Lecture Asphalt -Students 1 PDF

2022‐03‐16 CIVI321 ENGINEERING MATERIALS Asphalt CEMENT A.M. Soliman, PhD, P.Eng Associate Professor Department of Building, Civil & Environmental Engineering (BCEE) 1 Asphalt History Asphalt materials have been used since 3500 BC. Waterproofing: boats, vessels for carrying liquids. Basket boats Bas...

2022‐03‐16 CIVI321 ENGINEERING MATERIALS Asphalt CEMENT A.M. Soliman, PhD, P.Eng Associate Professor Department of Building, Civil & Environmental Engineering (BCEE) 1 Asphalt History Asphalt materials have been used since 3500 BC. Waterproofing: boats, vessels for carrying liquids. Basket boats Basket was waterproofed inside and out with asphalt Egyptians used the Asphalt as adhesive mortar for rocks along the banks of the Nile to prevent erosion 2 1 2022‐03‐16 Asphalt History 625 B.C. The first recorded use of asphalt as a road‐building material in Babylon. The word asphalt comes from the Greek "asphaltos," meaning "secure." 3 Asphalt History Pavement on French Highway 1852 ‐ French Highway: 1st modern natural asphalt pavement Asphalt roads come to America 1870 1870 ‐ 1st hot mix pavement (with tar binder) placed in US Edward J. de Smedt (Sheet Asphalt Pavement) 4 2 2022‐03‐16 Definition Asphalt cement: A viscous cementitious material composed primarily of high molecular weight hydrocarbons. Asphalt Cement Asphalt Concrete: Asphalt Concrete A complex material consisting of asphalt cement, mineral aggregates, and possibly some admixtures. 5 Asphalt cement Sources and Properties Asphalt cement is a bituminous material. Bitumen occurs: Naturally: as rock asphalt (sandstone and limestone deposits filled with 6‐20% bitumen, e.g. in Switzerland, France, Italy, California, Texas, etc.), and lake asphalt (e.g. In Trinidad: 40% bitumen mixed with silt and clay, in Venezuela: 65% bitumen). Rock asphalt Trinidad Lake Asphalt 6 3 2022‐03‐16 Industrially: The leftover obtained when lighter constituents of crude oil are distilled away during refining. 7 Most petroleum asphalt (75‐80%) is asphalt cement used in road construction and paving purposes. The reminder is being used by the roofing industry or in the manufacture of linings, sealants, insulation, etc. 8 4 2022‐03‐16 Properties of Asphalt cement  Asphalt cement is waterproof and has the ability to adhere to solid particles such as aggregates, which makes it ideal for the construction of pavements.  Asphalt cement is a Viscoelastic materials that depending on temperature can be either solid or liquid. 9 Melting Dissolving Emulsifying 10 5 2022‐03‐16 Asphalt cements can be made temporarily fluid (liquefied) for construction operations by: i. Melting: i.e. heating above 140C. After construction, the material cools down to a visco‐elastic solid. This is the hot‐mix construction method. 11 ii. Dissolving: in selected petroleum solvents. This process is called Cutting back. The diluted asphalt is called cutback asphalt. This material is mixed with aggregates to form “cold‐mixed asphalt”. Hardening occurs as the solvents evaporate and secondary bonds are reformed in the asphalt cement. 12 6 2022‐03‐16 Type Base Asphalt Cement Solvent Slow‐ curing Low Viscosity /high penetration Diesel fuel Medium ‐curing Medium viscosity /medium penetration Kerosene Rapid‐ curing High viscosity/low penetration Naphtha gasoline 13 Types and applications of Cutback Asphalts Type Base Asphalt Cement Solvent Solvent Content [% vol.] Application Slow curing Low Viscosity /high penetration Diesel fuel 0‐50 Cold‐laid pavement bases Medium curing Medium viscosity /medium penetration Kerosene 15‐45 Cold‐pavement bases Rapid curing High viscosity/low penetration Naphtha gasoline 15‐45 Mixed in place pavements Mixed in place pavements Cold‐laid pavement bases Cold‐pavement bases 14 7 2022‐03‐16 iii. Emulsifying: or dispersing the asphalt cement in water (12‐15% water). Asphalt and water ordinarily do not mix but emulsifying agents such as soaps, fine clay, etc. make them mixable. The resulting product is a fluid called emulsified asphalt. After construction, water evaporates and asphalt particles recombine into a continuous film that cements aggregates together. Water + Soap Asphalt Binder 15 Melting Dissolving Emulsifying Heating above 140C Petroleum solvents Emulsifying agents + Water 16 8 2022‐03‐16 Asphalt cement Chemical Composition Asphalt cements have a very complex and variable chemical composition depending on source They are mainly made of high‐molecular weight hydrocarbons. General chemical formula: CnH2n+bXd Where: n: range from 25 to 150 d: typically a small coefficient b: a coefficient that may be negative X: represents elements such as sulphur, Nitrogen, oxygen, trace metals, etc. 17 Typical composition of asphalt cements Carbon 80‐87% Nitrogen 0‐1% Hydrogen 9‐11% Sulphur 0.5‐7% Oxygen 2‐8% Trace metals 0‐0.5% Because of their complexity, a complete chemical analysis of asphalt cements is very difficult. Therefore, specifications for asphalt cements are currently based only on their physical and rheological properties. 18 9 2022‐03‐16 Asphalt Cement Physical Structures Asphalt cement composition influence its binder behaviour and performance of asphalt concrete. Phase Component Contribution 1 2 Dispersion Oil Viscosity and fluidity Dispersed Asphaltene Strength and stiffness 3 Interfacial Resin Adhesion and ductility Asphaltene Resins Fluid when heated, brittle when cold 19 resins The oil acts as a solvent for the resins 20 10 2022‐03‐16 Asphaltenes The Resin acts as a solvent for the Asphaltenes 21 As temperature increases: Asphaltenes become more soluble in the Resins, which in turn become more soluble in the Oils the material becomes less viscous. If the temperature decreases: Asphaltenes become less soluble, form micelles, and the material becomes more viscous. 22 11 2022‐03‐16 Asphalt Cement Viscosity Viscosity ()= Resistance to flow A fundamental property relating the rate of shear strain (d/dt) to the applied shear stress (). [in Poise (1P = 1 x 10‐1 Pascal.sec)] Water  = 1 x 10‐3 Pa.s Asphalt Vs.  = 105 to 107 at service temp. = 1(when heated) 23 Asphalt cement is a thermoplastic material, i.e. its properties are very sensitive to temperature. The glass transition temperature (Tg) 24 12 2022‐03‐16 The viscosity of asphalt cements is very sensitive to temperature:  T>140 °C Newtonian fluid The slope is the viscosity Newtonian fluid ‐ linear relationship between shear stress and shear strain rate at a given T.  T