dams with impervious membrane of asphalt concrete - Balwois

DAMS WITH IMPERVIOUS MEMBRANE OF ASPHALT CONCRETE 

Kusari Laura 1 , Ahmedi Figene 2 

1. Msc. of Civil Engineering, University of Prishtina, Technical Faculty, p.n., 

+381 38 554 899/103, Kosovo, 

Email: laurakusari@yahoo.com 

2. Msc. of Civil Engineering, University of Prishtina, Technical Faculty, p.n., 

+381 38 554 899/103, Kosovo, 

Email: figene_ahmedi@yahoo.com 

ABSTRACT 

Even though the earth dams have been constructed since the earliest times, it is the increase of our ability 

to build safer and economical structures, which makes those dams even more acceptable. The earth 

dams can be constructed with impervious membranes of manufactured materials such as concrete, steel 

and asphalt concrete. These dams are safer against shear failure than any other type of earth or rock fill 

dam. Consequently, for a given safety factor, the embankment slopes can be made steeper and the 

embankment volume smaller. Also they tend to be less costly and more easily and rapidly build up than 

the dams with earth core. 

In this paper, the focus is given on construction of impervious asphalt concrete membrane as well as 

some of its general advantages and disadvantages. Also, the circumstances favoring the use of upstream 

asphalt concrete membranes are given, in order to make easier the decision whether it can be used or 

not. Special attention is paid to the critical connection details, at the interfaces of membrane-plinth-cutoff. 

So, it can be concluded that dams with impervious membrane of asphalt concrete are concurrent to other 

types of dams, because of their easy and fast construction, and their lower costs. If the design and 

construction of those dams is based on favoring circumstances, than the dams with impervious 

membranes are acceptable and sustainable. 

KEY WORDS 

Bituminous concrete membranes, layers, plinth, dams. 

INTRODUCTION 

A bituminous concrete membrane as a water barrier for a dam is a competitive and cost-wise solution 

then the other conventional designs, like an earth core or other alternatives. According to the 32 nd bulletin 

of International Committee on Large Dams (ICOLD), there are about 332 dams constructed with 

bituminous concrete upstream membrane all over the world. Only in Italy, starting from the early 1959 

there are 38 dams constructed with bituminous membrane. According to the same sources, the recent 

dams with bituminous concrete membrane completed in Italy are: Menta Dam (1997), 90 m high and 

Chiauci Dam (1997), 78 m high. If compared the time of construction of these kinds of world’s dams with 

their height, we can see that there are great achievements as the height of dams is increasing every year. 

Bituminous concrete membranes are frequently used as water barriers on the upstream face of dams, 

thanks to some of their advantages. As early as 1300 BC, in Mesopotamia, according to Baron Van 

Asbeck, the oldest known dam Assur, was constructed with a kind of primitive bituminous concrete 

membrane. It is of a great importance, because it gives testimony of the antiquity of the design concept. 

BALWOIS 2008 - Ohrid, Republic of Macedonia - 27, 31 May 2008 1

As for the modern times, the construction using bituminous membranes starts in 1910 with Central Dam 

built in the United States. As time went by, since 1960, improvements have been mainly in the areas of 

construction equipment and construction practice, as well as improvements in some construction details, 

particularly connections to the plinth. In order to have a quite clear view on the asphalt concrete 

membranes used in dam construction, some general advantages and disadvantages will be listed first. 

GENERAL ADVANTAGES AND DISADVANTAGES OF IMPERVIOUS MEMBRANES 

OF ASPHALT CONCRETE 

The main advantage of a dam with upstream impervious membranes of asphalt concrete, is that it has a 

greater margin of safety against shear failure than any other type of earth or rock fill dam. With a suitable 

drain behind it, the impervious membrane of asphalt concrete prevents seepage from entering the 

embankment and so eliminates the reduction in the stability, which is associated with the development of 

seepage pore pressures. This way, the embankment strength is higher and the margin of safety against 

shear failure is increased for the upstream and the downstream slopes. Other advantages are that the 

membranes: 

• Cost less than either concrete or steel membranes, 

• Are more flexible, and thus are able to follow differential settlement without cracking, 

• Can be constructed simply and rapidly, 

• Under certain circumstances, the leaks which develop are self-sealing, 

• The parts above water level are easier to repair, than either concrete or steel, 

• Can serve a secondary function as wave protection, 

• Are not subject to progressive erosion under the action of water flowing through concentrated 

leaks. 

As for the disadvantages of impervious membranes of asphalt concrete, they are: 

• The maximum height of a dam build with asphalt-concrete membrane is limited, 

• The asphalt concrete changes its properties due to the temperature change. 

• If the asphalt concrete is exposed to the light and ultra-violet radiation, it is becoming older, which 

mean it starts loosing its properties as time goes by. 

However the two last properties can be changed (lowered), with the right choice of ingredients 

participating in asphalt concrete composition. 

CIRCUMSTANCES FAVORING THE USE OF UPSTREAM ASPHALT CONCRETE 

MEMBRANES 

At sites with the foundation of hard rock or other strong material, these dams can have a large cost 

advantage because the embankment can be designed with minimum volume. At such locations the dam 

with impervious membrane should always be considered. 

Where no impervious soil for an earth core exists within an economical distance, then a manufactured 

impervious membrane should be considered. This situation is common in high mountain country, where 

the little soil available often has a basically pervious nature. 

Where severe wave action is expected in the reservoir, and where rock for a rip rap blanket involves an 

exceptionally long distance, the cost of any type of suitable wave protection may approximate the cost of 

an impervious upstream membrane which could also serve as a wave protection. 

During wet weather it is not possible to accomplish much work with fine-grained soils. In circumstances 

where long rainy seasons exist or where the construction period is limited, a dam with an upstream 

membrane may be the most economical and satisfactory solution. 


Where the appurtenant structures are imbedded within or abutted against the embankment, their length 

and cost often are directly related to the width of the dam at the base. The most economical design for the 

whole structure may be obtained with an upstream impervious membrane which allows minimum base 

width. 

CONSTRUCTION OF IMPERVIOUS ASPHALT CONCRETE MEMBRANE 

When projecting and constructing the impervious membrane of asphalt concrete, except its impervious, 

basic conditions that need to be fulfilled are: 

• To be stable enough, not to flow through the slopes, due to high temperatures during construction 

and latter during exploitation, 

• To be elastic enough and resistant to cracks, due to low temperatures, 

• Even though the deformations may occur, not to change its basic function-impervious, 

• To be resistant on the mechanical damages of the dam, as well as on the freezing conditions. 

In order to reach the desired properties, it should be designed and constructed in a proper way. There are 

basically two types of design: 

• The double lining membrane, type A 

• The single lining membrane, type B. 

When constructing the double lining membrane, a drainage layer is between two impervious layers. Each 

layer can be built with different materials and different thickness, and laid in single or multiple courses. A 

binder layer (BN) is laid down and compacted. The next layer is well compacted impervious bituminous 

concrete layer (I). Than the drainage layer comes, made of a bituminous open graded aggregate mix 

(DR). And above the drainage layer, a second impervious bituminous concrete layer is laid and 

compacted (I).The finished surface is sealed usually with a bituminous mastic (S). 

During the construction of single lining membrane, the binder layer (BN) may be designed to act as a 

drainage layer (DR), as well as a foundation for the membrane. Sometimes, the binder layer is referred to 

as the base layer. 


Binder Layer (BN) 

Figure I.1. Types of impervious asphalt concrete membrane 

a) The double lining membrane b) The single lining membrane, 

Serves as a binding and leveling layer and foundation for the membrane. It is usually (4-10) cm thick and 

should be placed only after a bituminous emulsion or hot bitumen is sprayed on the dam’s surface as a 

tack coat. The functions of this layer are: 

• Fixing the impervious layer by a good link of a aggregate, 

• Transition between the bituminous concrete and the dam, in terms of deformability and 

permeability, 

• Leveling the irregularities of the dam’s surface, 

• Bearing the capacity for the proper placing and compaction of the impervious layer. 

Impervious Layer (I) 

The next layer is well compacted impervious bituminous concrete layer (6-8) cm thick, which must be 

watertight, stable and protected against stripping and aging. 

The water-tightness results from the aggregate gradation, the percentage of asphalt-cement used and the 

compaction of the mix. When the mix is compacted to a void content of 3 %, it is virtually impervious. The 

compaction much beyond this point will cause the instability of the mix. 

The stability is associated with the type and percentage of asphalt-cement binder and the voids content as 

affected by compaction. The hot mix must be sufficiently stable to be placed and compacted on the slope 

and then remain stable against creep at the service temperatures. 

Stripping is an important consideration due to the constant contact between the membrane and the 

reservoir. To prevent stripping, the asphalt cement content must be sufficiently high to coat all of the 

aggregate particles. 


The protection against aging is provided by the protective layer, in order to reflect the ultraviolet rays, to 

serve as a “sacrificial” layer. 

Drainage Layer (DR) 

The drainage layer (5 - 15) cm thick, is a porous bituminous mix, consisting of uniformly graded aggregate 

and about 3 % asphalt cement. The minimum aggregate size is normally selected in the range (5-8) mm. 

The bitumen content must be adjusted to the mix, but it is in a range (2-5) % by aggregate weight. This 

layer is placed in a single coarse, with low compaction effort. 

The drainage layer is often the seat of undesirable creep (due to the higher percentage of voids and the 

low compaction), that is transferred to the impervious layer. 

Seal Coat (S) 

This layer consists of a cold- applied bitumen-emulsion or hot applied bitumen mastic, which contents 

about 30 % bitumen, 70 % filler and fine sand, and sometimes fibers. It is essential because it delays 

ageing process. Ageing is a result of evaporation of the volatiles of the bitumen from the surface of the 

bituminous concrete, a process which hardens bitumen, makes it fragile and subject to cracking. 

If coats are placed too thick, usually develops slumping. This is the reason why hot mastic seal coats 

should not be thicker than about 2 mm, and it is preferred to be spread in two courses. To avoid the 

slumping of thicker seal coats, the most advanced technique spreader boxes are provided with “rise and 

fall” adjustment. 

An example of a dam with an upstream membrane of asphalt concrete is Cesima Dam. It is a rock-fill dam 

constructed during a time period (1981-1987), with a purpose of water storage for power generation. 

Figure I.4. The main section of Cesima Dam 


The body of a dam, as shown in the figure, consists of quarry run limestone, placed in layers and 

compacted by vibrating rollers. It is divided into two zones, the grading and permeability of which 

increases from upstream to downstream. 

As for the watertight membrane on the upstream face, it extends to the walls and the bottom of the whole 

reservoir. The membrane consists of a single layer (I) of dense-graded bituminous mix, 8 cm thick, which 

is spread over a binding layer (BN) of semi-open graded bituminous mix, 10 cm thick. The binding layer 

rests on a drainage layer (DR) of crushed stone. The system of pipes and drainage galleries makes it 

possible to check and measure any seepage throughout the membrane. 

The downstream face of the dam is lined with a layer of top soil, placed inside appropriate prefabricated 

works. 

As we can see from this example, opposite from the two types of the design that we mentioned earlier, 

there are many other possibilities to arrange the layers. The Cesima Dam is just a case and not the only 

one when layers are spread in a different way. 

SPECIAL DESIGN CONSIDERATIONS 

In order to improve the asphalt concrete dam’s safety, the following advices are: 

• To control time after time the differential response to load along the membrane. 

• To improve the ability of the system to yield or deform without cracking. 

• To minimize the consequences of failures. 

• Regular inspection of the system. 

• To have an access for repairs and rehabilitation. 

• To increase the durability of the outer impervious layer of the membrane. 

Special attention must be paid to the critical connection details, at the interfaces of membrane-plinthcutoff, 

in order to prevent or minimize seepage. 

CONCLUSION 

Earlier, as an disadvantage of a dam with impervious membrane of asphalt-concrete was mentioned their 

height, nowadays this is no longer a problem. Since the height of those types of dams has started to rise, 

we can suggest their use, especially in the cases as followed: 

• Where the foundation for a dam consists of strong rock and where is an ample supply of strong 

granular embankment construction material. 

• Where no impervious soil for an earth core exists within an economical distance. 

• Where severe wave action is expected in the reservoir and where rock for a rip rap blanket 

involves an exceptionally long distance. 

• If the cost of appurtenant structures is considerable, the most economical design for the whole 

structure may be achieved with an upstream impervious membrane. 

• In circumstances where long rainy seasons exist or where the construction period is limited. 

Therefore, it can be concluded that earth and rock fill dams with asphalt concrete membrane are 

concurrent with other types of dams, because they are easily and faster build and are more economical. If 

the design and construction of those dams is based on the favorising circumstances, than dams with 

impervious membrane of asphalt concrete are sustainable. 


REFERENCES 

1. Patrick J. Creegan & Carl L. Monismith, “Asphalt-Concrete Water Barriers for Embankment Dams”, 

Published by American Society of Civil Engineers. 

2. Bulletin 32a. ”Bituminous Concrete Membranes for Earth and Rock fill Dams”. International 

Commission on Large Dams, ICOLD, 1982. 

3. Bulletin 84. “Bituminous Cores for Fill Dams”. International Commission on Large Dams, ICOLD, 

1992. 

4. James L. Sherard, Richard J. Woodword, Stanley F. Giziensky, William A. Clevenger, “Earth and 

Earth-Rock Dams, Engineering Problems and Design, 1963. 

5. “Embankment Dams with Bituminous Facing”, Review and Recommendations. International 

Commission on Large Dams, ICOLD, 1998. 

6. The Italian Commission on Large Dams, “Dams in Italy”, Firenze 1997.

dams with impervious membrane of asphalt concrete - Balwois

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