The rising emphasis on sustainable construction strategies has seen the entry of several new innovative technologies and solutions in recent times. In fact the Green Building movement has meant that today there is a multibillion dollar market exclusively for green products. With the construction industry booming over the last three decades in India and growing at a phenomenal rate, it is no surprising to find India now becoming a key global market for the latest sustainable construction technologies, solutions and products. Perhaps the most prominent technology that has gained enormous popularity in recent times is Autoclaved Aerated Concrete (AAC). The advent of AAC blocks with their unbeatable combination of superior thermal insulation properties, light weight, and importantly cost effectiveness has meant today they are offering stiff competition to red clay bricks.
Contrary to popular perception AAC is not a recent phenomenon. In fact the material was developed way back in 1924 in Sweden. It has now become one of the most used building materials in Europe and is rapidly growing in many other countries globally. AAC offers incredible opportunities to increase building quality and at the same time reduces costs at the construction site. AAC is produced out of a mix of quartz sand or pulverized fly ash, lime, cement, gypsum, water and aluminium and is hardened by steam cured in autoclaves. AAC contains 60%-80% air by volume. The silicium dioxide is obtained from silica sand, fly ash or crushed quartzite. It is possible to obtain silicium dioxide as a byproduct from other processes. The calcium oxide is obtained from quick lime, hydrated lime and cement. Gypsum is added in small quantities as a catalyst and for optimizing the properties of AAC. Aluminium powder/paste is used as an expanding agent.
In India with rising awareness levels about the numerous benefits offered by AAC blocks now the technology is gradually finding an increasing number of takers in the real estate sector, as well as in infrastructure development projects. Here I would like mention one point very clearly that AAC and CLC (Cellular Lightweight Concrete) are totally different. Lot of people are confused on this topic, with some sales persons knowingly or unknowingly spreading such wrong information. The quest for a greener and sustainable society with environment-friendly construction is the necessity of the future. Use of right products which supports the green initiatives offering thermal insulation , sound insulation, high dimensional accuracy, fire & termite resistance are few of the properties that we are looking at.
Apart from the above the main advantage for a country like India is in the form of disposing ash and optimum utilization of industrial by-products. Instead of dumping the ash for land filling or to ponds, the same could be used for the production of construction materials, in this case AAC blocks. Construction is the back bone of any economy, whether it is industrial, infrastructural, residential or commercial. At the same time pollution has become a major concern globally. Leading organizations like the UN, IMF and all the member countries have started the initiative long back to control pollution for a better future. We have recently seen how the pollution situation has got worse in cities like Shanghai and Delhi with foreign governments even instructing their missions to take preventive safety measures. Most of the leading countries are taking serious efforts on the issue and it is time that a country like India, which is now one of the most prominent emerging economies, should also be taking a leading position in such initiatives.
For a vast country like India mainly depending n coal based thermal power plants for electricity, the majority of coal is imported. Eastern and Central India is a rich source of natural resources like coal and we still import partially from Australia or Indonesia. After generating power the coal is converted into ash, which then becomes a major factor for air as well as water pollution. A part of the top ash is consumed by cement and ready mix industries and the majority bottom pond ash is used for land filling. This ash pollutes the air and the land filling, apart from contaminating the water bodies. The next generation will suffer due to our negligence, if proper steps are not taken to deal with the situation. There are several options available for the disposal of ash as motioned above, but still the major chunk of the ash is available. Hess Group, which is part of Top Werk, a globally renowned technology solution provider, offers the best solution for the proper disposal of total ash.
Hess is a German company with 65 years of rich experience in construction and related machines able to offer a completely automated and proven technology, which requires no manual interference or transportation. Hess systems are already playing a key role with major players like Jindal, KJS Ahluwalia, Ultratech, UAL and JK Lakshmi Cements. Depending on several factors Hess could advise the right solutions to suit each customer and implement the same within the stipulated time schedule. This could be for the production of AAC blocks or panels as well as fly ash bricks and concrete products. While we are particularly talking about AAC blocks in this feature, let me explain how the Hess AAC system differs from others in the market and the advantage of this proven technology.
Raw material preparation and mixing
The fly ash or grinded pond ash or silica sand is mixed with water to form a slurry which in stored in a tank. The mix is then pumped into weighing hopper in the mixer tower. The binders are stored in silos mixing them with aluminium to make the proper mix.
Casting, rising/pre-curing and mould circulation
The mould consists of four fixed sides and one detachable platform. The inner mould surfaces are covered with demoulding release oil before casting. This oil is applied either manually or automatically. The mix is then poured into the moulds. A mould circulation system conveys the moulds into the rising area, where the cake pre-cures for 2-3 hours after which it is ready for cutting. Depending on the plant design the moulds are handled by a mould traverse or by a tilting manipulator. All the components are accurately weighed and are released into the mixer in a predefined order. The Hess recipe and temperature control system constantly monitors this process.
Hess systems are also ideal for the production of large format reinforcement panels. Depending on the required capacity the reinforcement cages are outsourced or welded on site. The cages are then assembled as per mould and hung into holding frames with cross bars and needles. A corrosion protection coating is then applied. Immediate after the mix has been poured into the mould, the waiting reinforcement frame assembly is inserted. Before cutting of the cake, the holding frames with needles are lifted, leaving the reinforcement in the cake.
The tilting manipulator tilts the mould by 90 degree. The manipulator unlocks the mould and removes the mould body, so that the cake remains on one mould side/platform for cutting. This tilting system has proven to be the safest method for tilting the cake into the vertical cutting position, as the cake remains on the platform/mould side for the cutting process.
The cake is cut by high precision, cutting machines with pneumatically tensioned cutting wires. The pre-cutter and vertical cutter cut the block length and panel width. In this station the profiling can be cut into the cake with profiling knives. The horizontal cutter cuts the block and panel thickness. The cross cutter cuts the block height and the panel length. Optionally hand grips can be milled in the blocks in the green stage.
Back-tilting and bed removal
Hess plants have combined the advantages of the tilt-cake and flat-cake system. After the cutting is completed, the cake is tilted back by 90 degrees into a cooking frame. In the Hess system no part of the mould or platform used for cutting goes into the autoclaves. After the cake has been titled back into the horizontal orientation, the bottom /bed waste will be removed before autoclaving. The process of autoclaving the cake horizontally on the cooking frames allows efficient autoclaved loading and most importantly will prevent most of the sticking of the layers, which is a typical disadvantages with traditional tilt-cake systems.
No process related waste
One of the key Hess innovations is the ‘green separator’. Here the horizontal cuts are carefully separated before autoclaving leaving a small gap between the layers. This innovation eliminates any sticking which is typical for other tilt-cake systems. Further this green separation substantially improves the autoclaving process as steam can penetrate into the cake more effectively.
Frame and bogey circulation
The green cakes on the cooking frame are stacked high into the autoclaving cars, referred to as ‘bogeys’. Autoclave buffer tracks in front of the autoclaves ensure that the cutting and packaging processes are less dependent on one another. An autoclave traverser is used for loading and unloading the autoclaves ensuring that this process is performed in the shortest possible time in order to optimize autoclaving capacity.
In the autoclaves the cakes are cured for 10-12 hours at a temperature of 190 degrees with saturated steam at a pressure of 12 bar. The fully automatic autoclave control system ensures a safe and optimal autoclaving process also allowing for steam transfer and energy reuse in combination with the condensate system.
Unloading and packing
After the autoclaving is completed the cakes are destacked and unloaded from the cooking frames. Hess offers a large variety of packaging solutions ensuring that the finished products are packed according to local market requirements. Usually blocks will be delivered as packs on wooden pallets strapped and transported.
Process control and plant automation
The entire production process is controlled by modern automation systems designed by Hess on the basis of Siemens S7 control system using standard components that are available globally. User-friendly, multilingual operator interfaces with touch screen monitors allow easy and understandable operation. Hess remote diagnostic system allows for the possibility of online support.
For further details:
Hess Concrete Machinery India Pvt Ltd
54 Bommasandra Jigani Link Road,
Bommasandra Industrial Estate – Phase IV,
Bangalore – 560 105