What is the name of this fresh concrete test and purpose
- Thread starter archdevil
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It's KNOWN AS TEMPERATURE TEST FOR CONCRETE.
PURPOSES BEING:
Heat evolution in concrete is a very complex and extensively researched topic. To simplify this process, the heat evolution over time can be separated into five distinguished phases. The heat profile can change depending on the type of cement.
Phase I: Pre-Induction
A short time after the water comes into contact with the cement, there is a sharp increase in temperature, which happens very quickly (within a couple minutes). During this period, the primary reactive phases of the concrete are the aluminate phases (C3A and C4AF). The aluminate and ferrite phases react with the calcium and sulphate ions to produce ettringite, which precipitates on the surface of the cement particles. During this phase, at a lesser extent, the silicate phases (mainly C3S) will also react in very small fractions compared to their total volume and form a very thin layer of calcium-silicate-hydrate (C-S-H).
Phase II: Dormant Period
This phase is also known as the induction phase. During this period, the rate of hydration is significantly slowed down. Traditionally, this is believed to be due to the precipitation of the aforementioned compounds on the surface of the cement particles, which leads to a diffusion barrier between cement particles and water. Nevertheless, there is significant debate on the physical and chemical reasons behind the occurrence of this stage and the methods to predict it.
This is the period at which the fresh concrete is being transported and placed since it has not yet hardened and is still workable (plastic and fluid). The length of the dormant period has been shown to vary depending on multiple factors (cement type, admixtures, w/cm). The end of the dormant period is typically characterized by the initial set.
Phase III and IV: Strength Gain
In this phase, the concrete starts to harden and gain strength. The heat generated during this phase can last for multiple hours and is caused mostly by the reaction of the calcium silicates (mainly C3S and to a lesser extent C2S). The reaction of the calcium silicate creates "second-stage" calcium silicate hydrate (C-S-H), which is the main reaction product that provides strength to the cement paste. Depending on the type of cement, it is also possible to observe a third, lower heat peak from the renewed activity of C3A.
Phase V: Steady State
The temperature stabilizes with the ambient temperature. The hydration process will significantly slow down but will not completely stop. Hydration can continue for months, years, or even decades provided that there is sufficient water and free silicates to hydrate, but the strength gain will be minimal during such a period of time.
Concrete Temperature Control During Mix Design
An effective approach to controlling heat generation during cement hydration is to have a mix design that is suited to the application and the ambient conditions. Here are some things to consider:
PURPOSES BEING:
- The temperature measurement is typically done to make sure the concrete is in compliance with certain specifications that define a certain allowable temperature range.
- Typical specifications require the temperature of the concrete during placement to be within a range of 10°C to 32°C (50°F to 90°F).
- The temperature the concrete exhibits during placement affects the temperature of concrete during the next hydration phase.
- Monitoring the temperature of the concrete during phase III and IV is a quality control component that is regularly being performed
- The main reason behind this measurement is to ensure the concrete does not reach temperatures that are too high or too low to allow proper strength development and durability of the concrete
- Another reason for monitoring concrete curing temperature during this phase is to evaluate the in-place strength,
Heat evolution in concrete is a very complex and extensively researched topic. To simplify this process, the heat evolution over time can be separated into five distinguished phases. The heat profile can change depending on the type of cement.
Phase I: Pre-Induction
A short time after the water comes into contact with the cement, there is a sharp increase in temperature, which happens very quickly (within a couple minutes). During this period, the primary reactive phases of the concrete are the aluminate phases (C3A and C4AF). The aluminate and ferrite phases react with the calcium and sulphate ions to produce ettringite, which precipitates on the surface of the cement particles. During this phase, at a lesser extent, the silicate phases (mainly C3S) will also react in very small fractions compared to their total volume and form a very thin layer of calcium-silicate-hydrate (C-S-H).
Phase II: Dormant Period
This phase is also known as the induction phase. During this period, the rate of hydration is significantly slowed down. Traditionally, this is believed to be due to the precipitation of the aforementioned compounds on the surface of the cement particles, which leads to a diffusion barrier between cement particles and water. Nevertheless, there is significant debate on the physical and chemical reasons behind the occurrence of this stage and the methods to predict it.
This is the period at which the fresh concrete is being transported and placed since it has not yet hardened and is still workable (plastic and fluid). The length of the dormant period has been shown to vary depending on multiple factors (cement type, admixtures, w/cm). The end of the dormant period is typically characterized by the initial set.
Phase III and IV: Strength Gain
In this phase, the concrete starts to harden and gain strength. The heat generated during this phase can last for multiple hours and is caused mostly by the reaction of the calcium silicates (mainly C3S and to a lesser extent C2S). The reaction of the calcium silicate creates "second-stage" calcium silicate hydrate (C-S-H), which is the main reaction product that provides strength to the cement paste. Depending on the type of cement, it is also possible to observe a third, lower heat peak from the renewed activity of C3A.
Phase V: Steady State
The temperature stabilizes with the ambient temperature. The hydration process will significantly slow down but will not completely stop. Hydration can continue for months, years, or even decades provided that there is sufficient water and free silicates to hydrate, but the strength gain will be minimal during such a period of time.
Concrete Temperature Control During Mix Design
An effective approach to controlling heat generation during cement hydration is to have a mix design that is suited to the application and the ambient conditions. Here are some things to consider:
- Selecting the appropriate cement type changes the heat of hydration generated. Compared to Type I cement, Type III generates more heat while Type II generates moderate heat, and Type IV generates less than the others;
- Adjusting the finesse of the cement (a finer cement will generate more heat);
- Using supplementary cementitious materials (SCMs) is also an effective means of reducing the heat generated during hydration. Replacing a portion of the cement with, for instance, slag or fly ash, reduces the amount of reactive material in the early stages; in turn, this reduces the amount of heat generated and delays concrete strength gain; and
- Adding other types of admixtures such as retarders and accelerators (however, these mixtures will not typically affect heat generation; rather they will be used to control the length of the dormant period).
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