1. Role of Water-cement Ratio

  • The volume change in concrete results in cracks and the cracks are responsible for disintegration of concrete.
  • Permeability is the contributory factor to the volume change with higher water-cement ratio being the fundamental cause of higher permeability. Therefore, use of higher water-cement ratio can affect permeability, volume change, cracks, disintegration and even cause failure of concrete. 
  • Therefore, for a concrete to be durable, use of lower possible water-cement ratio is the fundamental requirement to produce dense and impermeable concrete.
  • Concrete with lower water-cement ratio is less sensitive to carbonation, external chemical attack and other detrimental effects that result in reducing the durability of concrete.
  • However, in concrete with lower water-cement ratio, there is not enough water available to fully hydrate all cement particles, only surface hydration of cement particles takes place leaving a considerable amount of unhydrated core of cement grains. This unhydrated core of cement grains constitutes strength in reserve.

2. Effects of water cement ratio

  • The concept of water-to-cement ratio (w/c) of concrete is a universally fundamental concept and is considered as the oldest law in the concrete technology.
  • The water/cement ratio influences the durability properties of concrete in a significant way. Decreasing the w/c value would lead to a reduction in concrete porosity and accordingly, lower permeability and higher durability.
  • In general, the capillary pores (ranges in size 10 – 100 μm) depends on the w/c ratio with lower capillary porosity for lower w/c. ratio. Lowering w/c makes the cement particles closer to each other as shown in figure.

Possible conditions with Higher W/C ratio

  • Cement particles are loosely packed.
  • High porosity and permeability.
  • Low strength and durability.
Cement particles are loosely packed in higher 'water-cement ratio' condition

Possible conditions with Lower W/C ratio

  • Cement particles are closely packed.
  • Low porosity and permeability.
  • High strength and durability.
Cement particles are tightly packed in lower 'water cement ratio'

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