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The over dependent on the utilization of industrially manufactured soil improving additives (cement, lime etc), have dept the cost of such stabilized soils financially high.  The hitherto have continued to deter the underdeveloped and poor nations of the world from providing accessible pavement to their rural dwellers who constitute the higher percentage of their population and are mostly, agriculturally dependent.  A number of researchers have studied the physical and chemical properties of rice husk ash.  The high percentage of siliceous material in rice husk ash indicates that it has potential pozzolonic properties.  Findings show that RHA which are waste materials can be used to upgrade expansive soil as a construction material.  Thus the use of agricultural waste (such as rice husk ash – RHA) will considerably reduce the cost of construction and as well reducing the environmental hazards they cause.  However it appears that none of these studies referred to any guideliens in the binder selection process.  Thus, the study obtained the empirical models of soil material characteristics such as California Bearing Ratio (CBR), Optimum Moisture Content (OMC) and Maximum Dry Density (MDD), which are desirable for road construction.  The empirical models which are based on Scheffe’s optimization theory were developed from the experimental results of soils obtained from three different locations in south – eastern Nigeria.  The results show that A – 6 soil type improved to A – 2 – 6 after stabilization with RHA.  CBR value of the soil improves to an average of 14.47% from 5.67%.  Surprisingly, the average value of the MDD reduces to 1.58kg/m3 from 1.89kg/m3.  While average OMC went up from 16.63% to 21.93%.  The empirical models show a very close result to the experimental results.  Since RHA is much cheaper than lime and cements, use of rice husk ash in soil stabilization can result in cost reduction in construction.





Cover Page                                                                                                                  i

Title page                                                                                                                    ii

Certification                                                                                                                iii

Approval                                                                                                                     iv

Dedication                                                                                                                  v

Acknowledgement                                                                                                      vi

Table of Content                                                                                                         x

List of Tables                                                                                                              xi

Fist of Figures                                                                                                             xiii



  • General Introduction 1
  • Statement of Problem 3
  • Study Objectives 4
  • General Methodology 6
  • Significance of Study 6
  • Scope of Work 7
  • Limitations of Study 7


2.1       Generation Introduction                                                                                 8

2.1.1    Types of Stabilization                                                                                     9

2.2       Rice Husk Ash                                                                                                15

2.2.1    Thermal Decomposition of Rice Husk                                                            17

2.2.2    Application of Rice Husk Ash                                                                        17

2.2.3    RHA for Cement and Construction Industries                                              18

2.2.4    Factors Influencing Ash properties                                                                 19

2.2.5    Summary of Review of Literatures on RHA                                                  21

2.2.6    Conclusions on the Review of Literature of RHA                                         22

2.3       Mix Design and Construction                                                                         23

2.4       Design and Analysis of Experiments                                                              24

2.4.1    Strategy of Experimentation                                                                           24

2.4.2    Mixture Designs                                                                                              27

2.4.3    Simplex Designs                                                                                             28

2.4.4    Derivation of Scheffe’s 2nd degree models                                                     31

2.4.5    Least squares Estimation of the Model Parameters                                        33


3.1       Specimen Procurement and Methods of Experiments                                    34

3.1.1    Soil Procurement                                                                                             34

3.1.2    Soil Identification and Classification                                                             34

3.2       Simple dry sieving BS 1377: Part 2: 1990                                                      35

3.3       Natural Moisture Content BS 1377: Part 2: 1990                                          37

3.4       Preparation of Rice Husk Ash                                                                                    41

3.5       The Engineering Properties after stabilization                                                41


4.1       Eke-Obunagu (A-7-5)                                                                                     49

4.2       Egbede Borrow Pit A-6                                                                                  53

4.3       Ugwuayi Nkanu (A-2-7)                                                                                 57

4.4       Model Verification                                                                                         61

4.4.1    Eke-Obunagu                                                                                                  62

4.4.2    Egbede                                                                                                                        65

4.4.3    Ugwuaji                                                                                                          68

4.5       Discussions                                                                                                     71


5.0       Conclusion and Recommendation                                                                  73

5.1       Conclusion                                                                                                      73

5.2       Recommendation                                                                                            73

REFERENCES                                                                                                          74






According to Brooks (2009), clays exhibit generally undesirable engineering properties. They tend to have low shear strengths and to lose shear strength further upon wetting or other physical disturbances. They can be plastic and compressible and they expand when wetted and shrink when dried. Some types expand and shrink greatly upon wetting and drying – a very undesirable feature. Cohesive soils can creep over time under constant load, especially when the shear stress is approaching its shear strength, making them prone to sliding. They develop large lateral pressures. They tend to have low resilient modulus values. For these reasons, clays are generally poor materials for foundations. Such characteristics exhibit by clay soils can be harnessed through soil improvement techniques.

Geotechnically, soil improvement could either be its modification or stabilization, or both. Soil modification is the addition of a modifier (additive and conditioner) to a soil to change its index properties, while soil stabilization is the treatment of soils to enable their strength and durability to be improved such that they become totally suitable for construction beyond their original classification. Stabilization can be mechanical or chemical and several types of stabilizing agents have proved to be suitable under different conditions of soil and environment.

Many procedures have been developed to improve the physical behaviour of soil. The soil stabilization techniques include:

  • Stabilization with lime.
  • Stabilization with cement.
  • Stabilization with a combination of lime and cement

The following are some of the important materials which have proved good.

  • Fly Ash for the construction of the embankments and stabilization of sub-base and base-courses.
  • Steel and copper slags for the construction of sub-base and base-courses.
  • Marble dust in sub-grade and sub base.

Undoubtedly the most widely applied methods involve the use of inorganic cementing agents (Jha & Gill, 2006). The effectiveness of such agents relies on the formation of cementing bonds between the particles in the soil system. Continuing, (Jha & Gill, 2006) noted that lime as an additive, brings several beneficial changes in the engineering properties of soil such as decrease in soil plasticity and shrink  –  swell potential apart from improving strength characteristics.

Stabilization of soil by lime is achieved through cation exchange, flocculation and agglomeration, lime carbonation and pozzolanic reaction. Cation exchange and flocculation agglomeration reaction takes place rapidly and brings immediate change in soil properties, where as, pozzolanic reactions are time dependent. These reactions involve interaction between soil silica and (or) alumina and lime to form various types of cementing agents thus enhancing the strength. The chemical processes modify the soil structure whereby larger grain aggregates are formed, leading to several advantages in the suitability of soil in road construction.

Certain natural substances, such as volcanic ash reacts with lime addition much better than do the ordinary soil types. If such materials are added to soil, the efficiency of lime stabilization may be greatly increased. The characteristics of compacted soil, if improved, resulting from residue utilization like fly ash, blast furnace slag, rice husk ash etc mostly brings environmental and economic benefits.

Soil stabilization has been widely recommended for developing countries for the construction of various elements of the pavements (Ting, 1971).

The reasons usually put forward are that the use of locally available materials will lead to lower costs. The over dependence on the utilization of industrially manufactured soil improving additives (cement, lime etc), have kept the cost of such stabilized soils high. This hitherto have continued to deter the underdeveloped and poor nations of the world from providing accessible pavement to their rural dwellers who constitute the higher percentage of their population and are mostly, agriculturally dependent. Thus the use of agricultural waste (such as rice husk ash – RHA) will considerably reduce the cost of construction and as well reduce the environmental hazards they cause.

Sear (2005), in his work showed that Portland cement, by the nature of its chemistry, produces large quantities of CO2 for every ton of its final product. Therefore, replacing proportions of the Portland cement in soil stabilization with a secondary cementitious material like RHA will reduce the overall environmental impact of the stabilization process.


With the increasing road making activities in the south – eastern Nigeria, and in the light of scarce desirable sub-grade materials in the region; efforts have been geared over the years towards finding economical alternative improvement techniques to soils of that locality. Just like in geotechnical engineering, where the underlying principle has always been “using better quality of sub-grade materials”, which decreases the thickness of pavement and thus reduces the cost of construction to cost effective road making and elongates the life span of the constructed roads. In the south eastern region, soils used for construction of sub-grade are in short supply. Further, the soil for sub-grade collected from extensive area along length of roads show deficient engineering properties for their road making use due to depositional history. Numerous works have proved that these can be improved to ensure the satisfactory performance of the constructed road.

Due to rapid industrialization throughout the world, the production of huge quantity of waste materials creates not only environmental problem but also depositional hazards. Safe disposal of the same is very vital issue and such situation can be addressed by the bulk utilization of these said materials mainly in the field of civil engineering applications.

As road construction benefited from the stabilization process, a number of guidelines based on soil stabilization have been developed throughout the globe. Most of the guidelines are equipped with comprehensive guide and mechanism in analyzing potential natural soils to be used in the soil stabilization process. In view of this an experimental program was undertaken to determine the characteristic variations on mixing the rice husk ash and clay in the locally available soil, to attain significant gain in engineering and supporting characteristics for sub-grade construction.

Among such areas in this soil improvement drive which are begging for attention is the development of mathematical models that would encourage wider application of soil improvement techniques. These models are sought to provide reference and ratios to the construction industries on the use of available soil and the agricultural paddy waste dust RHA to the enhancement of engineering properties of soils. This was done to facilitate the application of laboratory results and to serve as a guide in predicting relationship between variables, in addition to reducing the rigors of laboratory work; which enables estimation of results, thereby saving both time and energy.


Need for building materials is growing at an alarming rate and in order to meet the demand for new buildings, new ways and techniques must be evolved. The only binder used in most developing countries is Portland cement. Even though this binder is not a low cost material, its application is very common in the low income population. Although Portland cement is required for high-strength applications, Portland cement is predominantly used in low-strength applications as foundations, plasters, mortars and soil stabilization. The wrong application of cement in this manner is not only unnecessarily costly but, more important, technically defective. It is estimated that only about 20% of the word-wide use of cement requires the strength of Portland cement. One of the reason there is a greater demand of Portland cement in developing countries is because it has an “enormously powerful value”. Acceptance of low-cost materials by general population requires the generation of confidence that the materials being proposed can have the same behaviour as Portland cement but at much less cost.

The main objective of stabilization is to improve the performance of a material by increasing its strength, stiffness and durability. The performance should be at least equal to, if not better than that of a good quality natural material.

The objective of this study is to consider upgrading expansive soil as a construction material using rice husk ash (RHA), which are waste materials. Thus, encouraging the building of new roads in both urban and rural areas where there is shortage of quality construction materials, especially when expansive soils are encountered. Hence, the specific objectives of this study include the following:

  1. Finding alternative, economical and environmental friendly source of soil improvement techniques using RHA on the expansive soils in the south – east region.
  2. Determining the required ratios of Soil to RHA required for corresponding required soil improved characteristics.
  • Formulating models for soil engineering properties such as California Bearing Ratio CBR, Maximum Dried Density MDD and Optimum Moisture Content OMC as dependent variables, with the percentage of RHA and local soil as the independent variables.
  1. Verifying the ability of the models to predict reasonable results; results from the models were compared with results of other tests.



This study is imminent in geotechnical and soil material engineering. The approach to the realization of the objectives would be by reviewing the general properties of lime, rice husk ash and the anticipated soil material. Earlier work done in this regard would be thoroughly looked at. This is to enable the study form its basis and relevance.

Response surface methodology techniques would be studied to select the best workable function to suite the non – linear behaviour of soil. Hence, the solution of the expected function would be sought according to mixture design constraint. Scheffe (1958) suggested models for mixture designs. The study would use second degree polynomials of  Scheffe’s and shall be applied according to (Okafor & Oguaghamba, 2009).

The results of the experiments and the models shall be compared to ascertain the conformity of the models.


This study will hopefully be relevant in the following respects:

  1. The design and construction of pavements and foundations on expansive soils
  2. To the material engineering students and practicing engineers.
  • To the governmental agencies that are entrusted with the responsibility of ensuring quality control.
  1. To civil engineering consultants; contractors and their clients.

It is also perceived that it would generate further research in the following areas:

  1. Modeling of maximum dry density and California Bearing Ratio of soil – RHA mixture.
  2. Modeling of optimum moisture content and Atterberg limits of soil – RHA mixture.



This work is limited to soils from Eke – Obinagu borrow pit, Emene, Enugu State; Egbede Borrow Pit, Aba, Abia State; and Ugwuaji Nkanu, Enugu State. Laboratory and experimental study shall be carried out on soil samples from these locations to ascertain their insitu engineering properties. Literatures relating to Rice husk ash potentials and expansive soils are understudied to ascertain their interactive condition. The soil samples shall be modified and stabilized using RHA as an additive  and their subsequent properties such as: the California Bearing Ratio, Maximum dry density and optimum moisture would be examined through experimental and laboratory technique. The results of the stabilized soil samples shall be modeled using the Scheffe’s second degree polynomials. The predictive strength of the models shall be tested and verified using other laboratory results.



The results could be affected by the inherent limitations associated with laboratory results. Though, the deviation of the models results from their experimental results will be verified to for marginal, satisfactory and acceptable results.





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