Research Into Long-term Performance Of Self-compacting Concrete Beams

In the past ten years, self-compacting concrete has gained wide use in civil engineering for its superior constructability and high durability. However, self-compacting concrete differs from normal concrete in terms of mechanical behavior due to the use of different material and different mix proportioning. Research into long-term properties of self-compacting concrete beams has not been actively pursued for the past 15 years. Few papers have been written on this subject. In view of this, this dissertation has systematically made experimental research and theoretical analysis on long-term behavior of self-compacting concrete beams. The main content is listed below.(1) The parameters for mix design of self-compacting concrete were optimized and the stress-strain relationship and bonding stress-slip relationship of self-compacting concrete were established.(2) Long-term tests of 26 prestressed and non-prestressed self-compacting concrete beams were done. The effect of different parameters on long-term deformation of self-compacting concrete beams including curing condition, mix-proportion, degree of prestress, mode of consolidation, magnitude of load and structural type was investigated. The reliable experimental data presented in this paper is useful to engineering design and theoretical analysis. The experimental results indicate that extra preventions concerning shrinkage and creep behavior of the structure are not needed in engineering practice.(3) Experimental research on self-compacting concrete beams under static loading after long-term actions was done. The effect of different factors including casting technique, curing condition, degree of prestress at age of loading and degree of indeterminacy on load-deflection relationship, load carrying capacity, mode of failure and distribution of crack along beam length was explored.(4) The element stiffness matrix concerning the contribution of concrete and reinforcement was constructed based on element displacement mode and virtual work principle, and the equivalent node load due to creep and shrinkage was established. Based on recurrence formula for any kind of expression of specific creep, nonlinear finite element analysis was done, which considered bond-slip behaviour and crack width. The analytical results show good agreement with the measured ones.(5) A formula for creep deflection of self-compacting concrete beams was constructed by section analysis using modified MC 90 creep and shrinkage model and age-adjusted effective modulus method. A design method for creep deflection was proposed, which will further perfect "Guidelines for design and construction of self-compacting concrete in China"(6) The extended grey dynamic model was used to predict the long-term deformation of self-compacting concrete beams on the basis of short-term experimental data. The predicted values are in good agreement with the measured ones, which shows that this method presented in this paper characterized by simplicity and high precision in prediction is practical and feasible.