Along with economic,social quick development and urbanization,dams and reservoirs are of strategic importance for flood control,water supply,electricity production,irrigation,etc.,both for developed countries and for developing countries.Climate change is a new challenging issue to be considered which will speed up the development of hydropower in developing countries.More and more attention will be paid on the long-term better behavior of dams to guarantee the safety of the people involved and the better development of the world.There are about 50000 old dams in the world and a lot of them have been completed and operated for more than 50 years.However,how do we evaluate the dams’safety?How do we make the decision to do rehabilitation work or to rebuild a new dam based on evaluation results?The life span and the real safety status of old dams becomes a challenging task for the dam society,especially for China because it has more than 6000 dams to be evaluated and rehabilitated within the next few years.Based on the investigation of the Fengman gravity dam,which is 91.7 m high,operated since 1943 and suffered uplift pressure,freeze and thaw problems,etc.,discussions on the life span evaluation of old concrete gravity dams have been made.The reasonable coefficient of dam safety has been discussed.The social decision for the final choice after comprehensive studies has been introduced.
Based on the fluidity, strength, heat of hydration and loop crack resistance experiment of multi-powder paste, the components and proportion of multi-powder were optimized and the concrete properties were studied. The multi-powder consists of limestone powder, slag, fly ash and moderate heat Portland cement (PMH cement). The results show that the compressive strength of the multi-powder paste and mortar is close to those of PMH cement, fly ash paste and mortar currently used in dam concrete, yet the flexural strength is relatively higher. The multi-powder paste is featured by larger fluidity, lower heat of hydration and delayed cracking time. In comparison, less unit water consumption and cement is used in multi-powder concrete, and under premise of equal mechanical performance, deformation, thermal performance and durability, the adiabatic temperature rise at 28 d is reduced by 2 ℃. In this way, the crack resistance is improved and it is feasible both technically and economically to produce HPC for dam concrete.
