Abstract
This research focuses on accessing the suitability of specific igneous rocks for their potential use as aggregates in road pavement layers. During the current research, several quality control tests were carried out on andesite and dacite rocks, obtained from the areas of Methana and Agioi Theodoroi, approximately 60 Km West of Athens, Greece. The quality control tests were conducted under the specific guidelines of Hellenic Technical Specifications (ELOT) for aggregate properties determination, while the procedure focused on the estimation of the following parameters:
1. Geometrical properties (grain size analysis, flakiness index, and sand equivalent value)
2. Physical properties (apparent density and water absorption)
3. Mechanical properties (Micro - Deval index, Los Angeles Abrasion Value, Aggregate Impact Value)
The laboratory testing results led to the general conclusion that the most samples obtained from the andesite and dacite rocks cannot be used as aggregates in road pavement layers, due to their high Los Angeles Abrasion Values (LAAV). High values of LAAV represent a low strength in mechanical corrosion and crush and contribute to the low quality of these geomaterials as aggregates. Some of the collected samples were determined as suitable for use in subbase road pavement layers, whereas some other samples were determined as suitable for use in base road pavement layers. Furthermore, correlations between the properties of the referred geomaterials were evaluated and empirical equations regarding the mechanical as well as their geometrical properties were established.
Keywords: Aggregates; Igneous rocks; LAAV; Pavement layers
Introduction
Aggregates are generally low cost classified natural materials, which are essential for the construction of infrastructure and buildings in urban areas [1] and are necessary for the preparation of concrete and mortars, in road pavement layers, road embankments, bituminous mixtures, track ballast, drainage and filter materials, and armour stones. At the same time, they are increasingly used in various environmental applications such as protection of soils from erosion, filters for water purification, the stability of natural and artificial slopes, and stabilization of landslides [2]. The role of road pavement layers is to receive loads from traffic and to distribute them back to the ground. The subbase layer protects the base layer from ‘infection’ from any soil material (clay, organic, etc.) and transfers loads safely to the subgrade. The base layer is the main layer of a road pavement, that receives and distributes traffic loads to the underlying layers and reduces the vertical compressive stresses which are loading the subgrade. Because of that, in road construction, the aggregate materials must be healthy and of high strength. Specifically, those used on the bituminous mixtures should have high strength and resistance to friction and impact, as well as a high polishing resistance index. Aggregate specifications are becoming increasingly stringent for materials used in the upper road pavement layers (bases), designed to support high-localized loading. The upper road pavement layers are also subject to greater influence from other external factors, such as atmospheric temperature [3]. In order to fulfill the above requirements, the quality control tests that were conducted in the examined aggregates focused on the estimation of their Geometrical, Physical and Mechanical properties.
Location of the Sampling Areas
The examined aggregates were sampled from the areas of Methana and Agioi Theodoroi, located in the northeastern part of Peloponnese, next to Athens, Greece (Figure 1). Methana is part of the northwest edge of the Aegean volcanic arc. The volcanic activity in Methana was strongly revived during the Middle Pleistocene with the most recent volcanic activity occurred in 230 BC, creating the basaltic andesite of Kammeni Chora. The biggest part of the peninsula is covered from igneous rocks such as andesites and dacites. Three lithological types were sampled from four different locations and a total of nine samples were finally collected. More specifically, sampling involved four samples of andesites, one sample of basaltic andesite and four samples of dacites (Figure 2). Agioi Theodoroi area is mainly covered by limestones, dolomites, serpentinites and peridotites, marls, flysch, and dacites Petrounias et al. [4]. From this area, samples were collected from two different locations and consisted of dacite rocks (Figure 3) (Figures 1,2,3).
Methods and Materials
Initially, block samples were collected from the outcrops of the referred geological formations (total block sample weight per site over 50kg) and were broken in the lab into smaller for further processing in the rock crusher. Then, with the help of the crusher and the appropriate setting, particles of 14 mm diameter or smaller were created. By using the appropriate sieves, the necessary quantity of the required material for each laboratory test was finally collected. Laboratory tests that were carried out in the sampling material focused mainly on:
1. Calculation of Water Absorption (Wa) and Apparent Density (ρa)
2. Particle shape test for the calculation of Flakiness Index (IF)
3. Sand Equivalent (SE) test for the determination of clay lumps
4. Los Angeles Abrasion test (LAAV)
5. Micro-Deval (MD) test
6. Aggregate Impact Value (AIV) test
7. Uniaxial Compressive Strength (UCS) test
Three of the most important tests conducted for aggregate quality control is the Los Angeles Abrasion test (LAAV), the Micro- Deval test and the Aggregate Impact Value (AIV) test, with their devices presented in Figure 4. The Los Angeles Abrasion Value is one of the most common test methods used to calculate aggregate toughness and abrasion characteristics and determination of aggregates resistance to fragmentation in dry conditions. The total sample mass was about 5000 g for each sample and after 500 revolutions in the device, the mass loss of aggregate was calculated. A lower numerical value of LAAV index indicates a more resistant material.
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