| Alkali-activated slag cement?AASC?,which is a enviromentaly friendly and high performance cementicious material,meets the requirement of energy saving and omission reducing strategy.The hardened alkali-activated slag cement is brittle and easy to crack,while traditional methods for toughening and reducing cracks are greatly limited by many factors.One of the most significant ways is to develop a new toughening material,which can not only develop good adhesion with AAS matrix,but also obstract the expansions of micro-cracks.Then focusing on its effect to the hydration and properties of alkali slag cement is an important issue to solve that problem.Two-dimensional nanosheet material with large surface area,excellent performance,high hydrophilic and activity,Graphene oxide?GO?,was introduced to improve the microstructures and matrix adhesions,and obstract the expansions of micro-cracks of alkali-activated slag cement by utilizing its structural properties and functional group activities,which producing crystal nuclei effect and template of hydration products.Resulting in improving in toughness while reducing micro-cracks of AAS matrixs.The effects of GO,such dosages,oxidation'degree and nanosheets'sizes,on the hydration characteristics and microstructure of AAS were considered,and mechaniclal properties of alkali-activated slag motar was tested.In addition,GO and GO-Polynaphthalene sulphonate superplasticizer?FDN?mixture were introduced to investigate its effecs to the rheological properties of AAS paste,in return recognized the interaction of GO and alkali-activated slag cement particles,and futher looking for a way to improve the fluidity of AAS paste with GO.Main results can be summarized as follows:?1?GO played crystal nucleation effect in AASC,promoting the early hydration and increasing the hydration degree of AASC.The dosages of GO was in the range of 0.01%to 0.05%,with the higher dosages of GO,initial hydration exothermic peak of AASC was earlier,in addition,the corresponding peak intensity increassed with the increase of GO's contents.With the higher oxidation's degree of GO,the initial hydration exothermic peak of AASC was promoted while this peak intensity still increased.With the decrease of GO's nanosheet sizes,the initial hydration exothermic peak of AASC was postponed while this peak intensity still increased.Cumulative hydration heat of AASC was increased with the increase of GO's contens and oxidition degree,but increaed with the decreasement of GO's nanosheet sizes.?2?GO played as a template to hydration prodcuts of AASC,then promote flower-like Layered Double Hydroxides?LDHs?with larger crystal dimensions and greater numbers.GO was well dispersed and stable in alkaline solution,and in addition,it produced good adhesions with AASC matrix,as a result of improved microstructures of harded AASC mixtrx.?3?GO significantly decreased the fluidity of AASC paste,and at the same time increased the yield stress and consistency index of the paste.When GO was 0.05%by weight of the binder,yield stress and consistency index of the paste increased from 8.179Pa to 35.245Pa and from 0.726 Pa·S9)to 3.774 Pa·S9),respectively,which is comparing to the blank group.The dosages of GO was between 0.01%0.05%,with the increase of GO's dosages,the hysteresis loop and rheological index of paste decreased gradually,then GO reduced the thixotropic properties and improved the stability of the AASC paste.?4?FDN can significantly improve the fluidity of AASC paste with GO.The fluidity of AASC paste with 0.03%-GO coulde be improved from 147.5 mm to 172.5 mm by incorporating 1.5%-FDN.With in dosages range from 0.01%0.05%for GO,1.0%1.5%for FDN,the fluidity of the paste with mixture contained GO and FDN,was bigger than the paste with equivalent GO,while smaller than the blank group and the paste with equivalent FDN.Which indicated,directly mixing GO with FDN or treating this mixture with additional ultrasonication couldn't behave synergistic plasticizer effect on the AASC paste. |
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