(is cheaper really better?)
There is a growing trend towards the use of unreinforced concrete floors in slab designs. There are merits and concerns with this approach, especially in heavily-loaded forklift environments. There are many factors to consider in slab design for an owners particular usage, and an unreinforced solution should only be employed after carefully considering the advantages and disadvantages.
There are essentially two types of unreinforced floors being employed today: Type 1: with dowel reinforcing at construction joints but without any reinforcing at the sawcut contraction joints and Type 2: with reinforcing at all floor joints. A type 1 floor may be suitable for foot traffic in the short term, but without any reinforcing at the sawcut contraction joints, curling and differential joint movement are very possible (especially in architectural pavements). Floors without any reinforcing across the sawcut contraction joints typically exhibit poor load transfer across joints after 1–2 years of exposure to forklift traffic, which are free to move vertically from one side of the joint to the other. Floors without any reinforcing at the sawcut contraction joints in heavy vehicular traffic environments are simply not a good solution for an industrial floor. While the cost may be low, the performance of these floors in the long run may prove to be problematic in terms of material handling concerns, repair expenses and downtime.
The theory behind unreinforced Type 1 floors (without any reinforcing at the sawcut contraction joints) is that the interlock of the concrete aggregates across a joint will provide for the transfer of loads across the joint. The problem with this theory is that: 1) concrete aggregates are not very durable and wear under heavy traffic over a short period of time and 2) “aggregate interlock” is based upon the notion that the floor joints will not widen by more than 0.035″ (when they commonly open by double this amount).
“Steel is the best thing that ever happened to concrete.”
If your floor is subject to forklift traffic then you need to understand that the high frequency and concentrated impact that is induced by this type of traffic creates significant fatigue across these joints that must be managed by the inclusion of steel fibres, wire mesh, dowel baskets, or rebar and a good joint filler. It is as simple as that.
Unreinforced concrete is notorious for cracking easily at any sources of stress. All points of restraint need to be carefully managed to avoid these drying shrinkage stress cracks. Unreinforced concrete cracks at all thickenings, ends of embedded steel, bollards, pit corners and down the middle of aisles. The inclusion of additional jointing, at a shorter spacing, is a necessary component of a good unreinforced slab plan. The problem arises however that more joints are generally not a good solution for a floor subject to forklift traffic (more joints = more maintenance over time).
Unreinforced floors are generally 1″–3″ thicker than reinforced floors as well. Thicker does not equal better. In this new age of designing green structures it is common to minimize the cement component whenever possible. A thicker concrete design, using more cement and aggregates, is less GREEN than a thinner reinforced design based upon steel fibres. It is imperative that low shrinkage plasticized concrete mixes be used with unreinforced slab designs (using “water only” mixes increases problems with shrinkage and performance).
If you have any questions, please feel free to e-mail.