. The new products hardened with age to form a permanent compound binding the soil particles thus increasing the shear strength of the treated soils. Regarding the short term response of the three soils to lime addition, it is observed from Table 5 that the addition of lime immediately increased the compressive strength (0.5 hours) of Soil 1 whereas the other two soils showed some delay in strength development. This observation coupled with the X-Ray results, which showed formation of CSH on the first day for Soil 1, indicate that montmorillonite reacts faster with lime compared to kaolinite and illite

Vol. 18 [2013], Bund. X 5496 minerals. The immediate reaction is often attributed to cation exchange. Soil 1 has the highest cation exchange capacity CEC (Table 1) therefore this deduction seems to be logical. CONCLUSIONS The following conclusions have been drawn from this study: The three soils, having different mineralogical constituents, reacted with lime resulting in fast drop in plasticity index, increase in stiffness and formation of new reaction products. Montmorillonite is the dominant clay mineral (~90%) detected in the untreated Soil 1 followed by kaolinite (~10%). The addition of the OLC resulted in the formation of new reaction products. These reaction products were calcium silicate hydrates (CSH) detected on 1st day, 7th day and 360 days and calcite detected on 7th day. Two mineral types were detected in the clay fraction of Soil 2; these are kaolinite (~90%) and chlorite (~10%). When Soil 2 was treated with OLC, the intensities of the characteristic kaolinite peaks were both decreased and broadened. Calcium aluminates hydrate (CAH) and calcites (CaCO 3 ) were observed after 7 days of reaction in Soil 2. Two reaction products reflections, calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH), were detected after 360 days. Previous studies confirmed that CAH is the main chemical reaction formed as a result of the reaction of lime with Kaolinite [5, 20], therefore the CSH is probably formed due to reaction with the chlorite mineral in the soil. The clay fraction of Soil 3 constitutes three different clay minerals: montmorillonite (~60%), kaolinite (~30%) and illite (~10%). When Soil 3 was treated with optimum hydrated lime calcium silicate hydrate (CSH) and calcite (CaCO 3 ) were observed on the 7th day of curing. Three reactions products were detected after one year, namely calcium silicate hydrates (CSH), calcium aluminate hydrates (CAH) and calcium aluminates silicate hydrates (CASH). It is noticed that, although Soil 3 contains appreciable amount of kaolinite clay mineral the CAH did not appear on the seventh day. It appears from Table 3 that montmorillonite retarded the reaction of lime with kaolinite in the early stages and therefore delayed the formation of the consequent reaction product (CAH). The addition of lime immediately increased the compressive strength of Soil 1 whereas the other two soils showed some delay in strength development. This observation coupled with X-Ray results indicate that montmorillonite reacts faster with lime compared to kaolinite and illite minerals. The high CEC of Soil 1 compared to Soil 2 and Soil 3 suggests that the immediate reaction can be attributed to cation exchange. The strength of Soil 1 showed fast increase for the first 56 days and then increase at a very slow rate for the remaining period (up to 360 days). The other two soils showed continuous increase in strength with time. Since the only reaction product detected by X- ray diffraction for Soil 1 was CSH, it is justifiable to state that CSH had no contribution to the long term pozzolanic reaction. The very small increase, after 56 days, may be attributed to reaction of lime with the small quantity of kaolinite (~10%) in Soil 1. The reaction products CAH and CASH were detected after one year for Soil 2, therefore the long term development of strength could be attributed to these products.

Vol. 18 [2013], Bund. X 5497 Lime increased the strength and rigidity of the treated soils. The SEM results indicate that the bonds created by the reaction of lime with kaolinitic clay soils harden with age, becoming stronger than those formed by the reaction with montmorillonitic clay soils. Long term stabilization for one year, has led to the development of new crystalline phases, which consisted of an interlocking network of needle like crystals. ACKNOWLEDGMENT The authors would like to thank the staff of the Geotechnical Laboratory of King Saud University and Dr Muawia Elturabi for facilitating the SEM and part of the XRD tests. REFERENCES 1. Locat.J and Choquette.M (1990), Laboratory Investigations on the Lime Stabilization of Sensitive Clays: shear strength development, Canadian Geotechnical Journal, 27(294-304.). 2. Little.D.N (1995), Stabilization of pavement sub-grades and base courses with lime,technical report made for Lime association of Texas. 3. Elsharief, A. M. and Mohamed S. A (2000), Technical and economical viability of lime stabilization of expansive soils for road construction in Sudan, Sudan Engineering Society Journal, Vol. 47 No. 38, 5-16. 4. Mohamed, A. E. M (1986), Microstructure and Swelling Characteristics of Untreated and Lime Treated Compacted Black Cotton Soil, PhD. Thesis, University of Strathclyde, Glasgow. 5. Rajasekaran, G. and. Narasimharao.s (1996), Reaction Products Formed in Lime- Stabilised Marine Clays.ASCE, Journal of Geotechnical Engineering, 122(5): p. 329-336. 6. Eades, J. L. and Grim R. E (1960), Reactions of Hydrated Lime with Pure Clay Minerals in Soil Stabilization, Highway Research Bulletin 262. 7. Little, D. N. Males. E. H. Prusinski. J.R and Stewart. B (2000), Cementitious Stabilization, 79th Millennium, Rep Series, Transportation Research Board. 8. Al-Rawas,A. A. and Al-Sarmi H (2005), Effect of Lime, Cement and Sarooj (artificial pozzolan) on the Swelling Potential of an Expansive Soil from Oman, Building and Environment, 40(5): p. 681-687. 9. Bell, F. G (1996), Lime Stabilization of Clay Minerals and Soils, Engineering Geology 42, p 223-237 Elsevier Science 10. De Bel R., B. Q., Gomes Correia A., Duvignaud P. H., Verbrugge J. C (2007), Time and Temperature Dependency of the Geomechanical Properties of Silty Soils Treated with Lime. 11. Arabi, M., W. S (1986), Microstructural Development in Cured Soil-Lime Composites. Material science, p 497-503.

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