Testing Method Study On The Resistance Of Temperature Fracture Of Dam Concrete In The Early Age

Temperature stress of mass concrete is related to temperature,concrete materials,such as elastic modulus,creep relaxation,linear expansion coefficient,and practical engineering constraints.In practical engineering,the hydration temperature rise in the early age and the overall temperature drop in the long age of the dam concrete are both likely to have a great thermal stress,while we do not hava an appropriate means of laboratory tests to research the temperature load resistance of concrete.The author investigated domestic and foreign fracture toughness test method of concrete and found they are mostly used in traditional direct mechanical force applied load,while in practical engineering,hydraulic mass concrete cracks due to temperature stress are generated by the temperature gradient,which has a great difference from those load testing machine above.Under the direct force providing load conditions,the determinant of concrete failure is mainly concrete strength,but under a temperature loading conditions,it never means concrete with bigger strength will have better crack resistance,because the temperature stress is also associated with other concrete characteristics and constraints,besides temperature gradient.Thus,conventional laboratory test methods can not well test fracture performance of concrete under temperature load.The author designed two test methods which can be applied directly with temperature loads: a test means providing an internal temperature rise,and a test means to test the overall temperature drop.The two test methods are expected to research the temperature fracture resistance properties of the concrete more accurately by applying the load conditions closer to the load in practical engineering.Inspired by conventional fracture toughness test and restrained shrinkage ring test,the author developed two new ring test devices to evaluate the temperature fracture resistance properties of the concrete: concrete temperature test device applies high temperature loads to the inner side of the concrete specimen ring,with free cooling of the other sides,prompting to produce concrete expansion and causing fracture at the outer ring side;a rigid core concrete ring test device provides a high curing temperature of the concrete specimen ring,using invar,a kind of metal with small linear expansion coefficient,to provide constraints to the concrete ring,and cools the concrete when it reaches a predetermined age,to promote concrete shrinkage deformation and causing fracture.Use the two ring test device,doing the concrete test,measuring the time of fracture,crack width,crack length and other characteristics,we can compare temperature fracture properties of different concrete,and verify the validity of the test instruments.With further improvement and promotion of these two ring test devices,we can provide corresponding recommendations for hydraulic engineering applications.