碱对混凝土性能的影响

INFLUENCE OF ALKALI ON PROPERTIES OF CONCRETE

对北京永定河芦沟桥产地的粗集料短龄期的混凝土试验表明，高碱影响混凝土的抗压强度和抗弯强度·当碱量从３．０ｋｇ／ｍ３提高到８．０～９．０ｋｇ／ｍ３、试件６０℃养护８１周后，抗压强度下降约３０ＭＰａ。为防止抗压强度损失，安全碱量必须低于３．５ｋｇ／ｍ３。试件中仅发现少量碱集料反应环，大多数试件膨胀率低于０．０５％。因此，碱集料反应不是导致强度下降的唯一原因，正如其它研究所示。

Study on the coarse aggregate taken from Lu Gou Qiao at the Yong Ding River,Beijing shows that a high alkali content influences compressive and flexural strengths of concrete.When the alkali content increases from 3.0kg/m 3 to 8～9kg/m 3 and after the concrete is cured for 81 weeks at 60℃,the compressive strength decreases bya bout 30 MPa. The safe alkali content needs to be below 3.5kg/m 3 to ensure against a loss of compressive strength. Only a few reaction rings of alkali-aggregate reaction were found in the samples.The expansion of most of the concrete specimens was smaller than 0.05%.There fore in this case alkali-aggregate reaction is not the only reason for the reduction in the strength. As shown by other researches, the loss of strength may be attributed to the influence of additional alkali on cement hydration and nature ofthe solid phases produced.