Ternary cements with low‐grade calcined clay and limestone

Abstract

In view of the challenges of decarbonisation of the cement industry, the use of ternary low‐clinker cements especially with calcined clays is becoming increasingly important. Many projects on LC3 cements have shown that the combination of the main cement constituents calcined clay (Q) and limestone (L, LL) beside Portland cement clinker (K) is very promising in terms of the cement and concrete performance. However, most of these have been carried out with high‐grade (kaolinitic) clays which are often not available and too expensive for cement manufactures

Therefore, in this project two different Portland cements (CEM I 42,5 and 52,5) without minor constituents, one limestone and four calcined clays (impure kaolinitic, smectitic, illitic and mixed clay composition) were used for ternary cements. In the presented study statistical analyses with varying ternary cement compositions (max 45 % Q, max 30 % L, and min. 50 % K) were conducted. In total 48 mixtures were tested using two calcined clays and the two reference cements.

As expected, at 28 days of hydration a significant strength contribution of the calcined clays could be observed. Even cements with low‐grade clays (∼170 J/g acc. R3 test) can be used as Q‐component in ternary low clinker KQL‐cements in 42,5‐compressive strengths class. The better calcined impure kaolinitic clay (518 J/g) showed potential for higher compressive strengths even with clinker contents below 50%.