| In the mass concrete engineering under the marine environment,due to the large amount of cement pouring in the mass concrete structure,the internal temperature caused by the airtightness is too high,which often leads to low strength,poor stability,poor rheology and poor anti-ionic erosion ability.In order to ensure the durability of marine engineering infrastructure and improve the performance of use,in recent years,a large number of scholars have studied and developed a high-iron Portland cement("HIPC")which is excellent in the resistance to chloride ion resistance and sulfate attack resistance.However,there are few studies on the hydration heat release process and rheological properties of such cement.In view of the above problems,this paper compared HIPC with ordinary Portland cement("OPC"),systematically studied the hydration heat release rate,the hydration kinetics and rheological properties of two different iron-phase Portland cements.The advantages and disadvantages of the use of HIPC were revealed.In addition,the effects of curing temperature,dosages of fly ash(FA)or slag(SL)on hydration heat and rheological properties of HIPC were studied,and the best mix ratio was determined.At the same time,the minerals composition and microstructure of hydration products were studied by means of BET,XRD and SEM.And to find out the mechanism of hydration heat and rheological properties of modified HIPC cement.The main conclusions of this paper are:(1)HIPC is superior to OPC in hydration heat and rheological properties,and HIPC is more suitable for construction in high temperature environments.At low temperatures,HIPC has the characteristics of high early hydration heat release rate and intense reaction.At high temperatures,HIPC has a faster hydration rate than OPC and lower hydration heat.The hydration kinetics fitting results show that the hydration mechanism of HIPC at 20? is NG?I?D,and the hydration mechanism at 40? and60? is NG?D.HIPC is less sensitive to temperature at high temperatures,and its hydration product is also relatively more stable.The hydration structure of its slurry for3 d is more dense than OPC.The rheological test results show that HIPC does not prematurely condense in the initial stage of hydration in high temperature environment,and the slurry is more stable than OPC.Moreover,HIPC has a larger modulus than OPC,which is more resistant to deformation,and is capable of maintaining excellent stabilityand fluidity in a high temperature environment.(2)The HIPC-FA system can stimulate the activity of fly ash,so that the pozzolanic effect occurs in advance,and its hydration heat and rheological properties are better than OPC-FA system.In the HIPC-FA system,the 3d pozzolanic effect of HIPC-40%FA system at 40? is the most exothermic,while at 60?,HIPC-20%FA has the strongest pozzolanic effect.The hydration kinetics of HIPC-FA system is considered to be NG?I?D at 20?,and at 40? and 60? is NG?D.The microscopic test results show that the refining effect of FA on the pore structure of cement system increases with the increase of temperature,and the pore size distribution of HIPC-20%FA system is optimal at 60?.From the results of SEM and XRD analysis,it can be seen that the fly ash is activated in the HIPC system under high temperature environment,the volcanic ash effect occurs in advance,the strength of the cement stone increases,and the structure is more compact.(3)The performance of HIPC-SL system at room temperature is slightly worse than that of OPC-SL system,but in high temperature environment,its hydration heat and rheological property are better than OPC-SL system.In the high temperature environment,HIPC-40%SL system has the fastest exothermic rate of pozzolanic effect in the early stage of hydrationFrom the results of hydration kinetic,the hydration mechanism at 20? is NG?I?D,the hydration mechanism at 40? and 60? is NG?D in the system with slag content of not more than 40%.In the HIPC-60%SL system,the hydration mechanism at 20? is NG?I?D,40? is NG?D,and at 60?becomes NG?I?D.With the increase of temperature,the high temperature environment provides a better hydration environment for the development of low aluminum iron phase,so that it can maintain good activity.The HIPC-40%SL system has good stability in the early stage of hydration,it can obtain a slurry with good fluidity and homogeneity,and the flocculation structure has the highest strength and the best rheological properties. |
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