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Corrosion & construction chemicals

Published

9 years ago

August 31, 2015

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Corrosion in reinforced concrete is one of the most frequent features of buildings, especially those exposed to aggressive environments such as onshore marine atmospheres, feels Arunendu Ta.

Corrosion is a process of chemical reaction in which metal converts to their stable oxides. This is basically electrochemical oxidation where oxygen acts as oxidant. The formation of iron oxide, commonly known as ?rusting? is an example of electrochemical corrosion. Generally oxides or salts of original metals form in corrosion. Corrosion is also seen in ceramic and polymers although more appropriate term for this is degradation. In this case material looses properties like appearance, strength, permeability, etc. Many cases corrosion in structural elements is seen because of exposure condition to air or many vapours.

In electrochemical reaction, the iron goes into solution as ferrous ions at anodic sites on the surface, thus constituting the anodic reaction. In this oxidation process, iron atoms release electrons whose negative charge would quickly build up in the metal and prevent further anodic reaction or corrosion. Thus this dissolution will only continue if the electrons released can pass to a site on the metal surface where a cathodic reaction is possible. At a cathodic site the electrons react with some reducible component of the electrolyte and are themselves removed from the metal. The ?corrosion current?, flow of electrons continue to degrade the original metal in this process. The corroding piece of metal behaves as a ?mixed electrode? since simultaneous anodic and cathodic reactions are proceeding on its surface.

The most common and important electrochemical reactions in the corrosion of iron are thus:
Anodic reaction (corrosion):

Fe ? Fe² + + 2e -(i)
Cathodic reactions (simplified):
2H+ + 2e ? H₂

or
H 2O + ? O2 + 2e ? 2OH– -(ii)

Reaction (i) is most common in acids and in the pH range 6.5-8.5 the most important reaction is oxygen reduction (ii). In this latter case, corrosion is usually accompanied by the formation of solid corrosion deposits from the reaction between the anodic and cathodic products.

Fe2+ + 2OH– = Fe (OH)2 – Iron (II) Hydroxide Pure iron (II) hydroxide is white but the material initially produced by corrosion is normally greenish in colour due to partial oxidation in air.

2Fe(OH)2 + H2O + ? O2 ? 2Fe(OH)3 – hydrated iron (III) oxide.

Due to further hydration and oxidation reactions, the reddish rust that eventually forms is a complex mixture whose exact constitution will depend on other trace elements which are present. As the rust is precipitated due to secondary reactions it is porous and absorbent and tends to act as harmful substrate which encourages further corrosion. For other metals or different environments different types of anodic and cathodic reactions may occur.

If solid corrosion products are produced directly on the surface as the first result of anodic oxidation these may provide a highly protective surface film which retards further corrosion, the surface is then said to be ?passive?. An example of such a process would be the production of an oxide film on iron in water, a reaction which is encouraged by oxidising conditions or elevated temperatures.
2Fe + 3H2O ? Fe2O3 + 6H+ + 6e

Corrosion protection by construction chemicals
Corrosion can be taken into account as prevention during construction or usually we are forced to take action after corrosion is found in later stage.

Concrete is a composite material composed of cement (usually Portland cement, fly ash), fine aggregate (sand), coarse aggregate (gravel or crushed stone), chemical admixtures, and water. During this mixing, cement reacts with water & form hydrates around the aggregate to form a solid, bonded conglomerate. While concrete is a relatively inert and durable building product, there are mechanisms by which it can degrade. Perhaps the most common is not degradation of the concrete material itself, but corrosion of the embedded steel reinforcement. When the steel corrodes, it expands and damages the concrete, often resulting in delamination and spalls. Corrosion in reinforced concrete is one of the most frequent features of buildings, especially those exposed to aggressive environments such as onshore marine atmospheres. Under this condition, repairs & preventive actions required by using construction chemicals which is post treatment of any construction.

Other degradation mechanisms include sulfate attack and alkali silica reaction (ASR). Prevention of these degradation mechanisms at the time of construction is typically done by selecting proper ingredients & designing good dense concrete mix to protect the concrete from aggressive environments. Once damage has progressed, the problem becomes much more complicated-and expensive-to solve.

The best way to use epoxy coated/galvanised steel reinforcement to avoid corrosion during any construction. Always better to cover the reinforcements inside concrete elements so that there will be less possibility for migration of oxygen from moisture to facilitate corrosion.

During the last few decades the corrosion issues in reinforced concrete has been extensively investigated by many scholars and researchers. Corrosion inhibitors are one of the most efficient chemicals for reinforced concrete. Corrosion inhibiting admixtures specialised admixture category and are used to slow down corrosion of reinforcing steel in concrete. In order to protect metallic substrates against corrosion, certain inorganic and organic products, called corrosion inhibitors, are added in small concentration to the aggressive medium.

Inorganic corrosion inhibitor
The addition of corrosion inhibitors to the concrete mix, offers a viable corrosion protection measure. There are generally three groups of inhibitors: anodic, cathodic and mixed inhibitors. Anodic inhibitors reduce the corrosion rate by reacting with the corrosion products and form a protective film. Cathodic inhibitors reduce the corrosion rate by reacting with the cathode sites (as an oxygen-barrier) on the steel. Passivating inhibitors like nitrites represent special types of anodic inhibitors and they are generally very effective if present in sufficient concentrations.

Mixed inhibitors both influence the anodic and cathodic reaction sites, by forming an adsorption film on the metal surface. These adsorption type inhibitors are typically organic compounds. In recent years, results of many investigations on organic migrating corrosion inhibitor (MCI), which is mainly, composed of an amino carboxylate or amino alcohol shows very encouraging results.

Organic corrosion inhibitor
These inhibitors like ?CHRYSOCorrocrete? generally acts through bipolar mechanism. The functional group responsible for this organic compound adsorption on metal surface through the lone pair of the atom while iron ions on metal surface act as acid by accepting electrons from a donor group. By this, organic corrosion inhibitors form a strong corrosion protecting passive film on steel surface. The adsorption of these compounds on anodic sites decreases anodic dissolution of stainless steel by the electron-rich heteroatom in the organic compound, which adsorbs on the anodic site through their lone pairs of electrons of an atom thus reduces the anodic dissolution of metal. In acidic solution, these compounds can exist as protonated species; these protonated species may adsorb on the cathodic sites of the stainless steel and decrease the evolution of hydrogen. In some researches it was found that organic corrosion inhibitors effectively delayed the onset of steel corrosion and inhibited the steel corrosion even when the passive film was compromised. According to the strong absorption of organic corrosion inhibitors onto the steel surface inhibited the cathodic reaction of steel corrosion by limiting the access of oxygen to the steel. It is necessary to check the concrete properties with & without corrosion inhibitor in fresh (workability, retention, setting time, pH of medium, etc.) as well as harden state (compressive strength).

It has been found through exhaustive studies by researchers that the bi-polar corrosion inhibitors are effective enough to protect/delay corrosion of reinforcements in concrete if used properly during production of concrete. The only concern is the optimum dosage of Corrosion inhibitor to be determined before its use for effective results.

Once concrete is cracked, the easy path for corrosion opened up & we need to think for various solutions for rectification & retrofitting of structures to protect corrosion. In this category, different anti-corrosive coating systems, grouts etc exist for application depending upon the nature of criticality, location & substrate.

In conclusion, our target should be to produce impermeable concrete to the maximum extent possible to block pores inside concrete matrix to restrict entry of water & migration of various harmful ions. By this, we can eliminate maximum risk of corrosion together with using good ingredients like aggregate, supplementary cementitious material along with corrosion inhibitor (for aggressive environment is must) during production of concrete as well as giving sufficient attention for curing (either with water or with good curing compound like CHRYSOCure AC) at early age (we often forget & start after cracking) makes the system perfect to limit corrosion at later ages. Needless to say the use of galvanised / anti corrosive coated reinforcement bar ID must to protect corrosion.

Arunendu Ta, Head, R&D and Product Development, Chryso India

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Price hikes, drop in input costs help cement industry to post positive margins: Care Ratings

Published

3 years ago

October 21, 2021

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Region-wise,the southern region comprises 35% of the total cement capacity, followed by thenorthern, eastern, western and central region comprising 20%, 18%, 14% and 13%of the capacity, respectively.

The cement industry is expected to post positive margins on decent price hikes over the months, falling raw material prices and marked drop in overall production costs, said an analysis of Care Ratings.

Wholesale and retail prices of cement have increased 11.9% and 12.4%, respectively, in the current financial year. As whole prices have remained elevated in most of the markets in the months of FY20, against the corresponding period of the previous year.

Similarly, electricity and fuel cost have declined 11.9% during 9M FY20 due to drop in crude oil prices. Logistics costs, the biggest cost for cement industry, has also dropped 7.7% (selling and distribution) as the Railways extended the benefit of exemption from busy season surcharge. Moreover, the cost of raw materials, too, declined 5.1% given the price of limestone had fallen 11.3% in the same aforementioned period, the analysis said.

According to Care Ratings, though the overall sales revenue has increased only 1.3%, against 16% growth in the year-ago period, the overall expenditure has declined 3.2% which has benefited the industry largely given the moderation in sales.

Even though FY20 has been subdued in terms of production and demand, the fall in cost of production has still supported the cement industry by clocking in positive margins, the rating agency said.

Cement demand is closely linked to the overall economic growth, particularly the housing and infrastructure sector. The cement sector will be seeing a sharp growth in volumes mainly due to increasing demand from affordable housing and other government infrastructure projects like roads, metros, airports, irrigation.

The government’s newly introduced National Infrastructure Pipeline (NIP), with its target of becoming a $5-trillion economy by 2025, is a detailed road map focused on economic revival through infrastructure development.

The NIP covers a gamut of sectors; rural and urban infrastructure and entails investments of Rs.102 lakh crore to be undertaken by the central government, state governments and the private sector. Of the total projects of the NIP, 42% are under implementation while 19% are under development, 31% are at the conceptual stage and 8% are yet to be classified.

The sectors that will be of focus will be roads, railways, power (renewable and conventional), irrigation and urban infrastructure. These sectors together account for 79% of the proposed investments in six years to 2025. Given the government’s thrust on infrastructure creation, it is likely to benefit the cement industry going forward.

Similarly, the Pradhan Mantri Awaas Yojana, aimed at providing affordable housing, will be a strong driver to lift cement demand. Prices have started correcting Q4 FY20 onwards due to revival in demand of the commodity, the agency said in its analysis.

Industry’s sales revenue has grown at a CAGR of 7.3% during FY15-19 but has grown only 1.3% in the current financial year. Tepid demand throughout the country in the first half of the year has led to the contraction of sales revenue. Fall in the total expenditure of cement firms had aided in improving the operating profit and net profit margins of the industry (OPM was 15.2 during 9M FY19 and NPM was 3.1 during 9M FY19). Interest coverage ratio, too, has improved on an overall basis (ICR was 3.3 during 9M FY19).

According to Cement Manufacturers Association, India accounts for over 8% of the overall global installed capacity. Region-wise, the southern region comprises 35% of the total cement capacity, followed by the northern, eastern, western and central region comprising 20%, 18%, 14% and 13% of the capacity, respectively.

Installed capacity of domestic cement makers has increased at a CAGR of 4.9% during FY16-20. Manufacturers have been able to maintain a capacity utilisation rate above 65% in the past quinquennium. In the current financial year due to the prolonged rains in many parts of the country, the capacity utilisation rate has fallen from 70% during FY19 to 66% currently (YTD).

Source:moneycontrol.com

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Wonder Cement shows journey of cement with new campaign

Published

3 years ago

October 21, 2021

admin

The campaign also marks Wonder Cement being the first ever cement brand to enter the world of IGTV…

ETBrandEquity

Cement manufacturing company Wonder Cement, has announced the launch of a digital campaign ‘Har Raah Mein Wonder Hai’. The campaign has been designed specifically to run on platforms such as Instagram, Facebook and YouTube.

#HarRaahMeinWonderHai is a one-minute video, designed and conceptualised by its digital media partner Triature Digital Marketing and Technologies Pvt Ltd. The entire journey of the cement brand from leaving the factory, going through various weather conditions and witnessing the beauty of nature and wonders through the way until it reaches the destination i.e., to the consumer is very intriguing and the brand has tried to showcase the same with the film.

Sanjay Joshi, executive director, Wonder Cement, said, "Cement as a product poses a unique marketing challenge. Most consumers will build their homes once and therefore buy cement once in a lifetime. It is critical for a cement company to connect with their consumers emotionally. As a part of our communication strategy, it is our endeavor to reach out to a large audience of this country through digital. Wonder Cement always a pioneer in digital, with the launch of our IGTV campaign #HarRahMeinWonderHai, is the first brand in the cement category to venture into this space. Through this campaign, we have captured the emotional journey of a cement bag through its own perspective and depicted what it takes to lay the foundation of one’s dreams and turn them into reality."

The story begins with a family performing the bhoomi poojan of their new plot. It is the place where they are investing their life-long earnings; and planning to build a dream house for the family and children. The family believes in the tradition of having a ‘perfect shuruaat’ (perfect beginning) for their future dream house. The video later highlights the process of construction and in sequence it is emphasising the value of ‘Perfect Shuruaat’ through the eyes of a cement bag.

Tarun Singh Chauhan, management advisor and brand consultant, Wonder Cement, said, "Our objective with this campaign was to show that the cement produced at the Wonder Cement plant speaks for itself, its quality, trust and most of all perfection. The only way this was possible was to take the perspective of a cement bag and showing its journey of perfection from beginning till the end."

According to the company, the campaign also marks Wonder Cement being the first ever cement brand to enter the world of IGTV. No other brand in this category has created content specific to the platform.

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In spite of company’s optimism, demand weakness in cement is seen in the 4% y-o-y drop in sales volume. (Reuters)

Published

3 years ago

October 21, 2021

admin

Cost cuts and better realizations save? the ?day ?for ?UltraTech Cement, Updated: 27 Jan 2020, Vatsala Kamat from Live Mint

Lower cost of energy and logistics helped Ebitda per tonne rise by about 29% in Q3
Premiumization of acquired brands, synergistic?operations hold promise for future profit growth Topics

UltraTech Cement
India’s largest cement producer UltraTech Cement Ltd turned out a bittersweet show in the December quarter. A sharp drop in fuel costs and higher realizations helped drive profit growth. But the inherent demand weakness was evident in the sales volumes drop during the quarter.

Better realizations during the December quarter, in spite of the 4% year-on-year volume decline, minimized the pain. Net stand-alone revenue fell by 2.6% to ?9,981.8 crore.

But as pointed out earlier, lower costs on most fronts helped profitability. The chart alongside shows the sharp drop in energy costs led by lower petcoke prices, lower fuel consumption and higher use of green power. Logistics costs, too, fell due to lower railway freight charges and synergies from the acquired assets. These savings helped offset the increase in raw material costs.

The upshot: Q3 Ebitda (earnings before interest, tax, depreciation and amortization) of about ?990 per tonne was 29% higher from a year ago. The jump in profit on a per tonne basis was more or less along expected lines, given the increase in realizations. "Besides, the reduction in net debt by about ?2,000 crore is a key positive," said Binod Modi, analyst at Reliance Securities Ltd.

Graphic by Santosh Sharma/Mint
What also impressed analysts is the nimble-footed integration of the recently merged cement assets of Nathdwara and Century, which was a concern on the Street.

Kunal Shah, analyst (institutional equities) at Yes Securities (India) Ltd, said: "The company has proved its ability of asset integration. Century’s cement assets were ramped up to 79% capacity utilization in December, even as they operated Nathdwara generating an Ebitda of ?1,500 per tonne."

Looks like the demand weakness mirrored in weak sales during the quarter was masked by the deft integration and synergies derived from these acquired assets. This drove UltraTech’s stock up by 2.6% to ?4,643 after the Q3 results were declared on Friday.

Brand transition from Century to UltraTech, which is 55% complete, is likely to touch 80% by September 2020. A report by Jefferies India Pvt. Ltd highlights that the Ebitda per tonne for premium brands is about ?5-10 higher per bag than the average (A cement bag weighs 50kg). Of course, with competition increasing in the arena, it remains to be seen how brand premiumization in the cement industry will pan out. UltraTech Cement scores well among peers here.

However, there are road bumps ahead for the cement sector and for UltraTech. Falling gross domestic product growth, fiscal slippages and lower budgetary allocation to infrastructure sector are making industry houses jittery on growth. Although UltraTech’s management is confident that cement demand is looking up, sustainability and pricing power remains a worry for the near term.