# Durability Considerations in Replacing Blast Furnace Slag with Low-Grade Calcined Clay and Natural Pozzolan in Quaternary Cements

## TL;DR

This study explores using low-grade calcined clay and lava as sustainable alternatives to traditional cement additives, finding them less durable but more environmentally friendly.

## Contribution

The paper introduces a new quaternary cement blend using low-grade calcined clay and natural pozzolan as sustainable alternatives to blast furnace slag.

## Key findings

- Mixtures with calcined clay show slightly lower 28-day strength compared to those with GGBFS.
- Blends with lava gain strength at later ages due to delayed pozzolanic activity.
- LC3 mix with low-grade clay and lava has lower global warming potential than CEM III/A.

## Abstract

Belgium and the EU-27 face a shortage of suitable supplementary cementitious materials (SCMs) capable of supporting high levels of Portland cement substitution. To reduce CO2 emissions from the cement industry, blended cements incorporating low-grade calcined clay, limestone, and lava (a natural pozzolan) are investigated. Calcined clay is combined with limestone to produce a limestone–calcined clay cement (LC3). The reactivity of these new blends is assessed using isothermal calorimetry and compared to a reference blend with ground-granulated blast-furnace slag (GGBFS). Results show that mixtures with calcined clay develop slightly lower 28-day strength than those with GGBFS, while blends with lava exhibit strength gains only at later ages due to delayed pozzolanic activity. Overall, concrete made with low-grade calcined clay and lava achieves comparable compressive strength to the reference (CEM III/A), but with higher capillary porosity, leading to increased water absorption, drying shrinkage, and reduced freeze–thaw resistance. Despite these durability limitations, the sustainability assessment reveals that the LC3 mix with low-grade clay and lava has a lower global warming potential per unit strength at 28 days than CEM III/A and is competitive with CEM III/B.