CONCRETE TECHNOLOGY

Concrete

is the product of mixing aggregates with cement and water with possible admixtures to attain a desired property

Two components of concrete:1. Paste2. Mineral Aggregates

Types of Concrete1.Paving Concrete is designed to withstand flexural stress (roadways, runways, basketball courts, tennis courts).

is designed for compressive stress (buildings, bridges, culverts,gutters ).

2. Structural Concrete -

Volume components in typical concrete mix :Air Voids -5 %Water -15 %Cement -10%Aggregates -70 %

Physical Properties of Concrete

1.Workability2.Strength3.Durability4.Impermeability

Slump Test - measure the consistency of concrete

Hydration - chemical combination of water and Portland cement

Different tests of Aggregates (Coarse)

1.Abrasion2.Unit Weight loose and rodded3.Specific Gravity & Absorption4.Grading5.Soundness Test

Fine Aggregates 1.Grading2.Specific Gravity & Absorption3.Unit Weight loose and rodded4.Soundness Test5.Mortar Strength6.% Clay7.% Shale8.Organic Impurities

ITEM 311PORTLAND CEMENT CONCRETE PAVEMENT

DESCRIPTIONconsists of a pavement of Portland cement concrete with or without reinforcement, constructed on a prepared base and in conformity with the lines, grades, thickness and typical cross-section shown on the plan.

STRENGTH REQUIREMENTconcrete for this item shall have a flexural strength of not less than 3.8 mpa (550 psi) when tested by the third point or 4.5 mpa (650 psi) when tested by the mid-point method or a compressive strength of 24.1 mpa (3500 psi) when tested at 14 days.

CONSISTENCY OF CONCRETE

a workable concrete having a slump of 40 to 75 ( 1-1/2 & 3 in) mm if not vibrated or 10 to 40 ( and 1-1/2 in) mm if vibrated.

FORMSForms shall be of steel and of depth equal to the thickness of the pavement

Forms shall be in contact firmly with the foundation and shall not deviate from the true line by more than one (1) cm at any point

Forms shall remain in place undisturbed for not less than 24 hours after concrete pouring

The alignment and grade elevations of forms shall be checked prior to the placing of concrete

MIXING CONCRETE

The concrete maybe mixed at the site in a central mixing plant or in truck mixers

When mixed in a central mixing plant, the mixing time shall not be less than 50 sec nor more than 90 sec

When transporting mixed concrete, the time elapsed from the time water is added to the mix until the concrete is deposited at the site shall not exceed 45 min when using non-agitating trucks, nor 90 min when hauled in truck mixers or truck agitators.

PLACING CONCRETEConcrete should be proportioned, placed and consolidated such that only sufficient mortar is available at the surface for finishing purposes

Concrete shall be consolidated by means of vibrators inserted in the concrete in a vertical position. Vibrators shall operate no longer than 15 sec.

LONGITUDINAL JOINTIf the lanes are concreted separately, a longitudinal construction joint in the form of a key and keyway is used

Deformed steel bars of specified length, size and spacing are placed perpendicular to this joint

Tie bars shall not be coated nor painted with asphalt or other materials

TRANSVERSE CONTRACTION JOINT (Weakened plane joint)

This is formed by installing a parting strip to be left in place or depressing an approved device into the plastic concrete where it shall remain in place until the concrete has set initially, or sawing grooves in the surface of the pavement with a concrete saw. The width of the weakened joint should at all times not less than 50 mm while the width should not be more than 6 mm

Sawing of joints shall commence as soon as the concrete has hardened sufficiently, usually within 24 hrs ( all joints shall be sawed before uncontrollable shrinkage cracks occurs.)

Sawing operations shall be carried during the day and night regardless of weather conditions. Sawing shall be discontinued when a crack develops ahead of the saw. In general, all joints should be sawed in sequence.

TRANSVERSE CONTRACTION JOINT ( Cold joint)

This joint also called cold joint is constructed when there is an interruption of more than 30 min in the concreting operations

No cold joint shall be constructed within 1.5 meters of an expansion joint, contraction or weakened plane joint.

DOWELSDowels are used as load transfer device and are held in position parallel to the surface and center line of the slab by a metal device

Dowels are generally coated with a thin film of bitumen to protect them against corrosion and to facilitate sliding in the concrete.

Their installation midway in the slab should be carried out accurately, so dowels run parallel to the surface and centerline of the pavement

FINAL FINISHThe surface of the pavement shall be broom-finished before the concrete is in such condition that the surface will be roughened by brooming

The corrugations produced in the surface shall be uniform in appearance and not more than 1.5 mm in depth.

CURING By covering the concrete with mats saturated with water

By wetting the pavement and covering the top surface and sides with waterproof paper

By ponding, which involves maintaining a layer of water on the surface of the pavement by means of earth or sand dikes

By spraying uniformly with white pigmented curing compound immediately after finishing of the surface

CONCRETE TECHNOLOGY

SELECTION OF MATERIALSDESIGN OF THE CONCRETE MIXTURECONCRETE IN PRODUCTION CONTROLCONTROL IN PLACING CONCRETECONTROL OF CONSISTENCYSAMPLING OF CONCRETETESTING OF CONCRETE SAMPLESCURING OF CONCRETE SAMPLESPROTECTION OF CONCRETEMINIMUM TEST REQUIREMENT FOR CONCRETE & CONCRETE PRODUCTS

OTHER SPECIFICATIONS AND METHODS OF TEST

AASHTO T 26 Water Test T 97Flexural Test T 22Compressive Test T 71 Test for Fine Aggregates T 27 Sieve Analysis for FA/CA T 19Unit weight of aggregates T 84SG/Absorption of FA T 85SG/Absorption of CA T 96Abrasion Test of CA

ABRASION TESTEvaluates the structural strength of coarse aggregate. It gives an indication of quality as determined by resistance to impact and wear.

Apparatus: LA machine, sieves, abrasive charges or spheres, balance & weights, oven

Oven temp. 110 +/- 50C

The abrasive charge shall consist of cast-iron or steel spheres approx. 46.8 mm in diameter and weighing 390-455 gramsGrading # of Sphere Wt of charge,g A 12 5000(+/-)25 B 11 4584 -do- C 8 3330(+/-)20 D 6 2500(+/-)15

Procedure:

Place test sample and abrasive charge in the LA machine rotated at a speed of 30 to 33 rpm 500 rev.Discharge material from the machine. Make a preliminary separation of the samples on a sieve coarser than 1.70 mm ( # 12 sieve)Sieve finer portion on the 1.70 mm sieve, using the standard procedure of sieving aggregates

Wash all materials coarser than 1.7 mm, dry to constant weight/mass at about 105 to 110 deg C and weigh accurately to the nearest 1 gram.

Calculation:

Original mass Sample retained% Wear= of sample - on #1.70mm sieve Original mass of sample,g

Determination of Absorption & Specific Gravity of Fine & Coarse Aggregate COARSE AGGREGATES: Absoption =A B X 100 B Spec. Gr. = A A - CWhere: A = wt in air of saturated surface dry (SSD) sample in grams B = wt in air of oven dry sample, grams C = wt of sample in water

FINE AGGREGATESAbsorption =A C x 100 CSpec. Gravity = A A - B - D Where: A = wt in air of saturated surface dry sample, SSD in grams B = wt of pycnometer bottle filled w/ water C = Wt in air of oven dry sample D = pycnometer bottle + water + sample in bottle, g.

CURB AND GUTTER

ITEM 600 CURB & GUTTER

Bedding for bed course materials shall pass through 12.5 mm sieve

Concrete shall be of class conforming to the requirement of Item 405

Bed course materials shall be placed and compacted to form a bed of the required thickness

Forms shall conform to the requirement of Item 407

Plastering shall not be allowed

Forms for at least 50 meters shall be in place and checked for alignment

The curb and gutter shall be constructed in uniform sections of not more than 50 meters in length and no section shall be less than 2 meters long.

The forms shall be removed within 24 hrs. after concrete has been placed.

When completed the surface is kept moist for a period of 3 days or a membrane forming comp. is applied

Minor defects are repaired with mortar containing one part cement and two parts fine aggregates

The exposed surface shall be finished while the concrete is still fresh by rubbing the surfaces with a soft brick or wood until they are smooth. After the concrete has been rubbed smooth using water, it shall be rubbed with a thin grout containing 1:1 cement/agg.

The spaces at the back of curb shall be filled to the required elevation compacted in layer at 150 mm compaction.

ITEM 601 - SIDEWALKBed course materials shall pass 12. 5 mm sieve

Bed course materials shall be placed as Item 200, ABC

If preformed joint filler is used, the top of the filler shall be placed 5 mm below the top surface of the finished sidewalk

The surface shall be cut to a depth of 10 mm with a trowel at intervals of 1 m. or as required .

CONCRETE SURFACE FINISHINGClass 1 Ordinary Finish All concrete shall be given this kind of finish unless otherwise specified.Used on all surfaces to clear from holes, cavities, honeycombs, broken edges and corners.Surfaces shall be saturated with water for a period of not less than 1 hr.Mortar used shall be 1 hr old or less.

Class 2 Rubbed Finish

After removal of forms, the rubbing of concrete shall be started upon 3 hrs of water saturationSurfaces to be finished are rubbed with a min.coarse carborundum stone using a small amount of water. It shall continue until all marks & irregularities are removed, all voids have been filled and a uniform surface has been obtained, finally finished with fine carborundum stone, and rubbed with burlap to remove loose powder.

Class 3 Floated finish

After striking and consolidation, the longitudinal or transverse float shall be worked with a sawing motion while held in a floating position parallel to the road centerline and passing gradually from one side of the pavement to the other.

After the floating has been completed and excess water removed, the slab surface is tested with a 3-meter straight edge.

Area showing high spots of more than 3 mm but not exceeding 12 mm shall be marked and ground down with an approved grinding toolWhere the departure from correct cross-section exceeds 12 mm, the pavement shall be removed and replaced at the expense of the contractor.When the concrete has hardened sufficiently, the surface shall be given broom finish. The broom shall produce regular corrugations not over 1.5 mm depth.

Daghang Salamat

Hours