CLIMATE, ENGINEERING PETROLOGY AND THE DURABILITY OF NATURAL ROAD BUILDING MATERIALS IN SOUTHERN AFRICA
A NATURAL ROADBUILDING MATERIAL IS DURABLE ONLY IF THE CHANGE IN ITS PHYSICAL AND CHEMICAL PROPERTIES DURING CONSTRUCTION AND THE LIFE OF A ROAD REMAINS WITHIN LIMITS WHICH DO NOT INVALIDATE THE DESIGN. THE DURABILITY OF A NATURAL ROAD BUILDING MATERIAL DEPENDS ON THE ENVIRONMENTAL CONDITIONS OF ITS PLACE OF OCCURRENCE AND ON ITS PETROLOGICAL PROPERTIES. CLIMATE IS A PARTICULARLY IMPORTANT ENVIRONMENT FACTOR. THE N-VALUE, A NUMERICAL EXPRESSION DERIVED USING THE CLIMATIC FACTORS WHICH DETERMINE THE MODE OF WEATHERING, HAS BEEN DEVELOPED TO DEFINE THESE CLIMATIC ENVIRONMENTAL CONDITIONS. WHEN N IS MORE THAN 5 ALL ROCKS DISINTEGRATE, AND WHERE N IS LESS THAN 5 CERTAIN TYPES OF ROCK MAY DECOMPOSE AND CHANGE INTO CLAY. DECOMPOSITION AND DISINTEGRATION ARE THE TWO PRINCIPAL FORMS OF WEATHERING. THE FORMER, WHICH OCCURS ONLY IN ROCKS CONTAINING MINERALS WHICH CAN OXIDIZE OR HYDRATE UNDER ATMOSPHERIC CONDITIONS, AFFECTS THE DURABILITY AND THEREBY THE QUALITY OF A ROAD BUILDING MATERIAL MORE THAN THE LATTER. ROCK MAY BE TESTED FOR DECOMPOSITION BY DETERMINING THE PERCENTAGE OF SECONDARY MINERALS FORMED AND FOR DISINTEGRATION BY CRUSHING TESTS, ESPECIALLY THE 10% FINES AGGREGATE CRUSHING TEST ON DRY AND WET MATERIAL. SOUTH AFRICAN NATURAL ROAD BUILDING MATERIALS ARE DIVIDED INTO NINE GROUPS ACCORDING TO THE SIMILARITY OF THEIR ENGINEERING PROPERTIES. THE GREAT IMPORTANCE OF QUARTZ IN ASSESSING DURABILITY IS STRESSED AND MATERIALS ENGINEERS ARE ADVISED TO BECOME FAMILIAR WITH THIS MINERAL. /RRL(A)/
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Supplemental Notes:
- Vol 8, No 3, PP 889-896, 2 FIG, 1 TAB, 31 REF
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Authors:
- Weinert, H H
- Publication Date: 1970-5
Media Info
Subject/Index Terms
- TRT Terms: Climate; Decomposition; Durability; Engineering; Environment; Fracture mechanics; Materials; Petrography; Road construction; Rocks; Weathering
- Old TRIS Terms: Disintegration
- Subject Areas: Geotechnology; Highways; Materials;
Filing Info
- Accession Number: 00217727
- Record Type: Publication
- Source Agency: Road Research Laboratory /UK
- Files: TRIS
- Created Date: Jul 12 2000 12:00AM