Crystallization of the Amorphous Phase in Foam Glass as a Method of Decreasing the Alkali-Silicon Reaction

Crystallization‐induced stabilization of foam glass aggregates for heat‐insulating concrete

“…As it has been demonstrated by the tests according to the ASTM standards, 2‐4 classical panel foam glass with amorphous walls of the pores cannot resist alkali‐silica reactions unlike the glass‐ceramic foams 21,22 . ASR‐research by chemical methods of foam glass and glass‐ceramic foams shown the same results 26,27 .…”

“…The percentage of devitrite relatively to external standard became the highest (57% at 850°C and 64% at 900°C) in both sample types after 60 minutes calcination but did not increase much (<2%) as the annealing time was extended up to 120 minutes (Figure 4). With this development of the crystallization process, high percentage of devitrite in the pore walls of aggregates can be obtained at prolonged annealing and/or at a certain cooling regime as panel glass‐ceramic foams 21,22 …”

“…During the final stage of crystallization process (after 60 minutes of annealing) following phases were detected: silica modifications (tridymite and quartz), devitrite, and Na 4 CaSi 3 O 9 ‐phase in the D‐type samples (same as in ASR‐resistant panel glass‐ceramic foams 22 ); silica modifications, and devitrite in the L‐type samples.…”

“…The crystallization degree of the calcined granules was estimated by XRD relative to the known composition of commercial panel glass‐ceramic foams in which the main crystalline phase exists as elongate 20‐40 μm crystals of devitrite (Na 2 Ca 3 Si 6 O 16 ), together with sub‐micron dark particles of the Na 4 CaSi 3 O 9 ‐phase, tridymite, and trace quartz 22 (Figure 2). The content of devitrite ( hkl ) were evaluated according to the intensity of its strongest (021), (212) and (213) peaks at 2θ = 32.17°, 18.63° and 28.73°, respectively, relative to the reference compositions of panel glass‐ceramic foam used as an external standard.…”

“…An area of panel foam glass application is also limited by ASR with gluing or decorative cement composites followed by formation cracks close to the border between cement composites and panel foam glass. This problem was solved by crystallization of micro‐ and nanoscale Ca‐Na‐silicate crystals in glass walls of the pores with the formation of panel glass‐ceramic foams (Foamsital) 21‐22 . According to this technology, thermo‐induced foaming is carried out simultaneously with the crystallization of pyroplastic pore walls.…”