The Sensitivity Analysis On Thermal Stress Of Autogenous Volume Defortmation Mixed MgO Concrete

Roller Compacted Concrete dam is a new type dam developed in recent 20 years. Cracks occur on many built dams, especially on RCC dams in harsh climate region. Cracks decrease the integrity, anti-seepage, durability and safety of concrete dams. Research indicates that thermal stress is the chief load leading to cracks in RCC dam, and stresses caused by other loads are smaller. Therefore, research on thermal stress during construction period and temperature control is very important to prevent cracks and guarantee the safety. Dam materials and structure type also play an important role in causing cracks. In harsh climate region, the air changes greatly between winter and summer. RCC dam are usually free in winter. Thus, it's unique placed without bulk and longitudinal joints, and left thermal stress time-space distribution rule increases the difficulty of temperature control and crack control of RCC dam.The engineering practice proves that the using of dam-building technology of MgO concrete with some other assistant appropriate measures can replace the traditional temperature-controlled measures of concrete dam partly or completely(such as no-cooling by water pipe,no-mixing round with ice, and so on), and it can solve problem of crack prevention of hydraulic dam concrete effectively. Meanwhile, it can achieve long blocks,thick layers,open silo,all-weather continuous concrete pouring so as to expedite the construction rate of progress and economize engineering investment. The main contents are as follows:(1) In this paper the author overviews mass magnesia concrete dam thchnical origin, the present status here and abroad, and the MgO expansion characteristics and mechanism, and available primal problems;(2) Transformation rules of MgO-mixed autogenous volume deformation are studied. Hyperbola model of MgO-mixed concrete's especially deduce of the model's parameter and building process of the model are analyzed in detail;(3) Calculating method of autogenous volume deformation and creep are discussed. Based on these, apply the programs to analysis the temperature field and temperature stress field of a roller compacted concrete dam, proving the programs are right, timely-simulation theory of roller compacted concrete dam temperature field,stress field and pre-process,back-process method are mainly studied;(4) The influence of gentle MgO expansive volume in different part and its adjustable delaying are the two keys in MgO concrete technique. The effect of the thermal stress of mixed gentle MgO concrete slab are studied in detail. Mixing with MgO in concrete dam can make tensile stress lessen in structure. It is important to ensure that the swelling of MgO must be coincidence with up-down different slabs each other. The results show the property of mixed MgO concrete thermal stress.