Experimental Study On Autogenous Shrinkage Of Cement-based Materials

The shrinkage of the cement is one of the main reasons for the cracking ofconcrete,especially high-performance concrete and high-strength concrete have lowwater-cement ratio and high early autogenous shrinkage,therefore more prone tocracking.The Best appropriate technology to control autogenous shrinkage is usingshrinkage-reducing agent.This article summarizes the analysis of the mechanism ofconcrete shrinkage, using the orthogonal experimental method to develop a reductionagent (code C), the contrast experiment tested the reduction agent on cement properties,the influence of the reduction agent on autogenous shrinkage, used no contact resistivitymethod to study the influence of the shrinkage reducing agent to cement hydrationprocess.Selection of two polyhydric alcohol compound and a polyether compound as the rawmaterial of the trial reduction agent C,Orthogonal experiment results show that theshrinkage-reducing agent C can inhibit drying shrinkage, content of1:20shrinkage-reducing agent C is0.2%of the cement quality. Found in the study shrinkagereducing agent of cement nature: When content of the shrinkage reducing agent C is0.2%,28d cement paste strength increased by5.6%; shrinkage reducing agent C has no effecton the strength of cement paste.0.2%shrinkage-reducing agent C will extend the initialsetting time, and does not affect the final setting time. SBT-SRA is a higher market shareshrinkage-reducing agent, content of SBT-SRA is1%,28d cement paste strength reducedby10%, and SBT-SRA has a retarding effect. The SBT-SRA and reduced agent C inhibitautogenous shrinkage.At3day age, the reduction rate of1%SBT-SRA,3%SBT-SRAand0.2%shrinkage reducing agent C were42%,49%,15%, the effect of improveSBT-SRA dosage to increase the reduction rate is not obvious, therefore, Only byincreasing the dosage of shrinkage reducing agent to reduce the effect of shrinkage isneither effective nor economical.In the case of shrinkage-reducing agent and superplasticizer admixture single doped,study cement resistivity change. In the dissolving of SBT-SRA could slow ions eluted,thereby reducing the concentration of ions in the pore solution, resulting in the slurry wasincreased resistivity. Ion concentration is relatively low, is not conducive to the formation of hydration products, resulting in induction period of time, and also show that theSBT-SRA retarding effect on the hydration of cement. Into the setting and hardeningperiod, the resistivity of the SBT-SRA is always lower than the control group, there is anincreasing trend in the latter part of the growth rate. Shrinkage-reducing agent C in lyticinduction period to the resistivity has no effect in the setting and hardening of slightlylower resistivity blank group. In both cases, co-doped single blending shrinkage reducingagent on the resistivity is basically the same, on the other hand reflects theshrinkage-reducing agent and superplasticizer have good compatibility.