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China possesses abundant pumice resources and thereby makes the utilization of pumice in the preparation of pumice aggregate concrete (PAC) a significant strategy for environmental protection and resource conservation. To obtain the effect of pumice pore structure variation on the compressive strength of PAC, PACs with strength classes LC20, LC30, and LC40 were prepared. Moreover, the pore structure of PAC was characterized using nuclear magnetic resonance to investigate the effect of pore structure variation on the compressive strength of PAC. Results showed that the higher the coarse aggregate content of PAC, the higher the percentage of large capillary and non-capillary pore sizes of PAC, corresponding to higher porosity and lower compressive strength. The hydration products in PAC continuously fill in the pore structure, the proportion of large capillary pores and non-capillary pore size gradually decreases, the proportion of small capillary pores and medium capillary pore size gradually increases, the pumice concrete matrix gradually becomes dense, and the compressive strength increases. The prediction model of the pore structure and compressive strength is established based on gray theory, and the relative error between predicted and tested values is not significant, which can effectively predict its compressive strength. It provides effective guidance for the engineering practical application of PAC.

In order to realize the synergistic utilization of calcium silicon slag, fly ash and blast-furnace slag, this paper researched on hydration mechanism of calcium silicon slag composite geopolymer through preparation experiments of the calcium silicon slag composite geopolymer under different ratio of fly ash / blast-furnace slag.The results show that the calcium silicate slag base geopolymer is a binary composite cementitious material mainly composed of C—S—H and C(N)—A—S—H, which is formed by the hydration of β-calcium silicate itself and alkali-activated hydration.Compared with crystalline minerals, glass minerals are more prone to reaction with Ca(OH)2 and sodium silicate, resulting in a large amount of unreacted mullite remaining in the hydrates of 7 d when the fly ash / blast-furnace slag ratio is more than 0.5, but the mullite will continue to hydrate with the extension of curing time, and worm-like tetranatrolite and strip-like beidellite will be formed at 28 d.At the same time, when fly ash / blast-furnace slag ratio is 1.0, micromorphology of calcium silicate slag composite geopolymer is the most evenly distributed and dense, and its 28 d compressive strength reaches maximum 37.9 MPa.So, it indicates that the best synergistic effect among calcium silicon slag, fly ash and blast-furnace slag can be released under this condition.

Homogeneous integration of ultrafine TiO2 nanoparticles into a conductive sulfur-doped carbon skeleton was readily crafted by unusual space-confined twin-polymerization of a titanium-containing single-source coupled monomer and subsequent carbonization, producing a robust hetero-architecture for boosting lithium storage with large reversible capacity, high rate capability, and long-term cycling stability. [ABSTRACT FROM AUTHOR]

Natural pumice concrete (NPC) is a building material with the advantages of light weight and high thermal resistance. In cold regions, NPC undergoes damage from freeze–thaw cycles. Freeze–thaw damage is closely related to changes in the pore structure of concrete. Therefore, it is meaningful to investigate the evolution characteristics and damage threshold of pore structure for NPC under freeze–thaw cycles. In this study, freeze–thaw cycle tests and nuclear magnetic resonance (NMR) tests were designed. The characteristics of the evolution of the pore structure during freeze–thaw cycles were discussed. The results showed that the porosity in NPC specimens increases with the number of freeze–thaw cycles and the main evolution of the pores showed the degradation of fine capillary pores (10 nm < r < 100 nm) into coarse capillary pores (100 nm < r < 1000 nm) and non-capillary pores (r > 1000 nm). After freeze–thaw cycles, the proportion of coarse capillary pores and non-capillary pores increased by 4.83–10.59%. This evolutionary feature directly leads to the degradation of the mechanical properties of NPC. Additionally, a pore damage model was established, and the pore damage threshold was also calculated based on the experimental results. The obtained damage threshold of pore structure can provide the theoretical foundation for the application of NPC in cold regions. [ABSTRACT FROM AUTHOR]