Materials of Construction
Materials of Construction CE 332
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This 4 page Class Notes was uploaded by Jermain Lindgren on Thursday October 15, 2015. The Class Notes belongs to CE 332 at North Carolina State University taught by P. Khosla in Fall. Since its upload, it has received 181 views. For similar materials see /class/223737/ce-332-north-carolina-state-university in Civil Engineering at North Carolina State University.
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Date Created: 10/15/15
CE 332 Materials of Construction Solution to Homework Problem Set A1 Problem 1 What is the difference between tar and asphalt cement Solution Tar is a product of destruction distillation of organic materials such as wood7 coaland sugar and is odorous Tar is not a good material for paving Asphalt also referred to as asphalt binder or asphalt cement7 which is the binder material that holds the aggregates together7 is obtained from fractional distillation of crude petroleum Tar is much more temperature sensitive than asphalt Problem 2 List some uses of asphalt other than paving Solution Uses of asphalt7 other than paving of roads include o Waterproo ng 0 Roo ng felt for shingles 0 Roll roo ng o Pipeline coating 0 Base for paint 0 Insulator for electrical wiring Problem 3 Brie y discuss the chemical composition of asphalt cement Solution About 90 to 95 percent of asphalt by weight is composed of carbon and hydrogen called a hydrocarbon The remaining portion consists of two types of atoms heteroatoms nitrogen7 oxygen7 sulfur and metals Heteroatoms often replace carbon atoms in the asphalt molecular structure These contribute to many of asphalt7s unique chemical and physical properties by causing much of the interaction between molecules The type and amount of heteroatoms that exist in asphalt are a function of both the crude source and its exposure to aging Heteroatoms7 especially sulfur7 react more easily than carbon and hydrogen to incorporate oxygen oxidize Oxidation is the primary part of the overall asphalt aging process evaporation volitization and degradation associated with light photo degradation also contribute Metal atoms7 such as vanadium7 nickel7 and iron7 are present in trace quantities7 typically far less than one percent The main signi cance of the metal atoms is that these can provide some indication of the asphalt7s crude source Problem 4 Discuss the effect of aging that occurs in asphalt cement during mixing with aggregates and in service How can the short term aging of asphalt cement be simulated in the laboratory Solution Aging makes asphalt stiffer and much more susceptible to cracking When the hot asphalt binder is mixed with the hot aggregates7 the asphalt cement exists in thin lms covering the aggregate and the mixture is maintained at elevated temperatures for a long period of time This allows oxidation to take place at a faster rate Oxidation results in a more brittle asphalt mix oxidation hardening The Rolling Thin Film Oven RTFO test simulates this in a laboratory Problem 5 What is the signi cance of each of these tests a Flash point test b RTFO procedure c Rotational viscometer d Dynamic Shear Rheometer test e Solubility test Solution a Flash Point Test Indicates the temperature to which the binder material may be heated without danger of instantaneous ash in the presence of an open ame The ash point is well below the re point the temperature at which the asphalt will actually burn b Rolling Thin Film Oven RTFO Procedure Tests short term aging hardening Firstly7 provides an aged binder that can be used for further testing of physical properties Determines the mass quantity of volatiles lost from the asphalt during the process c Rotational Viscometer Used to determine the ow characteristics of the asphalt binder by measuring its viscosity7 which in turn is used to determine the temperature range within which it can be pumped and handled at the hot mixing facility d Dynamic Shear Rheometer Determines rheological properties at intermediate tem peratures to determine binder resistance to fatigue cracking and high temperatures to determine binder resistance to permanent deformation or rutting Parameters include G and 6 e Solubility Test Measures the purity77 of the asphalt cement Problem 6 Show how various Superpave tests used to characterize the asphalt binder are related to pavement performance Solution Test Method Performance Rotational Viscometer Handling amp pumping Dynamic Shear Rheometer DSR Fatigue cracking7 Rutting Bending Beam Rheometer BBR Thermal cracking Direct Tension Tester DTT Thermal cracking Rolling Thin Film Oven RTFO Short term plant aging Pressure Aging Vessel PAV Long term p avement aging Problem 7 As a materials engineer working for a highway department7 what standard PC grade would you specify for each of the following conditions Fill in the following table Solution 50 Reliability 98 Reliability Seven day maximum Mean 50 52 58 pavement temperature QC SD 4 One day minimum pavement Mean 12 12 18 temperature QC SD 3 PG Grade Superpave binder grade PG 52 16 PG 58 22 Problem 8 Sketch and label a typical asphalt concrete pavement section Solution Seal Coat applied on top of n t39 Asphalt Concrete SurfaceWearing Course 3 ace course Op Iona aver Tack Coat applied between two asphalt concrete layers Asphalt Concrete BinderIntermediate Course E Prime Coat applied between asphalt concrete and granular base Base Course Unbound GranularTreated Subbase Course Subgrade Figure 1 Typical Cross Section of Asphalt Concrete Pavement An asphalt concrete pavement may have some or all of the layers shown above However7 the most simple pavement structure consists of at least an asphalt concrete layer on top which serves as both surface and binder course base course and subgrade
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