August_1967 — Page 41

CIVIL ENGINEERING AND PUBLIC WORKS

BITUMINOUS PAVEMENT WITH POTTERY AGGREGATES

NE-TENTH of the terrestrial sur- face. mostly in the middle latitudes of Northern and Southern Hemispheres, is covered by loess and in most loess coteaus rock is a rarity.

In China, the loess-covered area is larger than in any other country. Estimates put it at more than 400,000 sq. kilometres, about 300,000 sq. kilometres of which surrounds the Yellow River and is found at thick- nesses ranging from 80 to 250 metres.

The construction of an all-weather road surface in such territory is an arduous task often involving the haulage of stone aggregates over vast distances. Consequently it is often more economical in under-developed regions to process the local soil as a road surfacing material.

There are two methods of soil pro- cessing. One is to change the trait of the soil through a stabilizing agent. Normally this is done by mixing the soil with cement or lime to produce what is commonly known as a soil- cement road surface or a lime-treated clay road.

or

The second method is to broil the soil, changing it into pottery bricks, and using this material as ag- gregate for a bituminous pavement.

Experiments with Pottery Aggregates

The constituents of soil consist mainly of silicate, aluminium oxide and ferric oxide. The more silicate it contains, the more tenacious it will be, and the more oxides it contains the stronger will be the pottery pro- duced.

Table 1.

Grading Requirements of Soil for producing pottery aggregates

Grain Class

Particle Diameter

Grading

Requirement

(mm)

(%)

Fine Sand

over 0.25

0.2-2

0.25-0.05

2-26

Silt

0.05-0.01

12-46

0.01-0.005

10-55

0.005-0.002

6-25

9-38

Clay

smaller than 0.002

The tenacity of soil is related to the texture of soil particles; the smaller the particles, the better the tenacity. Grading requirements of

Far East Architect & Builder August, 1967

by Zenith Chuang *

When an all-weather road surface is to be built in an area where stone is not produced nor available, there are two ways to obtain the necessary surfacing material: One is to haul stone aggre- gates from an outside source; the other is to make the most of the indigenous soil by processing it. This article describes the simple process of broiling soil into pottery and gives a brief ac- count of the use of pottery as aggregate for bituminous pavement.

soil for producing pottery aggregates is shown in Table 1.

Through the process of high tem- perature, the original plastic soil will no longer be soft when in contact with water, nor deformable under pressure. More than that, such kiln-dried soil can stand attrition and antifreezing.

The author has taken samples of the local pottery and conducted phy- sical experiments, with the following results:

Specific gravity

2.215

Percentage of absorbing

water

Percentage of absorbing oil Los Angeles abrasion value Soundness

9.95 % 9.35 %

28.9 % 1.79 %

In order to further ascertain whe- ther pottery aggregates can be the main material of bituminous concrete, the author conducted mix design tests according to the Marshall Method. These experiments showed that the best assortment was 46% of pottery aggregate, 37% of coarse sand, 11% of fine sand and 6% of lime powder. A series of test specimens indicated that the optimum asphalt content was 7.33%. From data curves, as shown in Fig. 1, the mix yields the follow- ing:

Maximum stability Unit weight

2180 lb.

139 lb ft3 16.3 % 4.7 %

Flow value Voids in the total mix Aggregate voids filled

with asphalt

76.5 %

Producing Pottery Aggregates

In China. the manufacture of porcelain pottery is one of the oldest industries and there is no difficulty in producing pottery aggregates as road surface material.

To keep cartage to the minimum, the pottery kiln is set up along the road; the number of kilns and the distance of their sites in a large mea-

sure depend upon the quality of soil, the quantity of pottery required, the capacity of the kiln and the construc- tion season.

In under-developed or developing areas, modern equipment may not be available and where manual labour is used the kiln has to be as simple as possible in its architecture. The ideal kiln is the truncated inverted-cone structure which is approximately 5 metres in height and 6 metres aver- age diameter.

The paste-like crude clay, with a water content not exceeding 5%, is prepared and dumped into the kiln. Usually it takes six days before the pottery aggregates are available, in- cluding such procedures as loading, burning, suffocating, cooling and un- loading.

Main Material

For a bituminous road surface, the base course is most important. With gravel or stone aggregates unavail- able along the road, pottery aggre- gates may be adopted. The base course thickness should be in ac- cordance with the soil test, but if testing facilities are not available the base course should be as thick as 4 to 6 in. in conformity with the water- bound method.

If no bituminous surface is planned for the time being, the pottery base course can serve, except that it must be topped by a layer of wearing course. The grading requirement of pottery aggregates available for the base course is shown in Table 2.

* Mr. Zenith Chuang is director of the China Road Federation, supervisory en- gineer of the Taiwan Highway Bureau and professor of civil engineering, National Taiwan University. This article is based on a paper presented by Mr. Chuang to the Fifth World Meeting of the Interna- tional Road Federation, held in London last September. It is published by kind permission of the China Road Federation.

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