Properties of autoclaved sand-lime brickswith an addition of lime-reach ashes

Z. Pytel

AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Building Materials Technology,

Av. Mickiewicza 30,Pl-30-059 Cracow, Poland, e-mail: pytel@agh.edu.pl

1. AbstractThe paper summarises the results of laboratory testing ofautoclaved sand-lime bricks containing sulphate calcium flyash from brown coal installations. The rationale behind theuse of such ashes in this type of construction materials is therelatively high content of free CaO which may help reducethe demand for burnt lime or play the role of a binder inmanufacturing of sand–lime based construction materials byconventional methods. The free lime content in ashes isvariable and strongly depends on the grain size distributionas fine particles of ash tend to be richer in CaO than coarsegrains. Besides, ashes contain high amounts of silica,typically occurring in the form of crystalline quartz, and thatmay result in partial substitution of natural silica sand, whichacts as a natural filler (aggregate) in manufacturing ofautoclaved sand-lime materials. The investigated rawmixtures are obtained from conventional mixtures, thoughtheir composition is slightly modified as variable amountsoffly ash are added. This ash occurs in its natural state and issubjected to the grain separation process. The fly ash is thenmixed with the raw materials, acting as a partial substituteofconventional mixture components used in manufacturing ofsand-lime products, i.e. natural silica sand and burnt lime.Investigations of these materials cover the testing of theirfunctional properties and of selected structural and micro-structural behaviours.

2. MaterialsSamples of autoclaved products are made from mix followedcomponents:- natural silica sand (symbol QS-LU),- high-reactivity burnt lime obtained in industrial processconditions (symbol L-HR),- fly ash from a brown coal installation (symbol K-001,K-001/F1, K-001/F2),- distilled water.

Chemical analysis of fly ash K-001

3. Sample preparationPreparing of mixtures:The precisely controlled amount of mixture components were carefully weighted and homogenised in a dry process and followed by a wet process.The mixture was then placed inside an air-tight glass container for the purpose of mixture slacking. The slacking process lasted for 2 hours at the temperature 70°C.

Sample forming:Samples were shaped like cylinders with following parameters: dxh = 25 mm. They were formed in a process of axial, two-sided and double-stage pressing, including interstage deaeration. The initial and final pressure of pressing were 10 and 20 MPa, respectively.

Sample autoclaving:After pressing samples were subjected to hydrothermal treatment, with the use of steel pressure cylinders. The conditions of the synthesis reproduced the conditions of sand-lime materials treatment in industrial autoclaves:

saturated steam pressure – 1.02 MPatemperature – 180 °Cautoclaving time – 9.5 hours

4. Properies of autoclaved materials

5. Microstructure of autoclaved materials

Final conclusions1. In the context of process technology, the control of actual proportions of components of the mixture containing sulphate-calcium fly ashes or their selected grain

fractions allows for obtaining autoclaved products, such as sand-lime bricks, whose properties and parameters compare well with those obtained from traditional mixcomponents.

2. In the solution applied here, fly ash or its selected grainfractions play a double role, acting both as a micro-aggregate modifying the grain size distributioncharacteristics and hence improving the level of compaction of press-formed semi-finished products and acting as an active mineral additive improving the rate offormation of the desired products of synthesis.

3. As the fly ash contains significant amounts of free and reactive calcium oxide, the potential exists for partial substitution of burnt lime required for manufacturingconventional sand-lime materials, leading to reduction inburnt lime consumption and hence manufacturing costs of these construction materials can decrease, too.

4. The proposed technology can be used in manufacturing of autoclaved construction materials, such as sand-lime bricks, in industrial conditions as the processes ofmanufacturing of the conventional autoclaved materials are very similar, the process line requiring minor modifications only.

AcknowledgementThis study is a part of a research project sponsored by National Science Centre from the resources allocated for years 2011-2013, as a project No N N506 282140.

MaterialSample

designation

Rheological properties

Functional parameters of finished silicate products

W%

A%

ρ0n,u

[g/cm3]ρ1

n,u

[g/cm3]fb

[MPa]cw

[%]Po

[%]

Reference material

1 4.4 7.5 1.78 1.86 32.8 13.2 24.6

Experimental materials

2 3.6 8.2 1.67 1.76 18.3 17.7 31.2

3 5.1 8.2 1.69 1.73 26.9 18.7 32.4

4 4.2 8.1 1.55 1.57 12.9 24.9 38.9

5 4.5 8.6 1.44 1.45 10.4 30.1 43.6

6 1.7 10.3 1.61 1.66 17.9 21.9 36.4

7 1.9 11.4 1.32 1.40 9.2 33.4 45.8

8 1.4 12.7 1.10 1.18 6.6 44.9 53.1

9 1.5 13.8 1.01 1.03 1.6 56.1 57.3

10 2.6 8.2 1.55 1.60 19.3 23.9 37.9

11 2.9 8.2 1.71 1.75 31.0 18.6 32.5

12 2.4 8.2 1.35 1.40 9.3 38.5 48.9

13 2.5 8.4 1.31 1.47 5.3 28.9 42.4

14 5.2 9.8 1.08 1.13 5.3 50.0 56.1

15 4.4 18.4 0.82 0.94 1.2 60.5 65.4

16 3.9 8.5 1.15 1.16 7.2 47.3 54.6

Analysed component

Tested material

K-001 K-001/F1 K-001/F2

L.O.I. 0.78 1.04 0.28

SiO2 50.75 19.27 48.66

Al2O3 6.09 8.20 7.87

Fe2O3 5.97 6.18 9.50

CaO 24.76 43.93 22.35

MgO 3.57 6.29 3.64

SO3 6.18 12.29 5.31

K2O 0.46 0.39 0.70

Na2O 0.11 0.70 0.13

Sample 1 (reference material) Sample 11 Sample 15Sample 6

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