SPECIFICATION FOR MIXING/ CASTING/ CURING IN SITU CONCRETE SECTION E10

Transcription

1 SPECIFICATION FOR SECTION E10 Revision Date Issue Authorised By Approved for Issue Date clarkebond Page 1 of 14

2 To be read with Preliminaries/ General Conditions. CONCRETE 101 SPECIFICATION Concrete generally: To BS Exchange of information: Provide concrete producer with information required by BS , clauses 4 and DESIGNATED CONCRETE FOR KERB BEDDING AND BACKING Designation: GEN0 Consistence class: S1 Chloride class: Cl A 105B 105C DESIGNATED CONCRETE FOR BLINDING AND MASS CONCRETE FILL Designation: GEN 1 Consistence class: S3 Chloride class: Cl 1.0 DESIGNATED CONCRETE FOR UNREINFORCED STRIP AND PAD FOUNDATIONS Designation: FND2 Consistence class: Contractors choice Chloride class: Cl 0.40 DESIGNATED CONCRETE FOR NOMINALLY REINFORCED CONCRETE STRIP AND PAD FOUNDATIONS Designation: FND2 clarkebond Page 2 of 14

3 Consistence class: Contractors choice Chloride class: Cl D 105E 105F 105G DESIGNATED CONCRETE FOR FULLY REINFORCED FOUNDATIONS Designation: RC32/40 Consistence class: Contractors choice Chloride class: Cl 0.40 DESIGNATED CONCRETE FOR GROUND BEARING SLABS Designation: RC28/35 Consistence class: Contractors choice Chloride class: Cl 0.40 DESIGNATED CONCRETE FOR REINFORCED CONCRETE SUPERSTRUCTURE Designation: RC32/40 Consistence class: Contractors choice Chloride class: Cl 0.40 DESIGNATED CONCRETE FOR REINFORCED CONCRETE POOL TANK OTHER WATER RETAINING STRUCTURES Designation: RC32/40 clarkebond Page 3 of 14

4 Consistence class: Contractors choice Chloride class: Cl SUBSTITUTION OF STANDARDIZED PRESCRIBED CONCRETE FOR DESIGNATED CONCRETE: General: Conform to BS , clause 9. Substitution: In accordance with BS , table A Proposals: Submit for each substitution, stating reasons. Site mixing: Not Permitted Rate of sampling for compressive strength testing: as specified in clause 522 B. 200 B EQUIPMENT Provide the following equipment on site and maintain in good condition: Slump Cone and rod 150mm steel cube moulds Max/ Min Thermometer and standard tamping rods 30m Tape 3m Tape Soil Thermometer Spirit Level Plumb Bob (light & heavy) Curing Tanks with Temperature Control. MATERIALS, BATCHING AND MIXING 215 A READY-MIXED CONCRETE Must be used for all concrete Production Plant: Currently certified by a body accredited by UKAS to BS EN for product conformity certification of ready-mixed concrete. Source of ready-mixed concrete: Obtain from one source if possible. Otherwise, submit proposals. - Name and address of depot: Submit before any concrete is delivered. - Delivery notes: Retain for inspection. Declarations of non conformity from concrete producer: Notify immediately. Addition of water to the concrete on site: Prohibited. 216 B CHEMICAL DRUM WASH SYSTEMS FOR READY MIXED CONCRETE Usage: Prohibited. 217 B CHLORIDE CONTENT OF MIXES The total chloride ion content of the constituents of each mix, expressed as a percentage by weight of cement in the mix, must not exceed the following: Pre-stressed concrete: 0.1 Concrete made with sulphate resisting Portland cement or super-sulphated cement: 0.2 Concrete made with Portland cement, Portland blast furnace cement and containing embedded metal: 0.4 Submit calculations demonstrating compliance. 219 B SULPHATE CONTENT OF MIXES clarkebond Page 4 of 14

5 The total sulphate content of the constituents of each mix, expressed as SO 3, must not exceed 4% by weight of the cement in the mix. Submit certification and calculations demonstrating compliance. 221 A INFORMATION ABOUT PROPOSED CONCRETES Prior to production submit: - Details listed in BS clause 5.2: - Additional information: Anticipated strength gain curves up to 54 days. 222 B EVIDENCE OF SUITABILITY For each designed mix, before making concrete for use in the works and whenever a change in the materials or mix proportions is proposed, submit and obtain approval of: 1. Details of proposed quantities of each ingredient per cubic metre of compacted concrete and proposed workability. 2. Either existing data or details of appropriate tests on trial mixes to show that the proposed constituent materials and method of manufacture will produce concrete of the required quality, which will not segregate or bleed and will be capable of being fully compacted. 225 CHANGES TO SPECIFICATION Changes to specification of fresh concrete (outside concrete producer s responsibility): Prohibited. 230 INTERRUPTION OF SUPPLY DURING CONCRETING Elements without joints: Where elements are detailed to be cast in a single pour without joints, make prior arrangements for a back-up supply of concrete. Elsewhere: - Preparation: Manage pour to have a full face, and have materials available to form an emergency construction joint while concrete can still be worked. - Before pour is completed: Submit location and details of joint, make proposals for joint preparation. 240 B CEMENT Mmanufactured by a BSI Registered Firm of Assessed Capability. Cement test certificates must declare the BSI Registered Firm's Certificate number. High Alumina Cement will not be permitted. 241 B CEMENT Provide manufacturer's test certificates before making trial mixes or concrete for use in the works. Manufacturers test certificates for cement to be obtained every 14 days or at any change in source/ supplier. Copy of test certificates to be retained on site and further copy to be sent to Engineer's office. 242 B WATER The water used for mixing and curing concrete to be obtained from a Statutory Water Authority if available, or equivalent. Otherwise it is to be tested in accordance with BS EN 1008 and the results interpreted in compliance with Annex A of BS EN B AGGREGATES GENERALLY Type(s) and sizes as specified in the mix clauses, and complying with BS EN unless otherwise stated. 251 B QUALITY OF AGGREGATES Aggregates shall be hard, durable and clean and shall not contain deleterious materials in such a form or in sufficient quantity to adversely affect the strength at any age or the durability of the concrete including the resistance to frost and to corrosion of reinforcement. Deleterious materials include: Adherent Clay particles clarkebond Page 5 of 14

6 Mica, shale or other laminated materials. Coal and other organic impurities. Iron Pyrites and soluble sulphate salts. Aggregates reclaimed from mine waste and tailings will not be used. 252 B SEA DREDGED AND/OR SEA WASHED AGGREGATES Usage: Permitted if complying with BS EN B ALKALI-SILICA REACTION Concrete mixes must be made with cement with a mean alkali content such that the total reactive alkali (Na 2 O equivalent) content of the concrete mix is not more than 3 kg/m 3. The proposed combination of cement and aggregates is to have a long history of satisfactory use in concrete so that the risk of Alkali-Silica reaction can be reasonably judged as negligible. 272 B MARINE AGGREGATES Do not use for pre-stressed concrete water retaining structures. 280 B WATER ABSORPTION OF AGGREGATES FOR WATERTIGHT CONCRETE Mix type: E10/ 105G Requirement: Not more than 3% measured in accordance with BS B MECHANICAL PROPERTIES OF AGGREGATES: for concrete pavement wearing surfaces (mix type E10/ [ ] ). 10% fines value not less than 100kN or, alternatively, aggregate impact value not more than 30%. 305 B DRYING SHRINKAGE Drying shrinkage of concrete (maximum): 0.045% - Test method: To BS EN A AGGREGATES FOR EXPOSED VISUAL CONCRETE Mix type: E10/ 105F Standard: To BS EN Limitations on contaminants: Free from absorbent particles which may cause 'popouts', and other particles such as coal and iron sulphide which may be unsightly or cause unacceptable staining. Colour: Consistent. Supply: From a single source and maintained throughout the contract. Samples: Submit on request. 325 MATERIALS FOR EXPOSED VISUAL CONCRETE Alterations to sources, types and proportions: Submit proposals. 330 B AGGREGATES - SUBMISSIONS: 1. All specified preliminary samples, results of specified preliminary tests and required preliminary information on properties to be submitted and approved before making concrete for use in the works. 2. If it is proposed to change any aggregate or source of supply, repeat all relevant preliminary samples, tests and submissions of information and obtain prior approval of the change. 3. Results of specified tests carried out during the progress of the works to be submitted to CA without delay, a copy being retained on site. 380 B STORAGE OF CEMENT: 1. Arrange delivery in suitably small consignments so that cement will be used within 4 weeks of delivery. 2. Deliver in undamaged, dry sealed bags or purpose made bulk delivery vehicles. 3. Store dry in weather tight structures with a raised floor, or in suitable silos. 4. Store different consignments (if bagged) and types separately and use in order of delivery. clarkebond Page 6 of 14

7 5. Reject any cement which is set such that it cannot be easily crumbled between the fingers. 390 B STORAGE OF AGGREGATES: 1. Store different aggregates separately on hard paved self-drained areas or in suitable hoppers or containers. 2. Check by visual inspection each load before tipping and each batch before mixing for consistency of particle shape, accuracy of grading, segregation of particle sizes and cleanliness. 3. Ensure consistency of moisture content of fine aggregate at time of batching, if necessary by allowing stockpiles to drain for not less than 16 hours before use. 411 B MIXING CONCRETE: shall be mixed until there is uniform distribution of the materials and the mass is uniform in colour, in an approved mechanical mixer. 415 A ADMIXTURES Obtain approval for use. Usage: In accordance with the manufacturers instructions. Calcium chloride and admixtures containing calcium chloride: Do not use. Compatibility: Ensure admixtures are compatible with all other materials, including other admixtures. 419 B AIR ENTRAINED CONCRETE The total quantity of air shall be ± 1.5% of the required volume. The air-entraining admixture used shall comply with BS EN PROPRIETARY STEEL FIBRES Requirement: [ ] Standard: To BS EN Manufacturer: [ ] - Product reference: [ ] Size: - Length: [ ] - Aspect ratio (length diameter): [ ] Addition rate (minimum): [ ] - Increase addition rate if necessary to achieve required properties. Dispersion in fresh concrete: Uniform without balling. 427 STEEL FIBRES Requirement: [ ] Standard: To BS EN Material: [ ] Type: [ ] Fibre properties (minimum): [ ] Size: - Length: [ ] - Aspect ratio (length diameter/ equivalent diameter): [ ] - Shape: [ ] Tensile strength: [ ] Coating: [ ] Addition rate (minimum): [ ] - Increase addition rate if necessary to achieve required properties. Dispersion in fresh concrete: Uniform without balling. 429 POLYMER FIBRES Requirement: [ ] Standard: To BS EN Material: [ ] clarkebond Page 7 of 14

8 Manufacturer: [ ] - Product reference: [ ] Size: - Length: [ ] - Aspect ratio (length diameter): [ ] Addition rate (minimum): [ ] - Increase addition rate if necessary to achieve required properties. Dispersion in fresh concrete: Uniform without balling. 436 B PUMPED CONCRETE: Prior to placing of concrete by pumping obtain approval of the CA. Submit details of the mix proportions, slump and maximum free water/cement ratio. Do not pump air entrained concrete. 440 B CEMENT CONTENT: If the cement content of any designed mix is changed, ensure that this does not result in non-compliance with any specified minimum or maximum cement content. 450 B WATER CONTENT: of concrete must be carefully controlled and adjusted to allow for moisture content of aggregates to give consistent quality and workability. 490 PROPERTIES OF FRESH CONCRETE Adjustments to suit construction process: Determine with concrete producer. Maintain conformity to the specification. PROJECT TESTING/ CERTIFICATION 501 B RATES Include in the rates for concrete work for all samples, tests and submissions which are specified but not covered separately by a priceable item or provisional sum. 505A PROJECT TESTING OF CONCRETE GENERAL Purpose: to confirm conformity of compressive strength and identity of mix supplied. Testing: To BS EN 206-1, Annex B and BS , Annexe B. - Cubes: 150mm. - Nonconformity: Obtain instructions immediately. Recording: Maintain complete correlated records including: - Concrete designation. - Composition of the mixes tested, including any admixtures. - Sampling, site tests, and identification numbers of specimens tested in the laboratory. - Location of the parts of the structure represented by each sample. - Location in the structure of the batch from which each sample is taken. - Date of sampling. 520 A TESTING LABORATORY All specified testing to be carried out by one laboratory. Laboratory: Independent and accredited by UKAS. - Name and UKAS reference number: Submit well in advance of making trial mixes or concrete for use in the works. 522 B RATE OF REGULAR PROJECT TESTING SAMPLING Samples for testing of compressive strength shall be taken at the following rate: ITEM Sample to represent a volume of cu. metres Foundations 20 Columns 15 Beams 20 Walls, Floors & Stairs 30 clarkebond Page 8 of 14

9 or at least one sample to be taken each day from each concrete mix placed. Each sample shall consist of 4 cubes, for testing at the rate of one at 7 days and two at 28 days. The remaining cube is to be tested only if either of the two 28 day test results falls below the required strength. 530 TEST RESULTS Submission of reports: Within one day of completion of each test. - Number of copies: 2 Reports on site: A complete set, available for inspection. 540 B CUBE TEST REPORTS: must include at least the following: Test laboratory and name of person responsible for testing Title of project Identification mark or number marked on site thus: - Day/Month/Identification letter i.e., first cube taken on 5th October would be marked 5/10/A, second cube taken that day 5/10/B etc. Certificate of sampling as BS EN Certificate of method of making cubes as BS EN and -2. Curing place and conditions. Date of receipt by laboratory. Condition on receipt by laboratory. i.e. dryness, compaction, damage. Actual or checked nominal dimensions Weight and density Date of test Age when tested Confirmation of testing in accordance with BS EN Load at failure Compressive strength Type of fracture Date of despatch of report to CA. 550 BROKEN CUBES FROM FAILED STRENGTH TESTS Nonconformity: Keep separately the pieces of each cube which fails to meet the conformity requirements for individual results. Period for keeping cubes: Obtain instructions. 551 B FAILURES: If a concrete sample fails to achieve specified criteria or to pass specified tests, inform the CA without delay and submit: 1. Confirmation of the validity of the test results, and/or 2. Proposals for further tests to assess the strength of the concrete in the structure, as set out in BS 6089, and/or 3. Proposals for rectification. Obtain approval of all such evidence and proposals before proceeding. The CA may issue instructions for the work to be stopped or delayed until reasons for the failure have been established, possible consequences assessed, and appropriate preventative and remedial measures taken. 552 B FAILURES: Wherever the specified sampling, testing and compliance procedures show that a concrete mix is not in accordance with the specification (even if the work is eventually accepted), all consequential investigations, additional testing, instructions and remedial measures: 1. will be at the expense of the Contractor, and 2. will not be considered as grounds for extension of time. 564 B AIR ENTRAINMENT: shall be checked in accordance with BS EN Initially one air test shall be carried out on each bay poured. If early tests prove to be satisfactory this frequency may be reduced, subject to approval by the CA. If any test gives a clarkebond Page 9 of 14

10 result outside of the permitted range further tests shall be carried out immediately and the average and range of the results shall be calculated. If the average air entrainment is greater than the required volume, ± 1.5% or the range is greater than 2%, before any further concrete is used in the works the Contractor shall take such steps as may be agreed with the CA to adjust air content or improve its uniformity. 570 B EARLY AGE STRENGTH TESTING: A regime of accelerated or normal curing and early testing which is capable of predicting the 28 day strength of Designed mixes may be used for determining compliance, subject to prior approval. If such a regime is adopted, two additional cubes must be made from each sample and cured normally so that, in the event of non-compliance, they can be tested at 28 days to provide information which will help in deciding the action to be taken. 575 B WATER/ CEMENT RATIO: Where slump testing is specified for assessing compliance with specified free water/ cement ratio, submit preliminary test results to establish relationship between the two properties, and obtain approval of the CA. 576 B SLUMP TESTS: to be taken at least twice daily. PLACING/ COMPACTING/ CURING AND PROTECTING 610 CONSTRUCTION/ SEQUENCE/ TIMING REQUIREMENTS: Ground floor slabs should be cast after the roof decking has been installed. 615 B PLACING AND COMPACTING: The contractor shall take cognisance of the weather conditions expected (hot or cold) during the placing and curing of concrete. Method statements giving details of precautions to be taken during adverse weather shall be prepared and submitted to the engineer for approval well in advance of any concreting works. The contractor must be in a position during any concreting works to rapidly instigate the agreed protective measures, or postpone or discontinue casting, should the weather conditions change in a manner detrimental to the placing and curing of concrete. 618 B TEMPORARY STABILITY Contractor to ensure that stability of the building is maintained at all stages of construction. Provide temporary bracing as required. 620 A TEMPERATURE OF CONCRETE Application: Water retaining concrete. Objective: Limit maximum temperature of concrete to minimise cracking during placing, compaction and curing. Take account of: - High temperatures and steep temperature gradients: Prevent build-up during first 24 hours after casting. Prevent coincidence of maximum heat gain from cement hydration with high air temperature and/or solar gain. - Rapid changes in temperature: Prevent during first seven days after casting. Proposals for meeting objective: Submit proposals designed to achieve these objectives (taking into account the nature of the design, the mix specification and the prevailing climatic conditions) and obtain approval before placing concrete. 630A PREMATURE WATER LOSS Requirement: Prevent water loss from concrete laid on absorbent surfaces. - Underlay: Select from: Polyethylene sheet: 250 microns thick. - Installation: Lap edges 150mm. 640 A CONSTRUCTION JOINTS: Locations of joints: - Submit proposals where not shown on drawings. clarkebond Page 10 of 14

11 - Agree position of construction joints with CA. Stopboard: closely notched over the reinforcement and secured, all to the approval of the CA. Concrete: - Place continuously up to construction joint. - Bring up in full width and thickness against the stop board. Preparation of joint surfaces: - Brush and spray surface while concrete is still green to remove surface laitance and expose aggregate finish. - Other methods: Submit proposals and obtain approval. Condition of joint surfaces immediately before placing fresh concrete: Clean and damp. 645 SPACING OF CONSTRUCTION JOINTS Type of construction: All concrete. - Distance between joints (maximum): 6m for water retaining structures. Submit proposals. - Area of pour (maximum): Submit proposals. - Other requirements: Submit proposals. 648 ADVERSE TEMPERATURE CONDITIONS Requirement: Submit proposals for protecting concrete when predicted ambient temperatures indicate risk of concrete freezing or overheating. 650 SURFACES TO RECEIVE CONCRETE Cleanliness of surfaces immediately before placing concrete: Clean with no debris, tying wire clippings, fastenings or free water. 660 INSPECTION OF SURFACES Notice: Give notice to allow inspections of reinforcement and surfaces before each pour of concrete. - Period of notice: Obtain instructions. Timings of inspections: submit proposals 661 B BLINDING Lay 50mm blinding concrete under all foundations and insitu reinforced ground beams, unless noted otherwise. 670 A TRANSPORTING General: - Avoid contamination, segregation, loss of ingredients, excessive evaporation and loss of workability. Protect from heavy rain. - Clean transporting equipment immediately after use and whenever cement or aggregate is changed, and remove free water. - Use suitable stools, walkways and barrow runs for traffic over reinforcement and freshly placed concrete. - The concrete should be deposited as close as practicable to its final position, to avoid rehandling. Entrained air: Anticipate the effects of transport and placing methods in order to achieve specified air content. 671 B COLD WEATHER: When concrete is placed at air temperatures below 2 C or in frozen ground the precautions specified in BS 8110, Part 1, Clauses and must be observed. 672 B HOT WEATHER: At time of placing no part of the concrete shall have a temperature exceeding 30 C. When concrete is placed in hot weather, the precautions specified in BS 8110, Part 1, Clause 6.2.5, must be observed. 680 A PLACING Supervision: All placing and compacting shall be carried out under suitable supervision. clarkebond Page 11 of 14

12 Records: Maintain for time, date and location of all pours. Timing: Place as soon as practicable after mixing and while it is sufficiently plastic for full compaction. Addition of water or re-tempering of mixes will not be permitted. Temperature limitations for concrete: 30 C (maximum) and 5 C (minimum), unless specified otherwise. Do not place against frozen or frost covered surfaces. Continuity of pours: Place in final position in one continuous operation up to construction joints. Avoid formation of cold joints. Discharging concrete: Prevent uneven dispersal, segregation or loss of ingredients or any adverse effect on the formwork or formed finishes. Thickness of layers: To suit method of compaction and achieve efficient amalgamation during compaction. Poker vibrators: Do not use to make concrete flow horizontally into position, except where necessary to achieve full compaction under void formers and cast in accessories and at vertical joints. Reinforcement: Avoid displacing reinforcement. Ensure a competent steel fixer is available wherever concrete is being placed. Concrete placed through water: - Use tremies or pipelines. - Method to be agreed with CA. - Concrete shall not be placed in water. 690 A COMPACTING General: Fully compact concrete to full depth to remove entrapped air. Continue until air bubbles cease to appear on the top surface. - Areas for particular attention: Around reinforcement, under void formers, cast-in accessories, into corners of formwork and at joints. Consecutive batches of concrete: Amalgamate without damaging adjacent partly hardened concrete. Methods of compaction: To suit consistence class and use of concrete. Mechanical vibration: Use as required; vibration shall be applied continuously during the placing of each batch of concrete until the expulsion of air has practically ceased and in a manner which will not promote segregation. 700 LIGHTWEIGHT AGGREGATE CONCRETE Placing and compacting: Prevent flotation of coarse aggregate and formation of excessive blowholes. 720 VIBRATORS General: Maintain sufficient numbers and types of vibrator to suit pouring rate, consistency and location of concrete. External vibrators: Obtain approval for use. 730 PLASTIC SETTLEMENT Settlement cracking: Inspect fresh concrete closely and continuously wherever cracking is likely to occur, including the top of deep sections and at significant changes in the depth of concrete sections. - Timing: During the first few hours after placing and whilst concrete is still capable of being fluidised by the vibrator. Removal of cracks: Revibrate concrete. 810 CURING GENERALLY Requirement: Keep surface layers of concrete moist throughout curing period, including perimeters and abutments, by either restricting evaporation or continuously wetting surfaces of concrete. - Surfaces covered by formwork: Retain formwork in position and, where necessary to satisfy curing period, cover surfaces immediately after striking. clarkebond Page 12 of 14

13 - Top surfaces: Cover immediately after placing and compacting. If covering is removed for finishing operations, replace it immediately afterwards. Surface temperature: Maintain above 5 C throughout the specified curing period or four days, whichever is longer. Records: Maintain details of location and timing of casting of individual batches, removal of formwork and removal of coverings. Keep records on site, available for inspection. 811 COVERINGS FOR CURING Sheet coverings: Suitable impervious material. Curing compounds: Selection criteria: - Curing efficiency: Not less than 75% or for surfaces exposed to abrasion 90%. - Colouring: Fugitive dye. - Application to concrete exposed in the finished work: Readily removable without disfiguring the surface. - Application to concrete to receive a bonded construction/ finish: No impediment to subsequent bonding. Interim covering to top surfaces: Until surfaces are in a suitable state to receive coverings in direct contact, cover with impervious sheeting held clear of the surface and sealed against draughts at perimeters and junctions. 812 PREVENTING EARLY AGE THERMAL CRACKING Deep lifts or large volume pours: Submit proposals for curing to prevent early age thermal cracking, taking account of: - Temperature differentials across sections. - Coefficient of thermal expansion of the concrete. - Strain capacity of the concrete mix (aggregate dependant). - Restraint. 815 ADDITIONAL CURING REQUIREMENT WATER CURING Commencement of water curing: As soon as practicable after placing and compacting concrete. - Surfaces covered by formwork: Expose to water curing as soon as practicable. - Top surfaces: Cover immediately with impermeable sheeting to prevent evaporation before commencement of water curing. Water curing: Wet surfaces continuously throughout the curing period. - Select methods from: Mist spray. Wet hessian covered with impermeable sheeting. 820 A CURING PERIODS [ ] General: Curing periods are in days (minimum). - Definition of t : The average surface temperature of concrete in degrees Celsius during the curing period. Curing periods for concrete surfaces which, in the finished building, will be exposed to the elements; concrete wearing surface floors and pavements; water resistant concrete: Drying winds or dry, sunny weather (relative humidity < 50%) Concrete made using CEM 1 strength class 42.5 or 52.5; SRPC class 42.5 Concrete made using cements indicated in BS , table A.6 except those listed in adjacent column and supersulfated cement t+10 t Intermediate conditions t+10 t+10 clarkebond Page 13 of 14

14 Damp weather, protected from sun and wind (relative humidity > 80%) t+10 t+10 Curing periods for other structural concrete surfaces (cements/ combinations as above): Drying winds or dry, sunny weather (relative humidity < 50%) t+10 t+10 Intermediate conditions t+10 t+10 Damp weather, protected from sun and wind (relative humidity > 80%) No special requirements No special requirements Curing periods for concretes using admixtures or other types of cements/ combinations: Submit proposals. Other requirements: Increase curing period by any time during which surface temperature of concrete is less than 5 C. 822 B CURING PERIODS Curing period: Not less than: - Surfaces which will be exposed to frost, and wearing surfaces of floors and pavements, regardless of weather conditions: 10 days. - Other structural concrete surfaces: 5 days. 840 PROTECTION Prevent damage to concrete, including: - Surfaces generally: From rain, indentation and other physical damage. - Surfaces to exposed visual concrete: From dirt, staining, rust marks and other disfiguration. - Immature concrete: From thermal shock, physical shock, overloading, movement and vibration. - In cold weather: From entrapment and freezing expansion of water in pockets, etc. 845 B EARLY LOADING Concrete shall not be subjected to loading including its own mass which would induce a compressive stress in excess of 0.33 x cube strength at the time of loading, or 0.33 x specified 28 day strength. clarkebond Page 14 of 14