Legend of diamonds

Diamonds are not only the most valuable gemstones in the world but also the hardest natural substance on Earth. With a history spanning at least 4 billion years, they have existed almost as long as our planet itself. Composed mainly of carbon, diamonds can burn at extremely high temperatures, producing carbon dioxide with minimal residue. This combination of beauty, purity, and unyielding strength gives them an enigmatic allure that has fascinated humans for millennia. Historical records suggest that the first diamond was discovered around 3,000 years ago in the Krishna Valley of ancient India. At the time, people were unsure of what they had found and believed it to be a divine object with protective powers. In Sanskrit, the word for diamond means "thunder and lightning," reflecting the belief that these gems were born from storms. The ancient Greeks thought diamonds were fragments of stars that fell to Earth, while others believed they were tears of the gods or formed from celestial dew. In many ancient cultures, diamonds were seen as powerful talismans, capable of warding off evil spirits. Some even claimed that swallowing diamond powder could purify the body and prevent madness. During the Middle Ages, diamonds became symbols of invincibility, courage, and masculinity in Western culture. They were reserved for royalty and the aristocracy, and by the 15th century, presenting a diamond ring during a proposal became a formal part of marriage traditions. These early rings featured rough, uncut diamonds—natural crystals that lacked the brilliance of today’s precision-cut stones. By the 16th century, diamond cutting and polishing techniques advanced significantly, making diamonds more accessible and prominent in royal courts and weddings. In 1919, the modern diamond cut, developed by Marcel Tolkowsky, became the standard based on optical properties. This led to the creation of various shapes like round, square, oval, and triangular diamonds. In 1953, the 4C system (Carat, Cut, Color, Clarity) was introduced, establishing universal criteria for evaluating diamond quality and influencing consumer choices. One of the most famous and cursed diamonds is the "Koh-i-Noor," known as the "Mountain of Light." Discovered in 1304 in the Golconda region of India, this massive 793.50-carat diamond was later stolen and eventually presented to Queen Victoria of England. After being cut into smaller stones, one of them, weighing 186.10 carats, was named "Koh-i-Noor" and another, 186.90 carats, became the "Orlov." Despite its dazzling beauty, the diamond has been associated with bloodshed and misfortune throughout history. The Koh-i-Noor is now part of the British Crown Jewels, prominently displayed on the Queen's crown. It symbolizes both wealth and power, yet its history is steeped in violence and tragedy. According to Hindu texts, "Whoever owns it has the whole world; whoever owns it must bear the catastrophe it brings. Only God or a woman who owns it will not suffer punishment." Over centuries, the diamond changed hands multiple times, often leading to conflict and death. Eventually, it came under the possession of Queen Victoria, bringing temporary peace. However, she herself faced two mysterious incidents linked to the stone. No member of the British royal family has ever worn it publicly, and it remains locked in the Tower of London, silently recording its bloody past. In 1997, during Queen Elizabeth II’s visit to India, a Sikh leader claimed descent from the former Maharaja of Punjab, Dalip Singh, and demanded the return of the diamond. Though the request was made, the British government refused to acknowledge the claim, maintaining its ownership. No one knows if the diamond’s curse can be broken if owned by a woman. Similar fates have befallen other famous diamonds like the Hope, Orlov, Wittelsbach, and Dresden. Their histories are filled with bloodshed, betrayal, and struggle. These gems have no true owner—they belong to no one, and all who possess them are merely temporary custodians. Compared to these cursed stones, many other famous diamonds have had calmer journeys. They serve as cultural artifacts, witnessing the evolution of human civilization. War, conflict, and power struggles have shaped history, and diamonds, whether cursed or not, remain symbols of both beauty and chaos.

Polycarboxylate Superplasticizer

Some 20 years ago, a new type of Superplasticizer based on polycarboxylate polymers (PCE) was commercially introduced to the North American concrete construction industry. Just as the application of naphthalene-based admixtures starting in the 1970s enabled significant improvements in the numerous engineering properties of plastic and hardened concrete, polycarboxylates have further extended the performance of concrete mixtures.

For example, self-consolidated concrete and slump retention beyond two hours without significant set time extension have been made possible with PCEs. I was fortunate to be on the R&D/marketing team for a major chemical admixture company that launched the first group of polycarboxylate-based admixtures in the 1990s. Like all new technologies introduced into the building industry, there has been a long learning curve which underscores the highly diverse set of materials and applications with concrete construction. This article summarizes a few key performance attributes which have been learned from both commercial concrete applications and the research laboratory. Some of the benefits provided by polycarboxylate superplasticizers have been discussed and previously published in The Concrete Producer.

The Polycarboxylate Family

The term “polycarboxylate” actually applies to a very large family of polymers, which chemists can design to impart a special performance to concrete mixtures. Subsequent to the introduction of so-called general purpose PCE superplasticizers, new PCE products have been developed especially designed to provide high early strength and different levels of slump retention, as well as provide different capabilities to manage air contents in concrete. One such class of polycarboxylates has little impact on initial slump, but because of a time-release function built into the PCE polymer, concrete slump increases generally in a predictive manner as a function of mixing time (see Figure 1). Thus, such a product can be added at various dosages to an already admixed concrete to dial in slump retention as a function of job conditions (haul time, temperature, delay before discharge, etc). Very often, a superplasticizer will be formulated with a blend of two or more PCEs to achieve a combined performance of both early strength and long slump life. Researchers will continue to actively manipulate PCE polymer structure to meet the ever changing material and construction requirements.

  • Air entrainment: Essentially all polycarboxylate-based admixtures are formulated with a defoamer to control unwanted air entrainment inherent with the PCE polymer. For both air-entrained and non-air entrained concrete applications, air contents can usually be effectively managed with selection of the PCE-based superplasticizer product most compatible with job materials. Varying carbon content in fly ash can make consistent air contents challenging as the hydrophobic nature of defoamers leads to adsorption by fly ash carbon. In general, compared to polynaphthalene sulfonate polymer (PNS) based superplasticizers, PCE-based products can make air-entraining admixtures (AEA) more efficient, meaning a lower AEA can be required to achieve the same air content.
  • Impact of clays: Unlike PNS superplasticizers, the PCE polymer will be readily and irreversibly adsorbed by certain clay fines that could be present in various aggregate sources. Figure 2 illustrates the impact that a clay- bearing sand, having a methylene blue value of 1.30, can have on the dosages of PNS verse PCE-based superplasticizers to achieve compatible slump. Normally, with clay-free or low-clay sands, PCEs are dosed about one-third that of PNS-based superplasticizers for comparable slump. However, when clays are present in certain sands, up to a 50% higher dosage of PCE versus PNS can be expected. Therefore, if the dosage of a PCE superplasticizer were to unexpectedly increase, checking for clay fines in the aggregate supply should be prioritized.
  • Flexible dosing: Again, unlike PNS-based superplasticizers, which invariably should be added in a delayed addition mode (that is, after the cement and water have begun to mix), PCEs are relatively insensitive to the time of addition, allowing for greater flexibility in the concrete batching process.
  • Incompatibility with PNS superplasticizers: Use of PCEs and PNS-based products in the same concrete mixture results in rapid loss of workability. Thus, the two technologies, PNS and PCE, should not be used in the same concrete mixture.
  • Strength Synergy with calcium-based set accelerators: When PCE-based superplasticizers are used with set accelerators and corrosion inhibitors comprised of calcium salts, unexpected strength gains have been observed compared to a similar concrete mix admixed with a PNS-based product. This synergy in strength gain with PCEs was first observed in a mix containing a calcium nitrite-based corrosion inhibitor. The data summarized in Table 1 was reported by a concrete producer who had been using a combination of a lignosulfonate-based ASTM C494 type A water reducer and a Type G PNS/Lignin-based superplasticizer to manufacture prestress piles.

This remarkable strength difference, obtained by merely changing the superplasticizer type from a PNS to a polycarboxylate, was verified from a scientific study, and can be useful in reducing cement contents while still meeting strength specifications. Interestingly, the strength difference does not seem to be associated with increased heat of hydration, but rather is related to a denser microstructure produced by the combination of a calcium-based accelerating or corrosion-inhibiting admixture and polycarboxylate-based admixture.

The PCE superplasticizer replaced both the PNS/lignin and Type A water-reducing products at about one-third the dosage rate. Also, note the 50% drop in AEA dosage rate with the PCE admixed concrete to obtain the same air content.

To summarize, though the concrete industry has learned much about harnessing the versatility and understanding the limitations of PCE-based superplasticizers, chemists, working with concrete technologists, will continue to modify the polymer structure to achieve new capabilities for the production, placement and service life of concrete mixtures.

by-Ara

PCE based plasticizer

Shanghai Hongyun New Construction Materials Co., Ltd , https://www.hongyunpce.com