<aside> ℹ️ Here you will read about:

• What the usual composition of concrete, and of ordinary Portland cement (OPC), is.
• Why OPC is a carbon-intensive material.
• What the potential decarbonisation pathways for the industry are, and which pathways have the largest impact in emission reductions. </aside>

Table of content

3.1. Cement and concrete

Cement is a key component of concrete, which is the final construction product. However, even though cement only makes up a relatively small part of concrete, it is responsible for most of its emissions. The production of cement emits 0.9 tonne of CO2 per tonne of cement produced [19].

Concrete

Concrete is a composite material made of aggregates bound together with a binding material, most commonly cement mixed with water. The share of each component is a range; for example, for cast-in-place concrete, aggregates can represent from 60 to 75% of concrete, cement from 7% to 15%, from 14 to 21% of water, and up until 8% of air [20].

Figure 3: Usual composition of concrete.

Even though OPC only makes up 11% of concrete, 90% of concrete emissions are directly linked to the production of clinker, the main ingredient in cement [21].

Nowadays, cement is commonly combined with one or more supplementary cementitious materials (SCM), such as fly ash, silica fume, blast furnace slag, or limestone powder [22].

Figure 4: Concrete and cement lifecycle emissions (data from China’s building sector, 2017). Source: ClimateWorks (2021).

Cement

Cement is the binder in concrete, which makes it an integral component in the construction industry. However, as mentioned before, most emissions also happen during its production. Emissions in cement come from two main sources: process emissions and fuel combustion emissions. Process emissions are those related to the calcination of limestone (which decomposes into lime and CO2) and are indeed unavoidable emissions in clinker production. Fuel combustion emissions are those related to the chemical reactions that happen when fuel is burned to heat up the kiln.

3.1.1. Overview of standard production process

The most commonly used type of cement is Portland cement (abbreviated OPC). Portland cement gets its name from the Isle of Portland in Dorset, England, where it was first developed and produced. Its widespread adoption is due to its strength, versatility, and ability to endure different environmental conditions.

Production process of Portland cement (OPC)

3.1.2. Decarbonisation pathways for the cement industry

In this section, we will run through the main decarbonisation pathways identified in the concrete and cement industry. A brief description of each will be provided, and a final analysis of the technologies will be carried out, according to the three Bellona criteria for climate solutions (climate impact, trade-offs, and timeframe).