• Ouf, Mohamed Elsadek
• Mostafa, Abdelzaher
• Ibrahim, M.

Abstract

igid pavement rested on clayey soil may be adversely affected by the behavior of sub-grade soil. The clayey soil may swell or shrink which causes unexpected cracks in pavement and therefore needs greater thickness to sustain the expected loads. The objective of this study is to achieve an economic design of rigid pavement on expansive clay. Specimens of reinforced concrete slabs were tested on a bed of Egyptian soil and were loaded until failure. Firstly, a reinforced concrete slab supported on a well compacted natural soil was tested to sustain the expected traffic loads without any additives. Secondly, improve the sub-grade soil under the rigid pavement using ground granulated blast furnace slag, cement dust, and lime. Thirdly, improve the sub-grade soil under the rigid pavement using ground granulated blast furnace slag (GGBS), cement dust (CD), and lime (L) stabilizers. Fourthly, replace the expansive soil (ES) using sand layer Firstly, improve the in-situ materials by normal compaction methods and design for the modified properties to sustain the expected traffic loads without any additives. Secondly, improve the sub-grade soil under the rigid pavement using ground granulated blast furnace slag (GGBS), cement dust (CD), and lime (L). Thirdly, improve the sub-grade soil under the rigid pavement using ground granulated blast furnace slag (GGBS), cement dust (CD), and lime (L) stabilizers. Fourthly, replace the expansive soil (ES) using sand layer. The results of this study proved that the best alternative to obtain the best stress / strain ratio was using GGBS and lime (3:1 ratio) to stabilize the natural soil and the percentage of total binder was 6% by dry weight of soil. Keywords: Airport, rigid pavement, expansive clay, waste materials, blast furnace slag 1. IntroductionThe cost of any roads and airports project includes initialcosts and subsequent maintenance costs. The initial costsinclude many items such as land, bridges and subways,drainage, pavement construction etc. Therefore, decreasingthe cost of pavement construction is very beneficial. It is essential to take into consideration the conditions of thesubgrade soil before designing the type and the thicknessof the pavement (Bari 1995, Ouf 2001).Airfields rigid pavement rested on clay soil may be adversely affected by the behavior of sub-grade soil.Expansive clays are those which suffer volume andbehavior changes with changes of water content whichresults in the break-up of road pavements and damage to light structures. Replacement of such clays by othermaterials is generally expensive due to the high costs of excavation and disposal of unsuitable materials and theimport and placing suitable fill. This is a particularproblem in developing countries where construction costsare critical. The most appropriate method will usually be determined by economic considerations, for example it may be cheaper to stabilize a soil using relativelyexpensive additives rather than excavate and dispose of unsuitable materials and import and place suitable fill, as well as the properties of the subgrade (Ouf 2001). Thevolume change of some clayey soils due to change in theirwater content represent one of the most serious problemsin the field of foundation engineering. Volume change andswelling pressures in clayey soils depend on clay type,pore volume, pore solution (including salt concentration)and particle-to-particle forces (Mowafy et al.1990).Volume change and swelling pressure are closely relatedand estimation of volume change of soil gives an indication of its swelling pressure and vice versa. In chemical soil stabilization processes, it has beenestablished that new cementations materials are formedand alter the particle-to-particle forces through thecementations effects that these reaction products impart.Due to the formation of these cementations materials, thepore fluid and pore pressure will then be decreased, thusreducing the swelling pressure and the swelling potentialand leading to volume stability (Kinuthia 1997).Soil heave due to soil swelling is common in the field andcauses tensile stresses in the upper parts of the structure.Alternatively, shrinkage may cause dishing, resulting in tensile stresses in the foundations, which can better resistsuch stresses (Ouf 2001, Kariuki and Meer 2004, andXidakis 1979). Heave is mainly due to an increase in moisture content under the covered area not depending on the environmental conditions, (Eren and Filiz 2009).There are many methods to control heave potentialincluding control of compaction such as compaction at lower density and higher moisture content and chemicalstabilization with lime and cement (Mowafy et al. 1990, Ouf 2001).Researchers have considered the use of some by-productmaterials as alternative materials to cement and also to lime. The use of by-products has environmental andeconomic benefi

Topics

• density
• impedance spectroscopy
• pore
• crack
• cement
• lime