The most commonly used materials in construction are aggregates. They are extensively distributed with a variety of potential sources and are used in very large quantities because of its low cost. They are important for construction and maintaining what is literally the framework of the buildings and infrastructure on which our society depends.
Aggregates are generally defined as being hard, granular, materials which are suitable for use either on their own or with the addition of cement, lime or a bituminous binder in construction. Essential applications include road stone, concrete, mortar, asphalt, railway ballast, drainage courses and bulk fill. European Standard (BS EN12620: 2002) defines aggregates as ‘granular material used in construction.
Due to the increasing expansion and construction of highway and other construction structures with diminishing natural aggregate resources in the world, the demand for crushed stone aggregates has increased as the years pass by. (Kahraman and Fener, 2007). Aggregates must conform to certain standards for optimum engineering use: they must be clean, hard, strong, durable, particles free of absorbed chemicals, coatings of clay, and other fine materials. Aggregates are normally described as fine and course. Coarse aggregates are greater than 4.75um whereas fine aggregates are less than 4.75mm.
Aggregate used in the surface course (running surface) of roads must be resistant to the polishing action of vehicle tyres, otherwise, the road can become slippery, especially when wet. It is important that aggregates used for construction purposes must be strong, suitable and durable. The characteristics of aggregates suitable for constructions are assessed through the following tests: strength, water absorption, abrasion resistance, shape tests, specific gravity, sound tests and resistance to weathering. (Ndukauba Egesi et al, 2012.). By assessing aggregates in terms of its physical, mechanical and mineralogical properties, its suitability for use in a given type of construction can be determined. Understanding the mechanical properties of rock aggregates is vital in the performance of rock aggregates. Mechanical tests on the parent rock can give suggestions of the probable mechanical properties of the aggregates since rock aggregates are usually obtained from the bedrock. (SGU Project Report, 2005). Most qualifications for aggregates require the material to be strong. (Al-Harthi, 2001; Ugur et al., 2010). Aggregates used must be tough and abrasion resistant to prevent crushing, degradation, and disintegration when stockpiled, fed through an asphalt plant, placed with a paver, compacted with rollers, and subjected to traffic loadings. Aggregates, which do not have the adequate toughness and abrasion resistance, may cause construction and performance problems (Wu et al., 1998). Most of the road aggregates are prepared from natural rock and slags derived from the metallurgical process (steel plants). (Vinod.B.R). Aggregates can further be classified according to production methods, petrological characteristics, particle size and unit weight.
The properties that make rocks suitable as an aggregate are dependent on the availability, workability, suitability as aggregates, affinity for binding materials (cements, bitumen or asphalt), binding properties and the ability to resist alternating climatic (wet and dry) conditions of its environment (Rangwala et.al., 2008; Kutu et.al., 2014).
Recent studies show that the mineral composition and grain-size distribution are generally key parameters in accessing the mechanical properties of aggregates but the roles of other textural features like mineral grain-shape, the geometry of grain boundaries, and orientation of grains also have a role to play. Studies by Akseli and Leinonen (2015) shows that the mechanical properties of aggregates clearly correlate with their geological characteristics.
Aggregate has three properties, which are the physical properties, mechanical properties, and chemical properties.
1.2 PROBLEM STATEMENT
From the beginning of creation, transportation, especially by road has been a key element in our human lives. Roads make a crucial contribution to economic development and growth and bring important social benefits. With regards to the growth and development of a nation, roads are of vital importance. In addition, providing access to employment, social, health and education services makes a road network crucial in fighting against poverty. Roads open up more areas and stimulate economic and social development. For those reasons, road infrastructure is the most important of all public assets and several kilometres of it have been built over the world. (http://www.worldhighways.com).
It has been estimated that the number of people killed in road traffic crashes each year is in excess of 1.1 million, while some 50 million or so are injured. Although road traffic injuries occur for a multitude of reasons, the condition of the road surface is an important factor in preventing crashes. Also, most newly roads under construction fail before they are commissioned and this is because the geologic features and the mechanical properties of the road aggregates are not properly studied before the construction. Aggregates form the major components of road pavement and their properties affect the durability of the road.
1.3 AIM AND OBJECTIVE OF STUDY
The main objective of this project is to examine the effect of aggregate types, content, and sizes for road construction. The research aim is to evaluate the strength and durability of roads produced from differing nominal sizes and types of aggregates from different quarries. Similarly, this project tries to find the influence of the mineral composition of aggregates on road pavements. In addition, the research is also geared to compare aggregates from different quarries and make recommendations based on their geological, physical and mechanical properties for construction purposes.
1.4 STUDY AREAS
Samples for this project were collected from Eastern Quarry and Biglebb’s Quarry in Shai hills, Sarcom Quarry in Budumburam, Ghacem Quarry in Oterkpaulu and Dorwenya. Shai-Akuse district is in South-eastern Ghana and forms part of the Dahomeyide Orogoneic terrane in West Africa. Budumburam is in the Gomoa East District which forms part of the Birimian rocks and Oterkpaulu is in the Yilo Krobo District which also forms part of the Voltaian Basin in Ghana.
1.4.1 SHAI HILLS
The Shai Hills area is located in the Dangme West District of the Greater Accra Region Ghana. It is bounded by the coordinates (0o01’E, 5o 56′ N) (0o 06’E, 5o 56’N), (0o 01’E, 5o 50’N) and (0o, 06’E, 5o 50’N). It is within the field sheet number 0500A1. It has an approximate area of about 60km2. The Shai Hills area is a hub of several stone quarries which generate huge revenue for Ghana through taxes.
The study area can be accessed by road through the Tema – Akosombo highway. Notable towns are Dzopaanya, Dedenya, Mampong and Kissehkope and surrounding areas. The Tema to Ho road is a first class road which passes through the study area at the Southwestern corner through the study area to the northeastern part. It has also other roads footpaths leading to various villages in the study area. Through the footpaths and roads, the field mapping exercise was successful.
188.8.131.52 Physical Features
The study area is a SW-NE trending range of hills and inselbergs which are the most obvious physical feature on the base map. The Shai Hills vary in width from 65 to 95 km. Waterways and dams are also conspicuous physical features in the area. The waterways flow in the valleys between the rocks and join others to form dams.
The study falls within the wet semi equatorial climatic region (Dickson and Benneh, 1988). The mean annual rainfall is between 125 and 200 cm. The rainfall pattern of the study area is of a double maxima type where two rainy seasons occur in a year. The first rainy season is from May to June and the second rainy season is from September to October. Heaviest rainfall mainly occurs in June. The mean annual temperature is 26.6oC (Dickson and Benneh, 1988). Average relative humidity is about (75-80%) during the two rainy seasons and the lowest (70-80%) during the rest of the year (Dickson and Benneh, 1988).
The area of study has a low cover of vegetation cover but due to the Shai Hills forest reserve there is a quiet dense forest which is kept as a resource. The areas east of the Shai Hills and the north eastern part of the field of study have very low and thin vegetation which could be due to clayey nature of soil and are referred to as the lowlands. Some of the highland areas have thick and impenetrable vegetation. Vegetation, where it is present, forms an important part of the physical environment and helps greatly in the definition of the recourses and character of the area (Dickson and Benneh, 1988). The forest areas are mainly highlands and exhibit semi deciduous forest type during the long dry season from November to March. The lowland is mainly the Guinea savannah (Dickson and Benneh, 1988). They are covered by low bushes and open grassland (Dickson and Benneh, 1988). The principal soil is the forest ochrosols at the highlands. A soil that is highly coloured soil from highly weathered parent mafic or felsic materials. The soil at the lowlands is the lateritic sandy soil. The nature of the soils impedes downward drainage and causes waterlogging during the wet season (Dickson and Benneh, 1988). These hills are poorly covered with soil, and their slopes are mostly covered with gneiss debris. The area is covered with dark brownish-black silt and clayey soil (Mani, 1977).
The area has a relief system with the highlands running gently into the lowlands. Some of the low areas are wide valleys which are characterized by waterways and dams. The highlands run as stretches of hills from the NE-SW with the highest peak around 290m above sea level. The highlands mostly occur as ridges and a few isolated hills. They mostly consist of gneissic rocks. The lowlands on the other hand occur just east of the area of study then downwards towards the south with the lowest altitude around 50m above sea level. The lowlands have relatively flat topography with quite a number of waterways running across in different directions but most of them are dried up.
184.108.40.206 Settlement, Population and Occupation
The study area is sparsely populated when compared to urban cities. Major towns and communities include Doryumu, Dzopaanya, Dedenya and Mampong. The people of these communities speak the Krobo language and Ga-Adangme. There also some Fulanis herdsmen who live in the study areas with a main occupation of cattle farming. The people in the semi-urban areas live in modern semi-detached homes while the people in the smaller communities live in mud houses and wooden buildings. The major occupations of the people in these communities are farming, cattle rearing and trading. Stone quarrying is also an occupation of the inhabitants.
The breakup of the Rodinia supercontinent resulted in the Pan-African (Neoproterozoic) orogens and encompasses the long Trans-Saharan orogeny is interpreted to have resulted in the assembly of the NW Gondwana from different cratonic fragments. (Hoffman1991; Cordanietal.2003). In the south eastern part of Ghana and the adjoining parts of Togo and Benin, the southeastern segment of the Trans-Saharan belt is exposed and comprises the Dahomeyide orogeny.
The principle tectonic elements of the Dahomeyide orogeny are (i) the deformed edge of the WAC with its cover rocks consisting of craton-verging nappes and thrust sheets bounded by ductile shear zones (ii) the suture zone representing the eastern boundary of the autochthonous WAC (iii) exotic rocks that form the granitoids gneiss complexes east of the suture zone. (Nude & Attoh 2008; and references therein).
Granitic augen gneisses are mainly the rocks of the deformed edge of the WAC and are referred to as the Ho Gneiss. They are overthrust by rocks of the suture zone comprising of high-pressure mafic granulites and eclogites represented by the Shai Hills Gneiss unit (Attoh,1998; Attoh et al. 2007; and references therein).
The Shai Osudoku District (formerly Dangme West) is situated in the Southeastern part of Ghana, lying between latitude 5°45′ and 6°05′ North and longitude 0°05′ and 0°20′ West (Dangme West District, 2014). Dodowa is the Administrative Capital of the district. Oyibi is located 40 km from Accra off the Adenta-Dodowa Highway within the Dangme West District with a projected population of about 1,568 (Tema Municipal Assembly, 2008). The geographical coordinates of Oyibi are 5°49′ North and 0°07′ West (Mapland, 2015).