SIGNIFICANCE OF ACCELERATED DURABILITY TESTS OF CONCRETE

PROCEDURES ARE REVIEWED THAT ARE APPLIED TO CONCRETE TO EVALUATE ITS DURABILITY IN FUTURE SERVICE, WITH PARTICULAR REGARD TO ITS RESISTANCE TO FREEZING AND THAWING AND DELETERIOUS CEMENT-AGGREGATE REACTIONS. OTHER EXPOSURE CONDITIONS ARE NOTED, SUCH AS ATTACK BY AGGRESSIVE SOLUTIONS AND OTHER MEDIA, ABRASION AND CAVITATION, AND HIGH TEMPERATURE. AN ACCELERATED TEST OF DURABILITY OF CONCRETE IS A PROCEDURE INTENDED TO EVALUATE RAPIDLY, IN EITHER ABSOLUTE OR RELATIVE TERMS, THE ABILITY OF THE MATERIAL TO WITHSTAND A SPECIFIED EXPOSURE. APPLICATION OF SUCH PROCEDURE REQUIRES THE FOLLOWING STEPS:(1) ESTABLISHING THE QUALITIES THAT CONTROL THE RATE OF DISINTEGRATION OF THE CONCRETE, (2) DEVELOPING PRACTICAL PROCEDURES BY WHICH THE CONTROLLING QUALITIES CAN BE MEASURED, (3) ESTABLISHING THE ACCURACY AND PRECISION OF THE PROCEDURES IN PREDICTING THE RATE OF DISINTEGRATION OF THE CONTRACT, AND (4) SPECIFYING QUALITY ASSURANCE PROGRAMS IN THE SELECTION OF CONCRETE- MAKING MATERIALS, MANUFACTURE OF THE CONCRETE, AND CONSTRUCTION PROCEDURES THAT WILL GUARANTEE THAT THE CONCRETE IN PLACE POSSESSES THE REQUIRED PROPERTIES. A BRIEF SUMMARY IS PRESENTED OF THE ESSENTIAL PHENOMENA BY WHICH CONCRETE CAN BE DAMAGED BY FREEZING AND THAWING. THE CONDITIONS THAT MUST BE ACCOMMODATED SO THAT AN ACCELERATED TEST WILL AFFORD A REALISTIC MEASURE OF THE RESISTANCE OF A GIVEN CONCRETE TO FREEZING DURING SERVICE ARE: (1) RATE OF FREEZING, (2) MINIMUM TEMPERATURE ATTAINED, (3) DURATION OF FREEZING CONDITION, (4) FREEZABLE WATER CONTENT OF THE CEMENT PASTE AND AGGREGATE, (5) AIR VOID VOLUME AVAILABLE FOR ACCOMMODATION OF THE WATER EXPELLED FROM THE FREEZING ZONES, AND (6) PARTICLE SIZE, PORE CHARACTERISTICS, AND PROPERTIES OF THE AGGREGATE PARTICLES. THE FOLLOWING PROCEDURES ARE REVIEWED WHICH HAVE BEEN DEVELOPED TO PROVIDE FOR ACCELERATED EVALUATION OF THE RESISTANCE OF HARDENED CONCRETE TO FREEZING AND THAWING: (1) ASTM METHODS OF TEST, (2) POWERS' TEST, AND (3) SCALING TESTS. THE FOLLOWING ACCELERATED TESTING METHODS ARE REVIEWED: (1) HEATING-COOLING AND WETTING-DRYING EXPOSURE OF CONCRETE, (2) THE ALKALI-SILICA REACTION IN CONCRETE, (3) EXPANSIVE REACTION IN CONCRETE CONTAINING CARBONATE ROCK AGGREGATES, (4) RESISTANCE OF CONCRETE TO ATTACK BY AGGRESSIVE MEDIA, (5) EVALUATION OF AGGRESSIVE MEDIA FROM INTERNAL SOURCES, (6) ABRASION RESISTANCE OF CONCRETE, AND (7) HIGH- TEMPERATURE EXPOSURE OF CONCRETE. THE VALUE OF ANY ACCELERATED TEST LIES IN THE DEGREE TO WHICH THE SERVICE CONDITION IS SIMULATED AND THE EXTENT TO WHICH THE PHYSICAL, CHEMICAL, AND MECHANICAL RESPONSES OF THE CONCRETE IN THE SERVICE CONDITION ARE REPRODUCED IN THE METHOD OF TEST.