In-situ concrete retaining wall and garden steps.

In-situ Concrete

In-situ concrete, also known as Cast-in-Place concrete, is an outstanding landscaping construction technique. In terms of long-term quality, robustness, and longevity, very few landscape construction techniques come close. To many people, in-situ concrete is better known 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. For these reasons, in-situ concrete is now widely used by commercial landscapers in Melbourne. 

Other names for in-situ concrete include "poured in place" concrete or "cast in place" concrete.

What is in-situ concrete?

In-Situ concrete is cast in place.

In-situ means concrete that is 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 - Reds Landscaping & Design
In-situ Concrete pumped into the formwork through a boom.

In-Situ Concrete: Strong connection to footings

An additional advantage of in-situ is that 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 vibed in-situ retaining 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 the quality advantages of in-situ concrete.

Retaining Wall Footings - Reds Landscaping & Design
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.

Another advantage of precast concrete is that it is manufactured under controlled conditions in a factory. This ensures a consistent, high-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 walls 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. For this reason, always employ only skilled commercial concrete contractors.


Stripping the formwork off the walls - Reds Landscaping & Design
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, 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 within the surface of the wall. The formwork for commercial concrete construction 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 - Reds Landscaping & Design
Strong supports for the formwork keep the wall dimensionally correct.


Accurately Positioned Formwork - Reds Landscaping & Design
Accurately positioned formwork under construction.


Pouring the concrete retaining walls - Reds Landscaping & Design
Pouring the concrete retaining walls. Using the concrete vibrator to get a quality finish and good adhesion to the reinforcement.



Commercial Concreting - Reds Landscaping & Design
Stripping the formwork after the concrete pour. The top tip from commercial concreting is that 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.


Commercial Concreting Melbourne - Reds Landscaping & Design
Commercial Concreting Melbourne at our Balwyn North Construction site. 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 be well encased within the concrete wall. Reinforcement too 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 the in-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 or 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 part of our commercial concrete construction Melbourne portfolio - Reds Landscaping & Design
In-situ concrete curved seating. Shapes like this are difficult with other landscape construction techniques.


Concrete Stairs Cast in Place - Reds Landscaping & Design
Concrete stairs Cast in Place. This process is ideal for intricate or bespoke designs.



In-situ curved garden retaining wall - Reds Landscaping & Design
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 - Reds Landscaping & Design
In-situ retaining wall and steps


Curved In-Situ Retaining Wall - Reds Landscaping & Design
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.

In-Situ Retaining Wall - Reds Landscaping & Design
A very straight In-Situ retaining wall.


Exposed Aggregate Pathway and In-situ Retaining Wall - Reds Landscaping & Design
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.

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© 2020 Reds Landscaping and Civil quality commercial landscaping Melbourne

More Information on Commercial Landscaping with In-Situ Concrete.

More information on visual concrete for landscape design

See also Concrete Architecture in Landscaping

Concrete For Landscape Design & Construction

Exposed aggregate Concrete Pathway

Landscaping Concrete

Landscaping Concrete must be the correct grade with the correct reinforcement for the job it is selected for. If this is not the case, cracking can occur. To properly decide on which mix to use, it is important to understand what it is and what factors affect its physical properties. There are many different grades of concrete available, so it's important to pick the correct one for the job. Coupled with this, there are different grades of steel reinforcement to choose from.

Pre-mixed Multipurpose Concrete for garden walls - Reds Landscaping & Design
Pre-mixed Multipurpose Concrete for garden walls


Garden Paving and Concrete Path Construction

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 from opening in the pavement.

Generally, the path should be at least 100 mm thick (N25) of concrete. N25 means that the concrete will achieve a compressive strength of 25 mPa after 28 days. If you are in a part of Melbourne with reactive clay soil, you need to ensure there is a sufficient thickness of roadbase under the paving to cope with the expansion and contraction of the soil.

Preventing Cracks in Landscape Concrete

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 design of the path. In these cases, the concrete needs to be at least 125 mm thick and N32 (32 mPa) concrete with SL92 mesh laid on at least 100 mm of class 2 roadbase.

Thermal Expansion and Contraction of Concrete

To allow for thermal expansion of concrete, saw cuts and isolation foam are essential for preventing cracks. It is important that the landscape architect as well as the concrete contractors keep this in mind.

concrete path needs an allowance for expansion - Reds Landscaping & Design
A concrete path needs an allowance for expansion.


Landscaping Concrete: Steel reinforcement helps to prevent large cracks from opening up in your concrete.

For paving, the steel mesh should be placed about 30 mm 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 and accelerate the concrete cancer.

Concrete block garden retaining wall - Reds Landscaping & Design
Concrete block garden retaining wall with coping next to the alternating exposed aggregate path.

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 the bending strength of the wall.

Concrete in-situ steps Mill Park Leisure centre - Reds Landscaping & Design
Melbourne Landscaper - Concrete in-situ steps Mill Park Leisure centre.

Landscaping Concrete - Reds Landscaping & Design
Melbourne Landscaper - Concrete in-situ steps Mill Park Leisure centre - Landscaping Concrete

Architectural Landscaping 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 - Reds Landscaping & Design
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.

Commercial Landscaping

In commercial landscaping, all the concrete must be to the grade specified by the architect and poured exactly to the drawing. Test samples are kept by the concrete supplier for each batch for testing after the appropriate cure time.

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Contact us

For help with the design and development of your landscaping ideas, contact one of our experienced landscape gardeners.

We can help with small garden design all the way up to commercial landscape design.

Our specialities include fast growing screening plants, plant health and horticulture, garden lighting  and in-situ concreting.

By Callum O’Brien – Landscaper Melbourne

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For more information on concrete

How to minimise thermal cracking

How it is made and the scientific principles.