混凝土中碱-硅反应的膨胀机理研究

An experimental study on the expansion mechanism of alkali-silica reaction in concrete

利用高碱活性的蛋白石和低碱活性的天然水晶研究碱—硅反应的膨胀力来源。试样粉磨至40￣80μm后与0.7 mol/L的NaOH溶液混合,至反应达平衡,反应产物用真空干燥。取约1 g产物,压制成直径14 mm,厚约3￣4 mm的薄片后,采用自行设计的FLM1-凝胶膨胀自动测量仪分别在无半渗膜和有半渗膜条件下测量其吸水膨胀量。在无半渗膜条件下,反应产物的吸水膨胀量都很小;在有半渗膜条件下,反应产物吸水后都表现出明显的膨胀现象,其中蛋白石反应产物的膨胀量达85.5%,水晶的膨胀量有5.1%,这与反应溶液的pH值降低趋势相对应,也与样品本身的碱活性大小一致。结果表明,产物吸水肿胀所引起的膨胀量是很有限的,渗透压是碱-硅酸反应的主要膨胀来源,从而为碱-硅反应的渗透压假说提供试验论据。

Opal, a high alkali active mineral, and crystal, a low alkali active mineral, are employed to experimentally study the source of expansion force of alkali-silica reaction （ASR） . Samples were ground to granules of diameters of 40-80μm and mixed with a NaOH solution of 0.7 mol/L, respectively. When the reaction reached equilibrium, the products were dried in vacuum. Then, about lg of each of the dried products was pressed into a slice of a diameter of 14mm and a thickness of 3mm to 4mm. The slices were moved to a FLM1-Gel automated measuring device designed by the writer to test the expansion properties of the specimens after imbibing water. Without semi-permeation membrane, the expansion of each slice was small. With semi-permeation membrane, the expansion of each slice was obvious. The expansion of opal slice amounts to 85.5% and crystal slice 5.1%, which is consistent with the decreasing trend of the pH value of each mixture solution and the alkali active level of the sample. The results indicate that the expansion caused by osmotic pressure was remarkable, whereas the expansion caused by swelling pressure was small. These results provide an experimental evidence of the osmotic pressure hypothesis of ASR.