What causes concrete to crack?

Concrete cracks result from several factors: plastic shrinkage from rapid surface drying, drying shrinkage as concrete loses moisture, thermal stresses from temperature changes, inadequate joint spacing, overloading, and settlement of underlying soil. Most cracks can be prevented through proper mix design, curing, jointing and placement practices.

What is honeycomb in concrete?

Honeycomb refers to voids and rough areas in concrete where mortar is missing and aggregate is exposed. It is caused by inadequate compaction, leaking formwork, or placing concrete that is too stiff. Prevention requires proper vibration, sealed formwork and appropriate concrete workability.

How do you prevent concrete spalling?

Concrete spalling is prevented by using adequate cover to reinforcement, low water-cement ratio concrete for reduced permeability, proper compaction and curing, and protective coatings in aggressive environments. Quality concrete with washed sand and graded aggregates provides the best defence against spalling.

Why does concrete scaling occur?

Scaling occurs due to improper finishing (overworking or adding water to the surface), premature sealing before bleeding completes, poor concrete quality with high water-cement ratio, and chemical damage. Proper finishing timing and quality concrete prevent scaling.

Can cracked concrete be repaired?

Yes, depending on the crack type and severity. Surface cracks can be sealed with flexible sealers. Structural cracks may require epoxy injection or carbon fibre reinforcement. Honeycombing can be repaired with high-strength repair mortar. Prevention is always more cost-effective than repair.

Common Concrete Failures And How To Prevent Them

Plastic Shrinkage Cracking

Plastic shrinkage cracking is one of the most common concrete defects encountered in Tanzania, occurring within the first few hours after placement while the concrete is still in a plastic state. These cracks appear as fine, random patterns on the surface or as parallel cracks running across the slab, typically 1 to 2mm wide and several centimetres deep. The primary cause is rapid evaporation of moisture from the concrete surface, which exceeds the rate at which bleed water rises to replace it. In Tanzania's hot climate, where daytime temperatures regularly exceed 30 degrees Celsius and dry winds accelerate evaporation, plastic shrinkage cracking is a significant risk. The concrete surface dries and shrinks while the underlying concrete remains wet and plastic, creating tensile stresses that exceed the concrete's very low early-age strength. Prevention strategies include windbreaks and sunshades to reduce evaporation, fog spraying to maintain humidity at the concrete surface, applying evaporation retarders immediately after finishing, and scheduling pours for early morning or late afternoon when temperatures and wind speeds are lower. Starting the curing process immediately after finishing is critical — every minute of delay increases the risk of plastic shrinkage cracking. The cost of prevention through proper planning and materials is negligible compared to the expense of repairing cracked concrete after placement.

Drying Shrinkage Cracking

Drying shrinkage cracking occurs over a longer timeframe than plastic shrinkage, typically developing days to weeks after concrete placement as the concrete gradually loses its internal moisture to the environment. These cracks are usually larger than plastic shrinkage cracks, often extending through the full depth of the slab, and typically follow a pattern related to the slab geometry and restraint conditions. Drying shrinkage is an inherent property of concrete — all concrete shrinks as it dries, with typical shrinkage values ranging from 0.04 to 0.08 percent of the original dimensions. The magnitude of shrinkage depends on the concrete mix design, with higher water content and lower aggregate content producing greater shrinkage. Inadequate joint spacing is a common contributor to drying shrinkage cracking, as the shrinkage stresses exceed the tensile strength of the concrete between joints. Prevention methods include using low-shrinkage mix designs with optimised water-cement ratios and adequate aggregate content, providing construction and control joints at appropriate intervals, ensuring proper curing to reduce total shrinkage, and using reinforcement or fibres to control crack widths. For slabs in Tanzania, control joints should be spaced at intervals not exceeding 25 to 30 times the slab thickness, and joint locations should be planned during the design phase rather than left to chance during construction.

Scaling And Surface Defects

Scaling is a surface defect where the top layer of concrete peels, flakes or delaminates, exposing the underlying concrete. It typically appears within the first few years of service and is characterised by progressive loss of the surface mortar. Scaling is most commonly caused by improper finishing practices, particularly overworking the surface which creates a weak, laitance-rich layer that is susceptible to damage. Other causes include adding water to the surface during finishing, applying sealers or curing compounds to concrete that has not yet finished bleeding, and freeze-thaw cycling in cold climates — though this is less relevant in Tanzania. Poor concrete quality with high water-cement ratio or inadequate air entrainment also increases scaling susceptibility. Prevention focuses on proper finishing techniques: wait for bleed water to evaporate before finishing, do not over-trowel the surface, avoid adding water during finishing, and use concrete with appropriate air content if the surface will be exposed to freeze-thaw conditions. Using quality concrete from a reputable supplier like Tanzibaba with properly controlled water-cement ratios and appropriate mix designs is the first step in preventing surface scaling defects on your construction project.

Honeycombing And Voids

Honeycombing refers to areas of concrete with missing mortar and visible aggregate particles creating a porous, rough-textured surface or internal voids. It typically occurs at corners, edges and interfaces between old and new concrete where air and water become trapped during placement and cannot escape. Honeycombing is primarily caused by inadequate compaction, where the concrete is not properly vibrated to consolidate it and remove entrapped air. Other causes include leaking formwork that allows cement paste to escape while retaining aggregate, placing concrete that is too stiff to flow around reinforcement and into corners, and dropping concrete from excessive heights causing segregation. The structural implications of honeycombing range from cosmetic defects to serious structural deficiencies, depending on the extent and location. Large areas of honeycombing reduce the effective cross-section of structural elements and expose reinforcement to corrosion. Prevention requires properly designed and constructed formwork with adequate sealing, using concrete with appropriate workability for the placement conditions, applying mechanical vibration thoroughly and systematically, and training workers in proper concrete placement techniques. Tanzibaba ensures all concrete delivered has the correct workability for the intended placement method, reducing the risk of honeycombing on your project.

Corrosion-Related Failures

Reinforcement corrosion is one of the most serious long-term concrete durability issues, causing cracking, spalling and eventual structural deterioration if not properly addressed. Corrosion occurs when the protective passive layer on the steel reinforcement is broken down by chloride ions from de-icing salts or marine exposure, or by carbonation of the concrete which reduces its alkalinity. As the steel corrodes, it expands to several times its original volume, creating internal pressure that causes the concrete cover to crack and eventually spall off, exposing the reinforcement to further deterioration. In Tanzania's coastal regions, particularly Dar es Salaam, chloride-induced corrosion from salt-laden air is a significant concern for concrete structures. Prevention strategies include specifying adequate concrete cover to reinforcement as per design standards, using low water-cement ratio concrete to reduce permeability, specifying washed sand and quality [aggregates](/products/aggregates) to produce dense concrete, applying protective coatings or surface treatments in aggressive environments, and ensuring thorough concrete compaction and curing to achieve maximum density. Regular inspection and maintenance of concrete structures can identify early signs of corrosion before significant structural damage occurs. The cost of corrosion prevention during construction is a fraction of the expense of structural repairs after corrosion has progressed.

How Tanzibaba Prevents Concrete Failures

Tanzibaba prevents concrete failures through a comprehensive quality assurance system that addresses every potential failure mode from material selection through to delivery and placement support. Our process begins with rigorous raw material testing, using only premium [washed sand](/products/aggregates) and quality [aggregates](/products/aggregates) that meet strict grading and cleanliness specifications. Computerised batching ensures precise mix proportions with water-cement ratios carefully controlled to achieve the target strength and durability. Every batch undergoes slump testing before dispatch to verify workability, and cube samples are cast for compressive strength verification at 7 and 28 days. We design our mixes to address Tanzania's specific challenges, including hot weather concreting with appropriate admixtures to control setting time and reduce water demand. Our delivery tickets include detailed information about the concrete grade, mix design and recommended placement, compaction and curing procedures. Our technical team is available to advise customers on site preparation, formwork requirements, placement techniques and curing methods to ensure the concrete achieves its full potential. When you choose [ready-mix-concrete](/products/ready-mix-concrete) from Tanzibaba, you are choosing a partner committed to preventing failures and ensuring the long-term success of your construction project with concrete that consistently meets or exceeds its specified grade.

Common Concrete Failures And How To Prevent Them

Plastic Shrinkage Cracking

Drying Shrinkage Cracking

Scaling And Surface Defects

Honeycombing And Voids

Corrosion-Related Failures

How Tanzibaba Prevents Concrete Failures

Frequently Asked Questions

What causes concrete to crack?

What is honeycomb in concrete?

How do you prevent concrete spalling?

Why does concrete scaling occur?

Can cracked concrete be repaired?

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