USE OF BITUMEN IN COASTAL STRUCTURES

CETN-III-24

11/84

USE OF BITUMEN IN COASTAL STRUCTURES

PURPOSE:

To call attention to the use of bituminous mixtures in coastal

structures.

B A C K G R O U N D : Bitumen or asphaltic bitumen is produced by refining crude

petroleum oil. It is a durable cement with adhesive and waterproofing proper-

ties. It is also an elasto-plastic substance which imparts controllable

flexibility to mixtures of mineral aggregate with which it is usually

Asphaltic bitumen is chemically inert; therefore, it is

combined.

environmentally

inoffensive.

TYPE OF BITUMINOUS MIXTURES:

The three general categories of bituminous

mixtures used in coastal structures are:

(1) Asphalt Concrete - This type of mixture is similar to asphalt con-

crete for roadway paving.

The bitumen content is designed to be equal to the

void volume of the fine and coarse aggregates to ensure an essentially

voidless mix after compaction. Its mechanical properties are determined by

both the bitumen and the mineral skeleton, while the permeability is governed

by the efficiency of compaction. In most cases, the asphalt concrete for

coastal works is applied on slopes such as the lining of dikes or revet-

m e n t s . Special attention has to be paid to the stability of the mixture as

well as the stability of the subsoil or sublayer.

Slopes steeper than 1:1.7

(vertical:horizontal) are not recommended.

A modified asphalt concrete, called stone asphalt, produced with a

higher content of coarse aggregates, was developed for application to break-

waters in the open sea. The two-stage mixing procedure for this material,

discussed by van Garderen and Mulbers (1983), requires special mixing

equipment.

U. S. Army Engineer

Waterways Experiment Station, Coastal Engineering Research Center

P. 0. Box 631, Vicksburg, Mississippi 39180