Commonly used cement and admixtures for drilling

In drilling construction, cement is needed to reinforce the orifice pipe and water stop casing, and also often encounter complex problems such as collapse, leakage, and broken off blocks of the formation, which require cement for wall protection and plugging. However, due to the low early strength of ordinary cement, setting time is too long, the slurry liquidity is poor, it is necessary to use cement additives to improve and adjust a variety of cement properties, the use of cement additives to improve and adjust the performance of certain cements is an effective way. For example, to improve the early strength is appropriate to use early strength admixture; to shorten the setting time, then use rapid setting agent; if you need to improve the fluidity, to use drag reducing agent and so on.

A. Definition of cement

Cement, powdered water-hard inorganic cementitious material. Add water and mix into a slurry, can be hardened in the air or better hardened in water, and can be firmly cemented together with sand, stone and other materials. cement, is the meaning of gravel and flakes. The mixture of early lime and volcanic ash is very similar to modern lime volcanic ash cement, and concrete made from it glued gravel is not only stronger after hardening, but also resistant to fresh or saline water. For a long time, it has been widely used as an important cementitious material in civil construction, water conservancy, national defense and other projects.

Classification of cement

Cement is classified according to its usage and performance as follows

(1)General purpose cement: the cement usually used in general civil engineering and construction projects. General-purpose cement mainly refers to: GB175-2007 six categories of cement, namely, silicate cement, ordinary silicate cement, slag silicate cement, volcanic ash silicate cement, fly ash silicate cement and composite silicate cement.

(2) Special cement: Cement for special purpose. For example: oil well cement, road silicate cement.

(3) Characteristic cement: Cement with some kind of outstanding performance. For example: fast-hard silicate cement, low-heat slag silicate cement, expanded sulfo-aluminate cement, phosphate aluminate cement and phosphate cement.

Cements are classified according to the names of their main hydraulic hardening substances as follows

(1) Silicate cement, which is commonly known as Portland cement abroad.

(2) Aluminate cement.

(3) Sulfur aluminate cement.

(4) Iron aluminate cement.

(5) Fluoroaluminate cement.

(6)Phosphate cement

(7) Cements with volcanic ash or potentially hydraulic materials and other active materials as the main components.

Cements are classified according to the main technical characteristics as

(1) Fast hardness (hydraulic hardness): divided into two categories: fast hard and extra fast hard.

(2) Heat of hydration: divided into two categories: medium heat and low heat.

(3) sulfate resistance: divided into medium sulfate corrosion resistance and high sulfate corrosion resistance two categories.

(4) expansion: divided into two categories of expansion and self-stress.

(5) high temperature resistance: the high temperature resistance of aluminate cement is graded by the alumina content in the cement.

Principles of cement naming:

The naming of cement according to different categories respectively to the cement's main hydraulic minerals, mixed materials, uses and main characteristics, and strive to be concise and accurate, the name is too long, allowed to have abbreviated.

General-purpose cement is named after the name of the cement's main hydraulic minerals crowned by the name of mixed materials or other appropriate names.

Special cement is named after its special purpose, and can be crowned with different models.

Characteristic cements are named after the main hydraulic minerals of the cement with the main characteristics of the cement and can be named with different models or mixed material names.

The cement with volcanic ash or potential hydraulic materials and other active materials as the main components is named by the name of the main components crowned with the name of active materials, and can also be crowned with the name of characteristics, such as gypsum slag cement, lime volcanic ash cement, etc.

Third, cement admixture

There are many types of cement admixtures. Cement admixture used for geological drilling according to its function and composition, there are different classification methods:

Classification by function

(1) adjust the cement setting and hardening speed of the quick-setting agent and retarding agent.

(2) Early strength agent for the early strength of the cement to increase.

(3) reduce the water-cement ratio, improve the flowability of the slurry, water reducing agent or water reducing agent, diluent.

(4) reduce the precipitation and water loss of the slurry water loss agent.

(5) Reducing agent to reduce the specific gravity of cement slurry.

(6) expansion agent to enhance the bonding strength of cement and rock layer.

(7) Plugging agent to prevent slurry loss, etc.

Classification by chemical composition

1. Inorganic compounds

Including a variety of inorganic salts, some metal monomers, a small number of oxides and hydroxides, etc.. Most of these substances are used as early strength agents, quick setting agents, etc.

2. Organic substances

There are many kinds of these substances. Most of them belong to the category of surfactants, such as anionic, cationic, nonionic and polymeric surfactants. In order to meet the construction needs of various projects, cement admixtures in the use of certain properties to improve the cement, the following five aspects should be considered:

① reasonable selection of admixtures according to cement varieties.

② selection of admixtures should be clear to improve and adjust the performance of the cement purpose.

③ selection of admixtures appropriate amount of admixtures.

④ consider the specific construction conditions, such as temperature, hole temperature, pressure, filling method, filling tools, etc..

⑤ As far as possible to use compound admixture.