Mechanism And Application Of High Flowability And Ultra-high Early Strength Solidification Materials

As the development and growth of constructional engineering, the scope of ap-plication of the inorganic bond materials are more and more widely; and the function is rapidly increased, it is applied to many special fields and major engineering such as high speed railway, military engineering and major infrastructure. The important part of special projects requires material system to have good forming property and char-acteristics of short cycle, high efficiency and high mechanical properties in a short time (everal hours after molded) during the construction and molding. In recent years, as the development of economy and science and technology, we need the buildings and structures to have longer period of service, to meet more strict construction re-quirements. The destruction of the inorganic bond material is more serious than ever before and the durability also drops greatly because of the increasingly load and se-vere environment even the threat of natural disasters. However, the rapid develop-ment of the technologies in recent years requires inorganic bond materials to have excellent properties such as high workability, high rigidity and high durability. Ac-cording to the current development situation and application of common early strength materials, we think up a research thought that is using SAC which has good durability to develop HUSM (High Flowability and Ultra-high-early Strength Solidi-fication Materials).This paper which bases on the sub-project of "973program"(2009CB623201-1) and NSFC (51178363) aims at studying the influence of the rheological components, slow-release components, enhanced components and modified components on the related characters of HUSM mainly based on SAC which has advantages in properties of rapid hardening, early strength, high-strength and good durability, etc, by testing flowing property, mechanical property and micro property. Curing mechanism of high flowability and ultra-high-early strength SAC-based materials is also discussed in this paper which is intended to expand areas of special cementitious system and provide theoretical guidance and application reference of ultra-high-early strength materials based on SAC. The main work and the results obtained are as follows:1、HUSM high flow system design and rheological model High flow materials mean materials can fill complicated or irregular model de-pends on dead-weight without vibrating, non segregation and good mechanical prop-erty and durability. This paper sets up a model which can describe the rheological behavior of mortar more realistic according to the requirements of high flow materials. In the model, the shear stress of cement mortar is made up of collision mechanical force between aggregate particles, flowing mechanical force and indirect stress trans-fer mechanism; the irregular shape of aggregate particles are simulated as rigid spherical particles which are uniformly dispersed and suspended in high mobility and viscous cement pastes. In this situation, all mortar shear stress τM is the sum of yield stress τ0and flowing shear stress τp of cement mortar, interaction force τFA-P between aggregates and cement mortar and yield stress τFA resulting from aggregates moving. That is τM=τ0+τp+τFA-P+τFA.According to rheological model, we studied the influence of the slurry viscosity, particles of aggregates and aggregates volume content to mortar shear stress, at the same time, we studied the components of MSF, PCS and PCS+C to the influence of mortar rheological behavior by testing fluidity, flow curve and thixotropy. A dedi-cated retarder BM is developed to legitimately regulate the operating time of the HUSM.The results indicate that the yield stress and viscosity of mortar are enhanced with the increase of the yield stress and viscosity of the cement paste. As the aggre-gate volume fraction increased from10%to40%, the fulidity of mortar is also en-hanced nonlinearly. For a given aggregate volume fraction, the nonlinear trend of the large aggregate particales is more obvious than that of the small aggregate particales.The mortar contained smaller aggregate particales shows higher yiled stress and viscosity.The fluidity at the strating and30min and the setting time of the sulphur aluminate cement can be effectively regulated by using the super plasticzer PCS+C and the retarder BM.2. Design and reliazation of ultra-high-early strength of HUSMThe binding material has a good graduation by taking advantage of the suerfine modification effect of the CaCO3powder and silica fume. The effect enhances the compactness of the system on the microscale and adjusts crystalline texture of the hydration products Aft produced form sulphur aluminate cement. For these reasons, the structure in the interface region and the crystallization stability are enhanced. On the basis of using the retarder BM, the introduction of the superfine admixture in-creases the heat of hydration and accelerates the crystallization and generation of the hydration products. It reduces the porosity of the system because of micro fine filler effect and so the strength of material was increased.Based on the project objective, Ca(NO2)2and Ca(HCOO)2which play better role for strength are elected. The influences of Ca(NO2)2and Ca(HCOO)2on the hydra-tion performances of materials based on sulphoaluminate cement and the influencing rule of the two enhanced components on strength were studied. By addition of Ca(NO2)2and Ca(HCOO)2, the setting process of sulphoaluminate cement is substan-tially accelerated, the interval of initial and final setting time is shortened. It provides advantages for HUSM based on sulphoaluminate cement with strength structure formed quickly. The addition of Ca(NO2)2and Ca(HCOO)2promot the hydration re-action of sulphoaluminate cement observably, improve the hydration heat greatly and accelerate the crystallization and generation of the hydration products (AFt) availably. The strength of HUSM based on sulphoaluminate cement could achieve more than20MPa with PCS+C and BM by adjusting Ca(NO2)2and Ca(HCOO)2. But the strength of HUSM is unconspicuous without Ca(NO2)2and Ca(HCOO)2. The strength of HUSM based on sulphoaluminate cement maintains the momentum of steady growth by synthetic action of superfine admixtures and enhanced components and the later strength does not shrink. The strength of HUSM could reach above70MPa at28days3. Research of durabilities on modified HUSMBased on the high fluidity and ultra-high early strength of HUSM produced by sulphoaluminate cement, the mixing ratio of HUSM was optimized by the introduc-tion of cracking agent AA and composite modifier CM and some performances of the HUSM were tested. The results showed that:the2h strength of optimized HUSM can reach to25MPa or more and gain stable development. The28d strength of optimized HUSM can reach to75MPa or more at5℃,10℃and-5℃conditions and they have good dimensional stability. The linear expansion of HUSM can be controlled between0.01and0.2mm/m range. HUSM does not have any cracks and micro cracks within72h when the heat of hydration reaction generates fastest. Tested at different concen-trations of sulfate ions in solution resist coefficient, determined HUSM good sulfate resistance; through "quick freezing method" test HUSM after200freeze-thaw cycles of quality changes and dynamic elastic modulus the amount of the loss, modification HUSM draw antifreeze level reaches F200; electric flux and porosity test results show that HUSM has good resistance to chloride ion penetration, thus indicating that the modified HUSM with excellent durability.4. Commercial process and application on high speed railway project of HUSMAccording to the HUSM theoretical research of curing mechanism and mixture ratio determined on the basis of carried out HUSM industrial production, the estab-lishment of HUSM industrial production lines, and will HUSM successfully used in high-speed railway bridges framing project.