23 October 2019

Guest Article-K Senou, Head Precast Initiatives, Larsen & Toubro

Challenging the status quo in housing construction

Inflationary trends of the Indian economy have increased the cost of construction materials, hire charges of plant and machinery, wages of staff and labourers to such an extent that many developers are finding it difficult to venture into the affordable and mass housing category explains K.SENOU, HEAD-PRECAST INITIATIVES, LARSEN & TOUBRO LTD.
 

 

In general, carpet areas of EWS and LIG category houses vary from 30 to 60 Sqm but due to an increase in wall to slab ratios, the rate/sq ft has substantially increased. On the other hand, the availability of skilled labour is on the decline while the percentage of the unskilled labour force has been steadily rising since 2005. The Government of India’s initiative to build about 2 crore ‘economic’ housing units for the poor and for those living under the EWS and LIG categories in the country’s urban establishments, over the next seven years, challenges the status quo of technology providers. This scenario is similar to those faced by many developed countries during their transition phase. Many European countries like Denmark, Germany, Finland, South East Asian countries like Singapore, Malaysia, Thailand, and countries in the Middle East like Dubai, Abu Dhabi, Saudi Arabia have resorted to the precast shear wall concept to meet their housing needs.

 

Precast shear wall concept is a manufacturing method wherein the entire housing unit is produced in a factory with labour dependency based on the degree of automation. In this method, a 160mm thick precast concrete wall can replace a 230mm brick wall creating more carpet area or decreasing built up area by about 3-5 per cent that translates into cost savings. Since this technology eliminates the need for block work and plastering, it reduces the dependency on natural sand and skilled manpower. Concrete precast walls require zero maintenance post construction when compared to the conventional methods of construction and problems like spalling of roof plaster, efflorescence, cracks on walls, etc. can be avoided. Extensive use of Plant and Machinery and the elimination of second stage work reduce construction duration by about 25-35 per cent. Quick conversion of land parcels into tenements promises assured return, healthy cash flows and protects the developer from escalations and increase in cost of capital on investments (Land). For the end user, timely possession of the housing units helps him/her to start the EMIs and avail tax benefits.

 

Some of the major challenges this technology faces are Excise duty, Octroi (in cities like Mumbai) and Transportation charges from the central plant to the project site that significantly increases the cost of precast elements.

 

Residential building construction is an evolving process meant to accommodate the aspirations of the end users. Hence it is imperative to study this technology from the end user’s perspective before putting into practice who is primarily seeking flexibility, low maintenance, optimal comfort, fair resale value and functional size which is why well established building materials that ensure durability of the buildings with nominal maintenance are widely preferred. Precast Technology that uses concrete as a primary building component fits perfectly with these requirements. This has led to considerable investments in Research and Development and several leading premier institutes have been roped in to continuously evolve various options suitable for all geographic regions in India. Building structures using precast technology conform to NBC/IS codes as applicable to ensure structural stability, durability (more than 50 years), safety, and adequate acoustic & thermal performance.

 

The structural integrity of slab-wall building system with PLCP depends on the performance of vertical and horizontal joints of walls. To ensure the integrity of the structure in seismic zones, the joints have to be designed and validated for construction. Structural Engineering Research Centre (SERC), Chennai carry out quasi-static reverse cyclic load tests on prototype structures to validate the seismic performance of horizontal connections of PLCP wall systems.

 

The highlights of Precast technology are as follows:

  • Precast components are produced in a factory under controlled environment thus ensuring quality. Since 50 per cent of the construction activity is happening at ground level, both labour productivity and safety increase multi fold.
  • Speed and quality of construction is dependent on the number of construction activities. Precast eliminates plastering, blockwork, chasing works for electrical conduit fixing and surface preparation for finishing works by as much as 35 per cent and thereby reduces material and skill requirement in these trades; in fact, labor requirement is reduced by almost 30 per cent.
  • It contributes to sustainable development by predominantly using manufactured sand and reduces the carbon footprint thanks to factory-based production resulting in pollution-free construction as compared to conventional methods of construction.
  • It is well suited for seismic zones due to its inherent redundancy in the structural system.
  • It can produce 5 floors per month as against 2 per month by conventional methods.
  • The role of Design Coordinators and Project Management Consultants is minimal in Design and Build precast construction, thereby saving in overhead spends.

 

 

L&T and precast technology

The Precast Concrete technology adopted by L&T uses the Precast Large Concrete Panel (PLCP) system for residential buildings. The Precast Panels are produced in a factory controlled environment that ensures superior quality control and eliminates the time consuming second stage site activities such as block-work and plastering seen in the traditional Column, Beam and slab precast system. This improves productivity as well as quality of the construction work. The emulative design philosophy adopted by L&T ensures adequate structural performance in terms of strength and serviceability. The precise structural detailing ensures that the requisite ductility and toughness are achieved in response to lateral seismic and wind loads as per the prevailing building codes. All building components such as walls, slabs, columns, beams and stairs are factory produced and assembled at site using on-site emulative connections that perform equivalent to conventional RCC Shear wall buildings

 

L&T offers Design-and-Build in residential building construction using the state-of-the-art Precast Large Concrete Panel technology. The L&T advantage is single point responsibility from concept to commissioning with commitment to Ownership, Responsibility and Accountability for construction thus ensuring timely completion with efficient coordination of various activities through the design and construction phase of a project. As a pioneer in precast concrete construction, L&T took the lead by putting up a hollow core slab factory in Khopoli, near Mumbai for commercial buildings and established a dedicated site based plant. Six 23-floor towers with 2084 flats were handed over in Mumbai. The uniqueness of this project was the prefabrication of 4048 toilet pods ensuring maintenance free toilet and bath units. Another 1440 flats have been handed over to a private builder in Bengaluru with another 4512 flats under construction.

 

L&T is in the process of setting up a precast production facility to produce 4830 housing units in Chennai for the same developer. In sync with the spirit of the Make in India initiative, all the requisite production equipment has been indigenously developed. In essence, the value propositions offered by Precast technology are an increase in carpet area, faster construction, insignificant second stage works, minimal wastage and ready to receive surface for finishing materials with superior quality and safety.




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