The Influence of some calcined clays from Nigeria as clinker substitute in cementitious systems

This paper examines the possibility of the use of some clays calcined from Nigeria as partial substitutes for clinker in the production of Limestone Calcined Clay Cement (LC3). The clays were calcined in the oven at a temperature of 800 degrees C and for one hour. Dehydroxylation of raw and calcined clays with TGA were carried out between 400 degrees C and 650 degrees C after which the materials were again characterized with XRD. The R-3 pozzolanic test was then carried out to evaluate the reactivity of calcined clays based on the heat release at 24 hours of a model system of portlandite, calcined clay and limestone with adjusted sulfate and alkali content. After the characterization, two clay samples were deemed fit for use as partial replacement of cement because they contain more than 30% kaolinite content. Concrete cubes prepared with the cementitious blends (PC, LC3-50A, LC3-50D and LC3-35D) were cast for mechanical and durability tests, while mercury intrusion porositometry (MIP) was used to determine the porosity of the cementitious blends. The results showed that LC3-50D with about 50% kaolinite content gave the best mechanical and durability results followed by LC3-50A and whereas, LC3-35D containing only 35% cement can still be used for good construction which is a demonstration of the advantage offered with the use of LC3 in cementitious systems. (C) 2020 Published by Elsevier Ltd.

Impacting factors and properties of limestone calcined clay cements (LC3)

François Henri Avet, Aurélie Rosine Favier, Wilasinee Hanpongpun, Hamed Maraghechi, Karen Scrivener, Julien Ston, Franco Alberto Zunino Sommariva

This paper details the main factors influencing the performance of limestone calcined clay cements (LC3). The kaolinite content plays a major role in the rheological properties as well as strength development. Even in the presence of secondary phases, kaolinite can be accurately quantified by thermogravimetric analysis. The performance of LC3 is slightly influenced by the calcination process of clay, but it can be optimized by using the correct calcination temperature and applying a specific mix design with adjusted sulfate and alkali content. The hydration reactions of LC3 are fully characterized. They vary slightly from plain cement. There is no significant change in terms of phase assemblage. The main properties of LC3 are also described. LC3 blends show a lower creep compliance and a delay in shrinkage strains compared with plain cement. Concerning durability, LC3 blends show outstanding performance with respect to resisting chloride ingress and expansion from the alkali-silica reaction.

ICE PUBLISHING2019

Influence Grinding Procedure, Limestone Content and PSD of Components on Properties of Clinker-Calcined Clay-Limestone Cements Produced by Intergrinding

Aurélie Rosine Favier, Albert Perez, Karen Scrivener

This paper looks at the study of intergrinding for the production of ternary cement based on clinker, calcined clay, limestone and gypsum with 50% of clinker substitution (LC3). The impact of grinding time on clinker, limestone and calcined clay PSD, and how this parameter influences the overall performance of the ternary cement is assessed. Laboratory cement blends were produced by grinding all components in a batch laboratory mill. Industrial cements produced through intergrinding in a continuous ball mill were used for comparison. Three fractions were identified: d

Springer2018

Adsorption de polycarboxylates et de lignosulfonates sur poudre modèle et ciments

François Perche

Placing concrete requires much more water than the cement needs for its hydration. This results in an important porosity in the hardened concrete, which accentuates the degradation of this material. By adding small amounts of polymeric admixtures, called superplasticizers, to the fresh concrete one can significantly reduce the amount of water required to obtain the suitable workability. The plasticizing effect of superplasticizers has been studied for many years, and remains today, an ongoing field of research. This research led to a better understanding of the forces that act during the deflocculation and dispersion of cement grains induced by superplasticizers. This research work was performed within the framework of the "Superplast" European project. Its main objective has been to determine which parameters (molecular structure, induced charge, adsorption mode, molar mass) influence the plasticizing effects of superplasticizers. The results of this study will allow synthesis new polymeric admixtures with better performances than those currently available. For this study, two types of superplasticizers were selected: lignosulfonates and polycarboxylates. For each one, different samples were synthesised and characterised. For each sample, adsorption, rheological and interaction forces measurements were performed by our partners while we have performed adsorption and electroacoustic measurements on model powder suspensions. Different cement model powders were investigated and a magnesium oxide was selected. The particle size distribution and reactivity were carefully characterized. The inert model system (MgO) allowed us to study adsorption mechanisms without the complexity linked to cement hydration reactions that modify surface and solution of the suspension. Particle surface charge and pH are the two main parameters that influence the polymer adsorption and the polymer conformation. Magnesium oxide which has a high isoelectric point (around at pH 12.4) allows a surface charge similar to cement suspensions at high pH. First, we have measured the adsorption isotherms of all superplasticizers on model suspensions in NaOH (0.01M). This study allowed us to evaluate the affinity of each polymer for MgO and its adsorption plateau. These measurements showed that the lignosulfonates have a higher affinity than the polycarboxylates. They also showed that lignosulfonate adsorption is mainly influenced by their molar mass and their carboxylic group content (for similar sulfonate group content) while polycarboxylate adsorption is mainly driven by the backbone length, the side chain length and the carboxylic group content. Adsorption plateaux allowed us to calculate the surface coverage ratio and to estimate the superplasticizer conformation on the surface. Adsorption isotherms were finally measured on a Portland cement. The polymer adsorption is influenced by the same parameters as on MgO. The model system MgO is representative for the polymer adsorption on cement. In a second step, different electrolytes were added to model suspensions. This practice allowed us to study separately the effect of the main ions present in cement suspensions (Na+, Ca2+, SO42-, OH-) and to mimic the ionic composition of the aqueous phase of the cement suspension. Lignosulfonate adsorption is neither influenced by the studied ions or the pH. Only an increase of ionic strength increases the adsorbed polymer mass. Polycarboxylate adsorption is influenced by calcium and sulfate ions and by the particle surface charge. Finally, superplasticizer adsorption was studied on different cements by our partners and on a fly ash and a silica fume by ourselves. Lignosulfonate adsorption isotherms on cements showed that affinity and adsorbed polymer mass increases with the C3A content and decreases with the alkalis content. The isotherms measured on industrial by-products showed that superplasticizers adsorb on fly ash, but not on silica fume.

EPFL2004

Adsorption de polycarboxylates et de lignosulfonates sur poudre modèle et ciments

François Perche

EPFL2004