Structure of hydrated cement
At any stage of hydration, the hardened paste consists of:
1. crystallized hydrates of the various compounds (calcium silicates hydrate, tricalcium
aluminates hydrate and calcium ferrite) , referred to collectively as gel.
2. crystals of Ca(OH)2 produced from the hydration of the silicates.
3. some minor components.
4. unhydrated cement.
5. Voids Capillary pores
Gel pores
a- Capillary pores: the capillary pores at any stage of hydration represent that part of the
gross volume which has not been filled by the products of hydration. The volume of the
capillary system is reduced with the progress of hydration.
Thus the capillary porosity of the paste depends on:
? The water/cement ratio of the mix. When w/c ratio > 0.38 – The gel volume is not
enough to fill all the available voids.
? The degree of hydration, which influence by the type of cement.
b- Gel pores: The gel pores are interconnected interstitial spaces between the gel particles.
The gel pores are much smaller than the capillary pores. It could be contain large amount
of evaporable water.
2
Water held in hydrated cement paste
We can see that water in hydrated cement is held with varying degrees of firmness and can be
classified as:
1. Free water: present in the capillary pores – with weak firmness, and evaporate quickly
leaving the paste.
2. Chemically combined water: form a definite part of the hydrated compounds.
3. Gel water: which found
a) Gel pores
b) Part of it is held by the surface force of the gel particles - It is known as the
adsorbed water.
A convenient division of water in the hydrated cement into two categories:
- Evaporable water – includes water in the capillary pores and some water in the gel
pores.
- Non-evaporable water – includes nearly all chemically combined water and also some
water not held by chemical bonds. The amount of non-evaporable water increases as
hydration proceeds.
Volume of Hydration Products
Volume before hydration = volume after hydration
Water before hydration = water after hydration
Vol. of pores
Vol. of gel
water (Wg)
Vol. of solid
products
Vol. of pores
Vol. of Gel
water
Vol. of solid
Vol. of
unhydrated cement
Water
Cement
Vol. of hydrated cement
Volume before
hydration
100% hydration Less < 100% hydration
Volume after hydration
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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