Effect of Mixing Method on the Freeze Thaw Dulability of Silica Fume Concrete

利用目前收集到的各种硅粉，研究了硅粉的形态和化学成分对混凝土流动性的影响，并与装料方式和搅拌时间有关。对硬化混凝土进行了冻融试验和气孔分布测量，从拌合方式和气孔分布两方面对其抗冻性进行了综合评价。本文的研究结果总结如下：1。水胶比大于或等于35%的非声发射混凝土的抗冻性随着硅灰替代比的增大而显著降低。高抗冻性非声发射混凝土的极限水胶比在25%左右。水胶比较高的混凝土需要适当的引气。水胶凝硅灰混凝土获得足够的抗冻性所需的空气含量，在10%和20%的替换率下，55%的替换率分别为6%和8%左右。因此，当使用硅气时，空气含量应增加2至4个百分点。随着水胶比的减小，空隙间距系数增大。当水胶比在35%或更高时，含硅灰混凝土的空隙间距系数往往比不含硅灰的情况略高。硅灰混凝土的夹带空气含量约为4%，水胶比较低，与搅拌时间无关，具有较高的抗冻性。当水胶比为55%时，混合时间的不同导致耐久性系数的差异很大，最大值是最小值的两倍。使用硅灰或降低水胶比可使硬化混凝土的微观结构致密化，但拌合时间对其影响不大。硅灰的使用减少了直径小于200米的空隙，增加了直径大于500米的空隙。孔径分布随混合时间的变化而变化。硅灰混凝土搅拌180秒时气孔总数最大。同时，小直径孔洞的数量增加，孔洞间距系数减小。少

Using various types of silica fume colleted so far, the authors investigated the effects of the form and chemical components of silica fume on the fluidity of concrete with relation to material charging methods and mixing time. Freezing and thawing tests and air-void distribution measurements were also made on hardened concrete, for the purpose of total evaluation of the resistance to freezing from the aspects of the mixing method and air-void distribution.The results obtained in this paper are summarized as follows :1. The freezing resistance of non-AE concrete with a water-binder ratio of 35% or higher significantly decreases as the silica fume replacement ratio increases. The limit water-binder ratio to produce non-AE concrete judged as having high resistance to freezing is around 25%. Concrete with a higher water-binder ratio will require appropriate air entraining.2. The air content required to obtain sufficient resistance to freezing for silica fume concrete with a water-binder r … More atio of 55% is around 6% and 8% at a replacement ratio of 10% and 20%, respectively. The air content should therefore be increased by 2 to 4 percentage points when using silica fume.3. The void spacing factor increases as the water-binder ratio decreases. With the water-binder ratio at 35% or higher, the void spacing factor of concrete containing silica fume tends to be slightly higher than the case without silica fume.4. Silica fume concrete with an entrained air content of around 4% and a low water-binder ratio has high resistance to freezing independently of the mixing time. When the water-binder ratio is 55%, a difference in the mixing time leads to a wide difference in the durability factor, with the maximum being two times the minimum.5. The microstructure of hardened concrete is densified by the use of silica fume or a reduction in the water-binder ratio, but is scarcely affected by the mixing time.6. The use of silica fume reduces air-voids smaller than 200 ()m in diameter and increases air-voids larger than 500 ()m in diameter.7. The pore size distribution varies depending on the mixing time. The total number of air-voids in silica fume concrete is largest when it is mixed for 180 seconds. Also, the number of small-diameter voids increases and the void spacing factor decreases at this mixing time. Less