Changes in ceramic blocks porosity with phosphate sludge ... · PDF fileChanges in ceramic blocks porosity with phosphate sludge due to salt crystallization ... wetting process by

Changes in ceramic blocks porosity with phosphate sludge due to salt crystallization

Civil Engineering Post-Graduation Course University of Vale do Rio dos Sinos, Brazil

Rosângela Andréia BERSCH

Feliciane Andrade BREHM

Claudio S. KAZMIERCZAK [email protected]

WASCON 2012 Towards effective, durable and sustainable production and use of alternative materials in construction

Phosphate sludge

Phosphate sludge is

originated by the cleaning

of the metallic surface in

the production of

automotive components

(during the phosphate

coating)

Composition:

higher quantity of iron (Fe)

and calcium (Ca)

Others:

sulfur (S)

zinc (Zn)

magnesium (Mg)

phosphorus (P)

silicon (Si)

(detected by X-ray fluorescence

spectrometer))

WASCON 2012

Main project: recycling of phosphate sludge in ceramic bricks

efflorescence

long term

performance

WASCON 2012

Bioblock ®

Development of a ceramic brick with phosphate sludge

- phosphate/clay ratio and sintering process

- mechanical properties

- environmental impact assessment

in situ

evaluation

?

Research project: consequences of salt crystallization

in ceramic blocks with phosphate sludge

mechanical properties

efflorescence

electrical

conductivity

of leaching

pore size distribution of

ceramic specimens

salt

characterization

WASCON 2012

soluble

salt

water porous

material

primary factors

material

weathering contact

time

secondary factors

dissolution and

salt

transportation

migration

through the

pores

evaporation

and

crystallization

Efflorescence Subefflorescence

Dissolution –

Crystallization

cycles

Crystals in the interior

(pores) Crystals in the surface

(1) (2) (3)

(4)

Bersch (2011)

Salt crystallization: mechanism

➙ pathology often observed in materials such as rocks, bricks and concrete

➙ complex phenomenon

➙ economic impact worry manufacturers and builders

WASCON 2012

Arnold & Zehnder (1987)

Subefflorescence

a. crystals are formed in pores between 1 and 10 μm ➙ crystals grows

b. crystal’s dimensions exceed the pore size and start to grow up to other pores

➙ internal tensile stress and cracking

c. cracking increases ➙ evaporation exceeds solution supply ➙ crystallization concentrates on the cracking ➙

solution is only supplied by one or two sides of the fissure ➙ crystal grows in a columnar habit

d. cracking are already too widened ➙ solution tends to finish ➙ crystalline growing stops

WASCON 2012

Experimental research

● reference (0%)

● 2.5% of phosphate sludge

● 5% of phosphate sludge

sludge was added with an average diameter of 7.63mm clay + sludge extrusion

sintered in an oven to different temperatures:

750ºC

850ºC

1050°C

heating rate of 2,5°C/min and plateau of 12 hours sinterization woven

WASCON 2012

Types of exposure

● reference

(no contact with water)

● 180 days with cyles

wetting process by partial immersion

in deionized water for three days

and drying for four days

(cycle repeated along 180 days)

● 180 days without cycles

partial immersion during the whole

exposition time (180 days)

wetting and drying

cycles aim to simulate the seasonal changes of humidity

and temperature due to weathering which

construction materials are subjected to

WASCON 2012

Pore size distribution

parameters calculated:

● volume of pores ≤10 μm according to Arnold & Zehnder (1987), crystallization from

the subefflorescence has a great influence in the pore’s

under 10 mm, which justified this specific analysis

● total pore volume

● percolation threshold

WASCON 2012

MIP samples of high porosity sintered in an oven to 750ºC

≤

Exposition type Analyzed parameters SG 2.5G 5.0G

Percolation threshold (m) 2 2 2

Pores volume 10 m (cc/g) 0.1074 0.1264 0.1132

Reference

Total pores volume (cc/g) 0.1100 0.1311 0.1165


Pores volume 10 m (cc/g) ND* 0.1079 0.1286

180 days without cycles

Total pores volume (cc/g) ND* 0.1109 0.1300



180 days with cyles


There were not significant changes between the pore size distribution of the

reference sample and the others

as the sample had high porosity, the soluble salts may have suffered a solubilization process

and migration to the surface (by capillarity and diffusion), since that an occasional alteration in

the samples’ porosity was not detected

≤

≤

WASCON 2012

MIP samples of medium porosity sintered in an oven to 850ºC

≤

Samples submitted to wetting and drying cycles ➙ it is observed a small decrease in the pore volume in the

samples SG and 2.5 SG with 180 days, as well as in the volume of pores ≤10 μm

soluble salts presented in the sample precipitated and formed crystals inside the pores (without migrating to the

surface), decreasing the total pore volume

≤

≤

Expostion type Analyzed parameters SG 2.5G 5.0G



Reference








180 days with cycles


↓ ↓

↓ ↓

WASCON 2012

MIP samples of medium porosity sintered in an oven to 850ºC

≤

Samples submitted to wetting and drying cycles ➙ it is observed a small decrease in the pore volume in the

samples SG and 2.5 SG with 180 days, as well as in the pores with diameter ≤10 μm

soluble salts presented in the sample precipitated and formed crystals inside the pores (without migrating to the

surface), decreasing the total pore volume

Sample 5.0 G, with higher PS addition, had an opposite behavior: an increase in pore volume which indicates

leaching

it is estimated that the soluble salt are undergoing the crystallization-solubilization process and migrating to the

surface, generating efflorescence

≤

≤




Reference










↓ ↓

↓ ↓

↓

↓

WASCON 2012

MIP samples of low porosity sintered in an oven to 1050ºC

≤

reference specimens ➙ lower total porosity and fewer quantity of pores ≤10 μm

increase in the percolation threshold (2 μm in hi-porosity specimens)

≤

≤

↓

↓




Reference










WASCON 2012




Reference











≤

● pores ≤10 μm of the reference samples (without PS) decrease due to the exposure to the wetting and

drying cycles ➙ soluble salts gone from the clay may be crystallizing in this pores

≤

≤ ↓




Reference










WASCON 2012


≤

● pores ≤10 μm of the samples SG (without PS) decrease due to the exposure to the wetting and drying

cycles ➙ soluble salts gone from the clay may be crystallizing in these pores

● by enhancing the amount of PS (to 5%), there is a sensitive decrease in the pores ≤10 μm. At 180

days without wetting and drying cycles, it was found a decrease in the volume of pores ≤10 μm around

50% when compared to the reference sample, which demonstrate that the soluble salts when

crystallized become trapped in these pores. At the same time, there is an increase in the percolation

threshold

≤

≤




Reference










WASCON 2012

Conclusions

WASCON 2012

● Soluble salts are susceptible of solubilization and

crystallization: depending on the pore distribution and the

concentration of PS incorporated to the ceramic, the crystallized

salts may be trapped in the lower pores of the ceramic specimen

(decreasing the quantity of micropores) or migrate to the surface,

generating efflorescence.

● The ceramic firing cycle demonstrated to be the most

significant variable (the substrate porosity).

● In ceramics with similar pore size distribution to those sintered at

1050ºC (low porosity), submitted to continuous wetting and drying

cycles: the crystals may precipitate inside the lower diameter pores

(without migrating to the surface), which may result, in a long term, in

internal tensions that may decrease the mechanical strength in a long

exposition time ➙ long term research !

Civil Engineering Post-Graduation Course University of Vale do Rio dos Sinos, Brazil

Rosângela Andréia BERSCH

Feliciane Andrade BREHM

Claudio S. KAZMIERCZAK [email protected]

WASCON 2012 Towards effective, durable and sustainable production and use of alternative materials in construction

Thank you !

The authors are gratefully acknowledged to CNPq and CAPES for financial support to this research

mailto:[email protected]

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Changes in ceramic blocks porosity with phosphate sludge ... · PDF fileChanges in ceramic blocks porosity with phosphate sludge due to salt crystallization ... wetting process by