In an attempt to improve the properties, lightweight aggregates were produced from clay with the addition of Na 2 CO 3 , SiO 2 , Fe 2 O 3 , and Fe in quantities between 2 and 10 wt% and examined with respect to strength, density and expansion behaviour. The additives were mixed into dry clay powder, water was added and pellets were formed by hand and fired at 1120°C in a chamber furnace. Particle densities of the products ranged from 0.31-0.57 g/cm 3 , porosities from 78-89% and the solid strength from 0,54-1,58 MPa. The addition of Na 2 CO 3 proved to decrease the viscosity of the glass phase at the surface of the pellets but resulted in a 2 reduced expansion, irregular shape and pellets sticking together. SiO 2 addition did not give any major change in properties. The addition of Fe 2 O 3 increased the pore size in the centre of the pellets, however with insignificant change in strength and density. Adding 5 wt% metallic iron powder led to LWA pellets with increased porosity, reduced density, larger pores and low mechanical strength and could be an useful additive in applications where low density is more important than strength.
Lightweight aggregates (LWA) were successfully produced both in a pilot-scale rotary kiln and in a laboratory chamber furnace. The mechanical properties of LWA were investigated in detail applying the European standard crushing resistance test (CR-test) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 stresses in the centre of the pellet and the strength was observed to increase exponentially with decreasing sample size. The relationship between the CR-and spc-test has been established facilitating "translation" of strength data between the two different test methods.
Carbon steel fibre reinforced lightweight aggregates (LWA) were produced in a pilot scale rotary kiln. Narrow size fractions as well as not-sieved (as received) material were investigated according to European standards with a main focus on strength and density and compared to a reference material without fibres. Depending on the size of the pellets a fraction of the fibres oxidized during firing. A strength increase proportional to the amount of non-oxidized fibres within the pellet was observed. The crushing resistance for as received fibre reinforced pellets (bulk density 452 kg/m 3 ) was 3.0 MPa corresponding to an increase in strength of 140 %. The enhanced strength was also confirmed by the single pellet compression test.fibre reinforced LWA-manuscript.docx Click here to view linked References
Lightweight aggregates (LWA) were produced from clay in the laboratory. After firing different heat treatments and cooling rates were applied and the resulting material was investigated with respect to strength and microstructure. Fast cooling led to the formation of micro cracks and weakened the material whereas slow cooling enhanced the strength of LWA. The residence time at temperatures between 700°C and 900°C led to differences in average oxidation state of iron in the matrix phase leading to substantial changes in thermal behaviour of the matrix phase. The combination of a highly oxidized shell and a reduced core 2 proved to enhance the strength of LWA. A two hour heat treatment at 800°C in air combined with a subsequent slow cooling rate (0.7°C/min) applied to LWA produced in an industrial rotary kiln led to a strength increase of 114 % compared to material of the normal production without changing any other property.
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