Influence Of Toughing Materials On Hydration Mechanism And Mechnical Properties Of Cement Based Materials

With the development of modern reinforced concrete to ultra-high-strength,ultra-long and super-span structures,the requirements of toughness of cementitious materials have become more and more rigorous.However,for trational cementitious materials,due to shortages of diversity of composition,high porosity and poor compatibility of hydration products,it is characterized by high brittleness,low toughness,poor deformation performance and small ductility,which is difficult to meet the needs of modern construction.The occurrence of nano-materials is providing a new method to improve the toughness of cementitious materials.In this paper,two types of toughing materials,namely sulfonation graphene nanosheet and cationic polyurethane,have been used.By the modern test analysis methods and macro test methods,the influences of toughning materials on the hydration of C3S,cement dissolution and hydration,as well as its mechanical properties have been investigated.Besides,toughness mechanism of cementitious materials by toughing materials was revealed by combining molecular dynamic simulation calculation method.Continuous reaction dissolution apparatus for powders was built.The dissolution kinetics of gypsum powders was also been systematically explored,as a result in the proposel of an empirical dissolution rate law.Meanwhile,the effects of toughning materials on the dissolution of cement were also studied.The results shows that the dissolution rate constant is 0.51 mmol m^-2 s^-1 based on the changes in calcium concentration.When concentrations of PUC are 0.02,0.08and 0.2 g L^-1,the dissolution rate constant of cement are respectively 0.47,0.46 and 0.27 mmol m^-2 s^-1;while when concentrations of PUC are 0.02,0.08 and 0.5 g L^-1,the dissolution rate constant of cement are separately 0.49,0.47 and 0.46 mmol m^-2 s^-1.With the high dosage of SGN,owing to its high acidity resulting in the pH changes of the solution,the dissolution rate of cement was accelerated.In a word,the two toughning materials will decrease the dissolution rate of cement,particularly for the PUC.Owing to the random adsorption onto the ratactive site on the surface of cement（C3S）particles,the addition of toughning materials will prolong the induction period of cement hydration.As the dosage increases,the delay effect becomes more obvious,while,both PUC and SGN can promote the accumulation heat.Based on the results of Quantative X-Ray diffraction（QXRD）and Scanning electron miscopy（SEM）,both PUC and SGN will slow down the consumption of C₃S at 1 day,but it will promote its consumption at 3 day and 28 day.Also,both PUC and SGN will decrease the formation of CH and affect its morphology.Particularily,because of the charge effect,noth PUC and SGN will adsorb those ions in silutions,directly affect the morphology of CH,induce its crystal rearrangement,change the microstructure of cement and finally make its overall structure become more similar to the natural shell structure.Then,PUC can significantly increase the flexural strength and tensile strength of cement pastes without the decrease in compressive strength（comparing with the controlling sample,the compressive strength at early stage exert a little bit decrease,however,it will increase at later stage）.When the dosage of PUC was 0.5%,the flexural strength and tensile strength of cement pastes at 3 days will increased by about by 30%and 90%comparing with the controlling samples.In the mean time,for the mortars,its action law is similar to the cement pastes,but its effect tends to be slightly reduced because of the introduction of its interface.Similarly,the incorporation of SGN can effectively enchance the flexural strength and tensile strength of cement pastes.When the content of SGN was 0.01%,cmpring with the controlling samples,the flexural strength of cement pasets at 1 day will promote by roughly 40%,while for the tensile strength at 3 day it increased by 70%.In general,the daaition of toughning materials can effectively promote the ratio of flexural strength to compressive strength and also the ratio of tensile strength to compressive strength,which presented that it was possible to improve the toughness of cement based materials by using those two toughning materials.In a word,in this paper,the effects of those two toughning materials on cement hydration and its mechanical property have been studied,including the hydtaion mechanism and the crystal rearrangement of CH leading to the changes in the microstructure by layer by layer,which is probably the reason for the promotion in the toughness of cement based materials,providing the theoretical basis for in-situ toughning of cement based materials.