Several poor construction practices, such as inadequate concrete curing, lack of formwork support, insufficient concrete compaction, and adding water to concrete in the field can cause crack development in plastic and hardened concrete. These mistakes reduce concrete strength, which makes concrete prone to cracks at lower tensile stress than the design calculations.
Therefore, contractors and site engineers should follow the right procedures to avoid poor construction practices. This can be achieved through appropriate supervision of construction works and by hiring skilled laborers.
How do Poor Construction Practices Cause Crack Development in Concrete Elements?
The poor construction practices, their cases, and corresponding crack types are presented below:
Adding Water to Fresh Concrete on Construction Site
The addition of water to concrete at the construction site to increase workability is a common error that needs to be avoided; it reduces concrete strength and increases drying shrinkage and plastic settlement. Eventually, shrinkage cracks and plastic settlement cracks begin to develop. The pattern of the former is isolated or individual in nature and commonly running in the same direction, whereas the latter is mostly diagonal.
Increasing Cement Content to Offset Strength Reduction due to Addition of Water to Concrete
An increase in cement content would automatically increase cement paste volume and raise temperature differentials between the interior and exterior sections of the concrete element. As the cement content increases, both thermal stress and drying shrinkage stress increase. These stresses are the factors that cause cracking in concrete.
Lack of Formwork Support, Inadequate Consolidation, and Incorrect Placement of Construction Joints
Lack of formwork support and inadequate consolidation will increase settlement, and the concrete setting would have insufficient supports. Moreover, incorrect placement of construction joints leads to the opening of joints at points of high stress.
Inadequate Concrete Curing
Inadequate concrete curing reduces the hydration of cement and subsequently decreases the strength of concrete. As a result, concrete cracks develop due to self-weight before it has developed enough strength to support itself.
The influence of insufficient curing is paramount when cement replacement materials like silica fume, slag, and fly ash are used. These cementitious materials need to be cured properly; otherwise, high drying shrinkage will develop, which in turn, leads to excessive concrete tensile strength, making the crack development inevitable.
The common construction errors in the field are found to be inadequate curing, lack of formwork support, insufficient compaction, and addition of water to concrete.
By and large, shrinkage cracks are limited to the surface of concrete and do not extend into the depth of concrete. As a result, it may not influence concrete workability. Similarly, the structural integrity of a building is not affected by shrinkage cracks.
Adequate monitoring of construction works will ensure the prevention of poor construction practices. Additionally, it guarantees that the final product meets design requirements.