Anti-freezing Material Used In RCC In Extremely Cold And High Altitude Areas And Its Action Mechanism

hysteresis loop. Furthermore, smaller particle size of MAP, lower the strength loss and higher drying shrinkage rate.2. Comparative study of influence of various air entrained or pore created materials including MAP, AEA and SAP on workabitity, mechanical property, water absorption performance and freeze-thaw resistance of RCC was carried out. The feasibility of MAP rather than AEA used as anti-freezeing compononent in RCC was demonstrated.Influence of different air entrained or pore created materials on workability was different. Adding AEA improved workability of fresh roller compact concrete, increased air content and postponed the setting time obviously. SAP was incorporated by entraining extra water, resulting in increasing Vc value and shortening setting time, whereas dry MAP particles was mixed into concrete, bringing little effect on Vc value under appropriate content or applicaiton of water-reducing agent. It was worthy to note that the entrained air content by SAP or MAP can not be observed in fresh concrete.The strength of RCC was greatly improved by incorporation of MAP. The compressive strength of RCCs at 90d increased by 16.6% and 28.3% when the MAP1 dosage was 0.3% and 0.6% respectively, and 28.7% and 20.8% when incorporated with 0.3% and 0.6% of MAP2 respectively, in comparsion to the control RCC specimen. In contrast, incorporation of AEA into RCC brought almost 30% compressive strength loss compared the control one. The effect of SAP on RCC strength was closely related with its particle size and absorptivity, and the compressive strength loss ranged from 6% to 37% at different ages.The pore system created by MAP was dominated by its particle size and content, which significantly affected the freeze-thaw resistance of RCC. The pores entrained by MAP was spherical, and the sizes ranged from tens of microns to hundreds of microns, appromaxitely 2-3 times of its dry particle size. The bubble spacing factors of pores system created by MAP decreased with increment of MAP content, yet the air content in concrete increased. Therefore, the freeze-thaw resistance can be dramatically improved by adding MAP. The total sum of scaled materials and relative dynamic elastic modulus of MAP-RCC were lower compared with AEA-RCC after the same freeze-thaw cycles. Results showed that RCC behaved best freeze-thaw resistantce when the size of MAP ranged between 80-150 microns and the dosage was 0.6%. By contrast, the air pores entrained by SAP were characterized with irregular and large size, which could slightly improve freeze-thaw resistance of RCC with proper dosage and particle size. However, the ability to prevent from freezing and thawing was rather lower than MAP or AEA.3. The influences of MAP on hydration process, pore structure, C-S-H polymerization, Qn distribution in C-S-H, Al replacement content in C-S-H gel, HD/LD ratio in C-S-H gel in cement (fly ash) paste were studied. The mechanisms of MAP to improve freeze-thaw resistance and strength of RCC were revealed from the perspective of micro and nano scale.Incorporation of MAP accelerated the hydration reaction rate of cement both at the acceleration period and inducing period, but the hydration degree of cement was not been largely improved at later age. A few hydration products grew into the pores created by MAP, yet the structure of cement matrix became more compact. The acrylic monomer dissolving out from MAP combined with Ca2+ to form an unstable complex compound, leading to the existence of silicate root monomer in cement paste, resulting in promotion of early hydration of C3S. Affected by MAP, the average chain length of C-S-H increased, leading to increment in polymerization degree. Q2 content in C-S-H gel increased while Q1 content decreased. Q2/Q1 ratio increased with increment of MAP content. Al replacement in C-S-H gel decreased.The existence of MAP decreased capillary porosity of cementitous paste, and the pore size refined. Results showed, HD/LD ratio increased in C-S-H structure around pore wall created by MAP in contrast to the pore wall entrained by AEA, resulting in improvement of the nano mechanical property of pore walls. Results of nano indentation indicated that proportion of LD C-S-H and HD C-S-H was almost the same in C-S-H gel around pore walls entrained by AEA, while HD C-S-H content was respectively. But around the wall of pores introduced by MAP, the content of HD C-S-H was three times the LD C-S-H content.Reasons of concrete strength improment due to incorporation of MAP included:(1) the average chain length of C-S-H increased, the polymerization degree of C-S-H increased. Q2/Q1 ratio in C-S-H gel increased, and Al replacement decreased. C-S-H gel packed more compacted while HD/LD ratio increased. (2) The volume of water space in paste at early age was changed due to MAP absorption and desorption behavior. As a result, not only the structure of paste become more compacted and well-distributed, but also the capillary pores content decreased and the pore size refined. (3) HD/LD ratio in C-S-H gel around the pore wall created by MAP increased, which indicated C-S-H packed denser.The roller compacted mixed with MAP provided with high freeze-thaw resistance contributed to following factors:(1) Effect of creation of micro pore and accomdation of hydrostatic pressure. The pores system created by MAP can be designed and customized to satify the demand of freeze-thaw resistance through control of MAP particle size, absorptivity and dosage. The pores created by MAP can well accomdated the hydrostatic pressure caused by volume expansion due to transformation of water to ice. (2) released water were mostly spherical pores with a diameter range from 100μm to 400μm and had an apparent bleed air expansion effect; (2) Effect of optimization of pore structure and strengthen of pore wall. Incorporation of MAP resulted in decrement in capillary porosity and refinement of pore size, leading to reduction in available frozen water content. The mechanical property of pore wall was also strengthen, consequently the ability to resist hydrostatic pressure was improved. (3) Effect of strengthen of solid phase. The strength of solid phase was improved, and the structure was denser, thus the deformation resistance was significantly improved. (4) Effect of core-shell. MAP can be acted as "shell", isolated the ice cystal grow in MAP structure, and prevent ice cystal to grow.4. It studied and developed the technology to customize and design pore. The calculation method of pore radium and content created by was proposed.The micro pore radius created by MAP was only affected by MAP content, particle size, absorptivity and density, but not affected by hydration environment and water to binder ratio. The computational formulas of pore radius and content created can be showed, the pore diameter entrained by was approximately 3 times of dry MAP particle diameter. The air content in hardened concrete with incorporation was the sum of the air content entrained into fresh concrete and the pores content created by MAP. The calculation results were well mathched with the test results. The pore system entrained by MAP can be predesigned and quantitive controlled, which was not affect by water to cement ratio and high altitude. The difficulty in air entrainment in RCC in extremely cold and high altitude areas can be well solve by incorporation of MAP. To achieve equivalent freeze-thaw ability, adding MAP was more effective than traditional air entrainment agent. Therefore, MAP as anti-freezing material widely used in concrete has tremendous technological, environmental and economic effects.