sustainable concrete alternatives
January 30th, 2019 by Mark Laurence
The Roman Pantheon Dome

Concrete is a wonderfully versatile material, which has been in use since Roman times and with it we can build amazing structures that would otherwise be impossible. Unfortunately it also carries a huge environmental cost, caused mostly in the cement binding used. Whilst gravel extraction is also an issue, for that there are some alternatives such as recycled, crushed concrete.

The production of modern cement (OPC – ordinary portland cement) is a hugely polluting process and produces around 8% of the world’s carbon emissions – at least twice that of the aviation industry. Whilst the Romans used a volcanic dust called pozzolona as their binding agent, until the invention of OPC, we used lime, in various forms. Lime too has to be processed by heat and so is not without it’s environmental cost, but it uses less energy to produce than cement and lime concrete/mortar reabsorbs carbon over its lifetime (if exposed to the air), offsetting some of the initial pollution. Moreover, because it is softer, materials can be disassembled easily, for re-use.

cement factory
A typical cement factory

In a landscape, there is ubiquitous use of concrete in a range of structures – walls, paving, sub-bases, ponds etc. some of which could be reduced or avoided altogether. Whilst landscaping will always use an insignificant amount of concrete compared to urban development and infrastructure, there are good reasons to minimise the volume of cement and other hard landscape materials used.

Some of these reasons are for obviously sustainable goals: reducing material/resource input and carbon and other wastes. Equally important in my view, is to increase the soft elements exposed in a garden – soils – and to increase the levels of planting and foliage biomass/diversity. This thinking is about the increase of biophilic benefits.

However, if sustainability is to be given top priority – as it must – then the use of cement has to be reduced as much as possible. This is quite a challenge to us all, as it is not always easy to find an alternative and I don’t suggest for one minute that it should never be used, but it should be reserved for essential structural use only. Even then there may be alternatives. Recycled concrete can make a suitable aggregate (or part of) and low cement alternatives such as CEM 1 reduce the energy and carbon emissions tally.

I have used – and continue to use – concrete in many of my own designs and so this challenge is personal – but then aren’t all sustainability issues.

Let’s look at the different areas of the garden where cement is used:


garden walls
Could these concrete-block walls have been made from rammed chalk?

Walling

Many walls use cement, either in mortar or in concrete blocks as well as in cement renders. In this garden (left) we built retaining walls using hollow concrete block construction on concrete footings with cement render and mineral pigments for the final colouring, with concrete paving slabs as coping. As the site was on a chalk hillside, it may have been possible to construct this using rammed chalk or earth. Indeed, we had a surplus of chalk on the site from the house construction and it would have made perfect eco-sense to have used this to build the walls. The walls could have been rendered using lime based mix, and the coping could have been stone. As the chalk hillside is inherently quite stable, rammed chalk could possibly have been used for the footings too. However, there are so many unknowns, and so few UK examples that it is a risk to do this, especially on such structurally critical terracing. Long-term effects of damp creeping into the walls would have been my main concern.

The cost of rammed earth construction may have been cheaper than conventional construction , both in time to do and in material purchase, especially when the removal off site of subsoil is taken into account.

rammed earth garden walling

Rammed earth garden walling and Cement-substitute coping, GDL.

The picture at right shows rammed earth walls in a sustainable landscape I designed for Grand Designs Live, ExCel, 2006. Rammed earth walls are made by compacting subsoil inside timber or metal formwork. The soil must be kept dry so it needs some kind of footing and capping, here provided by cast copings made with recycled aggregates and partial cement substitute (CEM 2 furnace slag). The gravel to the main paving area is a recycled brick/concrete mix, laid through a geo-grid membrane made from recycled plastic. The aim here is to be as carbon neutral as possible. Planting aspired to be edible (you can eat daylily flowers).

Walling alternatives to concrete include:

  • Cement alternatives/recycled aggregates
  • Rammed Earth
  • Timber walling (railway sleepers etc)
  • Round pole walling (preferably coppiced hardwood)
  • Fences & crib-type embankment walls
  • Brick/stone with lime mortar (brick also has high energy input)
  • Dry Stone walling

reclaimed paving
Reclaimed brick and stone flags have charm and have exhausted their carbon dues. (Apart from cleaning and transport).

Paving

Modern paving is often made from concrete and in some instances it is quite hard to find realistic substitutes. Stone paving is the obvious one but can be expensive. There are many cheaper stone imports available these days, such as Indian Sandstone, which are cost-effective but which carry a high transport and pollution price tag. Reclaimed York paving is highly desirable and of course, reused, so environment friendly but will cost 2-3 times that of cast concrete or Indian Sandstone. Brick is also traditional as paviors but as for walling, still carries a high energy/pollution cost in production, plus is expensive to lay.

For larger areas and drives, self-binding gravels may be one of the better answers, as these form a firm surface, once compacted, without the use of cement. Recycled or local gravels are also acceptable and can be held in place using recycled plastic grids/membranes.

A geo-grid with gravel creates a stable and permeable surface

Paving is one of those areas which highlights the question of just what is sustainable. Is it better to use imported sandstone with its high transport miles but relatively low energy production, or locally made concrete paving with cement and aggregate use, but low transport miles? In either case, the (financial) costs may be similar. There are also ethical and human welfare considerations for stone imported from third world countries, especially in terms of working conditions, health & safety and child labour.

Timber decking can be a viable alternative, especially on sites with changes of levels. Local timbers of the more durable softwoods (like Douglas fir or larch), green oak, Sweet chestnut or recycled tropical hardwoods. All new timbers should be FSC (Forest Stewardship Council) certified. New hardwoods should be avoided even if the have an FSC certificate as there is much illegal timber that still gets sold and even managed plantations may still involves some environmental degradation. They certainly have high transport emissions.

Possible paving alternatives:

  • Recycled stone, brick, cobbles – and concrete slabs
  • Self binding aggregates don’t need cement
  • Fired paviors and tile look beautiful, but are still energy intensive
  • local or recycled aggregates and gravels
  • Decking can be used where appropriate
  • Locally produced concrete slabs minimise transport and can have lower carbon footprint than imported stone
  • Third-world stone may be low energy, but high transport emissions

concrete in a pond

A “natural” pond marginal shelf with protective concrete pad

Ponds

Even natural looking ponds may use concrete in their construction and formal ponds may be dominated by it. Again choice of alternatives is limited.

Concrete is often used to retain rocks and place protective pads over liners, etc. In many places it may be possible to do without concrete pads, which are often used in a “belt-and-braces” approach to protecting a liner. Felt geomembranes are used as standard as a layer underneath and often inside the liner (this may in fact be degraded by contact with concrete) and in many cases, use of additional layers of felt may eliminate the need for concrete. Felt is usually a synthetic, petroleum based product, so also has its environmental considerations (as do liners!). I have successfully used old carpet as replacement for felt, under the pond (I wouldn’t recommend it inside) but be VERY wary of tacks that may have been used. Non-synthetic carpet will degrade over time, which must be born in mind. Of course, before the advent of felt, liners were simply bedded on a layer of sand.

Where rocks and stones create waterfalls, they are used to form spillways and to prevent stones moving when climbed over or stepped upon (an important safety consideration). It may be possible to use hydraulic lime based concretes for this, although I haven’t tried this out. Perhaps well laid rocks, without the use of cement are the key, which would require a careful re-thinking of the construction method. Nature doesn’t use concrete, but then natural streams don’t retain water within an artificial environment (liner). A more holistic approach to water features, where the roof water and household grey water are recycled and the pond design doesn’t hold a fixed level or amount of water, may be the long term answer.


So looking at alternatives to cement raise as many questions as answers and in the 12 or so years since this article was first written, there has been some progress, but not much. Best advice is to minimise the use wherever possible, recognising the long-term durability and benefits of strength that concrete possesses.


First published in 2007, updated 2019

Posted in Climate Change, Environment, landscapes, Sustainability, Urban Landscapes Tagged with: , , , , , , , , ,

A good transitional entrance space between house and garden
November 6th, 2018 by Mark Laurence

This article was first published in 2009.

There are few aspects of our built environment more emotive that that of the entrance door. It can mean shelter, warmth, food, security, friendship. All of life involves the act of entrance, from the earliest caveman to the present day.

How many times per day do we go in and out of buildings and our homes? We scarcely stop to think about it, yet entrances all convey subconscious messages which can affect us on deeper levels, for good or ill. Some doorways are enticing, friendly; some oppressive; some just dingy and neglected. Most are probably functional and non-descript, of itself a message just as powerful as the others.

We move from our homes to cars, to shops, offices or other houses. Each time we do this we experience a subtle shift in light levels, humidity, warmth, expectations and intentions. Our mood shifts and adjusts with our purpose and our expectations. Going to work we might subconsciously don a mask as we enter busy offices or a large railway station. Arriving home again, we relax as we walk up the path, shedding the mask as we close the door behind us.

A Wisteria-covered pergola gives a deep connection

A Wisteria-covered pergola gives a deep connection between the kitchen door, driveway, outhouse and rear garden

The physical structure of a building and its entrances tell us what to expect: grand doorways with tall columns tell us of status, power and authority. Grim entrances to prisons have an unmistakable message. In public buildings especially, proportion is everything, where tall ceilings and doors give formality. By contrast a humble cottage door or an old garden gate recessed into an ivy-covered wall might look secretive or inviting, asking us to explore the spaces beyond. What do the doors to our homes tell us? Most front doors are rather bland or feel inauthentic, for example the many mock-Georgian style doors on modern houses offer us nothing more than a thin veil of pseudo-style applied over a nondescript structure.

In the home, layout and door position is also important. The front door is our formal entrance to the world, the back for our private comings and goings. Yet how many house layouts truly observe such simple criteria? Some houses have both the front and back doors equally visible, with no clear indication as to which is which. Or the back door opens onto a narrow side passage, rather than directly onto the garden. Many of us live with awkward house layouts.

Overcoming the problem of awkward flow is, however, fundamental to the harmonious functioning of a house and its occupants. On occasions when looking at a house and the way it connects to the garden, I have recommended the re-location of the rear door. It sounds extreme but I have had several clients who were very glad they took my advice. Fundamental problems sometimes need bold solutions and the picture below is one such example.  Here, a new connection from kitchen into the garden via a (new) seating area made a big transformation.

French doors give connection to the garden

New French doors give connection to the garden, creating a new experience in this house

French or patio doors aren’t always the bonus they’re meant to be, though. Sometimes these confuse the traffic-flow and can destroy the usability of the room in which they occur. Lines of movement (inside or out) should not cut through a still-point. Of course, sliding doors which truly open up the house and invite a more relaxed transition can be fantastic. It’s all down to careful thought and good design.

So much for placement, what of the physical act of entering and leaving? All too often it’s a bit, well, abrupt. Ground and wall meet at the perpendicular, at which point, there’s a door. You open it, go in or out. That’s it – all over with. Yet it takes a moment to adjust, from one environment to another, both physically (light and warmth) and mentally (tasks, purpose, relaxation). Ideally therefore, we need a space in which to adjust, to experience transition, even if it’s for just one second. That space becomes an area that is “in-between” – it could be a porch to the front entrance or a pergola to the rear. A covered walkway might lead to the car, a path or set of steps might connect us to the garden.

How this transitional space is styled will of course depend upon its use. For a front door, nothing beats a good porch or recessed doorway. The visitor waits in this transitional space for the door to be opened, the owner pauses to find their keys. Both might be glad to be out of the rain, or bathed in a welcoming light at night. Where possible, the porch should be preceded in the approach by a path and suitable planting, building up the sense of arrival. In these days of open-plan front gardens, attention to these simple things can make a big difference.

Where a door fronts onto a street, a roof canopy over the door and some tubs or wall planters might serve. A step up onto a different level might be frowned upon by planners, but where disabled access is not an issue, a step up, off the pavement can make a huge difference – suddenly we are in stasis, out of the busy flow of the main path.

To the rear, where a door connects you to the garden, there are multiple ways to enrich the experience of transition. A pergola might frame a door and be part of a larger structure which defines an outdoor room. Conservatories and lean-tos might be the connecting space. Loggias and verandas make a great transitional area. Where the back door has to be to the side of the house, perhaps make a shady passage covered by pergola, with ferns, foliage and climbers to give dappled light. Choose a good brick or stone and make it feel like a tunnel leading out into the garden proper.

So think about the way you move in and out of your house. Imagine the use, mood and character you wish to create and then find the structure to answer that need. A good entrance can really root a building into its environment and enhance the user experience considerably. If a building feels settled, like it belongs, you will too. Don’t put up with the merely adequate – enrich that transitional moment and rediscover the lost art of entrance.

Posted in Design, design principles, Garden Design, landscapes, Uncategorized, Urban Landscapes Tagged with: , , , , , , ,