The Use of Burnt Earth
(clay) in Guyana`s Road
Construction Programme
Presenters:
Cecil Morrison
and Lawrence Mentis
Analytical Chemist
Civil Engineer
Consultant
Head of Force Account Unit
Serum Institute
Ministry of Public Works
Uses and Perception of Burnt Earth
(clay)
Introduction
Burnt earth can be readily processed on the coast of Guyana ,
preferably in areas where the soil (clay) has a high percentage
of salt. It must be noted that burnt clay was the foundation
material of some of the inner city roads along with some
highways constructed during the early and latter parts of the
20th century. However, in recent time, burnt earth has been
regarded as old fashioned and replaced by mainly crusher run. This study is made up of photographs of usage,
analytical tests results (compare/contrast with crush-run),
engineering and mathematical model showing aggregate
size/ distribution of burnt earth vs. crush-run, socioeconomic
implications, and perception on barriers on the use of burnt
earth for road construction as a surface and sub-base
material.
Perception
The use of burnt earth (clay) in the construction of roadways
has diminished mainly due to the perceived old fashioned
methodology used in its production and lack of knowledge of
its properties. With the advent of new technology in the
quarry industry, the demand for burnt earth (clay) plummeted
as a result of the main stakeholders educating their customers
about the product(crusher – run). Further, the process by
which crusher- run is derived is geological in nature compared
with burnt earth (clay) which is man-made; hence the buy-in
for the extensive use of crusher-run.
However, based on the study conducted burnt earth (clay) has
proven to be comparable with crusher-run and in some cases
more suitable as a surface material due to aggregate and cost
factor.
The Findings
The Findings revealed that the key factor
inhibiting the use of burnt clay for road
construction is low material demand due to a
lack of knowledge. The findings provide a
platform for stakeholders to address the barriers
and thus enabling the extensive use of burnt
clay/earth in road construction.
Historical Perspective
Historically, burnt earth (clay) has played a major
role in the advancement of civilisation in the area of
art and other aspects of human development which
include but not limited to making cooking utensils
and blocks used for building construction.
Locally, burnt earth was widely used in the 1940s
and 50s mainly as surface material for low volume
roadways. This continued until about the 1980s
where it was used in the construction of NDC
roadways as well as in the maintenance of Guysuco
and MMA all weather roads.
Socioeconomic Impact
Undoubtedly investment in the production of burnt
earth (clay) would pay dividends to Guyana`s
economy and by extension the society at large.
The raw materials are easily accessible since they
are ( with the exception of gasoline) a part of the
country`s geographical structure. The process
requires unskilled labour which would create jobs
and increase the spending power of family units.
Raw Materials
The raw materials required in the production of burnt earth (clay) :
• Wood (Courida logs)- these are the foundation for the heap and
are stacked in a particular way;
• Earth (clay)- Clay is the most important raw material used for
processing burnt earth. Clay is the common name for earthy
materials that become plastic when wet. Chemically, clays are
hydrous aluminum silicates usually containing small amounts of
impurities such as potassium, sodium, calcium, magnesium, or iron.
One of the common process of clay formation is the chemical
decomposition of feldspar. Essentially clay consist
of
interconnected silicates combined with a second sheet like grouping
of metallic atoms, oxygen and hydroxyl, forming a two layer mineral
such as kaolinite.
Raw materials cont`d
• Earth (Clay) cont`d
Properties of clay minerals are plasticity, shrinkage under firing and
air drying, fineness of grain, color after firing, hardness, cohesion,
and capacity of the surface to take decoration. Generally, clay
particles are smaller than 0.004 mm.
Classes of clay:
 Residual clay
 Transported clay
Groups of clay:
 Koalinite – are held together by fairly weak bonds
 Illite – strong bonding, presence of potassium
 Montmorillonite – presence of calcium and sodium
+ + + + + +
-
-
-
-
-
-
Raw Materials Cont`d
• Gasoline – the fuel used to light the mound.
Gasoline is refined from crude oil. The generally accepted
origin of crude oil is from plant and animal life from 100
to 600 million years ago. “Anaerobic digestion” of
vegetable matter by bacteria, decomposing through heat
and pressure .The result is the molecular structure of
petroleum hydrocarbons and other compounds present
in fossil fuels can be linked to the leaf waxes and other
plant molecules of marine and terrestrial plants believed
to exist during that era.
Raw Materials cont`d
Gasoline cont`d:
Some properties of gasoline:
 It has a flash point of about -50° F (-65° C). Flash point is the
temperature needed to produce sufficient vapour for
combustion if an open ignition source is brought into
contact with the vapour – i.e. an open flame or spark.
 The minimum auto-ignition temperature is about 495° F
but usually it is between 232° C and 280°C.
 The flammability range of gasoline is between 1.4 and
7.6%. If the ratio of gasoline to air is less than 1.4%, by
volume, then the mixture is “too thin or lean” to burn.
Processing
The production of the burnt earth(clay) takes approx.
three (3) weeks. Courida logs is used as the foundation
material for the heap (mound).The logs are approx. 3-4
feet in length and are packed joining each other length
wise. Large quantities of ploughed earth (clay) are packed
onto the logs which is then set alight using gasoline and
burns for three to five days. As many as two to three
mounds can be operated simultaneously.
After this period of burning all that remains is the hard
lumpy red brick, ready for use as road building materials.
Diagram of a Heap (mound)
• Process Flow
Burnt
Earth
Acquire
Wood
(Courida)
Plough
clay
Heap
(Mound)
Add clay
Pack Wood
Low Volume Road Design
Lawrence Mentis
Civil Engineer
Head of Force Account Unit
Ministry of Public Works
What is a low volume road?
• This presentation covers the design of lowvolume roads for flexible pavement surface with
the addition of burnt earth as a base material.
The information is applicable to rural roads
• A low volume road is commonly defined as a road
that has an average daily traffic (ADT) of less than
400 vehicles per day, and usually has design
speeds of less than 80 kmph (50 mph).
Why a burnt earth designed road?
• The objectives of the use of burnt earth designed
road are to accomplish the following:
•
•
•
•
Produce a safe,
Cost effective,
Environmentally friendly,
Practical road design that is supported by and
meets the needs of the users;
Design Characteristics
• Parameters of the design requirements or characteristics of
the design
• The maximum number of heavy vehicles over the design life
in the design lane considered for low-volume pavement
design is limited to 750,000 a year. Heavy vehicles which
include buses, single-units (with six or more tires), and multitrailer trucks. This level represents approximately 70 trucks
and/or buses per day in the initial year that grows 4%
compounded annually over 20 years.
• The range of Structural Number (SN) values for each condition
is based on a specific range of 18-kip ESAL applications at each
traffic level.
Design Characteristics – Structural Number
• What is the Structural Number in Pavement Design?
• In designing and building pavements, we sometimes
casually assume that making a pavement thicker also
makes it stronger, but even to the extent this is true,
how thick is thick enough? One of the key questions in
the structural design of an asphalt pavement is how
thick each layer of the structure should be. During
design, these thicknesses are related to the Structural
Number (SN), which is an abstract value that expresses
the structural strength of the overall pavement.
Design Characteristics – Structural Number
• Function of a Structural Number
• Formal pavement design relies on engineering
calculations based on established design equations,
such as the empirical equations found in the 1993
AASHTO Guide for Design of Pavement Structures. A
critical element of the flexible pavement equation is
the Structural Number, which represents the overall
structural requirement needed to sustain the traffic
loads anticipated in the design. The required Structural
Number depends on a combination of existing soil
support, total traffic loads, pavement serviceability,
and environmental conditions.
Design Characteristics – ESAL
• What is ESAL?
• ESAL is the acronym for Equivalent Single Axle
Load. ESAL is a concept developed from data
collected at the American Association of State
Highway Officials (AASHO) Road Test to
establish a damage relationship for comparing
the effects of axles carrying different loads.
The reference axle load is an 18,000-lb. single
axle with dual tires.
Results from using AASHTO 1993 for Burnt
Earth (CBR 53%)
Item
ESALs
SNreq
Burnt Earth
Thickness
AC Thickness
1
0.1x10^6
2.788
18 Inches
2 Inches
2
0.2x10^6
3.00
20 Inches
2 Inches
3
0.3x10^6
3.211
21 Inches
2 Inches
Results from using AASHTO 1993 for Crusher Run
(CBR 70%), White Sand/ Sand Clay (CBR 30%) and
White Sand (CBR 20%).
Item
ESALs
SNreq
CR Thickness
WS/SC
Thickness
WS Thickness AC Thickness
1
0.1x10^6
2.788
6 Inches
6 Inches
8 Inches
2 Inches
2
0.2x10^6
3.00
6 Inches
7Inches
9 Inches
2 Inches
3
0.3x10^6
3.211
6 Inches
8 Inches
9 Inches
2 Inches
Low Volume Roads Analysis
• Data from charts from Low Volume roads using
AASHTO 1993
•
•
•
•
•
•
•
Reliability = 75%
Standard Deviation = 0.45
Drainage condition = 1.0
Initial Serviceability = 3.5
Final Serviceability = 1.0
Design Serviceability Loss = 3.5-1.0 =2.5
Resilient Modulus (MR) = 4ksi
Cost analysis of Burnt Earth vs. Crusher Run, White
Sand/Sand Clay, White Sand
Item
ESALs
SNreq
AC Thickness
Burnt Earth
Thickness
1
0.1x10^6
2.788
2 Inches
18 Inches
2
0.2x10^6
3.00
2 Inches
20Inches
3
0.3x10^6
3.211
2 Inches
21 Inches
Cost of Burnt
Earth per Cubic
Yard
$5,500
Item
ESALs
SNreq
CR
Thickness
WS/SC
Thickness
WS
Thickness
AC
Thickness
1
0.1x10^6
2.788
6 Inches
6 Inches
8 Inches
2 Inches
2
0.2x10^6
3.00
6 Inches
7Inches
9 Inches
2 Inches
3
0.3x10^6
3.211
6 Inches
8 Inches
9 Inches
2 Inches
$9,000
$3,000
$2,000
Cost per Cubic Yard
Conclusion
• In executing the community road in
Georgetown (Area Q Turkeyen) Burnt Earth
was used to expedite the conclusion of the
road network since Crusher Run could not be
obtained promptly. Burnt Earth was more
cost effective and also met the design
requirements based on AASHTO 1993.
Photos of Finished Area Q Turkeyen Road
Photos of Finished Area Q Turkeyen Road
Recommendations
• More studies should be done on burnt earth (clay) high
volume roads/ highways;
• The Ministry should make known to burnt earth (clay)
producers estimated quantities required
monthly/quarterly/annually with the necessary inhouse specifications;
• The Ministry should provide the engineering data to all
Regional Democratic Councils on burnt earth (clay)
specifications and usage; and
• Additional studies should be done on the use of burnt
earth (clay) as a finished surface (wearing surface)
Thank You