A. Favier

Flow properties of MK-based geopolymer pastes. A comparative study with standard Portland cement pastes

Geopolymers are presented in many studies as alternatives to ordinary Portland cement. Previous studies have focused on their chemical and mechanical properties, their microstructures and their potential applications, but very few have focussed on their rheological behaviour. Our work highlights the fundamental differences in the flow properties, which exist between geopolymers made from metakaolin and Ordinary Portland Cement (OPC). We show that colloidal interactions between metakaolin particles are negligible and that hydrodynamic effects control the rheological behaviour. Metakaolin-based geopolymers can then be described as Newtonian fluids with the viscosity controlled mainly by the high viscosity of the suspending alkaline silicate solution and not by the contribution of direct contacts between metakaolin grains. This fundamental difference between geopolymers and OPC implies that developments made in cement technology to improve rheological behaviour such as plasticizers will not be efficient for geopolymers and that new research directions need to be explored.

The Maya blue nanostructured material concept applied to colouring geopolymers

Maya blue is an ancient nanostructured pigment synthetized by assembling indigo, a natural dye, with palygorskite, a microfibrous clay mineral. The novelty of our approach is to mimic “pre-Columbian nanotechnology” and to functionalize geopolymers with a sepiolite-based hybrid organic–inorganic nanocomposite inspired from the Maya blue. It is acid- and UV-resistant, as confirmed by the stability of Maya mural paintings over time. We synthesized analogous pigments, using methylene blue (MB) and methyl red (MR) as organic dyes and sepiolite as fibrous clay mineral. We used an aqueous and a solid-state method, both leading to encapsulation of dye monomers into the clay micropores, as confirmed by UV-vis spectroscopy. This nanostructured pigment was then included into a geopolymer matrix at room temperature. The stability of the new material to UV and acid was tested. It was confirmed that it is the prior encapsulation of the dye into sepiolite that leads to the stability of the pigment in the geopolymer matrix. This first study opens the way to numerous possibilities for functionalizing inorganic binder materials with organic elements that would be otherwise sensitive to thermal treatment in conventional ceramic processing.

Influence of the Manufacturing Process on the Performance of Low Clinker, Calcined Clay-Limestone Portland Cement

This paper discusses influence of manufacture parameters of a new type of cement (low carbon cement, LC3) which can substitute up to 50 % of clinker by calcined clay and limestone. Limestone powder accelerates the early hydration and calcined clays and contributes to strength development at later ages due to its pozzolanic reaction. Further, it facilitates improving rheology of the fresh mix without compromising strength, possibly due to the synergetic interaction between calcined clays and limestone. Workability of this new system is strongly affected by the Particle Size Distribution (PSD) and PSD is affected by the grinding process, therefore, due to the different hardness and grindability between the materials forming this cement, new production parameters must be defined. This study compares the results obtain by separate grinding and intergrinding, especially the impact at rheology and early strength. The influence of clinker and limestone on both properties has been assessed, aided by microstructural studies using different techniques (XRD, TGA, IC, etc.) to determine the best fineness combination and analyze the effect of PSD of the new system in cement properties. Intergrinding seems to give reasonable good results in terms of rheology and early strength.

The Effect of Limestone on the Performance of Ternary Blended Cement LC3: Limestone, Calcined Clays and Cement

This project explores the influence of different particle size distributions of limestone on the workability and early-age strength development of LC3 materials. To quantify, and subsequently optimize, the packing, the modified Andreasen and Andersen model was used. Different systems were selected and studied using minicone tests and compressive strength (at 2, 7 and 28 days) to see which parameters govern workability and strength.

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

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<7 µm, 7 µm < d < 40 µm and d< 40 µm, for each of the cements studied and the amount of each component were assessed. Fresh and hardened state properties of blends were tested. Results indicate that in intergrinding most of clinker remains at the medium fraction, and further grinding cannot improve clinker fineness due to fine calcined clay muffle clinker fineness gaining. PSD of limestone and calcined clay is wider than clinker PSD, with a high amount of each material on fine fraction, having a strong impact on rheology. A change in calcined clay/limestone ratio from 2:1 to 1:1 improves clinker grinding and rheology but has a negative impact on strengths due to the less proportion of calcined clay that impact negatively on the pozzolanic reaction.

Alkali Silica Reaction Mitigating Properties of Ternary Blended Cement with Calcined Clay and Limestone

Supplementary cementitious materials (SCMs) are widely used in concrete either in blended cements or added separately in the concrete mixer. SCMs such as calcined clays, slags or fly ashes are widely used to partially substitute plain Portland cement (PC). A particurlarly promising blend is a blend with a high level of substitution by widely available SCMs such low grade calcined clay and limestone. The use of such materials, where no additional clinkering process is involved leads to a significant reduction in CO2 emissions per ton of material. Further, blended systems have numerous well established benefits in terms of durability. ASR is the most important such issue not related to reinforcing steel. Prevention of this phenomenon is critical as sources of non-reactive aggregates are increasingly scarce. The most economical path to ASR resistant concrete is through ternary blends. Since the reaction occurs between alkalis in pore solution and reactive silica, most mitigation methods rely on lowering the alkalinity of the solution through Supplementary Cementitious Materials (SCMs). The effectiveness of SCMs in mitigating ASR is attributable to pore refinement, alkali binding by secondary hydration due to replacing part of the Portland cement, but mainly to the inhibition of silica dissolution when Al ions provided by the SCM are present in the solution. Due to yet uncommon usage in the field, the performances and mechanisms which underlie the properties of such blends are still not wholly understood. In this study, we demonstrate the performance of blends with high level of replacement (reaching 50 %) of cement with limestone and calcined clay. The use of these two SCMs at such high level of replacement promise improvement of the resistance to expansion compared to PC in environmentally friendly blends.