Level to datum is a measure of departure from a fixed plane (datum) specified by the designer. The tolerance is usually ±15mm about that plane. In general the actual level of any edge formwork and the concrete placing and compacting process will influence the level accuracy of the finished surface.
The surface profiles of a slab need to be controlled so that departures from a theoretical flat plane are limited to an extent appropriate to the planned use of the floor.
A method of assessing flatness was given in CP 204: 1965 In-situ floor finishes (metric edition 1970) which used a 10ft (~3m) straight edge that was not set directly on the slab but on feet.
As the name implies, formwork liners are mainly sheet materials which are incapable of withstanding the pressure of fresh concrete without continuous structural support from the formwork. A variety of different materials can be used as linings to formwork to produce textured and patterned finishes to concrete.
Dry-shake toppings are used for horizontal elements such as slabs. They are combinations of cement, pigments, surface hardener and well-graded fine aggregate. The material is broadcast onto the surface of the fresh concrete and then floated and trowelled-in. As well as colouring the concrete it forms an impervious hard-wearing surface which is well suited to applications such as warehouse flooring. The quality of the surface achieved is dependent upon good workmanship and finishing skills.
There is often debate about the time limit between placing fresh concrete against fresh concrete already placed and compacted i.e. minimising the risk of a cold joint being formed.
Kickerless construction for positioning vertical formwork off a slab has the following advantages over the construction of a traditional kicker against which the vertical forms are clamped:
The trend for recycling of municipal refuse in the UK has led to the construction of a significant number of new domestic waste transfer facilities. In many of these facilities the domestic waste is tipped directly on to concrete floors from refuse collection vehicles and then handled by loading shovels. It has been observed that some of these concrete floors have experienced extremely high levels of abrasion resulting in a rapid surface loss. Wear rates in excess of 25mm in one year have been reported. Floors experience lower levels of abrasion where waste is tipped directly into a waste bunker and is then handled by grab crane.
In cold weather, it may be an advantage to raise the temperature of the fresh concrete at the batching plant so that the concrete retains a sufficient temperature to promote setting and strength development to off-set the risk damage caused by early age freezing. Heating the mixing water is the simple way to warm the fresh concrete.
Concrete geothermal piles are structural concrete piles which incorporate pipework for a geothermal heat exchange system.