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LANDSCAPING & EXTERNAL WORKS
Casting cast stone in a new light
Devanshu Mudgal at Haddonstone explains why the durability of cast stone enables it to play an environmentally-responsible role in a wide range of construction projects
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The cast stone steps and flooring manufactured today can be expected to offer a maintenance-free life of many decades
or anyone who has stood and marvelled at the beautifully preserved floors within the 4th century Roman villa at Chedworth in the Cotswolds, it is worth remembering that these extensive areas of mosaic, set in mortar, are among the later examples of the artform to be found across Europe. Some date back over 2,000 years, having survived everything from being buried in volcanic ash to submersion in aggressive groundwater. The durability and longevity of the mosaics’ structure are important to consider, because they shed light on the true environmental impact of many cement-based products. Manufacturers of cast stone products can rightly argue that the energy required to convert limestone and clay into the ubiquitous grey powder employed across the construction industry should be viewed in the context of their whole life sustainability credentials.
Contemporary cast stone as a construction material
Contemporary cast stone products such as cills, lintels and string courses may not be destined to survive for millennia, but they bear very favourable comparison to common construction materials including PVC extrusions or energy intense aluminium components.
While some cast stone manufacturers use just a pigmented sand and cement mix for their production runs, finely graded limestone, such as Bath stone, is recognised as offering the best outcomes. Semi-dry cast stone incorporates 60% crushed limestone and a 2% water content to achieve a minimum design strength of 35N. Waterproofing admixtures reduce moisture penetration and, along with vapour curing, help protect against frost while also accelerating the gain of strength to enable products such as quoin stones
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to offer excellent durability and general resistance to weathering.
The so-called wet cast process also features a 2% water content, with the increased slump and workability being created using ‘super plasticisers,’ making the mixes self-compacting. In addition, the target compressive strength rises to 45N, without any need for vapour curing, further enhancing the likely lifespan of cast stone products. In fact, cast stone steps and flooring manufactured today can be expected to offer a maintenance-free life of many decades, while items such as copings – which are permanently exposed to the elements – should provide solid service for as long as the walls that they sit atop remain standing.
A sustainable option Research has further shown that the extended working life offered by cast stone means that its embodied energy becomes insignificant, while the natural process of carbonation – where carbon dioxide is absorbed from the atmosphere and changes state – constitutes a form of carbon capture. Then from a local perspective, the fact that most projects here make use of products manufactured in the UK means the energy involved in transportation is also minimised. In addition, production standards and supply chain monitoring are higher than in many other countries from where products are imported. There is an industry-wide consensus on the need to improve environmental performance, underlined by the UK Cast Stone Association announcing the launch in May this year of its Sustainability Charter – whereby the membership has committed to adopting a series of measures, including cutting waste, pollution and energy usage. The UKCSA will also work constructively
ADF OCTOBER 2023
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