Experimental Study On The Relationship Between Pore Characteristics Of Hardened Paste And The Amount Of Ettringite In Hydration Products Of Cementitious Composite Materials

With the influence of shrinkage cracks in concrete and the delayed ettringite formation fracturing,the water leakage appears constantly in engineering projects,which is difficult to find and solve these microcracks in time by conventional repair measures.This thesis uses cementitious materials as the research object and silica fume,fly ash and slag powder as the main admixture materials.The pore characteristics of hardened paste of cementitious composite materials at different age were tested by using mercury intrusion porosimetry(MIP)and low-field nuclear magnetic resonance,while the changes of the content of ettringite in the hydration products were analyzed by using Rietveld full spectrum fitting quantitative.The relationship between the pore characteristics and the content of ettringite in the hydration products of composite cementitious materials was studied preliminarily.Combined with the corresponding flexural strength and compressive strength,this thesis choose a reasonable cementitious composite materials' mixing proportions with better pore characteristics and higher strength.The formation and development of micropores are controlled by the modifed cementitious composite materials,which lay the experimental foundation for the research of self-healing concrete,and draw the following conclusions:(1)When the amount of mineral admixture is appropriate,the flexural strength and compressive strength of the hardened paste of the cementitious composite materials are higher than the hardened paste of pure cement.And the multicomponent cementitious composite materials's strength is lower than the strength of cementitious composite materials of single admixture at the same age.The strength of the hardened paste of cementitious composite materials is inversely proportional to the porosity.(2)The pore of hardened paste of cementitious composite materials is mainly distributed in the range of 3.5nm?100nm,as the curing age increases,the most probable pore diameter moves towards small pore sizes overall by using MIP,which decreases quickly in the early age and changes slowly in the later age.The pore of hardened paste of multicomponent cementitious composite materials is mainly distributed in the range of 1nm?300nm,and the most probable pore diameter is almost unchanged by using low-field nuclear magnetic resonance after 7 days.(3)As the curing age increases,the average pore diameter and the porosity of hardened paste of cementitious composite materials with different mixing proportions decrease continuously,which decrease quickly in the early age and change slowly in the later age.As the amount of admixture increases,the average pore diameter decreases overall.The porosity and the average pore diameter and the most probable pore diameter of hardened paste of multicomponent cementitious composite materials at an appropriate amount obviously decrease than the cementitious composite materials of single admixture.(4)The amount of ettringite in the hydration products of cementitious composite materials with different mixing proportions is mainly in the range of 0?3%at different age,then the corresponding porosity is mainly in the range of 15%?30%,and the average pore diameter is in the range of 14nm?30nm.(5)Considering the flexural strength and compressive strength,pore size distribution,average pore diameter and porosity of the test results,the optimum content of cementitious composite materials of single admixture is determined,in terms of,silica fume is about 6%,fly ash is about 4%?8%,slag powder is about 12%.Similarly,the optimum content of admixture of multicomponent cementitious composite materials is also determined,in terms of,silica fume is about 6%,fly ash is less than 7.5%,slag powder is about 4%?8%,and cement is about 80%.