Where Do Concrete Cracks Come From?
Concrete cracking is a phenomenon where the surface of concrete splits into lines or grooves. These cracks often lack uniformity in size, direction, or thickness. Over time, if not properly treated, these cracks may develop further and lead to unpredictable consequences.
This phenomenon is one of the main causes of reduced structural lifespan. Its impact may not be immediate, but it's difficult to determine the exact timeline. The consequence of concrete cracking is ultimately structural failure, causing not only property damage but also potentially threatening human lives. Therefore, treating concrete cracks is an extremely important issue that should be addressed as early as possible. However, before finding a solution, it is necessary to understand the reasons behind this phenomenon to propose the most reasonable approach.
What Causes Concrete Cracks?
Shrinkage Cracks: These cracks appear shortly after pouring concrete. They are narrow and resemble bird footprints. They occur because water evaporates too quickly from the surface, causing a deformation between the top and bottom of the slab. This often happens when concrete is poured during noon, in hot and dry weather.
Prevention: Avoid pouring concrete in intense heat. After pouring, properly finish the surface. Use wet sacks to cover and continuously moisten for 3 days.
Settlement Cracks: These occur when the foundation of a structure shifts. Settlement cracks are usually serious and may result from poor foundation treatment. Other causes include soil erosion or weak foundation soil. In shallow residential foundations surrounded by large trees, roots may cause cracking.
Structural Calculation Errors: These cracks are caused by design mistakes, where the load exceeds the concrete’s bearing capacity, leading to cracking or collapse. Although this issue is rare due to meticulous planning, it can happen when homeowners expand their houses without recalculating load capacity.
Material Issues: In modern construction, concrete is often sourced from mixing stations. From mixing to transportation and setting, concrete is affected by distance, method of transportation, mix ratio, heat of hydration, etc. These factors influence its quality. Additionally, variations in cement types, additives, cement strength, aggregate size, and flake content give concrete different material properties, contributing significantly to crack formation.
External Forces: These are forces acting on concrete from outside sources, such as earthquakes or human activities like drilling or geological surveys. Cracks from such forces are unpredictable and sudden, making them dangerous due to the lack of timely response. However, these cases are rare and not usually a major concern in practice0.
Time-Related Cracks (Corrosion): When reinforced concrete is exposed to moisture and oxygen, corrosion may occur. This happens through small cracks that allow water to reach the steel reinforcement, causing it to rust and expand, pushing the concrete out and creating larger cracks. Regular inspection and early treatment of small cracks can prevent serious damage.
What is the MICP Method?
Crack healing in concrete using MICP (Microbially Induced Calcium Carbonate Precipitation) is an advanced biotechnology that uses bacteria to precipitate calcium carbonate (CaCO₃), sealing fine cracks in concrete. This is an environmentally friendly, self-healing method that is gaining attention in sustainable construction.
How Does the Crack-Healing Process Work?
Stage 1: Preparation
Select bacteria (Sporosarcina pasteurii)
Prepare a nutrient medium for the bacteria
Use aggregate capable of alkali-silica reaction
Stage 2: Bacterial Culture in Solution
Bacteria are cultured for strong growth
They produce urease – the enzyme that breaks urea into NH₄⁺ and CO₃²⁻
Stage 3: Biological Reaction
Bacteria hydrolyze urea
Generate NH₄⁺ and increase pH
Create CO₃²⁻ ions
Stage 4: CaCO₃ Precipitation
CaCO₃ precipitates on aggregate surfaces, forming a protective layer
Bibliography
[1] C. T. T. S. - X. T. P. KHÁNH, "Nguyên nhân của nứt bê tông," Chống Thấm Phú Khánh, [Online]. Available: https://chongthamphukhanh.com/tin-tuc/nguyen-nhan-cua-nut-be-tong-43.html
[2] C. T. T. T. K. V. X. D. SBS, "Nguyên nhân và biện pháp xử lý vết nứt sàn bê tông," SBS House, [Online]. Available: https://sbshouse.vn/nguyen-nhan-va-bien-phap-xu-ly-vet-nut-san-be-tong/
[3] G. Magtech, "Phân tích nguyên nhân gây ra vết nứt trong kết cấu bê tông," Precast Concrete Magnet, [Online]. Available: https://vn.precastconcretemagnet.com/news/analysis-on-the-causes-of-cracks-in-concrete
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