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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.
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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.
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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.
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