If the ambient temperature is too low, the hydration of the cement will drastically slow down or completely stop. Cold weather slows down the setting process or stops it completely, negatively impacting the concrete's strength gain.
The major factors affecting the time of setting are cement composition, water-cementitious material ratio (w/cm), temperature, and admixtures.
One consideration during the construction process is the fact that salt water tends to speed up the setting of the concrete. However, adding 20 percent fly ash will slow the setting and help make the concrete even more effective.
You can slow your set time by adding retarders to the concrete. Retarders slow the set time to allow concrete to receive an appropriate amount of time to complete the chemical reaction and maintain a higher slump.
It takes so much time for concrete to harden if we add coke to it. The reason is, sugar (in the coke) reduces the hardening property of concrete . “In technical terms, sugar (coke) acts as a retarder and delays the setting time of concrete.”
Will Vinegar Damage Concrete? Cleaning concrete with vinegar will not damage it! However, saturating concrete for an extended period will damage the cement that binds concrete together. Over time, vinegar erodes the concrete itself, so be careful.
However, calcium chloride and (to a lesser extent) sodium chloride have been shown to leach calcium hydroxide and cause chemical changes in Portland cement, leading to loss of strength, as well as attacking the steel reinforcement present in most concrete.
How Do You Break Hard Concrete? Breaking hard concrete is easier if you undermine its external support, so dig out underneath it if possible, or use a pry bar to lift it a little at a time, so it's weaker when hit with a sledgehammer or other tool.
Calcium Chloride is the most effective accelerator for concrete because of its strength and quality.
Sugar delays the setting time of cement by up to 1.33 hours at dosage level of 0.06% by weight of cement. No effect on workability, compaction by the use of sugar as admixture in concrete. Higher long-term compressive strength can be achieved in concrete by the use of sugar as admixture.
Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component.
Sulfates of sodium, potassium, calcium, or magnesium dissolved in soil, seawater, or groundwater can penetrate the concrete, react with hydrated compounds, and expand, causing concrete damage.
Salt does not chemically react with hardened concrete. Salt does however lower the freezing point of water, attract moisture, and increase pressure of frozen water.
When salts are put into concrete, they draw up to 10% extra water into the concrete's pore structure. This process reduces the pore structure's ability to expand, resulting in increased pressure inside the concrete when it freezes, causing the surface to chip, flake, and pop, a process known as spalling.
You can add more Portland cement to bagged concrete to make it stronger. You can also add hydrated lime.
In simple terms, sugar acts as a retarder and delays the setting time of concrete.
Hydrated lime improves the strength of the mortar by several mechanisms: Carbonation - Hydrated lime reacts with carbon dioxide in the atmosphere to form limestone. Cementitious Reactions - Pozzolonic reactions can occur between hydrated lime and silica compounds in the mortar mix.
Add warmer water. As one of the key ingredients in concrete, water is essential for the curing reaction to occur. The curing time can be hastened by using a slightly warmer water in the mixture as this will encourage the reaction to occur more quickly – do not, however, use blazing hot water as this could be damaging.
Supplementary Cementing Materials
Typical cementing materials include fly ash, slag, silica fume and other natural pozzolans. These materials are used to make concrete mixtures more economical, reduce permeability, increase strength, or influence other concrete properties.
Generally, concrete takes 28 days to fully cure. Concrete cures as the water in it evaporates. The key to slowing concrete curing time is it moist.
Optimal mixing time is important for strength. Strength tends to increase, with mixing time, up to a point. However, over-mixing causes excess water evaporation and the formation of fine particles within the mix. This weakens the concrete and makes it harder to work with.
Most mechanical failures occur because of physical impacts such as collisions. Vibrations, overloading and other movements can also result in cracking and loss of entire concrete sections.