Adhesive

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Published on Thursday, 06 June 2024 09:52

Written by Super User

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“Hitech Tile Adhesive” is a cementitious readymix powder which is thin-bed and a highly tensile polymer modified product. Its unique properties make it ideal for fixing ceramic / vitrified tiles /mosaic tiles / natural stones like granite, marble etc., to most building substrates.

Special Properties of “Hitech Tile Adhesive”:

• Preparation is simple, just add water.
• Although cement based, requires no curing.
• It can be used in damp areas.
• Excellent tensile adhesion strength.
• Grouting is possible on the same day.
• Polymer modified formulation enhances its durability.
• Being ready to use, the product saves considerable time and labour.
• Non-hazardous.

Areas of Use:

• To fix wall and floor tiles, natural stones likes granite, marble etc.
• Cementitious screeds.
• Cement Mortar beds.
• Bathrooms and kitchens.
• Fixing the facades.
• Swimming pools.

Surface Preparation:
The surface should be clean, dry, and free from dust, grease / oil and other contaminates.
 

Concrete Floors and Walls:
Allow at least 4 weeks for concrete to cure prior to tiling. Screeds must be 5-7 days old and properly cured. The surface should be properly leveled for best results of "Hitech Tile Adhesive". Remove curing compounds, if any, from the surface.

Existing Tiles:Existing tiles must be roughened mechanically with wire brush.

Painted Surfaces:Oil-based paint should be removed by roughening mechanically and loose flaking paint should be removed completely. Allow the surface to dry after cleaning.

Fibre Cement Sheets:Fibre cement sheets must be primed with water and all joints must be taped with PVC duct tape and fixed according to the manufacturer's instructions.

Preparation of “Hitech Tile Adhesive”:

• Take a small amount of water in a bucket and gradually add "Hitech Tile Adhesive" in it. Mix the product with water in the ratio of 1:4
• Mixing can be done manually or by stirrer.
• Mixing to be done till homogenous mix is obtained.
• After proper mixing, leave the paste for 5-10 minutes for polymeric dispersion before application.
• The paste should be kept away from direct sunlight and heat, and used within 60-90 minutes of preparation (after mixing with water).

Do’s about “Hitech Tile Adhesive”:

• Before fixing the tiles, natural stones etc., clean the backsides of these with wet cloth to remove all dust particles.
• Apply a layer of adhesive on the substrate and spread it by notch trowel.
• Lay the tiles/stones and press firmly. Then knock properly with rubber hammer in order to spread the adhesive equally and for a good contact.
• Remove any surplus adhesive on the face of the tiles.
• Any adjustment should be done within 30 minutes and before adhesive starts hardening.
• Wait for at least 12 hours before grouting for better contact.

Don’ts about “Hitech Tile Adhesive”:

Avoid very high speed mixing when electric mixing equipments are used.

Coverage: 55 - 65 sq.ft per 20 Kg. bag with notch trowel for a bed of 3 - 4mm thickness.

*Please note that coverage will depend upon the undulation of base substrate and thickness of material used.

Useful Tips:

• Hitech Tile Adhesive should be stored in a dry place.
• It is recommended that when fixing tiles, a minimum spacing of 3mm should be left around each tile.
• Excess adhesive should be removed using a damp sponge or cloth before material has set.
• Floors are ready to receive light foot traffic after 24 hours and may be put into full use after 48-72 hours

* Although “Hitech Tile Adhesive” is non-hazardous, following precautions should be adhered:

• Keep out of reach of the children.
• Avoid inhalation the dust.
• In case of contact with eyes, rinse eyes with plenty of water and consult a doctor immediately.

Packaging: "Hitech Tile Adhesive"is available in 20 kg and 30kg PP bags.

Hitech-block

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Category: Uncategorised

Published on Thursday, 06 June 2024 09:50

Written by Super User

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Hitech blocks are manufactured by using proportionate blend of cement, high quality fly ash and lime . These blocks are made lightweight by adding alumina powder to the slurry made of cement –fly ash-lime - this alumina powder reacts with the slurry/paste and releases hydrogen gas and thus creates millions of tiny air cells leading to a strong cellular structure . A cake formed with this process is further strengthened by high pressure steam curing in the autoclave. Stringent quality control is ensured throughout the process .

Brought to you by the promoters of Hindustan Concrete Blocks Pvt. Ltd. a new generation, well needed, revolutionary product.

Discovery of AAC Blocks

AAC was developed in 1924 by a Swedish architect  A J Ericsson, who was looking for an alternate building material with properties similar to that of wood – good thermal insulation, solid structure and easy to work with – but without the

Comparison Between Hitech Block, Concrete Block & Clay Brick

Why AAC Block

Hitech blocks are high quality building material that combines strength, ease of use, cost effectiveness and eco-friendliness to offer the most reliable alternative to traditional construction material. Hitech block is a steam cured mix of pulverized fly-ash, cement, lime and aeration agent. The high pressure steam curing in autoclaves achieves the desired physical and chemical stability that has had average density which is 1/5th of a normal concrete block and 1/4th of a clay brick. Hitech block consists of 80% air by volume making it the lightest available walling material.

Hightech Bricks v/s Clay Bricks

Hitech-bond

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Category: Uncategorised

Published on Thursday, 06 June 2024 09:51

Written by Super User

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“Hitech Jointing Mortar” is a thin bed, high strength, pre-mixed, quality assured mortar comprising of Ordinary Portland Cement, specially graded sand and Polymers. It is specially formulated and easily applied, giving a better bonding with higher air entraining properties. “Hitech Jointing Mortar“ is a masonry mortar for use in laying various types of fly ash / concrete bricks, AAC blocks and stones. It replaces conventional jointing mortar of 12- 18 mm thickness with highly versatile 3-4 mm thickness mortar.

Special Properties of “Hitech Jointing Mortar”:

• Our Quick setting proprietary mortar essentially “glues’ the block together and the next course is ready to lay within a very short time.
• Higher bonding strenth increases durabilty and eliminates future maintenance.
• Non-metallic doesn’ trust out, will not discolor wall.
• Ready mixed mineral based products designed for new construction as well as for renovation purpose.
• Being premixed, it saves considerable time and labour and increases dimensional stability of the blocks.
• It doesn’t cause damage to eco system.
• Being pre-mixed and less porous, It inhibits efflorescence.

Areas of use:

• Laying bricks and blocks:
• To join fly ash bricks, cement block, hollow blocks, aerated block etc.
• Jointing of prestressed concrete slabs, panels.
• Jointing of cement window and door frames.
• Barbecues and fire places.
• Garden and boundary walls.
• Screed and compost bins, sand pits.
• Bench stands, bicycle stands.
• Terracing.
• Ornamental Pools.
• Repairing of masonry walls.

Surface Preparation:

• When laying new brick or block walls first construct a sound footing below the first line.
• All substrates should be cleaned and free from dust, oil, grease, curing agents, paints, which may affect adhesion.
• Wet the substrates before the application, without leaving excess water.
• When repairing mortar joints, remove all loose foreign materials.

Preparation of “Hitech Jointing Mortar”:

• Take a small amount of water in a bucket and gradually add "Hitech Jointing Mortar" in it. Mix the product with water in the ratio of 1:4.
• Mixing can be done manually or by stirrer.
• Mixing to be done till homogenous mix is obtained.
• After the proper mixing, leave the paste for 5-10 minutes for polymeric dispersion before application.
• The paste should be kept away from direct sunlight, heat, and used within 60-90 Minutes of preparation (after mixing with water.)

Application of “Hitech Jointing Mortar”:

• Layout the wall you are going to work on and mark openings like door, windows, and any architectural appurtenances, you are including in your design.
• Put a thin layer of Jointing Mortar in the thickness of 3 to 4 mm on the clean and leveled surface using proper trowel on which the block work is to be carried out. Place the block on the laid jointing mortar in proper line and level.
• After placing the first block apply the jointing mortar of the same thickness i.e 3-4mm for both horizontal and vertical joint of the block.
• Space “mortar boards” about every six feet along the wall, or on each side if the project is small.
• Brush the face of the brick with a foxtail brush to wipe away excess mortar and finish smoothing the joint.
• Continue laying the brick with 3-4 mm thickness of jointing mortar until you are leveled with the leads you laid up.

Filling the joints:

Spread the mortar across the whole surface using the rubber blade of the trowel and work thoroughly into the joints.

Brushing Off :

After approximately 10-15 minutes, the mortar should have achieved a semi-dry consistency.Don't brush this residual mortar into any unfilled joints.

Useful Tips:

• It should be kept in dry and cool place.
• Keep out of reach of children.
• Avoid inhalation of dust .
• Use proper tools while cutting bricks.
• Tools should be thoroughly cleaned in water to remove excess materials immediately after use.

Packaging:

“Hitech Jointing Mortar” is available in 40kg PP bag.

Coverage : 

125 - 140 sq.ft per 40 kg bag at 3 - 4mm thickness (100mm AAC Blocks).

* Please note that coverage will depend on the thickness and finishing of the AAC blocks used.

Process

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Category: Uncategorised

Published on Thursday, 06 June 2024 09:34

Written by Super User

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Process

Autoclaved aerated concrete is a versatile lightweight construction material and usually used as blocks. Compared with normal (ie: “dense” concrete) aircrete has a low density and excellent insulation properties.

The low density is achieved by the formation of air voids to produce a cellular structure. These voids are typically 1mm - 5mm across and give the material its characteristic appearance. Blocks typically have strengths ranging from 3-9 Nmm-2(when tested in accordance with BS EN 771-1:2000). Densities range from about 460 to 750 kg m-3; for comparison, medium density concrete blocks have a typical density range of 1350-1500 kg m-3 and dense concrete blocks a range of 2300-2500 kg m-3.

Autoclaved aerated concrete block with a sawn surface to show the cellular pore structure

Detailed view of cellular pore structure in an Aac block.

Autoclaved aerated concrete blocks are excellent thermal insulators and are typically used to form the inner leaf of a cavity wall. They are also used in the outer leaf, when they are usually rendered, and in foundations. It is possible to construct virtually an entire house from autoclaved aerated concrete, including walls, floors - using reinforced aircrete beams, ceilings and the roof. Autoclaved aerated concrete is easily cut to any required shape.

 AAC Blocks also has good acoustic properties and it is durable, with good resistance to sulfate attack and to damage by fire and frost.

Autoclaved aerated concrete is cured in an autoclave - a large pressure vessel. In aircrete production the autoclave is normally a steel tube some 3 metres in diameter and 45 metres long. Steam is fed into the autoclave at high pressure, typically reaching a pressure of 800 kPa and a temperature of 180 °C.

Autoclaved aerated concrete can be produced using a wide range of cementitous materials, commonly:

• Portland cement, lime and pulverised fuel ash (PFA)

or

• Portland cement, lime and fine silica sand. The sand is usually milled to achieve adequate fineness.

A small amount of anhydrite or gypsum is also often added.

Autoclaved aerated concrete is quite different from dense concrete (ie: “normal concrete”) in both the way it is produced and in the composition of the final product.

Dense concrete is typically a mixture of cement and water, often with slag or PFA, and fine and coarse aggregate. It gains strength as the cement hydrates, reaching 50% of its final strength after perhaps about 2 days and most of its final strength after a month.

In contrast, autoclaved aerated concrete is of much lower density than dense concrete. The chemical reactions forming the hydration products go virtually to completion during autoclaving and so when removed from the autoclave and cooled, the blocks are ready for use.

Autoclaved aerated concrete does not contain any aggregate; all the main mix components are reactive, even milled sand where it is used. The sand, inert when used in dense concrete, behaves as a pozzolan in the autoclave due to the high temperature and pressure.

The autoclaved aerated concrete production process differs slightly between individual production plants but the principles are similar. We will assume a mix that contains cement, lime and sand; these are mixed to form a slurry. Also present in the slurry is fine aluminium powder - this is added to produce the cellular structure. The density of the final block can be varied by changing the amount of aluminium powder in the mix.

The slurry is poured into moulds that resemble small railway wagons with drop-down sides. Over a period of several hours, two processes occur simultaneously:

The cement hydrates normally to produce ettringite and calcium silicate hydrates and the mix gradually stiffens to form what is termed a "green cake".

The green cake rises in the mould due to the evolution of hydrogen gas formed from the reaction between the fine aluminium particles and the alkaline liquid. These gas bubbles give the material its cellular structure.

Slurry being poured into moulds


Green cake rising in mould

There are some parallels between autoclaved aerated concrete production and bread-making. In bread, the dough contains yeast and is mixed, then left to rise as the yeast converts sugars to carbon dioxide.

The dough must have the right consistency; too hard and the bubbles of carbon dioxide cannot 'stretch' the dough to make it rise, but if the dough is too sloppy, the carbon dioxide bubbles rise to the surface and are lost and the dough collapses. With the right consistency, the dough is sufficiently elastic to stretch and expand, but strong enough to retain the gas so that the dough does not collapse. When risen, the dough is placed in the oven.

Although a much more complex process, Aircrete production conditions are precisely-controlled for, in part, somewhat similar reasons. The mix proportions and the initial mix temperature must be correct and the aluminium powder must be present in the required amount and with the appropriate reactivity an an alkaline environment. All of the materials be be of suitable fineness. A complicating factor is that the temperature of the green cake increases due to the exothermic reactions as the lime and the cement hydrate, so the reactions proceed faster.

When the cake has risen to the required height, the mould moves along a track to where the cake is cut to the required block size. Depending on the actual production process, the cake may be demoulded entirely onto a trolley before cutting, or it may be cut in the mould after the sides are removed.

Green cake being cut by wires

At the cutting stage, the blocks are still green - only a few hours has passed since the mix was poured into the mould and they are soft and easily damaged. However, if they are too soft, the cut blocks may either fall apart or stick together; if they are too hard, the wires will not cut them - here too, the process has to be carefully controlled to achieve the necessary consistency.

The cut blocks are then loaded into the autoclave. It takes a couple of hours for the autoclave to reach maximum temperature and pressure, which is held for perhaps 8-10 hours, or longer for high density/high strength aircrete.

"Green" blocks being loaded into an autoclave

When removed from the autoclave and cooled, the blocks have achieved their full strength and are packed ready for transport.

The essence of aircrete production is that lime from the cement and lime in the mix reacts with silica to form 1.1 nm tobermorite.

NB: Cement chemistry notation is used below. If you are not familiar with this, see ourcement chemistry notation explainedpage.

During the green stage, the cement is hydrating at normal temperatures and the hydration products are initially similar to those in dense concrete - C-S-H, CH and ettringite and/or monosulfate. After autoclaving, tobermorite is normally the principal final reaction product due to the high temperature and pressure.

Small amounts of other hydrated phases will also be present in the final product. Additionally, hydrated phases form in the autoclave as intermediate products, principally C-S-H(I). This is a more crystalline form of calcium silicate hydrate than occurs in dense concrete; it can have a ratio of calcium to silicon of (0.8<Ca/Si<1.5) but 0.8 to 1.0 is desirable as this ratio facilitates the formation of 1.1 nm tobermorite.

The compositions of the hydration products in aircrete are therefore quite different from those in dense concrete cured at normal temperatures (ie: calcium silicate hydrate (C-S-H), calcium hydroxide (CH), ettringite and monosulfate. See the “hydration” page for more information).

Looking at this in a little more detail from when the green blocks enter the autoclave, the main reactions that occur are broadly as follows:

• Over 2 hours or so, as the pressure and temperature increase, the normal cement hydration products that formed in the green state progressively disappear and the sand becomes reactive.
• C-S-H(I) forms, partly from silica derived from the sand.
• As more sand reacts, calcium hydroxide from the lime and from cement hydration is gradually used up by continued formation of C-S-H(I).
• With continued autoclaving, 1.1 nm tobermorite starts to crystallize from the C-S-H(I); the total proportion of C-S-H(I) declines and that of 1.1 nm tobermorite gradually increases. C-S-H(I) is therefore mainly an intermediate compound.

The final hydration products are then principally:

• 1.1nm tobermorite
• Possibly some residual C-S-H(I)
• Hydrogarnet

 
Unreacted sand is likely to remain in the final product. There may also be some residual calcium hydroxide if insufficient silica has reacted and some residual anhydrite and/or hydroxyl-ellestadite if anhdrite was present in the mix.

SEM image of polished section showing a detail - a cell wall - of a block made with cement, lime and sand mix. Some residual unreacted sand particles remain (examples arrowed), often with rims of hydration product showing the size of the original particle. Most of the matrix is composed of tobermorite. Black areas at top left and bottom right are epoxy resin used in preparing the polished section filling air voids (air cells).


The objective is to react sufficient silica from the sand to form tobermorite from the available lime supplied by the lime and cement. This will depend on a range of factors, including the inherent reactivities of the materials, their fineness (especially the sand),  and the temperature and pressure. If the autoclaving time is too short, the tobermorite content will not be maximised and some unreacted calcium hydroxide will remain and block strengths will be then less than optimum. If the autoclaving time is too long, other hydration products may form which may also be detrimental to strength and an unnecessary energy cost will be incurred.

There are different forms of tobermorite: 1.1 nm tobermorite and 1.4 nm tobermorite. Also, there are different types of 1.1 nm tobermorite and these behave differently when heated. Their crystal structure is that of layered sheets, with water molecules between the layers - on heating, the inter-layer water is lost; as a result, some 1.1 nm tobermorites shrink (a process known as lattice shrinkage) but some don’t.

1.4 nm tobermorite (C₅S₆H₉) - forms at room temperature and is found as a natural mineral. It decomposes at 55 °C to 1.1 nm tobermorite, and so is not found in AAC.

Calcium silicate hydrate compositions in AAC

• 1.1 nm tobermorite (C₅S₆H₅) is usually the main hydration product in AAC where cement, lime and sand are used
• C-S-H(I) - more crystalline than C-S-H in dense concrete, typically 0.8<Ca/Si<1.0.
• Xonotlite (C₆S₆H) - forms with longer autoclaving times, or higher temperatures

 'Normal'tobermorite shows lattice shrinkage, while non-shrinking tobermorite is called 'anomalous' tobermorite. Tobermorite in AAC made with cement, lime and sand is usually normal tobermorite. Tobermorite in autoclaved aerated concrete made with cement, lime and PFA is usually anomalous tobermorite. Aluminium and alkali together in solution (such as will be present in mixes of cement, lime and PFA) tend to produce anomalous tobermorite, with some aluminium and alkali taken up into the tobermorite crystal structure. The differences between the different forms of autoclaved calcium silicate hydrates are not well-defined; in an AAC block, intimately-mixed hydrates of different compositions and crystallinity are likely to occur.

The use of autoclaved aerated concrete has a range of environmental benefits:

• Insulation: most obviously, the insulation properties of aircrete will reduce the heating costs of buildings constructed with autoclaved aerated concrete, with consequent fuel savings over the lifetime of the building.
• Materials: lime is one of the principal mix components and requires less energy to produce than Portland cement, which is fired at higher temperatures. Sand requires only milling before use, not heating, and PFA is a by-product from electricity generation. NB: lime may require less energy to manufacture compared with Portland cement but more CO2is produced per tonne (cement approx. 800-900 kg CO2/tonne compared to lime at 1000 kg CO2per tonne).
• Carbonation: less obviously, the cellular structure of aircrete gives it a very high surface area. Over time, much of the material is likely to carbonate, largely offsetting the carbon dioxide produced in the manufacture of the lime and cement due to the calcining of limestone.