| As a new type of building materials, Lightweight aggregate concrete has many uniqueadvantages including light weight, high durability and outstanding economy. Howeversome drawbacks, such as small elastic modulus, brittle fracture so easily and control inworkability and pumpability so hard, seriously restrict the widespread use of lightweightaggregate concrete in civil engineering. Studies indicated that fracture resistance, crackresistance and toughness properties were improved in some degrees by blendingappropriate amount of plastics-steel fiber to lightweight aggregate concrete. Now inengineering ceramic pre-wet process for1h was commonly used to simply improve thework performance of lightweight aggregate concrete, however ceramic water saturatedstate has an influence on concrete strength and durability, therefore it is need todeterminate the reasonable pre-wet ceramic time based on the comprehensiveconsideration into all aspects of macroscopic properties of lightweight aggregate concrete.In this paper, ceramic of two structures was choose: Lytag and shale. The effect ofceramic water saturated state on the workability, strength, frost resistance of lightweightaggregate at macro level and the micro-mortar interface transition zones of lightweightaggregate-slurry was explored in four different degrees of its pre-wet and then the pre-wetceramic reasonable time was determined accordingly.the results are as followed:With the increase of lightweight aggregate moisture content, the concrete slump losstends to decrease over time. Especially in the case of loss of pressure pre-wet process, theminimum concrete slump loss value showed good workability.The incorporation ofplastics-steel fiber can make lightweight aggregate concrete from brittle failure modes ofdestruction into a certain plasticity. With the increase of ceramic moisture content, theintensity decreases when its concrete curing is for7d and14d, and the strength of thespecimen in each group were quite different. But in the conservation for28d and56d, theconcrete strength has little relation with ceramic water content, but was mainly related tothe intensity of the lightweight aggregate itself. The water content of lightweight aggregateconcrete is an important factor to frost resistance, frost resistance performed poorly with more water content, ceramic concrete frost level is greater than F300by atmosphericpre-wet process, but its concrete frost rating by pressurized pre-wet ceramic process is notable to reach F300, that is to say its pre-wet concrete frost resistance by pressurizedpre-wet ceramic process is seriously impaired. The shale antifreeze performance oflightweight aggregate concrete is better than that of fly ash lightweight aggregate concrete.For Lytag,1h pre-wetted time is needed before use. The pre-wet shale time may varyaccording to demand: When the need is focused on frost resistance, the pre-wet time is for0.25h~3h; when the work requirement is higher, pre-wet period may be extended to3h~6h.There were large number of plate-like and orientation Ca(OH)2crystals in concreteinterfacial transition zone when pressurized pre-wetted ceramic is for3d age andatmospheric pre-wet process are rarely found. For7d curing period, lightweight aggregate-cement paste become a relatively compact as a whole interface with small amount ofmicro-cracks in transition zone pores. For28d curing period, ceramic concrete of smalldegree of pre-wet aggregate is strong integrity and lower porosity with more smoothinterface transition zone between lightweight aggregate and cement paste. And the lagerpre-wet extent, especially pressurized pre-treatment ceramic interface region under itsconcrete structure is relatively porous, loose, poor integrity. |
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