Category Archives: Portland cement

What can you do using cement? Funny stuff made of cement

It is well known that cement is the most used construction material in the world. In the mind of most of people, cement is a kind of grey powder and only used as construction material, to build gardens, bridges, road etc. However, we can do more with cement, here are nice pictures showing some stuff made of cement. Creactive!

Even as a guy like me who deals with cement everyday, I really think these items are pretty funny. What do you think you can do using cement? make the most of your imagination, dare to think.

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The Importance of Cement and its Future

Concrete is the most used material in the world because of its cheap price and large quantity. It is needless to say concrete is made of cement. However, cement is also a criticized material by the public, for its intensive CO2 emission from production process. The production of cement accounts for about 5-8% of the non-natural CO2 worldwide.

Importance of Cement

Importance of Cement

Importance of Cement

People may ask, can we find an alternative construction material instead of cement? such as wood, steel. The annual usage of wood is much above the replanting level, and it is not possible to get wood in some places such as Africa and China. As for steel, it is costly and again the production of steel also gives CO2 emission. Furthermore, the production of cement is not that energy intensive compared with other materials.

Importance of Cement

Actually, it is not possible to find an alternative construction material. 98% of the earth’s crust is made of eight elements: O, Si, Al, Fe, Ca, Na, K, Mg, which are the main elements of cement as well. From the long term run, the world will still need a large amount of cement. The demand of cement mainly comes from developing countries, such as India and China because of the urbanization and its population growth.

Importance of Cement

Importance of Cement

Importance of Cement

Since we have to use cement in the future, how can we do to reduce the CO2 emission and what is the future of cement? Efforts have been doing ever since decades ago in the cement industry and research community.

On the one hand, cement plants nowadays burn (hazardous) waste, say, car tyres, as fuel to make cement. The wood floating on the water of Three Gorges Dam is even collected to make fuel for cement plants. On the other hand, the production process of cement has always been optimizing. Some cement plants can even reach 80% efficiency, which is a great achievement even from a theoretical standpoint.

Importance of Cement

Importance of Cement

Researchers of cement try to use less cement clinkers. One viable method is Supplementary Cementitious Materials (SCMs). SCMs are commonly industry by-products or raw materials, such as Slag, limestone, Fly ash, silica fume, natural pozzolan. Whether binary blended or even ternary blended, SCMs can replace part of cement without sacrificing equivalent engineering properties.

Importance of Cement

Considering the limited quantity and access of SCMs, SCMs are not a permanent sustainable way from a long term run. Some researchers are trying to utilize the unlimited amount of calcined clay, for the kaolinite content of clay has similar cementitious property. Work done replacing 30% of cement by calcined clay in Cuba shows the potential future of clay if well used.

Importance of Cement

Generally speaking, cement is a significantly important construction material, and it is not necessary to worry that much as for the CO2 emission in the future.

Concrete made with slag improves resistance to fire damage

Better performance of slag concrete exposing to high temperatures

Concrete made with GGBS cement is much better than concrete made with 100% OPC at maintaining its compressive strength when exposed to high temperatures.

OPC specimens heated to 400 °C or above have been shown to exhibit severe cracking to the point of disintegration after a few days. However, it was found that concrete made with blends of 35%, 50% and 65% GGBS performed much better. In the GGBS specimens there was no visible cracking after exposure to the higher temperatures. The concrete with 100% OPC degraded to powder over the following year, while the concrete made with GGBS maintained its strength over the same period.

Further studies showed that after exposure to 900 °C concrete with 0% GGBS maintained 6% of its original strength, concrete with 30% GGBS maintained 54% of its original strength and concrete with 70% GGBS maintained 70% of its original strength.

fire-slag-concrete
Date source: Ecocem.

How does slag improve the resistance to fire damage?

Why concrete made with GGBS has better resistance to fire damage? It is generally agreed that above 400 °C Ca(OH)2 which is the hydration products of OPC decomposes into CaO and H2O, then on cooling CaO and left H2O rehydrates into Ca(OH)2 which needs more space than CaO causing the concrete to crack and degrade. With the addition of GGBS into concrete, hydration product Ca(OH)2 is generally reduced compared with concrete made with 100% OPC, thus improving the performance of resisting fire damage.

House-Fire-concrete

Reference: Ecocem report–Technical Performance