Why is cement important

For much of the s, Roman cement dominated, but in the latter part of the century developments into the use of rotary kilns for cement production in the US led to Portland cement becoming the dominant cement type. By , Atlas Cement Company, based in the Lehigh Valley, had 29 rotary cement kilns producing cement 10 times more rapidly than earlier kilns. By this point Portland cement had undergone a large number of incremental improvements, but its place at the top of the global cement pile was far from assured.

Writing in , British construction consultant Henry Faija wrote, "I do not wish to frighten manufacturers, but my own impression is that in a few years Portland cement will be superceded by another material. Portland cement, as at present made, is a chemical combination carried out in the crudest way. Continued heating and reaction causes calcination in which varying calcium silicates are produced.

By adjusting the proportion of gypsum it is possible to give rise to cements with different setting times. A number of different classification schemes are in operation for cement around the world including ASTM and the European EN standards.

When cement is mixed with water, a variety of exothermic heat-producing chemical reactions begin Figure 3. The sulphates and some of the gypsum dissolve almost instantly, which gives rise to a highly alkaline sulphate solution. The most reactive non-soluble components then start to react with the water.

These are usually minerals that contain aluminium, which react to form aluminate gels. This process normally occurs in a few minutes and produces a lot of heat I Figure 3.

There is then a dormant period with little change II Figure 3. Then the calcium- and silicon-containing minerals begin to react III Figure 3. This forms crystalline hydration products such as calcium silicon hydrate and calcium hydrate that interlock to give high strength to the finished product. If sand or aggregate is present this will be bound strongly to the cement. Typically cement takes in the region of 40 — 50 hours to set but some cements continue to harden for years.

Global cement production was 1. This is due not only the high demand, but also because the process uses readily available raw materials and has low associated production costs. Figure 4 shows how demand has increased in the past, with massive increases in production around the turn of the century. The first year in which 1Bt of cement was produced was The first year that over 2Bnt was produced was , just 13 years later. The first year in which over 3Bnt was produced was , a tripling of the total global cement capacity in just 23 years.

The cost of a new cement plant is equivalent to around three years of turnover, which ranks the cement industry among the most capital-intensive industries. Long periods are therefore needed before these large investments can be recovered. Plant modifications have to be carefully planned, as typical investment cycles in the sector last about 30 years. Consequently, achieving the low-carbon economy roadmap for the European cement industry will be based on balancing recent investments with planning new investments in the coming decades.

Although produced from naturally occurring raw materials that can vary widely from plant to plant, cement is a product manufactured in Europe according to a harmonised standard. Despite the existence of specialised segments, many cements are interchangeable, which promotes a competitive cement market. This also means that European production can be very vulnerable to cheaper imports. Cement is mostly locally produced and locally consumed.

However, it is also transported over long distances by sea, river and land as plants rationalise and exploit efficiencies of scale. Land transportation costs are significant.

In addition, transport costs per tonne are lower to ship a large consignment of cement from the north coast of France across the Atlantic than to truck it to Paris. For plants not operating at capacity, the cost per tonne to produce an additional tonne can be relatively low.

With a substantial part of the European cement market within the economically viable range of a sea port, these factors together mean that European cement plants are vulnerable to imports. Cement consumption is closely linked to economic development in the local region or country. Insurance costs for concrete buildings during the construction and operating phases have also been shown to be significantly lower than for buildings constructed with combustible, moisture-sensitive materials. Concrete pavements are also cost- effective on a first cost and lifecycle cost basis, requiring only a third of the maintenance a comparable asphalt road would require over a year service life.

Concrete can be recycled as aggregate — for use as sub-base material in roadbeds and parking lots, for gabion walls, as riprap to protect shorelines or in other applications — or as granular material, thereby reducing the amount of material that is landfilled and the need for virgin materials in new construction. Concrete is typically manufactured within kilometers of a project site, using local resources. This greatly minimizes shipping and pollution and makes a significant contribution to the local economy.

Concrete And Life Cycle Assessment. Studies and real world examples show that concrete pavements are more cost-effective, need less maintenance and are more environmentally than asphalt pavements.