SUPERFLUID ADDITIVES ARE INDISPENSABLE FOR CEMENT

NİLÜFER MUTLU, LEVENT SOYSAL, DR. AYŞE ÖZGÜR ÖZSAR-
UGM Chemistry Laboratory

It is of great importance that all cement/concrete additives are "produced according to their place of use and a specific purpose". The performance of the superplasticizer admixture in concrete is a complex interaction affected by many parameters, especially the cement composition, "cement fineness, the presence and properties of other mineral and chemical admixtures, the time of addition of the admixture, the molecular weight of the admixture, the degree of sulfonation and polymerization, and air temperature."

Nowadays, chemicals appear in almost every aspect of life and are used in many industries, from food to oil. While some are beneficial, others threaten human health and harm the environment.

With the increasing population creating different demands and the development of technology, different chemicals have begun to be produced and used in various fields in recent years. Chemicals produced especially as additives have become used in various industrial branches.

The parameters that determine cement-concrete quality became the main agenda item after the Kahramanmaraş-centered earthquakes on February 6, 2023, which caused great loss of life and property. In this article, we would like to draw attention to chemical additives, one of those parameters.

Two of these chemicals are polynaphthalene sulfonate, which is "produced as a polymer and used in tanning in the textile industry, but also uses its superplasticizer properties in the cement and concrete industry," and SNF Sulfonate, "which is also used as a polymerization emulsifier in the rubber industry." Since such additives increase performance, they have become indispensable products of the cement and concrete industry.

FOR DURABLE, QUALITY AND HIGH PERFORMANCE CONCRETE…

Contributions; Other than water, cement, aggregate and fibers, they are materials "added to concrete or mortar during or just before mixing". Today, producing high-quality, high-performance concrete resistant to physical, chemical and biological effects makes it possible to use both chemical and mineral additives. Admixtures consist of organic or organic and inorganic components and are used to reduce the water required for a certain consistency in concrete.

These additives are called plasticizers or superplasticizers depending on the decreasing amount of water. At normal dosages, plasticizers can reduce mixing water by 5-11%, while superplasticizers can reduce it by 5-11%.

NATURAL AND SYNTHETIC TYPES OF PLASTICIFIER ADDITIVES…

The use of water-reducing chemical additives dates back to the 1930s. There are natural and synthetic types of plasticizing additives. Although natural polymer-based admixtures are limited, they are widely used in the concrete industry because their production costs are lower than synthetics. They contain natural polymers, starch, natural gum (resin), and plant protein. Examples of these are welam gum, lignin, and agar (a gelatinous substance obtained from seaweed).

Synthetic polymer-based modified additives are the most commonly used synthetic plasticizer additives in terms of water reduction capacity and functionality in cementitious systems.

1. The water reduction property of modified lignosulfonate bases (MLS) is approximately . They are used to increase workability in cementitious mixture applications.

2. Sulfonated naphthalene formaldehyde condensates, or polynaphthalene sulfonates (PNS), interact weakly with clay minerals and exhibit a water reduction effect down to 0.

3. Polymelamine sulfonate (PMS) or sulfonated melamine formaldehyde condensates enable the water content in cementitious systems to be reduced by more than-30.

4. Synthetic polymers such as polycarboxylates (PC) and acrylic copolymers (PCE) have water reduction properties up to @ due to their versatile chemical structure.

NEGATIVE EFFECTS OF CHEMICAL ADDITIVES ON CEMENT SYSTEMS…

While the addition of chemical additives to cementitious systems is generally beneficial, it's crucial to acknowledge that negative effects can also arise. This is particularly true when high amounts of water reducing additives and air entraining additives are used in combination. The complexity of this issue is evident in two main problems that can occur. Firstly, the consistency (slump value) of the concrete may increase, potentially leading to a decrease in the entrained air content. Secondly, changes in the air gap system and spacing factor in the mixture can occur. This underscores the need for careful consideration when selecting additives, a task that requires your expertise.

COMPATIBILITY BETWEEN CEMENT AND SUPER PLASTICIFIER

The fluidity of cement paste, a key factor in concrete quality, can be enhanced by the use of superplasticizer additives. However, the initial high workability of concrete containing superplasticizers, especially those with low water/cement ratio, may diminish over time. This is a clear indication of rheological incompatibility between the superplasticizer and cement. The potential consequences of this incompatibility, such as a decrease in workability, highlight the urgency of addressing this issue.

1-Cement Related Effects:

• Factors such as the chemical composition of the cement, its fineness and the solubility of the sulfates it contains are the most important factors affecting the rheological properties of high-performance concretes.

• Fineness of cement: The viscosity of cement paste containing superplasticizer additives also depends on the fineness of the cement. As cement fineness increases, the viscosity of the mixture increases.

• Calcium Sulfate Amount and Form: The type of calcium sulfate added to the cement as a set stabilizer during production (gypsum, CaSO4.2H2O, hemihydrate CaSO4.1/2H2O or anhydrite CaSO4) affects the viscosity of the mixture.

• Alkaline content of cement: It is known that cements containing high amounts of alkali generally show worse rheological behavior in mixtures that do not contain superplasticizer additives. Similarly, it has been reported that the workability of mixtures containing superplasticizer increases with decreasing alkali content of the cement.

2-Effects Due to Super Plasticizer:

Factors that determine the effectiveness of the superplasticizer:

• Position of the sulfonate group attached to naphthalene.

• Length of polymer chain and their cross-linking.

• The amount of residual sulfate and the type of counter ion used in the neutralization process.

• Effect of Additive Origin, Molecular Weight, Sulfonation and Polymerization Degree: While superplasticizers may differ from each other due to their origin, additives from the same origin may also differ due to molecular weight and chemical composition variability.

RELATIONSHIP BETWEEN THE MOLECULAR WEIGHT OF THE ADDITIVE AND FLUIDITY

Understanding the relationship between the molecular weight of the additive and fluidity is crucial for optimizing the superplasticizer's performance. It is observed that the fluidity increases as the molecular weight of the additive increases; However, after a certain point, it has been said that 'increase in molecular weight leads to increase in viscosity'. This is because the long polymer chain in the additive with very high molecular weight may cling to the cement grains and cause agglomeration. An optimum molecular weight of 206 was mentioned for the best fluidity of the mixture containing polycarboxylate-based additives with a certain water/cement ratio. It has been emphasized that admixtures with lower molecular weight provide greater fluidity as the water/cement ratio decreases. The degree of polymerization of the admixture and its effect on the strength development of the mixture vary depending on the type of polymer, and that low molecular weight polymers are more effective in dispersing cement grains.

It has been stated that the degree of sulfonation of the additive affects the processability more than its relative molecular weight. The binding position of the acidic sulfonate group (HSO3) to the naphthalene molecule affects the efficiency of the additive. Again, the base used for neutralization during production affects the performance of the additive through the Counter Ion Origin Effect. In SNF-based additives, the use of sodium (Na-SNF) as the counter ion resulted in better rheological properties than magnesium (Mg-SNF) and calcium (Ca-SNF). In producing polycarboxylate-based additives, sodium or magnesium did not affect the additive performance.

POLYNAPHTHALINE SULPHONATE BASED (PNS) ADDITIVES…

Polynaphthalene sulfonate-based additives (PNS) are among the additives we have frequently encountered imported recently. Developed in the 1930s, PNSs, also known as sulfonated naphthalene formaldehyde condensates (SNFC), were initially used in textile chemicals and the production of synthetic rubber. These polymers, synthesized as concrete additives in Japan in the late 1960s, produced water-reducing admixtures at high rates.

PNS type additives with high dispersion ability have more water blocking properties than natural polymer-based or other low-medium range water reducers. Although some synthetic plasticizing chemical additives show dominant steric effects, they can generally interact electrostatically with most cements. These additives have made it possible to successfully develop high-performance concrete in numerous applications today.

PRODUCTION ACCORDING TO THE PLACE OF USE AND A SPECIFIC PURPOSE…

As can be seen, the "production of all these cement/concrete additives according to their place of use and a specific purpose" is of great importance. The performance of the superplasticizer admixture in concrete is a complex interaction mechanism affected by many parameters, especially the cement composition, "cement fineness, the presence and properties of other mineral and chemical admixtures, the time of addition of the admixture, the molecular weight of the admixture, the degree of sulfonation and polymerization, and air temperature." However, analyzing these contributions, the structure determination, is very important. Various spectroscopic and chromatographic methods carry out structure analysis of such polymers.

CORRECT ANALYSIS IS THE MOST IMPORTANT STEP TAKEN IN FOREIGN TRADE…

It should not be forgotten that; Correct analysis is the most important step in foreign trade. The correct tariff must be determined for the goods (chemicals) to be released into free circulation. Correct tariff determination is only possible with correct analysis. In this context, T.R. According to our Customs Tariff Schedule, products with a polymerization degree of 5 or more are considered as polymers in Chapter 39. As a result, determining the polymer degree in all polymer-based additives mentioned above is important in determining the Customs Tariff Statistics Position (GTİP).

As it is known, the Customs Tariff Statistics Position (GTİP) shows everything from the tax and SCT of the goods (chemicals) to all legal permits and documents that need to be obtained. Therefore, the content and analysis of the goods have a very important place in GTİP determination.

Resources:

1. Chemical Admixtures on Structures 5th International Symposium and Exhibition, 19-20 October 2017, Ankara.

2. Factors Affecting Portland Cement-Superplasticizer Additive Compatibility, Prof. Dr. Kambiz RAMYAR, Ege University Faculty of Engineering, Department of Civil Engineering, Izmir, Türkiye.

3. The Effect of the Use of Polycarboxylate Based Water Reducing Additives Containing Different Surfactant Chemicals on the Properties of Cementitious Systems, Ayvaz Emin, Uludağ University, Institute of Science and Technology, Bursa, Turkey.

mechanism. Analysis of these contributions, that is, structure determination, is very important. Various spectroscopic and chromatographic methods carry out structure analysis of such polymers.