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Sulfate resistance and phase composition of shotcrete
Tunnelling and Underground Space Technology ( IF 6.7 ) Pub Date : 2020-12-26 , DOI: 10.1016/j.tust.2020.103760
Josef Kaufmann , Roman Loser , Frank Winnefeld , Andreas Leemann

Shotcrete is often in direct contact with groundwater containing sulfate. The resistance to sulfate attack of modern sprayed concretes produced with non-alkali aluminate-based accelerators in combination with different cement types is related to their microstructure, transport properties, porosity and phase composition. A characterization of these properties allows a comprehensive assessment of the sulfate resistance of shotcrete with the identification of the relevant physical and chemical influencing factors.

As with conventional concrete, the cement type and the water to binder ratio are also decisive for the sulfate resistance in shotcrete. On the one hand, capillary porosity and diffusion coefficient show cement-specific differences, and accordingly the sulfate solution uptake and the sulfur profile in the test specimen with cement type and w/b also are different. On the other hand, the type of cement defines the potential for ettringite formation and thus for damage to the concrete. Sulfate expansion is caused by the conversion of monocarbonate/hemicarbonate/monosulfate (AFm phases) to ettringite. The application of sulfate-resistant cements does not guarantee the sulfate resistance of sprayed concretes in each case. Their use, however, minimizes the damage potential.

In the sulfate resistance tests, damage in shotcrete causing a drop in the dynamic modulus of elasticity occurs at a higher sulfate expansion compared to conventional concrete due to the higher volume of hardened cement paste and the smaller maximum aggregate size.

The studied alkali-free accelerators, currently used in practice, are found to have no direct adverse effect on the sulfate resistance in the dosage investigated and behave more favorably than the aluminate based alkali-containing accelerators. However, the accelerators influence the sulfate resistance indirectly by causing higher porosity and permeability and thus by an increased sulfate solution uptake of the shotcrete.



中文翻译:

喷射混凝土的抗硫酸盐性和相组成

喷浆混凝土经常直接与含硫酸盐的地下水直接接触。用非碱性铝酸盐基促进剂与不同类型的水泥组合生产的现代喷涂混凝土对硫酸盐侵蚀的抵抗力与其微观结构,运输性能,孔隙率和相组成有关。这些特性的表征可以通过确定相关的物理和化学影响因素来全面评估喷浆的抗硫酸盐性。

与常规混凝土一样,水泥类型和水与粘结剂的比例对于决定喷射混凝土的耐硫酸盐性也起着决定性的作用。一方面,毛细管孔隙率和扩散系数显示出水泥比的差异,因此,水泥类型和w / b的试样中的硫酸盐吸收和硫分布也不同。另一方面,水泥的类型决定了钙矾石形成的可能性,从而损害了混凝土。硫酸盐膨胀是由单碳酸盐/半碳酸盐/单硫酸盐(AFm相)转化为钙矾石引起的。在每种情况下,抗硫酸盐水泥的应用都不能保证喷射混凝土的抗硫酸盐性。但是,使用它们可以最大程度地减少损坏的可能性。

在抗硫酸盐性试验中,由于硬化水泥浆的体积较大且最大骨料尺寸较小,与常规混凝土相比,在较高的硫酸盐膨胀下,喷射混凝土中的破坏会导致动态弹性模量下降。

已发现,目前在实践中使用的已研究的无碱促进剂在所研究的剂量中对耐硫酸盐性没有直接的不利影响,并且比铝酸盐基含碱促进剂的性能更好。但是,促进剂通过引起较高的孔隙率和渗透性,并因此通过增加喷射混凝土的硫酸盐溶液吸收量而间接影响耐硫酸盐性。

更新日期:2020-12-27
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