# Durability of Concrete Made with Coal Bottom Ash Portland Cements

## TL;DR

This study shows that using coal bottom ash in concrete improves durability and reduces costs, supporting climate change mitigation in the cement industry.

## Contribution

The first assessment of the durability of coal bottom ash concretes using water penetration tests under pressure.

## Key findings

- CEM II/B-Z and CEM II/C-M concretes meet water penetration requirements for all exposure classes.
- Concretes with CEM VI (S-L) and CEM VI (S-Z) comply with criteria for most exposure classes except XS3, XA2, and XA3.
- Using coal bottom ash reduces cement cost and supports clinker factor reduction.

## Abstract

What are the main findings?
The standardization of coal bottom ash (CBA) as a cement constituent contributes to climate change mitigation.Coal bottom ash (Z) is included as a new constituent in the EU Standardization Request published on 28 July 2025.For the first time, the durability of Z-concretes is assessed by the depth of penetration of water under pressure test.Clinker factor reduction with newly standardized constituents decreases the near- zero cement cost (~500 €/t).CEM II/B-Z and CEM II/C-M concretes meet water penetration requirements for all exposure classes.

The standardization of coal bottom ash (CBA) as a cement constituent contributes to climate change mitigation.

Coal bottom ash (Z) is included as a new constituent in the EU Standardization Request published on 28 July 2025.

For the first time, the durability of Z-concretes is assessed by the depth of penetration of water under pressure test.

Clinker factor reduction with newly standardized constituents decreases the near- zero cement cost (~500 €/t).

CEM II/B-Z and CEM II/C-M concretes meet water penetration requirements for all exposure classes.

The Portland cement industry, responsible for approximately 7.4% of global anthropogenic carbon dioxide emissions, must balance rising cement demand with ambitious greenhouse gas reduction targets. In parallel, the rapid accumulation of industrial solid waste highlights the need for effective valorization routes. Reducing the clinker factor remains a powerful measure to mitigate climate impacts in the cement sector. This study evaluates the durability of concretes made with ground coal bottom ash (CBA), a newly standardized Portland cement constituent, using the depth of penetration of water under pressure test (EN 12390-8). The experimental results show that concretes produced with CEM II/B-Z and CEM II/C-M cements meet both average (≤30 mm) and maximum (≤50 mm) water penetration criteria for mass, reinforced, and prestressed concrete across all EN 206-1 exposure classes. Concretes made with CEM VI (S-L) and CEM VI (S-Z) comply for XS1, XS2, XD, XA1, XM, and XF classes. However, for XS3, XA2, and XA3, compliance (≤20 mm and ≤30 mm) is not achieved when using mix design B (300 kg/m3, w/c = 0.50). These findings provide robust technical evidence supporting CBA as a viable cement constituent that enhances durability while enabling clinker factor reduction.