Chemical design of lightweight aggregate to prevent adhesion at bloating activation temperature

Abstract

The purpose of this study is to control the viscous behavior of lightweight aggregates through the chemical design of a lightweight aggregates material in order to solve the problem of the adhesion of lightweight aggregates by viscous behavior in the bloating activation temperature range of lightweight aggregates. In order to induce a reduction of Fe 2 O 3 inside the aggregates, Fe 2 O 3 and carbon were added to acid clay so as to produce aggregate. The particle density and the water absorption rate of the aggregates were measured, the cross-section was observed with an optical microscope, and the distribution of hematite of the lightweight aggregates was confirmed by a 3D CT analysis. Pilot scale rotary kiln experiments were performed. The optimal additive contents for the production of lightweight aggregates using acid clay were 8-13 wt% of Fe 2 O 3 and 2-3 wt% of carbon. The addition of additives decreased the bloating activation temperature, and viscous behavior was promoted in the core portion of the aggregates, resulting in a difference in the melting point between the shell and the core. As a result, the occurrence of adhesion at the aggregates surface was suppressed.

Investigation of Industrial Residues and Waste Materials to Expand the Raw Material Base for the Production of Lightweight Aggregates

“…Leismann [10], for example, used literature data to determine the phase proportions of natural clays that are favourable for bloating behaviour, as shown in Table 1. The most important gases produced during bloating are released between 850 and 1150 °C from the decomposition of the flux components Fe2O3, CaCO3, CaMg(CO3)2, CaSO4 and FeS2 [18,19]. These bloating gases are O2, CO2, CO, H2O, N2, SO2 and H2.…”

“…These bloating gases are O2, CO2, CO, H2O, N2, SO2 and H2. According to Hoffmann [14], the organic carbon content also has an important influence on The most important gases produced during bloating are released between 850 and 1150 • C from the decomposition of the flux components Fe 2 O 3 , CaCO 3 , CaMg(CO 3 ) 2 , CaSO 4 and FeS 2 [18,19]. These bloating gases are O 2 , CO 2 , CO, H 2 O, N 2 , SO 2 and H 2 .…”

“…These bloating gases are O 2 , CO 2 , CO, H 2 O, N 2 , SO 2 and H 2 . According to Hoffmann [14], the organic carbon content also has an important influence on the bloating capacity [19]. The carbon not only acts as a reducing agent but also as a regulator of the atmospheric environment in the granulate interior.…”

“…The carbon not only acts as a reducing agent but also as a regulator of the atmospheric environment in the granulate interior. Ideal carbon contents at the beginning of the pyroplastic melting phase are according to Hoffmann 0.3-0.5% but can vary depending on the material [14,19].…”

Analyzing the Role of Fe0 and Fe3+ in the Formation of Expanded Clay Aggregates

“…The results showed that both iron phases enhanced the bloating process, which was linked to pore formation in the lightweight aggregate. Wie et al [ 8 ] investigated clay mixtures with different percentages of activated carbon and Fe 2 O 3 . Again, the results indicated that Fe 2 O 3 reduction appeared to be a key factor in producing the lightweight aggregate, in which case it was necessary to add more than 5 wt.% of iron along with percentages higher than 2 wt.% of activated carbon.…”