Cracks, Causes & Corrections in Concrete
Cracks in concrete buildings have several causes. They may show the total extent of damage or problems of greater magnitude. They may represent critical structural distress, lack of durability, or they might influence appearance only. The importance of cracks dependent on the nature of cracking and type of structure.
The principal causes of cracks in a building are as follows:
Permeability of concrete
Several factors control concrete permeability like water-cement ratio, use of admixtures, curing, air voids due to deficient compaction, micro-cracks due to loading, cyclic exposure to thermal variations, and the age of concrete. As the deterioration process in concrete begins with the penetration of various aggressive agents. it dictates the ability of concrete to withstand weathering action, chemical attack, or any process of deterioration.
Thermal movement is one of the most potent causes of cracking in buildings. Ambient temperature changes and loss of heat of hydration in a portion of the structure at different rates lead to temperature variations and subsequent thermal movement. The thermal movement in a component depends on several factors such as temperature variations, dimensions, coefficient of thermal expansion and some other physical properties of materials. It is mainly the external walls especially thin walls exposed to direct solar radiation and the roof which are subject to the substantial thermal variations that are liable to cracking.
The solution for it would be Joints to be considered during the design and constructed properly. For example, expansion joints, construction joints, control joints, and slip joints.
Corrosion of Reinforcement
Reinforcement corrosion will produce iron oxide and hydroxide on the steel bar surface, consequently, its volume increases. This increase in volume causes high radial bursting stresses around reinforcing bars and result in local radial cracks. These splitting cracks results in the formation of longitudinal cracks parallel to the bar. Reinforcement corrosion will occur unless it is protected properly. Steel reinforcement can be protected by providing adequate impervious concrete cover. Steel corrosion will not occur as long as concrete surrounding it is alkaline having a high pH value.
A quick solution to this is that we opt to work on a few points when working on it like using low permeable concrete, with an adequate cover thickness. and also make sure the concrete-steel bond is as good as possible. This is because concrete alone is not capable of resisting tensile forces to which it is often subjected. Otherwise, concrete may crack and allow harmful substance materials to attack steel bars.
Most of the building materials with pores in their structure in the form of inter-molecular space expand on absorbing moisture and shrink on drying. Shrinkage can be of plastic or dry. Factors that cause cement or mortar to experience shrinkage include excessive water, and cement quantity; rich cement mixtures suffer greater shrinkage. It should be cleared by providing movement joints, with the minimum possible quantity of water for mixing cement concrete or cement mortar. And also avoid the use of excessive cement.
Poor Construction practices
There is a broad variety of construction practices that lead to concrete cracking. Normally, improper construction practices are due to ignorance, carelessness, greed or negligence.
main causes for poor construction practices:
o Improper selection of materials.
o Selection of poor quality cheap materials.
o Improper construction joints between subsequent concrete pour or between concrete framework and masonry.
o Addition of excess water in concrete and mortar mixes.
o Lastly, poor quality of plumbing and sanitation materials and practices Etc.
Improper Structural Design
Several problems can occur due to incorrect structural design, detailing, and specifications. Errors that may occur at this stage include inadequate thickness, insufficient reinforcement, incorrect geometry, improper utilization of materials, and incorrect detailing. Additionally, it is crucial that the designer consider the environmental conditions existing around the building site.
Measures to be taken:
Architects, Structural Consultants, and Specifies shall consider the following measure to avoid cracking and subsequent deterioration of structures:
o Proper specification for concrete materials and concrete.
o Proper specifications to take care of environmental as well as subsoil conditions.
o Constructable and adequate structural design.
o Proper quality and the thickness of concrete cover around the reinforcement steel.
A structure needs to be maintained after a lapse of a certain period from its construction completion. Moreover, regular external painting of the building to some extent helps in protecting the building against moisture and other chemical attacks. Waterproofing and protective coating on reinforcement steel or concrete are all second lines of defense and the success of their protection will greatly depend on the quality of concrete. Leakages should be attended to at the earliest possible before corrosion of steel inside concrete starts and the spalling of the concrete takes place. Furthermore, Spalled concrete will lose its strength and stiffness besides, the rate of corrosion increases because the rusted steel is entirely exposed to an aggressive environment.
Result to Chemical Reactions
The concrete may crack as a result of expansive reactions between aggregate, which contains active silica, and alkaline derived from cement hydration, which results in the form of swelling gel. This tends to draw water from other portions of concrete.
Measures to be taken:
o Use cement lower ph values
o Employ pozzolana
o Select proper aggregates.
Not only the above there are many other factors like nature related to mild earthquakes, Fire, etc which have to be taken care of.