Method Of Measurement Of Reinforced Concrete Works

Method Of Measurement of Reinforced Concrete Works:

1. The Quantities can be rounded off to the nearest two decimals.

2. Concrete in Structural members, such as columns, Beams and slabs shall each be measured separately.

3. No Deductions shall be made for the following

Opening up to 0.1 m2

Volume occupied by reinforcement.

Volume occupied by pipes, conduits, sheathing, etc not exceeding 100cm2 each in cross-section.

Moulds, drips moulding, chamfers, splays rounded or covered angles, beds, grooves and rebates up to 10 cm in girth.

4. Footings:

Volume of concrete = L x B x D for Rectangular and Square footing. For Trapezoidal Footing, Volume of Concrete is calculated in two parts. Bottom Rectangular portion is calculated separately and Trapezoidal volume is calculated separately.

Rectangular Volume = L x B x D

Trapezoidal Volume V= H/3 (A1 + A2 +  SQRT(A1 + A2) )

Where A1 and A2 is the area of top and bottom rectangles, H is depth of footing.

Total Volume = Rectangular Volume + Trapezoidal Volume

Where V= Volume; h= height;

5. Columns: Columns shall be measured from top of Column base to underside of first floor slab and subsequently from top of floor slab to underside of floor slab above. In case of Columns for flat slabs, flare of column shall be included with column for Measurement.

6. Beams: Beams shall be measured from face to face of columns and shall include haunches, if any, between columns and beams. The depth of beams shall be measured from bottom of slab to bottom of the beam except in case of inverted beam where it shall be measured from top of slab to top of beam.

7. Pedestals: Pedestals is measured from top of Footing to top/ Bottom of plinth beam depending on site conditions. If measured up to bottom of Plinth beam then Ground floor column can be measured from Bottom of plinth beam to underside of slab. The Height of Pedestal can be arrived from levels of footing and plinth beam. The Height shall be crosschecked with site also.

Concrete Mix Design As Per Indian Standard Code (IS)

Concrete Mix Design

Introduction

The process of selecting suitable ingredients of concrete and determining their relative amounts with the objective of producing a concrete of the required, strength, durability, and workability as economically as possible, is termed the concrete mix design. The proportioning of ingredient of concrete is governed by the required performance of concrete in 2 states, namely the plastic and the hardened states. If the plastic concrete is not workable, it cannot be properly placed and compacted. The property of workability, therefore, becomes of vital importance.

The compressive strength of hardened concrete which is generally considered to be an index of its other properties, depends upon many factors, e.g. quality and quantity of cement, water and aggregates; batching and mixing; placing, compaction and curing. The cost of concrete is made up of the cost of materials, plant and labour. The variations in the cost of materials arise from the fact that the cement is several times costly than the aggregate, thus the aim is to produce as lean a mix as possible. From technical point of view the rich mixes may lead to high shrinkage and cracking in the structural concrete, and to evolution of high heat of hydration in mass concrete which may cause cracking.

The actual cost of concrete is related to the cost of materials required for producing a minimum mean strength called characteristic strength that is specified by the designer of the structure. This depends on the quality control measures, but there is no doubt that the quality control adds to the cost of concrete. The extent of quality control is often an economic compromise, and depends on the size and type of job. The cost of labour depends on the workability of mix, e.g., a concrete mix of inadequate workability may result in a high cost of labour to obtain a degree of compaction with available equipment.

Requirements of concrete mix design

The requirements which form the basis of selection and proportioning of mix ingredients are :

a ) The minimum compressive strength required from structural consideration

b) The adequate workability necessary for full compaction with the compacting equipment available. 

c) Maximum water-cement ratio and/or maximum cement content to give adequate durability for the particular site conditions

d) Maximum cement content to avoid shrinkage cracking due to temperature cycle in mass concrete.

Types of Mixes

1. Nominal Mixes

In the past the specifications for concrete prescribed the proportions of cement, fine and coarse aggregates. These mixes of fixed cement-aggregate ratio which ensures adequate strength are termed nominal mixes. These offer simplicity and under normal circumstances, have a margin of strength above that specified. However, due to the variability of mix ingredients the nominal concrete for a given workability varies widely in strength.

2. Standard mixes

The nominal mixes of fixed cement-aggregate ratio (by volume) vary widely in strength and may result in under- or over-rich mixes. For this reason, the minimum compressive strength has been included in many specifications. These mixes are termed standard mixes.

IS 456-2000 has designated the concrete mixes into a number of grades as M10, M15, M20, M25, M30, M35 and M40. In this designation the letter M refers to the mix and the number to the specified 28 day cube strength of mix in N/mm2. The mixes of grades M10, M15, M20 and M25 correspond approximately to the mix proportions (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2) respectively.

3. Designed Mixes

In these mixes the performance of the concrete is specified by the designer but the mix proportions are determined by the producer of concrete, except that the minimum cement content can be laid down. This is most rational approach to the selection of mix proportions with specific materials in mind possessing more or less unique characteristics. The approach results in the production of concrete with the appropriate properties most economically. However, the designed mix does not serve as a guide since this does not guarantee the correct mix proportions for the prescribed performance.

For the concrete with undemanding performance nominal or standard mixes (prescribed in the codes by quantities of dry ingredients per cubic meter and by slump) may be used only for very small jobs, when the 28-day strength of concrete does not exceed 30 N/mm2. No control testing is necessary reliance being placed on the masses of the ingredients.

Factors affecting the choice of mix proportions

The various factors affecting the mix design are:

1. Compressive strength

It is one of the most important properties of concrete and influences many other describable properties of the hardened concrete. The mean compressive strength required at a specific age, usually 28 days, determines the nominal water-cement ratio of the mix. The other factor affecting the strength of concrete at a given age and cured at a prescribed temperature is the degree of compaction. According to Abraham’s law the strength of fully compacted concrete is inversely proportional to the water-cement ratio.

2. Workability

The degree of workability required depends on three factors. These are the size of the section to be concreted, the amount of reinforcement, and the method of compaction to be used. For the narrow and complicated section with numerous corners or inaccessible parts, the concrete must have a high workability so that full compaction can be achieved with a reasonable amount of effort. This also applies to the embedded steel sections. The desired workability depends on the compacting equipment available at the site.

3. Durability

The durability of concrete is its resistance to the aggressive environmental conditions. High strength concrete is generally more durable than low strength concrete. In the situations when the high strength is not necessary but the conditions of exposure are such that high durability is vital, the durability requirement will determine the water-cement ratio to be used.

4. Maximum nominal size of aggregate

In general, larger the maximum size of aggregate, smaller is the cement requirement for a particular water-cement ratio, because the workability of concrete increases with increase in maximum size of the aggregate. However, the compressive strength tends to increase with the decrease in size of aggregate.

IS 456:2000 and IS 1343:1980 recommend that the nominal size of the aggregate should be as large as possible.

5. Grading and type of aggregate

The grading of aggregate influences the mix proportions for a specified workability and water-cement ratio. Coarser the grading leaner will be mix which can be used. Very lean mix is not desirable since it does not contain enough finer material to make the concrete cohesive.

The type of aggregate influences strongly the aggregate-cement ratio for the desired workability and stipulated water cement ratio. An important feature of a satisfactory aggregate is the uniformity of the grading which can be achieved by mixing different size fractions.

6. Quality Control

The degree of control can be estimated statistically by the variations in test results. The variation in strength results from the variations in the properties of the mix ingredients and lack of control of accuracy in batching, mixing, placing, curing and testing. The lower the difference between the mean and minimum strengths of the mix lower will be the cement-content required. The factor controlling this difference is termed as quality control.

Mix Proportion designations

The common method of expressing the proportions of ingredients of a concrete mix is in the terms of parts or ratios of cement, fine and coarse aggregates. For e.g., a concrete mix of proportions 1:2:4 means that cement, fine and coarse aggregate are in the ratio 1:2:4 or the mix contains one part of cement, two parts of fine aggregate and four parts of coarse aggregate. The proportions are either by volume or by mass. The water-cement ratio is usually expressed in mass

Factors to be considered for mix design

• The grade designation giving the characteristic strength requirement of concrete.
• The type of cement influences the rate of development of compressive strength of concrete.
• Maximum nominal size of aggregates to be used in concrete may be as large as possible within the limits prescribed by IS 456:2000.
• The cement content is to be limited from shrinkage, cracking and creep.
• The workability of concrete for satisfactory placing and compaction is related to the size and shape of section, quantity and spacing of reinforcement and technique used for transportation, placing and compaction.

Procedure

1. Determine the mean target strength ft from the specified characteristic compressive strength at 28-day fck and the level of quality control.

ft = fck + 1.65 S

where S is the standard deviation obtained from the Table of approximate contents given after the design mix.

2. Obtain the water cement ratio for the desired mean target using the emperical relationship between compressive strength and water cement ratio so chosen is checked against the limiting water cement ratio. The water cement ratio so chosen is checked against the limiting water cement ratio for the requirements of durability given in table and adopts the lower of the two values.

3. Estimate the amount of entrapped air for maximum nominal size of the aggregate from the table.

4. Select the water content, for the required workability and maximum size of aggregates (for aggregates in saturated surface dry condition) from table.

5. Determine the percentage of fine aggregate in total aggregate by absolute volume from table for the concrete using crushed coarse aggregate.

6. Adjust the values of water content and percentage of sand as provided in the table for any difference in workability, water cement ratio, grading of fine aggregate and for rounded aggregate the values are given in table.

7. Calculate the cement content form the water-cement ratio and the final water content as arrived after adjustment. Check the cement against the minimum cement content from the requirements of the durability, and greater of the two values is adopted.

8. From the quantities of water and cement per unit volume of concrete and the percentage of sand already determined in steps 6 and 7 above, calculate the content of coarse and fine aggregates per unit volume of concrete from the following relations:

where V = absolute volume of concrete

= gross volume (1m3) minus the volume of entrapped air

Sc = specific gravity of cement

W = Mass of water per cubic metre of concrete, kg

C = mass of cement per cubic metre of concrete, kg

p = ratio of fine aggregate to total aggregate by absolute volume

fa, Ca = total masses of fine and coarse aggregates, per cubic metre of concrete, respectively, kg, and

Sfa, Sca = specific gravities of saturated surface dry fine and coarse aggregates, respectively

9. Determine the concrete mix proportions for the first trial mix.

10. Prepare the concrete using the calculated proportions and cast three cubes of 150 mm size and test them wet after 28-days moist curing and check for the strength.

11. Prepare trial mixes with suitable adjustments till the final mix proportions are arrived at.

What is the difference between concrete mix design and concrete proportion

Proportioning Concrete

Part of your design for the project is to develop mix ratios

that lead to high compression stresses at failure.

The two criteria for a successful mix ratio are:

(1) high compressive stress

(2) adequate workability

Calculate Quantities Of Materials Required For One Cubic Meter Of Concrete

How To Calculate Quantities Of Materials Required For One (per) Cubic Meter (Metre) Of Concrete

Quantity of materials such as cement, sand, coarse aggregates and water required per cubic meter of concrete  and mortar varies with the mix design of the concrete and mortar respectively. Following table gives the estimated quantity of materials (Cement, Fine Aggregate, Sand, Coarse Aggregate) required per cubic meter of mortar and concrete for various nominal mixes.

GRADE	NOMINAL MIX			WATER CEMENT RATIO	WATER PER 50KG BAG OF CEMENT	CEMENT		SAND (CUM)	CRUSHED STONES (CUM)
	CEMENT	FINE AGGREGATE	COARSE AGGREGATE			BY WEIGHT (KG)	BY NUMBER OF BAGS
	1	1	-	0.25	12.5	1015	20.3	0.71	-
	1	1.5		0.28	14	815	16.3	0.855	-
	1	2	-	0.3	15	687	13.74	0.963	-
	1	2.5	-	0.35	17.5	585	11.7	1.023
	1	3	-	0.4	20	505	10.1	1.06	-
	1	4	-	0.53	26.5	395	7.9	1.106	-
	1	6	-	0.7	35	285	5.7	1.197	-
	1	8	-	0.9	45	220	4.4	1.232	-
M25	1	1	2	0.3	15	560	11.2	0.392	0.784
	1	2	2	0.42	21	430	8.6	0.602	0.602
M20	1	1.5	3	0.42	21	395	7.9	0.414	0.828
	1	1.66	3.33	0.48	24	363	7.26	0.419	0.838
	1	2	3	0.5	25	385	7.7	0.539	0.808
	1	2	3.5	0.53	26.5	330	6.6	0.462	0.808
M15	1	2	4	0.55	27.5	310	6.2	0.434	0.868
	1	2.5	3.5	0.57	28.5	305	6.1	0.534	0.748
	1	2.5	4	0.6	30	285	5.7	0.499	0.798
	1	3	4	0.65	32.5	265	5.3	0.556	0.742
	1	2.5	5	0.65	32.5	255	5.1	0.446	0.892
	1	3	5	0.69	34.5	240	4.8	0.504	0.84
M10	1	3	6	0.75	37.5	215	4.3	0.452	0.904
M7.5	1	4	8	0.95	47.5	165	3.3	0.462	0.924

M5 - 1:5:10
M7.5 - 1:4:8
M10 - 1:3:6
M15 - 1:2:4
M20 - 1:1.5:3
M25 - 1:1:2

M30, M35, M40 - Design Mix Followed

Notes:

• F.A.= Fine Aggregates, C.A.= Coarse Aggregates
• The table is based on assumption that the voids in sand and crushed stone are 40 and 45 percent respectively.
• Air content of 1 percent has been assumed.
• For gravel aggregates decrease cement by 5 percent, increase sand by 2 percent and coarse aggregate in proportion to fine aggregate in mix.
• No allowance has been made in the table for bulking of sand and wastage.

Things To Remember When Doing Concrete Mix Design

Good quality concrete starts with the quality of materials, cost effective designs is actually a by-product of selecting the best quality material and good construction practices. Following are 10 Things to remember during Concrete Mix Design and Concrete Trials.

1. ACI and other standards only serves as a guide, initial designs must be confirmed by laboratory trial and plant trial, adjustments on the design shall be done during trial mixes. Initial design “on paper” is never the final design.

2. Always carry out trial mixes using the materials for actual use.

3. Carry out 2 or 3 design variations for every design target.

4. Consider always the factor of safety, (1.125, 1.2, 1.25, 1.3 X target strength)

5. Before proceeding to plant trials, always confirm the source of materials to be the same as the one used in the laboratory trials.

6. Check calibration of batching plant.

7. Carry out full tests of fresh concrete at the batching plant, specially the air content and yield which is very important in commercial batching plants.

8. Correct quality control procedures at the plant will prevent future concrete problems.

9. Follow admixture recommendations from your supplier

10. Check and verify strength development, most critical stage is the 3 and 7 days strength.

Important note:

Technical knowledge is an advantage for batching plant staff, even if you have good concrete design but uncommon or wrong procedures are practiced it will eventually result to failures.

What Is The Principle Of Asphalt Mix Design?

The main objective of asphalt mix design is to achieve a mix with economical blending of aggregates with asphalt to achieve the following :

(i) workability to facilitate easy placement of bituminous materials without experiencing segregation;

(ii) sufficient stability so that under traffic loads the pavement will not undergo distortion and displacement;

(iii) durability by having sufficient asphalt;

(iv) sufficient air voids

In asphalt mix design, high durability is usually obtained at the expense of low stability. Hence, a balance has to be stricken between the durability and stability requirements.

What Is Marshall Mix Design For Bituminous Materials?

The Marshall Mix Design method was originally developed by Bruce Marshall of the Mississippi Highway Department in 1939. The main idea of the Marshall Mix Design method involves the selection of the asphalt binder content with a suitable density which satisfies minimum stability and range of flow values.

The Marshall Mix Design method consists mainly of the following steps:

(i) Determination of physical properties, size and gradation of aggregates.

(ii) Selection of types of asphalt binder.

(iii) Prepare initial samples, each with different asphalt binder content.

For example, three samples are made each at 4.5, 5.0, 5.5, 6.0 and 6.5 percent asphalt by dry weight for a total of 15 samples. There should be at least two samples above and two below the estimated optimum asphalt content.

(iv) Plot the following graphs:

(a) Asphalt binder content vs. density

(b) Asphalt binder content vs. Marshall stability

(c) Asphalt binder content vs. flow

(d) Asphalt binder content vs. air voids

(e) Asphalt binder content vs. voids in mineral aggregates

(f) Asphalt binder content vs voids filled with asphalt

(v) Determine the asphalt binder content which corresponds to the air void content of 4 percent

(vi) Determine properties at this optimum asphalt binder content by reference with the graphs. Compare each of these values against design requirements and if all comply with design requirements, then the selected optimum asphalt binder content is acceptable. Otherwise, the mixture should be redesigned.

Understanding Nominal Mix And Design Mix - Concrete Mix Design

Cement concrete in India on large scale is being used since the last about 70 years. In the early days the following nominal ratio by volume for concrete were specified.

Cement	:	Sand	:	Aggregate
1	:	2	:	4	Correspond to M-15 Grade
1	:	1.5	:	3	Correspond to M-20 Grade
1	:	1	:	2	Correspond to M-25 Grade

IS : 456-2000 has recommended that minimum grade of concrete shall be not less than M-20 in reinforced concrete work. Design mix concrete is preferred to nominal mix. If design mix concrete cannot be used for any reason on the work for grades of M-20 or lower, nominal mixes may be used with the permission of engineer-in-charge, which however is likely to involve a higher cement content.

Accordingly all concrete of above M-20 Grade for RCC work must be of design mixes. The code allows nominal mix for RCC work of M-20 Grade, but what shall be the nominal mix, the reader will find from the following table that it is better to adopt design mix, rather than to go for M20 nominal mix which is too cumbersome to determine a fixed nominal mix value.

Nominal mixes as per IS : 456-2000 if fine aggregate is of Zone II as per IS : 383-1970.

Grade of Concrete	As per IS:383-1970 Maximum size of graded coarse aggregate	Mix Ratio by Weight			Max W/C Ratio	Max cement: Aggregate ratio by mass
		Cement	Fine Aggregate	Coarse Aggregate
M-20	10	1 : 1.8 : 2.7			0.6	1.5
M-20	20	1 : 1.5 : 3.0			0.6	1.5
M-20	40	1 : 1.3 : 3.2			0.6	1.5

Proportions by weight can be converted to proportions by volume, by dividing with the bulk density of the materials available for use at site. The bulk density of cement may be taken 1.44 kg/lit.

The above nominal mixes are worked out for Zone II fine aggregate. As per IS: 383-1970 there are three more zone of sands. Therefore, the total nominal mixes shall be 12 for 10, 20 & 40 mm maximum size of coarse aggregate.

Thus, it could be seen that nominal mixes cannot have a fix conventional proportions such as 1:2:4 or 1:1.5:3, but may vary according to maximum size of coarse aggregate and grading of fine aggregate. Hence nominal mixes are also needed to be designed according to the sizes of aggregates available at site. However, the ultimate aim must be to get the specified properties of concrete.

As per IS: 456-2000, volume batching may be allowed only where weight batching is not practical and provided accurate bulk densities of materials to be actually used in concrete have earlier been established. Allowance for bulking shall be made in accordance with IS: 2386(Part 3). The mass volume relationship should be checked as frequently as necessary.

The exposures of Indian Construction sites at most places are Moderate for which IS: 456-2000 specified that minimum grade of concrete for reinforced concrete should be M25. Accordingly for durability consideration the structural concrete must not be below M-25 grade. The high strength benefits obtained should be taken into account in the design consideration of the concrete structure.

If for practical purpose, we go deeper than we will find that for all reinforced concrete structures we must have concrete from design mixes.

In the IS: 456-2000 there is nothing mentioned of 1:1:2 ration for M-25 grade of concrete. Concrete of above M-20 must be design mixes. If one takes 1:1:2 ratio then the cement content comes to 528 kg/m3. Where as IS: 456-2000 on page 19 clause 8.2.4.2 mentioned that OPC in excess of 450 kg/m3 should not be used.

The concrete surfaces of the structure exposed to severe rain, alternate wetting and drying such as RCC OH water tank comes to severe exposure environment for which the minimum grade of concrete shall be M-30, minimum cement content 320 kg/m3 and maximum free W/C ration 0.45. The following table will show the compression of nominal and design mixes for RCC work.

Materials : OPC 43-grade, River sand of Zone II and 20 mm graded crushed stone aggregate. Specific gravity of sand and aggregate 2.65. Workability of design mixes 50±10mm slump.

Grade of Concrete	Mix. Free W/C ratio	Min. Cement content kg/m3	Nominal mixes by weight C:S:A	Design mixes by weight C:S:A	Saving in cement
M-20	0.55	300	01:05.5	1:2.22:3.48                Cement= 327kg/m3	65 kg/m3
			Cement= 392kg/m3
M-25	0.5	300	1:01:02	1:1.93:3.17	168 kg/m3
			Cement= 528kg/m3	Cement= 360kg/m3
M-30	0.45	320	—	1:1.67:2.84	—
				Cement= 400kg/m3

Note: For high strength concrete plasticizer/superplasticizer should be used which will reduce water and with the same W/C ratio reduction in cement content.

From the above table it can be calculated in nominal mixes of M-20 and M-25 how much extra cement is used in the construction, its total cost and how much CO2 is emitted in the production of this extra cement.

When a mix is referred for designing, it is design for target strength. For example M-30 (by Vol. ratio) is design for:

30 + 1.65 x 6 = 39.9 N/mm2 at 28 days age

The above is design target strength of the consultant Laboratory. When this mix is used at construction site, its concrete shall have strength as per table 11 of IS : 456-2000.

30 + 4 = 34 N/mm2 at 28 days age

For starting the work a construction site cannot weight for 28 days. Therefore according to various literatures, if at 7 days its strength is about 65% (22 N/mm2 ) the work may be started. However in all the cases 28 days cube compressive strength shall alone be the criterion for acceptance and rejection of the concrete.

Concrete Mix Design For Concrete Roads As Per IRC: 15-2011

ABSTRACT:

The stresses induced in concrete pavements are mainly flexural. Therefore flexural strength is more often specified than compressive strength in the design of concrete mixes for pavement construction. A simple method of concrete mix design based on flexural strength for normal weight concrete mixes is described in the paper.

INTRODUCTION:

Usual criterion for the strength of concrete in the building industry is the compressive strength, which is considered as a measure of quality concrete. However, in pavement constructions, such as highway and airport runway, the flexural strength of concrete is considered more important, as the stresses induced in concrete pavements are mainly flexural. Therefore, flexural strength is more often specified than compressive strength in the design of concrete mixes for pavement construction. It is not perfectly reliable to predict flexural strength from compressive strength. Further, various codes of the world specified that the paving concrete mixes should preferably be designed in the laboratory and controlled in the field on the basis of its flexural strength. Therefore, there is a need to design concrete mixes based on flexural strength.

The type of aggregate can have a predominant effect, crushed rock aggregate resulting in concrete with higher flexural strength than uncrushed (gravel) aggregates for comparable mixes, assuming that sound materials are used. The strength of cement influences the compressive and flexural strength of concrete i.e. with the same water-cement ratio, higher strength cement will produce concrete of higher compressive and flexural strength.

MIX DESIGN DETAILS

IRC: 15-2011 specified that for concrete roads OPC should be used. This code also allowed PPC as per IS: 1489 (Part-1) with flyash content not more than 20 percent by weight of PPC. Accordingly OPC + fly ash may be used in concrete roads. Flyash shall be not more than 20 percent by weight of cementitious material. However, IS: 456-2000 specified that fly ash conforming to grade-1 of IS” 3812 may be used as part replacement of OPC provided uniform blended with cement is essential. The construction sites where batching plants are used this may be practicable. In ordinary sites where mixer or hand mixing are done uniform blending of fly ash with cement is not practicable. At such construction sites, PPC may be used. PPC should be used with caution where rapid construction methods like slip form is being used. Joints cutting also need early strength.

1	Characteristic Flexural Strength at 28 days	:	4.5 N/mm2
2	Cement	:	Three mixes are to be designed
			MIX-A
			With PPC (Flyash 18 percent based) conforming to IS:1489-part-I-1991.  7 days strength 37.5 N/mm2. Specific Gravity : 3.00
			MIX-B
			With OPC-43- Grade conforming to IS: 8112-1989.  7 days strength 40.5 n/mm2. Specific Gravity : 3.15
			MIX-C
			With OPC of Mix-B and Fly ash conforming to IS:3812 (Part-I)-2003 Specific Gravity : 2.20
			Note: Requirements of all the three mixes are the same. Fine Aggregate, Coarse Aggregate and Retarder Super plasticizer are the same for all the three mixes.
3	Fly ash replacement	:	20% Fly ash is required to be replaced with the total cementitious materials.
4	Maximum nominal size of aggregates	:	31.5 mm Crushed aggregate
5	Fine aggregate and coarse aggregate grading	:	Given in Table 1
6	Minimum cement content for 4.5 N/mm2 characteristic flexural strength:	:	(a)  OPC shall not be less than 360 kg/m3.
			(b)  PPC shall not be less than 425 kg/m3. Fly ash in it 20% maximum by weight of total cementitious materials
			(c)   OPC + Fly ash mix OPC shall not be less than 340 kg/m3. Fly ash 20% maximum by weight of cementations material
7	Maximum free W/C Ratio	:	(a)  For OPC 0.45
			(b)  For PPC 0.50
8	Workability	:	40 mm slump at pour the concrete will be transported from central batching plant through transit mixer, at a distance of 15 Km during June, July months. The average temperature last year during these months was 300C.
9	Exposure condition	:	Moderate
10	Method of placing	:	Fully mechanised construction
11	Degree of supervision	:	Good
12	Maximum of cement content	:	(a) OPC 425 kg/m3
			(b) PPC 425 kg/m3
13	Chemical admixture	:	Retarder Super plasticizer conforming to IS:9103-1999. With the given requirements and materials, the manufacturer of Retarder Super plasticizer recommends dosages of 1% bw of OPC, which will reduce 15% of water without loss of workability. For fly ash included cement dosages will be required to be adjusted by experience/ trials.2% maximum by weight of cementitious material
14	Values of Z x  (for National Highway)	:	1.96 x 0.40

TEST DATA FOR MATERIALS AND OTHER DETAILS

1. The grading of fine aggregate, 1 & 2 aggregates are as given in Table. 1.

2. Properties of aggregates

Tests	Fine aggregate	Aggregate 1	Aggregate 2
Specific Gravity	2.65	2.65	2.65
Water Absorption %	0.8	0.5	0.5

3. Target average flexural strength for all A, B and C mixes

S = S+ Zq

=4.5 + 1.96 x 0.40

= 5.3 N/mm2 at 28 days age

4. For Mix A, B and C free W/C ratio with crushed aggregate and required average flexural target strength of 5.3 N/mm2 at 28 days from Fig. 1 Curve D found to be 0.42. This is lower than specified maximum W/C ratio value of 0.45 for OPC and 0.50 for PPC.

Note:

In absence of cement strength, but cement conforming to IS Codes, assume from Fig. 1

Curve C and D for OPC 43 Grade

Take curves C and D for PPC, as PPC is being manufactured in minimum of 43 Grade of strength.

5. Other data’s: The Mixes are to be designed on the basis of saturated and surface dry aggregates. At the time of concreting, moisture content of site aggregates are to be determine. If it carries surface moisture this is to be deducted from the mixing water and if it is dry add in mixing water the quantity of water required for absorption. The weight of aggregates are also adjusted accordingly.

DESIGN OF MIX-A WITH PPC

a) Free W/C ratio for the target flexural strength of 5.3 N/mm2 as worked out is 0.42 for first trial.

b) Free water for 40 mm slump from Table 2 for 31.5 mm maximum size of aggregate.

2/3×170 + 1/3×200= 180 kg/m3

From trials it is found that Retarder Super plasticizer at a dosages of 1.3% bw of PPC may reduce 15% water without loss of workability

Then water = 180 – (180 x 0.15) = 153 kg/m3

c) PPC = 153/0.42 = 364 kg/m3 (Required minimum PPC is 425 kg/m3)

d) Formula for calculation of fresh concrete weight in kg/m3

Um = 10 x Ga (100 – A) + Cm(1 – Ga/Gc) – Wm (Ga – 1)

Where,

Um=Weight of fresh concrete kg/m3

Ga=Weighted average specific gravity of combined fine and coarse aggregate bulk, SSD

Gc=Specific gravity of cement. Determine actual value, in absence assume 3.15 for OPC and 3.00 for PPC (Fly ash based)

A=Air content, percent. Assume for trial entrapped air 1.5%

For 31.5 mm maximum size of aggregate

There is always entrapped air in concrete. Therefore ignoring entrapped air value as NIL will lead the calculation of higher value of density. Take exact value of air as obtained in the test

Wm=Mixing water required in kg/m3

Cm=Cement required, kg/m3

Note:- The exact density may be obtained by filling and fully compacting constant volume suitable metal container from the trial batches of calculated design mixes. The mix be altered with the actual obtained density of the mix.

Um =10 x Ga (100 – A) + Cm (1 – Ga/Gc) – Wm (Ga – 1)

=10 x 2.65 (100 – 1.5) + 425(1- 2.65/3.00) – 153 (2.65 -1)

=2409 kg/m3

e) Aggregates = 2409 – 425 – 153 = 1831 kg/m3

f) Fine aggregate = 1831 x 0.45 = 824 kg/m3

Aggregate 1 = 1831 x 0.29 = 531 kg/m3

Aggregate 2 = 1831 x 0.26 = 476 kg/m3

g) Thus for 4.5 N/mm2 flexural strength quantity of materials per cu.m. of concrete on the basis of saturated and surface dry aggregates:

Water = 153 kg/m3

PPC = 425 kg/m3

Fine Aggregate (sand) = 824 kg/m3

Aggregate (1) = 531 kg/m3

Aggregate (2) = 476 kg/m3

Retarder Super Plasticizer 1.3% bw of PPC = 5.525 kg/m3

MIX- B WITH OPC

a) Water = 180 – (180 x 0.15) = 153 kg/m3

b) OPC = 153/0.42 = 364 kg/m3

c) Density: 10 x 2.65 (100 – 1.5) + 364 (1 – 2.65/3.15) – 153 (2.65 – 1)= 2416 kg/m3

d) Total Aggregates = 2416 – 364 – 153 = 1899 kg/m3

Aggregate 1 = 1899 x 0.29 = 551 kg/m3

Aggregate 2 = 1899 x 0.26 = 494 kg/m3

Fine Aggregate = 1899 x 0.45 = 854 kg/m3

e) Thus for 4.5 N/mm2 flexural strength quantity of materials per cu.m of concrete on the basis of SSD aggregates are given below:

Water = 153 kg/m3

OPC = 364 kg/m3

Fine Aggregate (sand) = 854 kg/m3

Aggregate (1) = 551 kg/m3

Aggregate (2) = 494 kg/m3

Retarder Super Plasticizer 1% bw OPC = 3.640 kg/m3

MIX-C WITH OPC + FLY ASH

With a total cementitious material of 430 kg/m3,

OPC = 430 x 0.80 = 344 kg/m3

Fly ash = 430 x 0.20 = 86 kg/m3

Mix on the basis of SSD Aggregates,

(1) Water as worked out earlier = 153 kg/m3

(2) OPC = 344 kg/m3

(3) Fly ash = 86 kg/m3

Density = 10 x 2.65 (100 – 1.5) + 430 (1 – 2.65/3.00) – 153 (2.65 – 1) = 2410 kg/m3

Total Aggregates = 2410 – 153 – 344 – 86 = 1827 kg/m3

(4) Fine aggregate 0.45 x 1827 = 822 kg/m3

(5) Aggregate (1) 0.29 x 1827 = 530 kg/m3

(6) Aggregate (2) 0.26 x 1827 = 475 kg/m3

(7) Retarder super plasticizer 1.5% bw of cementitious material = 6.450 kg/m3

Note:

(1) Cementitious material worked out as per IRC : 15-2011, which specified: In case fly ash (as per IS: 3912 Part 1) is blended at site, the quantity of fly ash shall be restricted to 20 percent by weight of cementitious material and the quantity of OPC in such a blend shall not be less than 340 kg/m3 .

(2) After the first trial mix, its actual density is to be determined, as specified elase where in this paper. The mix proportions shall then be worked out accordingly including the water content, the dosages of Retarder SP for required workability keeping the free w/c ratio with in the permissible limits and adjusting it according to the required flexural strength.

(3) The mix proportions given in this paper are for first trial and to be adjusted as per actual site materials, conditions and requirements.

For 4.5 N/mm2 flexural strength quantity of material per cu.m of concrete on the basis of saturated and surface dry aggregates of Mix ‘A’, ‘B’ and ‘c’ are given below:

Materials	MIX. ‘A’ with PPC	Mix. ‘B’ with OPC	Mix. ‘C’ with OPC+Flyash
Water kg/m3	153	153	153
PPC kg/m3	425	–	–
OPC kg/m3	–	364	344
Flyash kg/m3	–	–	86
Fine Agg. kg/m3	824	854	822
Agg. (1) kg/m3	531	551	530
Agg. (2) kg/m3	476	494	475
Retarder Super- plasticizer kg/m3	5.525	3.64	6.45
W/ Cementitious ratio	0.36	0.42	0.356

Note:-

1. For exact W/C ratio the water in admixture should also be taken into account.

2. PPC reduces 5% water demand. If this is found by trial then take reduce water for calculation.

3. If the trial mixes does not gives the required properties of the mix, it is then required to be altered accordingly. However, when the experiences grows with the particular set of materials and site conditions very few trials will be required, and a expert of such site very rarely will be required a 2nd trial.

CONCLUSION

1. For 4.5 N/mm2 flexural strength concrete having same material and requirement, but without water reducer, the OPC required will be 180/0.42 = 429 kg/m3

2. With the use of superplasticizer the saving in OPC is 65 kg/m3 and water 27 lit/m3.

3. In the financial year 2009-2010 India has produces 200 million tonnes of cement. In India one kg of cement produce emitted 0.93 kg of CO2. Thus the production of 200 million tonnes of cement had emitted 200 x 0.93 = 186 million tonnes of CO2 to the atmosphere.

4. If 50 million tonnes cement in making concrete uses Water Reducers 7500000 tonnes of cement can be saved. 3750000 KL of potable water will be saved and the saving of Rs. 3300 crores per year to the construction Industry. 6975000 tonnes of CO2 will be prevented to be emitted to the atmosphere. The benefits in the uses of water reducers not limited to this. When water reduces shrinkage and porosity of concrete are reduces which provides the durability to concrete structures.

5. India is facing serious air, water, soil, food and noise pollution problems. Every efforts therefore are necessary to prevent pollution on top priority basis.

6. As the stress induced in concrete pavements are mainly flexural, it is desirable that their design is based on the flexural strength of concrete. The quality of concrete is normally assessed by measuring its compressive strength. For pavings, however, it is the flexural strength rather than the compression strength of concrete which determine the degree of cracking and thus the performance of road, and it is imperative to control the quality on the basis of flexural strength.

7. As per IRC: 15-2011, in case of small size projects, where facilities for testing beams with three print loading are not available, in such cases, the mix design may be carried out by using compressive strength values and there after flexural strength will be determined as per correlation between flexural strength with compressive strength given the following equation.

Where fcr is the flexural strength in MPa or N/mm2 and fck is the characteristic compressive strength in MPa or N/mm2 as per IS: 456-2000.

REFERENCES

1	IS : 383-1970 Specifications for coarse and fine aggregates from natural sources for concrete (second revision) BIS, New Delhi
2	IS: 456-2000 Code of practice for plain and reinforced concrete (fourth revision), BIS, New Delhi
3	IS: 9103-1999 Specification for admixtures for concrete (first revision) BIS, New Delhi
4	IS: 8112-1989 Specifications for 43 Grade ordinary portland cement (first revision) BIS, New Delhi
5	IS: 2386 (Part-III) 1963 method of test for aggregate for concrete. Specific gravity, density, voids, absorption and bulking, BIS, New Delhi
6	IS: 3812 (Part-I) 2003 Specification for pulverized fuel ash: Part-I for use as pozzolana in cement, cement mortar and concrete (second revision) BIS, New Delhi
7	IS: 1489-Part-I 1991 Specifications for portland pozzolana cement (Part-I) Flyash based. (Third revision), BIS, New Delhi
8	IRC: 15-2011 – Standard specifications and code of practice for construction of concrete road (Fourth revision)
9	Kishore Kaushal, “Concrete Mix Design Based on Flexural strength for Air-Entrained Concrete”, Proceeding of 13th Conference on our World in Concrete and Structures, 25-26, August, 1988, Singapore.
10	Kishore Kaushal, “Method of Concrete Mix Design Based on Flexural Strength”, Proceeding of the International Conference on Road and Road Transport Problems ICORT, 12-15 December, 1988, New Delhi, pp. 296-305.
11	Kishore Kaushal, “Mix Design Based on Flexural Strength of Air-Entrained Concrete”. The Indian Concrete Journal, February, 1989, pp. 93-97.
12	Kishore Kaushal, “Concrete Mix Design Containing Chemical Admixtures”, Journal of the National Building Organization, April, 1990, pp. 1-12.
13	Kishore Kaushal, “Concrete Mix Design for Road Bridges”, INDIAN HIGHWAYS, Vol. 19, No. 11, November, 1991, pp. 31-37
14	Kishore Kaushal, “ Mix Design for Pumped Concrete”, Journal of Central Board of Irrigation and Power, Vol. 49, No.2, April, 1992, pp. 81-92
15	Kishore Kaushal, “Concrete Mix Design with Fly Ash”, Indian Construction, January, 1995, pp. 16-17
16	Kishore Kaushal, “High-Strength Concrete”, Bulletin of Indian Concrete Institute No. 51, April-June, 1995, pp. 29-31
17	Kishore Kaushal, “Concrete Mix Design Simplified”, Indian Concrete Institute Bulletin No. 56, July-September, 1996, pp.25-30.
18	Kishore Kaushal, “Concrete Mix Design with Fly Ash & Superplasticizer”, ICI Bulletin No. 59, April-June 1997, pp. 29-30
19	Kishore Kaushal. “Mix Design for Pumped Concrete”, CE & CR October, 2006, pp. 44-50.

Table. 1: Grading of Aggregates

IS Sieve Designation	Percentage of passing by mass
	Fine aggregate from river	Crushed aggregate		Combined grading of mix	IRC: 15-2011 recommended grading of combined aggregates for pavement quality concrete (PQC)
	45%	-1	-2
		29%	26%
31.50 mm	100	100	100	100	100
26.50 mm	100	100	98	99	85 – 95
19.0 mm	100	100	25	81	68 – 88
9.50 mm	100	46	0	58	45 – 65
4.75 mm	94	5		44	30 – 55
600 micron	42	0		19	8 – 30
150 micron	10			5	5 – 15
75 micron	2			1	0 – 5

Table. 2: Approximate free-water content (kg/m3) required to give various levels of workability for non-air-entrained (with normal entrapped air) concrete.

Maximum size of aggregate (mm)	Type of aggregate	Slump (mm)	25 + 10	40 + 1031.5
	Uncrushed		160	170
	Crushed		190	200

Note:- When coarse and fine aggregate of different types are used, the free water content is estimated by the expression.

2/3Wf+1/3Wc

Where,

Wfsub>= Free water content appropriate to type of fine Aggregate

And Wc= Free water content appropriate to type of coarse aggregate.

Concrete Mix Design For Concrete Roads