In India, although superplasticisers have been used in concrete for nearly one-and-a-half decades, there are still some concerns about specific quarters being used after that. The paper tries to answer some questions in the minds of practicing engineers, specialists, and other users.
The development of superplasticisers and admixtures has significantly altered the earlier concepts and techniques regarding concrete, particularly regarding delivering, putting, and compacting concrete and achieving strength.
In addition, it has likewise generated numerous novel applications of concrete-like high-volume fly ash concrete, extremely plasticized fiber-strengthened concrete and shotcrete, high-strength silica fame concrete having low permeability, and so on.
Globally talking in the preliminary days of advancements of admixtures, or even more specifically of the improvements of superplasticisers, the problems in the usage were generally related to loss of workability with time; however, these have been overcome as a result of constant advances in this field.
Therefore, although the concrete sectors in several nations have entirely accepted the essential existence of superplasticisers on the domestic scene, customers still have quite a few apprehensions. An attempt is made in this paper to identify these questions psychological of Indian engineers and to examine their legitimacy.
Because 1980, when the superplasticiser concept took root in this country, the following concerns have appeared in the minds of exercising engineers and individuals, and they continue to emerge.
- Whether the admixture being used is a plasticizer or a superplasticiser
- Whether one gets the uniform quality of the product and how can one characterize the admixture
- Whether one gets excessive loss of slump by using a superplasticiser
- The extreme slump would result in the segregation of concrete and hence what is the optimum dose, and whether an excessive amount will spoil the concrete.
- Whether the superplasticiser’s use will enhance the corrosion of steel in concrete
- Whether the steel-concrete bond is disturbed
- Whether the strength suffers on a long-term basis as a result of the chemical reaction of admixture and cement
- What can one choose from ligno, naphthalene, and melamine-based superplasticisers
- Whether it will excessively entrain air in the concrete
- Whether the quality of indigenous superplasticisers is at par with similar world-class products.
The above points are gone over in light of numerous study efforts and the site experience obtained over the years.
Whether the admixture being used is a plasticizer or a superplasticiser
Usually, a plasticizer or a water reducer can lower the water demand by 10-15 percent, although an additional reduction in water need can be impacted with higher dosages. Yet, this might have unwanted results on setup, air material, blood loss, segregation, and setting attributes of concrete.
Superplasticisers are chemically different from the standard plasticizers/ water reducers and produce a 30 percent cut in water demand with similar enhancements. Therefore, except for the degree of performance, both plasticisers and superplasticisers have similar impacts on the workability of concrete.
Nevertheless, their action device noticeably varies at a microscopic level due to effective deflocculation and the high diffusion of the cement bits obtained with superplasticisers. Varhasselt and Pairon’ have come out with basic deflocculating and vibratory compaction tests, which can exceptionally conveniently assist in successfully setting apart these two courses.
Similarly, the chemical characterisation of plasticisers and superplasticisers is well-recorded by numerous employees! These methods are not just valuable for developing whether one is using a plasticizer or superplasticizer; they can also mention whether the plasticizer/superplasticiser used coincides with the previous supply and can uncover the presence of potentially unhealthy elements.
Whether one gets the uniform quality of the product and how can one characterise the superplasticiser
Today, superplasticisers are readily available just in 3 classifications, viz.
(1) modified lignosulphonates (MLS).
(2) melamine formaldehyde sulphonates (MFS).
(3) naphthalene formaldehyde sulphonates (NTS).
Of these, the latter two, viz MES and NFS, are purely artificial products, and thus the response specifications can be managed whenever. In the case of customized lignosulphonates, it is gotten as waste alcohol during the production of paper-making pulp from wood. Also, its composition includes about 20-30 percent of lignin and it contains a complex mixture of sulphonation items of lignin, disintegration products of cellulose, lignin, different carbs, and sulfates.
Nevertheless, after establishing the accurate structure with the help of the succeeding procedures of neutralization, rainfall, and fermentation’, these admixtures can be given precise quality control standards.
Thus, based on the easy confirmation, one can rest assured that the supply of the material a consumer gets can be of relatively uniform high quality. In addition, several techniques can qualify the superplasticisers, as mentioned previously.
Whether one gets an excessive reduction in a slump by using a superplasticiser
Yes, it has been observed and reported that the workability of concrete, including a superplasticiser, is typically kept for about 30-60 mins as well, as the rapid reduction in workability is called “slump loss.”
It depends on variables like the kind and quantity of superplasticiser included, type and quantity of cement, time of addition of the superplasticiser, moisture, temperature, blending technique, visibility of various other admixtures in the remedy, and also the first downturn value.
Some ready-mixed concrete methods include the addition of a superplasticiser at the point of discharge to control the loss in a slump. In our nation, ready-mixed concrete is not much in style. However, where transit mixers are used, a superplasticiser can be added at the point of discharge with the help of an appropriate mechanical device.
Depression loss depends upon the sort of superplasticiser, and it is reported that at 0.6 percent dose, the loss rate is highest with MFS. Using more than the typical dosage will successfully retard the depression loss.
Even with a country like ours, where business economics is the main governing factor in the market, it might not be possible. An additional technique promoted to bring back downturn loss is to include superplasticisers at various intervals.
Malhotra and several others have revealed how enhancing NTS and MFS kinds of superplasticizers at different times can restore the downturn. Nevertheless, blending a suitable retarder in the superplasticiser is the most efficient and economically sensible alternative.
It has been observed that the enhancement of a retarder not only slows down the slump loss yet additionally enhances the first slump. Concrete content additionally controls the slump loss. It is seen that higher concrete content minimizes the rate of downturn loss.in
Whether the use of superplasticisers will enhance the corrosion of steel in concrete
Though superplasticisers are chemically sulphonates, they are ultimately spread in salt or comparable salt of the corresponding sulphonates. Usually, those sodium salts are prepared by responding to them with the alkalies. For this reason, the excess acidity is permanently neutralized, and an attempt is made to render it a little alkaline.
Nonetheless, some complimentary sulfates or chlorides are occasionally set in the solution specified in the case of chloride-based speeding-up superplasticisers, which may trigger corrosion. Such an event is unusual as chloride-based superplasticisers are not advised for enhanced concrete frameworks.
Experiments have shown that superplasticisers do not produce substantial rust formation on support. A correct enhancement of some not natural chemicals, like calcium nitrite, etc., to superplasticisers in traces has been reported to hinder the rust of steel to an enormous level.
Whether the polymeric nature of superplasticisers can disturb the concrete-steel bond adversely
This is an entirely unproven idea expressed in certain quarters of the industry. Bond stamina is reported to be lost in the case of polymer/epoxy-coated bars. Though superplasticisers utilize polymerized, they spread evenly in water and concrete to reduce the total surface tension of the system, and it is reported that the bond stamina is improved.
Collepardi and coworkers revealed that the enhancement of a superplasticiser for regular concrete elevated the steel-concrete bond strength from 1.2 to 3.5 MPa for smooth bars and also from 15.0 to 27.5 MPa for twisted bars, Table 1. These are outcomes obtained on 7-day concrete specimens.
Whether the strength of the concrete made with superplasticisers would suffer in the long run due to chemical reactions with cement
Superplasticisers, in any form, can not chemically respond to concrete or aggregates. Furthermore, stoichiometrically the amount of superplasticisers is so tiny that any opportunity for an ahead reaction is wholly eliminated.
It usually concurs that superplasticisers are adsorbed on concrete bits and exert an electrostatic repulsion resulting in the disassociation of the cement agglomerates right into primary bits. This is a surface sensation and not a chemical reaction and it causes a significant decline in the thickness of the cement-water-superplasticiser system.
The surface area stress of water additionally decreases. Hence, at no point in time, the stamina of the concrete can experience as a result of adding of a superplasticiser. On the other hand, if anything is to take place, its general resistance towards fighting outside chemical attacks will certainly improve due to much better compaction.
What can one choose from ligno, naphthalene, and melamine-based superplasticisers
Today, the building market is flooded with various brands of superplasticisers. Given that different permutations and mixes are feasible from those 3 basic types, some confusion is prevails in the profession.
Whenever a pure type of these three kinds is considered, the experiments have shown that lignosulphonates are slightly reduced in their moistening abilities than naphthalene or melamine-based superplasticisers. It is additionally seen that lignosulphonates entrain somewhat extra air in concrete than the other two though within appropriate limitations.
In the staying two types, as discussed earlier in this paper, naphthalene-based superplasticisers do marginally much better than melamine ones. Nevertheless, typically all the superplasticisers available today are blends of more than one component, which assist in lowering unfavorable residential or commercial properties of the basic materials and boosting their desirable properties. Therefore all the 3 types can be commercially brought to the same degree of efficiency.
Table 1: Increase in bond strength with the addition of superplasticisers
| Type of Concrete | Bond Strength, kg/m2 (MPa) | |
| Smooth Bars | Twisted Bars | |
| *Normal Weight | 12(1.2) | 150(1.5) |
| Normal Weight | 35(3.5) | 775(77.5) |
| *Light Weight | 4(0.4) | 66(6.6) |
| Light Weight | 9(0.9) | 142(14.2) |
*Concrete made without superplasticiser
At such a phase and particularly in the Indian context, the price would also become a definitive element; thus, for pure financial factors, duly-formulated ligno-based superplasticisers might become famous for general concreting tasks, and also the other 2 types would certainly be suitable for particular concretes.
Whether superplasticisers will excessively entrain air in concrete
As mentioned earlier, superplasticisers entrain 1 to 2 percent air in the case of naphthalene and melamine-based superplasticisers and 3 percent in the case of lignosulphonates.
Nevertheless, using many conveniently readily available detraining representatives can manage the excess air entrainment without impacting the performance of the admixture. For this reason, other than an average air-entraining admixture, other superplasticisers can be custom-made so as not to entrain too much air.
Whether the quality of indigenous plasticizers is at par with similar world-class products
There are only three basic types of superplasticisers: naphthalene and melamine based are pure artificial materials. In the case of synthetic materials, the quality all over the globe can only be varied to the nature of the packaging.
Similarly, lignosulphonates are the by-product materials of the paper and pulp industry; hence, there can rarely be any distinction between the indigenous byproduct generated in other countries.
The added blending products like hydroxycarboxylic acids, hydroxylated polymers, and so on are purely artificial materials, and the top quality should typically be the same worldwide.
Additionally, the innovation of the chemical know-how to make superplasticisers are today readily available worldwide. This can assure a consumer that the plasticizers readily available in this nation and other places might generically and performance-wise coincide.
Nevertheless, considering that the Indian construction industry at large is still not convinced to birth the added cost of these admixtures, some high-quality concessions in terms of energetic, solid materials may have happened sometimes to result in vast acceptability. Nevertheless, good and reputed manufacturers will not turn to such a compromise.
What needs to be done
The early depression loss and the doubts regarding the long-term longevity of the super-plasticized concrete were both factors of concern in the initial phases. Both these troubles are extra or less solved.
Nevertheless, the compatibility of superplasticisers with various sorts of cement, different sealing products, and various other admixtures remains to be solved in the Indian context.
The admixture industry in the nation may launch a study task in this regard with the help of reputed scholastic research study institutions. The function of antacids and also SO4 also requires to be settled. Some more quality assurance techniques which can rapidly decide the harmony and viability of the admixture are additionally called for to be developed.
And also, more significant than every little thing, as far as India is concerned, there is an urgent demand to create more understanding and education to popularise superplasticisers and, subsequently, to popularise excellent sturdy concrete.
Additionally, there is an urgent demand for appropriate additions/modifications in the codal markets, specifically those in IS:456 and TS-9103.
Another aspect that the manufacturing community needs to resolve is forming an independent and centralized checking authority. Chemical admixture supplier organizations could support such a panel or body.
In an unbiased way, this body can evaluate approval and provide quality certificates to different batches of numerous admixtures made by its member companies. In European nations, such a technique is considered very beneficial and well-appreciated.
As India likewise is taking fast strides in this field, comparable exercise can be beneficial from both users’ and makers’ perspectives.
Consequently, there will undoubtedly be fewer misconceptions and even more accuracy in using superplasticisers and admixtures in general.
