By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

In India 0.93 kg of CO₂ is emitted in the production of one kg of cement. In the financial year 2009-10 India produces 200 million tonnes of cement. In the production of this cement 186 million tonnes of CO₂ was emitted in the atmosphere during financial year of 2009-10.

The availability of water in India per person per year in 1950 was 5177 cu.m. In the year 2009 it is reduces to 1700 cu.m.

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 construction industry. This amount is worked out after adjusting the cost of water reducers. Less cement used means less cement required to be produce by the cement factories resulting 6975000 tonnes of CO₂ will be prevented to be emitted to the atmosphere. These are worked out with an average saving of 15% cement and 15% water.

CO₂ emission is word problem, but for India in addition to CO2 it has problems of Air, Water, Soil, Food and Noise pollutions. Less densily populated countries may cope with these problems but for India it is of the top concern. The population figures of 2009 is, India 350 person per sq.km, China 132 person per sq.km and USA only 34 person per sq.km. The figures of 2006 CO¬2 emissions are USA 658.60 tonnes per sq.km, China 611.76 tonnes per sq.km and India 459.35 tonnes per sq.km. Every one should contribute his or her efforts to save the environment from pollution. Those involve in the construction activities can contribute their share by proper design of concrete Mixes. This is best illustrated by the following examples.
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By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

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: 15-2002 specified that for concrete roads OPC should be used. This code also allowed PPC as per IS: 1489 may also be used. Accordingly OPC + fly ash may be used in concrete roads. 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.

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By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

There is no direct method for the determination of Fly Ash content in the PPC. However, based on the past test results of insoluble Residue in the PPC, Fly Ash content in the supplied PPC may be obtained.

REAGETS

1. Hydrochloric acid – Sp gt 1.16 (conforming to IS : 265-1976)
2. Dilute Hydrochloric acid with distilled water 1:99 (by volume)
3. 2N Sodium Carbonate Solution.

DETERMINATION OF INSOLUBLE RESIDUE
The sample of the PPC shall be moisture free and taken as per requirements of IS : 3535-1966. The representative sample of the cement selected as above shall be thoroughly mixed before using.

Take one gram of the above PPC sample add 25 ml of cold water and while the mixture is stirred vigorously add 5 ml of hydrochloric acid, if necessary, head the solution and grind the material with flattened end of a glass rod until it is evident that the decomposition of the cement is complete. Dilute the solution to 50 ml and digest for 15 minutes at a temperature just below boiling. Filter and wash the residue thoroughly with hot water. The filter paper with the residue shall be proceeded for further test.

Digest the filter paper containing the residue in 30 ml of hot water and 30 ml of 2N sodium carbonate solution maintaining constant volume, the solution being held at just below the boiling point for 10 minutes. Filter and wash with dilute hydrochloric acid (1:99) and finally with hot water till the residue is free from chloride. Ignite the residue in a tarred crucible at 900 to 10000C, cool in a desicator and weight

From the figure the insoluble residue obtained from the above test, Fly Ash content in the supplied PPC may be obtained. Read references to conduct experiments and find conclusions.

REFERENCES

1. IS : 3535 – 1966 – Method of sampling hydraulic cements, BIS, New Delhi.
2. IS : 265-1976 – Specification for hydrochloric acid (second revision BIS, New Delhi)
3. IS : 4032 – 1985 – Method of chemical analysis of hydraulic cement (First Revision) BIS, New Delhi.
4. IS : 1489 (Part-I) : 1991- (Reaffirmed 2005) (Third Revision) Portland Pozzolana Cement – Part-I Fly Ash based BIS, New Delhi.
5. Nagele, E (1981) – Application of the flotation method to analytical problems of concrete technology Diss, Universitat Karlsruhe, FRG.
6. Hilsdorf, H.K., Nagele, E (1980) a new method for cement content determination of fresh concrete, Cem. Concr. Res. 10, 23-34.

We are thankful to Sir Kaushal Kishore for sharing this important research paper here on the website.

By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

This method of test describes the procedures for determining concrete permeability to water by capillary absorption method for comparison between controlled specimens and the specimens containing admixtures having surface coatings. This method gives the waterproofing efficiency of admixtures and coating, thus also of the greatest interest for durability of concrete offers protection to reinforcement from corrosion.

For all test specimens materials, proportions, workability, mixing, compaction, casting, curing, temperature and testing method should be kept identical for conclusive comparison between controlled and admixture/coated specimens.

Casting of Specimens
10cm cubes of the following mix are to be cast by hand compaction filling the cubes in two layers each layer to be rammed 35 times by ramming rod 16mm dia 600mm in length one end bullet pointed. A set of 3 cubes shall be prepared with the recommended dosage of admixture. The other set of 3 cubes shall be made without any admixture (controlled cube). In case of surface coating is to be tested, then all the six cubes shall be made of the same mix.

Mix Proportions
OP Cement 43 grade = 200 Kg/m³
Sand Zone II = 850Kg/m³
20-5mm aggregate = 1115lg/m³
Water= To give slump of 40⁺_-5mm or compaction factor of about 0.90.

The above is a suggested mix of sand and aggregate having specific gravity of 2.6. Mixes may be designed as per local aggregates.
Cement:Aggregate ratio should be kept 1:9 to 1:10

Liquid admixtures usually reduce the water demand, but in very lean mixes there shall not be much reduction in mixing water.
The water of the liquid admixture should be accounted in the mixing water. A few trials of controlled concrete workability will be required for getting the exact quantity of mixing water for obtaining required workability. As far as possible this controlled concrete mixing water should not be exceeded with the admixture mix. The lean mix as recommended above will be desirable for this type of test.

Procedure of Testing
After 24 hours of casting, all the cubes shall be demoulded and cured in clean water in the same curing tank for 28 days. After 28 days of curing all the cubes shall be dried in a ventilated oven at the temperature of 100^oC to ⁺_-10^oC till constant weight. If surface coating is to be tested, then as per recommendations of the manufacturer three cubes to be surface coated at one face and upto the height of 5 cm on all the four faces. After coating and conditioning, these cubes along with the controlled cubes shall again be died in the oven at a temperature of 50^oC to ⁺_-2^oC till constant weight. Coated cubes faces should be kept upward while keeping them in oven, sot that coating should not be damaged. The coating after its application should withstand without any physical and chemical change a temperature of 50^oC, which is a temperature normally reached of concrete surfaces exposed to sun at most places of India during summer. A coating sensitive to this temperature should not be tested with this method.

All the six weighted cubes shall be placed in the same glazed or glass flat tray, so that the cubes are dipped up to a level of 1.2cm. The level of the water shall be maintained throughout the experiment by adding fresh water from time to time. Evaporation of water from exposed cubes surfaces and tray is prevented by covering the entire set up by polythene. Care should be taken that polythene should not disturb the set up. Determine the gain in weight of the cube at different intervals till the weight of cube become constant.

The permeability of each cube of a set shall be found by determining the coefficient of water absorption with the help of the formula:

A= M_w/t
Where A – Coefficient of water absorption.
M_w – Amount of water absorbed per unit area.
T – Time in second for absorption

From the test results the effectiveness of admixtures and coating may be compared with controlled specimens. This method is simple for testing waterproofing admixtures and coating without any special equipment.

This paper by Er. Kaushal Kishore was first published in NBM&CW magazine.

By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

PORTLAND CEMENT:
Joseph Aspdin, a mason at Leeds prepared a cement in 1824 by heating a mixture of finely-divided clay and hard limestone in a furnace until CO2 had been driven off; this temperature was much lower than that necessary for clinkering. The prototype of modern cement was made in 1845 by Isaac Johnson, who burnt a mixture of clay and chalk until clinkering, so that the reaction necessary for the formation of strongly cementitious compound took place. The name ‘Portland Cement’ was given due to the resemblance of the colour and quality of the hardened cement to Portland stone- a limestone quarried in Doset.

The process of manufacturing of cement consists essentially of grinding the raw materials ( calcareous materials such as limestone or chalk and argillaceous materials such as shale or clay), mixing them intimately in certain proportion and burning in a large rotary kiln at a temperature of upto about 14500C when the material sinters and partially fuses into balls known as clinker. The clinker is cooled and ground to a fine powder, with some gypsum added, and the resulting product is the commercial Portland Cement so widely used throughout the world.

MAKING CONCRETE:
Just mix cement, aggregates and water, cast this mix in a mould, open the mould next day. A uniform hard mass will be found, which is known as concrete, any body can make it. The simplecity in making concrete make this material to be look like very simple in its production, yet it as not so simple. Due to ignorance about concrete no other building materials ever mis-used as concrete in the construction. In India concrete is being used in the construction since the last 70 years. Yet 80% of the builders have no proper understanding of this materials. Go to any construction site (except big construction sites) you will find that sand and aggregates are being taken in iron tasla or cane baskets to charge the mixer without the consideration of site aggregates actual grindings, moisture content and bulking of sand. The water is poured in the mixer without any measured quantity. It could be well imagine what sort of concrete structure will be made with the concrete being produced in this crude method.

Most of the contractors, builders, masons etc. still follow 1:2:4 or 1:1.5:3 mixes they are not aware of Design Mixes and Concrete Admixtures. This paper described how Design Mixes can be converted into volume with 1 Bag Cement, 2 Boxes of sand and 4 Boxes of Aggregate. The site practical problem is the dispersion of water and liquid admixtures into the mixer. For this the site should fabricate a plastic circular graduated measuring container of 30 lit capacity with a tap fitted at its bottom. This container is to be fitted on top of the mixer. From this container water and liquid admixtures can conveniently poured direct into the mixer in a measured quantity.
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