Site Practice. Concrete Construction. Alistair Russell

Transcription

1 Site Practice Concrete Construction Alistair Russell

2 Site Practice Site practice affects finished product Handling & placing Compaction & finishing Curing Cracking & expectations Joints & tolerances Context: Concrete slabs 26 March 2015 Concrete Construction - Site Practice 2

3 CCANZ Courses We have 4 courses on offer including a 2- day course devoted to just this topic we can t do that in 1 hour! Guide to Concrete Construction book free Best practice video on YouTube free 26 March 2015 Concrete Construction - Site Practice 3

4 Handling & Placing Starts as soon as concrete discharged from truck 1 st step in concrete s life Move as quickly & efficiently as possible Workable, without segregation balance 26 March 2015 Concrete Construction - Site Practice 4

5 Handling & Placing Get this right and the life of the structure will go well Get this wrong, and your life will not go well compaction etc & remediation, cost 26 March 2015 Concrete Construction - Site Practice 5

6 Primary Considerations Workability basically means how easy concrete is to use and place More water = more workable Generally runnier concrete is easy to use TOO RUNNY = SEGREGATION Long term performance 26 March 2015 Concrete Construction - Site Practice 6

7 Workability (slump) Workability related to nature of job Thin forms more workable concrete Mass sections less workability required Concrete pumps require a plastic and cohesive mix 26 March 2015 Concrete Construction - Site Practice 7

8 Placing Avoiding Segregation Aiding Compaction Correct term is placing not pouring Implies some control over process 26 March 2015 Concrete Construction - Site Practice 8

9 Avoiding Segregation Flatwork General Principles Whatever method, place without delay Deposit in face already poured Slopes-start at bottom 26 March 2015 Concrete Construction - Site Practice 9

10 Distribution Methods Chutes Barrows Crane & skip or Bucket/skip Pumps and Pipelines Concrete must be uniform and delivered at appropriate rate x m 3 /hour 26 March 2015 Concrete Construction - Site Practice 10

11 Pumps and Pipelines 26 March 2015 Concrete Construction - Site Practice 11

12 Pumps and Pipelines Specialised pumping operations Notify concrete supplier of method of placement NZS 3109, 6.2 Pump mixes High slump High(er) shrinkage Not great off-form finish 26 March 2015 Concrete Construction - Site Practice 12

13 Compaction & Finishing Often compaction and finishing are part of the same operation Often for flat work flat horizontal surfaces Remember a smooth surface is not necessarily evidence of good compaction 26 March 2015 Concrete Construction - Site Practice 13

14 Compaction 26 March 2015 Concrete Construction - Site Practice 14

15 Compaction Compaction enables concrete to reach: Design strength Density Low permeability Specified surface finish Compaction sometimes merges into finishing 26 March 2015 Concrete Construction - Site Practice 15

16 Purpose of Compaction Expel entrapped air Pack aggregate particles Increase Reinforcement bond Ultimate strength Abrasion resistance Durability Minimise shrinkage and cracking Increases density 26 March 2015 Concrete Construction - Site Practice 16

17 Process of Compaction 2 stage process Liquefaction occurs quickly Expelling entrapped air more slow Compaction is complete when no more air bubbles rise to surface PROCESS: Liquefaction of the concrete which allows it to slump and fill the form TIME: 3 to 5 seconds. Total time: seconds PROCESS: The expulsion of air TIME: 7 to 15 seconds 26 March 2015 Concrete Construction - Site Practice 17

18 Effect on Hard Concrete 26 March 2015 Concrete Construction - Site Practice 18

19 Finishing 26 March 2015 Concrete Construction - Site Practice 19

20 Flatwork Finishing While concrete is still plastic: Levelling Floating Trowelling Other treatments Purpose of finishing is to achieve: Level or specified profile Flatness Surface density and texture 26 March 2015 Concrete Construction - Site Practice 20

21 Flatwork Finishing 1. Screeding hand/timber/mechanical screed 2. Floating To level surface Compact surface layers 3. Trowelling To produce smooth, hard and durable surface & densify surface 26 March 2015 Concrete Construction - Site Practice 21

22 Screeding 26 March 2015 Concrete Construction - Site Practice 22

23 Floating Even but open surface texture Embed large particles Remove imperfections Compact and consolidate fines at surface Close minor cracks When bleed water stops Must be able to stand on concrete minor indentations 26 March 2015 Concrete Construction - Site Practice 23

24 Floating Bull floating Hand floating Machine floating 26 March 2015 Concrete Construction - Site Practice 24

25 Trowelling Final surface treatment Working the surface Compact top surface Delay between floating and trowelling Stiffening of concrete Smoothness, density & wear resistance 26 March 2015 Concrete Construction - Site Practice 25

26 Trowelling Flat blade don t create ripples Subsequent trowels tilt the blade Once concrete is firm enough Blisters mean blade is too pitched Blisters reduce durability + ugly 26 March 2015 Concrete Construction - Site Practice 26

27 Trowelling Hand trowelling Should give a ringing sound Machine trowelling Regular pattern Hand trowel in corners 26 March 2015 Concrete Construction - Site Practice 27

28 Trowelling 26 March 2015 Concrete Construction - Site Practice 28

29 Trowelling 26 March 2015 Concrete Construction - Site Practice 29

30 Edging Footpaths, patios, paths & steps Not in industrial floors need crisp edge 26 March 2015 Concrete Construction - Site Practice 30

31 Curing 26 March 2015 Concrete Construction - Site Practice 31

32 Curing Cement hydration chemical reaction Requires water Takes days, weeks Starts fast, gets slower, will continue (forever) Curing process of controlling loss of moisture Allows time for hydration to occur 26 March 2015 Concrete Construction - Site Practice 32

33 Curing Prevent loss of moisture Leave formwork in place Cover with impermeable membrane Continuously wetting surface Ponding Spraying 26 March 2015 Concrete Construction - Site Practice 33

34 Methods of Curing Impermeable Membrane Formwork Plastic sheeting Water Ponding Sprinkling * Wet coverings Accelerated curing *Water blaster spraying upwards into wind 26 March 2015 Concrete Construction - Site Practice 34

35 Curing Compounds Comprehensive physical barriers not always practical/economical Curing Compounds achieve same results Sika Antisol Apply after bleed water stops Be aware of coatings Wax based no painting Resin based ok to paint (acrylic) 26 March 2015 Concrete Construction - Site Practice 35

36 Surface Treatments For appearance or function Surface treatments depends on: Traffic & frequency Chemicals Impact loads Warehouse floors with steel wheel loads (forklifts) high strength concrete Specified by designer Proper compaction, finishing and curing 26 March 2015 Concrete Construction - Site Practice 36

37 Polished Floors Densifiers for polishing floors 26 March 2015 Concrete Construction - Site Practice 37

38 Slip & Skid Slip for pedestrians Skid for wheels NZS 3114 defines surface finishes F Formed finish (from formwork) U Unformed finish (exposed to air) 26 March 2015 Concrete Construction - Site Practice 38

39 Slip & Skid Slip for pedestrians Skid for wheels NZS 3114 defines surface finishes F1 F6 26 March 2015 Concrete Construction - Site Practice 39

40 Slip & Skid Slip for pedestrians Skid for wheels NZS 3114 defines surface finishes U2 U5 26 March 2015 Concrete Construction - Site Practice 40

41 Floor Tolerances Examples U3 Trowelled Finish Gradual variations limited to a maximum of 5 mm. Abrupt variations limited to a maximum of 3 mm. 26 March 2015 Concrete Construction - Site Practice 41

42 Formwork Removal Formed Finish Classification Hot Conditions > 20 Beam and slab soffits Average Conditions 20 > 12 Forms 4 days 6 days 8 days Supporting members (shores or backprops) Vertical faces Finishes F6, F5, F4 Finishes F3, F2, F1 12 days 18 days 24 days 1 day 2 days 3 days 9 hours 12 hours 18 hours Cold Conditions 12 > 5 A minimum of 2 days applied to the stripping of vertical faces where frost damage is likely. Table 5.3 NZS 3109 minimum formwork stripping times for in situ concrete 26 March 2015 Concrete Construction - Site Practice 42

43 Other Finishes Exposed Aggregate Sand Blasted Brushed Polished 26 March 2015 Concrete Construction - Site Practice 43

44 Exposed Aggregate Natural rounded coarse aggregate Not quarried rock (too jagged) Chemical retarder on surface Apply after bleed stops Before setting 20MPa (not 17.5MPa) Reduces stone loss 26 March 2015 Concrete Construction - Site Practice 44

45 Exposed Aggregate Surface retarder e.g. Sika Rugasol Delays hydration of cement for 3-6mm depth Garden sprayer Uniform coverage is essential Retardation period 24h Wash off prior to set Wash low pressure 26 March 2015 Concrete Construction - Site Practice 45

46 Cracks in Concrete Concrete has low tensile strength 0 24 hours - plastic shrinkage cracks prevent rapid moisture loss - plastic settlement cracks revibrate concrete - thermal movement cracks use low heat mix (eg flyash) 7 days 2 years - restrained shrinkage cracking adequate reinforcing detailing of movement joints 26 March 2015 Concrete Construction - Site Practice 46

47 Crack Avoidance Fill well compacted and even Control joints Saw cuts initiate cracking hours after finishing Insert crack inducer Joint layout 5m between (6m in NZS3604) Align with walls where possible Square bays are best 26 March 2015 Concrete Construction - Site Practice 47

48 26 March 2015 Concrete Construction - Site Practice 48

49 Joints Contraction Joints Expansion Joints Concrete shrinks 6 10mm per 10m length 26 March 2015 Concrete Construction - Site Practice 49

50 Contraction Joints 26 March 2015 Concrete Construction - Site Practice 50

51 Coloured Concrete Oxides most coloured concrete Mixing is important Spray on coloured compounds Can fix as you go Less durable Coloured concrete usually doesn t affect the strength 26 March 2015 Concrete Construction - Site Practice 51

52 Colouring Oxides 26 March 2015 Concrete Construction - Site Practice 52

53 Colouring Oxides Powdered or liquids Penetrate all through the concrete Add to mixing concrete Peter Fell Permacolour NZ Rockwood Elements and Atmospheric range Part of the specification Seek expert advice Beware multi-batch variations 26 March 2015 Concrete Construction - Site Practice 53

54 Further Reading IB 18: Architectural Surface Finishes IB 33: Specification and Production of Concrete Surface Finishes IB 86: Self-Compacting Concrete CCANZ Concrete Construction Course 8-9 September, Auckland 26 March 2015 Concrete Construction - Site Practice 54

55 Site Practice Concrete Construction Alistair Russell

56 Concrete Mix designs and Applications Baldev Kesha

57 Concrete Standards NZS 3101 Concrete Structures- A Standard for designers NZS 3109 Concrete Construction- Should be on every job site outlines good construction practice. NZS 3104 Specification for Concrete Production- Outlines the quality controls rules for producing concrete. NZS 3121, NZS 3122, AS1478, Quality of materials which are use to make concrete NZS3111, NZS3112 Method of conducting tests to prove properties 57

58 Basic concrete materials Portland cement reacts with water to provide strength Sand (fine agg) provides cohesion & workability Stone (coarse agg) provides stiffness and limits movement Mixing water provides lubrication and hydrates cement 58

59 Chemical Admixtures Water reducers improve dispersion and cut water content Air-entrainers create micro-bubbles that improve workability Accelerators increase chemical reaction & reduce setting time Retarders decease chemical reaction & increase setting time Pump aids stabilisers that increase viscosity of concrete Shrinkage reduce drying shrinkage of concrete Others corrosion inhibitors, expansive agents, foamers 59

60 Supplementary Cementitious Materials (SCM s) Flyash, fine ash from burning coal, supplied by GBC from Huntly. GGBS, Ground Granulated Blast Furnace Slag. Waste product from iron manufacture. Sold as Duracem as a Slag/GP blend 65/35. Microsilica- very fine natural silica sold by GBC. All improve the durability of concrete but have differing characteristics. 60

61 Other Materials Recycled slurry water: Increasing plants are reusing washing water in concrete rather than disposing Steel and synthetic fibres: Increasing demand for fibre reinforced concrete in floor slabs, tunneling & mining Surface treatments, pigments Aesthetics of concrete is critical for some architectural projects 61

62 Components of Concrete 62

63 Concrete performance Fresh properties First 6-10 hours Performance Workability Bleeding Pumpability Finishability Setting time Hardened properties Next years Strength Durability Stability Aesthetics 63

64 Components of Concrete 64

65 Concrete performance Fresh properties First 6-10 hours Performance Workability Bleeding Pumpability Finishability Setting time Hardened properties Next years Strength Durability Stability Aesthetics 65

66 Displays 66

67 Making Samples Fontera Colaberation Internal and External finishes Client, Architect, Interior Designer, Landscape Architect, Main contractor, Placer Kerikeri Stone Store Historical site We will endeavour to find a suitable site to view 67

68 Muriwai Atmospheric Black 68

69 Silverdale Shopping Centre Concrete tells a History story 69

70 Waikato University 70

71 Speights Ale House - Nelson 71

72 ASB Black Polished Floor 72

73 Tait - Christchurch 73

74 Thank you 74