Construction Chemicals and Mortars

Admixtures for Concrete  Ready-to-use Mortars  Tunneling

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:
Buildings and infrastructure are constantly  subject to wear and tear due to  climate change and  harsh environments. To reduce the damage caused by these factors, builders can use high performance, ready-to-use mortars or high performance grouts for repair and maintenance. The repair system includes a bonding bridge, repair mortars, rendering mortars, coatings, and corrosion inhibitors..

Whithin Sika’s line of repair mortars are products which may be applied horizontally, vertically, or overhead. These products may be  hand-applied, formed and poured, formed and pumped, sprayed wet at high or low velocity, and sprayed dry.

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.

Mortar Solutions:

Non-sag polymer modified cementitious mortars may be used to repair vertical and overhead surfaces of any type of structure. Some of these may be used on high-performance mortars are effective for structures such as facades, where light-weight, easily applied mortars are needed.

• A special range of machine-applied mortars is used for dry and wet spray applications. These mortars are mainly used to repair large structures like bridges,  water tanks, and dams.., Fast setting gunites are used in tunneling to stop water ingress and to solidify rocks.
• Free-flowing, polymer-modified cementitious mortars may be used in horizontal applications such as a finishing coat for a parking deck, or for bridge deck repairs.
• Formed repair mortars may be utilized for vertical repairs to walls and columns, and overhead repairs to decks and beams.
• Epoxy modified cementitious mortars, for applications in harsh chemical environments, such as waste water and water plants, or when rapid curing for overcoating is required.Polymer-modified water proofing mortars for repairing clean water and drinking water reservoirs
• Fluid grouts do not segregate and have high strength for anchoring and casting.
• Various specialty products, including
• low-density flooring mortars for ship decks;
• high-density mortars for counterweights and noise dampening;
• cosmetic mortars;
• quick-setting mortars;
• power-packs for job site blends

Characteristics:

Ready-to-use mortars have to meet stringent  specifications, in many cases complying with  national (e.g. ASTM, ACI in the U.S., ZTV-SIB in Germany) or international (e.g. EN, ASTM standards.

The use of polymers as plasticizers or modifiers is necessary  in order to meet many specifications Sika's main efforts in the last few years have been  to develop highly fluid, zero bleed grouts for bonded post-tensioned bridge construction, and rapid setting repair mortars with low shrinkage for highway and bridge deck repairs.

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Tunneling + Mining
Sprayed Concrete Technology:

Sprayed concrete is an important tool for various types of work. It has enormous advantages in a construction and rock support process. There have also been major improvements in equipment, materials, and application know-how.

Thirty years ago, the only method available for applying sprayed concrete was the dry-mix process. This remained the dominant method until the mid-nineties, when the wet-mix process began to be used more widely.  Today, the wet-mix method is the preferred choice worldwide.

The wet-mix sprayed concrete process uses concrete batched in a way similar to conventional concrete. This way, it is possible to check and control the w/c ratio and thus the quality at any time. The consistency of the concrete 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

Innovation: 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, users have become reluctant to apply aggressive (caustic) products. As a result, shotcrete accelerators have become dominant.

In addition, requirements for strength and durability of concrete structures are increasing. Strength loss or leaching effects believed to be caused by strongly alkaline accelerators has forced our industry to provide products with better performance.

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 in-place sprayed concrete. Of much greater consequence are the time and rebound savings achieved, the improvement of  quality, and the safe working environment provided by these new accelerators.