Landscaping Concrete must to 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 important to pick the correct one for the job. Coupled with this, there are different grades of steel reinforcement to choose from.
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.
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. If you are in a part of Melbourne with a reactive clay soil, you need to ensure there is sufficient thickness of roadbase under the paving to cope with the expansion and contraction of the soil.
Preventing Cracks in landscaping 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 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.
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.
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 and accelerate the concrete cancer.
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.
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.
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.
Related Concrete information from Red’s Landscaping and Civil
For help with the design and development or 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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