Experimental research on the test methods for surface cracking of concrete

Surface cracking is mainly caused by intrinsic stresses (eigenstresses) which can not be measured directly. New test methods have been developed in order to estimate intrinsic and bending stresses caused by thermal and moisture gradients. The tests can be used to study the influence of various aggregates, cement brands, concrete mixes or curing temperatures on the tendency to surface cracking. The influence of the temperature gradient during hardening has been studied on thermally prestressed concrete beams.For studies on stress gradients caused by drying shrinkage, test methods for (1) the hygral coefficient of expansion, (2) the moisture conductivity and the shrinkage/swelling stresses caused by intrinsic stresses (3) prism splitting test and by bending stresses (4) hygral bending test, have been developed.