What causes concrete to crack?

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Posted on 20 May 2024

Concrete is extremely important in our built environment, forming the foundation of our infrastructure, buildings, and countless other structures. Its durability and versatility make it a material of choice for construction projects worldwide. However, despite its strength, concrete is susceptible to cracking, which can compromise its integrity and longevity. Understanding the causes behind concrete cracking is essential for engineers, builders, and property owners alike. Read on to find out what causes concrete to crack?


One of the primary causes of concrete cracking is shrinkage. When concrete dries and cures, it undergoes a process called hydration, where water reacts with cement to form a crystalline structure. During this process, water evaporates, causing the concrete to shrink. This can lead to internal stresses within the concrete, ultimately resulting in cracks.

Temperature ChangesCommercial Concrete Suppliers in Doncaster

Temperature fluctuations can also contribute to concrete cracking. As temperatures rise and fall, concrete expands and contracts. This thermal expansion and contraction can exert significant pressure on the concrete, leading to cracking, especially in areas with extreme temperature changes.

Improper Mix Proportions

The proportions of ingredients in concrete significantly affect its strength and durability. If the mix contains too much water or too little cement, the resulting concrete may be prone to cracking. Additionally, incorrect mixing or improper placement techniques can lead to inconsistencies in the concrete, making it more susceptible to cracking.

Inadequate Reinforcement

Concrete is often reinforced with materials like rebar or mesh to enhance its structural integrity. However, if the reinforcement is insufficient or improperly placed, it may not effectively distribute the stresses within the concrete. This can result in localised areas of weakness, increasing the likelihood of cracking under load.

Subgrade Issues

The quality and stability of the subgrade beneath the concrete play a crucial role in preventing cracking. Poorly compacted or uneven subgrade can cause settlement or shifting, leading to stress concentrations in the concrete above. These stress concentrations can start as cracks, particularly in areas with heavy loads or traffic.

Chemical Reactions

Certain chemical reactions can cause concrete to crack over time. For example, the alkali-silica reaction occurs when reactive silica in aggregates reacts with alkalis in the cement, forming a gel-like substance. This gel expands as it absorbs moisture, exerting pressure on the surrounding concrete and potentially causing cracks.


Exceeding the design load capacity of a concrete structure can result in immediate or gradual cracking. Overloading places excessive stress on the concrete, surpassing its strength limit and leading to structural failure. Whether due to heavy machinery, vehicular traffic, or other sources, overloading can weaken the concrete and induce cracks over time.

Concrete Suppliers MexboroughExternal Forces

External factors such as seismic activity, wind, or impact can also cause concrete to crack. Earthquakes subject structures to dynamic forces beyond their normal loads, leading to cracking and structural damage. Similarly, strong winds can exert significant pressure on tall or exposed structures, while impact from vehicles or falling objects can cause localised damage.

Ageing and Wear

Over time, concrete naturally deteriorates due to environmental exposure, chemical reactions, and mechanical wear. As concrete ages, its strength and resilience diminish, making it more susceptible to cracking. Factors such as freeze-thaw cycles, moisture infiltration, and abrasive wear can speed up the deterioration process, hastening the onset of cracks.

Design Flaws

Inadequate design or detailing of concrete structures can contribute to cracking. Poorly designed joints, inadequate expansion or control joints, and insufficient reinforcement can all lead to stress concentrations and eventual cracking. Thorough structural analysis and proper design considerations are essential for mitigating these risks.

In conclusion, concrete cracking is a complex occurrence influenced by a variety of factors, ranging from material properties to environmental conditions and design considerations. By understanding the causes behind concrete cracking, engineers and builders can put in place strategies to minimise it happening and ensure the long-term durability and safety of concrete structures. From proper mix design and construction techniques to regular maintenance and monitoring, proactive measures can help minimise the risks associated with concrete cracking, preserving the integrity of our built environment for generations to come.

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