STRUCTURAL LIGHTWEIGHT CONCRETE FOR BRIDGE BUILDING

KONSTRUKTIVER LEICHTBETON FUER BRUECKENBAU

RESULTS OF RESEARCH ON LIGHTWEIGHT CONCRETE SHOW THAT INSTANCES OF CREEP IN NATURAL CONDITIONS ONLY AMOUNT TO A THIRD OF THOSE OBSERVED UNDER CONTROLLED CLIMATIC CONDITIONS. LOW CREEP VALUES WOULD CONSIDERABLY IMPROVE THE ECONOMIC VIABILITY OF PRESTRESSED CONCRETE BRIDGES. IT IS NECESSARY TO CARRY OUT EXTENSIVE SHRINKAGE AND RELAXATION TESTS IN NORMAL CONDITIONS AND IN THE OPEN AIR, WITH THE CONCRETE BOTH PROTECTED AND UNPROTECTED FROM SUN AND RAIN. THE MAGNITUDE OF SUBSEQUENT HARDENING AND THE STRENGTH FLUCTUATIONS CAUSED BY MOISTURE CONTENT ARE IMPORTANT FOR THE SAFETY OF A STRUCTURE. THEREFORE THE COMBINED ACTION OF THE SUBSEQUENT HARDENING OF THE CEMENT AND THE INCREASE IN STRENGTH CAUSED BY DRYING OUT IS TO BE EXAMINED AND BROKEN DOWN INTO INDIVIDUAL EFFECTS. SINCE THE ELASTICITY MODULUS OF THE CONCRETE IS MARKEDLY INFLUENCED BY THE ELASTICITY MODULUS OF THE AGGREGATE, AND THE LATTER FLUCTUATES WITH THE MOISTURE CONTENT OF THE AGGREGATE PARTICLES, THE MOST REALISTIC DATA ARE NECESSARY IF RATIONAL DESIGN IS TO BE ACHIEVED. FOR MANY STRUCTURAL QUESTIONS A KNOWLEDGE OF THE STRESS-STRAIN CURVE AND THE COMPRESSIVE STRAIN OF LIGHTWEIGHT CONCRETE IS REQUIRED. WATER ABSORPTION IS TO BE DETERMINED BY STUDYING THE DEVELOPMENT OF SUCTION STRESSES IN LIGHTWEIGHT CONCRETE CONTAINING WATER-ABSORBING AGGREGATES AND NORMAL CONCRETE CONTAINING NON-WATER-ABSORBING AGGREGATES. THE LIGHTWEIGHT CONCRETES TO BE STUDIED ARE LB 225, LB 400, AND LB 600 WITH A SUITABLE EXPANDED CLAY. 796 TEST SAMPLES WILL BE USED FOR THE TESTS.