| Based on the situation of autogenous shrinkage and cracking of concrete at early age, SAP (Super-absorbent polymer) as a kind of additional material which is developed rencently in the world is admixed into mortar and concrete, the influence on shrinkage of mortar and concrete was investigated in this paper. On this purpose, the performence of free shrinkage of mortar and restrained shrinkage of concrete were studied. In the linear test, the latest apparatus was applied and tesing sets that match the standard of ASTM C1581-04 were used in the experiment of restrained shrinkage. Depending on the experiment, the author analyses the free shrinkage of morar, the effect and the mechanisim of shrinkage reducing effect of SAP. Besides, the influence of SAP on the strenth of concrete and mortar has been studied. And the self-induced stresses of concrete ring under restrained condition are measured and analyzed. The different stresses caused by materials and proportions have been compared, as well.Via a lot of experiment and the theory analyses, the authour assumed that the water from SAP would move into the cement paste if the concrete and mortars contain SAP, thus the relative humidity in the cement decreases more slowly. For another thing, if water is added, the extent to hydration is improved and the solid products become more. Both of the effcets contribute to make up the early autogenous shrinkage. Under the conditions of medium or low w/c concerete is restrained partially, the inner tensile stresses increase. If water saturated SAP is added to the mortar and the concrete, the swollen particles of SAP in the cement paste become spherical pores that are full of water, the volume of which is approximately 20 times larger. Equally, the pore volume is increased by 3% in the concrete, and the strenth is decreased to some extent, as the hydration continues in the later ages. Finally, SAP will be applied widely in the concrete some day.
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