Introduction
Hydration Of Portland cement is defined as the “ dissolution- precipitation” process. During this process cement in blend reacts with water and transforms from fluid phase to porous solid matter known as concrete.
This process of hardening during the hydration process is known as the setting of concrete. Strength continues to develop after the hardening stage.
The hydration process has several stages which will be explained latterly in this composition.
Clinker Phases Of Cement
In order to look nearly at the hydration process, it’s imperative to look at clinker ingredients of cement as they play a major part in hydration response. Then are following major phases of cement clinker.
1. Tri-calcium Silicate (C3S)
Tri-calcium silicate also known as Alite is the top phase of ordinary portland cement. In response to water, it forms Calcium Silicate Hydrate (CSH) of variable composition
2. Di-Calcium Silicate (C2S)
Di-Calcium silicate also reacts with water to form CSH but its composition is different and also rate of response is slow as compared to C3S
3. Tri-Calcium Aluminate (C3A)
Tri-Calcium silicate is a problematic phase as far as hydration of cement is concerned. It’s the most reactive phase of cement which reacts with water and a lot of heat is released.
4. Tetra-Calcium Alumino Ferite (C4AF)
C4AF doesn’t play a major part in hydration kinetics and is considered of little significance.
Hydration Kinetics
Hydration kinetics is the study of heat elaboration during hydration response which can be studied using different ways similar as
- XRD
- Calorimetry
Stage 1
Stage 1 shows a peak that is associated with C3A response with water. A lot of heat is released as shown in the graph in the small time span. This response produces rod-suchlike chargers known as ettringite.
Stage 2
After the original response of C3A there comes a brief period where little or no exertion takes place. This time period is known as the “ dormant period” Numerous propositions are presented in order to beneath stand dormant period ( also known as the induction period).
Some of the popular propositions are listed below, Explanation of these propositions is out of the compass of this composition and can be studied from another source.
- Defensive Subcaste Proposition
- Double Layer Theory
- Nucleation and Growth Theory
Stage 3
After the dormant period heat evolved again increases due to the response of C3S which is the principal phase of cement and is responsible for nearly 80 strength gain.
Stage 4
After C3S, C2S comes into play and continues to produce CSH gel over time. C2S response is slow as compared to C3S as apparent from the graph but it continues for a long time and is responsible for the long-term strength of concrete.
Hydration Products
- Calcium Silicate Hydrate (CSH)
CSH is the main product of hydration and is substantially responsible for concrete strength. CSH is an inadequately liquid material having a variable composition.
- Calcium Hydroxide (CH)
CH is also known as portlandite is produced alongside CSH. CH is a comparatively weaker material due to its chargers exposure. CH value can be reduced using pozzolanic supplementary cementitious accouterments.
Summary
C3S is primarily responsible for Concrete early strength. Nearly 80 of hydration is completed after 28 days, that’s why we take 28 days cylinder strength in design services.