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Philosophy of High Strength Cement/Concrete

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Dr SB Hegde, Professor, Pennsylvania State University, USA, delves into the aspects of durability and sustainability of high strength concrete.

The world is passing through difficult and troubled times, and we live in a rapidly changing world. The construction industry is facing many challenges – global warming, climate change forces and the capability to achieve sustainable development and economic progress without damaging our environment. The concrete industry in particular faces further challenges. There is extensive evidence to show that concrete materials and concrete structures all over the world are deteriorating at a rapid rate, and that we are unable to ensure their long-term durable service life performance.
To confound this situation, we are also faced with an urgent need to regenerate our infrastructure systems if we are to eradicate poverty and provide a decent ‘quality of life’ for all the peoples of the world.

Durability vs strength
This paper shows that the current emphasis on high strength and very high strength, and the design philosophy of durability through strength for concrete materials and concrete structures is fundamentally flawed. It is this misleading concept and vision that is primarily responsible for the lack of durable performance of concrete in real life environments.
To change this scenario, this paper advocates that concrete materials must be manufactured for durability and not for strength. It is shown that this concept of strength through durability can be achieved through careful design of the cement matrix and its microstructure. If concrete is to be an eco-friendly, and sustainable driving force and construction material for social change, the need is to produce durable concrete with strengths of 30 to 60 to 80 MPa rather than very high strength concrete without an assured durable performance.
Engineers are, by nature, fascinated and indeed obsessed, by high strength and very high strength concrete. Part of this fascination arises from the widely-held misconception that high strength concrete is, per se, highly durable.

Making it last longer
This intuitive association of strength with durability is again partly due to the current Ultimate Strength Design approach which creates an implicit belief and illusion that if concrete is proportioned to give high compressive strength, and then, if prescriptive code specifications in terms of cement content, water/cementitious materials (w/cm) ratios, types of cement, steel cover thickness and types and amounts of mineral and chemical admixtures are adhered to, then somehow the durable service life of the concrete structure will be automatically and adequately assured.
The impetus for higher and higher concrete strengths also came from demands for exceptional increases in the height of high-rise buildings and for long span bridges. Indeed, the higher concrete strengths also brought in visible economics in terms of use of materials, increased usable space and shorter times of construction. As a result the latter part of the last century saw the development and use of concrete with compressive strengths from about 40 to 100/120 MPa and beyond.
Holistic Durability Design Philosophy – an integrated material and structural design strategy – of strength through durability rather than of durability through strength where materials are manufactured for durability rather than for strength, and structures are designed for ductility and structural integrity. Holistic design envisages a global approach to all aspects of concrete and construction technology from material selection, design, construction, and maintenance to service life, integrating material characteristics with in situ performance. Use of cement replacement materials, design for material stability, design for structural integrity and
design for sustainability are the key elements of this holistic durability design to achieve durable service life performance.

About the author:
Awarded with the ‘Global Visionary Award’ for his contribution to the cement industry in November 2022, Dr SB Hegde has been an integral part of the industry and has worked as an expert consultant for various international bodies in the cement domain. He currently holds the role of visiting faculty at the Pennsylvania State University, USA.

Concrete

Thyssenkrupp Polysius wins orders in Vietnam

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ThyssenKrupp Polysius’ Asia Pacific division has secured an order for two Polflame-type main burners for an unnamed cement plant. The equipment supplier has highlighted the ability of its burner product to cope with low-grade coal and support high alternative fuel substitution rates as key selling factors. The order follows the purchase of an Impact Crusher by the same customer previously.

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Concrete

Lafarge Canada to donate to wild salmon project

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Lafarge Canada has announced a five-year in-kind donation with the Nicomekl Enhancement Society (NES) in British Columbia. The agreement will see the building materials producer donate around US$15,000/yr in aggregates, concrete and labour to enhance the sustainability of the wild Pacific salmon population and ecosystem within the coastal area of the Nicomekl River.

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Concrete

Holcim divests Holcim Russia

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Holcim has agreed to sell its Russian business to its local management. When the transaction is completed, the business will continue to operate under different branding. Holcim says that it remains committed to supporting Holcim Russia’s employees and ensuring an orderly transfer for its customers. DGAP Corporate News has reported that Holcim deconsolidated the subsidiary in March 2022, following Russia’s invasion of Ukraine.
The company’s statement said, “Holcim’s Board of Directors expresses its heartfelt concern about the tragic human suffering in the region, and is fully committed to supporting affected people, families and communities. The Board of Directors thanks all Holcim colleagues who are mobilising around the world alongside local NGOs to provide shelter, essential goods and medical supplies, as well as volunteering their time.”

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