Enhancement effect and mechanism of iron tailings powder on concrete strength

As one of the largest solid wastes, iron tailings seriously threaten the safety of personnel and environment. The sharp increase in the content of fine-grained tailings seriously restricts the comprehensive utilization of tailings. In order to improve the comprehensive utilization rate of fine-grained iron tailings, concrete was prepared with iron tailings powder (ITP) and slag powder (SP) as composite admixtures. The compressive strength of concrete at each age was tested and compared with limestone powder (LP) concrete under the same conditions. The hydration products and micro morphology of ITP composite admixtures at long age were analyzed by microscopic experiment such as SEM, BSE, XRD, IR and NMR. The results show that the strength ofITP concrete at each age is higher than that of LP concrete with the same content, so ITP has an enhancement effect on the strength of concrete. This effect is more significant under the condition of low water binder ratio and SP, and increases with the increase of age. For example, when the water binder ratio is 0.27 and the ratio of ITP to SP is 5:5, the 1080d strength of ITP concrete is 9.3MPa higher than that of LP concrete. The reaction took place on the surface of ITP particles at long-term age, 29 Si migrates to high polymer and 27 Al migrates to high coordination. The Si–O bond and Al–O bond on the surface will regroup with Ca 2+ under alkaline conditions to form composite salt minerals with calcium silicate and calcium aluminosilicate as the main components. This bonding reaction takes a long time, which improves the compressive strength of long-age concrete. • Iron tailings powder as admixture can improve the comprehensive utilization rate of tailings. • Compared with limestone powder, iron tailings can enhance the long-term strength of concrete. • Si–O and Al–O on tailings surface have bonding reaction in the slag composite admixture. • Iron tailings powder can be used as a concrete admixture.