Due to the high energy consumption and carbon emission of cement, using active supplementary materials in concrete is widely studied. In this paper, waste tuff micropowder and recycled fine powder (RFP) with maximum replaced ratio of 70 % were investigated by alkali activation in ultra-high performance concrete (UHPC), the mechanical properties and hydration process were studied with different dosages and activators. The results show that the strength activity index of tuff and RFP both enhanced after calcium hydroxide activation. The alkali activator accelerated the hydration speed of tuff and RFP, also leaded to a low heat generated. The compressive strength was reduced with the replaced ratio of tuff and RFP, but the flexural strength was improved once tuff added and cured in appropriate temperature. In the cement-tuff/RFP system, calcium hydroxide accelerates cement hydration and activates part of the tuff and RFP to generate C-(A)-S-H to improve the strength of the mortar. Due to the low degree of tuff activation, less hydration products were formed, leaded to an increase in porosity. The RFP was effectively activated by calcium hydroxide, and the generated C-(A)-S-H and CaCO effectively refined the pore structure. The activation of RFP consumed limited mixing water, while the excessive CaCO generated by activation will cause the loss of UHPC strength.

中文翻译：

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高比例活性凝灰岩和回收细粉低碳UHPC的制备与水化


由于水泥的高能耗和高碳排放，在混凝土中使用活性辅助材料被广泛研究。本文以最大替代率70%的废弃凝灰岩微粉和再生细粉（RFP）为研究对象，通过碱活化在超高性能混凝土（UHPC）中进行研究，研究了不同掺量和活化剂的力学性能和水化过程。结果表明，氢氧化钙活化后凝灰岩和RFP的强度活动指数均有所提高。碱活化剂加快了凝灰岩和RFP的水化速度，也导致产生的热量较低。随着凝灰岩和RFP替代比例的增加，抗压强度降低，但加入凝灰岩并在适当的温度下固化后，抗弯强度得到提高。在水泥-凝灰岩/RFP体系中，氢氧化钙加速水泥水化，并活化部分凝灰岩和RFP生成C-(A)-S-H，提高砂浆的强度。由于凝灰岩活化程度低，形成的水化产物较少，导致孔隙率增加。 RFP被氢氧化钙有效活化，生成的C-(A)-S-H和CaCO有效细化了孔结构。 RFP的活化消耗了有限的混合水，而活化产生的过量CaCO3会导致UHPC强度的损失。