Dispelling the myths: 10 misconceptions when working with concrete

 

 

 

 

 

The world of concrete construction is full of fictions and misconceptions, which, with the penetration into the broad masses, become almost a golden canon for most concrete workers. But true professionals do not agree with false politics. It's time to dispel common myths when working with concrete, often serving as the cause of poor quality work!

 

 

 

 

Myth #1: Water will help increase shrinkage.

 

 

In practice: this is far from the best way to increase shrinkage and it is better not to resort to it.

 

 

 

Indeed, the addition of liquid in an abundant amount enhances shrinkage well, but at the same time, it negatively affects the strength of the concrete structure, and makes it difficult to further maintain it. This is due to the fact that water has a diluting effect on the mixture, and also increases the ratio of liquid in comparison with binders. Excess water will not have the best effect on the frost resistance of the material.

 

The workability of mortars and mixtures plays a key role in concrete work. But achieving this property by increasing fluid flow is not the best solution. Such experiments will only worsen the resistance of cement. In order for concrete pouring to acquire plasticity, it is enough to correctly combine the proportions of aggregates and cement paste. When the latter is multiplied, the concrete will flawlessly succumb during laying, and its strength will remain untouched. It is also possible to noticeably improve shrinkage with the help of plasticizers, which are widely used by specialists in concrete construction to increase workability.

 

Most technical regulations state in black and white that it is PROHIBITED to add water to the concrete mixture at the construction site. Often, concrete workers who disregard this rule will end up disappointed. This especially applies to inattentive unfortunate craftsmen who use water "enriched" with chemicals. This "dilution" prevents the mobility of both the mixture itself and the air composition inside it.

 

 

 

 

Myth No. 2: the brand of concrete is easy to recognize by the number of bags of cement

 

 

In practice: composition proportion depends on technical requirements.

 

 

 

“How many bags of cement will be required per cube of concrete”  is the most pressing dilemma among concrete masters. But quality cannot be measured by bags. Cement is delivered to the construction site, most often in 50 kg paper bags, and often does not meet the proper standard. Its proportionality in concrete pouring is influenced by the purpose of construction.

 

But you should not abuse this astringent. Otherwise, there is a high probability of getting rolling stock and poor-quality shrinkage. In excess, cement also serves as an obstacle to maintaining optimal temperature conditions. It is better to use the minimum amount of binder building material. This will extend the durability of the structure, its wear resistance and aesthetic qualities of the surface.

 

 

 

 

Myth #3: Concrete is airtight.

 

 

In practice: porosity is characteristic of even the strongest concrete structure.

 

 

 

Concrete passes through itself any liquids and vaporous substances. Its porosity is only responsible for the duration of this process, which can last either a couple of minutes or several months.

 

To improve the tightness, concrete is saturated with sealing chemical and additional cementing impurities - pasteurizers, hydrophobic cement, silica, fly ash. For greater efficiency, you can treat the concrete surface with a moisture-repellent substance.

 

 

 

 

Myth #4: The durability of concrete depends on its strength.

 

 

In practice: in compression, the durability depends not only on the hardness index.

 

 

 

In compression, one of the most significant concrete characteristics is its strength threshold. But there are a number of individual qualities that have a much greater impact on the durability of concrete, even under harsh environmental conditions. The motives for early wear of the structure are:

 

• reinforcement corrosion;

• low frost resistance;

• redox reactions;

• weak indicator of sulfate resistance.

 

The golden rule says that reducing the permeability of concrete is the main source of its durability.

 

 

 

 

Myth #5: Calcium chloride will keep liquids from freezing.

 

 

In practice: calcium salt does not have antifreeze properties, and only accelerates the hardening of concrete.

 

 

 

By adding calcium chloride at the initial stage of manufacturing the building mixture, setting can be accelerated by almost half. But until fresh concrete gains starting strength, it needs to be protected from freezing. Without it, the building material will simply stiffen, and this will negatively affect its strength in the future. In order to avoid unnecessary trouble, when concreting the surface on the street on a cold day, it is important to make sure that the optimum temperature regime of the mixture is maintained.

 

 

 

 

Myth #6: You can safely cast concrete on wet, frozen ground without taking extra precautions.

 

 

In practice:  neglecting precautions, with the assistance of adverse weather conditions, you can earn a lot of trouble with the ground.

 

 

 

Concreting of frozen ground is fraught with uneven shrinkage and cracks, which may well appear after thawing. The temperature imbalance between the soil and concrete is dangerous because the latter cools too quickly, and the rate of its solidification decreases. Ideally, the temperature of the soil should match the temperature of the concrete mix. There are a couple of effective ways to warm up the soil before concreting, among which professionals distinguish artificial heating.

 

 

 

 

 

Myth No. 7: if the concreted surface is dry, you can safely proceed to the finishing part of the work.

 

 

In practice:  dryness is not yet the dominant criterion that allows you to start finishing manipulations.

 

 

 

An illiterate approach to processing a concreted structure is fraught with unpleasant aesthetic flaws:

 

• bulges;

• coating;

• cracks;

• flaking.

 

To determine whether surfaces are ready for finishing, you need to have a lot of experience in the field of concreting. Of course, you can resort, as they say, to the "old-fashioned method": fix polyethylene on the surface and monitor the appearance of condensate under the film. But for an accurate determination, it is better to use a professional moisture meter. Its accuracy will be one hundred percent, because the device takes into account many factors that affect the drying of concrete: weather conditions, type of construction.

 

 

 

 

Myth #8: A perfectly smooth surface guarantees a flawless finish

 

 

In practice: After shrinkage, hardening and complete drying, concrete tends to distort volumes.

 

 

 

The accumulated moisture and the imbalance of the temperature regime of the upper and lower parts of the concrete slab lead to its deformation. If the curing process occurs in a dry environment, the concrete shrinks, and if in a wet environment, it hardens and swells. Force loads also cause deformation. To avoid it, you can resort to the technology of drying concrete.

 

 

 

 

Myth #9: Reinforced concrete won't crack.

 

 

In practice:  reinforcement is not yet a guarantee of preventing cracks when volume changes.

 

 

 

If the increase in the volume of the concrete surface is constrained by structural features, then it is likely that it will crack under the onslaught of compressive stress. Often, it is the reinforcement that provokes the occurrence of microcracks. Structural reinforcements do nothing to prevent their formation, but help to contain the boundaries and keep the further expansion of the "holes" under control. In the process of destruction of the concrete surface, the compression deformation is transferred to the steel structural elements. For this reason, reinforced concrete structures are more resistant to heavy loads than monolithic ones.

 

 

 

 

Myth #10: Curing concrete and drying it are the same thing.

 

 

In practice:   concrete needs moisture to dry well.

 

 

 

Drying concrete does nothing to harden it. While maintaining optimal humidity and temperature conditions, hydration will continue. When the freshly poured mixture begins to dry out, that is, no more than 80% of the initial moisture indicator remains, the hydration process will stop. And if the temperature of fresh concrete drops to 5, it will slow down significantly.

 

For optimum hardening of concrete, a favorable temperature and degree of humidity are necessary, and these criteria are important at the very beginning of pouring. It depends on them whether the result will be good.