Experimental study on the effects of glass hollow microspheres and fly ash on the thermo-mechanical properties, pore structure, and interface characteristics of foamed concrete

The low strength and unstable pore structure of foamed concrete (FC) have restricted its application in low-carbon building envelope structures. To this end, this paper proposes a method that introduces glass hollow microspheres (GHM) as the physical framework, supplemented by fly ash (FA) to induce interfacial chemical enhancement, and collaboratively regulates the pore structure and interfacial characteristics of FC. The effects of water-binder ratio (W/B), H 2 O 2 dosage, GHM, and FA substitution rate on the thermal-mechanical properties, pore size distribution, and interface evolution of FC were systematically studied. The results show that under the optimal mix design (W/B = 0.6, H 2 O 2 dosage 5%, FA substitution rate 15%), the compressive strength of the GHM-containing GFA 0.15 is 42.53% higher than that of the reference group F W0.6-H0.05 , and the thermal conductivity is 21.99% lower. The mechanism reveals that the introduction of GHM increases the yield stress of the slurry. Under the condition of medium and low W/B ratio, it does not cause coarsening of the pore structure. The pozzolanic reaction of FA in situ generates an aluminum-rich C-(A)-S-H gel layer on the surface of GHM, reducing the Ca/Si ratio in the interfacial transition zone (ITZ) to 1.63 and increasing the Al/Si ratio to 0.42. This promotes the transformation of the interface from physical bonding to a strong bonding structure dominated by Si-O-Ca chemical bonds, thereby significantly enhancing load transfer efficiency and interface stiffness. This research provides a theoretical basis for the design of high-performance, low-thermal-conductivity FC and the high-value utilization of industrial solid waste.