IMPROVEMENT OF SELECTED PARTS OF BASRAH GOVERNORATE SOILS USING A MIXTURE OF CEMENT AND NOVOLAC POLYMER

A weak clayey silt soils from Garmmat Ali and a sandy soil from AL-Nashoa region were used from different sites and depths and mixed with (0.2%,0.4%,0.6 w/W) of Novolac polymer with (2%,4%,6% w/W) of Cement to know the profitable amount of Novolac, and improving some of engineering properties of the soils that include: the plasticity and compacting. A noticeable improvement in the plasticity of these clayey soils as result of adding a mixture by the rise in their plastic limit, dry densities, lowering in their optimum moisture contents, and increase in tensile strengths as compared with crude soils. There are also an improve in treated sandy soil properties. The cost of using this polymer as a soil binder was reduced by about 50% as compared to the usual practice which involve removing the clayey silt soils and replace them by sand or other materials.


Introduction
Top surface layers of the soils in the Basrah Governorate have been subjected to a continuous change resulting from rising and sinking of the terrain or loading and unloading of them by alluvial processes and sedimentation during the recent geologic history of the Basrah region. Chemical analysis of these fine-grained soils were shown in Table 1 indicates, the presence a mixture of clay and non-clay minerals Al-Marsoumi ,1997 and Hosain, 2000 . Mechanical grain size analysis of the top layer of soil in the Basrah region indicated a clayey silt type soil , where silt constitutes the higher percent (56%) followed by clay (34%) and approximately (6%) for sand. On these bases, Basrah soil is strictly determined by it's fine particles mainly silt, and clay, and also by the type and percent of clay minerals present in these soils. The X-ray diffraction analysis showed the presence of the following clay minerals, Illite, Palyogorskitc, kaolinite, chlorite, and Montmorrillonite, and other non-clay minerals such as Quartz, Calcite, Halite, Gypsum, and Feldspar. Therefore, these kind of soils usually become weak and soft, unless they experienced any solidification processes, resulting from physical, mechanical, or chemical means. Chemical soils stabilization methods were used in many cases of soil improvement or reinforcement by these methods require lengthy curing period and relatively large quantities of additives Horvath et al., 2000. Polymeric materials are considered to be the dominant foam materials such as polystyrene. Despite their low density could reach up to or less than (1-2 %) of the density of soil, yet there are sufficiently strong to support many types of loads encountered in Geotechnical practices Experiments also revealed that there is an optimum additive quantity for the maximum dry density and unconfined compressive strength. The optimum polymer quantity ranged between (2.5-6%) by weight. They also observed that the increase in temperature of the curing environment led to the increase of the strength and reduction in curing times to 3 hours only. Comparative studies using Urea-Formaldehyde (UF) and its copolymers to stabilize dune sand were performed Singh and Das 1983. Further studies were carried out using polyacrylamide (PAM) as a soil stabilizer for erosion control Kenneth and Nwankwa, 2001.
The primary objectives of this research is to stabilize the Basrah clayey silt soil with (a) profitable amount of a mixture of Novolac and Cement, (b) improving some engineering properties of the studied soils that include: the Plasticity, Compacting dry density, and lowering optimum moisture content, and also reducing the ability of these soils to absorb water. The expected structure of Novolac as an average of 5 -6 benzene rings per molecule as shown in Figure 1, given by Al Ali and Abm , 1997.

2.Materials and Methods
Sufficient quantities of clayey silt soil samples from (0.6-0.8) meters depth at three different sites from Garmmat Ali area were collected. Two types of stabilization additives were used. They include 1-Novolac 2-Portland Cement. This polymer powder prepared in the research chemistry laboratory, College of science, University of Basrah.
These analyses were done according to specific gravity test ASTM D856, D850, Atterberg's limits for treated and untreated soils according to ASTM D422-63, for grain size. Three chemical tests were conducted , they include organic matter test according to B.S. 1377, Walky and Black method. Walky and black method Akroyd, 1964 using ISS, 1998 modified Sheen and Kahler method. The carbonates content was determined by calcimeter methods Vantan, 1967. All tests are done in soil mechanics laboratory civil engineering department, in the marine science center laboratory, and in the chemistry laboratory, college of science at the university of Basrah. Compaction proctor test was done according to ASTM D1557. and split tensile strength test according to ASTM D3967.

3.Results and Discussion
Tests results for effects of untreated and Novolac , Cement and their mixtures treated Garmmat Ali soil samples of the specified locations are discussed in this section , The first investigation includes preliminary tests such as grain size, hydrometer, specific gravity , and atterberg's limits are shown in Tables 2, 3

4.Compaction Test Using Cement as Soil Stabilizer
Standard compaction tests results for clayey soil for Garmmat Ali after adding various amount of Cement only (6% w/W) to those investigated soils indicate some increase in their maximum dry densities and decline in their corresponding optimum moisture contents as shown in Figures 5,6, and 7.

5.Compaction Test Using Novolac as Soil Stabilizer
Standard compaction tests results for clayey soil for Garmmat Ali after adding various amount of Novolac polymer only (0.6% w/W) to those investigated soils indicate a noticeable increase in their maximum dry densities and appreciable decline in their corresponding optimum moisture contents (higher than when using Cement ) as shown in Figures 8, 9 and 10.

6.Compaction Test Using Mixture of Novolac and Cement as Soil Stabilizer
Standard compaction tests results for clayey soil for Garmmat Ali after adding various amount of mixture of Novolac and Cement (6.6% w/W) to those investigated soils indicate noticeable increase in their maximum dry densities and appreciable decline in their corresponding optimum moisture contents (higher than when using Cement or Novolac only) as shown in Figures 11,12 and 13.

7.Split Tensile Strength Test for Clayey Soil for Garmmat Ali
Split tensile strength cylinder tests of an atmospheric dried cylinders of treated and untreated clay silt soils show a considerable increase in their split tensile strengths as a result of adding (6% w/W) Cement , (0.6% w/W) Novolac, and (6.6% w/W) mixture of Novolac and Cement. The amount of increase in split tensile strength is increasing gradually when using Cement , Novolac, and mixture of them as shown in Figures 14,15 and 16. increase in their maximum dry densities and decline in their O.M.C. when using Cement only as shown in Figures 18,19 and 20 for three site, and indicate appreciable increase in their maximum dry densities and decline in their O.M.C. when using. Novolac only (higher than when using Cement) as shown in Figures 21,22 and 23 for three site, and finally compaction results indicate a good increase in their maximum dry densities and decline in their O.M.C. when using a mixture (higher than when using cement or Novolac only) as shown in Figures  24 and 25 for two sites. Shear tests indicated a rise in their angle of friction from 35° to 37.5° to 37.8° when using (6% w/W) Cement only, then when using (0.6% w/W) , finally when using (6.6%w/W) of their mixture to 39.5°. This rise could be attributed to the enveloping effect of Cement and Novolac to the sand grains of these soil.

9.Novolac Clayey Silt Soils Interaction
Clayey minerals are described as hydrous aluminum silicates minerals with isomorphic substitution in their mineral structures. These isomorphic substitutions usually involve: (1) AL +3 replacing Si +4 in the silicaterahedral layer, and usually replacement of aluminum with Mg +2 or Fe +3 in the octahedral layer, (2) the disassociation of OH ion, and finally the broken bonds of the edegs of clay particles. In general, this causes the overall mineral structure unstable and having a negative charge. The clay mineral family with the most isomorphic substitution is the semectite group, while the one with least is Kaolinite group, Both illite and chlorite have a moderate substitution . This negative charge imbalance needs to be balanced by the addition of water and cations or other most active groups of Novolac. Therefore, this improvement in the soil plasticity as a result of adding this polymer may due to the reaction occurring between Novolac and the above -mentioned functional group of the clay particles present in these soils, in turn causes a rise in the internal friction between silt and or sand grains as a filling material resulting from enveloping effect this added polymer. The mechanism involves using Novolac as soil stabilizer may be explained in the following manner. The binding Novolac form matrix with soil through the functional groups present in the clay minerals. Two main types of bonding may take place either secondary bonding as in the case of hydrogen bonding between the hydroxyl group of the polymer, while the second type of chemical bonding are concerned with bonds formed due to elimination of water.

10.Conclusions
Test results using a Novolac and Cement mixtures as a soil binder was significantly enhanced some physical and engineering properties of these investigated soils. These changes in soil properties are reflected in: 1-Considerable improvements in the plasticity of studied soils are noticed in the increase in their plasticity limits, and consequently reduction in their Plasticity Index as a result of adding (2.2-6.6% w/W) of a mixture of Novolac and Cement.
2-Increased the value of the dry density of the studied soils and a appreciable decline in their optimum moisture content as a result of adding (2.2 -6.6% w/W) of a mixture of the polymer and cement.
4-A reasonable rise in their split tensile strength after adding (2.2-6.6%w/W) of a mixture from Novolac and Cement.

5-
The cost of improving one cubic meter of clayey silt soil is reduced by about 50% at the present price as compared to the ordinary reinforcement by sand. 6-A noticeable rise in the maximum dry density of the studied sandy soils as well as appreciable decline in their O.M.C. was noticed.