Cement,  Concrete  and    Construction

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Question 001: 

How many mini cement plants are there in north India ?

- S K Sharma 

Answer:  

The up-to-date details of mini cement plants in India are available on the website of the Central Pollution Control Board.
Visit: www.cpcb.nic.in/NewItem/mini_cement_plant.html

 Question 003

Sustainable concrete technology calls for maximum

utilisation of fly ash in concrete. Yet IRC standard does 

not allow partial replacement of OPC with fly ash in 

bridge construction. Any justification?

Santibrata Datta, HCC 

Answer: 

Yes! The greater use of industrial and agricultural wastes in cement and concrete shall help sustainable development of both cement construction industry. The fly ash is today widely used in the structural concrete. The studies on engineering properties of concrete with fly ash, reported worlwide, point to the following facts:
(a) The compressive and flexural strength of fly ash concrete are slightly lower at th early ages but exceed at the later ages, than those of concrete without fly ash.
(b)  The addition of fly ash has practically no effect on the elastic properties of concrete
(c) The fly ash cocnrete is shown to produce consistently lower creep strain
(d) It has been generally reported that the use of fly ash in normal proportions does not significantly influence the drying shrinkage of concrete

The effect of fly ash addition on the durability of concrete, namely the resistance to corrosion, sulphate attack, alkali-silica reaction and carbonation are already well appreciated

The fly ash has been widely used in the bridge construction world over. The detailed information is available on the website of National Concrete Bridge Council, USA: www.nationalconcretebridge.org/cbc/

The issue should be brought to the notice of IRC with help of case studies, under Indian conditions

  Question: 004

Name: ashwin

Company: student

Email: architect_ashwin@yahoo.co.in

Question/comment: May I know what is is the option 

when sand is not available to the humans in near

future ?

Answer:

Natural sand is not easily available in many places even today, especially in urban centres like Mumbai. When it is not available as aggregate, you have the following alternatives:

(a) Use crushed sand, produced by crushing rock

(b) Use fly ash as fine aggregate, including that available from lagoons. Please note that, fly ash should be free from excessive unburned carbon, activated carbon, organic matter, ammonia and mercury, before it is used in cement and concrete. It should conform to the relevant National Standard.

 Question: 008

Name: R. Hariharan
Company: student
Email: hariharan49@gmail.com
Phone: 9840293271
Question/comment: Please explain what is bacterial concrete and how effective it is as self healing concrete

Answer:

The bacterial concrete makes use of calcite precipitation by bacteria. The phenomenon is called microbiologically induced calcite precipitation (MICP). It is a self-healing concrete.

Read more information on Bacterial Concrete

 Question: 009

Name: sachin mali

Company: govt. college of engineering, karad

Email: sachinmmali@gmail.com

Question/comment: what are the properties of crushed sand /manufactured sand which is used in concrete in Pune -Mumbai express highway? Is it possible to replace the natural sand with crushed sand or manufactured sand?

Answer:

Crushed sand or manufactured sand is as good as the natural sand. However if the mix design is based on natural sand, you will have to do it again for the crushed sand.

Name: anoop
Company: college
Email: young_blood27@sify.com

Question:

1) what is the scope of civil engineering?
2) what is role of fine aggregates in concrete technology?
3) Do different structures need different varieties of sand?

Answer:

 1) Scope of civil engineering: It is an ever-green branch of engineering and has tremendous scope for growth in the future.

 2 & 3) Role of Aggregates: Aggregates impart strength to concrete. The aggregates are graded  to make concrete impermeable. A properly designed mixture of cement, graded aggregates (coarse and fine) and water makes concrete workable when fresh and strong, impermeable and durable when fully set. To make strong concrete, the strength of aggregates as well as the bond (cement paste) between the aggregates should be strong. The naturally available mineral aggregates are strong enough to make normal strength concrete. The test of the strength of aggregates is required to produce high strength and ultra high strength concrete.

Name: Anand Srivastava

Company: MES

Email: anand439076@yahoo.co.in

Question:  What is the difference between inter-ground fly ash with clinker and not mixed with clinker, how inter-grinding is done in mini cement plant?

Answer:

The cement is manufactured by grinding clinker and gypsum together in a mill, which could be a ball mill or a vertical roller mill. The blended cement i.e. Portland pozzolana (PPC) or Portland Slag (PSC) cement is manufactured by partial replacement of cement with the mineral admixtures, namely fly ash or blast furnace slag, respectively. The addition of mineral admixture could be done either at the time of clinker grinding in the mill or the admixture ground to the desired fineness could be blended with ground cement later. Both methods of manufacturing blended cement are presently practiced in the cement industry.

 Question: 014

Name: PAWAN BIRLA
Company: SHREE CEMENT LIMITED.
Email: birlapawan@shreecementltd.com
Phone: 09214037019
Question/comment: Could tell me please that how much % of fly ash in cement can give all equal physical properties of OPC.  PPC users are not 100% satisfied with present quality of PPC produced by many cos.

Answer:

Thanks for your feedback. The amount of fly ash that can be added to OPC depends on the following factors:

(a) Fineness, generally finer the better

(b) Particle shape. Round shape particles give best properties. Fly ash produced in fluidised bed boilers of captive power plants do not have round shape

(c) Glass content

(d) Unburned carbon content

(e) OPC quality

A good quality fly ash renders concrete with better workability, long term strength and durability

Question: 16

Name: sushanta Bhattacharyya
Company: Gupta equities
Email: sushanta@guptaequities.com

Question:  What is the difference in the cost structure in setting up & operating cost of cement grinding unit & cement blending unit.

Answer: The blending unit requires silos for cement storage, facilities for handling of cement. Transportation of loose cement from the cement plant to the blending unit will also add to the cost. Although operating cost is lower, it gets compensated by the higher initial cost of cement viz-a-viz clinker. Therefore do not expect any substantial cost difference.

 Question: 17

Name: Jagat Bhavsar
Company: JK Lakshmi Cement Ltd.
Email: jag_8753@yahoo.com
Phone: 9825504179
Question/comment: how much strength differences at 90 days in OPC and PPC cubes for M-20 Grade concrete?

Answer:

There will be practically no difference in the strength, when standard practices are followed.

Question 002

The closed-circuit grinding is used where a product of close size range is required, i.e. the product size distribution is close and even around the median. That is achieved  by incorporating a classifier in the circuit. Whereas the open-circuit  grinding is used when the product size control is not critical and oversize can be tolerated in the product. Thus the RRSB slope for the same average size may differ in both systems.

 Question: 005: TRANSPARENT CONCRETE

Name: S.Sampath Kumar 
Company: Simplex Infrastructures Limited 
Email: planet.ssk@gmail.com
Question/comment: What is meant by Transperent 

Concrete? Can you give the economics of that 

& also the Pro's and Con's of that Concrete?

 Answer:

        The transparent concrete or translucent concrete is made with built-in optical fibers (about 4 percent). This Transparent Concrete is, strictly speaking, semi- transparent. To get more information, click here.

   Question: 006

 Heartly Thanks to You Dr J D Bapat ji for your reply. I would like to ask you if you don't mind. Im civil engg. and have a construction firm in faridabad and working in private sector. As we know that inflation rate is increasingly day by day and its very difficult to handle projects now a days. What is the reason behind of hike rates of cement. Sir, is  it safe to use mini plant's cement on site. pls do let me know properly difference between these two cement(mini plant Vs big plant) to satisfy my clients.

 Answer:

 Thanks for your feedback.

As you have correctly observed, the rates of all commodities have increased in the recent times due to inflation. The rising fuel prices is a major contributing factor. Due to increase in transportation costs, the cost of inputs to a cement manufacturing unit, namely raw material, coal, fly ash or slag and the cost of output i.e. cement to the consumer, have gone up. The cost of electric power has also gone up as many of the manufacturing units draw power from captive power units. Thus it is easy to understand why the cost of cement has increased.

Any cement, certified as per the Indian Standards, may be used for construction purposes. It is also desirable to get your cement and concrete tested, periodically.

In so far as the quality of cement is concerned, technically there should be no difference between the quality of cement manufactured in mini or large cement plant.

Question: 007

Name: Sagar Bhirange,  Advocate

Email: advsagar_bhirange@yahoo.co.in

Question/comment: I am an Advocate working in Pune Court. I need some information about Cement for my one case. My quistion is: When the Cement was invented in the world? In what year the Cement was first time introduced for construction work in India? If possibale pls. give the refearnce of book also.

Answer:

a) When the Cement was invented in the world?

Aspdin (UK)invented cement and patented it in 1824. It is named Portland Cement due to its similarity with the color of limestone rock from the Dorchester region in England, named as Portland.

b) In what year the Cement was first time introduced for construction work in India?

There are no records to show when cement was first used in the construction work in India.The foundation of cement industry in India was laid by India Cement Company Ltd. in the year 1912-13 at Porbundar ( Gujarat State ) and started production in 1914. The annual capacity of cement production then was just 10,000 t.

c) If possible please give the reference of book also.

Cement Data Book (Vol. 1, 2, 3)
Bauverlag GmbH
Wiesbaden
Germany

 Question: 011

Name: satyam

Company: kcepl

Email: satyam_dhruwa@yahoo.com

Question/comment: Why do we require curing ?

Answer:

When making concrete, cement, aggregates and admixtures are mixed together and water is added. The hydration of cement begins immediately. The reactions which occur during hydration consume water. The hydration is ultimately responsible for the development of strength in concrete. Therefore it is necessary that water is made available or must be retained in concrete after placing, for the hydration reaction to generate the desired strength giving compounds. The process of curing does that. The curing is done by applying a curing compound on the concrete surface or covering the concrete surface with wet burlap and plastic sheet or keeping the surface dipped in water (ponding). This process ensures the desired humidity and temperature regime  , as required for hydration.

 Question: 013

Name: amit shah
Company: JMC projects
Email: amitshah@jmcprojects.com
Phone: 9879622174
Question/comment: Is there any codal provision that if we want to use fly ash then mixing shall not be done through hand mixing or concrete mixture machine. Only Batching plant should be use for producing fly ash concrete ?

Answer:

Thanks for your feedback. The IS 456-2000 and other relevant Codes give guidelines on the use fly ash and other mineral admixtures in cement and concrete. They do not specify how it should be mixed with the other ingradients of concrete.

In general, it is difficult to mix ingradients with widely varying size distribution and the density, in dry condition. However, there are examples where excellent mixing has been achieved even in a one-bag mixer. Good supervision is a prerequisite to achieve that performance. The batching unit  normally has provisions for measuring, dosing and controling the mixing process; therefore it is recommended. In any case, there should be no problem providing a batching unit in large projects. In case of small and medium projects, blending can be done in a mixer under proper supervision.

The IS 456 has many other useful provisions on the use of mineral admixtures in concrete; it will be wortwhile to study those.

 Question: 015

Answer:

Thanks for your feedback. When compared to the bitumen road, concrete road has many advantages such as longer service life (30-40 years), lower maintenance hence lower life cycle cost, smooth traffic flow, low pollution and maintenance for vehicles, almost no water permeability, high surface reflectivity, no damage due to oil spillage and so on.

One shortcoming of paved roadway surfaces that needs to be adequately addressed is subsidence.Subsidence is the gradual sinking of the soil. It is seen more often in terrain that is of a higher porosity, especially near wetlands.

A roadway is only as strong as the roadbed underneath it. The standard of building roads was not developed with cities built on tributaries in mind. Unfortunately, because of the historical use of rivers as major means of transportation, many cities are built on land such as this. When a road is built over unstable land, as the soil subsides, the road begins to buckle, crack and water seeps in, increasing the damage. Over time, the integrity of the road fails and potholes begin to appear.

Subsidence cannot be stopped, but the continual cracking and failure of roads we see due to it can be, using the modern technology.

 Question: 18

Name:  Ravi Rathi

Profession:  CA

Email:  impression.rk@gmail.com

Question: Till now I understand that two types of Bags are used for Packaging of Cement: 1. HDPE bags, 2. Multiwall Paper bags. I want to know the benefit and drawback of both and current and future trend in your view.

Answer: Thanks for your feedback. The two varieties of bags mentioned in your email, namely HDPE and paper bags are presently under use for cement packing.

* HDPE bags are cheaper
* Paper bags are seepage and pilferage proof but burst when not handled properly.

The choice of the bags generally depends upon the customer. The future should be biodegradable HDPE bags.