Balwyn is an inner eastern suburb of Melbourne and lies in the northern part of the city of Boroondara. It was in this area that grazier John Gardiner settled near the point where Gardiners creek meets the Yarra River. The commercial editor of the Argus, Andrew Murray built house named Balwyn which gives the area its name.
How far is Balwyn from the Melbourne CBD?
Balwyn is only 10 kilometres from the Melbourne CBD and in an easterly direction. It was once serviced by the outer loop railway station at Deepdene.
Balwyn Community Centre
The Balwyn Community Centre at 412 Whitehorse Road Surrey Hills was upgraded to ensure it would continue to support the needs of the local Balwyn Community. As well as the upgrades to the buildings, there were landscaping works for the parkland, natural wetlands, exposed aggregate concrete pathways and tennis courts.
Balwyn Community Centre Scope of works.
The hard landscaping for the Community Centre
The scope of work for this project included the following hard landscaping construction;
Plain, coloured and exposed aggregate concrete,
In-situ or poured in place concrete garden retaining walls,
Nearly all of these existing trees were kept in the new landscape design.
Later in the project rehabilitation of native wetlands was added including a child proof fence.
Tennis Court Repairs and reconstruction
Part of the landscaping included repairs to a tennis court and the construction of another tennis court. A good sport surface must be stable, therefore the new tennis court was constructed with asphalt over 300 mm of roadbase.
Synthetic clay Tennis Court surface
A low maintenance synthetic clay tennis court surface was required to laid over the asphalt. Therefore, the surface chosen was Grassports Policlay. In addition to being low maintenance, Grassports Policlay is a fast draining low maintenance water free tennis surface resulting in the ideal surface for public tennis courts. A high quality sporting surface was required, therefore the asphalt surface was flattened rigorously in preparation. The very thick roadbase foundation will also help to maintain the stability of the playing surface. Root barriers we also installed to prevent invasive tree roots causing any unevenness to the playing surface.
Soft play surfaces
The soft play coloured surfaces in the landscape was required, so an EPDM rubber was chosen. In addition to its great colour range, EPDM is a synthetic rubber widely used in the automotive industry. Similarly, its mechanical properties make it ideal for this application. For instance, it has great UV stability, abrasion resistance, ozone resistance and it is water proof. So, the material used was Playkote which was installed as a rubber wet pour over SBR underlay. In addition to the added height, the SBR underlay makes the play surface a little softer.
Outdoor Exercise Equipment
Environmentally Friendly Garden Furniture
Garden furniture including picnic tables, benches and seats were installed to add to the public amenity. In addition to the the amenity and aesthetic provided, recycled materials were also used. To this end, the material used was Enviroslat. Enviroslat is an environmentally friendly low maintenance material produced from HDPE waste mixed with recycled cellulose. The recycled cellulose hardwood waste and rice husks.
Outdoor Furniture on Exposed aggregate concrete. ACLA Consultants landscape architects.
Table Tennis Table
Table Tennis Table with bespoke surface treatment.
The finished Commercial landscaping Project
About the Community Centre Commercial Landscaping Project
Exposed aggregate concrete is a great design solution for public spaces. The attractive durable not slip surface makes it an ideal choice for landscape architects. High traffic areas around public buildings often use this type of concrete path.
Exposed Aggregate Colours
The aggregates are available in a wide range of colours to suit your landscape design. The available colours include red, brown, dark grey basalt, green quarts as well as black and white. In combination with this selection, the fine grain aggregates or sands are also available in a wide range of selections. The colour of these these fine aggregate will also be the more dominant when the surface is lightly abraded. However, more heavily abraded surfaces will result in more of the colour of the course aggregates showing. This will result in a different appearance for the exposed aggregate concrete path. Coupled with this, the cement matrix can also have colour added. Always take these factors into account when selecting the aggregates and especially during the process of exposing the aggregates.
Exposing the aggregate
In addition to this, exposing the aggregate at a different concrete curing time can lead to different appearance. Similarly, this can result in colour differences for the same site for the same aggregate concrete pathway. To maintain quality, the landscaper must use a consistent approach to exposing the aggregates. As a rule of thumb, no more than 1/3 of the aggregate should be exposed.
The suitability of Exposed Aggregate Pathways
The landscape architect needs to also consider the use of the exposed aggregate concrete path when selecting the aggregate. Use a fine rounded aggregate for areas near swimming pools. For exposed aggregate concrete paths where water drainage is important, 19mm aggregates should be used. Exposed aggregates of more than 20mm can be very difficult to transport using a concrete pump.
Exposed aggregate concrete strength
When rounded pebbles are used throughout the path, the path will be slightly less strong. This is because the matrix will not bond to the aggregate as tightly as it will with rough shaped aggregates. Generally, the path should be at least 100mm thick N25 concrete. N25 means that the concrete will achieve a compressive strength of 25 mPa after 28 days.
Even the strongest concrete will be weak in tension or bending and even properly cured concrete will have microcracks. Therefore, to minimise cracking steel reinforcement must be used. For pathways, this should be at least SL 72 using saddles to keep it in the top 1/3 of the concrete. SL72 means that the bars are each 7mm in diameter with grids of 200mm. The path should be laid on 100mm thick class 3 roadbase , if it is for public spaces. If there is any possibility of a vehicle driving on the path, then the path needs to be built like an exposed aggregate concrete driveway. This will be the case with any vehicle crossovers in the path design. In these cases the concrete needs to be at lease 125mm thick N32 (32mPa) concrete with SL92 mesh laid on at least 100mm of class 2 roadbase.
Using alternating concrete colour to break up large areas of concrete.
When the customer requirements call for a large expanse of exposed concrete, alternating contrasting colours can help to break up the appearance. The public space at Balwyn Community Centre, Melbourne, used alternating exposed aggregate concrete of Hanson Bokhara with Hanson Galaxy. The artificial turf also helps to break the appearance of the large area of concrete and gives the area a more tranquil appearance. (ACLA Consultants landscape architects.)
Creating some shade with a tree in the concreted area. The tree roots are protected with a slotted stainless steel grate. The lighter colour Hansen Galaxy forms a geometric pattern around the grate.(ACLA Consultants landscape architects.)
Drinking Fountain and exposed aggregate concrete. Hanson Bokhara contrasts well with the natural concrete in-situ walls. (ACLA Consultants landscape architects.)
Exposed aggregate concrete is ideal for garden steps and stairs to help maintain grip. Recent sealing of the concrete makes it appear slightly darker. (ACLA Consultants landscape architects.)
Alternating exposed aggregate path. Garden beds also break up the space. Sunbury Global Learning Centre.
Alternating coloured path with centre native garden. Sunbury Global Learning Centre.
Building entrance and Alternating exposed coloured path. Sunbury Global Learning Centre.
Concrete block garden retaining wall with coping next to the alternating exposed coloured path. Sunbury Global Learning Centre. Hanson Bruthen and Hanson Galaxy.
The decorative finish of the alternating decorative finish of the entranceway looks striking when compared to the old concrete footpath in the foreground. Sunbury Global Learning Centre.
Frequently asked questions about Exposed Aggregate Concrete
Is Exposed aggregate concrete expensive?
Exposed aggregate will be more expensive than normal concrete solutions. It will however, add more value and landscaping interest to your property. There is also extra labour in exposing the aggregate. Alternating colours is also great way to break up the large expanses of concrete. It will similarly add to the cost, but will add great value to your property.
Should you seal Exposed Aggregate Concrete?
Sealing is essential for these paths. The high quality sealer we use helps to maintain the appearance of the coloured concrete by preventing stains getting into the pores of the concrete. The sealer also helps to prevent dust coming off the concrete.
It is important not to exposed too much of the aggregate during the water pressure cleaning part of the process. This is because exposing the aggregate excessively will result in it breaking loose from the matrix. Do not expose them more than 30%. The concrete we use for pathways is N25 with SL72 reinforcement over a thick layer of roadbase.
Residential Concreting Solutions
For residential concreting solutions a smaller version of the commercial landscaping concepts can be applied. In some cases it will be necessary to cart the aggregate mix in by wheelbarrow.
Exposed Aggregate Concrete Melbourne
Concrete Designs, textures and colours
Outwest Concrete have a great range of aggregate colours available.
In-situ Concrete, also known as insitu concrete, is an outstanding landscaping construction technique. In terms of long terms long term quality, robustness and longevity very few landscape construction techniques come close. To many people in-situ concrete is better know as landscaping architectural concrete and it is the point where landscaping, architecture and civil engineering all meet in landscape design. For the landscape design of public spaces, architectural concrete or in-situ concrete is a great choice for the severe use of our landscaped parks, gardens or commercial buildings. Some other names for in-situ concrete include “poured in place” concrete or “cast in place” concrete”.
What is in-situ concrete?
In-Situ Concrete cast in place.
In-situ is concrete that as poured into formwork at the building site. When compared to pre-cast concrete, in-situ requires no crane or forklift to get it into position. In comparison with concrete block and rendered retaining walls, the very low porosity of sealed and vibed in-situ walls will ensure a quality finish for decades of use. With concrete block retaining walls, the blocks themselves will have some porosity which will allow moisture to creep under the rendered surface and may cause it to lift in a few years. In-situ concrete has the colour mixed in and the texture is provided by the formwork but it can be rendered if required.
In-situ Concrete pumped into the formwork through a boom.
In-Situ Concrete – strong connection to footings.
An additional advantage with in-situ is it has a very strong and stable attachment to the very solid footings underneath. This is due to the reinforcement bars coming up from the footings and overlapping with the in-situ concrete steel reinforcement. When compared with concrete block retaining walls, although the steel reinforcement runs up through the centre of the blocks, any voids in the concrete around the reinforcement can lead to corrosion of the reinforcement bars and concrete cancer. The homogeneity of the of the vibed in-situ walls also ensures a good attachment to the steel reinforcing bars and does not suffer the risk of a poor attachment of the core concrete to the inner void of the concrete blocks. Pre-cast concrete will usually require mechanical fixings to the footing. These fixings can corrode over time or can be ground off by vandals. Being securely attached to the footings is a big advantage of in-situ concrete. Newly constructed public spaces such as parks and gardens will often rely on these quality advantages of in-situ concrete.
Retaining wall footings with steel reinforcement protruding to give the retaining wall a strong connection to the footing. The reinforcement bars must be accurately placed.
Precast concrete versus in-situ in landscaping concrete architecture.
One of the advantages of precast concrete is that it is manufactured under controlled conditions in a factory. This ensures a consistent quality product. There can be a risk however of coloured concrete coming from different batches resulting in slightly different colours close together. The quality advantages of precast concrete can be matched by in-situ concrete with close attention to the details and quality control of the processes.
Quality in-situ concrete retaining walls, stairs and seating.
Commercial Retaining Walls Melbourne
Good quality in-situ concreting requires a lot of attention to the materials and the processes. In-situ concrete wall also need to consider the safety as well as the aesthetics of a public space or residential landscape construction project. A well constructed, quality, curved in-situ concrete wall will achieve both of these aims.
Stripping the formwork off the walls. Extra effort and attention to detail will result in a quality finish on the retaining walls.
Quality In-situ concreting footings.
Concrete sets by a chemical reaction and not by drying. The chemical reaction is ecothermic and water is part of the reaction. If there is a difference in temperature within the concrete or if the water evaporates quickly from the top surface, then cracking can be the result. Concrete footings should not be poured in freezing conditions or below 5 degrees. Fortunately, in Melbourne there are very few days when it is too cold to pour. In hot weather the concrete should not be poured during the hottest part of the day or in extremely hot weather. The top part of the footing can be kept moist with hessian or a light sprinkling of water to prevent the top layer of the footing being weaker.
Concrete reinforcement bars in the footings.
It is essential that the vertical bars coming out of the footing are located accurately. When the in-situ walls are poured, these bars need to be closed to the centre of the retaining wall with good overlap with the wall reinforcement. The concrete reinforcement within the footing should be encased within the concrete as much as possible to minimise the paths for moisture to get into the reinforcement.
Concrete footing design
If designing for in-situ concrete retaining walls, the concrete footing should be a suitable size for the wall, keeping in mind all of the loads on the wall including hydrostatic and mass of the wall. The design of the footings must be to Australian Standards.
Formwork for in-situ concrete retaining walls.
Quality in-situ walls require formwork that is smooth strong and flexible. Any defect, imperfection of inaccuracy in the formwork will show up in the surface of the wall. The formwork needs to be strong enough to resist the weight of the wet concrete without bulging or deforming. Deflections in timer formwork will show up as ripples in the finished wall. A bulge in the formwork due to the hydrostatic load of the concrete will be a disaster when removing the formwork from the wall. The wall should be designed with a slight draft angle to make the removal easy without causing any damage to the retaining wall.
Strong supports for the formwork keep the wall dimensionally correct.
Accurately positioned formwork under construction.
Pouring the concrete retaining walls. Using the concrete vibrator to get a quality finish and good adhesion to the reinforcement.
Stripping the formwork after the concrete pour. The formwork should be left on as long as possible to prevent the concrete drying excessively during curing. Taking the formwork off too early can result in microcracks in the concrete.
Stripping the formwork after the concrete pour and curing to show a quality result.
In-situ concrete steel reinforcement
The steel reinforcement bars must have a good overlap with the footing reinforcement bars and well encased within the concrete wall. Reinforcement to close to the surface may result in water ingress and concrete cancer.
Pouring the in-situ concrete.
The concrete walls should be poured in one go and definitely from the same batch of concrete. Any interruption of the pour may show up as a line in the finished wall. The freshly poured concrete should be thoroughly vibed to ensure there are no voids within the concrete especially on the outer surfaces or at the interface with the reinforcement.
The steel reinforcement within tin-situ also helps to prevent surface cracking. To minimise the surface cracks, we leave the formwork in place a little longer to keep the moisture in during curing. The concrete should then be given a light sprinkle of water once the formwork is removed as it is still curing. The concrete will not be fully cured for a few weeks so consider this before applying any excessive loads.
Landscape and Concrete Design
Landscape Design with in-situ walls.
In-situ walls give the landscape designer or the landscape architect enormous freedom to design shapes for retaining walls, seating or concrete stairs that would be very difficult, if not impossible, using precast of other landscape construction techniques. In-situ walls can be designed into three dimensional shapes that would be impossible or expensive to do as Pre-cast. Curved retaining walls on an uneven landscape would be very difficult to achieve with any other landscape construction technique. Another advantage is the wide range of colours available.
In-situ concrete curved seating. Shapes like this are difficult with other landscape construction techniques.
Concrete stairs Cast in Place. This process is ideal for intricate or bespoke designs.
Exposed aggregate path and in-situ curved garden retaining wall. Overflowing Australian native grasses in the garden bed soften the look of the concrete. The exposed aggregate path provides an attractive contrast to the wall and plants. It is also a safe non-slip cost-effective solution.
In-situ retaining wall and steps
Curved In-Situ retaining wall prior to the final touch up and surface treatment. The joins in the formwork will be visible until the concrete is ground back to an even join.
As the concrete is pumped in, damage to other landscaping structures can be avoided, making it easier for the landscape project planner to schedule the construction. These are important factors to consider when landscaping Melbourne public spaces.
A very straight In-Situ retaining wall.
Exposed aggregate pathway and in-situ retaining wall prior to filling and grinding by the concrete finisher. There will always be a few small voids to fill, but theses can be minimised with the vibe during the pour.
Concrete architecture in landscaping is often seen of as a brutalist approach to landscape design. It is however possible to soften the design of concrete architecture with the use of landscape design techniques such as ponds or garden beds as well as using textiles such as cushions. The concrete architecture can also be softened with the use of naturalistic materials in the garden design such as timber or terracotta pots. The bringing together of cottage garden design with concrete architecture create a fusion of two very different garden design themes.
Naturalistic materials like these garden rocks help to soften the look of the in-situ concrete stairs.
Concrete Architecture design ideas
To see how to use concrete architecture in garden design, a visit to one of the bigger garden shows will help. Possibly the most famous of these shows is the annual Chelsea flower show held over 5 days in May each year. Unfortunately, there will be no show in 2020. Due to the time constraints of a 5-day garden show, much of the concrete will be precast elsewhere and craned into place. To see examples of in-situ concrete, a visit to some of the recently constructed Melbourne public spaces such as Balwyn Community Centre or the Sunbury Global learning centre will provide some ideas.
Concrete Architecture can be softened with garden plants and garden furniture. Sunken garden Chelsea Flower Show Gold Medal winner 2018. Kate Gould Gardens. Designed as a concept for a traditional square London West-End garden.
Formal blocks of stone and concrete with foxgloves. Skin Deep. Garden designed by Robert Barker design. The blocks represent different human faces and skin conditions. Note the use of colour and texture in the concrete blocks. Plants were also chosen for form and texture.
An outdoor kitchen design using a concrete bench with cooktop, wooden paling fence and vertical kitchen garden. Urban Flow by Tony Woods combines bold landscape design with practical solutions.
Garden Pond. Landscape design idea. A pond with overhanging flowers will soften the look of the garden.
Great colour coordination with the natural concrete colour with matching outdoor couches. Note how the cushions match the colours of the garden. Chelsea Flower Show 2018. Landscape design by Hay-Joung Hwang.
The LG Eco-City Garden by Hay-Joung Hwang, represents one housing unit in a vertical forest. Note the use of coloured stone to provide a theme through the garden. The concrete has been softened with the use of soft furnishings, abundant lupins and a pond with concrete stepping stones.
Garden idea. Pond with concrete stepping stones. LG Eco-City Garden Chelsea Flower show 2018.
Curved garden seat with irregular stone paving. Design by Naomi Ferrett Cohen – Chelsea Flower show 2018.
Concrete is without a doubt it is one of the most widely used materials in landscape construction. From sleeper retaining walls to pavers to post reinforcements to it has a wide range of uses. In this blog we will discuss some of the different types and its uses of in landscape design. To properly decide on which mix to use, it is important to understand what it is and what factors affect its physical properties.
What is it?
In technical terms, it is a structural material consisting of a hard, chemically inert particulate substance, known as aggregate that is bonded together by cement and water. It is a composite material as it consists of both a binder and a filler. The binder most commonly used is known as Portland Cement. This is a mixture of finely ground limestone (CaCO3) and shale or clay which has been combined together at around 1500℃. In this process, water and carbon dioxide are removed from the mixture (calcination), then calcium silicates are formed. A small amount of gypsum (CaSO4•2(H2O)) is added to regulate the setting.
Concrete with exposed aggregate.
The aggregate, that is the part of the mix made up of several smaller ingredients, will generally be the sand and gravel. The gravel itself will usually be hard stones of a certain size range. Fine aggregates are below about 10mm in size and are often used in small bags of cement mix or for smaller landscaping work. Larger stone aggregates range from 10 to 40mm in size and are commonly used in construction. It is the stone aggregates that give the mix its compressive strength. As the aggregate is around 70% of the mix, it provides much of the bulk and contributes to its dimensional stability. The rougher the surface of the aggregate and the greater the area in contact with the cement paste, the stronger a concrete will be.
Rounded particles like river pebbles or beach sand will result in lower strength than crushed aggregates. Larger size aggregates lead to relatively lower strength. Where extra strong mix is needed, a little less aggregate can be used.
A key ingredient is of course the water. When the water is combined with the cement as paste is formed which binds the aggregate together. Concrete does not harden by drying out, it hardens by a chemical reaction know as hydration. In this reaction, compounds in the cement react with water molecules to form strong chemical bonds. Ideally, the water should be as pure as possible to prevent the occurrence of any side reactions which may weaken or interfere with the chemical reaction taking place. Even small quantities of organic soil compounds result in chemical reactions that seriously affect the strength. In Melbourne access to good quality water is not usually a problem.
The other important point for the landscaper is to get the ratio of water to cement correct. The ratio of water to cement is critical if strong concrete is required. If too much water is added, the strength of the mix will be reduced. Excess water above what is required for the chemical reaction will result in pores on the concrete which will reduce the strength especially the tensile strength. Too little will make the it difficult to work, to fill spaces, or create a good connection to the reinforcement. Accurate measurements and thorough mixing of the cement and water will help prevent these problems.
Concrete sets with a chemical reaction not by drying.
It is set by a chemical reaction and not by drying. This means that it will even will set under water. It is important to remember this fact during the curing stage. The two main hydration chemical reactions from the calcium silicates are as follows;
Tricalcium silicate + Water—>Calcium silicate hydrate+Calcium hydroxide + heat
2 Ca3SiO5 + 7 H2O —> 3 CaO.2SiO2.4H2O + 3 Ca(OH)2 + 173.6kJ
Dicalcium silicate + Water—>Calcium silicate hydrate + Calcium hydroxide + heat
2 Ca2SiO4 + 5 H2O—> 3 CaO.2SiO2.4H2O + Ca(OH)2 + 58.6 kJ
Both of these reactions are exothermic, that is, they release heat. This heat will dissipate quickly in thin sections. In thicker sections, the internal temperature is transferred to the outside much more slowly. As the outer surface of the concrete will cool much more rapidly than the inner core, there can be a difference in reaction speed. This can lead to tensile stresses that can crack the surface as a result of this uncontrolled temperature difference across the cross section. For this reason, concrete should not be poured in very cold temperatures. In cases where thermal cracking does occur, it will be at early ages of curing. The heat can also cause moisture to evaporate from the surface of the concrete, making it weaker. This will be the case if there is insufficient water for the chemical reaction. For these reason excessively thick sections should be avoided in a single pour. Wooden formwork and damp hessian covers can help the curing process. Giving your concrete a very light spray of water as it is curing will often improve the strength.
History of concrete
What have the Romans ever done for us? The Romans are widely credited for the spread of building technologies including concrete throughout Europe. It was the Roman’ Empires’s engineering abilities that enabled them to built an enormous empire throughout Europe and through parts of North Africa and the Middle East. The concrete architecture of the Romans is famous amongst fans of history.
Durable Roman Concrete has lasted centuries.
The Roman formula for quality concrete
It was know to the Romans as “opus caementicium”. Opus meaning a fortification, composition or a piece of work and caementicium meaning quarried or unhewn stone. The Romans developed their recipe in the third century BC. The ingredient the Romans used was volcanic dust known as pozzolana. This volcanic dust included fine particles of alumina and silica which created the chemical reaction enabling the setting. To this they added a mixture of lime or gypsum, brick or rock pieces and water. Usually the mix was a ratio of 1 part of lime for 3 parts of volcanic ash.
Roman builders discovered that adding crushed terracotta to the mortar created a waterproof material which could be then be used with cisterns and other constructions exposed to rain or water. Recently, it has been found that the Roman mix used in seawall construction has better endurance to seawater than the modern stuff. This was mostly due to one of the minerals of the volcanic rock phillipsite, reacting with the seawater to form aluminous tobermorite which reinforced the concrete over time. After the fall of the Roman empire the technology for making concrete was lost for many years.
Assyrians Babylonians and Egyptians.
Among the ancient Assyrians and Babylonians, clay was often used as the bonding material. The Egyptians developed a substance more closely resembling modern concrete by using lime and gypsum as binders. Lime (calcium oxide), was derived from limestone, chalk, or (where available) oyster shells. (Pozzolans are actually a broad class of siliceous or siliceous and aluminous materials.)
In 1824 an English inventor, Joseph Aspdin, burned and ground together a mixture of limestone and clay. As the chemistry of concrete was not fully understood at the time, the proportions of the ingredients were developed by trial and error. This mixture, called Portland cement, has remained the dominant cementing agent used in concrete production. It is named Portland cement as it is an attempt to imitate the limestone from Portland in Dorset on the jurassic coast of England. Portland Limestone formed slowly over the last 150 million years or so as tiny grains of sediments and clays infused the limestone grew and compacted. This gives it both its unique physical properties when grown up for cement, but also its attractive appearance. Portland Limestone has been used in many of the iconic London buildings such as Saint Paul’s Cathedral and the palace of Westminster. As a building material Portland Limestone was popularised by architect Sir Christopher Wren.
On of the drawbacks of concrete, despite its great compressive strength, is its lack of tensile strength. This is largely due to its natural porosity. Plain unreinforced concrete does not easily withstand stresses such as wind action, earthquakes, and vibrations and other bending forces and is therefore unsuitable in many structural applications. Low tensile strength also means low strength in bending or when used as a beam. Steel on the other hand has great tensile strength. The solution is to embed the steel into the concrete. This is usually achieved with the use of steel mesh reinforcement. The reinforcing steel, normally takes the form of rods, bars, or mesh. The reinforcement bars are often coined along the surface to give them a good connection to the concrete. The addition of tightly bound reinforcement bars makes the concrete section into a true composite beam. For this reason, the reinforcements must overlap.
Bending stresses are not normally a problem with garden paving when a properly prepared sub base has been created. Steel reinforcement will however, help to prevent cracks opening in the pavement.
Landscaping concrete. Steel reinforcement helps to prevent large cracks opening up in your concrete.
For paving, the steel mesh should be placed about 30mm from the top surface. When reinforcement steel is placed too near the surface, it can corrode. Expansion results as steel is converted to iron oxide through corrosion. This expansion can crack the concrete surface. When the crack is caused by corroding steel, corrosion is typically visible at the slab surface. In the case of retaining walls, the wall is in effect a cantilever beam with the soil applying pressure to the wall. Steel reinforcement will help increase bending strength of the wall.
Reinforced concrete is usually attributed to Joseph Monier, a Parisian gardener who made garden pots and tubs of concrete reinforced with iron mesh.This was patented in 1867. In reinforced concrete, the tensile strength of steel and the compressional strength of concrete render a member capable of sustaining heavy stresses of all kinds over considerable spans. Despite the strength of reinforced concrete, efforts should be make to minimise the loads on garden retains walls. This can be achieved by adequate agricultural drainage near the wall. It is important to remember that a cubic metre of water weighs a tonne. Plant selection near the retaining wall is also important plants should be chosen that do not have an invasive root system. For your existing trees, consider the use of a tree root barrier.
Architectural Concrete in Melbourne
Modern concrete is now available with an enormous range of colours and textures. There are some available that can mimic the appearance of stone, but at a much lower cost to the landscaper. There are also some techniques by landscape architects to break up a large expanse of concrete by using alternating contrasting colours.
Exposed aggregate Concrete Pathway using alternating coloured concrete. The appearance is also softened by the mulched garden bed with plantings of native grasses. These architectural concreting techniques provide a very cost effective solution but maintain the aesthetic appeal.