CHAPTER 1: INTRODUCTION 1.1 BACKGROUND Housing is one of the basic human needs and is usually ranked third after food and clothing. In most developing countries housing is inadequate and the housing back log has been increasing rapidly. One key reason for housing inadequacy is the increase in population Racodi (1997). Cement is the most expensive component of concrete. Cement paste (cement and water) is the element filling the voids among aggregates, provides workability for fresh concrete and creates adhesion or bonding among aggregates once concrete is hardened.(De Larrard, 1999) Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule - to boulder -sized fragments. One cubic meter of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 pounds). Concrete provides wide range of mechanical and durability properties to meet the design requirements of a structure. The compressive strength of concrete is the most common performance measure used by the engineer in designing buildings and structures. Concrete compressive strength requirements can vary from 2500 psi (17MPa) for residential concrete to 4000 psi (28MPa) and higher in commercial structures. Higher strengths and exceeding 10,000 psi (70MPa) are specified for certain applications Nation already Mixed Concrete Association. ( Echo project 2008 ). Construction and demolition (C&D) waste consists of a range of materials including high-value materials and resources for new constructions. There are many opportunities to extract them through recycling the waste before disposal as land fill. Recycling is one of the fundamental strategies in waste management to gain benefits, by reducing the demand upon new resources and cutting down the transport and production energy cost. Some factors also provide an incentive to enhance the industry of recycling of C&D waste, such as increased land filling charges and increased reclamation rates for high-value materials.