module ii - concrete
TRANSCRIPT
MODULE II - CONCRETE
► General Information and Control of Concrete Materials
OUTLINE OF TOPICS
► Sampling and Testing of Fresh ConcreteMixes
► Molding Test Specimens of Concrete
► Design of Concrete Mixtures
► Determination of Compressive and Flexural Strength of Concrete
► Evaluation and Acceptance of Concrete
General InformationAbout ConcreteAbout Concrete
Definition of Concrete:
Concrete is the finished productof mixing aggregates with cementof mixing aggregates with cementand water together with the necessarymanipulations of placing andobserving curing requirements.
Composition of Concrete:
1. Pastea. Cementb. Waterb. Water
2. Mineral Aggregatea. Coarse Aggregateb. Fine Aggregate
Composition by Volume:
1. 7 - 14% cement1. 7 - 14% cement2. 15 – 20% water3. 66 – 78% aggregate
PHYSICAL PROPERTIESOF CONCRETE
1. Workability2. Strength2. Strength3. Durability4. Impermeability
PHYSICAL PROPERTIESOF CONCRETE
1. Workability – defined as the ease inplacing concrete without segregationinto the final position where it is allowedto harden.to harden.► degree of workability is dependent on the
type of construction and the methods of handling and placing concrete
► water function► grading and maximum size of aggregates
Measuring Workability:
There is no accurate method or instrument to measure workability. instrument to measure workability.
The method commonly used is the slump test.
2. Strength – capability to withstand loads,minimum strength requirements forcompression, flexure, shear and bond ofintended use.
►Strength of concrete is principally dependent ►Strength of concrete is principally dependent on the water-cement ratio.
►The strength of concrete continues to increase with age as long as it is protected from drying.
3. Durability – durability of concrete isimportant to be able to withstanddeterioration due to weathering action.
► After construction, durability ofconcrete decrease with time due toconcrete decrease with time due tophysical, chemical reaction andinternal factors.
► Durability is also a function of thewater-cement ratio.
4. Impermeability – Imperviousness isan essential requirement of concreteexposed to the weather.
► Concrete that does not leak is made by causing a small amount of water and curingcausing a small amount of water and curingit well for a long period.
► With less water used in the mixing, theconcrete product can be made dense whichcontributes to water tightness.
FACTORS AFFECTING PRODUCTIONOF HIGH QUALITY CONCRETE
1. Quality of Paste2. Quality of Aggregates3. Proper Handling and Placing4. Proper Curing
FACTORS AFFECTING PRODUCTIONOF HIGH QUALITY CONCRETE
1. Quality of Paste – The quality ofconcrete is largely dependent upon thequality of the paste which is water andquality of the paste which is water andcement that binds the aggregateparticles into a solid mass. Therefore, aproper proportion of the water tocement known as the water-cementratio is essential for successful results.
KINDS AND TYPESKINDS AND TYPES
OFOF
CEMENTCEMENTCEMENTCEMENT
IN THE PHILIPPINESIN THE PHILIPPINES
KIND OF CEMENT
TYPE HOW TO
IDENTIFY INTENDED USE OR APPLICATION
PORTLAND CEMENT
T – IOne color bond
RED COLOR
For general concrete construction use when the special properties specified for any other type are not required
T - II n/aFor general concrete construction, Moderate Sulfate resistance or moderate heat of hydration cement
T - III n/a For general concrete construction, High early strength cement
T - IV n/a For general concrete construction, Low heat of hydration cement
T - V n/a For general concrete construction, High sulfate resistance cement
White Portland Cement
T - I n/aFor general construction use when the special properties specified for any other type are not required
BLENDED CEMENTBLENDED CEMENT
Portland -Pozzolan
T – IP Three color bands
BRIGHT YELLOW
For general concrete construction use, Moderate sulfate resistant and moderate heat of hydration cement
T – I(PM) Two color bands
BRIGHT YELLOW
For general concrete construction use when special characteristics attributed to the larger quantities of pozzolan in the portland-pozzolan cement are not required.
T - POne color band
BRIGHT YELLOW
For general concrete construction use not requiring high early strength, sulfate resistant, Low Heat of hydration cement
Portland Blast-furnace Slag
T - IS Two color bands
BLUE COLORFor general concrete construction, Moderate sulfate resistant and moderate heat of hydration cement
SLAG CEMENT T – SOne color band
BLUE COLOR
For general concrete construction not requiring high early strength, sulfate resistant, Low Heat of hydration cement
MASONRY T – N One color band
Cement
Cement will retain its quality indefinitely if it does not come in contact with moisture.Proper storage of cement at jobsite must satisfy the following:
1. Warehouse or shed should be airtight as possible. No opening between walls androof should be tolerated.
2. Flooring of shed should be well above ground.
3. Cement sacks should be stackedclose together to reduce circulationof air but should not be stacked against outside walls.
4. Warehouse doors and windowsshould be kept closed.
Water
Generally, water that is suitable for drinking is satisfactory for use in concrete. Water from lakes and streams that contains marine life streams that contains marine life usually is suitable. No sampling is necessary when water is obtained from sources mentioned above.
When it is suspected that water may contain sewage, mine water, or wastes from industrial plants or canneries, it should not be used in concrete unless tests indicate that it is satisfactory. tests indicate that it is satisfactory. Water from such sources should be avoided since the quality of the water could change due to low water or by intermittent discharge of harmful wastes into the stream.
Chemical Admixture for Concrete
Approved set-retarding or water-reducing and set retarding admixtures are and set retarding admixtures are permitted in order to increase the workability of the concrete.
Chemical Admixtures as defined by AASHTO M 194 are as follows:
Type A - Accelerating Type B - Retarding Type C – Water reducing Type D - Water reducing High Range Type D - Water reducing High Range Type E - Water reducing and Accelerating Type F - Water reducing and Retarding Type G - Water reducing High Range and
Retarding
2. Quality of Aggregates – Since theaggregate constitute a large part of theconcrete ,equal importance should beundertaken as that of the quality of thepaste.
Utmost care in their selectionconcerning qualities such as: a) goodquality; b) strength; c) durability and d)freedom from injurious materials.
Fine Aggregate
Fine aggregate (sand) must be approved prior to use and meet the requirements of the specifications. Fine aggregate consists of relatively small aggregate consists of relatively small particles and does not tend to separate as much as coarse aggregate. Therefore, segregation generally is not a problem with the fine aggregate unless extremely careless methods of handling are employed.
Coarse Aggregate
Coarse aggregate is a graded material consisting of a combination of various particle sizes that require extreme care when handling to prevent the smaller when handling to prevent the smaller particles from separating from the larger ones. The separation that may occur during handling is known as segregation.
If aggregate is dropped from a bucket or belt and allowed to form a cone-shaped stockpile, or if it is pushed over the edge of a stockpile, the larger particles roll to the bottom outside edge of the pile. The smaller particles have less tendency to roll because of their small size and weight and remain nearer to the size and weight and remain nearer to the center. This results in a segregated stockpile. Non-uniformity results when such material is withdrawn for use in concrete and difficulty is encountered in controlling the water, slump, and yield of the resultant concrete.
3. Proper Handling and Placing –
The proper methods of handling andplacing the fresh concrete contributesto the production of quality concrete.
Segregation of the coarse aggregateSegregation of the coarse aggregateand improper tamping in placing theconcrete into final position are factorscontributing to weak concrete.
Concrete shall not be dropped morethan 1.5 m.
Concrete shall be placed as near aspossible to its final position to preventsegregation.
Excess water that may accumulate onExcess water that may accumulate onthe top layer of a deep pour should be removed carefully.
Vibration shall be of sufficient durationto provide thorough compaction, but notprolonged as to cause segregation.
4. Proper Curing – Equally important to beconsidered in the production of qualityconcrete is proper curing.
Neglect in the matter of proper curingespecially within the first 72 hours afterespecially within the first 72 hours afterconcrete is placed will impair theincrease in strength, and the loss ofstrength suffered within this period can inno way be recovered.
Curing is a serious phase of any concrete job, especially in hot weather concreting. Curing is the process of maintaining a satisfactory moisture content and a favorable temperature in content and a favorable temperature in concrete during the period immediately following final placement so that hydration of the cement may continue until the desired properties are developed to a sufficient degree.
The curing shall be one or more of the following:
Water Method – The concrete shall be kept continuously wet for a minimum of 7 days.
Curing Compound-The compound shall be Curing Compound-The compound shall be applied with a pressure spray to cover concrete with a uniform film.
Waterproof Membrane Method-Curing membrane of waterproof paper or plastic sheeting shall remain in place for not less than 72 hours.
Water method can be done by a number of ways like the application of water to counteract evaporation, such as ponding, sprinkling, spraying or applying wet burlap,wet earth, sand, sawdust or wet burlap,wet earth, sand, sawdust or straw. Extra care must be taken to prevent evaporation from the green concrete during hot weather construction.
CLASSES OF CONCRETEUSE IN STRUCTURES
Concrete can be made with widevariations in quality.
Standard Specifications includeseveral classes of concrete which areseveral classes of concrete which areselected on the basis of intended use:
1.Class A2.Class B3.Class C4.Class P5.Class Seal
Class A : All superstructures andheavily reinforced substructures.
The important parts of the structuresincluded are slabs, beams, girders,included are slabs, beams, girders,columns, arch ribs, box culverts,reinforced abutments, retaining wallsand reinforced footings and largediameter cast-in-place reinforcedconcrete piles (bored piles).
Class B : Footings, pedestals, massivepier shafts, pipe bedding, and gravitywalls, unreinforced or with a smallamount of reinforcement.
Class C : Thin reinforced sections,railings, precast R.C. piles and cribbingand for filler in steel grid floors.
Class P : Prestressed concretestructures and members.
Seal : Concrete deposited in water.
Class
Of
Concrete
Minimum Cement Content per m3
Kg(bag*)
Maximum Water/Cement Ratio
Kg/kg
Consistency Range in Slump
mm (inch)
Designated Size of Coarse AggregateSquare Opening
mm(U.S. Standard)
Minimum Compressive Strength of 150x300 mm concrete cylinder specimen at 28 days,
MN/m2
(psi)
A360
(9 bags) 0.5350 – 100(2 – 4)
37.5 – 4.75(1 ½” – No. 4)
20.7(3000)
Composition and Strength of Concrete for Use in Structures
A (9 bags) 0.53 (2 – 4) (1 ½” – No. 4) (3000)
B320
(8 bags) 0.5850 – 100(2 – 4)
50 – 4.75(2” – No. 4)
16.5(2400)
C380
(9.5 bags) 0.5550 – 100(2 – 4)
12.5 – 4.75(1/2” – No. 4)
20.7(3000)
P440
(11 bags) 0.49100 max.(4 max.)
19.0 – 4.75(3/4” – No. 4)
37.7(5000)
Seal380
(9.5 bags) 0.58100 – 200
(4 – 8)25 – 4.75
(1” – No. 4)20.7
(3000)
* Based on 40 kg/bag
SAMPLING AND TESTING OFFRESH CONCRETE MIXES
1. Sampling Fresh Concrete
2. Slump Test For Consistencyof Portland Cement Concreteof Portland Cement Concrete
3. Unit Weight and Yield ofConcrete
4. Making and Curing TestSpecimens in the Field
SAMPLING FRESH CONCRETE
Standard Method ofSAMPLING FRESH CONCRETE
AASHTO Designation: T 141-74(ASTM Designation: C 172-71)
1. SCOPE
This method describes the procedures for obtaining representative samples of fresh concrete as delivered to the project site and on which tests as delivered to the project site and on which tests are to be performed to determine compliance with quality requirements of the specifications under which the concrete is furnished. The method includes sampling from stationary, paving and truck mixers, and from agitating and non-agitating equipment used to transport central mixed concrete.
2. SAMPLING
The elapsed time between obtaining the first and final portions of the composite samples shall be a short as possible, but in no instance shall it exceed 15 minutes.
Transport the individual samples to the place where fresh concrete test are to be performed or where specimens are to be molded. They shall then be combined and remixed with a shovel to ensure uniformity.
3. PROCEDURE
a. Sampling from Stationary Mixers, Except Paving Mixers – Sample the concrete at two or more regularly spaced intervals during discharge of the middle portion of the batch. Take the samples within the time limit of 15 Take the samples within the time limit of 15 minutes and composite them into one sample for test purposes. Do not obtain samples from the very first or last portions of the batch discharge. Perform sampling by passing a receptacle completely through the discharge stream or by completely diverting the discharge into a sample container.
b. Sampling from Paving Mixers – Sample the concrete after the contents of the paving mixer have been discharge. Obtain samples from at least five different portions of the pile and then composite into different portions of the pile and then composite into one sample for test purposes. Avoid contamination with subgrade materials or prolong contact with an absorptive subgrade.
c. Sampling from Revolving Drum/Truck Mixers or Agitators – Sample the concrete at two or more regularly spaced intervals during discharge of the middle portion of the batch. Take the samples within the time limit specified for sampling fresh concrete and composite them into one sample for test purposes. In any case do not obtain samples test purposes. In any case do not obtain samples from the first or last portions of the batch discharge. Sample by repeatedly passing a receptacle through the entire discharge stream or by completely diverting the discharge into a sample container. Regulate the rate of discharge of the batch by the rate of revolution of the drum and not by the size of the gate opening.
SLUMP TEST FOR CONSISTENCYOF PORTLAND CONCRETE
Standard Method of TestSLUMP TEST FOR CONSISTENCY OF PORTLAND
CONCRETEAASHTO Designation: T 119-74(ASTM Designation: C 143-74)
Apparatus:
1.Galvanized Mold, No. 16 gage (Frustum of Conewith a base diameter of 8 in., to diameter of 4 in.and height of 12 in.)
2. Scoop3. Trowel4. Tamping Rod (5/8” diam., length of 24 in. with one
end bullet-pointed at the lower end)
SLUMP TEST FOR CONSISTENCY OF PORTLAND CONCRETE
Apparatus:
Procedure:
1.Dampen the mold and place on a flat, moist non-absorbent surface.
2. Fill the mold with concrete in three layers, each approximately one-third the volume of the mold. In approximately one-third the volume of the mold. In placing the concrete, move the scoop-full around top edge of the mold as the concrete slides from it, in order to insure symmetrical distribution of concrete within the mold.
3. Each layer should be rodded with 25 strokes of a 5/8” diameter rod having a length of 24 in. and bullet pointed at the lower end. The strokes should be distributed in a uniform manner over the cross-section of the mold and should penetrate into the underlying layer by ½ inch.penetrate into the underlying layer by ½ inch.
4. After the top layer has been rodded, strike off the the surface of the concrete with a trowel so that the mold is exactly filled.
5. Remove the mold from the concrete by raising it carefully in a vertical direction, then measure immediately the slump by determining the difference between the height of the mold and the height of the concrete:
Slump = 12” – height of concrete after its subsidenceSlump = 12” – height of concrete after its subsidence
6. After the slump measurement is completed, tap gently the sides of the concrete frustum with the tamping rod. A well proportioned workable mix will gradually slump to lower elevation and retain its original identity, while a poor mix will crumble, segregate and fall apart.
Slump Test
Slump is a measure of the workability of the concrete. This test is done at the point of placement.
Slump is controlled by the amount of water that is Slump is controlled by the amount of water that is batched into the concrete. Slump is increased as water is added to a batch of concrete. There are chemical admixtures (Water reducing) that can increase the slump chemically, without the addition of extra water.
UNIT WEIGHT ANDYIELD OF CONCRETEYIELD OF CONCRETE
UNIT WEIGHT AND YIELD OF CONCRETEAASHTO DESIGNATION: T 121-82
ASTM DESIGNATION: C 138-7
I. APPARATUS1. Balance2. Tamping Rod3. Measure – a cylindrical container made from3. Measure – a cylindrical container made from
metal that is not readily attacked by cement paste
- watertight and sufficiently rigid toretain its forms and calibrated volume underrough used.
4. Strike-off – a flat rectangular plate5. Mallet – with rubber or rawhide head
UNIT WEIGHT AND YIELD OF CONCRETE
Unit weight measure
II. SAMPLE
Obtain the sample of freshly mixed concrete in accordance with the Standard Sampling of Fresh Concrete.
III. PROCEDUREIII. PROCEDURE
1. Consolidation – consolidate by rodding for concrete having a slump greater than 75 mm, by rodding or vibration if the slump is 25 to 75 mm, and by vibration if the slump is less than 25 mm.
2. Rodding ►place the concrete in the measure inthree layers of approximately equal volume.
► rod the bottom layer throughout its depth but the rod shall not forcibly strike the bottom of the measure.
► distribute the strokes uniformly over the crosssection of the measure and for the top two layers, penetrate about 25 mm into the layers, penetrate about 25 mm into the underlying layer.
► after each layer is rodded, tap the sides of themeasure smartly 10 to 15 times with theappropriate mallet.
► add final layer so as to avoid overfilling.► 25 strokes if the measure used is 14 liters or
smaller in capacity.► 50 strokes for 28-liter measure
3. Internal Vibration
► fill and vibrate in two equal layers► insert vibrator at three different points for each
layer► in compacting the bottom layer, do not allow
the vibrator to rest on or touch the bottom or the vibrator to rest on or touch the bottom or sides of the measure
► in compacting the final layer, the vibrator shall penetrate into the underlying layer approximately 25 mm
► the duration of the vibrator will depend upon the workability of the concrete and effectiveness of the vibrator
4. Strike-Off► after consolidation, strike-off the top surface of the
concrete and finish it smoothly with the flat strike-off
plate
5. Cleaning and Weighing► after stike-off, clean all excess concrete from the
exterior of the measure and determine the net exterior of the measure and determine the net mass of the concrete.
6. CalculationUnit Weight = Net Mass of Concrete x Calibration Factor of
MeasureYield = Total Mass of Batch / Unit Weight of ConcreteCement Content = Mass of Cement in the Batch / Volume of
Batch
MAKING AND CURING CONCRETETEST SPECIMENS IN THE FIELD
Cylinder Samples Beam Samples
MAKING AND CURING CONCRETE TEST SPECIMENS IN THE FIELD
AASHTO Designation: T 23(ASTM Designation: C 31)
A. COMPRESSION TEST SPECIMENS
1. Size of Specimens
Diameter = 3 x maximum nominal size of aggregate
Height = 2 X diameter
2. Molding ► fill mold in 3 layers of approximatelyequal volume
► rod each layer with a bullet-shaped tamping rod at the lower end
► the strokes shall be distributed uniformly over the cross-section of the mold and shall just penetrate into the underlying layer
► the bottom layer shall be rodded throughout its► the bottom layer shall be rodded throughout itsdepth
► tap the side of the mold to close the voids left by the tamping rod
► after the top layer has been rodded, the surface of the concrete shall be struck off with a trowel and covered with a glass or metal plate to prevent evaporation.
Molding Concrete Cylinder Specimens
No. of Roddings per layer/Rod Diameter
Cylinder Dia., mm(in,) Rod Dia., mm(in.) No. of Strokes/layer
100(4) 10 (3/8) 25100(4) 10 (3/8) 25
150(6) 16 (5/8) 25
200(8) 16 (5/8) 50
250(10) 16 (5/8) 75
No. of Layers Required
Ht. of Cylindermm, (in.)
Mode of Compaction No. of Layers Approx. Depth of layer, mm (in.)
Up to 300 (12) rodding 3 equal -
Over 300 (12) -do- As required 100 (4)
300 (12) – 460 (18) vibration 2 equal Half depth
Over 460 (18) -do- 3 or more 200 (8) as near as practicable
Consolidation by vibrator – use 3 insertions of the vibrator at differentpoints for each layer
- allow the vibration to penetrate through layer being vibrated, andinto the layer below, approximately 25 mm (1 inch)
3. Curing ► after molding, cover top with wet burlap and store in a cold place
► remove from mold after 24 hours and soak in water
► tests specimens shall be sent to the laboratory not more than 7 days prior to the time of test not more than 7 days prior to the time of test (tests specimens shall be kept in the field at least three-fourths of the test period)
► while in the laboratory the specimens shall be kept at laboratory temperature until 24 to 48 hours before testing
GENERAL RULES:
1.Take samples from at least three parts of the load2. Use only non-absorptive molds3. Fill mold in three equal layers, rod each layer 25
times with a spherical-nose rod4. Let cylinders stand undisturbed from 12 to 244. Let cylinders stand undisturbed from 12 to 24
hours, with tops covered at temperaturesbetween60° and 80° F (20° - 26°C)
5. Pack cylinders carefully in sawdust and ship tolaboratory for testing.
B. FLEXURE TEST SPECIMENS
B. FLEXURE TEST SPECIMENS
1. Size of Sample
Depth = 3 x maximum nominal size of aggregateWidth = depth, or may be wider by not more than halfLength = 3 x depth + 2 inches or moreLength = 3 x depth + 2 inches or more
2. Molding ► fill mold with concrete in layers ofapproximately 75 mm ( 3 inches) in depth► rod each layer 50 times for each square foot
( or 1stroke for each 2 square inches)► the top layer shall slightly overfill the mold► after each layer is rodded, the concrete shall
be spaded along the sides and ends with a be spaded along the sides and ends with a mason’s trowel or other suitable tools
► when the rodding and spading operations arecompleted, the top shall be struck off with astraightedge and finished with a wood float
Rod Size and No. of Strokes per Layer
Top surface area of specimen, sq.cm. (sq.in.)
Rod dia., mm (in.) No. of Strokes/layer
160 (25) or less 10 (3/8) 25
165 – 310 (26 – 49) 10 (3/8) 1 for each 7 sq.cm.(1 sq.in.) of surface
310 (50) or more 16 (5/8) 1 for each 14 sq.cm(2 sq.in.) of surface
No. of Layers
Depth, mm (in.) Mode of Compaction
No. of Layers Approx. Depth per layer, mm (in.)
150 – 200 (6 – 8) rodding 2 equal half depth150 – 200 (6 – 8) rodding 2 equal half depth
over 200 (8) -do- 3 or more 100 (4)
150 – 200 (6 – 8) vibration 1 depth of sample
over 200 (8) -do- 2 or more 200 (8) or as near as practicable
Various Sizes of Cylinder and Beam Molds
Sampling
► A set of 3 cylinder samples for structural concrete or a set of 3 beam samples for paving concrete shall be obtained for each paving concrete shall be obtained for each day of concreting operations.
► A set shall represent 75 cu.m. or fraction thereof for each class of concrete.
COMPRESSIVE STRENGTH OF CYLINDRICAL CONCRETE SPECIMEN
I. APPARATUS
1. Compression Testing Machine – of sufficientcapacity capable of providing a rate of loadingof 0.05 in. (1.3mm) / min. or 20 to 50of 0.05 in. (1.3mm) / min. or 20 to 50psi/second (0.14 to 0.34 MPa per second).
2. Capping material and facilities
III. PROCEDURE
1. After removal from the curing room, cap the specimen as soon as practicable with the melted capping compound to distribute the applied load uniformly during the test.
2. Determine the diameter of the test specimen to the 2. Determine the diameter of the test specimen to the nearest 0.01 in (0.25mm) measured at right angles to each other at about midheight of the specimen. This average diameter will be used to calculate the cross sectional area of the specimen.
3. Place the specimen at the table of the compression tester directly under the upper bearing block.
4. Apply the load continuously at a rate of travel of approximately 0.05 in/min or 20 to 50 psi/sec. until the specimen fails.specimen fails.
5. Record the maximum load carried by the specimen during the test.
IV. CALCULATION
Maximum Load, lbs.Maximum Load, lbs.Compressive Strength, psi = ---------------------------------
Cross Sectional Area, in2
FLEXURAL STRENGTH OF CONCRETE( Using Simple Beam with Third-Point Loading )
I. APPARATUS
1. Flexure Testing Machine
II. PROCEDUREII. PROCEDURE
1. Measure the average depth of the test specimen.
2. Adjust the test span of the tester such that it isthree (3) times the average depth of the testspecimen.
3. Place the specimen on the support blocksof the tester.
4. Apply the load rapidly up to approximately50 percent of the expected loadcontinuously at a rate between 125 and continuously at a rate between 125 and 175 psi (861 and 1207 KPa) per minute untilrupture occurs.
5. Record the maximum load carried by thespecimen during the test.
> 5%L
II. CALCULATIONS1. If the fracture initiates in the tension surface
within the middle third of the span length, calculate the modulus of rupture as follows:
1. If the fracture initiates in the tension surface within the middle third of the span length, calculate the modulus of rupture as follows:
PLR = -------------
bd2bd2
Where: R = modulus of rupture, psi, (or KPa)P = maximum applied load, lbf, (or N)L = span length, in., (or mm)b = average width of specimen, in., (or mm)d = average depth of specimen, in., (or mm)
< 5%L
2. If the fracture occurs in the tension outside of the middle third of the span length by not more than 5 percent of the span length, calculate the modulus of rupture as follows:
a
2. If the fracture occurs in the tension outside of the middle third of the span length by not more than 5 percent of the span length, calculate the modulus of rupture as follows:
3PaR = -------------R = -------------
bd2
Where: a = average distance between line of fracture and the nearest support measured on the tension surface of the beam, in., (or mm)
3. If fracture occurs in the tension surface outside the middle third of the span length by more than 5 percent of the span length, discard the results of the test.
> 5%L
EVALUATION AND ACCEPTANCE OF CONCRETE
1. The strength level of the concretewill be considered satisfactory if theaverages of all sets of three (3)consecutive strength test resultsequal or exceed the specifiedequal or exceed the specifiedstrength, fc’ and no individualstrength test result is deficient bymore than 15% of the specifiedstrength, fc’.
2. Concrete deemed to be not acceptable using the above criteria may be rejected unless the Contractor can provide evidence by means of core tests, that the quality of concrete represented by failed test results is acceptable in place. At least three (3) representative cores place. At least three (3) representative cores shall be taken from each member or area of concrete in place that is considered deficient. The location of cores shall be determined by the Engineer so that there will be least impairment of strength of the structure.
3. Concrete in the area represented bythe cores will be consideredadequate if the average strength ofthe cores is equal to at least 85% ofthe cores is equal to at least 85% ofand if no single core is less than75% of the specified strength, fc’.
4. If the strength of control specimensdoes not meet the requirements, andit is not feasible or not advisable toobtain cores from the structure due tostructural considerations, payment ofstructural considerations, payment ofthe concrete will be made at anadjusted price due to strengthdeficiency of concrete specimens asfollows.
Deficiency in Strength ofConcrete Specimens,
Percent (%)
Percent (%) of ContractPrice Allowed
Less than 5 100
5 to less than 10 805 to less than 10 80
10 to less than 15 70
15 to less than 20 60
20 to less than 25 50
25 or more 0
DESIGN OF CONCRETE MIXTURES
The design of a concrete mixture isthe determination of the relativeproportions of cement, fine aggregate,coarse aggregate and water. Theconcrete mixture shall be designed toconcrete mixture shall be designed togive the most economical and practicalcombination of the materials that willproduce the desired workability, strengthand durability.
Based on mix having a water-cementratio of 0.57 by weight of 22.8 kg. per bagof cement (22.8 L/bag of cement), 75.0mm slump and natural sand having amm slump and natural sand having aFineness Modulus of 2.75.
Maximum size of
Aggregate
mm (inch)
Rounded Coarse Aggregate Angular Coarse Aggregate
Sand
% of Total Agg. by Absolute Vol., cu.m.
Net Water Content per cu.m.
Sand
% of Total Agg. by Absolute Vol., cu.m.
Net Water Content per cu.m.
Kg. Liters Kg. Liters
12.5 (1/2) 51 199 199 56 214 214
TABLE V
APPROXIMATE SAND AND WATER CONTENTS PER CUBIC METER OF CONCRETE
19.0 (3/4) 46 184 184 51 199 199
25.0 (1) 41 178 178 46 192 192
37.5 (1 ½) 37 166 166 42 181 181
50.0 (2) 34 157 157 39 172 172
75.0 (3) 31 148 148 36 163 163
150.0 (3) 26 131 131 31 146 146
Based on mix having a water-cement ratio of 0.57 by weight of 22.8 kg. per bag of cement, 75.0 mm slump and natural sand having F.M. of 2.75.
Changes in Conditions Stipulated in Table V
Effect on Values in Table V
Percent Sand Net Water Content
Each 0.05 increase or decrease in water-cement ratio ± 1 0
Each 0.1 increase or decrease in
Adjustments of Table V for Other Conditions
Each 0.1 increase or decrease in Fineness Modulus of sand ± 1/2 0
Each 25 mm increase or decrease in slump 0 ± 3 %
Manufactured Sand + 3 + 8.9 kg.
For less workable concrete as pavement - 3 - 4.7 kg.
Illustrative Example :
Structural Concrete Mix DesignStructural Concrete Mix Design
Illustrative Example:
Portland Cement Concrete PavementMix DesignMix Design
Corrected Batch Weights Due toChanges in Moisture Content ofAggregates
Corrected Weights:
Supposing MC of FA = 6.1 and MC of CA = 2.45
When M.C. is greater than Absorption, there is Free Water
Corrected wt. = Uncorrected Wt. x (1+ (MC-Absorption)/100 )
Corrected Wt. of F.A. = 75.80 ( 1+(6.1-2.71)/100)= 78.37 Kg.
Corrected Wt. of C.A. = 139.50 ( 1+(2.45-1.34)/100)= 141.05 Kg.
Corrected Wt. of Water = ( 75.80 + 139.50 + 17.44) – (78.37 + 141.05)
= 13.32 Kg.
Preparation of Trial Mix
Materials for Three Cylinders:
Volume required = 0.0212 cu.m.
Cement = (0.0212/0.11111) x 40 = 7.63 Kg.Cement = (0.0212/0.11111) x 40 = 7.63 Kg.F.A. = (0.0212/0.11111) x 78.37 = 14.95 Kg.C.A. = (0.0212/0.11111) x 141.05 = 26.91 Kg.
Water = (0.0212/0.1111) x 13.32 = 2.54 Kg.
Thank You!!!