For the problems of lime cracking in the production line of clay brick making casued by
calciumOxide(CaO)content 10-15% in the clay raw materials, there are some methods can effectively
address when the clay bricks in production;
In actual production, a combination of raw material modification, high-temperature sintering, and
post-treatment is recommended to reduce the risk of bursting to <0.5%.
1. Raw Material Pretreatment
A. Aging and Homogenization:
Storing the clays in the open air for an extended period (over 3 months) which allows for natural leaching by
rainwater in roder to reduce the free CaO content and promote homogenization of the raw materials.
B. Adding an Inhibitor:
Adding 2%-5% of a siliceous material (such as powdered quartz, rice husk ash) or a pozzolanic material (such
as metakaolin) reacts with CaO to form stable calcium silicate, reducing the amount of free CaO remaining
after calcination.
2. Optimizing the Sintering Process when do the production
A. Extending the Preheating Time:
Raising the temperature slowly between 400°C and 600°C (at a rate of ≤2°C/min) allows the CaCO₃ to fully
decompose into CaO and release CO₂, thus preventing cracking in the later period.
B. Raising the sintering temperature when firing the clay bricks:
Raising the firing temperature from the conventional 950-1,050°C to 1,100-1,150°C promotes the reaction of
CaO with SiO₂ in the clay to form a calcium silicate glass phase.
C. Extending the holding time:
Keeping the fired bricsk at the highest temperature for 1-2 hours ensures sufficient solid-phase reaction.
3. Formula Adjustment
A. Adding a flux:
Adding 3%-5% feldspar or Fe₂O₃ lowers the liquidus temperature and promotes the melting reaction of CaO
at high temperatures.
B. Controlling particle fineness:
Grinding the clay to a particle size of <0.1mm increases the contact area between CaO and the matrix, and
accelerating the reaction.
4. Post-treatment Measures after firing
A. Steam curing:
After the fired bricks leaving the kiln, they are subjected to saturated steam treatment (100°C for 6-8
hours)Immediately to hydrate the residual CaO to Ca(OH)₂ and carbonize and stabilize it.
B. Carbonization by Soaking:
The fired bricks are immersed in a 3% CO₂ aqueous solution for 24 hours to promote the conversion of
Ca(OH)₂ to CaCO₃.
5. Quality Control
A. Free CaO Testing:
The free CaO content in the sintered bricks is determined by using the ethylene glycol-ethanol method,
ensuring it is ≤1%.
Planetary Verification:
Laboratory brick sample firing (simulating actual operating conditions) and boiling tests are performed (a
5-hour boiling test indicates no visible cracking).
B. Mechanism Analysis
Lime bursting is caused by the volume expansion (approximately 148%) of CaO to Ca(OH)₂. The above
method can:
① Reduce free CaO residue (high-temperature solid-phase reaction);
② Slow the hydration rate (densifying the sintered bricks to hinder water penetration);
③ Preliminary stress relief (pretreatment allows expansion to occur at a controlled stage).
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