INDEPENDENT CONSULTING ENGINEERS N.V. P.O. BOX 390 PHILIPSBURG ST MAARTEN N.A. TEL.: (5995)-22421 FAX. (5995)-22597 Technical specifications Zone 1 - Cupecoy Yacht Club & Villas
033000CAST IN PLACE CONCRETE
3.3.1 General conditions
3.3.1.1Description of Works:
The works as specified in these specifications consist mainly of:
3.3.1.1.1Execution of the structural concrete works for the buildings and site structures, consisting of:
Floor slabs, foundation slabs
Columns, beams, walls, stairs etc.
3.3.1.1.2All works and deliveries pertaining to proper execution of the specified works.
3.3.1.1.3Embedding of conduits, pipes, sleeves, anchors, etc., and keeping openings or attachments as to be given on detail drawings and/or as shown on the installation drawings.
3.3.1.1.4The contractor shall be responsible for the coordination of recesses, feed through apertures, etc. of water, sewage-, and electrical lines.
3.3.1.1.5Unless otherwise stated all reinforced concrete and its components shall comply with the Dutch Regulations for concrete (VBU(NEN 6722), VBC(NEN 6720), and VBT(NEN 5950). These regulations shall be present on the site.
3.3.1.1.6All concrete coverage and reinforcement, if not stated elsewhere on the drawings, shall be in accordance to these specifications.
3.3.1.1.7The contractor shall erect all concrete structures as shown on the drawings and detail drawings that will be supplied during construction, including edges, holes, bolts, etc., according to the drawings and instructions by the project management.
3.3.1.1.8Weekly the contractor shall present schedule of concrete casting for the coming week. The contractor shall notify the project management 1 day before the date, and the time when concrete will be placed.
3.3.1.1.9Recesses, feed through apertures, etc. of water, sewage-, and electrical lines. A list of these apertures and recesses is to be provided by the general contractor in coordination with installation subcontractors.
3.3.2Concrete composing elements
3.3.2.1Cement
All cement used in the works shall comply with Dutch Standard NEN 3550 or ASTMC105 and with any amendments issued prior to a date 3 months before the date on which the call for tenders is issued.
The type of cement to be used will be Portland cement, Class A (NEN) or Portland cement, Type I (ASTM).
A test certificate issued by the manufacturer and further certificate stating the name and address of the merchant from whom it has been purchased and the date of importation into St Maarten N.A., shall be submitted to the project management for approval.
Cement to be stored on site shall be stored according to the project management's instructions:
in a waterproof building
on a raised floor, min. 15cm (6 ins) above ground level
storage is permitted in stocks 2m (6 feet 6 inches)
each delivery to be stored separately
other instructions
The project management may from time to time take samples of the cement being used in the work for testing. The project management will condemn any cement which fails to comply with the requirements of this paragraph or which he considers to have deteriorated, and the contractor shall promptly remove such condemned cement from the site.
3.3.2.2Coarse Aggregate
Aggregates will have to comply with VBT(NEN 5950) as far as possible, final approval lies with the engineer.
In no case a deviation will be allowed concerning chloride content and CaCo3 content of aggregates.
In case the percentage of particles < 63ìm in the aggregates is higher than the allowable by mentioned standards, these particles will not be allowed to show any clay characteristics.
Sand to be used for concrete production will have to have a sand equivalent value of minimum 75, to be determined in accordance with applicable ASTM - standard.
Prior to the commencement of the work the contractor shall provide the project management with typical samples of each type of aggregate and shall obtain its approval to their use. These samples will be retained by the project management for comparison with deliveries (at the site) during the work.
3.2.2.3Fine aggregate
Fine aggregate will have to comply with VBT(NEN 5950). Deviations will only be permitted after written approval by the project management.
Prior to the commencement of work the contractor shall provide the project management with a sample of fine aggregate he proposes to use in the work and shall obtain the project management's approval for its use.
This sample will be retained by the project management for comparison with deliveries at the site during the work.
3.2.2.4Storage of aggregate
All aggregates for the manufacture of concrete shall be stored on a drained concrete floor or other approved surface to prevent the aggregate from being contaminated by the ground or other foreign matter, and each type or grading of aggregate shall be kept separate by the use of partition walls, etc. to the satisfaction of the project management. The contractor shall ensure that graded coarse aggregates do not segregate in the storage heaps.
3.2.2.5Water
Water used for mixing concrete shall be potable water, obtained from GEBEwater lines or other sources approved specifically by the project management.
3.2.2.6Admixtures
All eventual admixtures, which the contractor might desire to use, require previous approval by the project management.
The contractor shall hereto submit complete specifications of the admixtures concerned for the approval by the project management.
3.2.2.7.Concrete qualities and types
The following minimum concrete qualities and types shall be used for the elements of the works as mentioned hereunder:
a.For all structures and slabs:
concrete B25, class I
maximum aggregate size: 31.5mm
b.For blinding and filling of soft spots:
concrete B15, class I
maximum aggregate size; 31.5mm
3.2.2.8.Reinforcement steel
3.2.2.8.1Reinforcement steel will be of quality FeB500 according to NEN 6720. All rebars as shown on the drawings are in metric dimensions.
3.2.2.8.2Welded reinforcement mesh ASTM A 185 welded steel mesh, or NEN 6008 FeB 500 HKN.
3.2.2.8.3The contractor shall, for each shipment of reinforcement steel, supply a manufacturer's certificate to the project management.
Reinforcement steel not complying with the abovementioned specifications will be removed from the site at first notice.
3.2.2.8.4Rebars will be installed strictly in accordance with the drawings and further shop drawings.
Reinforcement shall be checked by the project management before placing of concrete. Changes to be made after the engineer's inspection shall be immediately effected.
3.2.2.8.5Welding or heating of reinforcement steel shall not be allowed.
3.2.2.8.6Reinforcement of all types shall be stored on site in racks above ground in an approved manner so as to avoid damage.
3.2.2.8.7Reinforcement shall not be straightened or bent for a second time, in a manner that may cause injury to the material. Bars with kinks or shapes not shown on the drawings shall not be used. Reinforcement that shows cracks or fails, when bending, will be condemned and removed at first notice.
All reinforcement bars shall be carefully bent to the correct dimensions by experienced steel benders and in a manner that will not injure the materials. In particular no reinforcement shall be heated before bending.
3.2.2.8.8All reinforcement shall be rigidly fixed in position and the concrete cover specified shall be carefully maintained.
Spacing blocks have to be used to provide the necessary concrete cover to reinforcement. The type of spacing blocks, such as chairs or rings, to be used, is subject to the project management's approval.
Steel supports for floor reinforcement, made of bent reinforcement steel, will have to be at least 10mm in diameter.
Number of supports and spacing blocks to be used:
Floors: minimum 3 per m2
Beams and columns: depending on the type proposed by the contractor.
3.2.2.8.9At intersections the reinforcement bars shall be tied together with soft iron wire, and the end of the wire shall be turned towards the inside of the member.
3.2.2.8.10All reinforcement shall be free from loose scale, rust, oil, grease or any other harmful matter. If required by the project management, the reinforcement shall be thoroughly cleaned with wire brushes.
3.2.2.8.11 The contractor shall provide adequate scaffold boards or similar, to ensure that the reinforcement is not displaced by being walked upon during the placing of the concrete or other operations.
Prior to concreting, the contractor shall ensure that the reinforcement is cleaned of all concrete adhering from previous pours.
3.2.2.8.12Amounts of reinforcement steel in different construction elements:
-amounts are not related to a specific order of execution.
-amounts do not include losses due to limited bar
lengths.
-amounts do not include "help reinforcement" such as steel supports in floor slabs nor "cut losses".
-amounts are based on structural drawings of building documents.
-amounts do not include anchor bolts, chemical anchors
etc.
-construction elements not mentioned below do not relief the contractor of his obligation to meet VBC 1995 standards.
3.2.2.8.13Amounts of reinforcement steel per m3 concrete for the structural elements as indicated on the drawings.
3.2.3Concrete proportions
3.2.3.1.Before placing any concrete, the contractor shall prove to the project management that the requested qualities can be reached with the proposed concrete compositions.
A trial mix, of which six test cubes shall be made, will be presented to the project management.
Before placing any concrete the proposed mixes will have to be approved by the project management.
In case of changes in gradation or type of aggregates, the contractor will have to produce a new trial mix with 6 new test cubes, to prove that the required concrete quality will be reached.
The contractor will at all times remain responsible for the quality of the concrete produced.
Trial mixes will have to be made in accordance with instructions from the project management or in accordance with VBC 1995 & VBT 1995.
If, in the opinion of the project management, the materials in use or delivered to site are not conform to the specifications or to the originally approved samples, he may direct that fresh samples shall be submitted for his approval. Should these samples fail to meet the requirements of the specifications then the materials shall be removed from the site or otherwise disposed of as directed by the project management notwithstanding any previous approval of the materials.
3.2.3.2.Measuring materials for concrete
All material for concrete shall be measured by weight, unless otherwise approved by the project management.
3.2.3.3.Concrete quality control
A slump shall be made in accordance with VBC 1995 and VBT 1995, whenever the project management may require.
Number of test cubes to be made in relation to the casting schedule will be in accordance with VBC 1995 and VBT 1995. Costs for concrete testing to be borne by contractor
Concrete made in accordance with NEN regulations and under supervision of the project management. Cubes will be tested at a laboratory of Independent Consulting Engineers N.V. (ICE). Test results of all test submitted by contractor to the project management directly upon testing.
For each set of test cubes in accordance with VBT 1986 one extra cube will be made and tested at 7days after manufacturing.
Water cement ratio max. 0.55. For concrete types for which the water cement factor is limited, control of water cement factor will be done in accordance with VBC 1995 and VBT 1995.
In case of failure of concrete, the contractor shall, on management's instructions, take one or more of the following steps:
1.He shall alter the design of the mix to increase its average compressive strength.
2.He shall alter the method of making the concrete and controlling its quality to reduce the variability of the concrete.
3.He shall cut out and replace concrete placed in the works on any day in which a defective cube-set was made, if in the opinion of the project management such concrete is not likely to be capable of fulfilling its purpose.
4.If required by the project management, 3 cores shall be taken from the area represented by the test cubes. The actual location shall be decided by the project management. If the average strength of the 3 cores, when reduced of the corrected equivalent test cubestrength at 28 days, falls below the specified strength, further cores are to be cut in order to determine the extent of the unsatisfactory concrete.
To the judgment of the project management, eventual extra cores can be replaced by Schmidthamer tests.
The area of concrete shown to be below the required strength shall be cut and replaced at the contractor's expense.
The project management may require the contractor to cut out defective concrete from the works, even though test cubes made from that concrete or cores have not failed.
The contractor shall be deemed to have included in his tendered rates and prices for all tests and all work in connection with tests specified and for making modifications in the mixes and cutting out and replacing defective works.
3.2.3.4.Transportation of concrete
3.2.3.4.1Concrete mixing
3.2.3.4.1.1Use of ready mix concrete is permitted if: -
- The concrete supplier guarantees the compressive strength and composition of the concrete in writing to the contractor. The contractor will give copy of said guarantee to the project management.
-A time limit of one hour between mixing of concrete and placing is not surpassed.
The project management reserves the right to be present at the concrete plant at the time of mixing and to take the necessary test samples.
3.2.3.4.1.2In case the concrete is mixed on site, the following specifications will be in effect:
Concrete mixers, the manner of mixing and the way in which dosage of components is carried out are subject to the project management's approval.
Time of mixing has to be at least 1 1/2 minute.
Components will have to be on site in time, so as to enable the project management to take the necessary samples and perform the necessary tests.
All material will have to be approved by the project management prior to use for concrete.
Materials rejected by the project management will have to be removed from the site at first notice.
Materials have to be on site in sufficient quantities, so as to ensure continuous execution of pours.
3.2.3.5.Placing concrete
The concrete has to be placed immediately after mixing.
-Transport of concrete mortar has to be organized in such a way that no traffic or transport over insufficiently hardened construction parts will take place, nor that damaging vibrations can occur, nor segregation or loss of ingredients takes place. This subject to the project management's judgment.
-Means of transportation have to be adapted to the plasticity of the concrete.
Before placing any concrete, formwork and rebar have to be approved by the project management.
-The project management will be notified at least 24 hours before placing concrete. The contractor remains, in all cases, responsible for the proper execution of concrete works.
Concrete can only be placed in the presence of the project management, except with the permission of the project management.
To prevent walking on rebar put in place, the necessary walkbridges or other provisions should be installed before placing concrete.
Concrete mortar spilled on finished work must be removed immediately.
Concrete mortar spilled during transportation or mixing cannot be used in the works.
The sequence of placing concrete will be determined in consultation with the project management.
Concrete walls have to be poured in layers of maximum 40 cm (16 inch) height.
The necessary measures have to be taken (elephant's trunk or other) to prevent free fall of concrete of more than 1.20 m (4 feet).
3.2.3.6.Compaction
Compaction of concrete shall be carried out by mechanical vibrators in order to avoid honeycombs.
Mechanical vibrators shall be of the immersion or exterior type and shall be demonstrated to be of sufficient capacity.
Vibrators have to present on the site in sufficient numbers and must be handled by qualified personnel, to the judgment of the management. No concrete shall be placed unless said vibrators and personnel are present and available.
3.2.3.7.Construction joints
Concrete shall be placed in such manner that every day’s concreting finishes against properly erected and braced stopends. Prior to the start of concreting the location and position of such stopends have to be approved by the project management.
Interruption of concreting can only be done with approval of the project management. If necessary, the project management can request the contractor to continue pouring after normal working hours, without this causing an increase in the contractprice.
Artificial lights shall be available for this purpose.
Construction joints shall be properly positioned as shown on the drawings or as directed by the project management. Where indicated on the drawings or on the indication of the management the necessary neoprene water stops will be incorporated in the joints. The type of water stop will need the approval of the project management.
When work is resumed against a horizontal concrete surface which has hardened or commenced to set, the surface of the old concrete shall be roughened by chipping and all laitance shall be removed from it together with the porous layer below the laitance.
The chipping shall be carried out by mechanical means unless otherwise approved by the project management. The surface shall then be swept clean, brushed with a steel wire brush to remove all loose material, thoroughly wetted with a thin and fluid cement paste.
The contractor shall deliver and place the injector system, or equal, in those construction joints that have to be waterproof (pools and basin).
When work is resumed against a vertical concrete surface which has hardened or commenced to harden, all laitance, pours and loose material and badly compacted concrete shall be removed from the old surface, which shall then be roughened by hacking, cleaned and brushed with a steel wire brush and thoroughly wetted with a thin and fluid cement paste.
The new concrete shall then be thoroughly compacted, while extreme care shall be taken not to touch present reinforcement.
3.2.3.8.Curing
3.2.3.8.1Vertical surfaces
Immediately after removal of forms a curing compound, subject to approval by the management, will be applied to the concrete surface, either by brushing or spraying.
The curing compound will be applied in the quantities prescribed by the manufacturer for tropical conditions and will cover the complete concrete surface.
The curing compound will be such that it does not prevent bonding of bonding agents, Inertol or others.
3.2.3.9.Horizontal concrete surfaces
Horizontal concrete surfaces will be covered with plastic sheets immediately after initial setting of the concrete. Water will be sprayed on the plastic sheets.