Document No.: ECS-002
Version: 1.0
Status: Approved

Early-Age Cracking in RCC Slabs

Engineering Investigation of Random and Linear Cracking in Cast-in-Situ Concrete Slabs

Project:
Multi-Storey Commercial Building

Client:
Confidential

Date:
July 2026

Site Observations: Early-Age Cracking in RCC Slabs

This Engineering Case Study is based on an actual engineering investigation undertaken by DM Strategic Advisors (DMSA). To maintain client confidentiality, the project name, client identity and other identifying information have been anonymised.

A site visit was carried out to investigate cracking observed in reinforced concrete slabs of a multi-storey commercial building.

The investigation focused on understanding the observed crack patterns, assessing their probable causes and determining whether the cracking indicated structural distress.

The assessment was based on visual inspection of accessible RCC slabs and beams, observation of crack patterns and discussions with the project team. No destructive testing was carried out during the investigation.

Site Observations

During the site inspection, the following observations were recorded:

• Random interconnected cracks were observed at several locations on the slab soffit.
• Most cracks formed an irregular interconnected pattern.
• A few cracks were comparatively straight and extended over longer distances.
• No major cracks were observed in the supporting beams.
• No exposed reinforcement or significant honeycombing was noticed.
• Overall concrete quality appeared satisfactory except for the observed cracking.

The observed cracking pattern indicated a need to distinguish between early-age concrete behaviour and structural cracking before deciding on the appropriate repair methodology.

Engineering Assessment

The observed cracks were assessed to be mainly early-age shrinkage and thermal cracks. The crack patterns did not resemble typical structural flexural cracks.

The absence of major cracking in the beams, exposed reinforcement or significant honeycombing, together with the overall satisfactory appearance of the concrete, did not indicate major structural distress during the visual inspection.

The possible contributing factors included plastic shrinkage, drying shrinkage, restrained shrinkage, early-age temperature variation and concreting, finishing and curing practices.

At a few locations, the comparatively straight crack pattern may also have been influenced by embedded electrical conduits. The crack locations may be compared with the electrical conduit layout to verify any correlation.

Probable Causes of Early-Age Cracking

Plastic Shrinkage

Plastic shrinkage can occur when moisture is lost from the concrete surface during the early stage of setting. If the rate of surface moisture loss is high and the concrete cannot compensate for this loss, tensile stresses may develop and result in early-age cracking.

Restrained Shrinkage

Concrete undergoes volume changes during hardening and drying. When these movements are restrained, the resulting tensile stresses can contribute to cracking, particularly where the tensile strength of the concrete at that age is relatively low.

Engineering Conclusion

Based on the site investigation and engineering assessment, the observed cracking was attributed to the combined effects of high binder content, autogenous shrinkage and thermal gradients developed during the early stages of concrete hydration.

The cracking was assessed to be non-structural in nature and did not affect the load-carrying capacity of the RCC columns. However, if left untreated, these cracks could become pathways for the ingress of water, carbon dioxide and other aggressive agents, potentially affecting the long-term durability of the structure.

Early-Age Temperature Variation

Temperature changes during the early stages of concrete hardening can produce expansion and contraction. Where the resulting movement is restrained, thermal stresses may contribute to early-age cracking.

Embedded Electrical Conduits

The comparatively straight crack observed at one location may have been influenced by an embedded electrical conduit.

Where required, the crack location should be compared with the electrical conduit layout to establish whether the two are aligned.

Engineering Recommendations

The observed crack locations should be recorded for future reference.

Where repair is required, the cracks should be repaired using a suitable crack repair material before plastering or other finishing work.

The repair methodology should be selected based on the observed crack characteristics and site conditions and should be reviewed by the Project Consultant before execution.

Remaining works should proceed after completion of the required repairs as recommended by the Project Consultant.

Preventive Measures

The following measures should be followed during future concreting works to minimise the possibility of similar cracking:

• Follow the approved concrete mix without adding extra water at site.
• Ensure proper vibration and compaction, particularly around congested reinforcement and embedded conduits.
• Start curing at the appropriate time and continue curing as per project requirements.
• Avoid unnecessary congestion of electrical conduits and maintain adequate concrete cover.
• Follow the recommended formwork removal and re-propping schedule.
• Avoid early loading of newly cast slabs.
• Ensure proper supervision during concreting, finishing and curing.

Use of Polypropylene Fibres

Polypropylene fibres may be considered in terrace slabs as a measure to help reduce the risk of early-age cracking.

The use of fibres should form part of the approved concrete mix and construction methodology and should not be considered a substitute for proper concreting, finishing and curing practices.

Engineering Outcome

The investigation indicated that the observed slab cracks were mainly early-age shrinkage and thermal cracks.

No signs of major structural distress were observed during the visual inspection.

The assessment demonstrated the importance of considering crack pattern, location and surrounding concrete condition before determining the nature of cracking.

Appropriate repair before plastering or other finishing work, together with good concreting, curing and construction practices, will help minimise the possibility of similar cracks in future.

SM Engineering Insight

A crack should not be judged by its appearance alone.

The crack pattern, location, orientation, surrounding concrete condition and likely timing of crack development should be considered together before deciding whether the crack is structural or related to early-age concrete behaviour.

A systematic engineering assessment helps avoid unnecessary structural concern and leads to more appropriate repair decisions.

Photographic Record

The photographic record documents the different crack patterns observed during the investigation, including interconnected cracking, random cracking, linear cracking and cracking near the beam-slab junction.

The photographs support the site observations and engineering assessment presented in this case study.

Disclaimer

This Engineering Case Study is based on visual observations made during the site investigation and is intended for technical knowledge sharing.

The observations and recommendations are limited to the areas inspected and the information available during the investigation. The case study should not be interpreted as a structural safety certification or as a substitute for project-specific assessment by the responsible design and project consultants.

Need Technical Assistance?

If your project is experiencing concrete cracking, durability concerns, mix desigor quality-related issues, SM Ecosystems provides engineering consulting, technical investigations, root cause analysis and practical solutions based on field experience and sound engineering principles.

Related Engineering Case Studies

Additional Engineering Case Studies will be published as part of the SM Knowledge Hub to share practical field investigations, engineering solutions and lessons learned from real construction projects.

Related Technical Notes

For additional guidance, refer to the DMSA Technical Notes library covering concrete quality, mix design, investigation methodologies and engineering best practices.

Tags

Surface Cracking, RCC Columns, Mass Concrete, High Strength Concrete, Autogenous Shrinkage, Thermal Cracking, Mix Design Optimisation, Concrete Durability, Site Investigation, Root Cause Analysis, Engineering Case Study, SM Ecosystems