Construction Spec for Concrete Work 2

 

1.               MIXING

1. The concrete shall be concrete mix design, which shall be mixed in accordance with ASTM C94. Concrete mixer used shall be portable type which capable of combining the aggregates, cement, and water thoroughly into a uniform mass within the specified mixing time and of discharging the concrete without harmful segregation.
2. The operation manual including the following information on the batching and mixing plant proposed shall be submitted to CONSULTANT for approval.

• Accuracy of scales for weighing concrete ingredients.
• Rated capacity of mixer.
• Recommended revolutions per minute of mixer.
• Method of charging aggregates and cement.
• Water tank capacity and type of water‑measuring device.
• Maximum daily capacity of plant (8 hours).

3. Except as provided in point 4 below, batches of 0.75 cubic meters or less shall be mixed for not less than 1 minute. The mixing time shall be increased 15 second for each 0.75 cubic meter of fraction thereof additional capacity thereof. At least three-quarter of the required mixing time shall take place after the last of the mixing water has been added.
4. A shorter mixing time may be permitted if performance tests indicate that the time is sufficient to produce uniform concrete.
5. In hot weather mixing time shall be held to the minimum, which will ensure adequate concrete quality and uniformity. Mixer drums and blades shall be checked frequently during hot weather, and the interior of the mixer shall be free of accumulations that will interfere with mixing action.
6. Tolerances for measuring ingredients shall be as specified in Table 7.
7. Air‑entraining admixture and other chemical admixtures shall be made in accordance with ASTM C494.
8. The use of admixture shall be approved by the CONSULTANT. Any request for approval of use admixtures shall be accompanied by comprehensive documentation setting out the particular benefits and effects of the product on the concrete mix that is intended to be used.
9. The results of crushing tests (3 days, 7 days, 28 days and the other day if necessary based on ACI 347 schedule removal of formwork) shall be reported to CONSULTANT.
10. Two weeks before it started pouring samples which have been taken in selected criteria and selected type shall be tested in accordance with ASTM C136.
11. Concrete Design Mix.

• Concrete mixture plan shall follow ACI 318 M chapters 5. Any change in the quality or source of aggregate or cement shall be approved by CONSULTANT. The CONTRACTOR shall prepare a new mix design according to the standard and to be approved by CONSULTANT.
• After the materials to be used in the concrete mixture have been approved by CONSULTANT, the CONTRACTOR has to conduct trial mix using the same mixture materials. During construction, the CONTRACTOR shall maintain the same mixture materials.
• For each proposed mixture at least three compressive of cylinders for each age shall be made and tested by independent authority that approved by CONSULTANT.

 

Table7 Typical Batching Tolerances

Reference: ACI 304, Section 3.1.2

Ingredient	Batch weights greater than 30 percent of scale capacity		Batch weights less than 30 percent of scale capacity
	Individual batching	Cumulative batching	Individual batching	Cumulative batching
Cement and other cementitious materials	+ 1 percent of + 0.3 percent of scale capacity whichever is greater		Not less than required weight or 4 percent more than required weight
Water (by volume or weight), percent	+ 1	Not recommended	+ 1	Not recommended
Aggregates, percent	+ 2	+ 1	+ 2	+ 0.3 percent of scale capacity or + 3 percent of required cumulative weight whichever is less
Admixture (by volume or weight), percent	+ 3	Not recommended	+ 3	Not recommended

 

2.               CONCRETE COVER

Concrete cover to reinforcement, including links or ties, shall be indicated on drawings, but shall not be less than specified below. Cover to reinforcement shall be carefully checked before any concrete is cast, as lack of adequate cover can be the cause of premature chloride access to reinforcement. The bending of reinforcement at a concrete cold joint shall not be permitted without approval. Exposed reinforcement, inserts and plates for providing connections to future extensions, shall be protected from corrosion.

Table 8 Concrete Cover

Reference: ACI 304, Table 3.1.2 and EN 1992-1-1:2004

Concrete exposure	Minimum cover (mm)
Concrete cast against and permanently exposed to earth	75
Concrete exposed to earth or weather: – Bar D 19 through D 32 – Bar D 16 , f 6, and smaller	50 40
Concrete not exposed to weather or in contact with ground: – Slabs, walls, joist : > Bar D 44 and D 56 > Bar D 36 and smaller – Beam, columns (primary reinforcement, ties, stirrups, spirals) -Shells, folded plate members                            : > Bar D 19 and  larger > Bar D 16 , f 6, and smaller	40 20 40     20  15
Marine conditions or other sea water services	55

3.               CONCRETE TRANSPORTING

1. Concrete shall be transported from the batching plant to the place of final deposit by the method approved by CONSULTANT.
2. The method shall be such that will prevent segregation, loss or contamination of the ingredients.
3. The maximum time from concrete mixing to final placing of concrete shall be as follows:

 

Table 9 Time Limit from Concrete Mixing to Placing

Concrete grade	Ambient temperature	Maximum time
High grade concrete (fc’> 280 kg/cm2)	≤ 25o C	45 min.
	> 25o C	30 min.
Odinary grade Concrete (fc’≤ 280 kg/cm2)	≤ 25o C	60 min.
	> 25o C	60 min.

Concrete transported for more than Table 9 may be used if it is proved by tests that the concrete satisfies all requirements give in this specification and any other relevant document.

 

4.               PLACING CONCRETE

1. Prior to CONSULTANT/OWNER inspection for concreting an individual section or structural element, CONTRACTOR shall perform the following checks :

• Check of the interior of the form shall be thoroughly clean and be free from all foreign matter and accumulated water. The interior of wooden forms shall be wetted prior to concreting.
• Check of the formwork for proper installation, stability and rigidity.
• Check of the shoring, strutting and false work for safety and stability.
• Check of formwork for tightness and cleanliness.
• Check of guides, markings and joints for proper position.
• Check for reinforcement for proper placement, concrete cover and bar spacing.
• Check of embedded items, template and block-out forms for proper installation and tight fit.
• Check of type of concrete delivered for conformity with the type of concrete specified.
• Check of all equipment for mixing and transporting the concrete shall be cleaned.

2. Concrete shall be deposited as nearly as practicable at its final position to avoid segregation due to re-handling or flowing.
3. Concrete shall be placed at such a rate that concrete is plastic at all times and flows readily into the spaces between the bars.
4. Concrete that has partially hardened or been contaminated by foreign material shall not be used.
5. Concreting, once started, shall proceed continuously until the placing of concrete for the specific pour is completed.
6. The drop height for the concrete shall not exceed 1.0 meters.
7. All concrete shall be thoroughly consolidated by suitable means, preferably by vibration during placing, and shall be thoroughly worked around the reinforcement, anchor bolts and other embedded fixtures, and into the corners of the forms. An adequate number of spare vibrators shall be kept always at the site during all concrete placing operations. The vibrator is not allowed to touch reinforcement during compaction.
8. No concrete shall be poured without approval from CONSULTANT.
9. Construction joints other than those shown on the drawings shall be minimized and, if necessary to revise the quantity and positions, shall be approved by the OWNER.
10. Where joints are to be made the surface of the hard concrete shall be cleaned thoroughly, roughened, and all laitance shall be removed by brushing or chipping and treated with a thin layer of neat cement before additional fresh concrete is placed.
11. The concrete surface of vertical joints shall be thoroughly wetted and coated with neat cement grout immediately before placing adjoining concrete.
12. Grooves shall be formed at construction joints as directed on the drawings.
13. All horizontal surfaces, unless otherwise specified, shall be given a wooden trowel finish. Where non‑skid surfaces are required the surfaces shall be broom finished.
14. Concrete showing structural defects shall be demolished and replaced. Concrete showing only surface defects shall be chipped out to sound concrete, treated with an epoxy bonding agent and then patched with concrete of rich mortar or epoxy mortar. The repair method for the above shall be subject to the approval from CONSULTANT.
15. Holes left by withdrawal of tie‑rods shall be filled solidly with cement mortar and be made flush.
16. Reinforced concrete must not be placed directly upon the ground. Base could be of either a blinding concrete or polyethylene sheeting of suitable thickness.
17. All concrete slab shall be monolithic throughout the thickness.

 

5.               CRACKWIDTH

ACI 224R established a guideline for tolerance crack widths. The maximum crack width shall be as follows (mm):

–     All slabs and walls beginning below the maximum ground water level or below the highest astronomical tide: 0.15

–     Slabs covered with coating system: 0.20

–     Thick slabs unless if above requirements are not applicable: 0.4

 

6.               CURING

1. All concrete surfaces shall be kept wet at least 7 days after placing except that high early strength concrete shall be so maintained for at least 3 days.
2. The concrete surfaces not in contact with the forms shall be kept continuously moist for 24 hours by covered with wet burlap, cotton fabric or other suitable material, such as a curing compound, immediately after finishing the surface.
3. The covering material shall remain in place during the full curing period. The covering material may be removed when the concrete has hardened sufficiently, provided that the surface is immediately covered with sand, straw, or other similar materials. In either case, the materials shall be kept thoroughly wet during the full curing period.
4. Wood forms in contact with the concrete shall be kept wet during the curing period and to prevent moisture loss.
5. Curing shall be in accordance with the appropriate provisions of ACI 301 and ACI 308 unless noted otherwise herein.
6. In hot weather requirement when the air temperature is at or above 80⁰ F (28⁰ C), provisions for windbreaks, shading, fog spraying, sprinkling or ponding shall be made in advance to the delivery of any concrete. Such protective measures shall be as quick as concrete finishing and hardening operations allow. All work shall conform to ACI 305.
7. Sea water or water contaning acid or chloride shall not be used for curing.
8. The curing compound shall be applied in accordance with the manufacturer’s directions.
9. No load shall be placed on the concrete during the curing period unless permission is given by CONSULTANT.

 

7.               BLINDING CONCRETE

1. Blinding or lean concrete shall be installed under all foundations.
2. The minimum compressive strength (cylinder specimen) of lean concrete shall be follow table 4 at 28 days unless noted otherwise on design drawings.
3. In order to provide a hard and clean surface, the sub soil shall be well consolidated and free from loose material before the blinding concrete is placed.
4. In order to avoid the disturbance of soil by rain or ground water, the blinding layer shall be laid immediately after excavation.
5. Concrete paving slabs shall be laid on water proof membrane (polyethylene sheet 0.2 mm).

 

8.               REPAIRING DEFECTIVE CONCRETE

CONSULTANT shall be immediately notified if defects, such as honeycombing or detrimental cracking are found in the concrete after the forms are removed. All defects in the concrete shall be repaired in accordance with the requirements given in ACI 301, Chapter 9, and the following stipulations:

1. Honeycomb, voids, sand pockets and damage area shall be cut out to sound concrete by chipping so as to cut back to behind the reinforcement all around. Any loose particles and dust shall be removed from cavity by vacuum cleaning, by blowing out with oil free compressed or by flushing with pressured water.
2. Repairs shall not be carried out unless the repair procedure is approved by CONSULTANT. All defects detrimental to structural strength, durability, and water tightness shall be repaired by the method approved.
3. All honeycombed and other defective concrete shall be removed down to sound concrete. The sound surface shall be inspected by CONSULTANT prior to patching.
4. For large repairs, generally exceeding 150 mm in depth or 0.2 m³ in volume, a coating of an epoxy resin adhesive shall be neatly applied over the surface of void to be patched immediately before placing dry pack or repair concrete. The adhesive compound shall be approved by CONSULTANT/OWNER. Application shall be in accordance with manufacturer’s instructions.
5. Sealing of crack can be required for corrosion protection of the reinforcement. Method and procedure base on manufacturer’s directions.

 

9.               FORMWORK

Formwork shall conform to the requirement given in ACI 347 and shall be accordance to as follows:

1. All forms shall be leak proof and of sufficient strength to sustain construction and concrete loads without excessive deflection. Design of the form work as well as its construction shall be done to attain safe installation, removable without any damage to the concrete and shall be approved by CONSULTANT.
2. Before concreting is commenced the forms shall be thoroughly cleaned and free from all dust, dirt and other debris. Temporary openings shall be provided where necessary to drain away water and rubbish.
3. All formwork, whether wood or steel, shall be fixed in perfect alignment and securely braced to withstand displacements and deflections due to construction loads, such as vertical, horizontal and impact construction loads.
4. Where necessary to maintain the specified tolerances the formwork shall be cambered to compensate anticipated deflections caused in the formwork by the weight and pressure of the fresh concrete and by construction loads. The tolerances for the installation of the formwork shall be as specified by ACI 347.
5. Waterproofed plywood forms (film type) shall be used for surfaces visible after construction (expose type). Conblock/non film type plywood shall be used for no expose concrete type (such as foundation, U/G facilities)
6. Suitable moldings or chamfer strips shall be placed in the corners of column, beam, and wall forms where the concrete will be exposed to view with maximum 25 mm chamfer (for detail see table below).
7. All anchor bolts, pipes, angles, insert plates etc., to be embedded in or through the concrete shall be fixed firmly in the forms which shall be cut neatly and accurately for a tight fit.
8. The internal surface of the forms shall be coated with form oils or other releasing agents approved by CONSULTANT prior to installation.
9. Temporary openings shall be provided at the base of column and wall forms, and at other points where necessary, to facilitate cleaning and inspection immediately before the concrete is deposited.
10. Removal of forms

• Forms shall be removed in such manner as to ensure the complete safety of the structure. Where the structure as a whole is adequately supported on shores, side forms of beams, girders, and columns, and similar vertical forms may be removed after a lapse of 12 hours during which the air temperature exceeds 10^oC, or when the compressive strength of the concrete reaches 5 MPa.
• Forms and shoring in the formwork used to support the weight of concrete in beams, slabs, and other structural members shall remain in place until the structure attains sufficient strength to support the dead load and other imposed loads. Field‑cured specimens shall be used to estimate the structural strength.
• Forms other than mentioned above and shoring shall remain in place for periods of time not less than those shown in Table 10. If high‑early‑strength concrete is used this period may be reduced if approved by CONSULTANT.
• Removal of formwork shall be approved by CONSULTANT/OWNER.
• After removal of forms for the cable pit the concrete surface shall be cleaned and all burrs and any injurious obstructions shall be removed.

11. All form surfaces shall be cleaned and repaired before re‑use.

Figure 1 Form-work of Simple Wall

Table 10 Schedule Removal of Forms

Reference: ACI 347

Structure Element	Clear Span Between Structural Support ( CS )	LL < DL	LL > DL
Walls , Column, Sides of Beams & Girders	–	12 hr*
Joist, Beam or Girder Soffit	CS <= 3.0 m 3.0 m< CS <= 6.0 m 6.0 m< CS	7 days** 14 days** 21 days**	4 days 7 days 14 days
Floor Slab	CS <= 3.0 m 3.0 m< CS <= 6.0 m 6.0 m< CS	4 days* 7 days* 10 days*	3 days 4 days 7 days

*  Where such form also support formwork for slab or beam soffits, the removal times of the latter should govern

* * Where forms may be removed without disturbing shores, use half of values shown but not less than 3 days

where,    CS  =   Distance in meter between supports, referred to structural supports and not to temporary form work or shores.

LL   =   Live Load

DL   =   Dead Load

 

10.           REINFORCED BAR WORK

1. Reinforcing shall be detailed and bent in accordance with ACI 315. Heating bars to facilitate bending will not be permitted. All reinforcing bars shall be bent cold before being placed in position. Reinforcing steel shall not be bent or straightened in a manner that will injure the material. Bending or straightening of bars after their embedment in concrete will not be permitted.
2. Reinforcing bars shall be free from mud, dirt, loose mill scale, oil, grease, and any other foreign matters that may reduce the bond between the bar and the concrete.
3. All reinforcing bars shall be placed exactly as shown on the drawings and be supported by an adequate number of small precast mortar blocks with tie wire cast‑in, or with other approved chairs and spacer. The strength of the mortar shall be same or greater than that of the concrete.
4. Reinforcing bars shall be tied adequately at the inter sections with annealed steel wire and be held in position rigidly by using spacers, chairs, or hangers to prevent displacement by construction loads or by the placing of concrete.
5. Splices shall be located as shown on the drawings. Additional splices not shown on the drawings shall be subject to the approval of CONSULTANT.
6. Reinforcing bar shall not be spliced in a line at one location but staggered at a distance equal to 40 times the bar diameters as a minimum.
7. Length of lap for splicing and concrete to reinforcing bar shall be as indicated on the drawing and conform to the requirements of ACI 318.
8. Bars may be moved as necessary to avoid interference with other reinforcing bar, conduits or embedded items. If bar are moved more than one bar diameter or sufficient to exceed the above tolerances the resulting arrangement of the bar shall be approved by CONSULTANT.
9. Splicing of reinforcing bars by welding will not be permitted under any circumstances.
10. Fabricating and placing tolerances shall be specified in ACI 117 section 2 as follow.
    1. Fabrication and placing tolerances

• Reinforcing bars shall be fabricated in accordance with the standard fabricating tolerances in fig 2.1(a) and 2.1(b) of ACI 117.
• Tolerances shall not permit a reduction of concrete cover except as set forth in below.
• Reinforcement shall be placed to the following tolerances:

 

Table 11 Reinforcement Tolerances

Reference: ACI 117 Sec 2.2

No	Description	Tolerances (mm)
1.	Clear distance to side form and resulting concrete surfaces and clear distance to formed and resulting concrete soffits in direction of tolerance. –     Member size is 4 in or less –     Member size is over 4 in but not over 12 in –     Member size is over 12 in but not over 2 ft –     Member size is over 2 ft	-9.525, +6.35 +9.525 +12.7 +25.4
2.	Concrete cover measured perpendicular to concrete surface in direction of tolerance –     Member size is 12 in or less –     Member size is over 12 in Reduction in cover shall not exceed 1/3 specified concrete cover, reduction in cover to formed soffits shall not exceed 6.35 mm.	-9.525 -12.7
3.	Distance between reinforcement : 1/4 specified distance not to exceed 1 in. Providing that distance between reinforcement shall not be less than the greater of the bars diameter or 1 in unbundled bars. For bundled bars, the distance between bundles shall not be less than: –     2 bar bundles   –     3 bar bundles     –     4 bar bundles	+25.4       Greater of +25.4/1.4xDia Greater of +25.4/1.7xDia   Greater of +25.4/2xDia
4.	Spacing of nonprestressed reinforcement, deviation from specified location: –     In slabs and walls other than stirrups and ties	+76.2
5.	Longitudinal locations of bends and ends of bars : At discontinuous ends of members At other locations	+25.4 +50.8
6.	Embedded length of bars and length of bar laps: For bar sizes No. 3 through 11 For bar sizes No. 14 and 18 (embedment only)	-25.4 -50.8

1. When it is necessary to move bars to avoid interference with other reinforcement, conduits or embedded items exceeding the specified placing tolerances, the resulting arrangement of bars shall be subject to acceptance.

 

 

Continued to Construction Spec for Concrete Work 3