Materials and Equipment for Concrete Works
This section contains requirements for the manufacture, transportation, placement, fin¬ishing, repair and curing of concrete; for the detailing, supply and placing of reinforcement; for formwork, for joints, joint materials, joint treatment and bearing pads; and for all other work associated with cast-in-place and precast concrete. Requirement specific to roller com¬pacted concrete (RCC) are set out in Section 6 of this Specification.
1. Materials and equipment
(1) Cementitious materials. Cementitious materials shall normally consist of a combina¬tion of Ordinary Portland cement (OPC) and pozzolanic material (either raw or calcined nat¬ural pozzolan, fly ash or blast-furnace slag). The sources of cement and pozzolanic material shall be proposed by the Contractor and shall be subject to approval by the Engineer.
(2) Aggregates. Aggregates for concrete shall be processed and shall consist of natural parti¬cles or a blend of natural and manufactured particles. Aggregates shall be produced from suitable material from required excavations or borrow areas as approved by the Engineer. The approval of any sources from which aggregates are to be produced by the Contractor shall not be construed as constituting approval or acceptance of all materials taken from the source.
(3) Water. Water for washing aggregates and mixing concrete shall be reasonably clean and free from the detrimental amount of salts, alkalis, oil, organic matter or other deleterious substances and shall comply with the recommendations contained in the Appendix to BS 3148. The concentration of sulphates and chlorides shall be such that the concrete mix as a whole complies with the limits of salts content also recommended in BS 3148.
Both the groundwater and suitably filtered river water are considered suitable for the mixing and curing of the concrete. However, during the flood season the river water contains a considerable a-mount of silt. The silt containing water may be required some ponding to settle out the sediments.
The Contractor shall make arrangements to protect water from direct sun and contami¬nation by wind-blown materials. The Engineer shall order retesting of water whenever deemed necessary.
(4) Admixture. Admixture shall mean chemical materials added to the concrete materials during mixing for the purpose of altering the properties of the concrete mix. They shall not contain calcium chloride.
The Contractor shall furnish and use a water-reducing or water-reducing set-retarding admix¬ture as approved by the Engineer. The water-reducing and/or water-reducing set-retarding admix¬ture shall conform to ASTM C 595, Type A or D as appropriate. The amount of admixture used per batch shall be proposed by the Contractor for the Engineer's approval following suitable tests but, in general, the amount will be in accordance with the manufacturer's recommendations. No admixture shall be considered for approval that has not been used with satisfactory service in works of similar nature. A manufacturer's technical data sheet and certification of compliance with ASTM C494, Type A or D as appropriate, shall be submitted at the time of request for approval. After approval is granted, a manufacturer's certificate of compliance shall be furnished with each shipment to the Site. Admixture may be sampled and tested by the Engineer for compliance with ASTM C494. If tests prove that any admixture which has been delivered is unsatisfactory, it shall be promptly removed from the Site.
The Contractor shall furnish and use an approved air-entraining admixture in all concrete unless otherwise approved or instructed by the Engineer. The air-entraining admixture shall be a neutralized vinsol resin and shall conform to the requirements of ASTM C260.
The admixtures shall each be accurately batched by mechanical batcher and shall be add¬ed in a manner which ensures uniform distribution throughout the batch.
The compatibility of different admixtures used in the same batch shall be established to the satisfaction of the Engineer.
Admixtures which have been in storage for more than 6 months shall not be used unless retest proves them to be satisfactory. Cost of all such retests shall be borne by the Contrac¬tor. Rejected materials shall be removed immediately from the Site.
2. Concrete Classes
The concrete grades required for the Works shall be as follows:
Class Minimum Compressive Cylinder Strength Characteristic Strength)(MPa) Age at test(days) Maximum size of aggregate(inches)
C 28 28 3/4
Dl 1/2 21 28 1 1/2
D3 21 90 3
E (Blinding Concrete) 14 28 11/2
In addition mix designs for bedding mortar having nominal thickness of 1/2 inch will be required. Such bedding mortar shall have a Minimum Compressive Cylinder Strength which is 125% of the strength of the concrete which will cover it.
3. Jointing materials and waterstops
Jointing materials include waterstops, fillers, paints, caulking compounds, sealants, adhesives and other such materials required for the making of joints in concrete and between existing and new concrete.
Jointing materials shall be proposed by the Contractor and approved by the Engineer. They shall be handled, used and stored in accordance with the manufacturer's recommenda¬tions.
4. Formwork
Form work shall be constructed of timber, sheet metal or other approved material depen¬ding on the class of finish to be obtained, as specified in Clause 5-4.30. The Contractor shall use only approved material for exposed surfaces of the same class of finish.
Ties shall be of the rod and cone or other approved proprietary type. Embedded material rods shall terminate not less than 2in (50mm) inside the formed faces of the concrete. Wire ties shall not be permitted.
Ties for use in water-retaining structures, which are continuous through the section, shall incorporate a diaphragm, not less than 50mm diameter and 4mm thick, welded normal to the midpoint of the tie, designed to prevent water passing along the tie.
5. Steel reinforcement
Steel for reinforcement bars shall be hot rolled deformed steel bars conforming to ASTM A615, grade 40 and 60. Fabricated reinforcement mats shall conform to the requirements of ASTM A 184 or ASTM A185,as specified on the Drawings.
The Engineer shall have the right to witness routine testing of steel reinforcement at the manufacturer's workshop.
When required by the Engineer, the Contractor shall take samples from the reinforce-ment delivered to the Site and shall arrange for the samples to be tested by an approved tes¬ting agency. Test certificates from that agency shall be submitted to the Engineer.
The actual yield strength based on mill tests of grade 40 or 60 reinforcement shall not exceed the specified yield strength by more than 120MPa (retests shall not exceed this value by more than an additional 20MPa) and the ratio of the actual ultimate tensile stress to the actual tensile yield strength shall not be less than 1.25.
6. Bitumen emulsion
Bitumen emulsion for coating concrete surface in contact with the core, as required under Clause 5-6. 23, shall comply with BS3940, Type 3a (iii) .
7. Accessories
Spacer blocks for maintaining concrete cover to reinforcement shall be of concrete of the same texture, color and composition as the in situ concrete. They shall be cast in the form of a truncated cone or pyramids with the smaller face having a minimum dimension of 50mm (2in).
PVC spacer blocks of color matching with the concrete shall be used where formed sur¬face are designated F3 or F4. The Contractor shall submit samples and manufacturer's techni¬cal data to the Engineer for his approval. They shall not be used for any surface that may be in contact with water.
Chairs and other accessories for maintaining reinforcement in position shall be of steel and shall not be placed within the specified minimum cover to steel. Binding wire shall be 2 mm soft iron wire.
8. Equipment
Plant and equipment shall be sufficient to meet the requirements of both the Specifica¬tions and the Construction programmed.
Workmanship
1. Mix designs
The Contractor shall propose mix designs for the trial mix programmed. The procedures used for mix design shall be in accordance with ACI211. 1, Standard Practice for selecting Proportions of Normal, heavyweight and Mass Concrete.
A report including mix design calculations shall be submitted to the Engineer for ap-proval not less than 28 days prior to commencement of the trial mix programmed.
The mix designs shall include mixes for each Class of concrete given in Clause5-3. 02 as well as bedding mortars and the like required for execution of the Works.
For the purpose of mix design, the Contractor shall obtain test data defining the relation¬ship between strength and water cementitious ratio. The cementitious content is the content of cement and pozzolanic materials. Alternatively, the Contractor may assume a reasonable range of water/cementitious ratios for a given strength and design trial mixes accordingly. The chosen water/cementitious ratios in the trial mixes for any one class of concrete shall be well to each side of the ratios expected to give the required strengths.
The maximum water/cementitious ratio for concrete in the Main Spillway orifices shall be 0.45. For all other concrete exposed to air and water the water/cementitious ratio shall not exceed 0.50 unless the Engineer so expressly permits. No concrete shall have a water/cementitious ratio greater than 0.70.
Water reducing agents may be used if the required workability (slump) cannot be ob¬tained within the required limiting water/cementitious ratios.
The Contractor shall demonstrate to the satisfaction of the Engineer that the content of the cement and pozzolan is the minimum required to yield the required strength for the con¬crete and which will satisfy other criteria set out in this Section of the Specification.
2. Concrete properties and requirements
Concrete mixtures shall be composed of cementitious materials, water, fine and coarse aggregates, and air-entraining admixtures unless otherwise specified. Water reducing agents may be used to improve workability subject to the approval of the Engineer. Cementitious materials shall consist of cement and pozzolanic materials. Epoxy resin shall be used to pro¬duce epoxy concrete/mortar when so ordered by the Engineer.
The design of the mixtures shall be based on securing a plastic workable mixture both suitable for the specified conditions at placement and, when properly cured, a production hav¬ing durability, impermeability, and strength in accordance with the requirements of the struc¬tures covered by these specifications. For all concrete placements, the Contractor will be re¬quired to handle and place low-slump mixtures in order to achieve high-quality concrete, ex¬cept for pumped concrete for which the slump will be appropriate for the application. In the placement of any single concrete lift, the Contractor may be required to handle and place sev¬eral different concrete mixtures containing different maximum size coarse aggregate for pro¬ducing higher quality, more durable exterior concrete and for placement in highly reinforced and congested areas. The mixtures shall contain no more cementitious material than needed to meet the structural design requirement. The use of pozzolanic material with OPC will re¬sult in a slow early rate of gain in concrete strength, and the Contractor shall have due regard for this when designing his formwork and planning his programme for form removal.
The combined grading and quantities of coarse aggregate for class D3 concrete (3inch MSA) shall be in accordance with the recommendations of ACI 211. 1 for Mass Concrete and for other concrete classes the recommendations for Normal concrete shall be followed, except as noted as follows. The aforementioned procedures can lead to over-sanded mixes and the Contractor shall keep the fine aggregate content to the minimum that is compatible with pro¬ducing a concrete with the maximum possible compacted density for that concrete class as well as other specified criteria.
Aggregate shall be a mixture of coarse and fine aggregate. Coarse aggregate shall consist of one or more of the specified size ranges to produce a well graded aggregate mixture with the required nominal maximum size aggregate.
In no event shall the nominal maximum size aggregate exceed one-fifth of the narrowest dimension between sides of forms; one-third the depth of slabs; nor three-fourth of the mini¬mum clear spacing between individual reinforcing bars, bundles of bars, or post-tensioned ca¬ble conduits.
The Contractor shall provide effective means such as pre-cooling of aggregates, refriger¬ating the mixing water, adding flake, chip, crushed, tube, or other forms of ice up to the full a-mount of added mixing water, or a combination of these or other methods, as necessary to maintain the temperature of concrete at or below the specified temperature as it is placed. The size of the ice particles shall be such that the ice is completely melted before the end of the mixing time for each batch.
3. Concrete consistency
The concretes shall have a consistency, as measured by the slump method (ASTM C143), conforming to the various limits specified below.
Specified concrete work Slump (mm)
Specified working limit Working range Margin for occasional inadvertent high slump Specified rejection limit
Mass concrete and rein¬forced concrete walls, slabs and piers more than 3 ft. thick 50 25~50 50~75 75
Walls, slabs and columns less than 1 ft. thick 75 50~75 75~100 100
Bedding mortars 150 100~150 150~175 175
Under no circumstance shall the quantity of water and ice added cause the water/ cementations ratio to exceed the maxima allowable as determined in the trial mix programmed. If these limits are exceeded in any batch of concrete, the batch will be rejected by the Engineer.
Concrete with a slump equal to or greater than the rejection limit as measured by the En¬gineer at the point of placement will be rejected by the Engineer. Concrete consistency shall be uniform from batch to batch. The Contractor shall vary the quantity of mixing water from batch to batch if necessary to offset variation in free moisture content or grading of the ag¬gregates. Water shall not be added to compensate for stiffening of concrete held in the mixer too long or for delays in placement.
The specified working limit is the permitted upper limit of a range of slumps selected to provide the required concrete properties including the ability to be readily compacted by the specified vibration equipment during concrete placement. The slump of the concrete as placed shall average approximately 10mm less than the specified working limit. The 25mm margin between the working limit and the rejection limit is provided for occasional inadvertent bat¬ches which may exceed the working range. Batches of concrete with slumps exceeding the working limit, but within the inadvertency margin, will be rejected if the frequency of their occurrence is such that the average of the three successive tests exceeds the working limit by more than 12 mm.
Concrete that has been rejected for failure to meet slump limit shall not be used in the Permanent Works.
4. Placing concrete
All concrete shall be placed so as to produce a set concrete that is hard, durable, dense, free from honeycombing, formwork irregularities and other surface blemishes.
At least 63 days before placing concrete in any major structure, the Contractor shall sub¬mit to the Engineer for his approval details of his proposed construction procedures including a description of the methods of the concrete placement. Approval of construction procedures and methods of placement will not relieve the Contractor of his responsibility for their ade¬quacy and the contractor shall remain solely responsible for satisfactory construction of the Permanent Works.
For each concrete placement, the Contractor shall provide the Engineer with written no¬tice^ drawing and a pre-placement checkout sheet signed by the Contractor's appropriate su¬pervisory personnel that demonstrate that foundation preparation, construction joints clean¬up, formwork, installation of reinforcing steel, block-out and all embedded items for the placement have been completed according to the Drawings or as specified. Before concrete placement is permitted, each item on the checkout sheet shall be initialed by the Engineer showing that the item has been inspected and is ready to receive concrete. Concrete place¬ment will not be permitted when, in the opinion of the Engineer, conditions prevent proper placement, consolidation, finishing and curing.
Concrete mixed in stationary mixers and transported by non-agitating equipment shall be placed within 30 minutes of mixing. When an agitator is used for transporting concrete, the concrete shall be delivered to the Site of the work and discharge shall be completed within 1. 5 hours after introduction of cement to the aggregates except that when the temperature of the concrete exceeds 21癈, the time shall be reduced to 45minutes, The concrete shall be placed within 20 minutes after it has been discharged. Concrete shall be carefully placed in horizontal layers not exceeding 450mm thick (18in). concrete shall not be allowed to slide or flow down sloping surfaces, except in underground galleries, but shall be placed in its final position from skips, trucks, barrows, down pipes or other placing machine or device or , if this is impossible, it shall be shoveled into position with care being taken to avoid separation of the constituent materials, concrete placed in horizontal slabs from barrows or other tipping vehicles shall be tipped into face of the previously placed concrete.
Bedding mortars shall only be used when the Engineer so directs. Where bedding mor¬tars are directed to be used they shall be spread to the thickness and over areas given by the Engineer. Bedding mortar shall be covered by concrete within 15minutes of the bedding mor¬tar placed. If this period should be exceeded the Engineer may direct the Contractor to re¬move the bedding mortar and halt the concrete placement until such time as the area has been prepared for receiving concrete in accordance with Clause 5-5,5.
Concrete dropped into place shall be dropped vertically. It shall not strike the formwork between the point of its discharge and its final place. Concrete shall not be dropped freely through a height greater than 1.5m (5ft). Chutes and conveyor belts shall be so designed that there is no segregation or loss of mortar and shall be provided with a vertical tapered down pipe, or other device, to ensure that concrete is discharged vertically into place.
Where a lift of concrete is built up in a series of layers, each layer shall be properly mer¬ged into the preceding layer before initial set takes place.
When pump are used, the end of the supply pipe shall be arranged so as to avoid segregation. Mortar or water used at the beginning or end of a run shall be discharged outside the formwork.
Where concrete abuts against earth or other materials to become loose or to slip, the Contractor shall take steps to prevent any such loose material failing onto the surface of the concrete.
5. Lift height and time between placements
The elapsed time between adjacent pours shall not be less than 14 days or as otherwise directed by the Engineer.
The maximum permissible difference in height between adjacent monoliths shall be 20 feet or as directed by the Engineer.
When slabs or beams are monolithic with supporting walls or columns, there shall be a construction joint near the top of the wall or column. The position of the joint shall be sub¬ject to the approval of the Engineer.
When placing concrete directly onto existing concrete or new concrete that is more than 21 days old the above maximum depths of concrete shall be half that given in the above table.
6. Compaction
All concrete, other than blinding concrete, shall be compacted with power driven, immer¬sion type vibrators supplemented by hand spading and tamping.
Vibrators shall be inserted into the un-compacted concrete vertically and at regular inter¬vals such that the radius of action overlaps that of the previously vibrated concrete. A layer shall not be covered with a succeeding layer until it has been thoroughly vibrated as speci¬fied. Where the un-compacted concrete is in a layer above freshly compacted concrete, the vi¬brator shall be allowed to penetrate vertically for about 100 mm (4in) into the previous layer. In no circumstance shall vibrators be allowed to come into contact with the formwork of embedded parts, nor shall they be withdrawn quickly from the mass of concrete, but shall be drawn back slowly so as to leave no voids. Internal type vibrators shall not be placed in the concrete in a random or haphazard manner, nor shall concrete be moved from one part of the work to another by means of the vibrators. Care shall be taken properly to vibrate concrete placed in contact with previously placed concrete or embedded parts.
The duration of vibration shall be limited to that required to produce satisfactory com-paction, without causing segregation. Compaction of the concrete by vibration shall be such as to produce a concrete that has the maximum practicable density, is free from pockets of coarse aggregates and entrapped air and makes complete contact with the foundation, previ¬ously placed hardened concrete, embedded items and the formwork.
Blinding concrete shall be compacted by hand spading and tamping.
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只看楼主 我来说两句抢地板Materials and Equipment for Concrete Works
This section contains requirements for the manufacture, transportation, placement, fin¬ishing, repair and curing of concrete; for the detailing, supply and placing of reinforcement; for formwork, for joints, joint materials, joint treatment and bearing pads; and for all other work associated with cast-in-place and precast concrete. Requirement specific to roller com¬pacted concrete (RCC) are set out in Section 6 of this Specification.
1. Materials and equipment
(1) Cementitious materials. Cementitious materials shall normally consist of a combina¬tion of Ordinary Portland cement (OPC) and pozzolanic material (either raw or calcined nat¬ural pozzolan, fly ash or blast-furnace slag). The sources of cement and pozzolanic material shall be proposed by the Contractor and shall be subject to approval by the Engineer.
(2) Aggregates. Aggregates for concrete shall be processed and shall consist of natural parti¬cles or a blend of natural and manufactured particles. Aggregates shall be produced from suitable material from required excavations or borrow areas as approved by the Engineer. The approval of any sources from which aggregates are to be produced by the Contractor shall not be construed as constituting approval or acceptance of all materials taken from the source.
(3) Water. Water for washing aggregates and mixing concrete shall be reasonably clean and free from the detrimental amount of salts, alkalis, oil, organic matter or other deleterious substances and shall comply with the recommendations contained in the Appendix to BS 3148. The concentration of sulphates and chlorides shall be such that the concrete mix as a whole complies with the limits of salts content also recommended in BS 3148.
Both the groundwater and suitably filtered river water are considered suitable for the mixing and curing of the concrete. However, during the flood season the river water contains a considerable a-mount of silt. The silt containing water may be required some ponding to settle out the sediments.
The Contractor shall make arrangements to protect water from direct sun and contami¬nation by wind-blown materials. The Engineer shall order retesting of water whenever deemed necessary.
(4) Admixture. Admixture shall mean chemical materials added to the concrete materials during mixing for the purpose of altering the properties of the concrete mix. They shall not contain calcium chloride.
The Contractor shall furnish and use a water-reducing or water-reducing set-retarding admix¬ture as approved by the Engineer. The water-reducing and/or water-reducing set-retarding admix¬ture shall conform to ASTM C 595, Type A or D as appropriate. The amount of admixture used per batch shall be proposed by the Contractor for the Engineer's approval following suitable tests but, in general, the amount will be in accordance with the manufacturer's recommendations. No admixture shall be considered for approval that has not been used with satisfactory service in works of similar nature. A manufacturer's technical data sheet and certification of compliance with ASTM C494, Type A or D as appropriate, shall be submitted at the time of request for approval. After approval is granted, a manufacturer's certificate of compliance shall be furnished with each shipment to the Site. Admixture may be sampled and tested by the Engineer for compliance with ASTM C494. If tests prove that any admixture which has been delivered is unsatisfactory, it shall be promptly removed from the Site.
The Contractor shall furnish and use an approved air-entraining admixture in all concrete unless otherwise approved or instructed by the Engineer. The air-entraining admixture shall be a neutralized vinsol resin and shall conform to the requirements of ASTM C260.
The admixtures shall each be accurately batched by mechanical batcher and shall be add¬ed in a manner which ensures uniform distribution throughout the batch.
The compatibility of different admixtures used in the same batch shall be established to the satisfaction of the Engineer.
Admixtures which have been in storage for more than 6 months shall not be used unless retest proves them to be satisfactory. Cost of all such retests shall be borne by the Contrac¬tor. Rejected materials shall be removed immediately from the Site.
2. Concrete Classes
The concrete grades required for the Works shall be as follows:
Class Minimum Compressive Cylinder Strength Characteristic Strength)(MPa) Age at test(days) Maximum size of aggregate(inches)
C 28 28 3/4
Dl 1/2 21 28 1 1/2
D3 21 90 3
E (Blinding Concrete) 14 28 11/2
In addition mix designs for bedding mortar having nominal thickness of 1/2 inch will be required. Such bedding mortar shall have a Minimum Compressive Cylinder Strength which is 125% of the strength of the concrete which will cover it.
3. Jointing materials and waterstops
Jointing materials include waterstops, fillers, paints, caulking compounds, sealants, adhesives and other such materials required for the making of joints in concrete and between existing and new concrete.
Jointing materials shall be proposed by the Contractor and approved by the Engineer. They shall be handled, used and stored in accordance with the manufacturer's recommenda¬tions.
4. Formwork
Form work shall be constructed of timber, sheet metal or other approved material depen¬ding on the class of finish to be obtained, as specified in Clause 5-4.30. The Contractor shall use only approved material for exposed surfaces of the same class of finish.
Ties shall be of the rod and cone or other approved proprietary type. Embedded material rods shall terminate not less than 2in (50mm) inside the formed faces of the concrete. Wire ties shall not be permitted.
Ties for use in water-retaining structures, which are continuous through the section, shall incorporate a diaphragm, not less than 50mm diameter and 4mm thick, welded normal to the midpoint of the tie, designed to prevent water passing along the tie.
5. Steel reinforcement
Steel for reinforcement bars shall be hot rolled deformed steel bars conforming to ASTM A615, grade 40 and 60. Fabricated reinforcement mats shall conform to the requirements of ASTM A 184 or ASTM A185,as specified on the Drawings.
The Engineer shall have the right to witness routine testing of steel reinforcement at the manufacturer's workshop.
When required by the Engineer, the Contractor shall take samples from the reinforce-ment delivered to the Site and shall arrange for the samples to be tested by an approved tes¬ting agency. Test certificates from that agency shall be submitted to the Engineer.
The actual yield strength based on mill tests of grade 40 or 60 reinforcement shall not exceed the specified yield strength by more than 120MPa (retests shall not exceed this value by more than an additional 20MPa) and the ratio of the actual ultimate tensile stress to the actual tensile yield strength shall not be less than 1.25.
6. Bitumen emulsion
Bitumen emulsion for coating concrete surface in contact with the core, as required under Clause 5-6. 23, shall comply with BS3940, Type 3a (iii) .
7. Accessories
Spacer blocks for maintaining concrete cover to reinforcement shall be of concrete of the same texture, color and composition as the in situ concrete. They shall be cast in the form of a truncated cone or pyramids with the smaller face having a minimum dimension of 50mm (2in).
PVC spacer blocks of color matching with the concrete shall be used where formed sur¬face are designated F3 or F4. The Contractor shall submit samples and manufacturer's techni¬cal data to the Engineer for his approval. They shall not be used for any surface that may be in contact with water.
Chairs and other accessories for maintaining reinforcement in position shall be of steel and shall not be placed within the specified minimum cover to steel. Binding wire shall be 2 mm soft iron wire.
8. Equipment
Plant and equipment shall be sufficient to meet the requirements of both the Specifica¬tions and the Construction programmed.
Workmanship
1. Mix designs
The Contractor shall propose mix designs for the trial mix programmed. The procedures used for mix design shall be in accordance with ACI211. 1, Standard Practice for selecting Proportions of Normal, heavyweight and Mass Concrete.
A report including mix design calculations shall be submitted to the Engineer for ap-proval not less than 28 days prior to commencement of the trial mix programmed.
The mix designs shall include mixes for each Class of concrete given in Clause5-3. 02 as well as bedding mortars and the like required for execution of the Works.
For the purpose of mix design, the Contractor shall obtain test data defining the relation¬ship between strength and water cementitious ratio. The cementitious content is the content of cement and pozzolanic materials. Alternatively, the Contractor may assume a reasonable range of water/cementitious ratios for a given strength and design trial mixes accordingly. The chosen water/cementitious ratios in the trial mixes for any one class of concrete shall be well to each side of the ratios expected to give the required strengths.
The maximum water/cementitious ratio for concrete in the Main Spillway orifices shall be 0.45. For all other concrete exposed to air and water the water/cementitious ratio shall not exceed 0.50 unless the Engineer so expressly permits. No concrete shall have a water/cementitious ratio greater than 0.70.
Water reducing agents may be used if the required workability (slump) cannot be ob¬tained within the required limiting water/cementitious ratios.
The Contractor shall demonstrate to the satisfaction of the Engineer that the content of the cement and pozzolan is the minimum required to yield the required strength for the con¬crete and which will satisfy other criteria set out in this Section of the Specification.
2. Concrete properties and requirements
Concrete mixtures shall be composed of cementitious materials, water, fine and coarse aggregates, and air-entraining admixtures unless otherwise specified. Water reducing agents may be used to improve workability subject to the approval of the Engineer. Cementitious materials shall consist of cement and pozzolanic materials. Epoxy resin shall be used to pro¬duce epoxy concrete/mortar when so ordered by the Engineer.
The design of the mixtures shall be based on securing a plastic workable mixture both suitable for the specified conditions at placement and, when properly cured, a production hav¬ing durability, impermeability, and strength in accordance with the requirements of the struc¬tures covered by these specifications. For all concrete placements, the Contractor will be re¬quired to handle and place low-slump mixtures in order to achieve high-quality concrete, ex¬cept for pumped concrete for which the slump will be appropriate for the application. In the placement of any single concrete lift, the Contractor may be required to handle and place sev¬eral different concrete mixtures containing different maximum size coarse aggregate for pro¬ducing higher quality, more durable exterior concrete and for placement in highly reinforced and congested areas. The mixtures shall contain no more cementitious material than needed to meet the structural design requirement. The use of pozzolanic material with OPC will re¬sult in a slow early rate of gain in concrete strength, and the Contractor shall have due regard for this when designing his formwork and planning his programme for form removal.
The combined grading and quantities of coarse aggregate for class D3 concrete (3inch MSA) shall be in accordance with the recommendations of ACI 211. 1 for Mass Concrete and for other concrete classes the recommendations for Normal concrete shall be followed, except as noted as follows. The aforementioned procedures can lead to over-sanded mixes and the Contractor shall keep the fine aggregate content to the minimum that is compatible with pro¬ducing a concrete with the maximum possible compacted density for that concrete class as well as other specified criteria.
Aggregate shall be a mixture of coarse and fine aggregate. Coarse aggregate shall consist of one or more of the specified size ranges to produce a well graded aggregate mixture with the required nominal maximum size aggregate.
In no event shall the nominal maximum size aggregate exceed one-fifth of the narrowest dimension between sides of forms; one-third the depth of slabs; nor three-fourth of the mini¬mum clear spacing between individual reinforcing bars, bundles of bars, or post-tensioned ca¬ble conduits.
The Contractor shall provide effective means such as pre-cooling of aggregates, refriger¬ating the mixing water, adding flake, chip, crushed, tube, or other forms of ice up to the full a-mount of added mixing water, or a combination of these or other methods, as necessary to maintain the temperature of concrete at or below the specified temperature as it is placed. The size of the ice particles shall be such that the ice is completely melted before the end of the mixing time for each batch.
3. Concrete consistency
The concretes shall have a consistency, as measured by the slump method (ASTM C143), conforming to the various limits specified below.
Specified concrete work Slump (mm)
Specified working limit Working range Margin for occasional inadvertent high slump Specified rejection limit
Mass concrete and rein¬forced concrete walls, slabs and piers more than 3 ft. thick 50 25~50 50~75 75
Walls, slabs and columns less than 1 ft. thick 75 50~75 75~100 100
Bedding mortars 150 100~150 150~175 175
Under no circumstance shall the quantity of water and ice added cause the water/ cementations ratio to exceed the maxima allowable as determined in the trial mix programmed. If these limits are exceeded in any batch of concrete, the batch will be rejected by the Engineer.
Concrete with a slump equal to or greater than the rejection limit as measured by the En¬gineer at the point of placement will be rejected by the Engineer. Concrete consistency shall be uniform from batch to batch. The Contractor shall vary the quantity of mixing water from batch to batch if necessary to offset variation in free moisture content or grading of the ag¬gregates. Water shall not be added to compensate for stiffening of concrete held in the mixer too long or for delays in placement.
The specified working limit is the permitted upper limit of a range of slumps selected to provide the required concrete properties including the ability to be readily compacted by the specified vibration equipment during concrete placement. The slump of the concrete as placed shall average approximately 10mm less than the specified working limit. The 25mm margin between the working limit and the rejection limit is provided for occasional inadvertent bat¬ches which may exceed the working range. Batches of concrete with slumps exceeding the working limit, but within the inadvertency margin, will be rejected if the frequency of their occurrence is such that the average of the three successive tests exceeds the working limit by more than 12 mm.
Concrete that has been rejected for failure to meet slump limit shall not be used in the Permanent Works.
4. Placing concrete
All concrete shall be placed so as to produce a set concrete that is hard, durable, dense, free from honeycombing, formwork irregularities and other surface blemishes.
At least 63 days before placing concrete in any major structure, the Contractor shall sub¬mit to the Engineer for his approval details of his proposed construction procedures including a description of the methods of the concrete placement. Approval of construction procedures and methods of placement will not relieve the Contractor of his responsibility for their ade¬quacy and the contractor shall remain solely responsible for satisfactory construction of the Permanent Works.
For each concrete placement, the Contractor shall provide the Engineer with written no¬tice^ drawing and a pre-placement checkout sheet signed by the Contractor's appropriate su¬pervisory personnel that demonstrate that foundation preparation, construction joints clean¬up, formwork, installation of reinforcing steel, block-out and all embedded items for the placement have been completed according to the Drawings or as specified. Before concrete placement is permitted, each item on the checkout sheet shall be initialed by the Engineer showing that the item has been inspected and is ready to receive concrete. Concrete place¬ment will not be permitted when, in the opinion of the Engineer, conditions prevent proper placement, consolidation, finishing and curing.
Concrete mixed in stationary mixers and transported by non-agitating equipment shall be placed within 30 minutes of mixing. When an agitator is used for transporting concrete, the concrete shall be delivered to the Site of the work and discharge shall be completed within 1. 5 hours after introduction of cement to the aggregates except that when the temperature of the concrete exceeds 21癈, the time shall be reduced to 45minutes, The concrete shall be placed within 20 minutes after it has been discharged. Concrete shall be carefully placed in horizontal layers not exceeding 450mm thick (18in). concrete shall not be allowed to slide or flow down sloping surfaces, except in underground galleries, but shall be placed in its final position from skips, trucks, barrows, down pipes or other placing machine or device or , if this is impossible, it shall be shoveled into position with care being taken to avoid separation of the constituent materials, concrete placed in horizontal slabs from barrows or other tipping vehicles shall be tipped into face of the previously placed concrete.
Bedding mortars shall only be used when the Engineer so directs. Where bedding mor¬tars are directed to be used they shall be spread to the thickness and over areas given by the Engineer. Bedding mortar shall be covered by concrete within 15minutes of the bedding mor¬tar placed. If this period should be exceeded the Engineer may direct the Contractor to re¬move the bedding mortar and halt the concrete placement until such time as the area has been prepared for receiving concrete in accordance with Clause 5-5,5.
Concrete dropped into place shall be dropped vertically. It shall not strike the formwork between the point of its discharge and its final place. Concrete shall not be dropped freely through a height greater than 1.5m (5ft). Chutes and conveyor belts shall be so designed that there is no segregation or loss of mortar and shall be provided with a vertical tapered down pipe, or other device, to ensure that concrete is discharged vertically into place.
Where a lift of concrete is built up in a series of layers, each layer shall be properly mer¬ged into the preceding layer before initial set takes place.
When pump are used, the end of the supply pipe shall be arranged so as to avoid segregation. Mortar or water used at the beginning or end of a run shall be discharged outside the formwork.
Where concrete abuts against earth or other materials to become loose or to slip, the Contractor shall take steps to prevent any such loose material failing onto the surface of the concrete.
5. Lift height and time between placements
The elapsed time between adjacent pours shall not be less than 14 days or as otherwise directed by the Engineer.
The maximum permissible difference in height between adjacent monoliths shall be 20 feet or as directed by the Engineer.
When slabs or beams are monolithic with supporting walls or columns, there shall be a construction joint near the top of the wall or column. The position of the joint shall be sub¬ject to the approval of the Engineer.
When placing concrete directly onto existing concrete or new concrete that is more than 21 days old the above maximum depths of concrete shall be half that given in the above table.
6. Compaction
All concrete, other than blinding concrete, shall be compacted with power driven, immer¬sion type vibrators supplemented by hand spading and tamping.
Vibrators shall be inserted into the un-compacted concrete vertically and at regular inter¬vals such that the radius of action overlaps that of the previously vibrated concrete. A layer shall not be covered with a succeeding layer until it has been thoroughly vibrated as speci¬fied. Where the un-compacted concrete is in a layer above freshly compacted concrete, the vi¬brator shall be allowed to penetrate vertically for about 100 mm (4in) into the previous layer. In no circumstance shall vibrators be allowed to come into contact with the formwork of embedded parts, nor shall they be withdrawn quickly from the mass of concrete, but shall be drawn back slowly so as to leave no voids. Internal type vibrators shall not be placed in the concrete in a random or haphazard manner, nor shall concrete be moved from one part of the work to another by means of the vibrators. Care shall be taken properly to vibrate concrete placed in contact with previously placed concrete or embedded parts.
The duration of vibration shall be limited to that required to produce satisfactory com-paction, without causing segregation. Compaction of the concrete by vibration shall be such as to produce a concrete that has the maximum practicable density, is free from pockets of coarse aggregates and entrapped air and makes complete contact with the foundation, previ¬ously placed hardened concrete, embedded items and the formwork.
Blinding concrete shall be compacted by hand spading and tamping.
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