1. RAR – 602, CONSTRUCTION & MATERIAL – VI
Module – 2 (Additives & Admixtures)
Content -
1- various additives and admixtures
a- Cementitious (crystalline) system
b- Integral system
c- Proprietary system
d- Cementitious Coating system
What are Additives
Additives are chemical components added to cement during manufacturing to get new properties
for cement.
The raw materials used in the manufacturing of cement are lime, silica alumina and iron oxide.
These material are ground into a fine powder and are mixed followed by roasting. Heating of this
mixture to about 1500oC will initiate a number of chemical reactions that give the final chemical
composition of cement.
In order to obtain desired properties, various additives are added to cement while manufacturing.
2. Accelerators
Accelerators are added to reduce cement settling time and to speed up the
development of compressive strength.
Retarders
Retarders extend the cement settling time. This helps the cement to have sufficient
time for slurry placement in deep wells.
Dispersants
Dispersants are added to reduce the viscosity of cement slurry and to ensure good
mud removal during placement.
Fluid Loss Control Agents
Fluid loss control agents control water loss from the cement into the
formation.
3. What are Admixtures
Admixtures are chemical components that are added to concrete mixtures while
mixing to get new properties. Admixtures are the components in concrete other than
cement, water and aggregates. Admixtures are added to cement immediately before
or during mixing the concrete mixture.
Admixtures are added to:
To accelerate or retard hydration or setting of cement Reduce water requirement
To improve workability
As water proofers
As air-entraining agents
To produce colored concrete
There are different types of admixtures classified as below
with some examples.
•Air entraining admixtures – salts of wood resins, some synthetic detergents, salts of
petroleum acids
•Plasticizers
•Water-reducing admixtures – lignosulfonates, hydroxylated carboxylic acids, etc.
4. •Accelerating admixtures – calcium chloride, sodium thiocyanate, etc.
•Retarding admixtures – lignin, borax, sugars, etc.
•Corrosion inhibitors, etc.
5. CEMENTITIOUS (CRYSTALLINE) SYSTEM
Cementitious waterproofing systems contain a base of Portland cement, with or
without sand, and an active waterproofing agent.
There are four types of cementitious systems:
• metallic,
• capillary system,
• chemical additive systems,
• and acrylic modified systems.
Cementitious systems are effective in both positive and negative applications, as well
as in remedial applications. These systems are brushed or troweled to concrete or
masonry surfaces and become an integral part of a substrate.
Cementitious systems are excellent materials for use with civil and infrastructure
projects, both above and below-grade, using both positive and negative applications.
These projects generally consist of large concrete components that make the same
generic composition cementitious systems relatively easy to specify and install
without compatibility problems.
6. Among the types of structures cementitious systems are used for:
● Tunnels
● Underground vaults
● Water reservoirs
● Water and sewage treatment facilities
● Elevator and escalator pits
● Below-grade concrete structures
● Swimming pools
● Cooling tower basins
In new construction, where costs and scheduling are critical, these systems are particularly effective.
They do not require a completely dry substrate, and concrete does not need to be fully cured before
application. This eliminates well pointing and the need for water control during construction. These
systems apply to both walls and floors at one time, thereby eliminating staging of waterproofing
operations. No sub slabs are required for horizontal applications in new construction preventative
waterproofing installations.
In cases such as elevator pits, the waterproofing can be completed any time during construction
7. INTEGRAL SYSTEM
What is it ?
Admixtures are mixed in the concrete in the mixing phase with the aggregates.
The whole concrete structure after setting behaves like a waterproofing membrane.
It is integrated in the concrete
Integral waterproofing uses chemical admixtures, usually a dry powder or liquid added
to the concrete mix at the batch plant or the jobsite. Some forms of integral
waterproofing will even self-heal minor cracking.
Integral waterproofing can be faster, cheaper, and more reliable than coatings and
membranes.
ADVANTAGES
integral waterproofing is especially useful in highly corrosive environments such as
bridges constructed over bodies of salt water and high-consequence projects… where
failure isn’t an option.”
Integral waterproofing is extremely useful for blindside work such as deep foundations
and bored tunnels
There are no workmanship issues to be concerned about because there is no
installation required
