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EGB273 (completed)
Concrete Construction
| Question | Answer |
|---|---|
| FORMWORK 1 | - QUALITY OF FINISHED CONCRETE DEPENDS LARGELY ON FORMWORK - FORMWORK REPRESENTS 40% OF THE COST OF A SUSPENDED CONCRETE SLAB - LABOUR INTENSIVE - PRESENTS OPPORTUNITY FOR INNOVATION TO CONSTRUCTOR |
| FORMWORK - INDUSTRY STANDARD PRACTICES 1 | - PLY FACING AND TIMBER BACKING ADOPTED FOR BASIC WORK - PLY FACING AND STEEL BACKING USED FOR REPEATED OPERATIONS - STEEL FORMS USED FOR MANUFACTURED PRODUCTS |
| FORMWORK - INDUSTRY STANDARD PRACTICES 2 | - TELESCOPIC STEEL PROPS/FRAMES USED TO SUPPORT FORMS - JUMPFORM TECHNIQUE USED IN HIGHRISE, SILO CONSTRUCTION, COOLING TOWERS |
| Slip Form | Slipform uses a structure’s core for its support, and it slowly moves up the structures' core while wet concrete is poured in a continuous, long pour, forming the concrete layer of the structure |
| Jump Form | The use of jumpform involves a progression of a series of “jumps” or levels of concrete pours vertically upwards. On each level, concrete is poured and sets before jumping or progressing to the next level until the structure's concrete layer is completed |
| QUALITY 1 | 1 UNIFORM TEXTURE, CLOSE TOLERANCES (“OFF FORM” SURFACES EXTERNALLY) 2 LIMITED IMPERFECTIONS, NO CLOSE SCRUTINY (CIVIL STRUCTURES) |
| QUALITY 2 | 3 TO BE RENDERED OR CONCEALED (BUILDING COLUMNS) 4 PERMANENTLY CONCEALED (FOOTINGS) |
| FORMWORK QUALITY - PREVENTING GROUT LOSS 2 | Implementing timber fillets, bed fillets in mould cream and plys around the concrete |
| FORMWORK QUALITY - Column Form | There is very high pressures at the base of the column form. There is also a foam strip to the bottom edge at the base of a column form for concrete |
| FORMWORK QUALITY ISSUES 1 | SURFACE IMPERFECTIONS DAMAGE OCCURRING TO PLASTIC FILM - FAILURE TO USE FORM RELEASE OIL - ABRADING WITH VIBRATORS - CARELESS STRIPPING |
| FORMWORK QUALITY ISSUES 2 | DAMAGE OCCURRING TO PLY UNDER FILM - HEAVY OBJECTS DUMPED ON SURFACE - GOUGING WITH REINFORCING BARS INSPECT AND REPAIR BETWEEN USES |
| FORMWORK QUALITY - DEFLECTIONS | - TRULY HORIZONTAL EDGES - APPEAR SAGGED (USE PRECAMBERING) - CARE TO ALIGN TOP EDGES BY EYE - LIMITED TO 1/360 SPAN (IMPORTANT WORK USE 1/500 SPAN) - CALCULATE FOR WEIGHT OF CONCRETE - BE AWARE OF CRUSHING OF TIMBER |
| FORMWORK QUALITY - STRIPPING FORMS | - DESIGN STRIPPING PROCEDURES INTO FORMS - ENSURE INSERT TO RELIEVE TRAPPED FORMS - AVOID METAL TOOLS – USE TIMBER WEDGING - REPAIR AND OIL FORMS IMMEDIATELY AFTER STRIPPING - STORE FORMS OUT OF WEATHER |
| CONCRETE CONSTRUCTION Code | (AS 3600-2009) |
| PLACING CONCRETE - PROCEDURES | - DISCHARGE DIRECTLY FROM TRANSIT MIXER (CONCRETE TRUCK) - HOIST BY CRANE AND BUCKET - PUMPING - CONVEYOR SYSTEMS - DELIVER THROUGH CHUTES (ALSO TREMIE) - SPRAYED USING PNEUMATIC PRESSURE |
| CONCRETE INTERFACE - SHRINKAGE STRESS 1 | - SIZE REDUCED DUE TO LOSS OF MIXING WATER DURING CURING - MOVEMENT RESISTED BY MECHANICAL BOND (SOME CHEMICAL) |
| CONCRETE INTERFACE - SHRINKAGE STRESS 2 | - INABILITY TO MOVE PRODUCES TENDANCY TO CRACK - SERIOUS FOR WATER RETAINING STRUCTURES DUE TO LIMITED REINFORCING - LOW WATER CEMENT RATIOS LIMIT SHRINKAGE |
| COMPACTION OF CONCRETE 1 | - WATER CEMENT RATIO MUST PERMIT PLACEMENT OF CONCRETE - OVER VIBRATION CREATES POOLS OF DESEGREGATED SLURRY - AVOID DIRECT VIBRATION OF REINFORCEMENT IN LARGE POURS |
| COMPACTION OF CONCRETE 2 | - PENCIL VIBRATORS NEEDED FOR AREAS OF DENSE REINFORCEMENT - DANGERS OF REVIBRATING CONCRETE WHICH HAS TAKEN INITIAL SET - RATE OF POUR MUST BE MATCHED TO MAINTAINING FRESH EDGE |
| PLACING CONCRETE - AIDS TO PLACEMENT - VIBRATION | - HIGH FREQUENCY, LOW AMPITITUDE - IMMERSION OR FORM MOUNTED |
| PLACING CONCRETE - AIDS TO PLACEMENT - CHEMICAL ADDITIVES | - PLASTICISERS – to reduce water ration - RETARDERS – help workability - ENTRAINED AIR – low temperatures for example |
| IMMERSION VIBRATION | A Pneumatic Vibrator is placed through the concrete surface and vibrates until bubbles of air reduce abruptly |
| FORM VIBRATION | PRODUCES COMPACTION OUTSIDE REINFORCING CAGE - VIBRATION CONCENTRATED OUTSIDE REINFORCING - FLAT VIBRATOR CLAMPED TO STEEL FORM - COMPLETE FORM VIBRATES |
| PLACING CONCRETE - QUALITY TECHNIQUES | - AVOID DROPPING CONCRETE THROUGH REINFORCING (WINDOWS IN FORMS) - CONSCIOUSLY BALANCE LOADING ON FORMS - PROVIDE FORMWORKERS TO MONITOR DURING CRITICAL POURS - PARTICULAR CARE TO AVOID TRAPPING AIR UNDER INCLINED SURFACES |
| SEGREGATION | - CONCRETE IMPACTS REINFORCING AND A SIEVING ACTION TAKES PLACE - LARGER COMPONENTS ARE RETARDED - SMALLER COMPONENTS FLOW MORE EASILY AROUND BARS - FINAL CONCRETE IS SEGREATED BY PARTICLE SIZE |
| SURFACE FINISHING 1 | - TIMING DEPENDS ON TEMPERATURE AND RELATIVE HUMIDITY OF AMBIENT AIR - A CRITICALTASK REQUIRING SKILL AND TIMING - DANGERS OF ADDING CEMENT OR EXTRA WATER TO SURFACE |
| SURFACE FINISHING 2 | - ADDITIVES USED TO PRODUCE NON-SLIP OR HARD WEARING - MECHANICAL PROTECTION OF FINISHED SURFACE - HIGH INCIDENCE OF HAND WORK |
| PLACING QUALITY - TESTING DURING POUR | Slump Test |
| PLACING QUALITY | - USE MOULD OIL AND MOISTEN FORMS BEFORE POURING - MONITOR FORMS DURING POUR - CHECK CAST-IN ITEMS IMMEDIATELY AFTER FINISHING PLACING - MAINTAIN CONCRETE TEMPERATURE BELOW 30O C (COVERS, ICE WATER) |
| CONCRETE CONSTRUCTION - CURING Code | (AS 3799-1998) |
| CURING CONCRETE | - NECESSARY TO MAXIMISE RETENTION OF FREE WATER IN CONCRETE - CONCRETE CONTINUES TO STRENGTHEN THROUGHOUT LIFE |
| METHODS USED FOR CURING CONCRETE | - WATER CURING - ENCAPSULATION IN IMPERVIOUS FILM (PLASTIC) - MEMBRANE CURING - STEAM CURING |
| CURING CONCRETE - WATER CURING | - KEEP SURFACE WET BY SPRAYING OR WRAPPING IN HESSIAN - INCONVENIENT ON MOST SITES - LACKS CONSISTENCY - SUITED TO SLABS, PARTICULARLY DOMESTIC CONSTRUCTION - ECONOMICAL SOLUTION FOR SMALL JOBS |
| CURING CONCRETE - ENCAPSULATION | - CONCRETE WRAPPED IN PLASTIC SHEET AND JOINTS SEALED - SUITED ONLY TO SMALL CRITICAL POURS - EFFECTIVE FOR TEST SAMPLES DURING TRANSIT - NOT WIDELY USED ON CONSTRUCTION SITES |
| CURING CONCRETE - MEMBRANE CURING 1 | - APPLICATION OF IMPERVIOUS FILM ON SURFACE BY SPRAYING OR BRUSHING - MATERIALS USED CURRENTLY DEGREGATE AFTER CRITICAL FIRST FEW WEEKS |
| CURING CONCRETE - MEMBRANE CURING 2 | - NOT DETRIMENTAL TO APPLIED SURFACE FINISHES WHEN DECAYED - WAX COMPOUNDS VERY EFFECTIVE BUT DO NOT DEGRADE |
| CURING CONCRETE - STEAM CURING | LOW PRESSURE STEAM PROVIDES HEAT AND MOISTURE ACCELERATES STRENGTH GAIN REQUIRES STEEL FORMS (DAMAGES TIMBER) PERMITS STRIPPING AND HANDLING ON MORNING AFTER POUR (MANUFACTURING) REQUIRES ATTENDANT THROUGHOUT STEAMING CYCLE |
| SPECIAL PROCEDURES - HIGH STRENGTH CONCRETE 1 | - 70 – 90 MPa CONCRETE COMMONLY USED IN HIGH RISE BUILDING FRAMES ($100,000 PER FLOOR SAVING CLAIMED) - PROVIDES SMALLER CROSS SECTION COLUMNS, EARLY STRIPPING, EXTRA STIFFNESS |
| SPECIAL PROCEDURES - HIGH STRENGTH CONCRETE 2 | - LOOKS AND BEHAVES LIKE NORMAL CONCRETE - SUPERPLASTICISER ADDED ON SITE TO ENABLE PUMPING - SITE MANAGEMENT OF PROCESS CRITICAL |
| MANAGEMENT OF HIGH STRENGTH CONCRETE 1 | - STOCKPILE ALL AGGREGATES TO ENSURE QUALITY - ORGANISE JOINT MEETINGS WITH ALL PARTIES INCLUDING WORKMEN INVOLVED - PREPARE A MANUAL OF PROCEDURE - ENSURE FIELD TECHNICIAN PRESENT AT ALL POURS |
| MANAGEMENT OF HIGH STRENGTH CONCRETE 2 | - ADD EXTRA TRUCKS TO DELIVERY FLEET AND OPERATE AT 15% BELOW CAPACITY - PLAN DELIVERY ROUTE - IDENTIFY ALL EQUIPMENT WITH TAGS - DO NOT ATTEMPT TO COMBINE TWO STRENGTHS IN ONE POUR |
| SPECIAL PROCEDURES - HOT WEATHER PROCEDURES 1 | - COMMENCE POUR AT FIRST LIGHT - PROVIDE COVER OVER POUR (WORKMEN) - SPRAY AGGREGATES AND USE ICED WATER FOR MIXING |
| SPECIAL PROCEDURES - HOT WEATHER PROCEDURES 2 | - BE PREPARED TO MAKE UNSCHEDULED CONSTRUCTION JOINT - PROVIDE ADDITIONAL LABOUR FOR FINISHING - APPLY CURING PROCEDURE IMMEDIATELY |
| SPECIAL PROCEDURES - COLD WEATHER PROCEDURES | - WARM MIXING WATER - HEAT OF HYDRATION WILL KEEP CONCRETE ABOVE FREEZING (ZERO AMBIENT AIR TEMP) - PROVIDE HEAT FOR WORKMEN (BRAZIERS) |
| COVER CONCRETE IMMEDIATELY (HAY BALES) | DELAY STRIPPING (NO STRENGTH GAIN WHILE TEMP BELOW 10 DEG) |
| MANAGERIAL IMPLICATIONS | - FORMWORK AND CONCRETE PLACING OPERATIONS PREDICTABLE - SUB-CONTRACT USED EXTENSIVELY (BUILDING) - CURING OFTEN SLOWEST PART OF CYCLE - CONCRETE NOT ACCEPTED UNTIL 28 DAYS AFTER POUR |
Created by:
Asher - S
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