再生混凝土在硫酸盐与干湿循环耦合作用下的耐久性能研究

为了研究再生混凝土在硫酸盐与干湿循环耦合作用下的耐久性能及寿命预测,以再生粗骨料取代率、水胶比、粉煤灰掺量为影响因素,通过试验的方法,将试件放入浓度为5%的Na₂SO₄溶液中浸泡3 d,然后取出置室内环境下晾干3 d,为一个干湿循环。分别在干湿循环0,5,10,20,30,40,50,60次时,测定其立方体抗压强度、劈裂抗拉强度、质量损失率,以此判定再生混凝土在硫酸盐与干湿循环耦合作用下的耐久性能,并基于质量损失率考虑再生粗骨料取代率、水胶比、粉煤灰掺量的影响,预测再生混凝土在硫酸盐与干湿循环耦合作用下的使用寿命。结果表明,无论是抗压强度还是劈拉强度均随着水胶比的增大而降低;相比未掺粉煤灰的再生混凝土,当粉煤灰掺量在20%~30%时,可以改善再生混凝土的抗硫酸盐干湿循环侵蚀性能;当粉煤灰掺量在40%时,达不到很好的抗硫酸盐干湿循环侵蚀效果;当再生粗骨料取代率为70%、水胶比为0.3、粉煤灰掺量为30%时,能达到比较好的抗硫酸盐干湿循环侵蚀效果,并将此条件代入预测模型求得T=128 a,相比重要建筑物设计使用年限为100 a,认为耐久性良好。

Durability and Life Prediction of Recycled Concreteunder Sulfate Attack and Wet-dry Cycle

In this paper the durability and expected life of recycled concrete under the combined action of sulfate attack and cyclic wetting and drying were investigated. Specimens of different recycled coarse aggregate ratio, water-binder ratio, and fly ash content were soaked in Na₂SO₄ solution of 5% concentration for three days, and dried in room temperature for three days as a complete wet-dry cycle.The cubic compressive strength, splitting tensile strength, and mass loss rate of original specimen and specimens after 5, 10, 20, 30, 40, 50, 60 times of wet-dry cycles were measured to determine the durability and predict the life expectancy of recycled concrete. Results revealed that both the compressive strength and the splitting tensile strength decreased with the increase of water-binder ratio.The corrosion resistance of recycled concrete against sulfate attack and wet-dry cycles can be improved by adding 20%-30% of fly ash.However, when the content of fly ash was 40%, the anti-corrosion effect was not good. A recycled coarse aggregate rate of 70%, water-binder ratio of 0.3, and fly ash content of 30% would result in a sound corrosion resistance against sulfate attack and cyclic wetting and drying and a durability of 128 years according to prediction model.