QUALITY CONTROL

on

CONCRETE STRUCTURESRepublic of the PhilippinesDEPARTMENT OF PUBLIC WORKS AND HIGHWAYS

Control in Measurement of Materials In order that uniform batches of concrete ofproper proportion and consistency are to be produced, it is essential that theweighing of all ingredients be carefully controlled.

Table I-23Requirement of Materialsfor Concrete Bridges & Road Projects

MaterialTest ItemSpecificationsReference StandardCementAutoclave Expansion 7-days compressive strength Initial SettingNot more than 0.8 More than 19.0 MPaNot less than 45 min and not more than 375 minAASHTO M-24 M-24 M-24 Coarse AggregateSieve AnalysisClay LumpsSoft FragmentsAbrasionPassing 0.075 mm sieveSoundness test (sodium sulfate)Not more than 0.25%Not more than 3.5%Not more than 40%Not more than 1.0%Not more than 12%AASHTO T-27 T-112 T-12 T-96 T-27 T-104Fine AggregateSieve AnalysisClay LumpsPassing 0.075 mm sieveSoundness test (Sodium Sulfate)Colormatic test for organic ImpuritiesNot more than 1%Not more than 3%Not darker than the standardAASHTO T-27 T-112 T-27 T-104 T-71 T-26Water Potable WaterpH Value 4.5 to 8.0AASHTO T-26Reinforcing SteelYield & tensile strengthBending, dimension & phosphorous content6% maximum under nominal mass AASHTO M-31

Storage of Materials Cementcement shall be stored immediately upon delivery at the site in a weatherproof building which will protect the cement from dampness. The floor shall be raised from the ground.bulk cement, if used, shall be transferred to elevated air tight weathered proof bins. cement bags shall be stacked closed together to reduce air circulation but should never be stacked against outside walls.

stack the cement bags so that the first in are the first out.on small jobs where a shed is not available, bags should be placed on raised wooden platforms at least 4 to 6 inches above the ground and water coverings should fit over the pile and extend over the cement and the platform.cement which has been in storage for so long a period that there is already doubt as to quality should be tested prior to use.

Storage of Materials Cement

Cement stored on an elevated airtight and weatherproof stockroom

Aggregates

Store on separate platforms at satisfactory location Different sizes of aggregates shall be stored in separate bins or in separate stockpiles sufficiently removed from each other to prevent the material at the edges of the piles from becoming intermixedStorage of Materials

Aggregates should be stored on separate platform at satisfactory location to prevent inclusion of foreign materials

Stockpile of reinforcing steel bars should be elevated above the ground to prevent detrimental rust

Flow Chart of Preparation for Fresh Concrete

CONSISTENCY

The consistency of concrete shall be gauged by the ability of the equipment to properly place it and not by the difficulty in mixing and transporting.

Consistency of the mixture should be check frequently by Slump Test

Measurement of Concrete SlumpFor economy the lowest slump which can be placed properly, should always be used.

BATCHING

Most specifications require that batching be done by weight rather than by volume because of inaccuracies in measuring aggregate by volume.

The use of the weight system for batching provides greater accuracy and simplicity and avoids the problem created by bulking of damp sand.

MIXING CONCRETE

at CENTRAL

BATCHING PLANT

Transit mixer transporting fresh concrete mix

MIXING CONCRETE at CONVENTIONAL BATCHING PLANT

Conventional Batching Plant

Placing of aggregates on sacks ready for weighing prior to mixing

Weighing of aggregates for conventional batching of concrete

Placing of known weights of aggregates on concrete mixer

Placing of calibrated sack of aggregates on the mixing bucket

ControlinPlacing Concrete

Setting of Formsforms shall be of steel and of equal depth to the thickness of the pavement at the edge and provided with adequate devices to withstand the impact and vibration of consolidation and paving equipment.

any roadbed, which at the form line is found below established grade, shall be filled with approved granular materials to grade in lifts of 3 cm. or less, and thoroughly re-rolled or tamped.

the forms after setting to the correct grade, shall not deviate from the true line by more than one (1) cm at any point.

Preparations Before PlacingMoistened the sub-grade especially in hot, dry weatherto keep the dry sub-grade from drawing too much water from the concrete

to increase the immediate air-moisture level

to decrease the amount of evaporation from the concrete surface.

BatchingMost specifications require that batching be done by weight rather than by volume because of inaccuracies in measuring aggregate by volume.

The use of the weight system for batching provides greater accuracy and simplicity and avoids the problem created by bulking of damp sand.

Mixing of Concretethe concrete may be mixed at the site of the work, in a central-mixing plant, or in truck mixers.concrete mix when supplied by a batching plant, shall only be allowed in DPWH projects provided it is duly accredited by BRS ( DO # 253, S. of 2003 ). batching plants installed/used in DPWH contract projects shall also be required to be accredited prior to supply of concrete mix.concrete when mixed at the site or in a central mixing plant, the mixing time shall not be less than 50 seconds nor more than 90 seconds.

the time elapsed from the time the water is added to the mix until the concrete is deposited in place at the site, shall not exceed 45 minutes when concrete is hauled in non-agitating trucks, nor 90 minutes when hauled in truck mixers. when volumetric measurements are authorized for small project requiring less than 75 cu.m. of concrete per day of pouring, the weight proportions shall be converted to equivalent volumetric proportions. Use of chute is allowed provided that a weighing scale for determining the batch weight will be used.Mixing of Concrete

re-tempering concrete by adding water or by other means shall not be permitted, except that when concrete is delivered in truck mixers, provided:- all these operations are performed within 45 minutes after the initial mixing operation, and- the water-cement ratio is not exceeded. Mixing of Concrete

Limitation of Mixingno concrete shall be mixed, placed or finished when the natural light is insufficient, unless an adequate and approved artificial lighting system is operated.

re-tempering of concrete or mortar which has partially hardened that is remixing with or without additional cement, aggregate or water, shall not be permitted.

Placing of Concreteconcrete shall be unloaded into an approved spreading device and shall be deposited continuously as near as possible to its final position to prevent segregation of the materials.

placing shall be continuous between transverse joints and the use of hand spreading shall be done with shovels not rakes. Workmen shall not be allowed to walk in a freshly mixed concrete with boots or shoes coated with earth or foreign substances.

when concrete is to be placed adjoining a previously paved lane and a mechanical equipment will be operated upon the newly paved lane, such equipment will be allowed to carry on that previously constructed lane provided it has attained the strength for 14 day concrete.

Placing of Concreteif only finishing equipment is carried on the newly paved lane, paving in adjoining lanes may be permitted after 3 days.

concrete shall be thoroughly consolidated by means of a vibrator inserted in the concrete in a vertical position and should not be operated longer than 15 seconds in any one location.

vibrators shall operate at a frequency of 8,300 to 9,600 impulses per minute under load and the space interval of inserting vibrators should be between 50 cm to 60 cm.

vibrators shall be used for consolidation only, and not for moving concrete horizontally along the forms. a well consolidated concrete is 20 % to 25 % higher in strength than that of concrete which is not thoroughly consolidated.

concrete not in-place within 90 minutes from the time the ingredients were charged into the mixing drum or that has developed initial set shall not be used.

Placing of Concrete

COMPACTION/CONSOLIDATION OF CONCRETE

Concrete during and immediately after placing shall be thoroughly compacted. The compaction shall be done by mechanical vibration.

Vibrator is inserted vertically to penetrate underlying lift for homogeneity between lifts

Final Finishbrooming operation should be executed that the corrugations produced in the surface shall be uniform in appearance and not more than 1.5 mm in depth.

the hardened surface of the finished pavement shall have a coefficient of friction less than 0.25 or more. Completed pavement that is found to have a coefficient of friction less than 0.25 shall be grounded or scored by the contractor at his own expense to provide the required coefficient of friction.

Broom finishing of fresh concrete deck slab meeting the required depth of 1.5mm

Protecting fresh concrete from rapid hydration or sudden rainfall

METHODS OF CURING CONCRETE

Water Method Curing Compound Waterproof Membrane Method4 Form-in-place Method5 Curing Cast-in-situ Concrete Curing Pre-cast Concrete Piles

Curing of ConcreteCuring of concrete shall be done by any of the following method:1.Water MethodThe concrete shall be kept continuously wet by the application of water for a minimum period of 7 days after the concrete has been placed. Cotton mats, rugs, carpets, or earth or sand blankets may be used to retain the moisture.2.Curing CompoundSurfaces exposed to the air may be cured by the application of an impervious membrane and shall be practically colorless liquid. The compound shall be applied with a pressurized spray to cover the entire concrete surface with a uniform film and shall be of such character that it will harden within 30 minutes after application.

Curing of Concrete3.Waterproof Membrane MethodThe exposed finished surfaces of concrete shall be sprayed with water, using a nozzle that so atomizes the flow that a moist and not a spray is formed until the concrete has set, after which a curing membrane of waterproof paper or plastic sheeting shall be placed.Curing membrane shall remain in place for a period of not less than 72 hours.

4.Forms in-place MethodFormed surfaces of concrete may be cured by retaining the form-in-place and shall remain in place for a minimum period of 7 days after the concrete has been placed, except that for members over 50 cm in least dimensions, the form shall remain in-place for a minimum period of 5 days. Wooden forms shall be kept wet by watering during the curing period.Curing of Concrete

5.Steam Curing Methodthis method is applicable on pre-cast concrete members.After placement of the concrete, members shall be held for a minimum 4 hours pre-steaming period. to prevent moisture loss on exposed surfaces during the pre-steaming period, members shall be covered immediately after casting or the exposed surface shall be kept wet by fog spray or wet blankets.Curing of Concrete

Curing by using waterproof membrane method

Curing using burlap mat or other absorbent materials

Curing by ponding or continuously saturated covering of sand

Protection

of

Concrete

Removal of Formsforms for concrete shall remain in place undisturbed for not less than 24 hours after concrete pouring.

In case portions of the concrete are spalled during the removal of forms, they shall be immediately repaired with fresh mortar mixed in the proportioned of one part of Portland Cement and two parts of fine aggregates.

in case major honeycombs occurs on sides of the pavement, it shall be removed and replaced at the expense of the contractor.

Sealing of Jointsjoints shall be sealed with asphalt sealant soon after the completion of the curing period and before the pavement is opened to traffic.prior to sealing of joints, it shall be thoroughly cleaned of all foreign materials including membrane curing compound and joint faces shall be in a surface dry condition when the seal is applied. the use of sand or similar material as a cover for the seal will not be permitted.the pouring of sealant shall be done in such a manner that the material will not spilled on the exposed surfaces of the concrete.

Protection of Pavementthe contractor shall protect the pavement and its appurtenances against both public traffic and traffic caused by his own employees and shall include watchmen to direct the traffic and the erection of and maintenance of warning signs, lights, pavement, bridges, etc.all boreholes after thickness and/or strength determinations of newly constructed concrete pavements shall be immediately filled/restored with the prescribed concrete mix after completion of the drilling works. ( Dept. Memo Circular No. 97, dated August 9,1991 )any damage to the pavement, occurring prior to final acceptance shall be repaired or the pavement shall be replaced.

In order that the concrete may be properly protected against rain before the concrete is sufficiently hardened, the Contractor will be required to have at all times, materials for the protection of the edges and surface of the unhardened concrete.Protection of Pavement

The falsework shall be constructed to conform to the falsework drawings. The materials used in thefalsework construction shall be of the quantity and quality necessary to withstand the stressesimposed.FORMWORKS AND FALSEWORKS

Formwork for concrete placed under water shall be watertight. When lumber is used, this shall beplaned, tongued and grooved.

Forms and falsework shall not be removed without the consent of the Engineer.

Proper construction of Formworks and Falseworks