 |
Construction Chemicals and Mortars
Admixtures
for Concrete Ready-to-use
Mortars Tunnelling
Admixtures for
Concrete
Technologies:
The use of cement, mortar and concrete admixtures to seal against
water pressure to increase water-tightness of plaster, to prepare
air-entrained concrete, to improve the workability of fresh concrete,
or to achieve other specific properties - both of fresh as well
as hardened concrete or mortar - has become an obvious necessity
today for most construction experts.
Concrete consists of aggregates, cement, water and admixtures.
The aggregates are the matrix of the concrete,
cement mixed with water, forms the binder; first as cement glue,
later as cement 'stone'. The water acts as well as a
processing material. The admixtures, on the other hand, take the
function of active ingredients.
The aggregate has a decisive effect on the properties of a concrete.
The matrix endows the final product with strength, density, permanence
and appearance, -the cement is the binder for the framework (glue)
and, therefore has the major responsibility for the properties of
the concrete.
Admixtures Have significant influence on both, the fresh
and the hardened concrete properties. They are added in an amount
of less than 5% on weight of cement.
Applications:
- High performance full range standard admixtures for concrete
and mortar and tailor made admixtures for big job sites.
- Low cost admixture range with multipurpose use.
- Environmentally friendly admixtures which show biodegradability
or are not leachable from concrete.
- Admixtures to be added at the cement plant to modify cement
properties, including grinding agents.
- Corrosion inhibiting admixtures for cement, mortar, concrete
and auxiliary products.
- Basic investigations on cement hydration and mode of action
of admixtures for the development of new products and systems.
Innovation
Superplasticizers :
High-range water-reducing admixtures (HRWR) or superplasticizers (SP)
have been widely used since their introduction in the late 60's in
Japan. They can be used either to reduce the amount of water and thereby
the amount of cement or to produce high strength concrete with increased
service life of the resulting structure. Used as superplasticizers
the flow of a concrete with a given w/c could be increased to produce
flowing concrete.
However with the upcoming new construction technologies mostly coming
from Japan, the need for new admixtures was evident.
New cost-effective polycarboxylate based polymers with
a low environmental impact, are replacing conventional admixtures such
as lignin sulphonate, naphthalene- and melamine sulphonate derivatives.
This new product technology has a wide range of uses: from construction
concrete through specific concrete qualities to prefabrication applications
and highest-quality Self Compacting Concrete (SCC).
The product technology is now to be globally anchored and introduced
to our subsidiary companies with the help of extensive for local specialists.
top
Ready-to-use
Mortars
Technologies:
Our buildings and the infrastructure are permanently exposed to
wear and tear, climatic changes and or aggressive environments.
High performance ready-to-use mortars for repair and maintenance,
mortars for industrial applications or high performance grouts are
being used for this purpose.
Applications:
- non sagging polymer modified cementitious mortars, for repair
of verticals, highly performing when structural demands
apply, light weight mortars for applications like facades where
the ease of application is important.
- The repair system includes bonding bridge as well as rendering
mortar and coatings.
- The mortars can be handapplied or machine applied by wet spraying.
- a special range of Gunite mortars covers dry spray applications,
main use is repair of large structures like bridges or cooling
towers, fast setting gunites are used in tunnelling, to stop water
ingress and to solidify rocks.
- free flowing polymer modified cementitious mortars, for horizontal
applications such as finishing coat in ice rinks, or for bridge
deck repairs.
- epoxy modified cementitious mortars, for applications with increased
chemical attack, (waste water sewage plants, e.g.), or when rapid
curing for overcoating is required (SikaFloor EpoCem)
- water proofing mortars for clean water and drinking water reservoirs,
with and without polymer modification.
- flowable grouting mortars, with rapid strength evolution and
high strength potential, for anchoring and casting.
- various speciality products, like
- low density flooring mortars for ship decks
- high density mortars for counterweights and
noise dampening
- cosmetic mortars
- rapid setting mortars
- powerpacks for other Sika companies or job
site blends
Characteristics:
Ready-to-use mortars have to meet narrow specifications, in many cases
according to national (ZTV-SIB in Germany, e.g.) or international
(upcoming EN, ASTM, e.g.) standards.
Use of polymers, as plasticisers or modifiers, is compulsory, in order
to meet the specifications which are in many cases contradictory.
The main effort in the last years was to adapt the products to powder
polymers, thus reducing the liquid polymer component, in order to
improve ease of application and to reduce the packaging waste.
top
Tunnelling
+ Mining
Sprayed Concrete Technology:
The enormous advantages of sprayed concrete as a construction and
rock support process and the improvement of equipment, materials
and application know-how have made it an important tool for various
types of work.
Approximately 30 years ago, the only method available for the application
of sprayed concrete was via the dry-mix process. This remained the
dominant method until the mid nineties, when eventually the wet-mix
process began to be used more widely. Currently the wet-mix method
is being adopted on a world-wide basis as the preferred choice.
The wet-mix sprayed concrete process uses concrete that is batched
in a similar way to conventional concrete, making it possible to
check and control the w/c ratio and thus the quality at any time.
The consistency can be adjusted by means of admixtures. With the
wet-mix method, it is easier to produce a homogenous product with
uniform quality throughout the spraying process. The ready-mix concrete
is emptied into a pump and forwarded through a hose by pressure
(thick stream transport). Today, piston pumps dominate the wet-mix
sprayed concrete pump market.
Innovations
The role of the shotcrete accelerators
Sika has developed a wide range of shotcrete accelerators. In the
past aluminate based materials were used. Today, due
to safety and ecological concerns, it has become dominant in the
sprayed concrete accelerator market, that applicators have started
to be reluctant to apply aggressive products. In addition, requirements
for strength and durability of concrete structures are increasing.
Strength loss or leaching effects suspected to be caused by strongly
alkaline accelerator has forced our industry to provide products
with better performances.
Due to their complex chemistry, alkali-free accelerators are more
expensive than traditional accelerators. However, accelerator prices
have very little influence on the total cost of on-place sprayed
concrete. Of much greater consequence are the time and rebound savings
achieved, the enhancement of the quality, and the safe working environment.
|
top