Sobha Limited, established in 1995 and headquartered in Bangalore, has by now executed over 360 construction projects. The company is today one of the leading and fastest growing building contractors in India and is also a manufacturer of construction products. The company is now setting up its own precast concrete element production, which signifies the next milestone in its history.
The recent Sobha Dream Acres housing project in Balagere, near Bangalore, is the first construction project implemented in the country completely as precast construction.
“At the beginning of the project, the advanced construction technology involved was a challenge for us. The significant knowhow from the company Vollert, as knowledge and technology supplier, however, helped us to take this step,” declared Ravi Menon, Chairman of Sobha Limited. “We advise our customers on current construction systems and technology standards and develop in close dialog with them the suitable turnkey system solution for advanced precast element production,” explains Steffen Schmitt, Executive Sales Director Asia at Vollert.
Stationary formwork technology from Nuspl
Up to 400,000 m² large-area wall and floor elements with many different precast element geometries and dimensions will in future be annually manufactured in the Sobha precast plant in Bangalore. In addition, complex special elements, precast stairs, façade elements, and structural reinforced-concrete members such as columns and beams have been manufactured in Bangalore since July of 2015.
To enable a production process with very high cycle times, these special elements are manufactured using stationary formwork technology from the formwork technologist Nuspl. “With Nuspl, part of the Vollert Group since 2012, we offer our customers cutting-edge production proc-esses for large-area and structural precast elements. We plan the complete plant engineering in a single step. At Sobha, for example, using 3D simulation, we have developed an optimal spatial solution for stationary formwork technology and a state-of-the-art circulation system for solid walls,” adds Steffen Schmitt.
German engineering and state-of-the-art technology
The degree of automation in precast element production in the new Sobha plant in Bangalore was optimally adjusted to the basic constraints encountered in India. Special attention was paid to machine technology – from concrete placement to logistic shipping procedures. A CADCAM-controlled, large-scale Smart Plot large-scale plotter draws the contours 1:1 onto the formwork surface with water-soluble markings at a scale of 1:1 and with a precision of ± 1 mm. The automatic operation and the speeds of the plotter of up to 5 m/s notably streamline the production processes.
The concrete is cast by a gantry-guided Smart Cast concrete distributor. A pneumatic screw-discharge unit assures precise concrete batching and can be infinitely adjusted for various concrete consistencies. A rotating distribution roller prevents formation of dump cones and ensures optimal concrete flow up to the point of discharge. The concrete is supplied by a state-of-the-art concrete mixer plant with Liebherr technology. Concrete compaction takes place in a low-frequency, low-noise Smart Compact2 vibration station by eccentric drives. By lowering the water-cement ratio, the cement content can be markedly reduced, resulting in the same early strength of concrete.
Screeding lines for architectural concrete
Special screeding lines ensure high-quality architectural concrete. A rotary trowel moves in longitudinal and lateral directions and smooths the surfaces of the solid-concrete walls by an electrically driven finishing head with adjustable blades and adjustable speeds of rotation. Subsequent curing of the concrete elements takes place in an insulated Vario Cure curing chamber, which consists of three coated rack towers, each with nine pallet compartments. In- and outstorage takes place by a floor-operated state-of-the-art Vario Store rack serving unit. For an annual output of up to 400,000 m² precast elements, both high-efficiency lifting and loading technologies in the storage yard were of equal importance. A high-performance tilting station with a maximum tilting angle of 80 ° performs vertical lifting of the solid-concrete elements.
A CADCAM-based, software-supported control system continuously regulates the individual processes in the entire plant structure for activating the automated machine systems and for centrally supervising and visually monitoring all in- and outstorage and transport proc-esses. The 33 positioning pallets move in closed circulation from work station to work station. “In this way, we achieve concise, reliable processes.
Stationary formwork systems for special elements
In addition to walls and floor slabs, Sobha will in future offer complete solutions for advanced residential and industrial construction: with techniques that substantially shorten construction time and simplify final assembly and erection work. The Variostep precast stair formwork systems produces stairs standing on the stringer side – which assures architectural-concrete quality on three sides. Any desired combination of stair slope and tread can be variably adjusted for up to ten stair steps. Step widths of up to 1,640 mm are possible.
The innovative construction system developed by Sobha for the Indian market also uses solid-concrete components with wall overhang to provide solar shading. These special elements are manufactured in various geometrical forms on several stationary Nuspl formwork tables. The surface consists of plane-ground sheet steel, 8 mm thick, for top-quality architectural-concrete surfaces: which also maximizes long-term stability. The formwork system was exactly designed to meet the requirements of the construction system, and fixed high-frequency vibrators ensure dense concrete compaction. The additionally planned solid walls in L-form were made possible by Nuspl engineers by using special L-shaped formwork with variably adjustable side walls and adapters. In addition, Sobha invested in advanced formwork systems for production of concrete columns and binding agents.
A milestone for the construction industry in India
Raj Pillai, Executive Director of Sobha Limited, summarized: “With our new precast concrete plant in Bangalore, where we have manufactured solid-concrete components and special structural elements for our construction products since July of 2015, we have set a real milestone for India with respect to construction-component quality and production-plant productivity.” He continued: “Construction with precast concrete elements, as an intelligent combination of optimally applied raw material and highly intelligent plant engineering technology will reduce construction costs in India by 10 to 15 %.”