A state-of-the-art review on delayed expansion of cemented paste backfill materials

Utilizing delayed expansion cemented paste backfill materials(DECPB) in mine backfill operations offers an effective solution to the challenge of achieving proper contact between the in-situ cemented backfill mass and the roof in mined-out areas(backfill-roof contact).This article presents recent progress in both theoretical and experimental research concerning DECPB.The types and mechanisms of expansive additives,including expansive agents,foaming agents,and expansive mineral materials relevant to DECPB,are explained,along with their impact on the expansive properties and mechanical characteristics of DECPB.The composition,material characteristics,preparation methods,and controlled release mechanisms of microcapsules are analyzed.Two methods for measuring the volume change rate of paste backfill slurries are discussed.Research indicates that an appropriate content of expansive additives not only enhances the expansive properties of cemented paste backfill materials but also contributes to improving their mechanical properties.Chemical foaming agents and bentonite are found to be more suitable for preparing DECPB compared to expansive agents.The delayed expansion of cemented paste backfill material is influenced by microcapsules,with their wall materials,preparation parameters,and the alkaline slurry environment affecting their controlled release mechanism.Developing and optimizing precise measurement devices and methods forfor the volume change rate of cemented paste backfill materials is essential requirement for studying the performance of DECPB.Combining delayed expansion technology with retarding techniques in cemented paste backfill materials can provide a reliable solution for achieving proper backfill-roof contact in the future.

Preparation and Properties of High-strength Ceramsite in Low Water Absorption

Fly ash used as the main raw materials,incorporated with sintering expansion additive and fluxing additive in different ratio,was sintered high-strength lightweight aggregates of fly ash (ceramsite) in the laboratory-controlled electric furnace.The results show that the optimal sintering system is the sintering temperature range of 1250 ℃ to 1280 ℃ and retaining time of 5 min-10 min.The bulk density,the apparent density and 24 h water absorption of ceramsites decrease with the increase of sintering additive and the decrease of the amount of fly ash.The addition of fluxing additive can significantly enhance the compressive strength of ceramsite pellets,reduce its water absorption at 24 h and improve pore-shape ofinner structure.The firing coefficient (Pk) changed within 7.8-8.1 of raw materials can prepare high strength and low water absorption ceramsites.Pk kept a good linear relationship with porosity and strength of ceramsite particles.

Effects of B addition on glass forming ability and thermal behavior of FePC-based bulk metallic glasses

The FePC-based bulk metallic glasses（BMGs）have been demonstrated to possess high plasticity and good soft magnetic properties.However,the relatively poor glass forming ability（GFA）and thermal stabilities limited their application in industries.The effects of microalloying with B in FePC-based BMGs on the GFA and thermal behaviors were systematically investigated.It was found that a small amount of B addition can dramatically enhance the GFA of FePC-based BMGs,which in turn leads to the critical maximum diameter up to 2 mm for full glass formation even using low cost raw materials.The underlying mechanism of the enhancement of GFA from the competing crystalline phase with amorphous phase,the average thermal expansion coefficient and dynamic viscosity were discussed in detail.