Carry Out Concreting to Simple Forms BCGCO2003B

Introduction Concreting is a commonly used task in the Building Construction Industry. As a plumber you will probably not be expected to do a large area of concrete. For this you are generally better off engaging the services of an experienced concreter.

Common Concreting Tasks for Plumbers Plumbers often have to:- Repair paths after cutting to make way for water or drainage pipes. Repair slabs around penetrations or boxed out areas for baths or shower traps. Form concrete mounds around wastes and drains at ground level. E.g. Disconnector gullies. Form and pour drainage pits. Make repairs to masonry walls around pipes.

Basics Even for these simple tasks, it will help to understand the basics of concrete. Such as:- What is concrete made of. Effects of too much water. Methods of mixing/delivering. Process of forming, screeding and finishing.

Making Concrete Generally a reasonable mix would be made from the following;- 4 parts aggregate 2 parts sand 1 part cement Enough water to make mix workable. (Depends on moisture content in sand)

Aggregate Crushed stone or 'metal', the most commonly used size being 20 mm. Usually basalt, granite or dolomite and must be clean with no clay or dirt included.

Sand The preferred sand for concrete is clean (washed) and sharp.

Cement For general use the Portland type A cement is recommended. It now comes in 20kg bags

Portable mixer Used mainly by brickies but suitable for small tasks or repairs in conjunction with wheelbarrows.

Mixing by Hand Measure the components by volume using a container such as a bucket. Using a shovel is not recommended for measuring ingredients. A heaped shovel of damp sand has a greater volume than the average shovel-load of cement or gravel.

Best Option Concrete trucks delivering directly to area via chutes.

Wheelbarrows Suitable for small quantities and short distance pouring.

Time is Money Using a minimum of two barrows ensures less waiting time for driver.

Concrete Pumps Pumps become economical to use for large volumes or hard to get to places.

Concrete Pumps Pouring directly from chute into hopper on pump.

Finished Levels Levels should be calculated using laser or Dumpy levels prior to concrete arriving. Keep in mind some surfaces need to be self draining and not completely level. Small off-cuts of reinforcing are often used as markers for levels. These may be removed as levels are achieved.

Concrete Vibrators Used to ensure maximum compaction and subsequent strength of concrete.

Rough Levelling This is achieved most effectively by placing slightly more concrete than required all over. Follow this by dragging a square mouth shovel across the surface towards yourself. Make sure the level is still slightly higher than final level required.)

Screeding A straight edge is used alternatively in a chopping and a sawing action to move the concrete along to one end.

Finishing Finishing consists of three processes:- Floating Trowelling Edging & Joints

Floating Trowelling is required to leave a dense, hard, smooth and durable surface. The first step in this process is called floating. After floating the concrete should be left to set before the final trowelling

Trowelling When the concrete is firm enough to stand on leaving few markings, the final trowelling may begin. This may be done by hand or a high quality job will be achieved with a power float.

Edging All edges should be done Neater and stronger edge Less prone to chipping

Joints Every concrete slab above 2.4 by 2.4 metres should have joints Joints are to prevent cracking They allow the concrete to move There are two types of joints in concrete slabs, Expansion Joints and Controlled Crack Joints

Expansion Joints They may be also called construction or isolation joints. They provide space between concrete slabs to allow for expansion on hot days and compression in cold days. Usually these Joints are installed during the initial installation of the concrete. Most are made of wood or some soft material so they can move with the expansion and compression of the concrete.

Control Joints Control joints are made during finishing. Usually these Joints are cut into the slab after the concrete hardens. A slab without crack joints will crack in random patterns and will reduce the life of the concrete slab.

Curing Means to cover the concrete so it stays moist while it hardens. Do it as soon as the surface will not be damaged by the sheeting touching it. The concrete will last longer, be stronger and less likely to crack. Sometimes the application of a fine water mist is required.

Show Concrete Video

Student Response Sheet 1. List 3 likely concreting tasks a plumber may undertake. (a) Path or slab repairs (b) Concrete mounds (c) Forming & pouring pits 2. What 2 items may be used to protect a person from coming into direct contact with concrete or cement. (a) Gloves (b) Barrier cream 3. Concrete is made by mixing: (a) Water (b) Cement (c) Coarse & Fine aggregates (d) Admixtures 4. The most common type of cement is: General purpose Portland cement Type A (GP)

a) Strong b) Hard c) Durable 5. Aggregates should be: a) Strong b) Hard c) Durable d) Chemically inactive (e) Clean (f) Graded 6. Cement should be stored in a well aired, clean, dry place off the ground. 7. Rounded aggregates give a more workable mix Angular aggregates make concrete Harder to place, work and compact but can make concrete stronger. Water must be Clean, fresh and free from any dirt, unwanted chemicals or rubbish that may affect concrete 8. What are the three states that concrete goes through? 1. Plastic 2. Setting 3. Hardening 9. The most important properties of plastic concrete are? Workability & cohesiveness .

10. Workability means how easy it is to? a) Handle b) Place c) Compact d) Finish 11. Never try to make a mixture more workable by adding water because this lowers the strength and durability 12. Cohesiveness is how well concrete holds together 13. Well made concrete – a naturally durable and strong material. It is: a) Dense b) Reasonably watertight c) Resists Temperature changes d) Resists weathering

14. How is strength measured? With the compression test 15. Compaction is removing air from the concrete 16. Curing is keeping the concrete damp for a period to allow it to reach maximum strength 17. What does the slump test show? Workability 18. What does the compression test show? The best possible strength concrete can reach in perfect conditions

19. When ordering ready-mixed concrete you will need 19. When ordering ready-mixed concrete you will need to tell the supplier:- a) Name and address for delivery b) What the concrete is for, e.g. driveway, footing. et c) Amount (M3) d) Strength in MPa. (e.g. 20, 25……..) e) Slump (mm) f) Maximum aggregate size (e.g. 20mm) g) Access -how you want to place the concrete. (Pump/barrow/directly from chute) h) Time of first truckload i) Time between truckloads j) Any admixtures (normally left to pre-mix concrete company) k) Always order more e.g. 10% for wastage etc.

20. If the cement content is increased, what else will increase a) Strength b) Durability 21. If the water content is increased, what will be the outcome? Weaker strength concrete 22. What does formwork do? Gives concrete its shape 23. What does reinforcement do? Increases strength and helps control cracking

24. Segregation makes the concrete: a) Weaker b) Less durable c) Poor surface finish 25a) How can segregation be avoided? Check concrete is not too dry or too wet. b) What is compaction? The shaking or vibrating of concrete to remove air. 26. It is worse to under vibrate than to over vibrate. 27. What are the two finishing stages? a) Initial (screeding with or without bullfloating) b) Final (Floating,Trowelling, edging joints, patterns)

28. What are the two stages in floating? a) BullFloat b) Power or handfloat 29. When can the final finishing be carried out? Once any bleed water dries up and the concrete can support a person’s weight leaving only slight marking. 30. Edging and grooving is done to? Give a neater, stronger edge less prone to chipping. 31. What is curing? Making sure the concrete stays moist while hardening. Often by being covered. 32. Why do you cure concrete? a) Less likely to crack b) More durable c) Stronger

33. What is the minimum time for curing concrete? House hold job – 3 days More strength & durability – 7 days 34. The longer concrete is cured, the closer it will be to its best possible strength and durability. 35. What is a control joint? A groove of 1/4 -1/3 the depth of the concrete creating a line of weakness in the slab. As concrete shrinks it will crack below this line. 36. There are two types of reinforcement, what are they? a) Mesh Sheets b) Loose bars c) Polypropylene fibres

37. Formwork must be? a) Accurate b) Strong c) Well made 38. How much concrete do you need to repair a path 900mm wide by 2 metres long and 75mm thick. Remember to add a 10% allowance. V = L x W x H = 2 x .9 x .075 = .135 + 10% of .135 = .0135 = .15 m3 In this case the minimum order would be .2 m3 anyway.

39. How much extra concrete should generally be ordered 39. How much extra concrete should generally be ordered to cover wastage? 10%

The Practical Task

Basic concrete

Make sure forms are square and fixed firmly.

Place formwork on a bed of sand so that moisture from concrete has somewhere to go.

The formwork should be treated with a releasing agent to ensure it comes away from the concrete when set.

Sand under the concrete must be well compacted

A gauge cut to the required concrete thickness should be used to ensure an even thickness of concrete.

Compact the sand well and remove any excess

Use the straight-edge to screed the concrete

Pay particular attention to edges and corners as this is where honeycombing may occur.

A slump test is done to check the consistency of your mix. A dampened, cylindrical cone is placed on a non-porous surface & filled with concrete in three even stages

Each stage should be vibrated (prodded 25 times) to expel excess air. The base of the cone needs to be held down to prevent concrete squeezing out underneath.

The prodding should be done all the way through the concrete.

Lift cone straight off, do not jiggle, allow concrete to slump

Place cone, upside down, next to slumped concrete, Lay rod across the base and measure down to the highest point of the slump.

Do not work (trowel /float) the concrete while it is too wet, usually this should be left until excess water has gone off the surface.

Edging-tool should be held as flat and square as possible Formwork should be cleaned and edging-tool run through to push stones in from the sides to allow a smoother finish Edging-tool should be held as flat and square as possible

Make sure you edge right into the corners.

When concrete is firm enough, a flat-trowel finish is non-slippery yet finer than a float finish.

Da-Daa

Clean around your work area and clean and put away all tools, straight-edges and equipment.