MMC (Modern Methods of Construction) and the advantages of using precast concrete in construction1

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MMC (Modern Methods of Construction)and the advantages of using precast concretein construction

MMC (Modern Methods of Construction) and the advantages of using precast concrete in construction2

This article explores the MMC agenda and the specific advantages of using precast concrete systems in Construction.

The term ‘Modern Methods of Construction’ refers to a collection of relatively new construction techniques that aim to offer advantages over traditional methods. Although referred to as Modern Methods of Construction, some of these have been used for some time. MMC are increasingly favoured as a means of improving quality, reducing time spent on site, and overcoming skills shortages. The eco agenda has also made an impact on construction, with sustainable materials and techniques becoming more popular.

Typically MMC involves the manufacture of building products and components offsite in a specially designed factory under strict quality control conditions and includes Timber-Frame, Steel-Frame, Precast Concrete Flooring Systems, Panelised Units, Modular and Volumetric Construction Units and Hybrid techniques.

In recent years there has been a real shift from using traditional concreting methods, as the benefits of precast concrete and MMC are recognised and grow in popularity. The advantages of precast are clear, faster erection time, the superior quality of the result, and the lifetime energy efficiencies from the thermal mass of the concrete. Precast concrete is seen by many as the best commercial solution for bespoke concrete work.

These modern methods and the increase in offsite construction mean that precast concrete products offer the following advantages:

Cost efficiencies, project efficiency, speed of construction (#1)

These modern methods of construction mean a reduction in construction time on site and an increase in the amount of manufacture that takes place in a controlled factory environment.

The significance of this material is in the way it is produced. Precast concrete products are prepared off-site in a production plant and are brought on-site ready to be installed, grouted and used for a platform. This applied production technique means that entire concrete floors can be pre moulded in sections and held in stocks until they are required. This means that precast concrete manufacturers can supply large quantities on demand and quickly. It also allows contractors to meet demand during skills shortages. In addition, bespoke and customised precast products can be manufactured and delivered at the same speed. Floor and wall units are produced off-site in a factory and erected on-site to form robust structures, ideal for all repetitive cellular projects. Panels can include load-bearing elements.

This fast-track construction allows construction contracts to be completed faster and buildings can be occupied sooner, this provides the developer and contractors a quicker return on their investment. Precast technology helps reduce construction cost and labour more than other constructing methods. Cost efficiencies are down to the timesaving elements from reduced labour costs due to less on-site construction time.

A precast concrete flooring structure can also provide an instant work platform. In particular flooring and staircases can provide an early, safe,

More construction industry decision makers are recognising the significant benefits of modern methods of construction (MMC); better products and processes, and improved business efficiency, quality, safety and environmental performance.

Spanwright Flooring have embraced the growing trend towards modern methods of construction (MMC) by offering a range of innovative precast, pre-stressed and reinforced concrete products which can be used to reduce construction time and promote sustainable development, as well as offering the developer significant cost savings.

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secure and broad platform from which subsequent construction site activities can be undertaken. Once the precast system is secured in place, it becomes a working surface for other trades such as mechanical contractors, electricians, and plumbers. This advantage accelerates the entire construction process, facilitating earlier occupancy of the completed building.

More efficient production and quality of product and design (#2)

Offsite production means that precast concrete benefits from superior quality control compared to conventional methods. Quality at this level is achieved because concrete mouldings are carried out in a controlled environment, where a rational and efficient manufacturing process is in place. This offers factory quality and accuracy, together with speed of erection on-site.

The selection of structural and architectural precast concrete products offers aesthetically pleasing yet economical solutions for many types of construction projects. Precast concrete has fewer defects and allows a more efficient design. Precast concrete systems are not only ideal for new construction projects, but can be matched to existing structures for additions making it ideal for commercial refurbishment projects. The precast concrete components themselves can easily be designed to accommodate future growth. Interiors can be reconfigured simply and quickly for the changing needs of the building. Precast products can span over long areas, resulting in large, open interiors without obstructions or expensive support structures.

Precast concrete can carry pre-installed services and fixtures, whether these are communications,

plumbing or even windows. Services can be cast within a precast element or panels can include connection plates ready to receive heating and lighting fittings on site. This makes both construction and maintenance easy. Precast also offers a superior finish which means that depending on the finish required, housebuilders and contractors can apply specialist paint directly to the concrete, providing a quicker, robust and first class finish.

Every process of producing reinforced concrete is controlled by modern technology. This makes sure the concrete has the same quality. Also, there is Quality Control process to assure that every piece of concrete is qualified according to eurocode 2.

Robust and durable products and structures (#3)

Precast concrete continues to develop its strength during its service life becoming stronger with time as opposed to some construction products which deteriorate with time Many concrete buildings from hundreds of years ago are still in use today. Some say concrete can last up to 2000 years. During that time it won’t shrink, warp, move or creep excessively so can be relied upon to perform consistently year after year.

Durability is the one quality that allows precast, pre-stressed concrete to outlast competing materials. Precast is very strong, it makes houses and buildings to be strong, durable, and long-lasting. Using pre-cast can save the cost of insurance premium more than other structures.

Precast concrete products are low maintenance. With its durable design, Precast is exceptionally resistant to impact, corrosion, weathering, and abrasion. It has superior resistance to factors such as impact and soil, mould, and mildew. The

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high-strength, high-performance concrete that is utilised in the production process resists weather, corrosion, accidental damage, fire and vandalism.

Precast can withstand many winters of freeze-thaw cycles, unlike other materials which can deteriorate quickly with such regular exposure to expansion and cracking.

Thermal efficiency (#4)

Precast concrete is energy efficient. The thermal mass of precast concrete absorbs and releases heat slowly, shifting air conditioning and heating loads to allow smaller, more efficient heating, ventilating, and air conditioning (HVAC) systems.

Due to the material’s high thermal efficiency, hollowcore and precast concrete floor units can absorb heat during the day and cool at night. When used at upper floor levels, concrete floors act as a thermal store, especially when under-floor-heating systems are used, this can reduce heating costs.

Precast flooring products have excellent thermal capacities which, combined with added insulation can meet the requirements of Part ‘L’ of the Building Regulations. Precast wall panels also contribute substantially to the overall thermal efficiency of a building.

Improved safety performance on construction sites (#5)

Benefits of using precast concrete include maximum health & safety performance on-site, due to minimal on-site construction activities. Recent innovations

make the use of precast concrete even safer. These innovations include air-inflated crash bags, nets and mats which can be used in an area under construction until such time as the precast units are securely installed.

In the worst case event of an accident, these bags, nets and mats break the fall of a worker or even a whole precast unit. Once installed, this solid footing can help to speed up the rest of the construction and gives site managers the peace of mind that site operatives can go about their work safely.

When the structure is complete, the building occupants benefit from improved indoor air quality and healthier indoor environments. Precast concrete is easy to clean and its hard, smooth finish does not accumulate dust which may exacerbate asthma. There are also no toxic or Volatile Organic Compounds (VOC’s) from concrete that can contribute to sick building syndrome.

Fire resistance, fire safety & fire design (#6)

Concrete is completely non-combustible, it is also wind, vibration, sound transmission, seismic resistant and flood resistant. It does not burn, it cannot be ‘set on fire’ like many other building materials and it does not emit any toxic fumes, smoke or drip molten particles when exposed to fire. Precast concrete is unsurpassed in providing fire protection and containment when incorporated into a comprehensive, balanced design.

Precast concrete does not burn or give off lethal fumes in even the hottest of fires, and it maintains its structural integrity longer, giving occupants more time to evacuate safely and extinguish the

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fire. Concrete and its mineral constituents enjoy the highest fire resistance classification (class A1) under EN 13501-1.

The excellent fire performance is due to concrete’s constituent materials (ie, cement and aggregates) which, when chemically combined, form a material that is essentially inert and has poor thermal conductivity. It is this slow rate of heat transfer,

that enables concrete to act as an effective fire shield between adjacent spaces.

For any building or structure, regardless of its complexity, design for fire safety should address the following four principal objectives:

- to ensure stability of the loadbearing construction elements over a specific period of time

- to limit the generation and spread of fire and smoke

- to assist the evacuation of occupants and ensure the safety of rescue teams

- to facilitate the intervention of fire fighters and other rescue parties

Good practice in design for fire safety incorporates these aspects and more in what is termed ‘fire engineering’ for large, complex structures that warrant additional design effort.

From a whole building standpoint, concrete can satisfy the four principal objectives of fire safety through its inherent fire resistance and the utilisation of its structural continuity in fire engineered design.

Information provided by The Concrete Centre.

Noise reduction means a reduced impact on residents (#7)

Precast is better sound proof material than bricks, wood, glass or most other construction materials. Because precast can be moulded to any shape, size and texture it can be used to deflect or absorb noise. This makes it a good acoustic host keeping noise in but also makes it an effective sound barrier to outside noises eg; alongside busy roads.

In recent years precast concrete has grown in popularity, among self-builders and developers in the domestic property market, who are looking for a solution for noise transfer and squeaky floors. The technological advancements of precast concrete means that 210mm deep slabs, and even specially manufactured 150mm deep high density prestressed units are enough to reduce travelling sound at an airborne sound resistance of 300kg.

The Building Regulation requirements for a precast concrete floor base remains unchanged since 1992 when the minimum mass for separating floors in dwellings was increased to 300kg/m².

Precast is a high-density material that provides excellent, if not unsurpassed, sound reduction, allowing the building occupiers to benefit from a quieter and less disruptive environment. Precast floors, roofs, and walls offer superior sound absorption and impact sound reduction. The use of precast elements in a building mean that privacy and effective sound reduction are ensured, this makes it an ideal choice for residential and multiple occupancy buildings.

Because precast is manufactured off-site, the construction sites are quieter too. No vibration, no sawing and no other noise-generating processes need be used to install a precast concrete structure.

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This results in substantially quieter construction sites, a genuine benefit to both local residents and workers alike.

Less downtime due to weather disruptions (#8)

The fitting of precast is a fast process and is less prone to disruptions caused by inclement weather. As production is completed at the factory, it is just a case of fixing at the site so the fitting procedure is less vulnerable to weather conditions.

Weather considerations include extremely cold weather (Continuing construction in wintertime down to -20°C), hot or wet weather; and as a result construction time is less than half of conventional cast in-situ concrete construction.

Because construction operatives work year-round, in all types of weather, the use of precast concrete helps contractors stay on or ahead of schedule even in the cold winter months.

Reduced impact on the environment (#9)

Precast concrete allows reductions in the level of dust, noise, waste materials and disruption normally associated with the more traditional forms of construction. It is an environmentally friendly way of building, by better use of available building materials and production systems, with a reduced impact on the environment.

Because the Precast is made offsite, Contractors benefit from reduced energy usage on-site and due to fewer materials deliveries, they see a reduction in disruption and fuel consumption. Precast concrete contributes to green building and eco building in a number of ways. Because precast concrete is factory-made, there is little waste created in the plant (most plants employ exact-batching technologies) and it reduces construction waste and debris on site, reducing construction Indoor Air Quality (IAQ) concerns.

Precast concrete contains recycled materials. Precast concrete’s performance can improve when several common industrial by-products are added. Fly ash, slag, and silica fume, which would otherwise go to landfills, can be incorporated into concrete as supplementary materials. These by-products can also reduce the amount of cement that is used in concrete.

Reinforcement can be made from recycled steel and this steel can be re-used. At the end of a structure’s life, precast units can be re-used in their entirety, for example reclaimed as whole elements such as floor slabs. These could be re-installed in the same building or even transported a short distance and used in another building project. Precast can be recycled. As with many concrete products, precast is easy to crush and recycle as aggregate. Demand for materials like this is growing every year in the UK – and the government is encouraging its use through networks for suppliers and customers.

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Summary

Traditionally Housebuilders and the Self–build market have led the way when it comes to MMC , particularly in terms of sustainable construction. The self-build sector in particular, seem more willing to research, invest and try something a little different in order to achieve an individual home that meets their needs.

In light of increasing housing demand, skills shortages and the targets set by The Code for Sustainable Homes, the Government is encouraging the housebuilding sector to use and develop MMC in an attempt to meet these challenges. The efficient production technology combined with skilled workers, a range of precast designs and quality control enables a cost effective solution, which results in precast units being environmentally friendly and extremely structurally efficient. Precast concrete is recognised by many as a best value construction solution.

Spanwright is a leading supplier of precast concrete flooring and concrete stairs throughout the UK.

Products manufactured include: - pre-stressed flooring- precast flooring- agricultural precast- concrete stairs- concrete wall panels

Spanwright offer a range of bespoke solutions and encourage you to visit the main website atwww.spanwright.co.uk or call 01793 441474 or email our sales team at sales@spanwright.co.uk

References:

- British Precast - The home for precast concrete and masonry for the construction industry.- The Concrete Centre- The advantages of precast flooring systems Phil Harris, The Precast Flooring Federation