Environmentally friendly lime melting slag-GBFS-titanium gypsum cementitious material: Mechanical properties, hydration characteristics and microstructure

Abstract

Lime melting slag (LMS) is the solid waste produced when high-purity magnesium hydroxide is made utilizing the ammonia-lime combination technology. This study discusses the impact of LMS on the strength growth and hydration behavior of the granulated blast furnace slag (GBFS)-titanium gypsum (TG) system, with the aim of realizing the resource utilization of LMS. XRD, FTIR, SEM-EDS NMR and hydration heat characterization were employed to identify the types and development processes of hydration products at various stages. The findings indicate that incorporating 2 % LMS into the sample yields the most effective excitation, enhancing the mechanical characteristics of cementitious materials at various curing stage, particularly after 3d. The 3d compressive strength of the samples with 2 % LMS was 99.2 %, 36.9 %, 43.6 % and 72.4 % higher than that of the samples with 0 %, 4 %, 6 % and 10 % LMS, respectively. The undissolved Ca(OH)2 in the LMS can selectively adsorb dissolved Ca2+ and OH- to form a double layer structure. The higher the content of undissolved Ca(OH)2 in GBFS- titanium gypsum system, the higher the adsorption capacity of Ca2+ and OH-, and the relative content of ions used in alkali excitation slag decreased. Therefore, in the GBFS-titanium gypsum system, with the increase of LMS content, the hydration degree of GBFS gradually slows down, and the generation of hydration products correspondingly decreases, which shows that the compressive strength decreases on the macro level. The analysis of hydration products shows that the appropriate amount of LMS can promote the dissolution of GBFS, generate a large number of C-(A)-S-H gels and ettringite, form an interlocking effect in three-dimensional space, and improve the mechanical properties of hydration products. However, CO2 in the air dissolves in the water pool of the curing test block to form CO32-, which reacts with the three-dimensional network gel to form fine needle-like thaumasite, resulting in a decline in the flexural strength of GTL2, but this does not affect the development of the compressive strength of the test block. GTL cementitious materials also have good ecological and environmental benefits. This study provides a new idea for the resource utilization of LMS, and provides a rich theoretical basis for the research of solid waste cementitious materials.