Concrete is a popular building material, but it can deteriorate over time due to a variety of factors. Material limitations, design and construction practices, and severe exposure conditions can all lead to concrete damage, which can cause major headaches for building owners. It is important to identify these defects early and plan appropriate repair strategies. Concrete deterioration can occur through spalling, disintegration, erosion, reinforcement corrosion, delamination, spalling, alkali-aggregate reactions and concrete cracking.
Causes of concrete degradation include fire, aggregate expansion, seawater effects, bacterial corrosion, calcium leaching, physical damage and chemical damage (from carbonation, chlorides, sulphates and non-distilled water). Corrosion is the deterioration of the steel reinforcement of concrete and can be induced by chloride or carbonation. Disintegration is the physical deterioration (such as flaking) or breaking of concrete into small fragments or particles. The freeze-thaw cycle also affects the soil and can crack and break concrete foundations.
Heavy machinery or building with heavy materials can induce too much stress in the concrete and cause severe damage. Future deterioration of concrete structures can stem in part from errors in concrete production, pouring or placement, and compaction. Recycling concrete is difficult and expensive, reduces its strength and can catalyse chemical reactions that accelerate deterioration. To reduce the need for concrete production and build more durable structures, research has been conducted on the shielding properties of ordinary, barite and ilmenite concretes after heating to 950°C.
Paramagnetic defects and optical centres form easily but very high fluxes are required to displace a sufficiently high number of atoms in the crystal lattice of minerals present in concrete before significant mechanical damage is observed. Carbonisation of concrete is a slow and continuous process that progresses from the outer surface inwards but slows down with increasing diffusion depth. Fly ash can reduce the non-durable binder in concrete which makes it permeable and susceptible to chloride attack. Consequently, bridge analysis must be based on the fundamental principles of structural mechanics with material behaviour assumptions for the expansive pressures exerted within the concrete bridge elements.
To prevent concrete deterioration it is important to correctly identify defects early on and plan appropriate repair strategies. Research should be conducted on the shielding properties of different concretes after heating to high temperatures. Paramagnetic defects should be monitored closely as they form easily but require very high fluxes to displace a sufficiently high number of atoms in the crystal lattice before significant mechanical damage is observed. Fly ash should be used to reduce the non-durable binder in concrete which makes it permeable and susceptible to chloride attack.