CONCRETE IN ALUM SHALE -WITH ENGLISH SUMMARY /IN NORWEGIAN/

IN SCANDINAVIA A BLACK SHALE CALLED "ALUM SHALE" IS FREQUENTLY ENCOUNTERED. THE BLACK COLOR IS DUE TO A CARBON CONTENT MOSTLY IN THE RANGE OF 7-10%. THE SHALE CONTAINS THE SULFUR BEARING MINERALS PYRITE AND PYRRHOTITE IN AN AMOUNT WHICH USUALLY CORRESPONDS TO A CONTENT OF 3-6% PURE SULFUR. THE ALUM SHALE WEATHERS EASILY WHEN EXPOSED TO OXIDIZING CONDITIONS RELEASING WATER SOLUBLE SULFATES. IN THE PERIOD 1920-1940 CONSTRUCTORS BECAME AWARE OF TECHNICAL PROBLEMS IN SHALE CONSTRUCTION: SWELLING OF THE GROUND, CORROSION OF IRON AND STEEL, AND CHEMICAL DETERIORATION OF CONCRETE STRUCTURES. IN 1943 THE ALUM SHALE COMMITTEE WAS THEREFORE SET UP TO RESEARCH AND CLARIFY THESE PROBLEMS. FIELD EXPERIMENTS ARE DESCRIBED WITH CONCRETE PRISMS (10 X 10 X 40 CM) PLACED IN A TUNNEL IN AN ALUM SHALE AREA CONTAINING THE GROUNDWATER OF A COMPOSITION DEVELOPED BY THE WEATHERING OCCURRING IN THAT AREA. ALL TOGETHER 7 DIFFERENT TYPES OF CEMENTS HAVE BEEN USED WITH ONE OF THE STANDARD NORWEGIAN PORTLAND CEMENT SERIES AS REFERENCE. IN 3 OF THE SERIES WITH STANDARD NORWEGIAN PORTLAND CEMENT SOME OF THE FINE AGGREGATES WERE REPLACED WITH CRUSHED PURE CALCITE OR CRUSHED LIMESTONE. IN 3 OF THE SERIES, 15% OF THE STANDARD PORTLAND CEMENT WAS REPLACED WITH DIFFERENT MATERIALS SUPPOSED TO HAVE POZZOLANIC ACTION (CRUSHED IRON WORK SLAG, TRASS AND A VERY FINE GRAINED SILICA FLUE DUST). IN TWO OF THE SERIES WITH STANDARD PORTLAND CEMENT AN AIR ENTRAINING AGENT, DAREX, WAS ADDED. THE RESULTS AFTER 12 YEARS FIELD EXPERIMENTS CAN BE SUMMARIZED AS FOLLOWS: (1) CONCRETE WITH STANDARD PORTLAND CEMENT IS STRONGLY ATTACHED IN ALUM SHALE WATER. (2) THE DETERIORATION OF CONCRETE WITH STANDARD PORTLAND CEMENT IN ALUM SHALE GROUND WATER IS A SULFATE ATTACK LEADING TO THE FORMATION OF ETTRINGITE. (3) THE ALUM SHALE WATER SEEMS TO BE MORE AGGRESSIVE THAN OTHER SULFATE CONTAINING WATER, E.G. WITH SODIUM OR MAGNESIUM SULFATE. (4) POROUS STRUCTURE AND HIGH PERMEABILITY SEEMS TO AUGMENT THE RATE OF DETERIORATION (5) REPLACEMENT OF SOME OF THE FINE AGGREGATES BY CRUSHED CALCITE OR LIMESTONE TURNED OUT TO BE UNFAVORABLE. (6) REPLACEMENT OF SOME OF THE STANDARD PORTLAND CEMENT WITH THE VERY FINE GRAINED SILICA DUST SHOWED TO BE VERY FAVORABLY, POSSIBLY DUE TO ITS POZZOLANIC ACTION. (7) REPLACEMENT OF SOME OF THE STANDARD PORTLAND CEMENT WITH A SPECIAL CRUSHED IRON WORK SLAG DID NOT SEEM TO HAVE ANY EFFECT. (8) SPECIAL CEMENTS, ESPECIALLY SULFATE RESISTANT CEMENTS OF THE SAME TYPE AS U. S. TYPE V SEEMS TO WITHSTAND ATTACK FROM ALUM SHALE WATER VERY SATISFACTORILY, AS A CONSEQUENCE OF THESE FINDINGS SULFATE RESISTANT CEMENTS WITH LOW TRICALCIUMALUMINATE CONTENT IS RECOMMENDED IN ALUM SHALE AREAS. IN SEVERE CASES EVEN A PROTECTIVE MEMBRANE WOULD BE RECOMMENDED IN ADDITION. /AUTHOR/