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Rice husk ash (RHA) is a highly active pozzolanic material produced by the controlled combustion of rice husks, which is widely used as a mineral admixture for the production of high performance concrete. The addition of rice husk ash has a complex effect on cement hydration. Current models do not account for all these complex effects. In this paper, by considering factors such as the dilution and chemical effect of rice husk ash on the composite cementing system, as well as the absorption and release of water by the porous structure of rice husk ash, a hydration kinetic model of RHA cement cementitious system is established. Taking water cement ratio, ambient temperature, RHA particle fineness and dosage as variable parameters, the model calculation is compared with the experimental results. It is proved that the model can simulate the hydration process of cement cementitious system with RHA and can be used to predict the hydration degree of cement cementitious system with age. The results show that the degree of hydration of the RHA-cement cementing system is directly proportional to the water-cement ratio, ambient temperature and specific surface area. The research can provide a basis for the application of rice husk ash in cement, and at the same time achieve the purpose of improving the economy of cement and saving resources. [ABSTRACT FROM AUTHOR]

High temperature stress caused by global warming posed a serious threat to rice high productivity. The increasing frequency and intensity of extreme high temperature stress have adverse effects on rice growth, development, and grain yield. Rice are susceptible to high temperature during booting, flowering, and grain filling stages. This paper reviewed the recent research progress in studying the effects of high temperature at 3 stages ( booting, heading & flowering, grain filling ) on rice grain yield formation. High temperature had detrimental effects on pollen development, anther dehiscence, spikelet fertility, and on accumulation and translocation of photoassimilates, grain filling and starch synthesis. Those effects subsequently resulted in grain filling rate and grain yield declining. Grain filling rate and grain yield were mainly parameters for evaluating rice tolerance to high temperature. On the basis of previous studies, this paper put forward several measures as genetic improvement, optimization in nutrient and water management, artificial auxiliary pollination, and application of plant growth regulators, which might mitigate rice high temperature stress. [ABSTRACT FROM AUTHOR]