Concrete silage clamp floors are part of the landscape, it’s what we have always done, but is there a better way? There might be - and there certainly should be - because there are loads of issues with traditional concrete floors. Concrete floors are tough, long lasting and can be formed without specialist kit or contractors so that’s probably why they have become the default choice. However the toughness leads to some disadvantages too. So let’s examine the pros and cons of a concrete clamp floor.

Concrete floors are tough

Concrete is tough and floors can withstand really high levels of trafficking without noticeable degradation. This is important in a silage clamp where you are moving several thousand tonnes of material in and then out every year.

This toughness also means that a concrete floor can compensate for local areas of poor sub base. Chances are you would never know if there was a soft spot or a small hollow in the stone under a really good concrete floor because it can “bridge” small areas without failing.

Concrete floors don’t melt in the summer

Concretes inherent properties mean that its thermal properties are robust. This means that it doesn’t become “soft in the sun” or “brittle in the cold” like some other materials and that’s a benefit in a silage clamp. Its thermal properties also mean that it needs movement joints so it can expand and contract and we will look at these in detail elsewhere.

Concrete floors can hold the walls up

This is also true as almost all wall types rely on a connection with the floor of the clamp; the weight of silage on the floor acting as a cantilever to resist the forces trying to push over the walls. Whilst it is possible to design a wall that’s completely independent of the floor – it’s not the most efficient (and therefore not the cheapest) solution.

On the downside, there are some significant issues with concrete floors that mean it’s far from an ideal flooring material for a silage clamp.

Most of the issues with concrete floor slabs in silage clamps come down to the presence of silage effluent on the floor. A concrete floor needs movement joints and these joints are a potential weak spot for leaking the effluent into the environment.

The other main problem is caused by the action of the silage on the concrete material. The big issue is the basic chemistry – silage and its effluent are highly acidic and concrete is highly alkaline. This will result in an inevitable chemical reaction that will see the concrete being broken down, and as with all chemical reactions, this will speed up in higher temperatures. In the clamp during fermentation we all know that it gets very hot so what we have created are the ideal conditions to destroy concrete! More effective than jack hammers or TNT, strong acids will destroy the bonds within the concrete matrix causing it to literally crumble.

So why are we using a material that’s inherently unsuitable to containing acids, for the floors of a silage clamp? Well let’s look at what we are really trying to achieve with the clamp floor. 

Until the implementation of pollution regulations, you didn’t actually need a floor at all; the earth was good enough, but not any longer. The SSAFO regulations now state that you must provide an impermeable floor slab to your silage clamp. Impermeable might not be the most appropriate term from the regulators to have chosen, as there is almost no material that is completely impermeable. We therefore have to interpret impermeable to mean “leak proof to silage effluent”?

OK, to make a floor that doesn’t leak, we want to make sure it doesn’t move and that’s why you don’t build on made up ground etc etc – as we have seen elsewhere in this blog series. It’s also really important that you get the sub base right; get this right and the floor slab is just a capping seal on top of the sub base. If the sub base isn’t right, then the floor has to be built like a motorway bridge to compensate for any settlement or movement – and that’s expensive and difficult. So number one – get the sub base right.

So what about tarmac as a silo base?

Tarmac has some benefits compared to concrete for use in a silage clamp. Most importantly it’s extremely resistant to silage effluent – or at least it can be if the material choice is correct.

Secondly the “flexible” nature of tarmac - or asphalt as we should really call it – means that a floor slab can be designed without any joints. This is a massive benefit as most failures of a silage clamp floor occur at the joints so designing a floor without joints is a great start. An asphalt floor can also be easily and quickly repaired without specialist detailing and long curing times.

And finally asphalt has lower permeability than concrete and this, together with a lack of joints, makes it more “SSAFO compliant” than concrete as a floor slab choice.

On the down side, you need a specialist contractor to form an asphalt floor and it’s more susceptible in high temperatures leading to softening and deforming under heavy traffic loads. It also doesn’t hold the walls up so the cost of building the walls will be a bit higher.

So should I choose concrete or tarmac for my clamp floor?

We you certainly have to choose one or other according the to SSAFO regulations. These now state that the floor has to be made or either concrete or asphalt – or maybe both?

It is possible to get the benefits of both materials! A good asphalt floor slab will be made up of 120mm to 200mm of base course with a topping of 40mm to 60mm of “wearing course”. As an alternative, you can use a 150mm concrete floor slab that can be employed to absorb the wall loads and then overlay this with the 40mm to 60mm of asphalt wearing course.

What’s the cheapest clamp floor?

This will obviously depend on circumstances but as a general rule of thumb, for smaller clamps concrete wins, and for larger areas asphalt will be cheaper. The hybrid will almost always be a bit more expensive in initial cost but may have benefits over the lifetime of the clamp.

If you want to discuss the benefits and relative costs of silage clamp floors with an independent consultant or to discuss any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com

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