Research On Silicon-oxy Tetrahedron Aggregate States Of Hydration Products CSH Gels Of Cement With High Content Of Fly Ash Materials

During the construction of mass concrete, high volume of fly ash are taken in order to reduce the hydration heat. Therefore, it is necessary to investigate the mechanism of hydration for these systems. In this article, the major systems for investigation are 50%fly ash-50%cement materials. The main research findings are including:High-resolution solid Si NMR whose results were supported by assisting testing techniques including XRD and FTIR was adopted to carry out deep and systematic research on development laws of silicon-oxy tetrahedron aggregate states of hydration products CSH gels influenced by curing condition, content of fly ash and curing days. The silicon-oxy tetrahedron aggregate states of hydration products CSH gels and changing laws of phases in the hardened pastes have been made clear with the single and corporate actions of erosive ions at the early stage when the serious destruction did not happen. Quantitative descriptions of reaction degree of cement and fly ash in cementitious materials have been realized according to the analyzing results of NMR spectrums, of which differences and relations between NMR and traditional methods.Curing for 7 and 28 days, maintenance at high temperatures(50℃,80℃) hardened pastes could increase silicon-oxy tetrahedron aggregate states of CSH gels and contents of aluminum-oxy tetrahedron, both of which were similar at two high temperatures. Curing at normal temperature was good for increasing silicon-oxy tetrahedron aggregate states of CSH gels and contents of aluminum-oxy tetrahedron at the periods from 7 days to 28days. The increasing range of main chain length was little for the hardened pastes curing firstly at 50℃for 28 days and secondly 20℃for 90 days. Its contents of aluminum-oxy tetrahedron were decreased by 25% and reaction degree of fly ash made slow progress. The reaction degree of fly ash for pastes curing at high temperatures for 28 days was about as 4 times much as at normal temperature. High temperatures sped the reaction degree of fly ash but its increasing trend was small after 28 days. The effects of fly ash contents on silicon-oxy tetrahedron aggregate states of CSH gels were that the value of FA50 was the highest, FA70 second and FA30 the last and that the effect of fly ash contents on contents of aluminum-oxy tetrahedron was small. Quantitative descriptions of reaction degree of cement and fly ash in cementitious materials have been realized according to the analyzing results of NMR spectrums which were in accordingly with the traditional methods including bound moisture and selective acid dissolution. Na2SO4 decreased silicon-oxy tetrahedron aggregate states of CSH gels. However, Na2CO3 and NaCl were the opposite. The existence of Na+ made more Al moleculars come into CSH gels.