A Review Of Precast Concrete Systems For Waste Reduction And Environmental Protection

The Problem of Waste in Construction

Question:

Discuss About The Precast Concrete Order TO Reduce Wastages?

With wastes accounting for close to 6% - 9% of total project costs in the construction industry, the amount of losses is very significant considering the high cost of projects (Blismas, et al., 2010). This industry still remains one of the most profitable sectors of the economy which leads to most attempts to mitigate wastage in construction sites being uneconomical, a factor which further facilitates construction to carry on without proper preventive measures. As a result, both the technical and client parties incur huge costs considering the fact that the wastes have to be accounted for. Building projects that utilize concrete as the main material, in most cases, usually end up with a wastage factor of between 5% - 10% of the overall costs. These wastes also contribute to a variety of environmental problems which have proven to be a setback in the construction industry. This waste material is mostly in the form of concrete, used formwork, steel and it is usually a result of human and environmental factors within the site environment (Tam, et al, 2005).

Whereas the disposal mechanisms currently being used help achieving a reduced waste impact on the environmental, the responsibility falls upon engineers and contractors to find a balance between waste free constructions and helthcare profit margins. More alternatives that reduce the amount of wastages and improve the quality of work too therefore have to be developed (Mao, et al., 2013). This is where modular construction techniques come in as manufacturers can come up with environmentally friendly materials while at the same time, implementing environmentally friendly building methods that also give way for the incorporation of sustainable energy. While relying heavily on existing literature, this review will concentrate on precast concrete systems explaining how and when these systems are used, their material saving and environmental friendliness, the gaps in the research and further link them to my research project.

Modular construction systems categorically offer a solution to the issue of waste reduction. This is advantageous for developers seeking to increase their profit margins based on the favourable economies of scale of the total cost of the development. As argued by Lu Aye, T. Ngo, R. H. Crawford, R. Gammampila and P. Mendisa, modular systems provides up to 51% material saving by mass by incorporating reused materials in modular construction that used timber, steel and concrete (Lu, et al., 2012). Concrete is one of these modular construction materials whose application has been increasing gradually over the years for this very reason. As a fact, a study by Weisheng Lu and H. Yuan indicates a wastage factor of only 2% or less when utilizing precast concrete in construction (Lu, 2013).

Modular Construction and Precast Concrete Systems

In using precast concrete systems, the person using it may choose to go with a fully modular approach or the inclusion in situ concrete during construction various stages. When construction teams utilize this precast approach, however, they may do so for specific member elements including slabs, columns and beams. The reasons for using these members include good insulation, easy demolition, higher frame strength and cost reduction (Arif, 2010).

When looking at the various approaches to this system, 2 main approaches stand out whose difference is in the percentage amount of precast elements used. They are discussed below.

Fully precast concrete systems: this is where all member elements are cast off site and transported to the site. Some of the best examples of these of the application of precast modular structures are artificial harbours and bridges. One of the most recognized examples is the Mulberry Harbour that was temporarily constructed by the British during the Second World War to provide a platform for quick offloading of cargo along the beaches of Normandy, France. At present, most bridges are constructed using prefabricated member elements where the only in situ components are the abutment (Li, Z., et al., 2014).

As argued by researchers R. Lawson, R. G. Ogden and R. Bergin, precast concrete systems have a proven record of maintaining high levels of structural durability and stability as all the member elements have better tensile and compressive strengths compared to the conventional in situ members (Lawson, et al., 2011). This provides the client and contractor with a better schedule management and waste saving system. When considering the economies of scale, larger projects that use precast concrete are ultimately much cheaper to run and develop than their in situ concrete alternatives.

The economic aspect of this system can however be non-existent when comparing to the conventional systems currently in use. This mean that, for smaller structures, the economies of scale apply. Where development projects are smaller, there are significantly less wastes and time spent and this usually less and this leaves very little room for extra economic recovery (Blismas, et al., 2010). In actual sense, they could end up being more expensive than the conventional concrete systems. This is because of their relatively higher production costs.  Questions have also been raised by researchers about their seismic performance with some researchers suggesting they could be weak.

Partial precast concrete systems: these is usually when the construction utilizes both precast and in situ concrete in the same project. These practices are currently incorporated in high-rise structures such as warehouses plazas, residential high-rise blocks, bridges, harbours. These may not be as strong as precast structures but they also exhibit high levels of structural durability and reliability (Azman, et al., 2010). Partial precast concrete systems can be an advantage to developers constructing small units as, they are much cheaper than their alternatives e.g. those with three floors or less (Azman, et al., 2010).

Fully Precast Concrete Systems

The major disadvantage that this system is that it is prone to wastages when comparing it to the alternatives. In actual sense, waste is significantly reduced when comparing the development to concrete structures cast right there on site. They are, prone to some slight wastage as using the in situ cast concrete system leads to wastage.

The research gaps existing in the in the body of knowledge relating to precast systems is in complementary sustainable material incorporation. While it has been noted that modular construction does, in a lot of cases utilize reused materials, very few materials have been researched on that complement the precast concrete systems. These materials could include recycled reinforcement fibres made of a variety of materials that could include steel, nylon, fibreglass, organic sisal fibres etc (Wang, et al., 2010). Cement admixtures and alternative, sustainable alternatives to both coarse and fine aggregates could also be researched on that are both environmental friendly and reduce overall construction costs.

The research conducted in this field indicated both positives and negatives, some of which are in direct contrast with each other. While Arif, in his journal paper highlighted precast systems as being more cost effective than other construction methods, W. Lu and H. Yuan greatly emphasize the additional costs of the transportation associated with precast systems (Arif, 2010), (Lu, 2013). These normally come about as some construction sites are far away from the factories which, in comparison to conventional methods using in situ material that are readily available, is fairly costlier.

Kamali and K. Hewage in their research on the life cycle of modular structures argue that modular construction provides a better life cycle, a point E. M. Generalovaa, V. P. Generalova and A. A. Kuznetsovaa agree with in a different research paper (­ Kamali, 2016), (Generalova, et al., 2016). With this in mind, further research can be done to increase this life cycle and overall sustainability. R. N. Swamy, in 1990, conducted a research in fibre reinforced concrete but their application was limited to in-situ cast concrete. Even then there was a reduction in the amount of reinforcement used and also member dimensions e.g. slab and beam depths were significantly reduced (Swamy & ed., 1990).

It is with this in mind that this research focuses on the effect of using sustainable fibres during the casting of precast elements that provide for a similar or better life cycle, cut down overall costs and are environmentally friendly. In utilizing them, material wastage will be assessed comparing the material saving qualities of systems using both precast with conventional reinforcement and those with environmental friendly reinforcement mechanism.

Partial Precast Concrete Systems

The reinforcement alternatives researched on will be limited to only those that are recycled wastes and by products of other production processes that would go to waste. The reasoning behind this research is that, while mitigating the amount of constructions event further, they would also provide a solution to the increasingly challenging task of providing reliable and safe disposal mechanism (Oyedele, et al., 2014). In reusing these waste materials, the construction costs are ultimately lowered and adoption would be easier to propagate by marketing. The strength properties are to be measured and compared to regular concrete with an objective target of examining whether they can provide a much better deal in the long run.

Conclusion

The review above illustrates the in-depth study that has been conducted in order to establish the suitability of precast concrete systems in waste reduction and environmental protection. While a lot of these systems have been adopted and are largely being utilized, the question of reducing material wastage and costs even further has been raised. It is with these in mind that further research has been suggested fibre reinforced precast concrete. These assumed result would be further reduction in wastages, costs and more environmental friendliness.

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