Mixing water control in concrete dosing is essential and important to obtain the best results in all types of constructions.
It is known that any rational dosage of concrete starts from the value known as the “water/cement ratio,” that is, the number of liters of water, divided by the number of kilograms of cement used for a given volume of concrete.
And the resistance of this concrete, for equality of materials and processing conditions, depends on the water/cement ratio. When it falls, the resistance increases, and if on the contrary, it rises, the resistance decreases.
The increase in water above the amount stipulated in the design inevitably decreases strength and other properties, unless an additional amount of cement necessary to keep the water/cement ratio constant is incorporated into the mixture.
Definition Of The Water / Cement Relationship
Concrete is a material that is obtained from a mixture of components: binder (cement), aggregates (sand and stone), water and, optionally, additives. The paste, composed of portland cement and water, joins the aggregates, usually sand and gravel (crushed stone), which creates a rock-like mass. In this water/cement relationship, the importance of water is of great magnitude, since it and its relationship with cement are highly linked to a large number of properties of the final material that will be obtained, where usually as more water is added, increases the fluidity of the mixture and, therefore, its workability and plasticity, which presents great benefits for the workforce; however, resistance also begins to decrease due to the greater volume of spaces created by free water.
Thus, it can be said that the strength of concrete depends highly on the weight ratio between water and cement.
Also, curing as mentioned in a previous article is very important, since, if this process is done badly, up to 30% of the expected resistance could be lost; Therefore, it would be advisable to do so for 28 days It should be noted that the resistance specified to concrete, approximately 70%, is generated in the first seven days. At 14 days, resistance has reached 85% of what is expected in 28 days.
Consequences Of Excess Of Water In The Concrete
Within the specified limits of bursting and water-cement ratio, all excess water should always be avoided. In this context, it is considered that there is excess water, in casting conditions, if supernatant water (vertical segregation) or water runoff from the sides of the formwork (horizontal segregation) is observed. Excess water also aggravates surface defects by increasing leaks in the formwork through any hole.
The final result can be:
- Formation of honeycombs, sand streaks, variations in color, or soft spots on the surface.
- In vertical formwork, the rise of water generates weak planes between each deposited layer. In addition to the damaging structural effect, these planes, when hardened, contain gaps through which water can pass.
- In horizontal elements, such as mezzanine or firm slabs, excess water tends to rise and forms a weak surface layer. The said layer offers little resistance to compression and abrasion, considerable shrinkage, and, in general, low quality.
- For the realization of the concrete mixture, it is necessary to keep in mind five very important factors: the Water / Cement ratio, granulometric distribution, water quality and of course the consistency of the mixture and finally concrete resistance.
- The excess of mixing water is a danger already recognized by the builders, and unfortunately, the damages that it entails appear at a too late age to be remedied without high costs.
- To obtain an appropriate specified concrete strength, it is always advisable to carry out the material and dosage tests in the Concrete Mix Design.