How to deal with the problem of cracks in the construction of lightweight insulation castables?

The cracking problem in the construction of lightweight insulation castables requires targeted treatment measures based on the type, cause, and working conditions of the cracks. The following is a systematic solution that integrates various search results:

1、 Analysis and Identification of Crack Causes

Shrinkage cracks

Lightweight castables are prone to vertical cracks due to high water absorption of aggregates and dehydration shrinkage of binders (such as water glass).

Characteristics: The cracks are slender and vertically distributed, often occurring in the early stages after demolding.

Temperature difference crack

The large temperature difference in the construction environment (such as day night temperature difference) leads to thermal expansion and contraction stress, and cracks appear in an irregular network.

Construction process defects

Excessive addition of water or binder can lead to poor fluidity, high porosity, and wet swelling and cracking during baking.

Premature demoulding (<10 hours) or unstable formwork support can cause vertical cracks.

Structural stress cracks

In circular structures such as chimneys, circumferential cracks are often located 100-300mm below the dark cow legs due to the concentration of shrinkage stress.

2、 Crack repair technology

1. Surface sealing method (applicable to micro cracks)

Epoxy resin grouting:

Chisel groove (depth 60-80mm, width 50mm) → clean and dry → bury grouting pipe → inject epoxy resin → seal and cure.

Suitable for non structural cracks, with high bonding strength and chemical corrosion resistance.

2. Structural reinforcement method (applicable to wide cracks or peeling)

Swallowtail groove excavation and repair:

Chisel the crack area into a swallowtail shape with a narrow upper part and a wide lower part, clean it, fill it with the original proportion of pouring material, and compact it layer by layer.

Key parameters: Repair depth ≥ 2/3 of casting thickness, width extending 50mm on both sides of the crack.

Blue Mud Quick Repair:

Chisel out the damaged area to a depth of ≥ 20mm → clean the surface → compact it with blue clay slices, and light the furnace without baking.

Suitable for small area peeling (such as the return feeder area), with a construction time of only 10 minutes.

3. Grouting repair method (applicable to leakage cracks)

Polyurethane grouting:

Pre embedded grouting pipe → water flushing joint (0.1-0.3MPa water pressure) → grouting → closed curing.

Advantage: Water reaction is required during gelation, suitable for sealing cracks in humid environments.

3、 Crack prevention measures

Optimization of Materials and Proportions

Control the amount of water added (15-17%) and the amount of binder used to avoid excessive dilution.

Adding fly ash or water reducing agent to reduce hydration heat, cement dosage ≤ 450kg/m ³.

Construction process control

Layered pouring: Each layer has a thickness of 300-500mm, and the vibration time is moderate.

Demoulding time: The formwork can only be removed when the strength is ≥ 0.8MPa or the curing time is ≥ 10 hours.

Expansion joint setting: Within 3 hours after demolding, use a toothless saw to cut the expansion joint (1500mm × 1500mm grid, 2.5mm deep).

Environmental Management

The construction temperature should be controlled between 5-30 ℃, with shading and anti riot measures in summer and anti freezing measures in winter.

In high humidity areas in the south, it is necessary to strengthen the storage and moisture prevention measures, and pre dry the aggregates before construction.

4、 Special working condition handling

Chimney circumferential cracks:

Repair after 45 days of stability, chisel out the crack area and fill it with the original proportion of pouring material, paying attention to strict control of the proportion of the hidden cow legs.

Cracks in high-temperature areas:

Select low heat cement (such as slag cement) and use secondary air cooling technology to reduce the pouring temperature.

summary

Cracks in lightweight insulation castables should follow the principle of "prevention first, repair as a supplement". The key control points include precision in proportioning, layered construction techniques, and environmental adaptability. For cracks that have already appeared, grouting, excavation or rapid repair techniques should be selected according to the type, and strict adherence to the baking curve (such as 72 hour gradual heating) should be followed

）To ensure the durability of repairs.