Cause of cracks:
Cause # 1. Movement Due To Creep: Creep of a material is defined as the property due to which the material continues to deform with time under sustained stress.
Creep increases with increase in water and cement, water-cement ratio, and temperature. It decreases with increase in humidity of the surrounding atmosphere and age of material at the time of loading.
Preventive Measures: Minimum use of cement mortar .
Cause # 2. Chemical Reactions: Certain chemical reactions in building materials result in appreciable increase in volume, developing internal stresses which result in outward thrust and formation of cracks.
The materials involved in reaction also become weaker in strength. Sulphate attack on cement products, carbonation in cement based materials, corrosion of reinforcement in concrete and brickwork, and alkali aggregate reaction are the common chemical actions on building materials.
Preventive Measures: Crack due to chemical reaction can be presented by using good quality of concrete and provide increase cover for RCC member
Cause # 3. Foundation Movement and Settlement of Soil: Shear cracks occur due to large differential settlement in foundation. Building constructed on expansive soils which are susceptible to swelling on absorbing moisture and shrink on drying due to change in moisture content of the soil. These are extremely susceptible to cracking. Special measures are needed to prevent the cracks.
Settlement of building built on made-up soil may occur when water due to heavy rains or floods gets into the foundation and causes settlement in the soil under load of the structure. Such settlements are generally not uniform in different parts and cause cracking.
Preventive Measures: proper Compaction of Soil to Prevent Settlement Cracks in Concrete:
The area below the concrete slab has to be compacted properly and in layers so as to ensure against settlement of soil later. If the soil is left loose it will settle over time and create cracks on surface. This applies in the home as well as constructions on highways.
Cause # 4. Cracking Due To Vegetation:
Existence of vegetation may be the cause of cracks in walls due to expansive action of roots growing under the foundation or in brick masonry. When soil under the foundation of a building happens to be shrinkable clay, cracking in walls and floors of the building may occur either due to dehydrating action of growing roots on the soil which may shrink and cause foundation settlement or due to upward thrust on portion of the building.
Preventive Measures: Do not let trees grow too close to buildings, compound wall, etc. taking extra care if soil under the foundation happens to be shrinkable soil. If any saplings of trees start growing in fissures of wall etc remove them at the earliest opportunity.
Cause # 5. Effect of changes in Temperature Various building materials are used for the construction of a building and all the materials have different coefficient of expansion. Due to changes in the temperature, the expansion and contraction of the building components takes place which result in the changes in the size and shape of the components.
Preventive Measures: Cracking due to temperature. Variation can be prevented by introducing expansion, contraction and slip joints at appropriate location. Painting top roof with reflective finish such as white wash.