www.www.buonovino.com

[kalirajans]

Dear friends and experts,



As riversand becoming a rare commodity in India due to various reasons, the concrete industry has already shifted to manufactured sand. Do we have the long term durability performance of concrete using M.sand?


While using M.sand in self compacting concrete, it was seen that the required mixing time is slightly more to have the flowability comparable. While transporting from a RMC plant, longer the distance better the flowability. Can we have expert comment on this subject? If possible, can anyone share their findings in this regard.


Regards,


S.Kalirajan

Posted via Email

[B.V.Harsoda]

Dear Er.S. Kalirajan,

Discussion is on going on this topic at below link:-

//www.buonovino.com/forum/viewtopic.php?t=11705



FOR SELF COMPACTING CONCRETE:-

RESEARCH REPORT ICAR 108-2F

AGGREGATES IN SELFCONSOLIDATING CONCRETE

Sponsored by the Aggregates Foundation

for Technology, Research and Education

Hudson (2003c) suggests using a manufactured sand with the same grading and volume as the natural sand it is replacing but cautions that the ideal grading depends on shape, angularity, and texture, and must be selected independently for each sand.

Source Link:-
http://www.icar.utexas.edu/publications/108/ICAR%20108-2F%20(Final%20Report).pdf

Regards
B. V. Harsoda

[lkjain.ngp]

Replacing natural sand by crushed sand, has following effects :
1. Finner portion is higher in crushed sand, compared to natural sand. Hence It give better grading of particles, which is an improvement.
2. In most cases it is observed that crushed sand does have particle as spherical or cubical as available in natural sand. Compared to natural sand, those are irregular, elongated & flakey. Earlier (few decades back) this was seen as a disadvantage, because The�achievable compressive strength was little less.� Now this is not a disadvantage, as it will need a little higher dose of plasticisers to achieve a particular compressive strength & a particular workability. However the ratio of flexural (or tensile) strength to compressive strength improves, which has become an advantage though marginal. Cracking is influenced by tensile strength, and increased resistance to crack should give better durability.
3.� The basis of comparison will show the difference. If mixes with two sands are compared with same compressive strength (rather constant w/c ratio), manufactured sand sand will appear advantageous.
4.�� One of the very important issue is the energy requirement in producing crushed sand, which makes it costly as well as not green.�
5.�� I have never understood the the basis of stopping the use of natural sand, by environmentalists. Taking out sand from river reduces the total silt transport to sea, which is no one's gain. Non removal of sand can make river flow shallower by silting, and will increase the flood plains on the bank river.�To me whole issue is more political than environmental.�

L. K. JAIN

On 7 March 2012 21:26, kalirajans forum@www.buonovino.com)> wrote:

[Jayant Kulkarni]

Dear Friends,

It has become inevitable to use Crushed Sand (Manufactured Sand) because of shortage of natural sand. The natural sand is round in shape & achieves this particle shape in flow/current of water. In this process all the loose material around the particles is washed out/ removed.

In case of Crushed Sand the manufacturing process is different. (As such crusher dust is not accepted as a replacement of natural sand. We need to have sand manufactured in VSI Crusher, which can produce properly graded sand with specified amount of fines below 150microns).

As per basic principle, the surface areas of Crushed Sand has to be more than that of river sand. This should increase the overall demand of water, per cubic meter of concrete required for desired workability.

The angular shape of Crushed Sand also demands more water as compared to the rounded river sand for given workability.(I am not clear about the soundness & integrity of Crushed Sand particles as compared to Rive Sand particles).

This implies that for given workability we require more water when we use Crushed Sand. Indirectly,it implies that concrete will achieve lesser compressive strength and flexural strength for given set of condition, all other factors remaining same.

I am not sure whether any research is carried out regarding flexuralstrength of concrete using Crushed Sand.The flexural strength should be directly related to Crack Width (under bending tension) & hence durability.

Whether anybody can throw more light on the aspect ofDurability of Concrete using Crushed Sand?

Jayant Kulkarni

consulting Structural Engineer

[B.V.Harsoda]

Dear Er. L K Jain SIr,

I fully agree with you from point 1 to 4, but not agree with point 5, because there is no question of stopping use of natural sand but day by day natural sources of sand depleting and demand of sand fast increasing due to fast developement in civil engineering fields,hence munufactured sand is only altrnative to natural sand w.r.t huge demand.

Regards,
B. V. Harsoda

[Dr. N. Subramanian]

Dear Er Jainji,

As indicated by Er Harsodaji, there is a severe shortage of natural sand in many parts of the country. Some people are even selling sea sand as sand! hence it has become imperetive use manufactured sand and future it will be the material that of choice in many future buildings.

Thank you for several valuable inputs!

Regards
Subramanian

[raghuveer_ks at yahoo.com]

Dear Friends,


有网站或生产细节吗explains in general, how the plasticizers or chemicals work on the concrete mixes . For eg. cement when reacts with water, a gel is formed which bonds the aggregates. A emulsion creates a thin layer on he plaster & acts as water proofing member.


When we use manufacured sand what chemicals should we use to get durable & strong concrete? What are the parameters that we need to consider?


Thanks

Raghuveer K S
98453 96592


Have a good day
From:lkjain.ngp
To:econf@www.buonovino.com
Sent:Friday, March 9, 2012 9:41 PM
Subject:[ECONF] Re: Use of M.sand


Replacing natural sand by crushed sand, has following effects :
1. Finner portion is higher in crushed sand, compared to natural sand. Hence It give better grading of particles, which is an improvement.
2. In most cases it is observed that crushed sand does have particle as spherical or cubical as available in natural sand. Compared to natural sand, those are irregular, elongated & flakey. Earlier (few decades back) this was seen as a disadvantage, because The achievable compressive strength was little less. Now this is not a disadvantage, as it will need a little higher dose of plasticisers to achieve a particular compressive strength & a particular workability. However the ratio of flexural (or tensile) strength to compressive strength improves, which has become an advantage though marginal. Cracking is influenced by tensile strength, and increased resistance to crack should give better durability.
3. The basis of comparison will show the difference. If mixes with two sands are compared with same compressive strength (rather constant w/c ratio), manufactured sand sand will appear advantageous.
4. One of the very important issue is the energy requirement in producing crushed sand, which makes it costly as well as not green.
5. I have never understood the the basis of stopping the use of natural sand, by environmentalists. Taking out sand from river reduces the total silt transport to sea, which is no one's gain. Non removal of sand can make river flow shallower by silting, and will increase the flood plains on the bank river. To me whole issue is more political than environmental.

L. K. JAIN

On 7 March 2012 21:26, kalirajansforum@www.buonovino.com)> wrote:
——自动删除

Posted via Email

[mohannaikleo]

Dear sefians,

�The views are right, water absorption mainly depends upon the shape and texture of particles present. Even though the M-sand is proved replacement for river sand, it is not upto 100%, bcoz for manufacturers the demand may not allow to complete the entire process for the final product. The resulted product will never be equal to the river sand. It is right time to change the mindset for conventional methodologies for huge constructions, like the sand shall be used only for structural works and the external finishes can be catered with exposed work, cladding with adhesivies etc., Even today the natural can be made available with the proper legal involvement. There is mafia behind creating shortage. But still as it is said by Gandhiji that " There are sufficient natural source for meeting the necessities of mankind but never for desires". As civil engineers we can by usage of natural resource with its best like design mix, usage of local available materials etc., I request Lets join hands for that...........


Thanks & Regards,
Mohan

On Sat, Mar 10, 2012 at 11:31 PM, raghuveer_ks atforum@www.buonovino.com(forum@www.buonovino.com)> wrote: