Suitability of Clinker Replacement by a Calcined Common Clay in Self-Consolidating Mortar—Impact on Rheology and Early Age Properties

Abstract

The use of a high amount of calcined clays as cement replacement presents a great challenge in designing self-consolidating concrete. This current attempt evaluates the influence of cement replacement with up to 40 vol.% by a calcined common clay (CC), dominated by 2:1 phyllosilicates in combination with a fixed limestone powder (LP) content on fresh and hardened properties of self-consolidating mortar (SC-M). The fresh properties of SC-M were investigated by mini-slump flow, V-funnel and rotational viscometer measurements. Setting and hardening behavior were observed via dynamic modulus of elasticity and plastic shrinkage. Hydration mechanisms were determined by isothermal calorimetry and thermal analysis. Hardened properties of SC-M were evaluated using compressive strength tests and mercury intrusion porosimetry (MIP). The results revealed a decreased rate of deformability in SC-M when cement is substituted increasingly by CC and a rising superplasticizer (SP) demand, but indicated an improved stability of SC-M even at a higher dosage of SP and hardly any impact on the setting behavior. CC enhanced the precipitation of monocarboaluminate phases and thereby refined the pore size distribution of the binder matrix. SC-M can be produced with up to 40 vol.% CC as cement replacement without having effect on its 28 days mechanical properties.

Calcined Clays from Nigeria—Properties and Performance of Supplementary Cementitious Materials Suitable for Producing Level 1 Concrete

“…As previously reported [ 18 , 70 ], the use of CC as a partial replacement for cement favors the precipitation of hemicarboaluminate phases from the aluminate and ettringite reaction, which occurred earlier and more broadly in the CC studied here in the following order: NCC-4 > NCC-3 > NCC-2 > NCC-1. A clear distinction also existed between the silicate and aluminate hydration maxima in all CC blended systems, except NCC-4, which had a strong overlap of these maxima.…”

“…In addition to mineralogical and chemical composition and the reactivity of the CC, physical properties such as water demand are important factors that significantly influence the possibilities of high replacement levels [ 17 ]. The higher water demand and higher specific surface area of CC in comparison to cement negatively affect the workability of the system [ 18 ], which is an important attribute, especially when considering the ease of compactability, which in turn affects strength and durability of mortar and concrete [ 19 ].…”

“…This is evidenced by a strong influence of the early clinker hydration in CC blended systems [ 26 , 27 , 28 ]. The released aluminum exploits its full potential, especially in the presence of LP [ 18 , 29 , 30 ]. When CC and LP are blended and used as a substitute for clinker, they promote the formation of monocarboaluminate/hemicarboaluminate AFm phases and densify the concrete microstructure, which in turn have positive effects on the mechanical and durability properties of mortar and concrete [ 18 , 31 , 32 , 33 ].…”

Properties of Self-Compacting Concrete Produced with Optimized Volumes of Calcined Clay and Rice Husk Ash—Emphasis on Rheology, Flowability Retention and Durability

“…PLC requires an average of 0.87 V w /V p to achieve self-compactability. Partial substitution of CC up to 20 vol-% has a minor effect on this value; CC partial substitution beyond 20 vol-% requires an adjustment of this value or an increase of the SP dosage to achieve a similar deformability class as the PLC system, as a previous investigation by [ 54 ] achieved self-compactability using the same V w /V p and increasing SP dosage, with up to 40 vol-% CC in SC-M. On the other hand, the partial substitution of PLC with RHA requires a significant increase of V w /V p to achieve self-compactability. At 10 vol-% RHA partial replacement, V w /V p already increased to 1.1, which is 21% higher than the value required for PLC.…”

Properties of Self-Compacting Concrete Produced with Optimized Volume of Calcined Clay and Rice Husk Ash—Emphasis on Rheology, Time Dependent Workability and Durability

“…PLC requires an average of 0.87 V w /V p to achieve selfcompactability. Partial substitution of CC up to 20 vol-% has a minor effect on this value; CC partial substitution beyond 20 vol-% requires an adjustment of this value or an increase of the SP dosage to achieve a similar deformability class as the PLC system, as a previous investigation by [54] achieved self-compactability using the same V w /V p and increasing SP dosage, with up to 40 vol-% CC in SC-M. On the other hand, the partial substitution of PLC with RHA requires a significant increase of V w /V p to achieve self-compactability. At 10 vol-% RHA partial replacement, V w /V p already increased to 1.1, which is 21% higher than the value required for PLC.…”