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“Never before, has the selection and implementation of the most suitable surface regularity specification been more critical than in today’s production, storage, and distribution facilities. As the demand for faster and more efficient Industrial floor increases and truck developments continues there is the role of surface regularity specifications.

The selection of the appropriate specification is crucial.  Especially because it is common to find over specified floors that are not suited for the clients' specific performance requirements, which require more time, resources, and money to accomplish.

Surface regularity specifications are divided into two main categories, according to the type of movement the Materials Handling Equipment (MHE) are able to do.

I) Free Movement (FM) specifications correspond to MHE that may operate in all directions and undefined paths within the facility.

ii) Defined Movement (DM) specifications correspond to MHE that may operate within a defined path, area, and direction within the facility. These facilities implement a Very Narrow Aisle (VNA) system.

Ground floor slabs in Warehouses and Distribution Centres are integral to the efficient operation of the facility. They are the tabletop on which an operator runs his business. On the surface, they appear to be one of the simplest parts of a structure to construct. However, this simplicity often leads to an underestimation of the design and construction requirements. A well designed and constructed floor will increase productivity, reduce maintenance of the building, and increase the life of the equipment using the floor.

A floor design should be performance-based, and this starts with understanding the requirements of how the floor will be used. Most Floor designers will be given a brief from the warehouse owner to ensure the floor will take the imposed loads, be flat, long-lasting, and aesthetically pleasing, and it will be able to fulfill their responsibility to draw up the performance specification. The specialist flooring contractor should consider the construction methods, program, cost, and any value engineering they can bring to the design. Compromises may have to be made in developing the final design of the floor, but the result should be one that is economically designed and built to meet the performance requirements.

This stage requires designing the total load on the floor, base, and subbase, grade of concrete, floor hardener, construction joint, contraction joint, expansion joint, type of sealant.

 

The structural design of a floor will follow engineering principles and calculations and requires knowledge of the following in order to determine the slab thickness and reinforcement.

1) Ground conditions

2) Strength of the concrete

3) Thickness of the concrete

4) Method of reinforcement    

5) Load transfer capability of the joints

6) Loading specification and loading pattern

Guidance on the design of a floor is specified in-detailed in the UK Concrete Society's Technical Report 34 (Tr34).

A detailed design covers key performance requirements, including-

1) Joint layout and joint design                          

2) Construction methods

3) Method of reinforcement

4)  Surface regularity (flatness and levelness)

5) Abrasion resistance

Advice from all the stakeholders of the floor should be sought before the design is finalized.

Suitable ground conditions are essential for ground supported slabs, and it is therefore important that a ground investigation is carried out and interpreted by a competent geotechnical engineer. The geotechnical engineer must advise on the suitability of the ground along with any recommendations for ground improvements.

The primary purpose of the sub-base is to provide a level base for the floor slab. It should be capable of carrying construction traffic without rutting. The sub-base should be of a minimum 200-250mm thick well-graded material. The level tolerance of the sub-base is of great importance. A high sub-base generally means a thinner concrete floor (+ Zero to – 25mm is recommended).

Slip membranes are used to reduce friction between the slab and the sub-base so as to reduce the restraint to drying shrinkage, thus reducing the risk of unplanned cracking. A 300-micron plastic sheeting is recommended.

Concrete not only plays an important role for durability and strength, but also for leveling course. This shows the extent to which the concrete shows flexibility if designed and executed properly.

There are comprehensive Standards for the specification and testing of concrete. High strength concrete is not needed and should be avoided because it tends to have higher cement content and is more likely to shrink than lower strength concrete. It can also be difficult to finish. 

Although reinforcement will give some enhancement to the structural load capacity of the floor slab, its primary function is to restrain the opening of sawn-induced joints and to maintain good load transfer properties.

The traditional method of reinforcement in jointed ground supported slabs is with steel mesh. The position of the mesh is usually specified to be 50mm from the bottom of the slab. Alternatively, floors can be reinforced with steel fiber also. The joints can become wider than predicted and load transfer between sections of the floor can be lost. This can result in floor movement at the joints and a breakdown of the joint.

Joints are the most critical element in a floor. Most maintenance requirements are related to the breakdown of joints in some form. Joints create unavoidable discontinuities in a floor which can be damaged by mechanical provided for two purposes:  To form the boundaries of each day's concrete pour (Construction Joints)  To reduce the risk of cracking as the floor shrinks (Contraction Joints and isolation details)Construction joints must incorporate dowels to provide a load transfer mechanism between the sections of the floor. 

Floors must be isolated from fixed elements of the building to allow the floor to contract without cracking. This is achieved by surrounding columns with compressible materials. These are known as isolation details.

Ground-supported slabs can be jointed or jointless.

 1. Jointed floors have construction joints at the edges of each day's concrete pour, and they typically have sawn joints at 6m intervals.

 2. The term jointless is something of a misnomer as all slabs have construction joints at the edges of areas of the floor that are poured in any one day. On a jointless floor, these are the only joints. Joints are provided to permit breaks in construction and to allow for shrinkage as the concrete dries out over a period of up to 2 years.

Floor Flatness (FF) controls the local bumpiness of the floor surface and is primarily affected by the finishing operations after screeding, including straightening, and power floating. Floor Levelness (FL) controls the departure of the floor surface from the specified slope or plane of the surface. FL numbers evaluate the elevation differences along a sample line at 3 m intervals. The higher the FL number, the more level the floor. The Levelness of the edge forms and the accuracy of the concrete screeding operation control the overall levelness of the floor.

 

A Surface hardener is applied to the concrete surface after it is smoothed and left to dry. This helps to improve the concrete's abrasion and chemical resistance, thus significantly improving the durability of the concrete surface. It is non-metallic in nature. Non-Metallic Floor Hardener is designed for use as a surface hardener for concrete floors, which are subject to wear due to abrasion or impact from light to medium traffic.

The floor shall be cured properly, the floor shall be submerged in the water for at least 7 days from the date of Pouring and no vehicle shall be allowed to move on the floor before 21 days of the Pour date. There are different ways of curing- by water flooding the panel or by a curing membrane. At our site, we used to cover the Panel with LDPE Sheets and above it, we used to pour the water. This way, we used to ensure that the floor is properly cured and taken care of.

 

In an environment where the Materials Handling Equipment (MHE) operates without suspension systems, the warehouse floor is the all-important surface that affects the speed, efficiency, maintenance needs, and often the safety and movement of the distribution center operatives and they are manually or automatically operated hardware. For this type of requirement, in today's time, the FM level floor has become mandatory.