Improving the environmental impact of supplementary cementitious materials

January 19, 2023

Tao Liu defended his PhD thesis at the department of Built Environment on January 19th.

Source: iStockPhoto.

The cement industry uses a lot of natural resources and energy in the production of cement, but alternative, more sustainable options are available. For example, supplementary cementitious materials are cementless binders that can be produced in a more energy efficient manner, and they offer improved building performance. However, challenges remain with regard to the wholesale use of supplementary cementitious materials. For his PhD thesis, Tao Liu looked at the alkali activation of various industrial by-products in the production of supplementary cementitious materials with the aim of promoting alkali activated materials.

Supplementary cementitious materials (SCMs) make a significant contribution to sustainable construction. The use of these materials in concrete production results in energy and materials savings, and offers improved efficiency and building performance.

Nonetheless, there are challenges to be overcome in terms of the large-scale use of SCMs. In their PhD thesis, Tao Liu first looked at the alkali activation of various waste materials such as slag, fly ash, waste glass, and municipal solid waste incineration bottom ash (MSWI BA) for the production of SCMs.

Thereafter, he considered applying waste-material-based alkali activated materials (AAMs) as a cementless binder. Furthermore, in-situ formed layered double hydroxides (LDHs), the secondary reaction products of AAMs, has a superior heavy metal ions binding capacity. The promotion of in-situ formed LDHs highlights the importance of environmental concerns.

Immobilization potential

The immobilization potential of AAMs can be improved by the in-situ formed LDHs. This research utilizes sodium aluminate to activate the SCMs. The results show that the in-situ formed LDHs are promoted with higher Al-O tetrahedra and Mg2+ contents, enhancing chloride resistance and heavy metal ion binding capacity of activated SCMs.

Liu’s work reveals the effect of extra Al-O tetrahedra and Mg2+ on the in-situ formation of LDHs. Based on the results, the mechanism of sodium aluminate activation is proposed.

Simultaneously, sodium aluminate stabilizes the relatively low pH environment of samples. It shows the potential to tackle the issue of the high pH of the normal AAMs to human health which significantly limits its engineering applications.

Title of PhD thesis: In-situ formation of Layered Double Hydroxides (LDHs) in Alkali Activated Materials (AAMs). Supervisors: Jos Brouwers and Qingjang Yu.