As “Materials Monday” draws to an end, we would like to share our thoughts on why we chose to start such a series on materials. Materials form the basis of everything around us, in general, and even more so in the civil engineering universe. So we thought that the vast abundance of materials around us ought to be revered and hence sharing their amazing properties on a public forum seemed the apt justice to their significance in our lives. We collected the information on these materials from the internet and it was exclusively done for just sharing knowledge.The prime focus was to bring those materials into spotlight which are not conventionally used but have a great deal of potential in terms of utility, sustainability and changing the current scenario of construction. The materials we covered in our posts include Self Healing Concrete, LC3 ( limestone, calcined clay, clinker cement ), RPC ( Reactive Powder Cement ), Aircrete, Geopolymer cement, TMT Bars, Polycarbonate and SIP ( Structural Insulated Panel ). Each of these materials has a unique property which will leave you spell-bound and this blog is a mouth-watering feast for those who missed some of our MM posts !!
“Bacillus” ever heard that name? A bacteria that thrives in alkaline condition and produces spores that can survive for decades without food or oxygen. A perfect resident for concrete, it remains dormant unless activated by water. What if we somehow got these bacteria to produce limestone? This is achieved by setting the bacteria and calcium lactate into capsules made from biodegradable plastic and adding the capsules to the wet concrete mix. When cracks eventually begin to form in the concrete, water enters and opens the capsules.The bacteria then germinate, multiply and feed on the lactate, and in doing so they combine the calcium with carbonate ions to form calcite or limestone, which closes the cracks!
A perfect blend of natural and construction material, the self healing concrete (SHC) can change the face of concrete healing and repair. With lot of development and research awaiting, SHC is really a nice example of tying nature and the built environments together in one new concept.
LC3 Features :
At high strength, the coarse aggregate becomes the weakest link in concrete, so why not eliminate the coarse aggregates? RPC is the solution! It involves optimization of the the microstructure by precise gradation of all particles in the mix to yield maximum density. Characterized by high silica fume content and very low water to cement ratio, RPC can develop compressive strengths ranging from 200 MPa to 800 MPa. So it can even replace steel in some cases!
Apart from fine powders (cement, sand, quartz powder and silica fume) and superplasticizer, Steel fibres are added to increase the flexural strength upto 150 Mpa. RPC has ultra-high durability characteristics resulting from its extremely low porosity, low permeability, limited shrinkage and increased corrosion resistance. It could, therefore, be a suitable choice for industrial and nuclear waste storage facilities.
Do you think a building is built by considering the human loads as a major factor? Then you are wrong. The human loads are negligible when compared with the self weight of the building.To bear this self weight, one has to design stronger columns with stronger materials and big dimensions. What if we reduce the self weight by replacing traditional heavy bricks with lighter bricks of same strength? The solution is the Autoclaved Aerated Concrete (AAC) or commonly called Aircrete!
With density as light as 400 to 500 kg/m^3, AAC is produced using no aggregate larger than sand. Quartz sand, calcined gypsum, lime (mineral) and cement and water are used. Aluminium powder is used at a rate of 0.05%–0.08% by volume (depending on the pre-specified density) to produce tiny air bubbles which act as fine particles with no weight! Remember that these bubbles of air are not interconnected but scattered, thus in a way reducing the permeability. Due to air voids, AAC also acts a great insulating material and is fire resistant.
Geopolymer cement is an innovative material and a real alternative to conventional Portland cement for use in construction. It relies on minimally processed natural materials or industrial byproducts to significantly reduce carbon footprint by 70%. The main constituent of geopolymers source of silicon and aluminium which are provided by thermally activated natural materials (e.g. kaolinite) or industrial byproducts (e.g. fly ash or slab) and an alkaline activating solution which polymerizes these materials into molecular chains and networks to create hardened binder. It is also called as alkali-activated cement or inorganic polymer cement.
Advantages of GPC :
Thermo-mechanical processing, also known as thermo-mechanical treatment (TMT), is a metallurgical process that integrates work hardening and heat-treatment into a single process. The quenching process produces a high strength bar from inexpensive low carbon steel. The process quenches the surface layer of the bar, which pressurizes and deforms the crystal structure of intermediate layers, and simultaneously begins to temper the quenched layers using the heat from the bar's core.
These bars therefore exhibit a variation in microstructure in their cross section, having strong, tough, tempered martensite in the surface layer of the bar, an intermediate layer of martensite and bainite, and a refined, tough and ductile ferrite and pearlite core. When the cut ends of TMT bars are etched in Nital (a mixture of nitric acid and methanol), three distinct rings appear: 1. A tempered outer ring of martensite, 2. A semi-tempered middle ring of martensite and bainite, and 3. a mild circular core of bainite, ferrite and pearlite. This is the desired micro structure for quality construction rebar.
In contrast, lower grades of rebar are twisted when cold, work hardening them to increase their strength. However, after thermo mechanical treatment (TMT), bars do not need more work hardening. As there is no twisting during TMT, no torsional stress occurs, and so torsional stress cannot form surface defects in TMT bars. Therefore TMT bars resist corrosion better than cold, twisted and deformed (CTD) bars.
Polycarbonates (PCs) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. It’s a very tough plastic that boasts being bulletproof yet it is a lightweight material that’s easy to size and handle. It is the ideal choice as a roofing material being lightweight yet extremely durable and it lets in the same amount of natural light as glass does without having the same fragility.
Structural insulated panel (or structural insulating panel), SIP, is a composite building material. They consist of an insulating layer of rigid core sandwiched between two layers of structural board. The board can be sheet metal, plywood, cement, magnesium oxide board(MgO) or oriented strand board (OSB) and the core either expanded polystyrene foam (EPS), extruded polystyrene foam (XPS),polyisocyanurate foam, polyurethane foam or composite honeycomb (HSC).
The rigid insulation core of the SIP acts as a web, while the sheathing fulfills the function of the flanges. SIPs combine several components of conventional building, such as studs and joists, insulation, vapor barrier and air barrier.
SIPs are manufactured under factory controlled conditions and can be fabricated to fit nearly any building design. The result is a building system that is extremely strong, energy efficient and cost effective. Building with SIPs save time, money and labor. By some estimates, SIPs save 50 percent in energy costs over houses built from conventional materials meaning less fossil fuel consumptions and fewer greenhouse gas emissions. Smaller heating and cooling systems are required with SIP construction. The material is fire resistant, and it can be used for foundations, floors, basements and load-bearing walls.
Content By: Aditya Jhunjhunwala
Designed By: Aaditya Taparia
Blog formatting By: Shantanu Singh Chauhan
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