Application of Expanding Polyurethanes for Lifting Settled Concrete Slabs: An Expert Guide

Lifting and restoring settled concrete slabs is a common challenge in modern engineering practice. Settlement of floors, industrial platforms, roadways, and production areas can reduce operational safety, cause equipment malfunctions, accelerate machinery wear, lead to production downtime, and disrupt day-to-day operations.

Traditional repair methods—such as demolition and full slab replacement—are time-consuming and costly. In recent years, injection polyurethane systems have emerged as an effective alternative, enabling faster, more cost-efficient repairs with minimal disruption to ongoing operations.

This article outlines the key principles, process steps, and advantages of using expanding polyurethanes for slab lifting.

Understanding the root cause of settlement is essential before starting any remediation work. The most common causes include:

• Erosion and washout of fine soil particles due to drainage issues or water ingress
• Inadequate compaction or poor subgrade preparation during construction
• Long-term dynamic loading (e.g., warehouse traffic, heavy equipment, vibration)
• Utility failures, leakage, or other man-made ground disturbances

A settled or deflected slab leads to uneven load distribution, increases the risk of structural damage, and requires timely corrective action.

Injection technology using expanding polyurethanes offers several key advantages:

• Rapid repair: Structures can be restored to design levels within hours, without extended downtime
• Targeted application: Treatment is applied only where needed, without affecting surrounding areas
• No demolition required: Eliminates the need for dismantling or slab replacement, reducing costs
• Simultaneous void filling: Expanding polyurethane fills voids and restores contact with the subgrade
• Quick return to service: Facilities can typically resume operation within hours
• Reduced operational risk: Eliminating uneven surfaces helps prevent equipment damage and safety incidents

Effective implementation requires a structured and controlled workflow:

1. Geotechnical Assessment

• Visual inspection of the slab and subgrade to determine the type of settlement (uniform, localized, edge-related)
• Ground-penetrating radar (GPR) surveys and in-situ testing of subgrade conditions
• Identification of voids and assessment of their extent and depth

2. Injection Design

• Marking and layout of injection points on the slab surface
• Estimation of required material volume and modelling of the lifting process

3. Equipment and Material Preparation

• Inspection and setup of equipment (pumps, dosing units, injection systems)
• Preparation of polyurethane components (e.g., PolyJet or equivalent), including control of temperature and viscosity

4. Injection Execution

• Drilling of injection holes (8–20 mm diameter) according to the layout
• Injection of polyurethane beneath the slab at controlled pressure
• Continuous monitoring of expansion, lift progression, and surface response

5. Final Quality Control

• Sealing of injection holes and surface restoration
• Instrumental and visual verification of slab level and flatness

Expanding polyurethanes have been successfully used in numerous slab lifting projects.

Case 1: Industrial Warehouse Floor Restoration

• Floor settlement in the loading area exceeding 80 mm
• PolyJet FT injected at 24 points; total project duration — 7 hours
• Cost savings of over 65% compared to slab replacement
• After 3 years, measured deviation remains within 2 mm

Case 2: Supermarket Floor Repair

• Settlement in a retail area corrected without interrupting operations
• Work carried out overnight; store reopened the following morning

The polyurethane resins used in injection applications are certified, do not release harmful substances, and become fully inert after polymerization. Ground disturbance is minimal.

The materials comply with environmental and health safety standards and are suitable for use in sensitive environments, including food production facilities.

Injection-based slab lifting using expanding polyurethanes is an efficient, reliable, and cost-effective solution for addressing settlement.

The method offers:

• durable results,
• minimal disruption,
• no need for structural demolition,
• reduced operational risks.

Recommendation:
Always conduct a proper site assessment and use certified materials that comply with applicable regional standards (e.g., EU, local regulations).