Guide to Concrete Floor

GUIDE TO CONCRETE FLOOR Our know-how for your applications Guide to Concrete Floor Applications 2 Guide to Concrete Floor Applications Contents Concrete ........................................................ 4 Concrete Vibration ....................................... 6 Floors of Concrete ........................................ 9 Preliminary Planning ................................. 11 Laying Floors ............................................... 12 Sideforms and Screed Guides ............................................ 13 Track Rail System ....................................... 23 Fixed Rail Supports .................................... 24 Floors on Floors Structures Cast in Situ .................................................. 25 Cleaning, pre-moistening, etc. ................. 27 Conversion Tables ...................................... 41 Glossary ....................................................... 42 3 Guide to Concrete Floor Applications Concrete Concrete is a mixture of water, cement, sand and stone. The cement content affects concrete properties. A high Water content divided with cement gives w/c-ratio. The cement content gives a high strength whereas shrinkage water/cement-ratio is a theoretical average value and it unfortunately also will increase. may change during transport or vibration. What does concrete consist of? Cement W/C ratio Concrete is a mixture of water, cement, Cement and water are two important com- Water/cement-ratio means the ratio relation sand and stone. These four components ponents. water (kg) per cubic meter of concrete can be varied to a great extent and the Cement content means the amount of divided by cement content. It can be any- characteristics of the mix and the hard, cement by weight per cubic meter concrete thing from 0.80 to 0.30 at the mixing plant hydrated product itself can thereby be and can vary from 500 down to 250 kg per or in truck mixer. changed to a great extent. cubic meter. Many architects and engineers think that it is the only factor you have to worry about when you want quality concrete. But it is a little bit more complicated if you wish to get good concrete for fl oors. The lower the water/cement-ratio, the better the quality you get. But note that when you place concrete on site you will change the w/c-ratio in the slab. We will explain that later. 4 Guide to Concrete Floor Applications In certain countries sand means all material between Sand/stone-ratio is amount of sand divided with amount of Max stone size normally should not exceed 1/4 of the floor 0–4 mm, in others all material between 0–8 mm. stone. thickness. In Sweden, all material between 0–4 is normally called sand. Sand Stone Additives Sand type and the grading curve for sand Max. size of stones is dependent upon the A lot of admixtures and additives are are also important. Coarse sand is normally thickness of the floor/slab and should nor- avail able today. In hot climate a retarder better for high-quality concrete. In some mally not exceed 1/4 of the floor thickness, is sometimes needed. We recommend countries sand is 0 – 4 mm, in others all i. e. for a 100 mm thick floor, never use larger (except sometimes retarder) only air en- material between 0 to 8 mm is called sand. stones than 25 mm. training agents in floors that are exposed Sand/stone relation is the relation of But always use the largest possible size. to freeze/thawing like outdoor floors and sand and stones in percent of the total The higher amount of coarse aggregates freezingplants etc. Not in ordinary indoor amount of aggregate in one cubic meter. you use, the lower shrinkage you get and floors and no other admixtures. The con- If your sand is 0 – 4 mm, a good relation you can save cement. A high cement concrete mix characteristic is already affected sand/stone is 35 to 40 % sand and 60 to tent increases unfortunately both shrinkage by so many factors that the addition of ad- 65 % stone. If sand is 0 – 8 mm, the relation and also curling in the floor. mixtures can spoil the mix itself or cause should be 40 to 45 % sand and 55 to 60 % production problems. stone. Stones can vary from 4 – 8 mm up to 32– 40 mm. Often the stone part in good concrete is combined of two parts, one fraction A, 8 to 16 mm and another fraction B, 16 to 32 mm. 5 Guide to Concrete Floor Applications Concrete Vibration Concrete vibration is undertaken to improve Adequate vibration of concrete Three basic types of vibration its overall performance. Compaction is the will: can be used: process that expels entrapped air from freshly increase its strength and density and immersion (pokers) placed concrete thus increasing its density. thus allow the design strength to be surface (screeds, screeds) achieved form (external vibrators) It is important that the concrete vibration con- tinues until no further air bubbles can be seen enhance the bond to mesh and bar emerging from the surface of the concrete reinforcement plus any inserted struc- Immersion (poker) vibrators without exceeding the vibration period given tural anchors and hold downs and thus The most common immersion vibrator for in the table page 6. provide anchorage residential work is the poker vibrator. increase the abrasion resistance of the Following table shows the maximum The most common form of compaction is vibra- surface and thus reduce wear from yield that will be achievable per poker tion, undertaken with poker vibrators or surface traffic diameter (m³/h): vibrators such as vibrating screeds. Other increase the general durability and thus methods of compaction include form (external) provide longer life Poker of 25 mm = 1.5 m³/h vibration, tamping and rodding (wood or steel decrease the permeability and thus Poker of 35 mm = 6 m³/h rod). limit penetration of water and other Poker of 45 mm = 10 m³/h aggressive substances (both from air- Poker of 55 mm = 20 m³/h borne and contained in ground water) Poker of 65 mm = 25 m³/h reduce the risk of plastic settlement Poker of 75 mm = 35 m³/h cracking over deep screeds and mesh/ Poker of 85 mm = 40 m³/h bar reinforcement (plus other restraints Poker of 100 mm = 45 m³/h within the concrete) as well as longterm Poker of 150 mm = 45 m³/h drying shrinkage cracking improve the quality of off-form finishes Smaller sizes are often referred to as by ensuring concrete completely fills needle vibrators. They are typically driven the forms. by petrol motors, although diesel, electric and compressed air are alternatives. Adequate vibration of slabs up to 100 mm They are also good for expelling en- thick can generally be achieved through the trapped air voids in deep forms such as placing, levelling and finishing operations. industrial floors, slabs, screeds, columns Concrete vibration can however addition- and walls, and allow easy placement of ally be applied on the edge of the form to concrete. ease the placement of the concrete. The homogenized concrete will have For deeper elements, additional con- less porosities left inside the concrete pro- crete vibration will be required by one of viding a better wheel load capacity and the methods outlined below. lower cracks risks. Concrete vibration must be done as Internal vibration reduces internal friction soon as the concrete is placed in the form, between aggregate particles in the con- while it is still plastic. Don’t let the concrete and will thus liquefy the mix and ob- crete dry-out and stiffen because it will be viate the practice of adding excess water too hard to compact, resulting in a lack of to improve workability. vibration. 6 Guide to Concrete Floor Applications The radius is dependent essentially on the For deeper elements such as walls and diameter of the head/tube and the frequency columns, adequate space between the re- and amplitude of the vibration caused by inforcement or to the form face should be the rotating eccentric weight contained in it. provided to allow use of the poker vibrator. The effective radius determines the in- Generally, the vibrator should be kept about sertion pattern that should be adopted to 50 mm clear of the form face. ensure adequate compaction of all con- Damaged form faces will result in streaks crete. and colour variations in the surface, while Poker vibrators should be inserted ver- inaccessible areas will result in inadequate tically into concrete as quickly as possible, compaction. and held stationary until air bubbles cease For concrete of average workability (i. e. to rise to the surface. They should then be slump of 80 mm) with a poker size between slowly withdrawn to avoid grout pockets. 25 –75 mm, concrete should usually be vi- They should not be dragged through the brated for between 5 and 15 seconds. concrete or over reinforcement as this may You can also refer to the table below to cause segregation of the mix. know the required vibration period as per For honed finishes where the aggregates the given workability (slump, consistency). will be exposed, care is required to compact consistently over the entire area to ensure uniform exposure of the aggregate. Earth moist Humid Plastic Semi-fluid Fluid Super-fluid Type 0 mm 10 – 40 mm 50 – 90 mm 100 –150 mm 160 –210 mm > 220 mm Bridge, digue, Silo, founda- Scale, ramp, Pilars, walls, Dams, harbors, Pavement, Applications foundations, tions, slab, in- roof, wall, floors, jetty… walls, precast… harbor… dustrial floor… column… precast… Standard Very light Very light Strong vibration Strong vibration Light vibration Vibration type vibration vibration (inter- vibration (inter- in layer of 50 cm in layer of 50 cm in layer of 60 cm in layer of 50 cm nal or external) nal or external) of vibrator 65 –160 mm 65 –160 mm 40 – 65 mm 25 – 55 mm 25 – 45 mm 25 – 45 mm Vibration period 1–3 min 10 – 40 s in layers 10 –20 s 10 –20 s 5 –10 s 5 –10 s Hourly vibration capacity 25 – 45 m³/hr 25 – 45 m³/hr 10 –25 m³/hr 1,5 –20 m³/hr 1,5 –10 m³/hr 1,5 –10 m³/hr 7 Guide to Concrete Floor Applications Under-vibration may cause serious defects Revibration is the vibration of concrete in concrete and is the most common prob- which has been compacted some time lem.

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