TAFE Slab on Ground

Carpentry - Housing

CARP07

SLAB-ON-GROUND CONSTRUCTION

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©TAFE NSW Construction and Transport Division

These notes were prepared by Teachers of Carpentry TAFE NSW 2003 Edition NSW TAFE Commission / DET CONSTRUCTION & TRANSPORT DIVISION WESTERN SYDNEY INSTITUTE OF TAFE For Construction and Transport Division TAFE NSW Victoria Road Castle Hill NSW 2154 Ph. (02) 9204 4600 First Published 1999 Second Edition 2003 ISBN 0 7348 1003 2 Construction and Transport Division TAFE NSW, 1999 Copyright of this material is reserved to Construction and Transport Division TAFE NSW Reproduction or transmittal in whole or part, other than for the purposes and subject to the provision of the Copyright Act, is prohibited without the written authority of Construction and Transport Division, TAFE NSW Published by Construction and Transport Division Printed and Distributed by Resource Distribution - TAFE Manufacturing and Engineering Division



Introduction 1 Site Preparation 2 site waste management 2 Manual Excavation 5 Slab and Paving Preparation 5 hardcore fill and sand blinding layer 5 Formwork for Simple Slabs and Paving 5 edgeboards or screeds 5 pegs 6 checking forms for square and panelled forms 7 removal and storage of edgeboards 8 Concrete - pre-mixed 8 ordering pre-mixed concrete and concrete trucks 9 Measuring Formwork and Concrete Volumes 10 Method of Calculating Dry Raw Materials for Concrete 15 Concrete Tests - slump test 16 compression test 18 Slab Types - stiffened raft slab, footing slab 19 waffle raft, stiffened slab with deep edge beam 20 pier and slab 21 Slab Materials and Special Requirements - formwork 21 vapour barrier / damp-proofing membrane 22 reinforcement, rebated slab edge 23 proximity of trees and shrubs to slabs, drainage 24 Termites and Termite Barriers - chemical treatments / barriers 25 physical barriers 26 other preventative treatments 28 Constructing a Slab-on-Ground 29 alternative slab edge rebate details, preparing and finishing the slab. 30 cleaning masonry surfaces 38 Glossary of Terms 39 Further Reading 41

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Acknowledgments: Acknowledgment is due to the following for their permission to reproduce product materials and copyright materials or for development of this text; • H. E. Evans - for use of earthmoving graphic • Phillip Hadlington - for use of entomology graphic • Standards Association of Australia - for use of AS 2870 standard for reference • TAFE Construction & Transport ESD - Fire Technology & Environment

Programs - for use of the Minimising Construction & Demolition Waste resource. • Bob Byrn and Chris Mackay - for your valuable contribution in the preparation of

this text. • Ivanka Susnjara - for desktop publishing and preparation work for printing. • Rob Young - for preparation and editing of these notes, including development

of new graphics. • Special thanks - to Bob Bulkeley for the many years of dedication to research,

development and production of quality resources for use in the area of vocational education.



ISBN 0 7348 1003 2

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©TAFE NSW Construction and Transport Division 1


This text introduces a variety of subject matter related to Building and Construction, at a basic level. It should be read in conjunction with “Basic Building and Construction Skills” , produced by TAFE and Addison, Wesley, Longman Australia Pty Limited, as between them they address the following; Details relating to manual excavation, including tools, basic formwork and basic methods of excavation, are also dealt with in “Basic Building and Construction Skills”. Descriptions of other types of formwork, preparation for simple slabs, sequence of setting up forms and environmental on-site controls, examination of slab types, uses and formwork. Also covered are termite barriers, slab reinforcement, release agents, transporting/batching/ mixing/placing/compaction/curing/finishing of concrete and the methods used to carry out these operations. Further examples are given relating to the calculation of irregular shapes, concrete volumes, brick and paving areas, quantities and costs of materials, etc. Volumes of wet and dry materials for concrete production are also covered. A comprehensive ‘Glossary of Terms’ is included at the end of the text, which provides a detailed description of trade terms, technical content and some trade jargon.



INTRODUCTION Slab-on-ground construction is the most commonly used method for residential floor construction as it provides an even, durable, waterproof, maintenance free structure designed to last a minimum of 50 years. Once the site waste management requirements have been assessed and implemented, the slab area is prepared by removing all vegetation, levelling the surface, excavating the perimeter beams (if required), erecting the edge forms, preparing the sub-grade, laying drainage, placing a waterproof membrane, laying the reinforcement and providing termite barriers to slab perimeters and penetrations. After the forms, reinforcement and appropriate barriers have been placed, the concrete is poured using wheel barrows and planks, chutes or , more commonly, pumped into position from a mobile concrete pump truck at street level. The fluid concrete is then vibrated to remove unwanted air bubbles and the surface is manually screeded to the required levels. After the water sheen has gone, hand and/or mechanical trowelling takes place to burnish the surface, which gives it a dense, hard wearing finish. The concrete is allowed to set before the curing process begins, which usually takes up to 28 days before it’s designed strength is reached. Curing involves a process which prevents excess moisture from escaping, as rapid evaporation creates shrinkage which leads to cracking. The following details provide a more comprehensive description of the processes involved: SITE PREPARATION SITE WASTE MANAGEMENT As a significant contributor to the production of waste, the Building and Construction Industry has an obligation to take steps to minimise the production of waste and to increase the rate of re-use and recycling. The Building and Construction Industry, Local Council and the Environment Protection Authority (EPA) are working together to reduce wastage and promote re-use/recycling.

Construction Waste Basically, construction waste is any type of building material, fill, packaging, vegetation, paint or finishing material which is thrown away on a building site. In the mid 1990’s, the estimated wastage from a typical residential building site was around 20 cubic metres (m³). Bricks, roof tiles, timber and plasterboard make up the bulk of residential site waste, i.e. accounting for approx. 90% of all site waste. Generation of unnecessary waste from a construction site is not only environmentally undesirable, but it can also end up costing a lot of money. Firstly, there are the costs and hassles of waste disposal. Secondly, there is the initial cost of the wasted materials, and Thirdly, the potential profit of the job is reduced by this wastage. The average waste costs on the construction of an average residential cottage is up to around 2% of the total cottage price, e.g. this equates to $2,600.00 for a cottage costing $130,000.00 to build. Measures which should be taken to reduce site waste are as follows:

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Retaining Site Vegetation Small trees, shrubs, plants and even grass may be stored on-site, after removal, so they can be re-planted at the end of the project. This saves on additional landscaping costs and preserves the natural vegetation for the area, which birds and other animals rely on for food and shelter. Stockpiling Soil Excavated soils, referred to as ‘spoil’, can be stored on-site in an area which doesn’t interfere with construction processes. This retained soil may then be re-used to fill hollows or for general landscaping. Where areas require ‘cut and fill’ it is usual to use the existing foundation material for filling, which is re-compacted in layers, to avoid differential movement between dissimilar materials, which may occur under slabs and driveways. The stockpiled soil should be covered with plastic sheeting to prevent erosion and excessive grass growth prior to re-use. The most suitable position on the site would be the lowest corner so that any eroded soil from the pile will e trapped by the sediment control fence. The relevant Australian Standard for residential soil management and use is AS 3798 - 1990 : Guidelines on earthworks for commercial and residential development. Control of Stormwater The site surface around the structure should be graded to allow surface stormwater to drain away from the structure and be graded towards a prepared rubble sub-soil drain, placed at the lowest corner of the site. (See chapter 5 “Basic Building and Construction Skills” for further information.) Sediment Control and Retention It is a mandatory Local Council requirement for any residential construction that soil and sediment control measures must be taken to prevent surface eroded surface materials ending up in the street gutters and stormwater pits/drains. To prevent this occurring, temporary silt fences must be constructed at the lowest corner or across the lowest side of the building site. These fences may be constructed of closely woven polypropylene, similar to ‘Shadecloth’, or made up of connecting bails of straw held firmly in position by driving steel star pegs through them. Straw bales or sand bags may also be used in the gutters at the entrance to the stormwater drain openings to prevent silt and debris washing into them.

Fig. 1 Typical sediment control detail provided by Council

Drainage area 0.6ha. max Slope gradient 1:2 max. Slope length 60m max.

DISTURBED AREA 3000 max.

200

600

max

SEDIMENT FENCE

UNDISTURBED AREA

Overlap

Posts driven 0.6m into ground

Geotextile filter fabric

Wire or steel mesh Direction of flow



Designated Wash Out Areas Wash out areas are designed to detain and filter water and liquid waste products before they reach the stormwater system. This may be done by preparing an area at the lowest corner of the block, excavating a trench and filling it with a variety of graded stone or rubble and sand to form a sub-soil filter bed. It should have a perforated agricultural type pipe installed to allow removal of the filtered water. All-weather Access To prevent sub-contractors vehicles and delivery trucks churning up the driveway, which may allow soil to be washed into the street gutters, a layer of crushed rock or road base should be laid and compacted. This will prevent surface erosion, allow access onto the site in any weather and provide a solid base for the future driveway. Reuse of Building Materials Where a project involves demolition, extension, renovation, etc. there will always be some material which is removed and not required to be re-installed for that project. Salvage of these components, in agreement with the client, will reduce waste and save the Builder money as they may be re-sold or used in another project. Items in a good condition which are suitable for re-use are windows, doors, fixings, cupboards, roof tiles, special timbers (e.g. Australian Red Cedar, Mahogany, Baltic pine, etc.), pressed metal ceilings, leadlight glass, wrought iron gates, electrical fittings, bathroom fixtures, flooring boards, Hot Water units, ceramic tiles and light fittings. Recycling Waste This is not always the first choice as it usually generates some cost in it’s initial removal from site. After all other avenues have been exhausted, i.e. re-use, initial waste avoidance, stockpiling, repair, etc., then many materials may be recycled. Suitable materials would include cardboard and paper packaging, timber, bricks, roof tiles, concrete, some plastics, plasterboard, glass, steel, Aluminium and ceramics. Many Council tips and recycling stations have designated areas for storage of these materials so they may be recycled. However, cartage to these sites will cost the Builder some money as there is not a pick up service available for all of these materials. Waste Minimisation Philosophy Reduce - waste by not over-ordering and using all offcuts. Tell manufacturers when they’ve

over-wrapped their products; Reuse - materials wherever possible, especially in renovations where the quality of older

materials is often better than those of today; Recycle - materials by separating them at source, on-site, rather than allowing them to

become a soggy mess which ends up being thrown at the tip; Repair - worn equipment, or even buildings, before throwing them away or demolishing.

Separate waste materials into covered skips or bins. This saves on costs and site clean up.

For further information on Waste Management, contact the Environment Protection Authority (EPA) or refer to the TAFE/The Waste Challenge Group publication - “ Minimising Construction and Demolition Waste”. Also, refer to The Waste Challenge video - “Not Just Another @#&! Form”

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MANUAL EXCAVATION Excavation involving the use of a variety of shovels and digging tools, safe excavating practices, preparing small pits, digging post holes, clearing light vegetation, installing barricade tapes and identifying underground warning tapes are dealt with in detail in “Basic Building and Construction Skills”. (refer to chapters 1 and 7) SLAB AND PAVING PREPARATION Hardcore Fill Where the slab/paving sub-surface is uneven, has been over excavated, has excessive hollows, requires deep compacted filling, etc. then the use of a dense mix of stone may be used to provide a stable, more even and compacted base. Materials used should be hard, have a dense nature and will not decompose. Suitable materials would include broken brick, old concrete or natural igneous type stone such as Basalt, Granite, Quartz and Trachyte. The igneous type stones are also relatively non-porous which assists in preventing moisture rising up under the slab where it may cause problems. Sand Blinding Layer This is a layer of sand approx. 50mm thick placed on top of the hardcore fill, but prior to the waterproof membrane. The purpose of the blinding layer is to provide an even, level surface which prevents sharp stones from penetrating the waterproof membrane and also allows the area directly under the slab to be topped to the desired level reducing concrete wastage. Now many residential slabs only use compacted sand for the sub-grade which allows for easy preparation of integral beams or specific slab thickening. Suitable sands for this purpose would be those which are reasonably cohesive such as loamy sand, which has no vegetable matter, and bush sand as these contain a mix of sand and clay which packs down well and retains shape. They are usually deep yellow to orange in colour and leave a slight stain when rubbed between the hands. Note: Cohesive sands also provide a better medium for the application of termite preventative chemicals as the chemicals are more likely to bind with the sand, rather than drain right through it. FORMWORK FOR SIMPLE SLABS AND PAVING Edgeboards or Screeds There are several types of material which may be used for simple concrete slabs, paths and driveways. The most commonly used materials are cold formed steel, sawn hardwood or softwood for straight runs, and hardboard or fibre cement sheet strips where curves are encountered. Generally the slab thickness will be constant throughout as these slabs do not have thickened edge beams. They are designed to carry light loads such as an outbuilding, small garage, garden shed, driveway, etc. which will usually be up to 100mm thick, whereas paths and paved areas are usually 75mm thick and designed for light traffic only.



It is more economical to set the edgeboards to run ‘in-to-over’ where regular parallelograms or rhomboids are used. Prior to placing of the edgeboards, the foundation surface is prepared by removing any vegetable matter, making the area level by cutting and filling using a suitable compacted material.

Fig. 2 Edgeboards run in-to-over

Pegs Pegs may be of steel or timber, which are driven using a lump hammer or sledge hammer, and set to finish flush with the top edge of the edgeboards to allow easier screeding of the concrete.

Fig. 3 Timber and steel pegs

Timber Edgboards

in to over

HARDWOOD TIMBER FLAT STEEL 'T' SOLID STEEL BAR

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Checking the Forms for Square The diagonals are measured for equal distance. If unequal, the edgeboards are adjusted to suit by pegging one side, levelling and fixing off, then the other three connected sides are moved together until the desired diagonal measurement is achieved. The remaining pegs are then driven, the forms lifted to the desired level and fixed off.

Fig. 4 Squaring the edgeboards Panelled Forms In some cases it is necessary to break paths, driveways or wide paving into panels and pour them separately. The long sides of the paving are placed and then shorter edgeboards are placed between them, at the desired spacing, which will allow every 2nd panel to be poured. This practice may be useful when access is awkward, access is required to the edges, expansion joint material is to be fitted, construction or contraction joints are required, etc.

Fig. 5 Edgeboards used to form panels

Poured driveway panel

Intermediate bay left

Move to adjust for square

Edgeboards placed out of square

One side pegged and fixed off

Position of squared edge boards



Removal and Storage of Edgeboards Once the concrete has set and the curing process is under way, i.e. after approx. 7 days to allow concrete to gain strength and to keep the moisture in on the edges, the edgeboards are removed and cleaned down to remove dags, slurry and nails. The edgeboards should be neatly stacked, stored off the ground and covered to prevent twisting and weathering so they may be re-used many times.

Fig. 6 Stored edgeboards

CONCRETE

PRE-MIXED CONCRETE Pre-mixed or ready mixed concrete is the most common method of obtaining concrete. The concrete is pre-mixed under factory conditions to exact proportions and may be mixed either wet or dry. For best results the materials are placed into the truck as a dry mix and water is added as the truck is approaching the job or when it arrives on the site.

Fig. 7 Dry mix loaded into the truck at the plant

Sawn timber edgeboards

Timber gluts

Dry mix

Mixing Cone

Cement dispenser

Aggregate collecting cone with scales

Cement collecting cone with scales

Cement bin Gravel bins

Sand bin

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The main advantages of pre-mixed concrete are: 1. Consistent proportions:

The proportions are batched by weight or mass which is very accurate as the moisture content of the raw materials is also taken into account;

2. Cost Control: As the batching process is so accurate there is no wastage of materials. Also, the raw materials are purchased in bulk which keeps the costs down.

3. No site congestion with concrete components: As all the storage of materials, batching at the plant and mixing in transit takes place away from the site, no site congestion occurs and the space is preserved for other materials.

Ordering Pre-Mixed Concrete When placing an order for pre-mixed concrete the following information should be given: Example 1:

Admixtures to Concrete:

CONCRETE TRUCKS Trucks of varying capacities are available to cater for a wide range of job sizes and site conditions. The most common capacities range from 0.4m³ to 7.0m³

Fig. 8 Typical concrete truck with agitating inclined drum

• Accelerators−to speed up the setting time • Retarders−to extend the setting time

• Waterproofing compounds - e.g. ‘Silasec’ • Colouring - variety of oxides

INFORMATION TO BE PROVIDED DETAILS

1. Name of company / Person requiring load FLY-BY-NIGHT CONSTRUCTIONS

2. Name and location of site 15 HUON STREET, SASAFRAS GULLY

3. Date and Time required SATURDAY 1ST JAN. 2000 4. Concrete strength 20MPa 5. Consistency or Slump 80mm 6. Special requirements, e.g. special cement, special additives

or concrete pump required Type GB (Blended Cement)

7. Volume of Concrete Note: Volume is to be ordered in multiples of 0.2m³

4.8m³

8. Spacing of trucks (usually for large pours) N/A



MEASURING FORMWORK AND CONCRETE VOLUMES Slab on ground (Path/Paving)

When pouring concrete for simple slabs such as a concrete path, some formwork is needed to get the shape and thickness required. To calculate the length of the edgeboards or screeds required to form a path it will be necessary to know the finished size of the path, so the perimeter may be measured. Where the path is poured against a wall or other solid structure it will not be necessary to include those sides in the calculation. Method Example 1: Calculate the length of Oregon edgeboards or screeds and the volume of concrete necessary to form and pour the simple 75mm thick slab below;

Fig. 9 Typical paving slab

Step 1 Perimeter = (L + B) x 2 = (1600 + 800) x 2 = 2400 x 2 = 4800 mm or 4.8 m

Step 2 Order : 75 x 50 Sawn Oregon - 1/5.1

Step 3 Volume of = L x W x T concrete 1.6 x 0.8 x 0.075 = 0.096m³ Say 0.1m³

Note: An allowance must be made for corner joints and waste, therefore increase the length to the next orderable length of 5.1m

1600 800

75

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Note: Larger slab areas will require multiple lengths of edgeboard material and where possible they should be run ‘in-to-over’ around the perimeter, to avoid cutting, timber wastage and allow for re-use of timber forms. If the above example was to be poured using ‘Ready-mixed’ concrete, then the minimum order would have to be 0.2m³, as it may only be ordered in multiples of 0.2m³. Example 2: Calculate the lengths of Hardwood edgeboards or screeds necessary to form the irregular shaped paving slab below. The slab thickness will be 75mm;

Fig. 10 Plan view of irregular shaped paving with dimensions

Step 1 Sketch the shape of the paving and include the measurements of all sides;

1200

5400 1500

600

3300 1800 3600

900

900

3900

3000

2100

3900

Step 2 List the orderable lengths, i.e. in multiples of 0.3m, required by starting on the right hand side and working clockwise around the perimeter; keeping in mind that the edgeboards or screeds are to run in-to-over wherever possible which will require additional length for most sides; 1/4.2, 1/3.6, 1/0.9, 1/1.8, 1/0.9, 1/3.9, 1/4.2, 1/1.5, 1/2.1, 1/5.7, 1/0.9, 1/1.5, 1/3.3, 1/0.9

Step 3 A timber order needs to be formed by grouping together like lengths and adding together as many short lengths as possible to make longer lengths. Note: The longest lengths are listed first through to the shortest; = 1/5.7, 2/4.2, 2/3.9, 2/3.6, 1/3.3, 1/3.0

Step 4 Order: 75 x 38 Sawn Hardwood - 1/5.7, 2/4.2, 2/3.9, 2/3.6, 1/3.3, 1/3.0



Example 3: Calculate the volume of concrete required to pour the irregular shaped paving in the previous example:

Fig. 11 Break up of the irregular shape into sections

Step 1 Sketch the shape of the paving and break the irregular shape into a number of simpler regular shapes, identify each one by placing a letter in the centre, and include all the relevant measurements of the sides;

Step 2 Calculate the area of each section and find a total;

600 1200

2100

18

00

3600 3300

900

900

3000

E

D

C

B

A

A = L x W = 2.1 x 1.2 = 2.520m²

B = L x W = 3.6 x 1.8 = 6.480 m²

C = L x W = 3.0 x 0.9 = 2.700 m²

D = L x W = 3.3 x 0.9 = 2.970 m²

E = L x W = 3.0 x 0.6 = 1.800 m²

TOTAL AREA = 16.470 m²

Step 3 Calculate the volume and orderable amount of concrete;

= Area x Thickness = 16.470 x 0.075 = 1.235m³ Say 1.4m³

Therefore, ORDER 1.4m³

3000

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Example 4: Calculate the volume of concrete required to pour the thickened edge beam slab, with a splayed edge underneath:

Fig. 12 Details of the proposed slab

Fig. 13 Section through beam to show how average width is achieved

Step 1 Draw a detail of the slab, showing a section through the thickened splayed edge beam;

Step 2 Break the slab into two areas, i.e. the slab and the thickened splayed edge beam. Firstly, calculate the volume of the slab;

= L x W x T = 7.5 x 3.8 x 0.1 = 2.850m³

7500

PLAN

SECTION Detail 'A'

200

3800

Step 3 Now calculate the volume of the thickened splayed edge beam. The simplest way of calculating the beam is to calculate the average area of the beam section and multiply it by the centre line length of the beam, which is also the same as working in-to-over around the perimeter;

Averaged Beam Size

350

100

200

300 100

45 100

100

Detail 'A'



Therefore, the area of the beam will equal:

Fig. 14 Plan of slab showing beam broken into in-to-over sections

This is the total amount of ‘Ready-mixed’ concrete required, however if there is no Ready-mix available or the amount is very small making it too expensive in Ready-mixed form or the site is in an isolated location or the travelling distance is vast, then site mixing may be an option. If materials have to be dry batched on-site, then the following procedure may be adopted to calculate the dry raw materials required;

= L x W = 0.350 x 0.100 = 0.035m²

Step 4 Now calculate the centre line length of the beam by working in-to-over. Identify each section using a letter starting at the right side and working clockwise around the slab;

a ↓ 3.800 - 0.350 = 3.450 b ← 7.500 - 0.350 = 7.150 c ↑ 3.800 - 0.350 = 3.450 d → 7.500 - 0.350 = 7.150

TOTAL LENGTH = 21.200m

Step 5 Now multiply the average beam area by the average length to calculate the volume of the beam;

= Area x Length = 0.035 x 21.200 =

0.742m³

7500

350

350

3800

Step 6 To calculate the total volume of concrete in the slab and the beam, add the two separate volumes together;

= Volume of slab + Volume of beam = 2.850 + 0.742 = 3.592m³

ORDER - 3.6m³

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METHOD OF CALCULATING DRY RAW MATERIALS FOR CONCRETE Concrete which is to be mixed on-site, although rare, will require the calculation of dry raw materials. The following example outlines the procedure involved: Example 1: To calculate the amount of dry materials required, the proportions of the mix must be known or decided upon. A typical mix would be - 4 : 2 : 1, i.e.:

• 4 parts by volume of coarse aggregate (blue metal) • 2 parts by volume of fine aggregate (sand) • 1 part by volume of matrix (cement)

It will take an average of 1.4m³ of dry material to make 1.0m³ of fluid concrete. The dry mix will shrink approximately 30 to 35%, when water is added. Therefore, if 1.4m³ of dry material is calculated to make 1.0m³ of fluid concrete at a ratio of 4 : 2 : 1, the following method is used; Firstly, add the parts together to find a common denominator so that each of the individual proportions will add up to the total amount, i.e. 4 + 2 + 1 = 7 ; Now find the volume, by proportion of the total dry mix, of each material; This provides the total amount of dry mix to make 1.0m³ of fluid concrete, therefore if greater quantities are required simply multiply the volume of each proportion by the desired amount, e.g. Example 2: If the amount of fluid concrete required was 3.6m³, then the following would be carried out; Course and fine aggregate is available for small bulk quantities, but cement is usually purchased by the bag. Therefore, convert the volume of cement into bags as follows; The volume of one (1) bag of cement is equal to 0.027m³, therefore the number of bags required to make 3.6m³ of concrete would be - 0.720 = 26.666, say 27 bags. 0.027

Course Aggregate (blue metal)

= 1.4 7

x 4 = 0.8m³

Fine Aggregate (sand) = 1.4 7

x 2 = 0.4m³

Matrix (cement)

= 1.4 7

x 1 = 0.2m³

Course Aggregate (blue metal)

= 0.8 x 3.6 = 2.88m³

Fine Aggregate (sand) = 0.4 x 3.6 = 1.44m³

Matrix (cement) = 0.2 x 3.6 = 0.72m³



CONCRETE TESTS There are two tests which are frequently carried out on concrete as follows: • Slump Test; and • Compression Test Slump Test The slump test is used to determine the consistency of concrete. This test should be carried out at regular intervals when a large amount of concrete is being placed to ensure uniform concrete mixes. The method of testing is outlined below;

Fig. 15 Slump testing equipment

Foot rest

SLUMP TEST EQUIPMENT

SLUMP TEST CONE

Riveted cover strip

Handles

Soldered joint

Slump cone made from 1.5mm galvanised steel sheeting

ELEVATION

PLAN 100

100 200

Flat non-porous surface

300

Slump

Rule

Inverted slump cone

∅15x600m long steel tamping rod with bullet-nosed end

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Slump Test Method

Fig. 16 Method of conducting the test

1. Hold cone firmly in place when filling, by standing on footrests

2. Fill cone one-third volume and rod with tamping rod 25 times, evenly distributed over surface.

3. Fill cone 2/3 of volume and rod 25 times as before, penetrating into first layer.

4. Overfill cone slightly and rod as before, penetrating into second layer.

5. Strike off excess con-crete from top with tamping rod and clean up the base.

6. Lift cone up slowly within 5-10 sec from striking off. Do not twist or jar.

7. Measure slump with the aid of a rule and tamping rod placed on top of inverted slump cone. Refer to table below for slump values.

TYPE OF CONSTRUCTION SLUMP MIN-MAX TYPE OF CONSTRUCTION SLUMP MIN-MAX

Thin walls (reinforced) 120-200 Slabs, pavements 50-80

Pumped Concrete 70-120 Plain Footings 50-80

Colums, beams 50-100 Heavy Mass Concrete 30-80

Footings (reinforced) 50-100



Compression Test This test is used to determine the strength of concrete. A steel test cylinder is filled with a sample of concrete, allowed to set, removed and then fully cured under controlled conditions. At 28 days the specimen is taken to a concrete testing laboratory where it is crushed and the pressure required to do this is noted. The pressure required to crush the concrete, measured in MPa (Mega Pascals − pressure units), is to be equal to or greater than the strength required, i.e. if the ordered strength required was 20MPa then it should reach 20MPa pressure before failing.

Fig. 17 Preparation of a concrete specimen for compression testing

Ø 16.600m long metal bullet pointed rod

Swinging locking bracket fixed to the top slightly off centre

Brackets welded to top and bottom plates

Metal mould with grooves at each end for fixing top and bottom cover plates

Metal top cover plate with two fixed brackets and one hinged locking bracket

Metal bottom cover plate

STEP 1 Mould filled to one third its height and concrete compacted by rodding at least 25 5imes

STEP 2 Second layer of concrete added and compacted by rodding. Allow rod to penetrate the previous layer.

STEP 3 Third layer of concrete added and com-pacted as in step 2. Surface struck off and mould capped to prevent loss of moisture

STEP 4 The completed test cylinder after curing and re-moval from the mould. (Test sample removed by approved testing laboratory)

Ø 150

300

Hit locking bracket with mallet to tighten the cover

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SLAB TYPES Various methods of construction are available for concrete slabs and their sizes vary also depending on the classification of the building site. AS2870-1996 - “Residential slabs and footings-Construction”, gives further technical detail of standard designs of slabs and strip footings for various site classifications. The main slab types outlined here are; Stiffened Raft Slab

The stiffened raft is a slab-on-ground, although it is embedded partly in-ground, with edge beams and internal beams which are poured as an integral part of the slab. The design of the beams allows for the prevention of sagging, (edge heave), and hogging, (centre heave). For stable sites (classes A and S), the internal beams are not required.

Fig. 18 Typical Section through a raft slab-on-ground

Footing Slab

The footing slab is a thickened edge concrete slab on the ground with it’s perimeter edge resting on a continuous strip footing. The slab is cast separately from the strip footings, but is tied to them using cranked reinforcement. Alternatively, the edge of the slab may not be thickened and be supported on a continuous wall or piers which rest on the perimeter strip footing. It is generally only suitable for Class A and S sites.

Fig. 19 Typical Section through a footing slab

500 300 300 >50

Non-load bearing wall <1000

Load-bearing walls

150

100

>150 300 500

300

Strip footing

Continuous wall or engaged piers

R10 Fitment 150

Strip footing

Load-bearing walls



Waffle Raft

The “Waffle Pod” raft system was developed as an alternative to conventional systems in the early 1980’s. It is a true ‘slab-on-ground’ system as it’s beams sit on top of a prepared level site rather than being embedded. The system consists of a concrete slab with a close grid of steel reinforced stiffening beams or ‘ribs’ supporting it. The Waffle Pod system is easily identified, when viewed on plan, by the square polystyrene void forms as opposed to the rectangular voids of the Ribbed raft slab. The Waffle Pod raft is ideally suited to very reactive clay sites as it floats on the surface, as opposed to the problems associated with stiffened raft slabs which have their beams embedded in the reactive clays. Other benefits include lower costs and material use of up to a third, due to the smaller rib and slab thickness required and the voids created by the polystyrene.

Fig. 20 Typical Section through the waffle raft system

Stiffened Slab with Deep Edge Beam

This is a slab edge treatment, also known as a ‘drop edge beam’ which must be Engineer designed, and only suitable for Class M sites where cut and fill of the site is not desired. It allows for the floor to remain elevated, which may prevent the necessity for high retaining walls created by lowering the slab. It is an expensive method which adds cost to the basic slab design, but this may be offset by the reduction in retaining wall costs.

Fig. 21 Typical Section through a deep edge beam

Load-bearing walls

Deep edge beam

>100

Horizontal bars (Y12)

Load-bearing walls Rib beams set at 90o to one another

Bottom bars only (2Y12 at 90o)

Bottom piers where required

Styrene void former

(in both directions)

1090 max. 110

150 300

150 85

20 3Y12 bars

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Pier-and-Slab

The size and spacing of beams and the depth and size of piers is generally detailed by a structural engineer. Bored piers are usually required where the bearing value of the foundation is low, a highly reactive foundation materials is to be penetrated or where a site has been filled or partly filled. The piers are set out, bored and poured prior to the stiffened edge slab being cast over them. Generally the slab is not connected to the piers with shear reinforcement, which will reduce the effect of beam sagging and hogging.

Fig. 22 Pier-and-slab detail

SLAB MATERIALS AND SPECIAL REQUIREMENTS

Formwork Prior to pouring the concrete, edge forms are placed to form the shape of the slab like a mould. A variety of materials may be used including steel, solid timber and plywood. A number of standard or patent systems may be used to form the slab edge rebate as well as keyed forms for construction joints. Forms should be firmly placed but designed for easy removal to prevent damage to the forms and the slab.

Fig. 23 Alternate deep edge forming systems

Load-bearing wall

<1000

300 300 Bored piers at engineers

spacings

Steel rod peg

Steel formed edge boards with stiffners

Hardwood peg Framed in timber

Formply facing

Trimmer



Vapour Barrier / Damp-proofing Membrane

This is a layer of 200 micron (0.2mm thick) polyethylene (black or orange in colour) placed on top of the sand blinding layer directly under the slab to prevent moisture rising through the slab, which may cause damage to the reinforcement, floor covering and walls. All joins should have a minimum 200 mm lap and be secured with flexible duct tape to prevent moisture penetration or movement when the concrete is being poured. All slab penetrations, i.e. waste pipes, conduits, etc., must have the membrane turned up and securely taped around them or be fitted with a close fitting sleeve. The vapour barrier / damp-proofing membrane is usually laid with it’s edge turned up to at least the ground level on the outside edge of the slab beam.

Fig. 24 Membrane in place for a prepared slab

Care should be taken not to puncture the vapour barrier / damp-proofing membrane during the construction of the concrete slab and any punctures should be taped. Note: Where plumbing and drainage pipes pass through internal or external beams horizontally, they must be ‘sleeved’ or ‘lagged’ with a compressible material such as polystyrene. This is to allow for concrete movement without crushing or shearing the pipes.

Sand blinding layer to protect membrane

Taped around PVC pipe

Lapped and taped join

SLAB PENETRATION DETAIL

SLAB EDGE DETAIL

Layer of 200 micron Polyethylene membrane

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Reinforcement Bulk steel reinforcement, due to it’s mass, is usually handled by crane or hydraulic lifting arms. Individual bars or sheets can be manually handled but some care needs to be observed. It is recommended that leather gloves be worn during both handling and cutting procedures to prevent hand lacerations caused by the sharp ends of the cut steel.

Minimum cover requirements Reinforcement needs to have sufficient concrete cover to prevent air and moisture reaching it, as this leads to rusting. The thickness of concrete around the reinforcement is known as ‘cover’. If the reinforcement rusts it can cause the concrete to spall and lose its strength. This is known as concrete cancer.

Table 1 Recommended Concrete Cover Note: Details relating to reinforcement fabric, trench mesh, bar chairs, bar types and fitments may be found in “Basic Building and Construction Skills” or the relevant Australian Standards, i.e. AS 1302 - 1991 Steel reinforcing bars for concrete, AS 1303 - 1991 Steel reinforcing wire for concrete, and AS 1304 - 1991 Welded wire reinforcing fabric for concrete. Rebated Slab Edge Rebated slab edges are designed to provide a waterproofing/weatherproofing barrier around the perimeter of the slab for brick veneer, cavity brick or masonry walling. Width The width of the step is determined by the size of the masonry being used and the width of cavity required, e.g. nominal 40mm but not less than 25mm for brick veneer construction. It must be of sufficient width to allow the masonry to sit on the outside edge with an allowable maximum of 15mm projecting past the edge.

Fig. 25 Detail of step proportions for single storey, Stiffened raft - class ‘M’ site

SITUATION MINIMUM COVER

Unprotected ground 40mm External exposed surfaces 40mm Membrane in contact with the ground 30mm Internal protected surfaces 20mm

15 max.

110 40 70 Weep hole

172

G.L.

150

min



Depth The depth of the step will depend on the height of the finished ground level which should include an allowance for minimum 75mm below the weep hole to the finished paving level for termite inspection, whether it is to be stepped along it’s length also but the depth of the concrete below the rebate is to be a minimum of 150mm. The minimum depth of the rebate shall be not less than 20mm and where the external wall is of a single leaf construction, however in the case of a single brick skin garage wall with engaged piers a rebate is not required.

Proximity of Trees and Shrubs to Slabs Trees and shrubs which are too close to a slab may cause substantial damage during their natural growing cycle. The roots of these plants grow and spread out in the search for moisture, which may lead to large roots actually lifting and/or cracking the slab. Also, due to the amount of moisture drawn in by the roots foundation materials are dried out, which leads to soil shrinkage. This soil shrinkage, in conjunction with soil swelling from adjacent garden watering, will cause differential foundation movement which often leads to slab cracking. The risk of termite attack is also increased when the roots penetrate perimeter soil barriers rendering them ineffective. To reduce the possibility of damage caused by trees and shrubs a number of steps may be taken as follows:

• 1.5 times the mature height for Class E sites (extremely reactive) • 1.0 times the mature height for Class H sites (highly reactive) • 0.75 times the mature height for Class M sites (moderately reactive)

Drainage Effective drainage requires proper preparation and location of surface drains and sub-soil drains to divert water away from the slab. Surface drains such as dish/spoon types are ideal to divert surface rainwater to a collection point away from the slab area. Rubble drains and agricultural lines are useful to divert sub-soil seepage away from the slab. It is important reduce the excessive moisture levels around the slab by ensuring that all plumbing and drainage is not leaking, gutters and downpipes are not blocked or leaking, taps do not constantly drip and paths are graded away from walls.

1. Before selecting a tree or shrub for landscaping, it would be wise to read the plant information tag to determine it’s mature height and ask a professional nursery person for information about the type of root system the plant has and it’s likely affect on surrounding soil and structures;

2. Place vertical in-ground root barriers adjacent to the slab to divert the root growth away from the slab, especially for established trees;

3. Don’t plant trees close to the slab which have extensive, invasive root systems such as Umbrella trees and restrict plants to types which have fine or shallow root systems such as most palms;

4. Restrict the planting distance to the following;

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TERMITES AND TERMITE BARRIERS Termites (sometimes referred to as ‘White ants’) have been around for approx. 130 million years and have changed very little over that period. They are compared to ants in appearance but in actual fact they are not ants and are more closely related to cockroaches. They are social creatures which are very successful converters of matter containing cellulose into a food source which provides them with the carbohydrates they require. There are several castes within the social structure of the nest of which the queen lays all the eggs, the king is only involved in the reproduction process, the soldiers protect the colony from invaders, and the workers do all the cleaning, feeding, nurturing and all the damage to timber in service. They obtain their protein from the fungus they harvest inside the humid mud galleries in which they travel, mostly undetected. Although they play a very important role in the environment, by converting tree stumps, branches dead trees, vegetable matter, etc into a rich source of food for other plants and themselves being food for a wide variety of birds and animals, they are considered to be pests when they attack houses and other structures. There are approx. 30 species of subterranean termites, out of around 350 species Australia wide, which are considered to be economic pests of timber in-service, i.e. timber used in construction. Therefore, a number of treatments and barriers have been developed to lower the risk of attack, since total prevention cannot be assured, in the form of Chemical treatments and Physical barriers.

Fig. 26 Main caste members of the termite colony

Chemical Treatments/Barriers There are a number of chemical options available for use which are classed as organophosphates and synthetic pyrethroids, which replaced the more mammalian toxic organochlorines in July 1995. Inorganic insecticides are also used in powder form such as Arsenic trioxide, which is mainly used for treating active mud galleries and the main nest site. The main organophosphate chemical registered for use is Chlorpyrifos, in the form of a product called “Dursban”. The main synthetic pyrethroid chemical registered for use is Bifenthrin, in the form of a product called “Biflex”.

SOLDIER

WORKER

QUEEN (with distended abdomen for egg laying) HEAD OF SOLDIER

Mandibles

Bead-like antenna

Palps

Labrum

Fontanelle (exudes a latex substance to repel invaders)

Head

Pronotum

(Coptotermes acinaciformis)



Note: These chemicals are toxic not only to termites but to mammals, which includes humans, and their mode of action is to disable the nervous system. These chemicals may accumulate in mammal body fats and be released when the these fat reserves are used which ends up poisoning the carrier. Therefore great care should be observed and PPE worn when digging around the perimeter of cottages or crawling underneath floors. Application These chemicals may be applied as an emulsion, which is the active chemical ingredient mixed with water and other enhancing chemicals, and is sprayed directly onto the surface under the slab prior to the waterproof membrane being placed. The perimeter of the completed cottage may also be sprayed prior to being covered with paving. The chemical is unstable, which means it will break down over time, and has an estimated life of approx. 10 years under a slab and 5 years as an unprotected perimeter barrier. An alternative to pre-treatment spraying is the installation of a ‘Reticulation’ system, such as “TERMGUARD” - Ultimate, which consists of a network of PVC pipes and spray heads laid prior to the slab being poured. This system can easily be re-charged by pumping additional chemical, Dursban or Biflex, into the piped system through a permanent manifold inlet mounted on the external wall. Arsenic trioxide is a dry powder, mixed with silica aerogel to keep it dry and allow it to float, which is applied directly into termite mud workings with a hand puffer to coat as many termites as possible. It is a stomach poison which works on the principle that when the coated termites return to the nest the other members will ingest the poison during the grooming process, die and be eaten by other the other termites in the nest, which will in turn kill them, and so on. If applied correctly it is the most effective method used to treat the active nest. Physical Barriers Physical barriers are placed to prevent the entry of termites or to force them into the open where they may be more easily detected. They may be used in conjunction with or instead of chemical barriers and the accepted methods are in the form of: a) Ant caps or termite shields b) Stainless Steel mesh c) Crushed Graded Stone a) Ant caps or termite shields Non-toxic and usually made from galvanised iron or ‘Zincalume’ and folded down at approx. 45° along the edge. They may be placed on top of piers, around posts, on top of stumps or built into brick walls in a continuous length. Ant caps DO NOT stop the entry of termites, but rather force them out into the open as they cannot pass through the metal, so they must go around it. Where cavity brick construction is used the ant capping must be continuous along the inside skin of brick work and pass across the cavity to be built into the external skin of brickwork. Where suspended concrete slabs are used and the physical access for inspection is less than 400mm in either height or width, then half continuous ant caps must be built into the supporting brick wall directly under the slab. (These will be dealt with in Unit 7 - Ground Floor Construction)

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b) Stainless Steel mesh Non-toxic and mainly designed for concrete slab-on-ground with brick veneer or cavity brick external wall construction. It is a tightly woven 316 marine grade stainless steel which has an aperture size of 0.66mm x 0.45mm designed to prevent termites passing through it. It should be installed by qualified persons to manufacturers specifications in the cavity and around slab penetrations. It may be placed under the whole slab with it’s edges built into the concrete, but this is not a very economical method. Generally the mesh is built into the external skin of brick work, the full width of the 110mm brick ,under the weep hole level with the other long edge being parged onto the vertical edge of the slab rebate. Slab penetrations have mesh collars fitted at the centre thickness of the slab and are held in place with stainless steel clamps. A common trade brand may be recognised as ‘TERMI-MESH”.

Fig. 27 Typical Section through a slab-on-ground showing mesh placement

c) Crushed Graded Stone Non-toxic and made from crushed graded igneous rock such as granite, basalt and quartz, it is designed to pack down tightly which will not allow termites to pass through and have a mass and density which they cannot devour or move. It is placed in the cavity up to weep hole level, compacted, and also packed around all slab penetrations. If used as a perimeter barrier, it is placed 100mm wide and to a depth of 200mm, with at least 100mm below the edge of the slab rebate or strip footing when the footing is covered by backfill.

Stainless steel mesh collar for slab penetrations NOTE: A PVC collar may be used as an alternative to mesh

Stainless Steel Clamp

Stainless Steel mesh cast into slab min 50mm (optional placement)

Flashing

Weep hole

75m

m

min

,

Stainless Steel mesh parged to slab edge



Waffle Pod slabs are placed on a bed of compacted crushed graded stone of 75mm Min. thickness which is to be placed over the full width and length of the slab, prior to the waterproof membrane being laid. A common trade brand maybe recognised as ‘GRANITGARD”.

Fig. 28 Typical Section through a slab-on-ground showing crushed graded stone

Other Preventative Treatments Naturally termite resistant timbers, such as white cypress pine, ironbark, tallowwood, turpentine, red bloodwood, etc., may be used in the construction of susceptible structures. (full list in AS 3660.1)

Treated timbers, including structural particleboard flooring, which have been impregnated with Copper Chromium and Arsenic salts (CCA), which turns the timber a distinctive green colour, is also termite resistant and very durable.

Laminated vapour barrier, similar to ‘Kordon - TBM’, is made up of a 200 micron top layer with a mid synthetic fibrous web impregnated with insecticide and a bottom protection layer of 50 micron. Steel frame construction is also an option, however any other timber in the structure, including furniture and fixtures, is still susceptible to attack. There are also other forms of non-toxic termite prevention being developed which include a fungus called ‘Metarizium’, a naturally occurring fungal termiticide. When it becomes commercially available, it will add to the safe arsenal which may be used in the control of termites. Further details and information may be obtained from AS 3660.1 - 1995 (reprinted 1998) and/or manufacturers brochures and technical data.

Graded stone in cavity to be min. 75mm deep

Flashing

Weep hole

Graded stone under slab min. 75mm thick

Graded stone around slab penetrations to be min. pipe diameter plus 50mm.

Graded stone perimeter barrier min. 100mm x 100mm

Vertical termite shielding cast into paving min. 75mm deep

75

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CONSTRUCTING A SLAB-ON-GROUND

The following details provide a step-by-step procedure which may be adopted to prepare, construct and finish a typical slab-on-ground for a residential cottage:

Fig. 29 Preparing the slab site

Fig. 30 Preparing the trenches and beams

Step 1 Excavate and level the site, then set out the structure Sloping sites for house slabs are often cut and filled to provide a level area for the slab. Alternatively, footing systems such as the stiffened slab with deep edge beam can be used. All vegetation and grass and roots must be removed from the area where the slab is to be poured. Any filling required must be controlled and compacted in accordance with AS 2870-1996. “Residential slabs and footings - Construction” and AS 1289.5 to .6 “Soil testing.”

Step 2 Excavate the trenches / beams The perimeter trenches and internal beams are usually excavated by backhoe and then cleaned up by shovel. Prepare trenches for drainage pipes at this point also.

Cleaning up the base of perimeter beams



Fig. 31 Perimeter formwork in place for brick veneer construction

Alternative Slab Edge Rebate Details Single Leaf External Walls For single leaf masonry no rebate is required, e.g. garage slab with single skin and engaged piers, and in such cases the formwork can be set up with its top edge level with the top of the proposed finished slab.

Fig. 32 Edgeboard detail for a garage slab

Step 3 Set up the formwork; Identify the surveyors ‘offset pegs’ , then drive in a series of formwork pegs to support the slab edgeboards. Keep the pegs vertical and at least the thickness of the edgeboard formwork away from the line. Square the edgeboards and fix off at the required height. The height of the top of the formwork differs according to whether a rebate is to be formed or not, and also how that rebate will be formed. Lay drainage pipes in the prepared trenches, pressure test for leaks and then backfill.

Edge treatment to garage door threshold

Finish to re-mainder of slab

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Brick Veneer and Cavity Brick External Walls A rebate is required where a wall is constructed with a cavity, such as for brick veneer or cavity brick construction. For slabs with a rebate the edgeboard formwork can be set up below the top of the slab level and the rebate is formed by either cantilevering timber ledgers, anchored with pegs, or using patent metal brackets to hold the secondary edgeboards. These secondary edgeboards form the face of the rebate and provide a finishing level for the main slab surface.

Fig. 33 Methods used to form a slab edge rebate

Fig. 34 Sand layer in place to form an accurate under-slab shape

Cantilevered ledger

Edge forms

Steel formwork bracket

Edge forms

Step 4 Screed and compact a sand bed or blinding layer; Spread a layer of packing sand under the slab. This will allow the final level of the ground under the slab to be accurately screeded and it also protects the vapour barrier / damp-proofing membrane from being punctured during the concrete pour.



Fig. 35 Polyethylene layer in place

Fig. 36 Reinforcement in position

Step 5 Lay the vapour barrier/ damp-proof membrane and termite barrier If a chemical termite barrier or reticulation system is to be placed, prepare the sand and carry out the treatment. Once the pre-treatments are complete, the membrane is laid, lapped at joints by 200 mm minimum and taped to keep it in place. Pipes and conduits which penetrate the slab should be fully taped to the membrane to seal any gaps.

Step 6 Install the reinforcement and physical termite barriers Closely follow the size and installation details given on the footing plans taking care to place the reinforcement so as to maintain the correct concrete cover. Measure and pre-cut the reinforcement before carrying it into position being careful not to damage the plastic vapour barrier / damp-proofing membrane with the sharp ends and edges. Once in place, the reinforcement can be lifted up onto bar chairs or trench mesh supports and tied with tie-wire at laps or joins. Tie the bar chairs to the reinforcement also to prevent dislodgment during the concrete pour, unless snap fit chairs are used. Fit stainless steel mesh termite barrier collars around pipes or fit a styrene sleeve to allow for crushed graded stone to be placed at a later date.

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Fig. 37 Applying a release agent to forms

Inspection Once the formwork is complete, the base prepared and the reinforcement placed, the Principal Certifying Authority (PCA) is notified to carry out an inspection at this stage prior to pouring the concrete. This will be the first of several inspections carried out during the whole construction. Note: Wear appropriate personal protective equipment (PPE);

Step 7 Apply a ‘Release agent’ Where concrete is in contact with bare timber a release agent should be applied to the face of the edgeboards. This prevents cement slurry or paste from sticking to the surface of the formwork, and allows the formwork to release from the hardened concrete when stripping or dismantling without damage. The simple operation of brushing, brooming, spraying or rolling on a diluted solution of light oil and diesel, or a prepared ‘Form oil’ , can overcome the need to patch surfaces and edges or waste time cleaning formwork.

Step 8 Pouring the concrete From the time the concrete arrives on-site to the final trowelling of the surface, the concrete will dictate how long the job will take. On a hot or windy day the concrete will dry out and stiffen quickly, making it very difficult to screed and trowel to a smooth finish. Therefore, when weather conditions are extreme it is vital that the concrete is placed, compacted and screeded as soon as possible. Larger slabs or those with restricted access, are usually pumped from the street. This tends to be the most popular method of placement as it is quick, fewer workers are required and the concrete may be placed by the pipe jockey anywhere within the slab with minimal disruption to the pour or damage to the reinforcement and plastic membrane. Small slabs may be poured directly from the concrete truck chute and barrowed to the middle of the slab, using planks as a temporary run way. Care should be taken not to flatten the bar chairs or cause damage to the reinforcement and plastic membrane during this procedure.

Forms for a rebate edge slab

Release agent



Concrete will ruin your hands (and leather boots) because it is alkaline (opposite to acid), so wear gloves and gumboots. Dishwashing gloves are ideal protection, but if gloves are not available or acceptable, a good quality hand cream is advisable. Pumping Procedure • Fill all the trenches / beams first, to the underside of the slab. This will mean that the

freshest, most workable concrete is in the slab and easier to work level and smooth. • After the trenches have been filled, fill the slab and allow some excess concrete to be raised

above the forms. • Work from one end of the slab to the other, filling to the desired level before moving on.

This will allow compaction and screeding to start immediately, while the concrete is being placed for the rest of the slab.

Fig. 38 Using the immersion vibrator to compact and remove air

bubbles

Step 9 Vibrating and Screeding the concrete The concrete is usually placed to finish just higher than the forms to allow for settlement during compaction with an immersion vibrator. The vibrator should be inserted and withdrawn vertically at intervals of approx. 500mm. Each insertion should be vibrated until the air bubbles cease to be visible at the surface. The additional concrete height will also allow hollows to be filled progressively as the surface is being screeded to a level plane. Excess concrete is spread or pulled away from the screed using a short handled square mouth shovel. Do not use the vibrator to spread the concrete as this causes segregation. ‘Level dots” can then be established using a levelling instrument, such as an automatic or laser level. The level dots are small areas of levelled concrete which have been accurately smoothed off to the finished slab level.

Hold vibrator hose firmly and lift vertically when moving to next position

Hold vibrator in place until the bubbles stop rising

Immerse to a depth just above the reinforcement

The level dots are small areas of levelled concrete which have been accurately smoothed off to the finished slab level. Additional concrete is placed between these dots, or removed as required, allowing the screed to link the level areas progressively until the whole slab surface is complete. The screed is moved towards the user in a sawing ‘side to side’ motion which allows the excess to be removed and the surface to be partly compacted.

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Fig. 39 Screeding the wet concrete surface



Fig. 40 Using the Bullfloat

Fig. 41 Using a mechanical trowel

Step 11 Surface finishing By the time the slab is ready for hand floating it should be possible to walk on, with the use of knee and foot boards. The steel hand float is used in a series of sweeping arcs, rocking it slightly from one edge to the other to change direction. This action works up a mortar / slurry which then fills in holes and cracks in the surface. Hand floating will bring up further surface bleed water. Mechanical trowel finishing (also known as a helicopter) can be used instead of hand floating. Wait until the concrete is hard enough to support the weight of a person, without significant surface marking, before commencing.

Step 10 Float the surface of the slab Floating of the surface is usually carried out with a Bullfloat, or wooden float for small surface areas. Screeding and Bullfloating will bring up surface ‘bleed water’ . Final finishing should not commence until the bleed water has disappeared. Note: Never use sand and cement, known as ‘driers’, onto the surface to soak up bleed water as this will make the finished surface weak and dusty.

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Fig. 42 Typical edging tools NOTE: Further information relating to surface finishing, applying a non-slip finish, stripping/ cleaning/storing of tools and formwork, preparation and patching of masonry surfaces, patching materials and finishing may be found in “Basic Building and Construction Skills” chapter 7.

Step 12 Edge finishing Where edges of the slab are to be exposed, i.e. the edges of patio’s, verandahs or a garage entry, they should be finished with an edging tool. This will improve the appearance and provide a stronger edge which is less likely to be chipped. The edging tool should be run along the edge as soon as possible after the first floating of the slab and again when the final trowelling is being done. The early run will ensure that the stones in the mix are worked down from the surface so they are not pulled out when final edging is carried out. This should also be done if centre control joints are to be run, especially for paving.



CLEANING MASONRY SURFACES Where masonry has been patched using a cement based product it is quite common for some smearing on the surface to remain. These smears may be removed by either hand or pressure cleaning. Hand Cleaning Small areas are commonly cleaned by hand using a bucket, two-knot brush, scraper and a weak solution of acid and water. Making sure the operator is protected by covering all exposed skin, wearing a face shield, hat, rubber boots and elbow length rubber gloves, the following procedure may be adopted; • Wait until the mortar has hardened, and remove all large mortar particles with hand tools

before applying water or cleaning solutions. A wooden paddle, a brick or a chisel may be used if necessary to remove hardened mortar or concrete;

• Mask or otherwise protect surrounding surfaces such as metal, glass, timber, finished concrete, face brickwork, etc., prior to using any cleaning solution. Saturate the area with clean water.

• Prepare a weak solution of Hydrochloric acid and water, i.e. 10 to 20 parts of water to 1 part acid, and working in small areas, say 1m² max. After cleaning dust and other loose particles off the area apply the acid solution with the knot brush. Rub the area vigorously with the brush, using a scraper or wire brush on stubborn marks, for 3 to 6 minutes;

• Rinse the area thoroughly with clean water making sure the acid is not allowed to dry, as this may cause salts to form on brickwork or it may turn green;

• Repeat process until the affected area is clean. Pressure Cleaning Larger areas of walls and floors are normally cleaned by pressure cleaning or water blasting. The pump is fed by tap water and forces this water through a high pressure hose, hose gun and pressure jet. The pressure and angle of the water spray is determined by the pressure jet orifice size and shape in the end of the gun. The pressures usually used for brickwork are up to 14,000 kPa and the gun should be continuously moved to prevent surface damage. Spraying of brick joints should be avoided as they are easily ‘blown out’ which leads to follow up mortar patching. The operator should be protected as for hand cleaning but should also have a full plastic suit to cover the body and a plastic hood to cover the head, before the following procedure is adopted; • Prepare and protect the surfaces as for hand cleaning and saturate the areas with clean water

prior to blasting; • Apply the cleaning solution, i.e. 10 parts water to 1 part Hydrochloric acid, by brush or low

pressure spray. Allow to soak for approx. 5 minutes then wash the wall down with clean water on low water blasting pressure to prevent acid droplets being sprayed everywhere.

• After initial light spraying, carefully pressure clean the affected areas working from top to bottom on walls and moving the gun continuously to prevent surface damage.

• After thorough cleaning, go back over the area and wash down with clean water including all surrounding surfaces.

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GLOSSARY OF TERMS Alkaline - Substances which are soda, caustic soda or soda ash - like and have

the capacity to burn human skin. Concrete has a mild burning affect on the skin which can cause irritation and some peeling of the skin.

Bleed water - Also known as ‘Laitance’, is the free water in a concrete mix which rises to the surface after compaction. It forms on the surface and usually has a tell-tale whitish coloured scum on it’s surface.

Cohesive - Any material or combination of materials which has the capacity to stick together when not confined or supported by a solid form. In this case sand which packs down tightly and retains it’s shape.

Constant - A quantity which does not change, i.e. a figure which may be used time and time again to achieve the same result using a constant base rate.

Damp-proof membrane -

This is any sheet material which will not allow water or moisture to pass through.

Driers - A mixture of dry sand and cement sometimes thrown over the surface of over-wet concrete to soak up the bleed water. Unless it is mixed with a partly course aggregate or carborundum dust, it tends to weaken the surface of the concrete and ends up going dusty, thereby exposing the course aggregate in the mix.

Erosion - This is the weathering or wearing away of rock and soils due to the action of wind and water. Fine upper layers are worn away and transported from their original setting to another location by the wind and/or rain stormwater

Form-oil - This is a release agent used to coat the faces of timber and steel formwork to allow the forms to be removed without sticking to or damaging the concrete face and edges. Form-oil is a proprietary product of light oil mixed with a wetting agent to allow easy spreading.

Fungus - A plant-like form which feeds off other plant matter rather than converting it’s own sugars and water into food, like a plant which uses chlorophyll. It usually grows on moist decaying vegetable matter and reproduces by spreading spores.

Heave - This is an upward movement of soil or foundation material caused by swelling, as with clay, or displacement due to a solid member being driven into the foundation, like a pile. Trapped frozen water within foundation material may also cause heave by the natural action of water expanding when frozen.

Hogging - This is the result of heave in a structural member , such as a concrete footing beam, which results in the underside of the beam having a concave curved surface. It may also refer to the purpose formed camber in a horizontal timber member, such as a truss bottom chord.

Igneous - This is any rock which has been formed due to heat and pressure during volcanic action, e.g. basalt, granite, quartz, etc. A crystalline or glass-like rock is formed from molten rock, when cooled.



Mandatory - Anything which must be carried out or completed. It refers to a compulsory act or action.

Orifice - A small opening or mouth-like formed shape in a material or tool.

Parallelogram - Any plain four sided figure whose opposite sides are parallel.

Parged - This is when a rough coat of material is applied to the inside of a chimney or plaster work, or it may refer to the application of a mixture of resin which is applied roughly to the face of a concrete slab to hold and seal stainless steel termite mesh in place.

Philosophy - In this case it relates to a system or theory put up by environmentalists. It is a summing up of one’s belief in an approach to life or carrying out work.

Rhomboid - A geometric quadrilateral figure which has it’s opposite sides and opposite angles equal, as opposed to a square which has all sides and angles the same.

Screeds - Thin strips of timber or metal used to form shapes which require striking off to a particular height or thickness. They are similar to edgeboards or edge formwork.

Segregation - This is the separation of materials due to vibration, impact or over wetting. When concrete segregates, the heavier particles sink to the bottom and the lighter particles and water rise to the top. This weakens the mix as the various particles are no longer evenly distributed.

Silasec - This is a proprietary, brand name, compound similar in appearance to a very wet mix of cement and water, which is used in waterproofing concrete, render, brickwork and masonry.

Spall - This is the action of concrete being squeezed and popping or cracking out. Where the concrete cover to reinforcement has cracked and popped off due to the rusting steel in concrete cancer, it is referred to as ‘spalling’

Spoil - This is excavated foundation material which becomes excess or unsuitable for re-use on a particular project. It may be removed and stockpiled on a site for later re-use as backfill.

Termiticide - This literally means that it ‘kills termites’. Any chemical or poison used to kill termites is classed as a termiticide. Any word containing ‘cide’ on the end means to kill, e.g. suicide, fungicide, herbicide, infanticide, homicide, etc.

Vapour barrier - A layer or sheet which prevents the passing of water vapour from a warm interior to a cooler exterior such as would occur under a slab when the warm moisture in the soil meets the cool underside of the concrete. It prevents this moisture being soaked into the concrete where it may rise and cause damage to internal fittings and fixtures.

CARPENTRY - HOUSING


FURTHER READING

Barrington, J., D. Mylius & S. Arden, 1989, Book 1 Practical Australian Carpentry, Framing and Construction, McGraw Hill, Sydney Brown, B. and H. Slatyer, 1985, First published 1958, Second edition 1966, Third edition 1975, Fourth edition 1981, Fifth edition 1985, The Australian Carpenter and Joiner - Volume 1, Standard Publishing Co Pty Ltd, Victoria. Cameron, A. D. and R.G. Williams, 1970, Metric Practice for Building Technicians, Collins, London and Glasgow. Evans, H. E., 1984, Insect Biology, Addison-Wesley Publishing Company Inc., USA and Canada. Hadlington, Phillip. W. and Judith A. Johnston, 1990, An Introduction to Australian Insects, NSW University Press, Kensington, Sydney. Hadlington, P., 1992, Termites and other common timber pests, NSW University Press, Kensington, Australia. McAdam, Peter. S., 1993, Formwork - a practical approach, Stuart Publications, Red Hill, Queensland. National Committee on Rationalised Building, 1994, Fourth edition, Glossary of Building Terms, Standards Australia, Sydney. Peters, B. C., J. King, F. R. Wylie, 1996, Pests of Timber in Queensland, Publishing Services - Department of Primary Industries, Queensland. Simpson, Charles. and Barry Hodgson, 1995, Building a House - Footing Systems, Macmillan Education Australia, South Melbourne. Standards Association of Australia, 1996, AS 2870: Residential slabs and footings - Construction, Standards Australia, Homebush, Sydney. Standards Association of Australia, 1995, AS 3660.1: Protection of buildings from subterranean termites - Part 1: New buildings, Standards Australia, Homebush, Sydney. TAFE / The Waste Challenge, 1997, Minimising Construction & Demolition Waste, Construction and Transport Educational Services Division, Castle Hill, Sydney Teachers of Building, 1996 Reprinted 1997, 1998, Second Edition 1999, Basic Building and Construction Skills, Addison Wesley Longman Australia Pty Ltd , South Melbourne.

VIDEOS

Construction and Transport Division, Concreting on a small scale, (CTV15) available from Resource Distribution, Yagoona.

Documents

TAFE Slab on Ground