Bamboo Reinforced Structures A Positive Green Option

Introduction

Bamboo is gaining worldwide interest as an eco-friendly material, and thus there is developing interest towards bamboo building technology based on recognized engineering principles. Bamboo construction has always been considered temporary and not surprisingly bamboo is replaced almost every year in many of the rural buildings.

Bamboo building techniques as they currently exist are mostly traditional in nature and based on knowledge gained over the years. In India, numerous studies have been carried out relating to the preservation of bamboo with a goal of enhancing its service life and understanding the mechanical properties of bamboo in order to assist engineers in selecting and designing. Factors such as its high strength to weight ratio, ease of construction, and particularly its rapid growth make it a green and sustainable building material.

In the modern context when forest cover is fast depleting and availability of wood is increasingly becoming scarce, the research and development undertaken in past few decades have established and amply demonstrated that bamboo could be a viable substitute of wood and several other traditional materials for housing and building construction sector and several infrastructure works. Its use through industrial processing have shown a high potential for production of composite materials and components which are cost-effective and can be successfully utilized for structural and non-structural applications in construction of housing and buildings.

In India, although bamboo is widely used in some regions, it must be emphasized that its use has been secondary as a semi load bearing element or as infill material in timber framed houses. It is in this context that the bamboo housing technology developed at IPIRTI is of greater significance.

The IPIRTI–TRADA Bamboo Housing system differs significantly from conventional bamboo constr- uction practices in many ways viz.–

(a) Use of round bamboo as columns, rafters and trusses as main load bearing element,

(b) Use of split bamboo grids/chicken mesh and plastered with cement mortar to act as shear walls for transmitting wind loads and to provide overall stability to the structure,

(c) Application of appropriate preservative treatment to bamboo depending on the degree of hazard and service conditions,

(d) Use of Bamboo Mat Board(BMB) as gussets in combination with mild steel bolts for load bearing joints in roofing structure, and

(e) Use of Bamboo Mat Corrugated Sheet (BMCS) as a roofing material.

Bamboo based housing system has very high potential for mass housing, housing in disaster prone areas and for earthquake resistant structures/houses and other applications. The low mass of the bamboo based building is an advantage under earthquake condition as compared to masonry structures. The buildings constructed in bamboo using this method are able to withstand the highest level of earthquake loading likely to be experienced in India. Bamboo has the potential of being used in sophisticated urban house construction and also for reinforcement in concrete. But due to absence of any standard building code for bamboo so far apart from method of test, it has not been officially recognized as a building material in house construction activity.

Steel Fibre Concrete Composites for Special Applications

Normal and High Volume Steel Fibre Concrete Composites for Special Applications

Steel Fibre Reinforced Concrete (SFRC)

Concrete is the most widely used structural material in the world with an annual production of over seven billion tons. For a variety of reasons, much of this concrete is cracked. The reason for concrete to suffer cracking may be attributed to structural, environmental or economic factors, but most of the cracks are formed due to the inherent weakness of the material to resist tensile forces. Again, concrete shrinks and will again crack, when it is restrained. It is now well established that steel fibre reinforcement offers a solution to the problem of cracking by making concrete tougher and more ductile. It has also been proved by extensive research and field trials carried out over the past three decades, that addition of steel fibres to conventional plain or reinforced and prestressed concrete members at the time of mixing/production imparts improvements to several properties of concrete, particularly those related to strength, performance and durability.

The weak matrix in concrete, when reinforced with steel fibres, uniformly distributed across its entire mass, gets strengthened enormously, thereby rendering the matrix to behave as a composite material with properties significantly different from conventional concrete.

The randomly-oriented steel fibres assist in controlling the propagation of micro-cracks present in the matrix, first by improving the overall cracking resistance of matrix itself, and later by bridging across even smaller cracks formed after the application of load on the member, thereby preventing their widening into major cracks (Fig. 1).

The idea that concrete can be strengthened by fibre inclusion was first put forward by Porter in 1910, but little progress was made in its development till 1963, when Roumaldi and Batson carried out extensive laboratory investigations and published their classical paper on the subject. Since then, there has been a great wave of interest in and applications of SFRC in many parts of the world. While steel fibres improve the compressive strength of concrete only marginally by about 10 to 30%, significant improvement is achieved in several other properties of concrete as listed in Table 1. Some popular shapes of fibres are given in Fig.2.

In general, SFRC is very ductile and particularly well suited for structures which are required to exhibit:

• 
  The behavior of SFRC under fatigue loading regime as compared to conventional concrete is shown in Fig. 3, while Fig. 4 illustrates the improvement in impact resistance of SFRC with the increase in the fibre content. The high ductility exhibited by normal SFRC and polymer-impregnated SFRC over conventional concrete is shown in Fig. 5.Resistance to impact, blast and shock loads and high fatigue
• Shrinkage control of concrete (fissuration)
• Very high flexural, shear and tensile strength
• Resistance to splitting/spalling, erosion and abrasion
• High thermal/ temperature resistance
• Resistance to seismic hazards.

The degree of improvement gained in any specific property exhibited by SFRC is dependent on a number of factors that include:

• Concrete mix and its age
• Steel fibre content
• Fibre shape, its aspect ratio (length to diameter ratio) and bond characteristics.

The efficiency of steel fibres as concrete macro-reinforcement is in proportion to increasing fibre content, fibre strength, aspect ratio and bonding efficiency of the fibres in the concrete matrix. The efficiency is further improved by deforming the fibres and by resorting to advanced production techniques. Any improvement in the mechanical bond ensures that the failure of a SFRC specimen is due mainly to fibres reaching their ultimate strength, and not due to their pull-out

Mix Design for SFRC

Just as different types of fibres have different characteristics, concrete made with steel fibres will also have different properties.

When developing an SFRC mix design, the fibre type and the application of the concrete must be considered. There must be sufficient quantity of mortar fraction in the concrete to adhere to the fibres and allow them to flow without tangling together, a phenomenon called ‘balling of fibres’ (Fig. 6). Cement content is, therefore, usually higher for SFRC than conventional mixes Aggregate shape and content is critical. Coarse aggregates of sizes ranging from 10 mm to 20 mm are commonly used with SFRC. Larger aggregate sizes usually require less volume of fibres per cubic meter.

Self Compacting Concrete

Self compacting concrete is a concrete which compacts itself, there is no further compaction required for self compacting concrete. Making concrete structures without vibration, have been done in the past. For examples, placement of concrete under water is done by the use of tremie without vibration. Mass concrete, and shaft concrete can be successfully placed without vibration. But the above examples of concrete are generally of lower strength and difficult to obtain consistent quality. Modern application of self-compacting concrete (SCC) is focussed on high performance, better and more reliable and uniform quality.

Recognising the lack of uniformity and complete compaction of concrete by vibration, researchers at the University of Tokyo, Japan, started in late 1980’s to develop Self compacting concrete. By the early 1990’s, Japan has developed and used SCC that does not require vibration to achieve full compaction. By the year 2000, the SCC has become popular in Japan for prefabricated products and ready mixed concrete. The utilisation of self compacting concrete started growing rapidly.

Self compacting concrete has been described as “the most revolutionary development in concrete construction for several decades”. Originally developed in Japan to offset a growing shortage of skilled labour, it has proved to be beneficial from the following points,

1. Faster construction,
2. Improved durability,
3. Reduction in site manpower,
4. Better surface finish,
5. Easier placing,
6. Safer working environment.

New Concrete Technology

New Concrete Technology

There have been a number of advances in new concrete technology in the past ten years. There have been advancements made in almost all areas of concrete production including materials, recycling, mixture proportioning, durability, and environmental quality. However, many of these innovations have not been adopted by the concrete industry or concrete users / buyers. There is always some resistance to change and it is usually based on cost considerations and lack of familiarity with the new technology.

The latest new concrete technology is beginning to gain acceptance in the industry. Some of the more interesting new concretes are called high performance concrete (HPC), ultra high performance concrete, and geopolymer concrete. They have significant advantages and little or no disadvantages when compared to standard concrete in use today.

High performance concrete usually contains recycled materials and thereby reduces the need to dispose of these materials. Some of these materials include fly ash (waste by-product from coal burning), ground granulated blast furnace slag, and silica fume. But perhaps the biggest benefit of using some of these other materials is the reduction in the need to use cement, also commonly referred to as Portland cement. The reduction in the production and use of cement will have many beneficial effects. These benefits will include a reduction in the creation of carbon dioxide emissions and a reduction in energy consumption, both of which will improve the global warming situation. It is estimated that the production of cement worldwide contributes five to eight percent of global carbon dioxide emissions. In addition, the use of fly ash and furnace slag is usually cheaper than cement and they have properties that improve the quality of the final concrete.

Today’s new concrete technology has produced new types of concrete that have live spans measured in the hundreds of years rather than decades. The use of fly ash and other by-product materials will save many hundreds of thousands of acres of land that would have been used for disposal purposes. Fly ash and other by-products from burning coal, are some of the most abundant industrial waste by-products on the planet. The elimination of burial sites for these waste by-products will translate into less risk of contamination of surface and underground water supplies. When compared to standard concrete the new concretes have better corrosion resistance, equal or higher compressive and tensile strengths, higher fire resistance, and rapid curing and strength gain. In addition, the production and life cycle of these new concretes will reduce greenhouse gas emissions by as much as 90%.

BSI is a new concrete technology that has a much higher tensile and flexural (bending) strength than standard concrete. It is a fiber-reinforced concrete that is combined with premixed dry components. It is much denser than standard concrete and structures built with it will need far less new concrete, perhaps as much as 80% less. The high density gives BSI concrete other properties such as extremely high resistance to corrosion from chemicals. The higher strength of BSI eliminates the need for placement of steel rebar in structural designs. BSI, or some variation with metallic fibers and/or superplasticizers, will be used to build some structural elements less than an inch thick. Overall, structures built with BSI will have much greater life spans and will require far less maintenance.

Ductal is another new concrete technology that is denser than BSI. Ductal uses steel or organic fibers to create a concrete that is stronger than BSI. Interestingly, the ancient Romans used horse hair in their concrete to improve its strength. Ductal is being tested for use in earthquake resistant structures, bridges, tunnels, and nuclear containment structures. Although it is more expensive than traditional concrete there are a number of cost savings that will make it price competitive. Among these cost savings are no steel rebar is needed, less material is needed with less related labor and equipment costs, and structures are thinner with less weight and require smaller foundations. In addition, both BSI and Ductal have low maintenance costs because of their very low porosity and are very resistant to penetration by water or chemicals. They are both resistant to salt water which is very corrosive and damaging to today’s bridges and roadways.