VP, Head CDIC & Product Development
Sr. Manager, Research and Development
The aggressive focus on infrastructural development in India, along with the country’s massive population, has revived the need for vertical construction, as the most effective utilisation of space. An efficient strength-to-weight ratio of the concrete used is a major factor in defining the design of high-rise concrete structures such as these. Owing to the widespread use of conventional concrete in such projects, the efficiency of the structural design is almost entirely dependent on concrete mixtures of high strength, while the weight of the concrete has been considered a constant. However, a significant part of the dead load that such structures have to bear is a result of conventional grade concrete, used widely and commonly in the sector.
Serving as an excellent alternative to this, structural Light Weight Concrete (LWC) is a specialised and technologically advanced product that is increasingly gaining in popularity in the Ready-Mix-Concrete (RMC) and construction industry today. LWC is comparable to regular concrete, offering high strength and a density of 1000 – 1800 Kg/m3, while being much lighter. Developed using various low-density aggregates like expanded or sintered clays, shale, slates, fly ash, pumice, and scoria, and a specific concrete mix design, LWC offers high building design flexibility, and economical benefit. As a result, it possesses immense potential for use in the construction of high-rise vertical structures and adding storey / floors to existing buildings.
Objective of Study
In order to leverage this underutilized potential for load reduction, design flexibility, and economical value generation, a research paper was presented by Nuvoco Vistas Corp. Ltd. at The University of Dundee, Scotland, which offers a comparative study of LWC. The paper aimed to provide a detailed analysis of the freshness, mechanical, and durability properties of structural grade LWC, compared to those of M25 grade normal concrete. The results of the study will offer a building design comparison of normal and Light Weight Concrete structures, to derive a value engineering proposal for using the two kinds of concrete in their construction.
The research aimed at studying the role of ECA proportioning in a triple binder blended mix of cement, fly ash and silica fume at a constant water binder ratio. The plastic, hardened, and durability properties of Light Weight Concrete were evaluated, in comparison to M25 grade normal concrete. It also studied the load reduction and value engineering benefits of using LWC, conforming to M25 grade concrete, for the slab design of high-rise structures with anywhere between 5 to 65 floors. Normal weight single sized 10mm and 20mm crushed stone sand (CSS), confirming to IS 383, was used, along with expanded clay aggregate, in a statured surface dry condition. Additionally, a sulphonated naphthalene formaldehyde (SNF) or polycarbxylate ether (PCE) based water reducing super plasticising admixture, was also used, along with set retarding admixture and air entraining admixture, all of which complied with IS 9103, and were completely chloride-free.
Findings of the study
The results of the tests found that the compressive strength, flexural strength, split tensile strength, and static MOE offered by ECA based LWC increases with an increase in density or reduced ECA proportion at the same binder content and constant water binder ratio, it was observed that M25 Grade LWC could be designed at 1800 kg/m3 density, that is 28% lighter than regular concrete. On the other hand, chloride ion penetration, water absorption under submersion, water absorption under low pressure, and capillary water absorption was observed to be considerably lower than regular M25 grade concrete.
Benefits offered by LWC
As such, structural LWC, such as XLite-Structural by Nuvoco, offers a wide range of benefits over regular concrete, by reducing the concrete density by 25%-50%, while offering a compressive strength of 8 Mpa to 25 Mpa, with its other properties being at par with regular concrete. As a result, it helps reduce the dead load on buildings and structures significantly, requiring lesser amount of concrete and steel, and reduced foundation, while offering enhanced design flexibility. This inherently allows for a longer span, increased width, reduced sub structure, and better thermal and acoustic efficiency, besides also incurring lesser transportation cost in the case of pre cast concrete being used for the project.
In addition to this, owing to the ceramic nature of the aggregate and its excellent bond and elastic compatibility with the cementations matrix, structural LWC manufactured using expanded shale, clay, or slate, offers remarkable durability and performance. It is also usable as a high-performance concrete (HPC), and allows for better internal curing through porous nature, because of its cellular structure, which helps improve the contact zone and prevent micro cracking. Furthermore, it offers high elastic compatibility and better shock absorption, making it excellent for withstanding the test of time.
Applicability in the construction industry
Owing to the host of advantages that LWC has over regular concrete, it can be used for countless projects with demanding criteria, such as in the top floors of high rise construction, steel structures, marine structures, long span bridges, screeds, and more. As a matter of fact, the low density, longevity, durability, and freeze and thaw resistance that it offers, led to it being used for the construction of ships during the first and second World Wars. The reason for this was that ships built using reinforced Lightweight Concrete incurred considerably lower maintenance costs, and had a much longer life expectancy than those constructed using steel.
LWC is also an excellent component for adding extra floors on top of existing structures, as it does not require the modification of the foundation to enable it to carry the extra dead load. Along with this, it also prevents microcracking, and offers lower autogenous shrinkage, enhanced freezing and thawing durability, and improved contact zone between aggregate and cement matrix, thereby reducing repair and maintenance costs significantly, for developers and homeowners. Owing to its high acoustic and thermal resistance, it is also perfect for the construction of residential buildings or hotels. Not only does this enhance the experience of the residents, it also requires lesser soundproofing and air conditioning, which in turn, leads to a more sustainable future for the construction industry as a whole.