Chapter 3 BASE COURSE MINERAL AGGREGATE Sri Atmaja

Chapter 3 BASE COURSE MINERAL AGGREGATE Sri Atmaja P. Rosyidi

Definition Aggregate is the term used to describe rock used for road making and refers to an assembly of discrete particles (i. e. pieces of rock).

Introduction 1. Generally account for 30 percent of the cost of a pavement structure 2. By weight: 92 to 96 percent of asphalt concrete to 65 to 85 percent of portland cement concrete 3. Aggregate (definition) : Combination of sand, gravel, crushed stone or other material of mineral composition with a binding medium (water, bituminous, portland cement, lime, etc. ) to form materials such as asphalt concrete, portland cement concrete, etc. Aggregates may be natural or manufactured.

PARTICLE SHAPES o Gravel: naturally rounded particles smooth texture o Crushed stone: artificial crushing of rock - generally with rough texture

The following definitions are from AASTHO M 146 (Terms Relating to Subgrade, Soil. Aggregate, and Fill Materials): o o o o Soil-Aggregate (Dense-Graded Aggregate): Natural or prepared mixtures consisting predominately of stone, gravel or sand containing silt-clay (minus 75 µm) material. Binder (Soil Binder): Portion of soil passing a 425 µm sieve. Stone: Crushed or naturally angular particles of rock which will pass a 75 mm sieve and be retained on a 2. 00 mm sieve. Gravel: Rounded particles of rock which will pass a 75 mm sieve and be retained on a 2. 00 mm sieve. Sand: Granular material resulting from the disintegration, grinding, or crushing of rock and which will pass the 2. 00 mm sieve and be retained on the 75 µm sieve. Silt-Clay: Fine soil particles which will pass the 75 µm sieve. Silt Fraction: Material passing the 75 µm and larger than 0. 002 mm. Clay Fraction: Material smaller than 0. 002 mm.

Additional definitions from AASHTO M 147 (Materials for Aggregate and Soil-Aggregate Subbase, Base and Surface Courses): o Coarse Aggregate: Aggregate retained on the 2. 00 mm sieve and consisting of hard, durable particles or fragments of stone, gravel or slag. A wear requirement (AASHTO T 96) is normally required. o Fine Aggregate: Aggregate passing the 2. 00 mm sieve and consisting of natural or crushed sand, and fine material particles passing the 75 µm. The fraction passing the 75 µm sieve shall not be greater than two -thirds of the fraction passing the 425 µm sieve. The portion passing the 425 µm sieve shall have a LL 25 and a PI 6. Fine aggregate shall be free from vegetable matter and lumps or balls of clay.

Principal Aggregate Sources o Igneous Rock (exp. adamellite, andesite, basalt, brecia, diorite, dolerite, granite, ect. ) Igneous rocks are largely cristalline and formed during the cooling of molten rock. They are usually composed of hard materials and the interlocking fine-grained crystal structure combines to product strong, hard rock at least in the fresh state.

Principal Aggregate Sources o Sedimentary Rocks (exp. alluvial (water-based), gravels, claystone, conglomerates, limestone, mudstone, sandstone, shale, siltstone) Sedimentary rocks are formed from (i) water deposition of granular soil, (ii) air deposition of fine the granular soil, (iii) deposition of organic remains of plants and animals, (iv) crystallisation of soluble materials from solution. Sedimentary rocks are usually mechanically weak and can be ripped and grid roller. They are not widely used in rock making as typically prone to abrasion and erosion and moisture sensitive and of suspect durability.

Principal Aggregate Sources o Metamorphosed Rock (i. e. argilite, gneiss, greenstone, hornfels, phyllite, quartz, slate, etc. ) These are rocks of igneous and sedimentary rock that have been subjected to heat and/or pressure of such magnitude that new materials and textures are formed. Although metamorphic rocks are widespread, they are little used in rock making because may often be closely fractures or jointed.

Principal Aggregate Sources o Organic Rock (i. e. coral, limestone (sedimentary rock), seashell) Coral has been used successfully for road making. Coral is composed of aragonite, calcite, and dolomite. Coral is widely used for pavement construction in the Pacific. Seashell has also been used for road making and some limestones are derived from prehistoric coral beds.

Principal Aggregate Sources o Artificial Rock flyash, slag) o Gravels (i. e. bottom ash, flue dust, (i. e. gravel, ironstone) Gravels are naturally-occurring particulate rocks that excellent fold making material. However, relatively poor gravels are the only road making materials available in some areas and therefore find use despite such problems as pro grading and shape and tendency to lose strength when wet.

Remainder Please for all of you that one of the classes after mid term exam will be arranged as a presentation class. Student should provide a project presentation regarding to the pavement construction method and related material testings. A submitted project is written in a power point (ppt) with maximum slides of 10.

Discussion Session Please arrange some groups in 4 – 5 person for per group. Discuss about the physical and mechanical characteristics of aggregate that are need in order to control the quality of aggregate. You have 30 minutes left for discussion.